Pablo Mohaupt

Marie-Laure Pons

Jérôme Vialaret

Constance Delaby

Christophe Hirtz

Sylvain Lehmann

β-Synuclein as a candidate blood biomarker for synaptic degeneration in Alzheimer's disease

Keywords: β-Synuclein, Alzheimer's disease, Blood biomarker, Synaptic dysfunction

Synaptic degeneration is an early event closely associated with the course of Alzheimer's disease (AD). The identification of synaptic blood biomarkers is, therefore, of great interest and clinical relevance. The levels of most synaptic proteins are increased in the cerebrospinal fluid (CSF) of patients with AD, but their detection in blood is hitherto either unavailable or not very informative. This paradigm is related to their low concentration, their peripheral origin, or the presence of highly abundant blood proteins that hinder detection. In recent years, significant progress has been made in detecting the presynaptic protein β-synuclein. This mini-review summarizes the results that highlight the role of β-synuclein as a candidate blood marker for synaptic degeneration in AD.

Background

The etiology of Alzheimer's disease (AD) remains controversial, despite recent developments in genetics and cell biology. AD is characterized by neuronal loss, extracellular amyloid-β plaques, and neurofibrillary tangles consisting of strings of hyperphosphorylated tau located within neurons [START_REF] Hardy | Alzheimer's disease: the amyloid cascade hypothesis[END_REF]. Until recently, only therapies were available to treat the symptoms of AD, and clinical trials building on the amyloid cascade theorem struggled to halt or delay disease progression [START_REF] Huang | Clinical trials of new drugs for Alzheimer disease[END_REF][START_REF] Mangialasche | Alzheimer's disease: clinical trials and drug development[END_REF]. Anti-tau antibodies have so far been unsuccessful, whereas the antiamyloid-beta antibody aducanumab was approved by the Food and Drug Administration (FDA). This treatment is supposed to target the underlying disease process of AD, while its effectiveness is moderate but controversial [START_REF] Kuller | ENGAGE and EMERGE: truth and consequences?[END_REF]. Thus, there is still a need for more effective or targeted approaches and to unravel the pathophysiological subtypes of AD [START_REF] Tijms | Pathophysiological subtypes of Alzheimer's disease based on cerebrospinal fluid proteomics[END_REF]. As treatments become available, there is also a clinical need for biomarkers that detect AD in its earliest stages and predict and monitor disease progression [START_REF] Mavrina | Multiomics interdisciplinary research integration to accelerate dementia biomarker development (MIRIADE)[END_REF]. Synaptic degeneration is the neuropathological hallmark most highly correlated with cognitive impairment in AD; hence, the interest in synaptic biomarkers that may complement the amyloid and tau panels already in use (Fig. 1) [START_REF] Terry | Physical basis of cognitive alterations in Alzheimer's disease: synapse loss is the major correlate of cognitive impairment[END_REF]. Synaptic degeneration in AD can already be determined by quantifying post-and presynaptic proteins in CSF and by measuring the levels of SV2A with positron emission tomography (PET) [START_REF] Chen | Assessing synaptic density in Alzheimer disease with synaptic vesicle glycoprotein 2A positron emission tomographic imaging[END_REF][START_REF] Kvartsberg | Characterization of the postsynaptic protein neurogranin in paired cerebrospinal fluid and plasma samples from Alzheimer's disease patients and healthy controls[END_REF]. The measurement of brain-specific synaptic proteins in blood is currently not available but can be of great relevance for clinical trials, disease monitoring, and early diagnosis. Here, we summarize recent findings and outline the rationale that the presynaptic protein β-synuclein is an early and prognostic blood marker for AD.

β-Synuclein in Alzheimer´s disease

β-Synuclein is a presynaptic protein encoded by the synuclein Beta locus (SNCB) and is predominantly expressed in the brain. β-Synuclein forms, together with α-synuclein and γ-synuclein, a group of proteins dubbed "Synucleins" and is shown to inhibit α-synuclein

Open Access

*Correspondence: christophe.hirtz@umontpellier.fr aggregation [START_REF] Hashimoto | β-Synuclein inhibits α-synuclein aggregation: a possible role as an anti-parkinsonian factor[END_REF]. α-Synuclein is extensively researched to assess its biomarker potential in synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), which are characterized by abnormal accumulation of α-synuclein aggregates [START_REF] Pons | Proteomics challenges for the assessment of synuclein proteoforms as clinical biomarkers in Parkinson's disease[END_REF]. As such, the presence of elevated Fig. 1 Pathophysiological hallmarks of Alzheimer's disease and its associated biomarkers in either blood or cerebrospinal fluid. Alzheimer's disease is characterized by amyloid plaques, neurofibrillary tangles, axonal damage, microglial activation, and synaptic dysfunction. These pathophysiological hallmarks are responsible for significant modification of CSF Amyloid-β42/40 ratio, levels of tau with abnormal phosphorylation at positions 181, 231, and 217, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) levels. These variations are also detected in the blood of AD patients. The levels of numerous proteins involved in synaptic function vary in CSF in (preclinical) AD. Proteins originating from the central nervous system are often present in low concentrations that are difficult to detect. A fraction of synaptic proteins is also expressed in other tissues and are therefore not suitable as specific blood biomarkers for synaptic dysfunction. To date, β-synuclein, whose expression is brain-specific, is the only synaptic protein that is determined to be significantly increased in the blood of AD patients β-synuclein in the CSF of AD patients was first detected serendipitously in an endeavor to identify abnormalities specific to a particular synucleinopathy [START_REF] Oeckl | Alpha-, beta-, and gamma-synuclein quantification in cerebrospinal fluid by multiple reaction monitoring reveals increased concentrations in Alzheimer's and Creutzfeldt-Jakob disease but no alteration in synucleinopathies[END_REF]. A significant increase with a high correlation with CSF tau was observed in AD and Creutzfeldt-Jakob disease (CJD). Of note, β-synuclein was slightly higher in dementia with DLB and PD-related dementia compared with controls and PD without dementia, suggesting that β-synuclein may be more associated with cognitive impairment than with motor impairment. The increase of β-synuclein in AD CSF was also observed in a study targeting synaptic proteins with mass spectrometry and was confirmed in an immunodetection study [START_REF] Halbgebauer | Beta-synuclein in cerebrospinal fluid as an early diagnostic marker of Alzheimer's disease[END_REF][START_REF] Nilsson | Cerebrospinal fluid biomarker panel for synaptic dysfunction in Alzheimer's disease[END_REF]. The latter suggests that β-synuclein is altered more specifically in amyloidopathies, as no changes were observed in non-amyloid pathologies such as frontotemporal dementia (FTD). Furthermore, the increase was already present in prodromal patients with mild cognitive impairment (MCI-AD), highlighting its potential as an early diagnostic and prognostic biomarker candidate. The AD-specific increase was also observed in a study researching synaptic dysfunction in different neurodegenerative diseases [START_REF] Nilsson | Cerebrospinal fluid biomarker panel of synaptic dysfunction in Alzheimer's disease and other neurodegenerative disorders[END_REF]. A major step in assessing the value of β-synuclein as a biomarker for AD was the development of an immunoprecipitation mass spectrometry (IP-MS) method that can be applied in both CSF and blood [START_REF] Oeckl | Targeted mass spectrometry suggests beta-synuclein as synaptic blood marker in Alzheimer's disease[END_REF]. This novel assay confirmed the previous results obtained in CSF and, in particular, showed that the levels of β-synuclein were also significantly higher in the blood of AD patients. This study positioned β-synuclein as the first synaptic blood biomarker for AD. The increase in MCI-AD was more moderate and did not reach significance, but this is likely due to the small cohort size. The increase was also confirmed in a study in adults with Down syndrome (DS), who are at high risk of developing AD due to overexpression of the APP gene located on chromosome 21 [START_REF] Oeckl | Serum beta-synuclein is higher in Down syndrome and precedes rise of pTau181[END_REF]. Of particular note, β-synuclein was already altered in preclinical AD and was elevated earlier than pTau181, confirming its early diagnostic and prognostic interest. More recently, blood β-synuclein levels were found to correlate with cognitive impairment and brain atrophy in AD, which indicates its association with disease severity [START_REF] Oeckl | Relationship of serum beta-synuclein with blood biomarkers and brain atrophy[END_REF].

The IP-MS analytical approach is innovative but requires large blood sample volumes and has low turnover, hindering the analysis of large cohorts and routine use. Recently, an ultrasensitive immunodetection assay with Simoa was developed to target β-synuclein in blood [START_REF] Halbgebauer | Blood β-synuclein and neurofilament light chain during the course of prion disease[END_REF]. So far, this test has been applied to CJD and it has yet to be determined if this assay can match the clinical performance of IP-MS in AD-related cohorts.

There is no comparison of blood β-synuclein with other synaptic markers such as SNAP-25, SYT-1, neuronal pentraxins (NPTXs), or neurogranin (Ng). Indeed, the presynaptic SYT-1 and SNAP-25, the postsynaptic Ng, and NPTXs which are present in both pre-and post-synapses all show altered levels in CSF [START_REF] Brinkmalm | SNAP-25 is a promising novel cerebrospinal fluid biomarker for synapse degeneration in Alzheimer's disease[END_REF][START_REF] Öhrfelt | The pre-synaptic vesicle protein synaptotagmin is a novel biomarker for Alzheimer's disease[END_REF][START_REF] Mavroudis | A meta-analysis on CSF neurogranin levels for the diagnosis of Alzheimer's disease and mild cognitive impairment[END_REF][START_REF] De San | Neuronal pentraxins as biomarkers of synaptic activity: from physiological functions to pathological changes in neurodegeneration[END_REF]. Nonetheless, most synaptic proteins are not yet assayable in the blood, even with ultrasensitive methods as tested recently for SNAP-25 [START_REF] Nilsson | Quantification of SNAP-25 with mass spectrometry and Simoa: a method comparison in Alzheimer's disease[END_REF]. Ng can be detected in blood, but its expression is not restricted to the brain; therefore, the changes observed in CSF are not specifically reflected in the blood [START_REF] Kvartsberg | Characterization of the postsynaptic protein neurogranin in paired cerebrospinal fluid and plasma samples from Alzheimer's disease patients and healthy controls[END_REF].

The combined results outlined in this mini-review show that β-synuclein could potentially complement the panel of blood biomarkers for AD as a marker for synaptic degeneration, whereas phosphorylated tau biomarkers reflect amyloidopathy and tau-pathology.

Conclusion

In conclusion, β-synuclein is to date the only detectable blood biomarker for synaptic degeneration in AD. The switch from mass spectrometry to an immunodetection method increases the accessibility of β-synuclein quantification in larger research cohorts. Its value as a marker for AD will have to be tested in cohorts and compared with blood markers such as pTau217 and pTau231, whose performances remain unmatched to date [START_REF] Milà-Alomà | Plasma p-tau231 and p-tau217 as state markers of amyloid-β pathology in preclinical Alzheimer's disease[END_REF].

LBPC-PPC, Université de Montpellier, IRMB CHU de Montpellier, INM INSERM, Montpellier, France Full list of author information is available at the end of the article

Acknowledgements

Not applicable.

Funding

This project has received funding (support for PM and the laboratory) from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 860197 MIRIADE.

Availability of data and materials

Not applicable.

Abbreviations

Declarations

Ethics approval and consent to participate Not applicable.

• fast, convenient online submission • thorough peer review by experienced researchers in your field

• rapid publication on acceptance

• support for research data, including large and complex data types • gold Open Access which fosters wider collaboration and increased citations maximum visibility for your research: over 100M website views per year

•

At BMC, research is always in progress.

Learn more biomedcentral.com/submissions

Ready to submit your research Ready to submit your research ? Choose BMC and benefit from:

? Choose BMC and benefit from:

Consent for publication

The figure is original, created with BioRe nder. com.

Competing interests

The authors declare no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Jimmy Petit

José Rouillard

François Cabestaing

Design and Study of Two Applications Controlled by a Brain-Computer Interface Exploiting Steady-State Somatosensory-Evoked Potentials

Brain-Computer Interfaces (BCI) allow users to interact with machines without requiring muscular activity. Thus, patients with heavy motor impairment can benefit from these systems. We have implemented an electroencephalography-based BCI which provides four distinct commands. Our system exploits the Motor Imagery of the subject and four different states of mind: imagination of a movement with the left or right arms, both arms simultaneously and no imagination at all. In addition, the BCI exploits specific neurological markers called Steady-State Somatosensory-Evoked Potentials (SSSEP). They are vibrating devices taped on the user's wrists. These markers are measurable on the cortex using electroencephalography. This paper focuses on the Computer Human Interaction aspects. We describes the design and study of two applications controlled by this BCI. The applications differ in two characteristics: their inertia, or rhythm of information flow perceived by the user, and the "punitiveness" of the application in case of mistakes.

To study the user experience in perfectly controlled conditions, we used a so-called "sham" feedback in the BCI loop rather than real feedback computed by analysing the user's brain waves. With sham feedback, the BCI provides commands with an a priori defined accuracy. We performed a user experiment of the two applications over a group of ten healthy participants. They tested both applications for different sham accuracies, varying from 45% to 90%. This permits the study and modelling of the relationship between the perceived usability of the system and the performance of the BCI.

INTRODUCTION

We implemented a Motor Imagery based BCI which provides four commands.

We conducted a user experiment to evaluate our applications over a group of ten healthy subjects. This user experience is the last session of a four-session-long experiment (ethical comity of Lille University, reference: 2020-417-S81). The other three sessions are more focused on studying the neurophysiological aspects of the BCI. Describing these sessions and their results is out of the scope of this paper dedicated to the Computer-Human Interaction aspect.

For the user experiment, we have developed two applications. However, BCI using Motor Imagery and four different commands tends to have a low accuracy, which greatly improves with a lot of training. Since the users had no time to train themselves, we used sham feedback to simulate various levels of performance [START_REF] Park | Improving Motor Imagery-Based Brain-Computer Interface Performance Based on Sensory Stimulation Training: An Approach Focused on Poorly Performing Users[END_REF].

The sham feedback has various advantages compared to testing the real performances of the system:

1. The classifier used by the BCI has already been trained before the user experiment session.

However, within one or two weeks between the two sessions, the mental activity would may have drastically changed, and it would be likely that the classifier would produce the same output to any given input, resulting in a succession of commands like Turn Left, Turn Left, Turn Left, … Sham feedbacks avoid locking the user in that situation. 2. A consequence of implementing sham feedback is that we must set the desired command (a "Good" action) for any given state of the application using a combination of level design and instructions. This allows us to then perform an offline relevant test of different classification algorithms and build on a dataset where the number of commands is reasonably balanced. For example, without sham feedback, the subject could be stuck in a state where they must use the same command repeatedly, which seriously unbalances data set. 3. For the user experiment, we use various levels of sham, ranging from 45% to 90%, which allows us to study the relationship between the system accuracy and various measured aspects in the questionnaires, which is not possible otherwise.

The objective of this article is to provide the details of the applications and how we encourage the user to use a balanced number of commands. In addition, we study the effect of the applications and the user experiment on the users themselves using questionnaires investigating fatigue, mood orientation, or mental workload, for example. Finally, we study the correlation between the perceived usability of the system, assessed with a System Usability Scale, and the performance of the system. Therefore, for a given BCI performance, we can predict what mean degree of perceived usability will be achieved, and vice versa.

APPLICATIONS DESIGN

In this section, we present in detail the applications, to allow their reproducibility. In addition, as our user experiment uses sham feedback, we introduce our definition of "Good" and "Bad" commands in the applications.

Description

The first application is a kart-driving application. The kart is controlled with the four available commands provided by the BCI: Move Forward (MF), Turn Left (TL), Turn Right (TR), and Do Nothing (DN). To balance the number of "active" commands, i.e., MF, TL and TR, the kart moves on an eight-shaped road. During a left turn of the road the user is instructed to perform a TL command, and vice-versa. In a straight part, the user is instructed to perform the MF command. Instructions are given using a sheet at the beginning of the experiment. A Turning command performs two actions on the kart: the vehicle turns and receives an additional pushing force. Therefore, one TL or TR command will make the kart follow a curved trajectory. To help stay on tracks, semi-transparent walls, with red arrows on them, follow the kart and apply a repulsive force to it as soon as it gets too close to them. Figure 1 shows two screenshots of the application. Figure 1 (a) shows the feedback given to the user: the kart moves or gains speed and an image is displayed on top of the kart. The kart is on a straight line, therefore, it has a fixed percentage, like 60%, of doing MF according to the sham feedback. If a "Bad" action must be performed, then the action is randomly and uniformly selected between TL, TR, and DN.

The second application is a puzzle-solving type of game called SokoBCI, inspired by the game Sokoban (Hiroyuki Imabayashi, 1982). The user controls the movement of a 3D avatar who must plant trees. The user must solve the levels using the smallest number of commands. To balance the number of active commands, one run of the application is composed of 2 levels. The first level is a simple symmetric level that forces the user to use an uneven number of TL and TR commands.

During the solving of the first level, the system counts the number of TL and TR commands. Level 2 is chosen to encourage the user to use the command least used during level 1. The actual vision from the user's point of view during level 2 is displayed in figure 2. The level designs and the aforementioned process are displayed in figure 3, which is a top view of the levels. When the user plants a tree, the tree appears on the red square and the red square turns green. During a run of the application, as soon as the user finishes level 1, the appropriate level 2 appears on the screen and the loop of commands starts again. To give time to the user to think about the best solution, the first command of level 2 is completely ignored by the computer, during a dozen seconds of break.

For both applications, a three-colour light is displayed at the top-left corner of the screen. The green light gives the cue to the user to start the Motor Imagery task to send a command to the BCI. After six seconds, the light turns to orange, indicating the feedback period, during which the kart or the avatar will react accordingly to the given command. After three seconds of feedback, a short break with random duration, between three to four seconds, is given to the subject with the red light.

Definition of "Good" or "Bad" Command: Specific Case of SokoBCI

The description of the Kart driving task is quite clear about the instructions given to the subject. We believe that the definition of "Good" or "Bad" command is straightforward in this case. However, for the SokoBCI it is less clear. In our user experiment, the user is instructed to "use the least number of commands to plant all the trees. If the system does an unwanted action, [example given], you might need to change your initial plan.". When observing the level design, one can verify that the solution for level one is to rotate once, left or right, and plant a tree, then rotate twice, in the same direction, to plant the second one. In this situation, the commands TL and TR are considered equally "Good" commands, the commands MF and DN, will have the same effect which is leaving the avatar motionless and are "Bad". However, during the Uturn, the initial rotation will dictate the next choice of the user, the first rotation will be either an error or not, depending on the user's mental decision. Given the instruction, the user will adjust their mental plan to pursue the rotation, end therefore the "Good" action becomes predictable.

In the first level, the avatar can face four different directions and the tree planting can have four different states (no tree planted, the left tree only, the right tree only, and both trees planted): there are thus twelve (4 * (4 -1)) different possible game states, the game state where all trees being planted being naturally ignored. Four of the game states have two "Good" actions. In the second level, left or right, the avatar can face four different directions, through two different locations, and the tree plantation can have eight different states (2 3 possible situations). Therefore, we have fiftysix (4 * 2 * (2 3 -1)) possible states of the game, of which thirteen states have two simultaneously "Good" actions.

Inertia and "Punitiveness"

The first difference between applications is in inertia. Indeed, the kart continues to move forward during the green light period. It is a vehicle that gains momentum by receiving the TL, TR, and MF commands. The user must therefore analyse the road and the speed of the kart to decide when to send the next command, even during the red-light periods which represent the breaks.

The second difference is the punishment for mistakes, which we call "punitiveness". In the kart application, the semi-transparent walls follow the kart as it moves along the track, pushing the kart in the opposite direction as it gets closer. In this case, even mistakes tend to move the kart forward, however slowly. In the SokoBCI, on the other hand, a mistake can be much more frustrating as the user will have to make a

TEST OF THE APPLICATIONS

We conducted a user experiment with a group of ten healthy participants, seven males and three females. The average age of the participants is 23.8 years (std: 3,2 years, min: 19, max: 28). In this section, we present the experimental protocol.

Protocol

The subject sits in front of the computer and fills out a pre-session questionnaire. Then, the experimenter gives an instruction sheet to the subject, who reads it and can ask any questions needed for good comprehension. Afterwards, the experimenter installs the brain-computer interface device on the user, as well as the devices that deliver the mechanical stimulation to the wrists. After this installation step, the proper tests can begin. We start by demonstrating one of the applications, chosen with a pseudo-random order across subjects, we remind the user the objective of the application and the instructions. After that, the user performs four blocks of recording with the application. Each block has a specific accuracy for the sham feedback, the four chosen accuracies are 45%, 60%, 75%, and 90%. The order is also pseudo-random. After four blocks of recordings, the demonstration and test steps are repeated for the other application. The subject has a mandatory break of 3 minutes (minimum) between each recording block.

The subject fills out questionnaires after each block and the experimenter conducts a debriefing interview with the subject at the end of the experiment. The experimenter asks the subject to fill out the questionnaire independently from one block to another. We have three different questionnaires. The first one is about behaviour measurement, the second one is a NASA Task Load IndeX without the pairwise comparison of the questionnaire's dimensions, called Raw TLX [START_REF] Hart | Nasa-Task Load Index (NASA-TLX); 20 Years Later[END_REF], and the last one is the System Usability Scale [START_REF] Brooke | SUS-A quick and dirty usability scale[END_REF] [START_REF] Brooke | SUS: A Retrospective[END_REF], or SUS. The last two are given to be completed at the end of each block. The first questionnaire is given as a pre-session questionnaire and after the first block, the fourth block (i.e., four blocks of the first application), the fifth block and the eighth block (i.e., four blocks of the second application), to measure changes in behavioural data during each application.

The Behavioural questionnaire contains four items assessing "Awakeness", Tiredness, Mood Orientation, and Emotion Intensity with a five-point Likert scale. Additionally, a space for comments is left for subjects to express themselves on the application they have just tried. The Raw TLX aims at measuring the mental workload of the application with six items: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration measured on a twenty-1) What did you think of the experiment? 2) What did you think about the difficulty to adjust your mental plan to the system's error during the SokoBCI? 3) Inform the subject about the sham feedback: what is it about, how is it done, and why we do it. 4) Did you ever suspect the sham feedback? [If yes, when?] 5) Did you suspect different levels of performance/accuracy? 6) Did you discuss about performances during the previous session [which also had sham feedback] with your friend/colleague? [Question optional, question asked only if the friend/colleague also participates in the experiment.]

Table 1: Interview guide for the experimenter point Likert scale. The SUS aims at measuring the usability of the system with a ten-item long questionnaire, also using a fivepoint Likert scale.

In the debriefing interview at the end of the session, we discuss with the subject different aspects of the whole experiment. Table 1 presents the different questions asked, and their order. At the end of the session, some subjects had strong time constraints, which led us to shorten some interviews.

Behavioral Data -Results

Results of the Behavioural data analysis are displayed in figure 4. We can observe that, "Awakeness", Mood orientation (positive to negative), or Emotion Intensity do not seem to evolve during the session. However, Tiredness tends to increase, indeed the majority mention (the mention that crosses the 50% threshold) became three (out of five) by the end of the session. A few subjects filled out the mention number four during the session too, which they did not at the beginning of the session. To conclude in a few words, the eight blocks of recording seem to cause a little fatigue to the subjects population, additionally, the three other dimensions do not evolve much.

The Raw TLX results are presented in figure 5. When observing the distribution of the Raw TLX score against the sham accuracy, no trends seem to appear. No difference can be observed between applications either. However, the individual dimensions of Performance and Frustration are highly inversely proportional to the sham accuracy. It seems to hold for the Effort dimension of the questionnaire too, however to a lesser extent than the previous two dimensions. The subjects seem to have well experienced the difference in the BCI performances and the frustration level diminished as the performance increased, likely caused by the decreasing number of mistakes performed by the system. Interestingly, as the accuracy increases, we measure a difference in Mental Demand between the applications. With sham accuracy at and above 75%, the subjects seem to experience a Kart application more mentally demanding than the SokoBCI application. This is confirmed using a dependent samples t-tests1 : at 75% a p-value of 0.0012 (< 0.05) and at 90% a p-value of 0.019 (< 0.05) are computed. At 75%, the mean difference in Mental Demand between the Kart and the SokoBCI is at 2.2 points (std: 1.6) while being at 2.5 points (std: 3.1) at 90% of sham accuracy. This difference can be explained by the difference in inertia between the two applications. In the kart, when the three-colour light is red, the kart is still moving, and the user must think to anticipate the movement of the kart. Additionally, the effect does not occur for low accuracies since multiple errors tend to slow down, or even stop, the kart. Finally, a weak difference between the application in the Frustration level is also observable for the lowest accuracy as the mean and median are systematically higher in the SokoBCI than in the Kart. This could be explained by the "punitiveness" of the SokoBCI, an error being much more costly in this application than in the Kart-driving one.

Relationship Between Performance and SUS

Figure 6 shows the results of the SUS questionnaires. Firstly, the SUS scores are positively correlated to the sham accuracy.

According to the slope coefficient of linear regression, the effect is stronger in the SokoBCI application than in the Kart. It can be also explained by the higher "punitiveness" of an error in SokoBCI than in the Kart.

Bangor et al. added an adjective rating scale to mean SUS scores, see figure 7 [START_REF] Bangor | Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale[END_REF]. In doing so they also provide an interpretation of SUS scores using an adjective, school grading system, or acceptability range from previous works. According to their results, a system would start to be acceptable with a SUS of 70 and everything below had usability issues and is cause for concern. Therefore, using these models, in a BCI with similar features to the SokoBCI, the system would become acceptable with a minimum performance level of 85.4%, whereas a system like the Kart application would need a minimum performance level of 74.3%.

Questionnaire Comments and Debriefing Interview Results

Reading the comments and notes during the experimenter's debriefing allowed us to identify four categories of feedback: Strategy, the strategy found by the subject to perform the task; Application Comparison, the subject expresses some preference toward one application over the other; Positive Comment, various adjectives that show the subject's appreciation for the application, the system or the experiment; and Improvement Tips, which is a list of things that could be improved to make the applications better.

The commentaries related to session comparison (see Table 1 -1) and the performance of the subject written during the session are ignored, as the subjects did not expect sham feedback. We have translated the comments from French to English as faithfully as possible. Finally, we added context to comments or shortened them, if necessary, when indicated in brackets.

Strategy

Two subjects spontaneously used the same strategy of Motor Imagery during the SokoBCI. They imagined themselves pulling the antenna of the avatar with one or two arms. For example, subject n°10 writes "The design of the character helped me to visualise the correct movements, I imagined taking the antennas on the head of the character and pulling them (the antenna on the right with the right hand to turn to the right, [etc])".

The subject n°6 comments that he found it easier to focus on the road instead of the kart: "I found it easier to concentrate when I wasn't looking at the vehicle (looking at the road instead) [After Kart 45%].".

Application Comparison

Subjects 2 and 10 comment about the higher complexity of the SokoBCI over the Kart driving application, subject n°2 writes: "[SokoBCI] is very funny (more than Kart), but more complex too". However, subject n°4 states during the debriefing having more trouble processing the scene and movement while performing the Motor Imagery task: it's hard to see the game and play at the same time. Acquire information and respond in time, that's difficult.".

Positive comments

Almost every subject commented something positive; the words "fun" or "playful" appeared a lot. The word "fun" was given by six different subjects. Subject n°10 noticed how time seems to pass much faster and subject n°3 highlights the intuitiveness of the system: "It's fun finally seeing the system working for me. It's pretty instinctive to use at this point [after SokoBCI at 75%]". Subject n°8 comments that the experiment was more ecological: "Last session with a concrete application is a bit more playful.".

Improvement Tips

Subjects 4, 5 and 8 commented that the inertia of the kart was disturbing them: subject 4 writes "I struggle focusing simultaneously on the stimulations and on the commands to be performed", and subject n°5 writes: "I struggle to focus simultaneously on the stimulations and on the commands to be performed [during Kart]: really tiring. [In SokoBCI] The character is static during the acquisition [START_REF] Bangor | Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale[END_REF] Figure 6: Mean and 95% Confidence Interval, computed by bootstrap, of the SUS Score in regard to sham accuracy.

[i.e. Green light] so we do not receive information, this helps to focus.". Interestingly, subject n°7 mentioned that the breathing animation of the avatar in the SokoBCI during the green light was a distraction: "The [IDLE] movement of the avatar are distracting.". Subjects 2 and 3 retain some ambiguity on the action to be performed during the Kart as they commented on the questionnaire: "Sometimes, I did not know which movement to imagine. For example: a turn arrives, should I turn by anticipation?" (Subject n°2). In this case, the instruction was repeated, however, the anticipation aspect seems uneasy. Subject n°4 advised to reduce the duration of the green light periods as it was too long, and subject n°5 advocates for a blue sky in the kart application and wished for a more comfortable EEG headset installation.

CONCLUSIONS, LIMITATIONS AND FUTURE WORKS

In this paper we presented the design of two applications controlled by a BCI: a kart driving application and a puzzle solving application called SokoBCI. The BCI provides four commands. The applications differs on two main points, SokoBCI is more punitive than the Kart in case of mistakes. Indeed, after a mistake the user must react to provide a corrective command in the SokoBCI, while in the kart, invisible walls on each side of the road push back the kart in the good direction as it gets closer in case of mistakes. Secondly, the Kart's motion is continuous and partly controlled by inertia while in SokoBCI the avatar steps from its current position to the next one. It means that the kart keeps moving during the Motor Imagery task and the breaks, and therefore that the user must maintain a significant level of mental activity in the decision-making process to choose the correct command to use.

We evaluated both applications using questionnaires, open written comment and discussions with a group of ten healthy subjects. We observed that some dimensions of the Raw TLX are highly correlated to the performance of the system, like Performance and Frustration, while others don't. In addition, the Mental Demand at high performance of the system, was more important in the Kart than in SokoBCI. It might be explained by the difference in inertia between the application. This was also confirmed by the users in the commentary and discussion.

Additionally, we proposed a model of the relationship between the performance of the BCI and the perceived usability, assessed with an SUS. Firstly, the models show a positive correlation between the variables for both applications. In addition, the correlation was stronger in the SokoBCI than in the Kart. This could be explained by the fact that the SokoBCI is more punitive to the user in case of mistakes. Therefore, one might be concerned by the design choice in the application creation process as it can make an application felt acceptable by the user for a performance level much lower or higher. In our case, we found a ten-point difference in accuracy between the application to reach the acceptability threshold.

One straightforward limitation of this work is the number of subjects included in the experiment, further inclusions are needed to increase the significance of results. Finally, elaborating a more general approach based on characteristics of various application, like inertia or "punitiveness", to model the impact of those application characteristics on the user might be an interesting tool to help in the design of serious games.

  Figure 1: Screenshots of the kart (a) on a straight line (b) at the cross section of the eight shaped road.

Figure 3 :

 3 Figure 3: Top view of the SokoBCI levels. (a) shows level 1. Depending on the number of TL or TR used to solve the level 1, one level 2 is chosen (b) or (c). The blue squares show the possible location of the avatar, accessible with the Forward command while facing the proper direction. The red squares show the targets. The user has to orient the avatar towards a target and use the command MF to plant a tree.

Figure 2 :

 2 Figure 2: User view at the beginning of a level 2 (Turn Left induced-design).

Figure 4 :

 4 Figure 4: Stacked bar plots showing the distribution and evolution of Behavioural data over the subjects.

Figure 5 :

 5 Figure 5: Box plots of the Raw TLX results, grouped by the application type. The six first lines show the individual dimension of the questionnaire, while the seventh line show the score of it.

Figure 7 :

 7 Figure7: Relationship between the adjective ratings, acceptability scores, and school grading scales, in relation to the average SUS score. From[START_REF] Bangor | Determining What Individual SUS Scores Mean: Adding an Adjective Rating Scale[END_REF] Figure6: Mean and 95% Confidence Interval, computed by bootstrap, of the SUS Score in regard to sham accuracy.

We failed to reject the hypothesis of normality of the four samples using Shapiro-Wilk tests and a rejection threshold of 5%, therefore we assumed the normality of the samples.

ACKNOWLEDGMENTS

The authors would like to acknowledge Camille Bordeau and Philémon Berne, both interns of the team at the time. CB helped the authors by contributing to the conception of the questionnaires and PB assisted the first author in recording few sessions of the experiment and greatly contributed to digitising the data from the questionnaires. The authors would also like to thank MD. PhD. Professor Arnaud Delval from the clinical neurophysiology department of the Lille Hospital for his supports by allowing us to perform the experiments within these infrastructures and with their electroencephalogram system.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available upon reasonable request from the authors.


Multidisciplinary study to highlight interaction between anthropogenic disturbance and natural coastal sedimentary processes. Complementarity of geochemical and granulometric methods and proposal of a new spatial geostatistical approach

Keywords: Geochemistry, Multi Sediment Trend Analysis (MSTA), Grain-Size Trend Analysis (GSTA), Geographic Information System (GIS), Bay of Seine, Dumping site

Abstract

Traditional geochemistry studies use mapping techniques and multivariate analyzes to highlight spatial distribution of chemical concentration parameters. Granulometric parameters are used to study sedimentary transport, especially through Grain Size Trend Analysis (GSTA) approach integrating mean, sorting and skewness parameters. Within the increasing pressure of human activities on marine coastal ecosystems, the study of sedimentary disturbances remains a challenge. The Bay of Seine is highly anthropized by harbour activities and dredging sediments from The Havre Harbour and their deposition on subtidal area. To understand sedimentary mechanism, a geochemical and sedimentological study was conducted at the beginning of 2016. Sediments from 179 subtidal stations and 16 stations in the harbour basins and in the Seine, estuary were studied. Geochemical elemental composition (18 calibrated elements) was obtained through X-Ray Fluorescence spectrometry and infrared spectrometry (TOC). On this dataset, multi-treatments were applied and the results compared: mapping spatial distribution of the concentrations of each chemical element; PCA analyzes and selection of the information-bearing parameters and mapping of the PCA results; application of the "classical" GSTA approach on the granulometric parameters, "Innovative" integration of the chemical parameters and PCA results in the GSTA approach. The results show the need of multidisciplinary research and the interest of geochemical tracers to study coastal sediment dynamics and to highlight the impact generated by anthropogenic activities. The geochemical GSTA approach confirms the sedimentary dynamics and appears more robust than the methods conventionally used. To generalize this approach, an adaptation of the concepts is currently being developed: The MSTA.


Alice Mouton

Christine Fournier-Chambrillon

Pascal Fournier

Jakub Skorupski

Przemyslaw Śmietana

Benoît Vacherie

Thomas Guérin

Emilie Payen

Laurie Bertrand

Ghislaine Magdelenat

European mink (Mustela lutreola) reference genome and population genomics

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

•

  European mink (Mustela lutreola) reference genome and population genomics A. Mouton, C. Fournier-Chambrillon, P. Fournier J. Skorupski , P. Śmietana , B. Vacherie , T. Guérin , E. Payen, L. Bertrand, G. Magdelenat, B. Mairey, C. Hamon, M. Leprêtre, N. Martins, E. Brun, O. Beluche, S. Lebled, C. Milani, B. Istace, C. Belser, K. Labadie, C. Cruaud, P. H. Oliveira, J.M. Aury, P. Wincker, M. Põdra, M. Gerbault-Seureau, I. Marchand, M. Marinov, T. Maran, C. Bellanger, B. Bed'Hom J. Michaux Mouton Alice, University of Liege 34th European Mustelid Colloquium September 2022 • February 2006 : skin biopsy taken from a male captured by GREGE in SW France, in the framework of PNA (National Action Plan) • Sent to MNHN (National Museum of Natural History, Paris) for establishment of cell culture in flasks • March 2006 : cryopreservation in liquid nitrogen (-196°C) of cryotubes containing mink cells ("suspended life") https://www.erga-biodiversity.eu/ Reference genome : ERGA pilot project • ERGA (European Reference Genome Atlas) Pilot projet European mink selected as a critically endangered species • June 2021 : New cell cultures initiated from samples cryopreserved in 2006 Control of karyotype, barcode • July 2021 : 27 million cells produced and transferred at Genoscope (sequencing center) for : o DNA & RNA extraction o sequencing (long reads, short reads, Hi-C…) o genome assembly • Mars 2022 : Assembly v1 • May 2022 : Assembly v2 European mink karyotype (2N=38) Bertrand Bed'hom (MNH Paris) https://www.erga-biodiversity.eu/pilot-project Main threats: habitat loss and fragmentation, road collision, animal bites, confusion with american mink, rat poison. • Current distribution into three isolated areas • High risk of inbreeding depression in western Europe (~ 500 individuals estimated) => Level of genomic diversity in Europe? Using 3RAD and Whole-genome resequencing • large sets of markers that increase the ability to detect and quantify genetic variation in the population • Identify chromosomal tracts of ancestry • Demographic modeling • Deleterious mutation

Acknowledgments

Whole Genome Resequencing


PhD Mika Kivimaki
email: m.kivimaki@ucl.ac.uk

MD Adam G Tabak

PhD G David Batty

PhD Archana Singh-Manoux

PhD Markus Jokela

PhD Tasnime N Akbaraly

MD, PhD Daniel R Witte

PhD Eric J Brunner

PhD Michael G Marmot

MD, PhD Debbie A Lawlor

Prof Mika Kivimaki

DC09-0716 Hyperglycaemia, Type 2 Diabetes and Depressive Symptoms: The British Whitehall II Study Running title: Glycaemia, Diabetes and Depressive Symptoms

ABSTRACT

OBJECTIVE-The recent suggestion that impaired fasting glucose may protect against depression, whereas a diagnosis of diabetes might then result in depression, warrants further examination.

RESEARCH DESIGN AND METHODS-Cross-sectional analysis of 4228 adults (mean age 60.7 years, 73.0% male) who underwent oral glucose tolerance testing and completed the Center for Epidemiologic Studies Depression (CES-D) scale. RESULTS-After adjustment for demographic factors, health behaviours and clinical measurements (BMI, waist circumference, lipid profile and blood pressure), there was a 'U'shaped association between fasting glucose and depression (Pcurve=0.001), with elevated CES-D at low and very high glucose levels. This finding was replicable with 2-hour postload glucose (p=0.11) and HbA1c (p=0.007).

CONCLUSION-The 'U'-shaped association between blood glucose and CES-D, with the lowest depression risk seen amongst those in the normoglycaemic range of HbA1c did not support the hypothesized protective effect of hyperglycaemia.

The association between type 2 diabetes and depression, both major public health challenges, remains unclear [START_REF] Palinkas | A prospective study of Type 2 diabetes and depressive symptoms in the elderly: the Rancho Bernardo Study[END_REF][START_REF] De Jonge | Prevalent and incident depression in community-dwelling elderly persons with diabetes mellitus: results from the ZARADEMP project[END_REF][START_REF] Maraldi | Diabetes mellitus, glycemic control, and incident depressive symptoms among 70-to 79-year-old persons: the health, aging, and body composition study[END_REF][START_REF] Polsky | Long-term risk for depressive symptoms after a medical diagnosis[END_REF][START_REF] Brown | Type 2 diabetes does not increase risk of depression[END_REF][START_REF] Kim | Vascular risk factors and incident late-life depression in a Korean population[END_REF][START_REF] Golden | Examining a bidirectional association between depressive symptoms and diabetes[END_REF][START_REF] Boyle | Depressive symptoms, race, and glucose concentrations: the role of cortisol as mediator[END_REF]. In a recent U. S. report, people with type 2 diabetes had an increased risk of depressive symptoms, whereas, conversely, in non-diabetic individuals higher impaired fasting glucose (IFG) appeared to confer protection against depression [START_REF] Golden | Examining a bidirectional association between depressive symptoms and diabetes[END_REF]. While an increased prevalence of depression in people receiving a diagnosis of a pernicious chronic disease such as type 2 diabetes is perhaps unsurprising, the apparent counter-intuitive protective effect of IFG warrants further scrutiny. In the Whitehall II study we were able to explore the relationship between depression and a greater range of glycaemia measures [fasting and postload glucose, glycated haemoglobin 1c (HbA1c)] than has previously been possible.

RESEARCH DESIGN AND METHODS-In 2003/04 data collection phase of the

Whitehall II study (described in detail elsewhere) [START_REF] Marmot | Cohort Profile: the Whitehall II study[END_REF], 4228 men and women aged 50 to 74 years completed a depression questionnaire and, if without known diabetes, underwent an oral glucose tolerance test (OGTT). Venous blood samples were taken after at least 8 hours of fasting, before OGTT, and at 2-hour post administration of a 75g glucose solution. Blood glucose was measured using the glucose oxidase method (10) on a YSI MODEL 2300 STAT PLUS Analyzer (YSI Corporation, Yellow Springs, OH, USA) (mean coefficient of variation (CV): 1.4%-3.1%) [START_REF] Astles | Evaluation of the YSI 2300 glucose analyzer: algorithm-corrected results are accurate and specific[END_REF]. Diabetes was defined by a fasting glucose ≥7.0 mmol/L or a 2-hour postload glucose ≥11.1 mmol/L or reported doctor diagnosed diabetes or use of diabetes medication [START_REF]Report of the expert committee on the diagnosis and classification of diabetes mellitus[END_REF]. In non-diabetic participants, we classified moderate hyperglycaemia as IFG (fasting glucose between 5.6 to 6.9 mmol/L) and Impaired Glucose Tolerance (IGT, 2-hour postload glucose between 7.8 and 11.0 mmol/L) [START_REF]Report of the expert committee on the diagnosis and classification of diabetes mellitus[END_REF]. HbA1c was measured on whole blood with a calibrated HPLC system (CV: 0.8%).

Depressive symptoms were assessed with the Center for Epidemiologic Studies Depression scale (CES-D) summary score [START_REF] Radloff | Center for Epidemiologic Studies Depression Scale (CES-D)[END_REF], a measure that has been validated among diabetic patients [START_REF] Fisher | Contributors to depression in Latino and European-American patients with type 2 diabetes[END_REF]. Ethnicity (white or non-white), body mass index [weight (kg) per height squared (m 2 )], waist circumference (cm), systolic and diastolic blood pressure (mm Hg), HDL-and LDL-cholesterol (mmol/L), triglycerides (mmol/L), current smoking (yes/no), alcohol consumption (none, 1 to 3 units per day, >3 units per day) and physical inactivity (<2.5 hrs moderate and <1 hr vigorous exercise per week) were measured according to standardised protocols.

Statistical methods

All 4228 participants had adequate data on CES-D and diabetes status, but there were some missing data for some of the different glucose parameters. Thus, our different analyses are based on between 3945 (93.3% of the 4228) and 4228 (100%) of the eligible participants.

Values for triglycerides were log-transformed prior to analyses due to skewed distribution. We used linear regression analysis to model the associations of IFG and IGT with the CES-D score. The shape of the associations between fasting glucose, postload glucose, HbA1c and CES-D were studied by treating all these measures as continuous variables. To test for curvilinear trends a squared term of the glycaemic measures was added to an equation containing the linear term. The models were adjusted for age, sex, ethnicity and clinical characteristics (BMI, waist, systolic and diastolic blood pressure, HDL-and LDL-cholesterol, triglycerides, smoking, alcohol consumption, and physical activity). The statistical tests were performed with Stata version 10.1.

RESULTS-Of the 4228 participants, 2038 (73.0%) were men and 3895 (92.1%) Caucasian.

Mean+SD age was 60.7+6.0 years and the levels of clinical characteristics were 128+17/74+10 mm Hg for systolic/diastolic blood pressure, 1.6+0.4 mmol/L for HDLcholesterol, 3.58+1.9 mmol/L for LDL-cholesterol, 26.7+4.4 kg/m 2 for BMI, and 94.2+10.7 (men) and 84.3+13.0 cm (women) for waist circumference. For triglycerides, median+IQR was 1.2+0.9 mmol/L. Of the participants, 7.9% were current smokers, 16.0% were physically inactive, 17.8% consumed more than 3 units alcohol per day and 16.2% did not consume alcohol regularly. Overall CESD-mean score was 9.9+6.6.

Fasting glucose-Mean+SD was 5 .

 5 55+1.51 mmol/L. Compared to participants with normal fasting glucose [n=3038, mean+SD CES-D=9.9+6.7], those with IFG (n=735) showed a marginally reduced CES-D score [Mean+ SD=9.0+ 6.1, P=0.05], while those with diabetes (n=455) showed an elevated CES-D score [Mean+ SD=11.2+ 7.0, P=0.002] after taking into account age, sex and ethnicity. As shown in Figure 1-Panel A, there was a Ushaped association between fasting glucose and CES-D (Pcurve=0.001 after adjustment for age, sex and ethnicity, n=3986), with elevated CES-D values at glucose levels <4.5 mmol/L and >9.0 mmol/L. The curvilinear trend was robust to additional adjustment for clinical characteristics (P=0.001). Postload glucose-Mean+SD was 6.38+2.09 mmol/L. IGT [n=423, CES-D mean+SD=9.49+6.58] and isolated IGT (n=284) were not associated with CES-D (P>=0.53). However, there was a U-shaped association between postload glucose and CES-D (Figure 1-Panel B, n=3455, P curve =0.05 after adjustment for age, sex and ethnicity; P curve =0.11 after additional adjustment for clinical characteristics). HbA1c-Mean+SD was 5.36+0.73%. Again, a curvilinear association with CES-D was evident (p=0.04, n=4160), Figure 1-Panel C. The lowest CES-D scores were between HbA1c levels 4.0% to 5.5% (nadir 4.4% in age, sex and ethnicity adjusted model) and this was also seen in raw data (Appendix). The curvilinear trend remained after additional adjustment for all clinical characteristics (P=0.007). CONCLUSIONS-We examined the associations of various glycaemic measures, including fasting and postload glucose and HbA1c with symptoms of depression. Our results show slightly lower levels of depressive symptoms among non-diabetic individuals with IFG (7). However, this finding was generated by a 'U'-shaped association between fasting glucose and CES-D with elevated depression scores seen at both ends of the glucose distribution, a finding which was replicated for 2-hour postload glucose and HbA1c. While low depression scores were observed both at normal and prediabetic ranges of fasting and postload glucose, findings from long-term glucose levels (HbA1c) clearly demonstrated that normoglycaemic individuals had the lowest depression risk. In summary, our results do not support the protective effect of long-term hyperglycaemia but they are in agreement with the recommendation that clinicians consider screening for depression among patients with diabetes. Future research should determine explanatory mechanisms for increased depressive symptoms among non-diabetic individuals with low glucose levels.

Figure 1 .

 1 Figure 1. Age, Sex and Etnicity/Race Adjusted Associations of Fasting Glucose (A), 2-hour Postload Glucose (B) and Glycated Hemoglobin (C) with Depression Assessed by the Center for Epidemiologic Studies Depression scale (CES-D).

Acknowledgements: The Whitehall II study has been supported by grants from the Medical Research Council; British Heart Foundation; Health and Safety Executive; Department of Health; National Heart Lung and Blood Institute (HL36310), US, NIH: National Institute on Aging (AG13196), US, NIH; Agency for Health Care Policy Research (HS06516); and the John D and Catherine T MacArthur Foundation Research Networks on Successful Midlife Development and Socio-economic Status and Health. MK is supported by the Academy of Finland; GDB is a Wellcome Trust Research Fellow; AS-M is supported by a 'EURYI' award from the European Science Foundation; JEF is supported by the UK Medical Research Council; MGM is supported by a MRC Research Professorship; DAL works in a centre that receives some core funding from the UK Medical Research Council. The funding bodies have not influenced the conduct of this study or any of its conclusions. The views expressed here are those of authors and not necessarily any funding body. Disclosure: No conflict of interest to disclose.


Tingjun Hu

Dr Mohammad Jaber

Dr Gaël Tran

Dr Didier Bouyssi

Prof Nuno Monteiro

Dr Abderrahmane Amgoune
email: abderrahmane.amgoune@univ-lyon1.fr

Photoinduced NiH Catalysis with Trialkylamines for the Stereodivergent Transfer Semi-Hydrogenation of Alkynes

Keywords: Alkyne semi-reduction, Hydrogen transfer, Nickel catalysis, Photoredox catalysis, Stilbenes

come   L'archive ouverte pluridisciplinaire

Introduction

The development of reliable and predictable methods that can convert alkynes stereo-selectively to Z-or Ealkenes, on demand, is of fundamental importance to industries and academia, owing to the prevalence of the alkene functionality in fine chemicals, pharmaceuticals and natural products, which include the high-value stilbenoids. [1] The privileged systems for selective hydrogenation to Zalkenes are based on palladium heterogeneous catalysts using gaseous hydrogen. These methods often suffer from fast catalyst deactivation, over-reduction, and the presence of toxic lead oxides or excess quinoline. On the other hand, conventional methods to access E-alkenes from alkynes rely on unpractical Birch-type reductions featuring harsh conditions and therefore poor functional group tolerance.

Over the recent decades, important research efforts have focused on the development of milder experimental protocols which led to significant advances in applying sustainable organic molecules like alcohols and organic acids, as well as water instead of gaseous hydrogen. New catalysts based on first-row transition-metals (Ni, Co, Cu, Fe, and Mn) have also been extensively developed as viable alternatives to Pd. [2a] Nevertheless, overcoming issues with chemo-and regio-selectivity has remained a recurrent challenge for the development of catalytic alkyne semi-reduction processes. [START_REF] Gregori | For reviews of catalytic semi-reductions of alkynes[END_REF] High-efficiency nickel-based catalytic systems have been recently reported for selective reduction of alkynes to E-or Z-alkenes with limited over-reduction, if any. While Zisomers are often easily formed as the preferred products under mild conditions, [3] selective methods for E-isomers have proved more challenging, often requiring harsh conditions (e.g., high temperature, high pressure of gaseous hydrogen, high loading of metal reductants) or specifically designed catalysts (Figure 1A), and they remain under-developed. [4]

More

interestingly, catalytic methods allowing stereodivergent semi-reduction to Z or E alkenes are very rare. [5] These strategies typically rely on the generation of a nickel hydride intermediate from diverse hydride sources, followed by the formation of a key alkenyl-nickel species and subsequent proto-denickelation that liberates the alkenes. In typical mechanisms, it is proposed that the alkyne is first converted to the Z-alkene, which may then be isomerized to the corresponding E-alkene by the nickel hydride species. [START_REF] Eberhardt | Nickel hydride-promoted Z to E alkene isomerization via the typical protometalation/-hydride elimination mechanism has been commonly proposed to account for E-selective alkyne semi-reductions. See for instance refs 4a,c and 5b-c. For a review of the chemistry of nickel hydride complexes[END_REF] The isomerization process can be controlled and tuned by changing various reaction parameters, i.e. by modifying the nickel catalytic system (nickel source, ligand) or via an additive. However, these methods still require quite harsh conditions and high temperatures that can limit their practical application. Today, the development of mild, operationally simple protocols allowing a stereodivergent production of Z-or Ealkenes remains a remarkable challenge in this research.

The recent advent of nickel and photoredox dual catalysis has stimulated new conceptual strategies toward the conversion of alkynes to functionalized alkenes under very mild reaction conditions. [7] However, applications to the simple semi-reduction of alkynes remain elusive in this area. Very rare examples have been recently reported, based on heterogeneous catalytic systems that provide Zalkenes, preferentially, with moderate levels of selectivity. [8] We envisioned that the development of a nickel/photoredox system, using mild hydrogen donors and allowing selective access to either E-or Z-alkenes by simple variations of the reaction parameters, would provide a valuable complementary strategy for the stereodivergent semireduction of alkynes.

From the outset of our endeavors, we realized that the set-up of a viable catalytic protocol under photocatalytic conditions would raise several challenges to address. Ideally, the stereo-outcome of the semi-reduction should be controlled by the nickel catalyst rather than by the sensitizer. Indeed, visible light photocatalysis has been shown to promote E/Z isomerization of alkenes through triplet energy transfer from the excited photocatalyst, which can complicate the design of stereodivergent methodologies. [9] One possible strategy would be to control the rate of isomerization and protonolysis of the postulated alkenyl-nickel intermediates through careful choice of the species to be involved in the protonolysis step or by ligand electronic tuning. A last but not least challenge would be to find a suitable, mild source of hydrogen atoms capable of promoting the generation of nickel hydride species under photochemical conditions. [10] Herein, we report a metallaphotoredox catalytic transfer semihydrogenation methodology that satisfies all these challenges (Figure 1B). Our strategy relies on the use of a simple trialkylamine serving not only as a reductive quencher, but also as hydrogen transfer reagent [11] capable of providing hydrogen atoms to the catalytic system via its photochemically generated amine radical cation. [12] An additional remarkable feature of the process is the possibility of inducing a complete selectivity switch by adjusting the pKa of a simple alcohol additive. Mechanistic studies provided some rational for the origin of stereoselectivity, notably dismissing typical post-reaction alkene isomerization pathways.

Results and Discussion

The feasibility of the redox process was primarily examined by reacting our model substrate, 1-fluoro-4-(phenylethynyl)benzene (1a), with triethylamine in the presence of a combination of nickel(II) catalyst and photocatalyst under visible light irradiation (Table 1). 9,10-Diphenylanthracene (DPA) was selected as an appropriate photocatalyst for our preliminary experiments. DPA is an inexpensive organic semi-conductor used in OLEDs and blue glow sticks, but remains under-utilized as a photocatalyst. [START_REF]For physical properties and uses of DPA[END_REF] The oxidation potential of its excited state [E*= +1.19 V vs SCE in DMSO] [13a] should allow access to amine radical cations via one-electron oxidation of trialkylamines, while the strong reducing power of its ground-state radical anion [E1/2(DPA •- /DPA) = -1.94 V] [13b] should be capable of reducing Ni species to sustain the catalytic cycle.

We were pleased to find that nearly full conversion ( 19 F NMR) of 1a into the desired semi-reduction products could be achieved by simply using catalytic amounts of Ni(dtbbpy)Cl2 (5 mol%) (dtbbpy (L1) = 4,4′-di-tert-butyl-2,2′bipyridine) and DPA (5 mol%) as the photocatalyst in the presence of 1.5 equiv of triethylamine. Our benchmark reaction was best conducted in MeCN at room temperature for 24 h under irradiation by a 18 W purple LED lamp (405 nm). Interestingly, under these conditions, the reaction provided a 16:84 mixture of Z and E-stilbenes 2a/3a, respectively, with no over-reduction to the corresponding 1,2-diarylethane being observed (Table 1A). This notably confirmed that triethylamine is indeed a potent source of hydrogen atoms in the absence of other H-donors. While the first hydrogen atom is likely to be transferred via the NiH intermediate, we postulated that the second one, which would be introduced via protodenickelation, could be provided by the α-amino C-H (pKa = 14.7 in MeCN) of the triethylamine radical cation species. [12] We thus postulated that the addition of other proton sources may impact the protonolysis step and therefore the stereoselectivity of our benchmark reaction. Nevertheless, the protonolysis reagent should be judiciously chosen to avoid potential protonation of triethylamine and quenching of the photo-oxidation process. In this respect, aliphatic alcohols seemed particularly suitable protonolysis reagents due to their moderate acidities. Interestingly, the addition of alcohol additives (up to 25 equivalents) to the reaction mixture did not affect the formation of the desired stilbenes, and a clear dependence of the reaction stereoselectivity on the acidity of the alcohol could indeed be observed (Table 1B). A slight increase in yield and selectivity towards E-isomer 3a (E/Z up to 88:12) was obtained when ethanol or isopropanol were employed. However, a gradual stereoselective enrichment of Z-isomer 2a was observed in the presence of fluorinated alcohols. [START_REF]For physical properties and applications of fluorinated alcohols, see[END_REF] While 2-fluoroethanol had only a slight effect on the selectivity, 2,2-difluoroethanol provided nearly equimolar amounts of both stereoisomers. Most remarkably, the more acidic 2,2,2-trifluoroethanol (TFE) induced a switch of the selectivity to afford a 68:32 isomeric ratio in favour of the Zisomer 2a. Importantly, the presence of triethylamine remained critical to the success of these experiments. Further increasing the pKa of the alcohol additive was shown to be detrimental to the reaction. Indeed, when the more acidic hexafluoroisopropanol (HFIP) was used, no reaction was observed (entry 13), probably due to the formation of strong hydrogen bond interactions with the amine, [15] inhibiting the photo-oxidation step. The use of other protic additives, such as carboxylic acids or phenols, also led to increased selectivity in favor of Z-isomer 2a, although in greatly decreased yields (see Table S1). F NMR spectroscopy using fluorobenzene as an internal standard. [b] 2.5 mL of MeCN were used. [c] 25 equiv of additive were added to the standard reaction mixture (2 mL of MeCN were used).

In order to gain more insights into the origin of the hydrogen atoms and of the stereoselectivity of the reaction, we carried out a series of control experiments (Figure 2). We first excluded the possibility of a post-reduction isomerization of the alkene that may involve either nickel hydride catalysis [START_REF] Eberhardt | Nickel hydride-promoted Z to E alkene isomerization via the typical protometalation/-hydride elimination mechanism has been commonly proposed to account for E-selective alkyne semi-reductions. See for instance refs 4a,c and 5b-c. For a review of the chemistry of nickel hydride complexes[END_REF] or photocatalysis. [9] Indeed, stereoisomerically pure Z-or E-alkenes, 2a and 3a, were engaged in the semi-reduction reaction using EtOH or TFE as additives. In both cases, the configuration of the alkenes was left untouched, which suggests that selectivity is intrinsic to the mechanism of product formation (Figure 2A). This was further confirmed by 1 H NMR spectroscopic monitoring of the semi-reduction reactions, which showed that the E/Z ratio was stable through the entire course of the reaction. The monitoring also revealed that the reaction is significantly slower with TFE compared to EtOH (Figure 2B). [16] Additionally, both reactions seemed to follow an apparent zero order rate law with respect to alkyne, as the rate of both reactions remained constant over most of the reaction course. We thus hypothesized that the slower reaction with TFE may originate from the formation of stronger H-bonding with Et3N which would result in slower quenching of excited DPA* by Et3N. [START_REF] Li | enhance the redox stability of aliphatic amines through the formation of H-bonds between the alcohol and the amine, which significantly slow down SET from the amine to the excited photocatalyst[END_REF] Having established that stereoselectivity is set during product formation, we sought to determine the source of the two hydrogen atoms incorporated in the product. To do so, the reaction was first carried out with deuterated alcohols. Diminished yields were obtained after 24 h in both cases, thus confirming the involvement of the alcohol in the rate determining step. Interestingly, we observed that in both E-and Z-selective protocols, the deuterium incorporation is only about 63-66%, which clearly indicates that the alcohol is not delivering the two hydrogen atoms. Remarkably, the ability of Et3N to act as a potent hydrogen source in the absence of alcohol additives was corroborated by a deuterium labelling experiment using fully deuterated triethylamine (Et3N-d15). In this condition, almost complete deuterium incorporation at both vinylic positions was observed (Figure 2C). Finally, we also showed that the reaction does not proceed via direct protonation of a Ni(0)-alkyne species. [16] Based on these experimental observations, we propose a general pathway for the formation of E-or Z-alkenes (Figure 3). The reaction starts with the photocatalytic generation of Et3N

•+ and Ni(I) species. The next important step involves the formation of a nickel(II) hydride intermediate C. [10] Among the possible pathways that could be envisioned for the photochemical generation of Ni-H species via H-transfer from triethylamine radical cation we postulate the formation of an -aminoalkyl radical species [12] that would be subsequently captured by Ni(I) and released as enamine through -hydride elimination [10d] (see Supporting Information for mechanistic discussion). The resulting nickel(II) hydride complex C would then perform a syn-insertion into the alkyne, intermediately leading to alkenylnickel complex E. In the presence of a sufficiently acidic proton source, such as TFE, this complex is rapidly protonolysed to give the Z-alkene 2. On the other hand, if the kinetics of the protonolysis are sufficiently slow, alkenylnickel isomerization to the less hindered alkenylnickel isomer E' can occur, most likely through the formation of an  2 -vinylnickel intermediate, [START_REF] Zell | The mechanism of isomerization of alkenylnickel species has been recently proposed to proceed through the formation of an  2 -vinylnickel complex[END_REF][START_REF] Liu | For reviews of recent applications of alkenylnickel isomerization processes[END_REF] ultimately leading to the E-alkene 3 after protonolysis. [START_REF] Barber | For other studies of alkenylnickel isomerization/protodenickelation sequences[END_REF] Noteworthy, such a mechanism differs from recently reported metallaphotoredox semi-reduction processes for which selectivity is generally observed due to post-reduction alkene photo-isomerization. [START_REF] Tian | For rare examples of alkyne semi-reduction processes combining visible light catalysis and amines as H-donors[END_REF][START_REF]An alternative yet similar pathway, involving single-electron reduction of complex E to a Ni(I)-alkenyl complex prior to isomerization and protonolysis is also possible and cannot be excluded at this stage of our study[END_REF] At this stage, we reasoned that the stereoselectivity towards the Z isomer could be further improved by adjusting the relative kinetics of the isomerization vs. protonolysis steps. As previously discussed, the use of more acidic protonolysis reagents is detrimental for the reactivity. Another option would be to slow down the isomerization process by tuning the electronic parameter of the nickel catalysts. [18a] Satisfyingly, using more electron withdrawing 4,4'-dCF3bpy ligand (L2) instead of 4,4'-dtBubpy (L1) led to an enhancement of the stereoselectivity towards the desired Z-isomer (E/Z ratio, 15:85). Accordingly, the more electron-rich 4,4'-dMeObpy (L3) further increased the amount of the E-isomer (E/Z ratio, 89:11) (Figure 4). With this information in mind, we then seek to reach optimal conditions toward each stereoisomer. The best protocol for Z-isomer 2a finally consisted in performing the reaction in toluene for 48 h using a combination of L2 as the nickel ligand and 4-CzIPN as an alternative organophotocatalyst. As mentioned earlier, the photooxidation of Et3N in the presence of TFE is more difficult due to the formation of hydrogen bond interactions, [START_REF] Li | enhance the redox stability of aliphatic amines through the formation of H-bonds between the alcohol and the amine, which significantly slow down SET from the amine to the excited photocatalyst[END_REF] the use of 4-CzIPN exhibiting a higher oxidation potential, afforded higher yields of the stilbenes. Although the use of 4-CzIPN as a photocatalyst featuring higher triplet energy (56.4 kcal.mol -1 ) with respect to DPA (40.9 kcal.mol -1 ) can open the possibility for E to Z photoisomerization to occur in a second process, [9a] the two photocatalysts afforded similar E/Z isomer distributions under the Z-selective protocol conditions. This protocol covered a wide substrate scope for aromatic alkynes (Table 2) by allowing the preparation of different electron donating or withdrawing groupcontaining (Z)-1,2-bis(hetero)aryl-ethylenes (2a-m) with synthetically useful yields and stereoselectivities (E/Z ratio up to 4:96). Importantly, even monoaryl-substituted internal alkynes reacted well, affording the corresponding conjugated Z-alkenes in good yield and selectivity (2n-p). This protocol was remarkably insensitive to the stereoelectronic parameters of the substituents, and a variety of functional groups such as ester, chloride, heterocycle, hydroxyl, and NBoc were well tolerated. [a] Reaction conditions: Alkyne (0.4 mmol), Ni catalyst (5 mol%), 4-CzIPN (5 mol%), Et3N (1.5 equiv), TFE (25 equiv), Toluene (3.2 mL), rt, 48 h. Crude yields and Z/E ratios are given as determined by 1 H or 19 F NMR from crude reaction mixtures using CH2Br2 or fluorobenzene, respectively, as internal standards. Isolated yields of the pure Z-isomers are provided in parentheses. [b] Hardly separable mixture of isomers. [c] 96 h. [d] GC-MS ratio. [e] Isolated yield of the mixture of isomers. [f] 0.2 mmol scale.

Regarding the selective formation of E-alkenes, the best results (95% yield and 89:11 E/Z selectivity for 3a) were obtained by only substituting the dtbbpy ligand by the electron-rich 4,4'-bis(methoxy)-2,2'-bipyridine (L3) under otherwise identical conditions. As shown in Table 3, in most cases the reaction proceeds to completion with high stereoselectivity toward E-olefins, except in the case of ortho-substituted alkyne (2i) and of mono-aryl alkynes (2np), which both evolved into mixtures of alkenes. This observation is consistent with the proposed mechanism since the isomerization of alkynylnickel E to E' should be less favored in these cases (Figure 3). The scope of aromatic alkynes could not be extended to substrates bearing particular functionalities, such as cyano, phenols and alkylamine that did not yield to satisfactory results. [16] Remarkably, a 5 mmol preparative-scale synthesis of alkenes 2a and 3a could be achieved without further optimization while still maintaining satisfying yields and stereoselectivities, thus demonstrating the robustness of our new protocol. 16

Conclusion

In summary, we have developed an efficient dual nickel/photoredox catalytic system for the stereo-divergent semi-reduction of alkynes to E-or Z-alkenes under mild photochemical conditions. The methodology is particularly well-suited to produce stilbenes with synthetically useful yields and selectivities. Mechanistic studies provided a set of interesting information: (i) a nickel hydride species is generated via a photoinduced transfer of hydrogen from triethylamine. While the photogeneration of Ni-H species from trialkylamine has been sporadically proposed, it has never been exploited for reduction applications. (ii) The stereoselectivity of the reaction was shown to not result from a post alkene photo-isomerization, which opened the possibility to design stereo-divergent protocols under photocatalytic conditions. (iii) The key parameter to control the stereoselectivity outcome was shown to be the relative kinetic of the isomerization and protonolysis of alkenylnickel intermediates. This has been achieved by fine-tuning the pKa of the alcohol additive and the electronic parameters of the ligand. Further applications of photoinduced NiH catalysis from trialkylamines for the functionalization of unsaturated substrates are currently explored in our laboratory. [a] Reaction conditions: Alkyne (0.4 mmol), Ni catalyst (5 mol%), 4-CzIPN (5 mol%), Et3N (1.5 equiv), EtOH (25 equiv), Toluene (3.2 mL), rt, 48 h. Crude yields and E/Z ratios are given as determined by 1 H or [START_REF] Liu | For reviews of recent applications of alkenylnickel isomerization processes[END_REF] F NMR from crude reaction mixtures using CH2Br2 or fluorobenzene, respectively, as internal standards. Isolated yields of the pure E-isomers are provided in parentheses. [b] Hardly separable mixture of isomers. [c] GC-MS ratio. [d] Isolated yield of the mixture of isomers. [e] 0.2 mmol scale.

Experimental Section

General procedure for Z-stilbenes. A 8 mL vial equipped with a magnetic stir bar was charged with the alkyne (1 equiv, 0.4 mmol), [(4,4'-dCF3bpy)NiCl2] (0.05 equiv, 0.02 mmol, 8.4 mg), and 4-CzIPN (0.05 equiv, 0.02 mmol, 15.8 mg). The vial was flushed under argon for 1 min. Then, toluene (3.2 mL), Et3N (1.5 equiv, 0.6 mmol, 60.7 mg), and CF3CH2OH (25 equiv, 10.4 mmol, 0.75 mL) were added under argon (NB: liquid alkynes were added after the solvent). The vial was capped, and the reaction mixture was stirred at room temperature under irradiation of a 405 nm purple LED lamp for 48 h. The reaction mixture was then concentrated under vacuum and the crude product was purified by flash chromatography (silica gel, appropriate mixture of cyclohexane/ethyl acetate) to afford the corresponding Z-stilbene.

General procedure for E-stilbenes. A 8 mL vial equipped with a magnetic stir bar was charged with the alkyne (1 equiv, 0.4 mmol), [(4,4'-dMeObpy)NiCl2] (0.05 equiv, 0.02 mmol, 7.1 mg), and DPA (0.05 equiv, 0.02 mmol, 6.6 mg). The vial was flushed with argon for 1 min. Then, MeCN (3.2 mL), Et3N (1.5 equiv, 0.6 mmol, 60.7 mg), and EtOH (25 equiv, 10.4 mmol, 0.6 mL) were added under argon (NB: liquid alkynes were added after the solvent). The vial was capped, and the reaction mixture was stirred at room temperature under irradiation of a 405 nm purple LED lamp for 48 h. The reaction mixture was then concentrated under vacuum and the crude product was purified by flash chromatography on silica gel (appropriate mixture of cyclohexane and ethyl acetate as eluent) or by reversed-phase chromatography (acetonitrile and HPLC grade water with 1% formic acid as eluent) to afford the corresponding E-stilbene.

Figure 1 .

 1 Figure 1. Ni-catalyzed E-and Z-selective semi-reductions of alkynes. (A) State of the art; (B) Present work.

Figure 2 .

 2 Figure 2. Mechanistic experiments.

Figure 3 .

 3 Figure 3. Proposed pathway toward E-and Z-isomers.

Figure 4 .

 4 Figure 4. Ligand effect on E/Z selectivity.

Table 1 .

 1 Benchmark semi-reductions of alkyne 1a: (A) Reaction development; (B) Additive control over E/Z-selectivity.

				[a]
	Entry	Deviation from above conditions	Yield (%)	Ratio 2a/3a
	A. Reaction development	[b]
	1	None			92	16:84
	2	No photocatalyst			0	-
	3	No light (dark)			0	-
	4	No Nickel catalyst		0	-
	5	NiCl2.glyme as catalyst (no ligand)	44	32:68
	6	Ni(COD)2/dtbbpy as catalyst		61	20:80
	7	No Et3N			0	-
	B. Additive effect over E/Z selectivity	[c]
	8	Isopropanol			94	12:88
	9	Ethanol			98	15:85
	10	2-Fluoroethanol			98	18:82
	11	2,2-Difluoroethanol		75	55:45
	12	2,2,2-Trifluoroethanol (TFE)		93	68:32
	13	Hexafluoropropan-2-ol (HFIP)	0	-
	[a] Selected experiments. Reactions were performed on a 0.25 mmol scale
	using a PhotoRedOx Box device equipped with one 18 W purple LED lamp
	(405 nm). Yields and ratios are given for crude E/Z mixtures, as determined by
	19

Table 2 .

 2 Scope for Z-selective semi-reduction reactions.

	[a]

Table 3 .

 3 Scope for E-selective semi-reduction reactions.

	[a]

Acknowledgements

This work was supported by the CNRS, the French Ministry of Research, the ICBMS, and the Université Claude Bernard Lyon 1. The NMR and Mass Centers of the Université Claude Bernard Lyon 1 are gratefully acknowledged for their contribution. Dr. Eugenie Romero (CEA Saclay) is warmly thanked for preliminary High-throughput screening. T.H. thanks the Chinese Council Scholarship for a doctoral fellowship. A.A. thanks the Institut Universitaire de France (IUF) for its support.

Entry for the Table of Contents

Insert graphic for Table of Contents here.

Dual nickel and photoredox catalysis enables the semi-reduction of internal aryl alkynes in the presence of a trialkylamine acting both as a reductive quencher and as a transfer hydrogenation reagent. The E/Z-stereoselectivity can be controlled with the aid of an alcohol additive.