C Thieulent

; E Hue

; G Sutton

; C Fortier

; P Dallemagne

; S Zientara

; H Munier-Lehmann

; A Hans

; R Paillot

P.-O Vidalain

S Pronost

83 | Identification of antiviral compounds against equid herpesvirus-1 using Real-Time Cell Analysis: screening of 2,891 molecules

cell-associated viraemia were also both significantly reduced in the VGCV treated group (p=0.02 and 0.03, respectively). All ponies seroconverted after infection.

Main limitations: Due to animal management procedures, blinding was not possible for clinical evaluation.

Conclusions: Oral administration of valganciclovir for 14 days from the first day of experimental EHV-1 infection induced no noticeable side effects but significantly reduced clinical signs, virus shedding and cell-associated viremia.

Oral administration of valganciclovir reduces clinical signs, virus shedding and cell-associated viraemia in ponies experimentally infected with equid herpesvirus-1

Côme Thieulent, Gabrielle Sutton, Marie-Pierre Toquet, Samuel Fremaux, Erika Hue, Christine Fortier, Alexis Pleau, Alain Deslis, Stéphane Abrioux, Stéphane Pronost, et al. C. Thieulent 1,2 ; G. Sutton 1,2 ; M. P. Toquet 1,2 ; S. Fremaux 1 ; E. Hue 1,2 ; C. Fortier 1,2 ; A. Pléau 3 ; A. Deslis 3 ; S. Abrioux 3 ; E. Guitton 3 ; S. Methods: Four ponies were treated with valganciclovir (VGCV, the oral prodrug of ganciclovir [GCV]) at 6.5 mg/kg bodyweight, three times on day 1 and twice daily until day 14 inclusive. Four other ponies received a placebo. All ponies were experimentally infected with a field EHV-1 strain (5e07 TCID 50 /pony). Clinical signs of disease, virus shedding and blood/cell associated viraemia were recorded and measured for 3 weeks.

To cite this version:

Results: Serum GCV concentration was maintained above the EC 50 (0.153 µg/mL) for at least 15 days. The overall cumulative clinical score was significantly reduced in VGCV treated ponies when compared with controls (p<0.009; pyrexia duration, nasal discharge and coughing). Infectious EHV-1 shedding measured on RK13 cells was significantly reduced in the VGCV treated group when compared with the control group between D+1 and D+12 (p=0.006). Blood and

  Côme Thieulent, Gabrielle Sutton, Marie-Pierre Toquet, Samuel Fremaux, Erika Hue, et al.. Oral administration of valganciclovir reduces clinical signs, virus shedding and cell-associated viraemia in ponies experimentally infected with equid herpesvirus-1. 11th International Equine Infectious Diseases Conference, Sep 2021, Online, France. pp.56-56, 10.1111/evj.82_13495. hal-03362463 traditional VN tests, the antibody titre was expressed as the highest serum dilution causing 50% inhibition (IC50). Results: Titres of EHV-1 PV were optimised and PVNT successfully performed and compared with a conventional EHV-1 VN assay (r=0.82). Main limitations: Cross-reactivity studies with other EHVs need further investigation. Conclusions: Functional EHV-1 PVs can be generated using a minimum of four glycoproteins gB, gD, gH and gL. The addition of gC neither enhances PV production nor is essential for cell entry. EHV-1 neutralising antibodies can be quantified in experimentally infected horse sera. Ethical animal research: The use of sera was authorised by the Loire Valley ethical review board (CEEA VdL, committee number 19). Informed consent: Not stated. Competing interests: None declared. Source(s) of funding: Fonds Eperon OVERLORD N12-2017, Normandy County Council (17E01598/17EP04324) and the University of Kent. 82 | Oral administration of valganciclovir reduces clinical signs, virus shedding and cell-associated viraemia in ponies experimentally infected with equid herpesvirus-1

  , 14280 Saint-Contest, France; 2 Normandie Univ, UNICAEN, BIOTARGEN EA7450, 14280 Saint-Contest, France; 3 INRAE, UE-1277 Plateforme d'infectiologie expérimentale (PFIE), Centre de Recherche Val de Loire, 37380 Nouzilly, France; and 4 School of Equine and Veterinary Physiotherapy, Writtle University College, Lordship Road, Writtle, Chelmsford CM1 3RR, UK. Email: romain.paillot@writtle.ac.uk Background: Equid alphaherpesvirus-1 (EHV-1) is a frequent respiratory pathogen of the horse, causing mild disease and occasionally myeloencephalopathy (EHM) or abortion. Current vaccines reduce the nasopharyngeal excretion and dissemination of the virus and therefore the extent of an epizooty, but their efficacy against secondary forms of diseases (abortion and EHM) is either limited or remains untested respectively. Several antiviral compounds are active against EHV-1 in vitro but no pharmaceuticals are licenced for in vivo treatment to date. Objectives: To measure the in vivo efficacy of antiviral compounds, starting on the day of experimental infection of the target species with EHV-1 (C2254), as assessed by any reduction of clinical signs, virus shedding and viraemia. Study design: Randomised semi-blinded experiment.

Sources of funding: Fonds Eperon OVERLORD N12-2017, Normandy County Council (17E01598/17EP04324), the IFCE (Institut Français du Cheval et de l'Equitation) grant number 2017-008, CENTAURE European project co-funded by Normandy County Council, European Union in the framework of the ERDF-ESF operational programme 2014-2020.


Thomas Ballul

Raphaël Borie

Bruno Crestani

Eric Daugas

Vincent Descamps

Philippe Dieudé

Antoine Dossier

Fabrice Extramiana

Damien Van Gysel

Thomas Papo

Raphael Borie

Philippe Dieude

Professor Karim Sacre
email: karim.sacre@aphp.fr

Treatment of cardiac sarcoidosis: A comparative study of steroids and steroids plus immunosuppressive drugs

Keywords: cardiac sarcoidosis, immunosuppressive drugs, treatment, relapse

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

INTRODUCTION

Sarcoidosis is a multisystem granulomatous disease of unknown cause characterized by noncaseating granuloma 1 . Symptomatic cardiac features are reported in 5-10% of patients with sarcoidosis, with a wide range of clinical manifestations, including congestive heart failure, conduction block or cardiac arrhythmias and heart involvement is the leading cause of death in sarcoidosis [START_REF] Kandolin | Cardiac sarcoidosis: epidemiology, characteristics, and outcome over 25 years in a nationwide study[END_REF][START_REF] Lynch | Cardiac involvement in sarcoidosis: evolving concepts in diagnosis and treatment[END_REF][START_REF] Iwai | Racial difference in cardiac sarcoidosis incidence observed at autopsy[END_REF][START_REF] Hunninghake | ATS/ERS/WASOG statement on sarcoidosis. American Thoracic Society/European Respiratory Society/World Association of Sarcoidosis and other Granulomatous Disorders[END_REF] . Corticosteroids therapy, although untested in randomized clinical trial, is the mainstay of treatment for cardiac sarcoidosis (CS) [START_REF] Yazaki | Prognostic determinants of long-term survival in Japanese patients with cardiac sarcoidosis treated with prednisone[END_REF][START_REF] Chiu | Prevention of left ventricular remodeling by long-term corticosteroid therapy in patients with cardiac sarcoidosis[END_REF] . Immunosuppressive drugs, such as methotrexate, azathioprine or cyclophosphamide, have also been used in the treatment of severe sarcoidosis, but specific data in CS are limited [START_REF] Muller-Quernheim | Treatment of chronic sarcoidosis with an azathioprine/prednisolone regimen[END_REF][START_REF] Demeter | Myocardial sarcoidosis unresponsive to steroids. Treatment with cyclophosphamide[END_REF][START_REF] Baughman | Combination therapy for sarcoidosis[END_REF][START_REF] Kim | Cardiac sarcoidosis[END_REF] . We conducted a single center collaborative retrospective study to compare the efficacy of steroids alone or combined with immunosuppressive drugs in preventing CS relapses.

METHODS (see supplementary materials for details)

Patients

All consecutive adults patients hospitalized over a 5-years period with histologically proven sarcoidosis from our tertiary referral university hospital were retrospectively reviewed.

Patients with symptomatic heart involvement were included using CS definition according to the Heart Rhythm Society (HRS) criteria [START_REF] Birnie | HRS expert consensus statement on the diagnosis and management of arrhythmias associated with cardiac sarcoidosis[END_REF] . Cardiac sarcoidosis relapse was defined by the onset of a new CS manifestation. The local ethics committee approved the study (Institutional Review Board IRB 00006477 of HUPNVS, Paris 7 University, AP-HP).

Data collection

International Classification of Disease code (ICD-10) for sarcoidosis (D86) was used for screening.

Statistical analysis

The primary outcome feature was cardiac relapse rate from the CS diagnosis over follow up.

Comparisons between patients with and without cardiac sarcoidosis relapse and between patients who did or did not receive immunosuppressive drugs (IS) were made using Mann-Whitney tests for continuous variables and Chi 2 or Fischer exact tests for categorical variables. Kaplan-Meïer method was used to represent cardiac relapse according to the treatment (i.e. with or without IS) initiated at cardiac sarcoidosis diagnosis.

RESULTS

Patients' characteristics at cardiac sarcoidosis diagnosis

From January 2012 to December 2016, 326 consecutive patients were admitted with histologically proven sarcoidosis. Among them, 36 (11%) suffered from symptomatic cardiac sarcoidosis (Figure S1). Twenty patients (55.5%) were male and 26 (72.2%) were black. The median age at sarcoidosis diagnosis was 48. 5 [22.8-76]. The delay between sarcoidosis diagnosis and heart involvement was 1.6 [0-32.2] years with 17 (47.2%) patients displaying a cardiac manifestation of sarcoidosis at sarcoidosis diagnosis. In addition to cardiac involvement, patients had a median of 2 [1-6] organs affected by the disease, including lung in all cases. Eight (22.2%) patients were already receiving steroids (prednisone, 14 [5-30] mg/d) at CS diagnosis.

Cardiac sarcoidosis

The symptoms and signs that revealed cardiac sarcoidosis were unexplained dyspnea (n=2, 5.5%), palpitation (n=5, 13.9%), syncope (n=5, 13.9%), chest pain (n=13, 36.1%) and/or abnormal EKG (n=26, 72.2%) consistent with atrial/ventricular tachycardia (n=9, 25%), advanced atrioventricular block (n=12, 33.3%) or LVEF <50% (n=13, 38.9%) identified after further investigations.

At CS diagnosis, all patients received high dose steroids (prednisone, 60 [20-100] mg/d) alone (n=24) or associated with immunosuppressive drugs (IS) (n=12) including oral azathioprine (n=5), oral methotrexate (n=5) or intravenous cyclophosphamide (n=2). Azathioprine was given at 2 mg/kg/day. Methotrexate was given at 15 to 20 mg/week. Cyclophosphamide was given at 0.7mg/m 2 every 4 weeks for 24 weeks. Methylprednisone intravenous pulses were administered in 9 (25%) cases. Pacemaker or implantable cardioverter defibrillator (ICD) insertion was required in 8 (22.2%) and 5 (13.9%) patients, respectively. Characteristics of patients are listed in Table 1.

Outcome

Over a median follow up of 3.6 [1-15.2] years, 13 (36.1%) patients suffered CS relapse. All patients were still receiving specific treatment (steroids alone or steroids and IS for 1.5 [0.5-6.8] years) at time of relapse. Relapse were severe in most cases (69.2%, 9/13) including reduced LVEF (n=4), third degree heart block (n=2), sustained atrio-ventricular (n=1) or ventricular (n=1) tachycardia and sudden cardiac death (n=1). In 4 cases, cardiac relapse was defined by the occurrence of left ventricular dyskinesia associated with myocardial FDG uptake on cardiac PET.

Interestingly patients who had cardiac relapse were more frequently male (p=0.052), less frequently black (p=0.008) and less frequently treated with immunosuppressive drugs (p=0.085) as compared with patients who did not relapse (Table S1). In the same line, the frequency of cardiac relapse was lower in patients treated with steroids and IS at cardiac sarcoidosis diagnosis (16.7%) than in patients treated with steroids alone (45.8%; p=0.048) (Table 1). Among the 9 patients who experienced severe cardiac relapse, 7 (77.8%) were treated by steroids alone. Although the frequency of black patients was higher in patients receiving IS (p=0.014), CS features at diagnosis did not differ between patients who did or did not receive IS (Table 1). In Kaplan-Meier analysis, treatment with steroids alone tended to be associated with a higher risk of cardiac relapse (HR 2.961, 95% CI 0.66-13.48; log-rank p=0.141) (Figure 1).

In patients receiving steroids alone (n=11/13, 84.6% of cardiac relapses), treatment of relapse associated increased of prednisone daily dose and initiation of IS in all cases including cyclophosphamide (n=5), methotrexate (n=4), azathioprine (n=1) and mycophenolate mofetil (n=1). In patients receiving steroids and IS (n=2/13, 15.4%) at time of cardiac relapse, treatment was modified by increasing prednisone daily dose and switch (mycophenolate mofetil instead of methotrexate) IS. In addition, pacemaker and ICD were inserted in 1 and 3 patients at cardiac relapse, respectively. At last visit, for a median follow up of 3.6 [1-15.2] years, patients had received 3.1 [1-12.8] years of steroids overall. Thirty (88.2%) and 21 (58.3%) patients were still treated by steroids and IS, respectively.

Adverse events

Severe infection occurred in 6 (16.7%) patients: 4 (16.7%) in patients receiving steroids alone and 2 (16.7%) in patients receiving steroids and IS. Infections were mainly respiratory (undocumented bronchitis and pneumonia) and no opportunistic infections were reported. Four (16.7%) patients receiving steroids alone and 3 (25%) receiving steroids and IS patients developed diabetes mellitus. One patient (steroids and IS) developed cardiovascular events.

No patients had cancers during follow up. Two (8.3%) patients receiving steroids alone died:

1 from severe influenza (n=1) and 1 from sudden cardiac death related to CS relapse (n=1).

One (8.3%) patient receiving steroids and IS died from severe undocumented infection.

DISCUSSION

Our single-center study of sarcoidosis patients with symptomatic heart involvement shows that 1-the frequency of cardiac relapse overtime is high, 2-cardiac relapse may be lifethreatening and 3-the association of steroids and IS started at CS diagnosis may have a better efficacy on cardiac relapse than steroids alone. To our best knowledge, no other study has addressed specifically the impact of adding immunosuppressive drugs to high-dose steroids on CS outcome.

Symptomatic heart involvement has been reported in 5 to 10% of patients, consistent with the 11% prevalence observed in our 326 consecutive patients with biopsy-proven sarcoidosis.

Differences in prevalence and severity of sarcoidosis have been linked to age, sex and ethnic origin 1,[START_REF] Iwai | Racial difference in cardiac sarcoidosis incidence observed at autopsy[END_REF] . In our series CS patients were mostly male and black. While cardiac sarcoidosis manifestations range from asymptomatic electrocardiographic changes to sudden death, our series included only symptomatic CS patients. Although isolated cardiac sarcoidosis has been reported [START_REF] Isobe | Isolated cardiac sarcoidosis: clinical characteristics, diagnosis and treatment[END_REF] , all patients in our study had evidence of extra-cardiac disease and almost half had cardiac involvement at sarcoidosis diagnosis.

The frequency of symptomatic cardiac relapse was high (36.1%) and consistent with previous reports [START_REF] Chapelon-Abric | Cardiac sarcoidosis: Diagnosis, therapeutic management and prognostic factors[END_REF][START_REF] Chapelon-Abric | Cardiac sarcoidosis: a retrospective study of 41 cases[END_REF] . Randomized trials are lacking and no consensus exists among experts regarding the treatment of CS [START_REF] Hamzeh | Management of cardiac sarcoidosis in the United States: a Delphi study[END_REF] . Although evidence-based data are poor, steroid therapy is considered mandatory [START_REF] Yazaki | Prognostic determinants of long-term survival in Japanese patients with cardiac sarcoidosis treated with prednisone[END_REF][START_REF] Chiu | Prevention of left ventricular remodeling by long-term corticosteroid therapy in patients with cardiac sarcoidosis[END_REF][START_REF] Chapelon-Abric | Cardiac sarcoidosis: a retrospective study of 41 cases[END_REF][START_REF] Sadek | Corticosteroid therapy for cardiac sarcoidosis: a systematic review[END_REF] . Immunosuppressive agents are usually considered for steroid-resistant cases or as a steroid-sparing strategy [START_REF] Sayah | Cardiac Involvement in Sarcoidosis: Evolving Concepts in Diagnosis and Treatment[END_REF] . A prospective study of 17 patients with a 5 years follow up reported benefit from the association of steroids and low dose methotrexate on CS relapse defined on subclinical parameters [START_REF] Nagai | Treatment with methotrexate and low-dose corticosteroids in sarcoidosis patients with cardiac lesions[END_REF] . More recently, a single-center cohort of 73 patients identified the use of mycophenolate mofetil treatment as associated with improved CS survival on univariate analysis [START_REF] Zhou | Cardiac Sarcoidosis: The Impact of Age and Implanted Devices on Survival[END_REF] . Our comparative study is the first to report on the benefit of high-dose steroids and IS combination started at diagnosis for clinically apparent CS.

Our study has several limitations. Its retrospective scheme from a single center and the small sample size limit the statistical power and impede the ability to generalize the findings. Since CS is rare, proper randomized trials are however exceedingly difficult to mount. Although the main clinical characteristics of the 2 groups of patients were not significantly different (Table 1), IS may have been added to steroids in patients with more severe disease, as suggested by a higher frequency of black patients and patients with reduced LVEF both known to be associated with impaired outcome 1,[START_REF] Kandolin | Cardiac sarcoidosis: epidemiology, characteristics, and outcome over 25 years in a nationwide study[END_REF][START_REF] Yazaki | Prognostic determinants of long-term survival in Japanese patients with cardiac sarcoidosis treated with prednisone[END_REF][START_REF] Chapelon-Abric | Cardiac sarcoidosis: Diagnosis, therapeutic management and prognostic factors[END_REF][START_REF] Zhou | Cardiac Sarcoidosis: The Impact of Age and Implanted Devices on Survival[END_REF] . With such a bias, a worse outcome would have been expected in the more severe patients treated with IS. In contrast, a lower relapse rate was significantly associated with combined steroids and IS treatment. Because of the small number of patients, no specific IS drugs (azathioprine vs methotrexate vs cyclophosphamide) efficacy analysis could be performed.

In conclusion, our preliminary study suggests that the combination of high-dose steroids and immunosuppressive drugs at diagnosis is more effective than steroids alone in preventing relapse in symptomatic cardiac sarcoidosis.

Figure 1

 1 Figure 1 Kaplan-Meier Curves of Study Population

Table 1 Baseline characteristics, relapse and follow up of patients according to cardiac sarcoidosis treatment

 1

	All	Steroids	Steroids + IS	P
	(n=36)	(n=24)	(n=12)

ACKNOWLEDGEMENTS

KS had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. TB, RB, BC, ED, VD, PD, AD, FE, DV, TP and KS contributed substantially to the study design, data analysis and interpretation, and the writing of the manuscript. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. We are thankful to Drs J.F. Alexandra, M.P. Chauveheid, and T. Goulenok for their help with patients' screening.

CONFLICTS OF INTEREST

The authors report no relationships that could be construed as a conflict of interest.


domain: spi chim phys

text:
Steven Daly

Sebastian Weske

Antonija Mravak

Marjan Krstić

Alexander Kulesza

Rodolphe Antoine

Vlasta Bonačić-Koutecký

Philippe Dugourd
email: philippe.dugourd@univ-lyon1.fr

Konrad Koszinowski
email: konrad.koszinowski@chemie.uni-goettingen.de

Richard A J O'hair
email: rohair@unimelb.edu.au

Vlasta Bonačić-Koutecký

Phenyl argentate aggregates [AgnPhn+1 ]-(n = 2-8): Models for the self-assembly of atom-precise polynuclear organometallics

published or not. The documents may come

[AgnPhn+1] -aggregates contain neither pronounced metallic cluster properties nor ligated metallic cluster features and are thus not superatom complexes. They therefore represent novel organometallic characteristics built from Ag2Ph subunits.

INTRODUCTION

An exciting and active research frontier in the past two decades has been the development of coinage metal nanoclusters for a range of applications in chemistry, biology and physics. They continue to attract attention since they provide a link between atoms and nanoparticles, 1 and they exhibit interesting electronic properties. 2 Polynuclear coinage metal organometallic aggregates have received less attention, even though they have been implicated as multi-metallic catalysts in organic transformations 3 and can exhibit interesting photophysical properties (e.g. luminescence). 4 These are exemplified by copper and silver aryls, which play important roles in organic synthesis, either as stoichiometric reagents or as reactive intermediates in catalytic cycles. [START_REF] Krause | Modern organocopper chemistry[END_REF][START_REF] Rappoport | The chemistry of organocopper compounds[END_REF][START_REF] Alexakis | [END_REF][8][9][10] The parent, insoluble phenyl silver, first reported by Krause and Schmitz in 1919, 11 was hypothesized by Hofstee et al in 1979 to adopt a polymeric chain like structure in which each phenyl group bridges between two silver atoms in an ipso fashion (Scheme 1A). 12 More than two decades later, the first examples of related infinite chains were reported from X-ray crystallographic studies [START_REF] Van Koten | Comprehensive Organometallic Chemistry II[END_REF][START_REF] Holloway | [END_REF] on perfluoro phenyl silver coordinated to nitrile solvent molecules (Scheme 1B). 15,16 More recently AgC6F5 has been shown to adopt a zig-zag polymeric chain structure (cf Scheme 1A). 17 Other X-ray crystallographic studies on silver aryls have revealed diverse structures ranging from singly coordinated mononuclear neutral complexes, 18 doubly coordinated mononuclear neutral 19 and "ate" complexes 20 (Scheme 1C) to various aggregates, which typically involve an aryl group bridging between two metal centers including dimers (Scheme 1D), 21 contact ion pair "ates" (Scheme 1E), 22 neutral tetramers with auxiliary ligands (Scheme 1F), 23 neutral tetramers without auxiliary ligands (Scheme 1G), [24][25][26] "ate" hetero pentamers (Scheme 1H). 27 The diverse structures of these solid state materials share a common PhAg2 subunit that involves two-electron three-center bonding (Scheme 1I) with contribution 9a involving the combination of the C(sp 2 ) molecular orbital of the bridging aryl group with a mutually bonding combination of Ag orbitals. 28,29 Scheme 1: Structures of silver aryls: (A) polymeric chain structure of phenyl silver;

(B) polymeric chain structure of perfluoro phenyl silver coordinated to nitrile solvent molecules; (C) mononuclear argentates; 20 (D) ligated cationic dimers; 21 (E) contact ion pair "ate" complex; 22 (F) tetramer with auxiliary ligand 23 ; (G) tetramer without auxiliary ligand [24][25][26][27] ; (H) pentamer 28 ; (I) orbital description of two-electron three-center bonding. 29,30 The powerful marriage of theory and gas-phase experiments employing mass-spectrometry (MS) based methods has been used to examine the structures and reactivity of a wide range of metal clusters and aggregates. [31][32][33] Given the diverse range of structures of silver aryls (Scheme 1), we have a continued interest in exploring these systems in the gas phase to establish what other structures might be possible as potential targets for new materials. The interplay of mass spectrometry, laser Ultraviolet Photodissociation (UVPD) "action" spectroscopy, and density functional theory (DFT) calculations confirmed that [AgPh2] -adopts a linear structure related to 3 (Scheme 1), 34 while PhAg2 + contains the same motif found in 4, where a phenyl bridges two Ag centers. 35 These phenyl silver complexes were formed in the gas phase via collision-induced dissociation (CID) decarboxylation reactions of silver benzoate precursors generated via electrospray ionization (ESI), 36 which potentially limits the numbers of such complexes that can be formed. While CID of silver tetraphenylborate aggregates generates related phenyl silver aggregates, many of these retain tetraphenyl borate ligands, adding structural complexity. 37 Given that ESI-MS of organocuprate solutions generates aggregates, 38,39 we were encouraged to explore such an approach to generate anionic phenyl silver aggregates.

Here we report the first ESI-MS studies on phenyl argentates formed by transmetallation reactions between phenyl lithium and silver cyanide, which provides access to the argentate aggregates, [AgnPhn+1] -. We focus on these anionic argentates because positive-ion mode ESI-MS of the same sample solutions affords only a limited number of organometallic cations, all of which contain not only silver, but also lithium (e.g., [Li2AgPh2(THF)2] + , THF = tetrahydrofuran). [START_REF] Weske | From Copper to Gold: Identification and Characterization of Coinage-Metal Ate Complexes by ESI Mass Spectrometry and Gas-Phase Fragmentation Experiments[END_REF] Due to their increased complexity and their smaller number, these heteronuclear cations do not lend themselves well for the systematic analysis of aggregation effects in organometallic oligomers. The [AgnPhn+1] -complexes where n = 2 -8 were individually mass-selected in order to generate their UVPD spectra. Theoretical calculations were key to determining their structural and optical properties, thereby allowing the assignment of the experimental UVPD spectra to specific isomer(s). The two key questions we wish to address are:

(1) At what size is there a transition from 2D to 3D for the metallic component of the aggregate? (2) Are these novel organometallic complexes built from Ag2Ph subunits (Scheme 1I)?

EXPERIMENTAL AND THEORETICAL METHODS

Materials:

All chemicals were sourced from Sigma Aldrich and used without further purification. They were: anhydrous and inhibitor free THF (≥ 99.9%); AgCN (99%); and phenyl lithium (1.9M in dibutyl ether).

Preparation of phenyl argentates:

Silver cyanide (83.7 mg, 0.625 mmol, 1 equiv.) was added to a 10 mL Schlenk flask. After repeatedly evacuating and flushing with argon, the flask was heated under vacuum for 1 h. After cooling to room temperature, 5 mL of anhydrous THF was added under argon. Then, the flask was cooled down to -78 °C. To this stirred suspension was added a solution of phenyl lithium (0.66 mL of a 1.9 M solution in dibutyl ether, 1.25 mmol, 2 equiv.). After stirring at -78 °C for 25 min, the solution was diluted to a concentration of 10 mM, transferred into a gas tight syringe and injected into the ESI source of the mass spectrometer.

Mass spectrometry and UVPD experiments.

The phenyl argentate solution prepared above was introduced into a modified quadrupole linear ion trap mass spectrometer (LTQ, Thermo Fisher Scientific, San Jose, CA, USA) via ESI using a syringe pump set to a flow rate of 1 mL hr -1 . The typical ESI conditions used were: spray voltage, 3.4 -3.9 kV, capillary temperature, 60°C, nitrogen sheath gas pressure, 8 -10 (arbitrary units). Standard CID experiments were carried out by mass selecting the precursor ion and subjecting it to multicollision conditions with the helium bath gas using an activation time of 10 ms and a Q of 0.15, and choosing a normalised collision energy (NCE) such that some of the precursor ion remained.

The modification to the mass spectrometer consists of the installation of a quartz window fitted on the rear of the MS chamber to allow coupling of the laser with the linear ion trap. [START_REF] Larraillet | [END_REF][START_REF] Antoine | Visible and ultraviolet spectroscopy of gas phase protein ions[END_REF] The laser used was a nanosecond frequency-doubled tuneable Horizon OPO (Optical Parametric Oscillator) laser pumped by a SureliteTM II Nd:YAG laser (both from Continuum, Santa Clara, CA, USA). The repetition rate of the laser was 10 Hz with pulse widths of 5 ns. The laser beam passed through a mechanical shutter electronically synchronized with the mass spectrometer, after which it was focused with a 1000 mm lens into the linear trap on axis. The laser power was monitored with a power meter located just before the injection in the ion trap. The mechanical shutter was used to synchronize the laser irradiation with the trapping of the ions. To perform laser irradiation with a single laser pulse, we added in the ion trap radio frequency (RF) sequence an MS n step with an activation amplitude of 0% and a reaction time of 100 ms, during which the shutter located on the laser beam was opened. The activation q value was set to 0.20.

For action spectroscopy, mass spectra were recorded after laser irradiation as a function of the laser wavelength as described in detail elsewhere. 43 At each laser wavelength from 304 nm to 399 nm (with a 0.1 nm step and 1 second dwell), a lasernormalized yield of photo-fragmentation was deduced from the mass spectrum through eq. 1:

σ = log((precursor + products)/precursor)/ Φ ( 1
)
where Φ is the laser fluence, precursor is the intensity of the precursor ion, and products represents the intensity of all the product ion peaks. Optical action spectra were obtained by plotting the normalized yield of photo-fragmentation as a function of the laser wavelength.

Theory

Structural and optical properties of the complexes were determined using density functional theory (DFT) and its time-dependent DFT (TDDFT) counterpart as implemented in the Gaussian09 suite of software (Revision D.01). 44 Structural optimization was carried out using the hybrid B3LYP [45][46][47] functional with def2-TZVP 48 atomic orbital basis, and Grimme's dispersion (GD3) 49 correction.

Relativistic effective core 50 potential was employed for Ag atoms. An extensive search for the lowest energy structures was performed including simulated annealing.

The absorption spectra at T = 0 K were obtained for the optimized geometries using TDDFT with PBE0 51,52 functional and def2-TZVP basis set with 30 electronic states being calculated. The plots cover the range between 300 and 400 nm. For determination of absorption spectra for [Ag6Ph7] -and [Ag8Ph9] -, the thermal ensemble of structures at T = 300 K obtained from constant temperature Molecular Dynamics (MD) based on AM1 53 was used. The structures along MD trajectories which were used for thermal ensemble are shown in Figures S5 andS6.

RESULTS AND DISCUSSIONS:

ESI-MS on reaction mixture of silver cyanide and phenyl lithium

Negative ion ESI of the phenyl argentate solution prepared as described in the experimental section gave a rich mass spectrum (Figure 1) showing a range of silver containing anions which were readily identified by their unique isotopic signatures as well as their m/z values (which are listed for the most abundant peak in the isotope pattern throughout this work). Oligomers [AgnPhn+1] -ranging from n = 2 to 8 were observed with sufficient abundance for UVPD studies. The formation of these types of well-defined even-electron oligomers is reminiscent of early studies of alkali metal halides cluster anions, 54 as well as the copper chloride cluster anions [CunCln+1] -. 55 Noteworthy is the lack of stoichiometries that are subvalent in silver, which contrasts with silver iodide clusters anions of the type [AgnI] -previously observed using other methods. 56 and losses of AgPh neutral aggregates (eq. 3). The latter are also observed under collision-induced dissociation (CID) conditions. No electron detachment was observed above 300 nm, but was observed at 260 nm for the smaller aggregates (n = 2 -5). In contrast, it was significantly lower for n = 6 -7. The action spectra taken between 304 and 399 nm for [AgnPhn+1] -are given in Figure S3 and all exhibit shoulders at ∼305 -310 nm. For the anions [Ag6Ph7] -, [Ag7Ph8] - and [Ag8Ph9] -a new band centered at ∼360 nm appears.

In order to assign these features to specific isomers, we turned to detailed DFT calculations. The structural properties of the aggregates have been determined by DFT approach and corresponding absorption spectra were calculated using TDDFT method.

This allowed for the structural assignment of the experimental UVPD spectra and determination of building blocks for different sizes of organometallic complexes. Regarding the structural properties shown in Figure 3, two classes with 2D and 3D metallic components have been identified. Within the 2D class of structures, in addition to Ag2Ph subunits, AgPh was identified as a terminating unit. This is the case for the lowest energy structures of [AgnPhn+1] -with n = 2 -4, where there are not enough silver atoms to form compact 3D structures. The described class of structures represents also higher energy isomers for n = 4 -8. Interestingly, the lowest energy structures for

[Ag5Ph6] -shows a transition to the compact 3D metallic component containing Ag2Ph subunits and the most stable structure is directly related to structures determined via X-ray crystallography (8 22 in Scheme 1 and [Cu5Ph6] -39 ). Thus, for n = 5 -8 these 3D metallic component class of structures are energetically favourable.

As reported already, for organometallic complexes dispersion interaction plays significant role in structural stability. 57,58 In order to understand the origin of the stability of observed 3D structures (n = 5 -8), we applied Grimme dispersion correction (GD3) 48 during DFT structural minimization of each 3D and 2D complex. Contribution of the dispersion term to the total energy of the structures in minimum is reported in the Table S1. Results clearly demonstrate that in all cases the compact structures had the larger GD3 correction and for bigger 3D complexes (n = 5 -8) the difference is more pronounced compared to the 2D counterparts. In those 3D compact structures organic parts having π electrons are closer to each other accounting for attractive dispersion interaction between subunits which contributes to the overall stability. This observation is fully in agreement with our experimental results and previously reported studies on organometallic complexes. 57,58 DFT calculations on the gas-phase IR spectra for the lowest energy 2D and 3D isomers of [Ag4Ph5] -, [Ag7Ph7] -and [Ag8Ph9] - show dominant features associated with the C-H vibrations of the phenyl rings (data not shown). The small differences in the other minor features mean that IR spectroscopy is not likely to allows isomer distinction for this class of aggregates. Recent work on related organocuprates suggest that ion-mobility might provide isomer differentiation. 59 S3). In addition, the intensities of excited states are low, which points to no delocalization of electrons and suggests that we are not dealing with ligated clusters containing metallic cores, but rather aggregates consisting of Ag2Ph building blocks, illustrating the concept for new materials. The transition from 2D to 3D metallic component not only influences the absorption spectrum and the nature of the excitations that leads to it, but also the experimentally observed relaxation channels. When the relaxation channels at 260 nm are examined (Table S2), structures up to [Ag5Ph6] -relax predominantly by electron detachment.

There is a clear demarcation between [Ag5Ph6] -and [Ag6Ph7] -, with the former show-

Figure S1 .

 S1 Figure S1. ESI-MS of a 10mM THF solution of the reaction mixture of PhLi and AgCN. The anions observed include (m/z values are for the most abundant peak in the isotope cluster): [Ag(CN)2] -(m/z 159); [AgPh(CN)] -(m/z 210); [AgPh2] -(m/z 261); [Ag2Ph2(CN)] -(m/z 396); [LiAg2Ph2(CN)2] -(m/z 429); [Ag2Ph3] -(m/z 447); [Ag3Ph4] - (m/z 631); [Ag4Ph5] -(m/z 817); [Ag5Ph6] -(m/z 1001); [Ag6Ph7] -(m/z 1187); [Ag7Ph8] - (m/z 1371) and [Ag8Ph9] -(m/z 1557).

  Each of the anions [AgnPhn+1] -(n = 2 -8) formed via ESI were mass selected and their UVPD spectra were measured. Mass spectra are shown in FiguresS1 and S2and the fragmentation channels are discussed in more detail in the SI. The fragmentation channels observed were loss of signal due to electron loss via photodetachment (eq. 2)

Figure 2 Figure 2 :

 22 Figure 2 highlights the similarities between CID and LID fragmentation channels for [Ag7Ph8] -as well as the unique UVPD fragmentation channels corresponding to losses of phenyl radicals (eq. 3) that are observed for the larger aggregates (n = 5, 7 and 8). The loss of phenyl radicals gives rise to the aggregates [Ag7Ph7] -and [Ag7Ph6] -that are subvalent in silver. Their CID spectra are given in Figures 2C and 2D reveal a richer set of fragmentation chemistry than [Ag7Ph8] -(Figure 2A).

Figure 3 .

 3 Figure 3. Optimized DFT structures of two classes of structural isomers of [AgnPhn+1] -, n = 2 -8 together with metallic components. The 3D compact structural isomers are shown at the left, while the 2D more open structural isomers are shown at

Figure 4 .

 4 Figure 4. Comparison of experimental action spectra taken over the range 304nm to 399nm of [AgnPhn+1]-, n=2-8 with calculated absorption spectra (a)-(e), (g)-(h) for lowest energy structures using TDDFT approach (cf. Figure1. for the structures). (f) and (i) Simulated thermally broadened absorption spectra of [Ag6Ph7] -and [Ag8Ph9] - (blue) at T=300K compared with experimental action spectrum (red). Thermal ensemble of 10 structures (containing 3D metallic subunits) at T=300K is obtained from constant temperature MD simulations (within AM1 approach) starting from the lowest energy structure. fe represents the calculated oscillator strengths. For experimental intensities arbitrary units have been used. The scaling factors are used to visualize spectra for different species.

Figure 5 .

 5 Figure 5. Comparison of experimental and DFT spectra for two classes of structures of [Ag5Ph6] -together with excitations among HOMO (H), HOMO-1 (H-1), HOMO-2 (H-2) to LUMO (L), LUMO+1 (L+1) responsible for the three lowest energy excited states S1, S2, S3.

  ing 53% electron detachment yield, and the later only 4%. At the same time, the fragmentation yield increases with the size of the aggregates. This change in photophysical properties between n = 5 and n = 6 indicates a change in the nature of the optically accessed excited states, and is entirely consistent with the change from 2D to 3D structures predicted from the theory.CONCLUSIONSAltogether, phenyl argentate aggregates show specific structural and optical properties for organometallic complexes. A transition from 2D to 3D structures of the metallic components is evidenced and is accompanied by a strong bathochromic shift in optical spectra, useful for tuning optical properties in such argentate aggregates. They contain neither pronounced metallic cluster properties nor ligated metallic cluster features. They are not superatom complexes but rather are systems with novel organometallic characteristics. The size effect shows the formation of structures due to interaction among Ag2Ph subunits representing building blocks of these complexes which bridges the role of metallic and organic components. Given the compact structure for [Cu5Ph6] -39 similar behavior might be expected for other polynuclear organometallates. An intriguing question is whether such structures might be translated to the solid state to generate new materials. A key issue is that the anionic charge will need to be balanced by a counter cation. Previous work on translating gas-phase cations to the solid state have shown that the counter ion (in that case an anion) needs to be non-coordinating in order to not disrupt structure. 60See supplementary information for: CID and LID (260 nm) spectra and discussion of fragmentation reactions for [AgnPhn+1] -; action spectra for [AgnPhn+1] -; DFT calculated gas-phase IR spectra for [Ag4Ph5] -, [Ag7Ph7] -and [Ag8Ph9] -; DFT calculated dispersion energy correction (eV) for two classes of isomers of [AgnPhn+1] -; relative yields for electron detachment and fragmentation at 260 nm for [AgnPhn+1] -; DFT calculated electron affinity (eV) for compact structures of [AgnPhn+1] -; ensemble of structures for [Ag6Ph7] -and [Ag8Ph9] -at 300 K obtained from MD; Cartesian coordinates of relevant DFT optimized structures.

ACKNOWLEDGEMENTS R.A.J.O. and P.D. thank the Australian Research Council for financial support (DP150101388). R.A.J.O. thanks the Alexander Humboldt foundation for a senior fellowship. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013 Grant agreement N°320659). This research was partially supported by the project STIM-REI, Contract Number: KK.01.1.1.01.0003, funded by the European Union through the European Regional Development Fund -the Operational Programme Competitiveness and Cohesion 2014-2020 (KK.01.1.1.01). S.W. and K.K. thank the Deutsche Forschungsgemeinschaft for financial support (KO 2875/6). VBK, MK and AM acknowledge computational facilities of the HPC computer within the STIM-REI project, Doctoral study of Biophysics at University of Split as well as Prof. Miroslav Radman at MedILS and Split-Dalmatia County for support.

DATA AVAILABILITY STATEMENT

Data available in article or supplementary material: The data that supports the findings of this study are available within the article and its supplementary material.

SUPPLEMENTARY INFORMATION


J L Jauberteau

I Jauberteau

O D Cortázar

A Megía-Macías

Langmuir probe in magnetized plasma: Study of the diffusion parameter

In low temperature magnetized plasma, Langmuir probe measurements must be corrected because of the electron diffusion through the sheath which is formed around the probe collector. The correction factor which is called the electron diffusion or electron sink parameter depends on many other parameters like the probe geometry, the electron diffusion coefficient, the sheath thickness or the potential profile through the sheath. Based on a previous work, we determine the values of this parameter under different experimental conditions and we study the effect of the electron energy, of the probe biased voltage and of the magnetic field intensity on this parameter. The results are compared with theoretical models published in literature. An empirical equation is determined to fit the diffusion parameter value versus magnetic field intensity.

Introduction.

. However, the I-V probes characteristics measured by means of electrostatics probes depend on plasma characteristics and can be drastically changed in case of high pressure or magnetized plasmas. The electron current collected by the probe at different negative bias voltages depends on the electron diffusion through the sheath produced around the collecting probe. So, the electron current measured value must be corrected to determine accurate plasma parameters. The measured current depends on a

macroscopic parameter, which is called the diffusion parameter or the electron sink parameter. This parameter is a function of the electron diffusion coefficient, of the sheath thickness and also is correlated to the probe geometry and other parameters [START_REF] Mal'kov | [END_REF]5,6]. In the case of high pressure plasma, the diffusion coefficient is isotropic and depends on collision processes in the sheath. However, when a magnetic field is applied, because of the Lorentz force on charged particles anisotropy appears and the current collected by the probe changes with the effective conductivity which depends on the probe geometry, on the orientation within the magnetic field and on three main mechanisms, the ion viscosity, the ion neutral collision and the ion inertia /7/. These mechanisms are efficient particularly in fully ionized plasma and when the probe radius is larger than the ion-gyro radius. The potential in front of the probe is disturbed on a transverse scale depending on the ion-gyro radius and the potential profile through the sheath drastically changes according to the experimental conditions. The purpose of this work is to determine and to study the diffusion parameter in the case of cold magnetized plasma, corresponding to partially ionized plasma (relative ionization lower than 1%). In this case the ion-gyro radius is larger than the probe radius (typically equal to 10 probe radius) and the conductivity within the sheath mainly depends on the electron diffusion coefficient anisotropy due to the magnetic field.

Probe characteristics in the electron diffusion regime.

In the case of high pressure plasma as well as for magnetized plasma, the electron current collected by a negatively biased probe decreases with decreasing electron diffusion through the sheath. The electron kinetic is governed by an electron diffusion regime in the sheath formed around the probe. When the region disturbed by the probe (equivalent to the sheath around the probe) is lower than the electron energy relaxation length λ ε the electron energy distribution function can be considered unchanged by the probe effect. The electron energy changes due to collisions and to the heating by the external electric field produced around the probe can be neglected [6]. The EEDF corresponding to the real EEDF within the plasma bulk is measured when the electron diffusion rate within the sheath is high enough to cope with the drain of electron from the plasma to the probe. The difference between the real EEDF and the measured EEDF increases with increasing gas pressure or radial magnetic field component, because of electron diffusion decreasing [6,[START_REF] Swift | Proc. Phys. Soc[END_REF].

In magnetized plasma the electron diffusion coefficient is anisotropic because of the electron motion in the magnetic field. In the case of a diffusion regime, assuming an isotropic EEDF in the plasma bulk, the electron kinetic equation depends mainly on the space gradient and is given by [6]

, 0 ) , ( ) ( = ∇ ∇ r f D e r e r r ε ε EQ(1)
Where ε e is the total electron energy at the sheath entrance, D r (ε e ) is the electron diffusion coefficient within the sheath and f(ε e ,r) is the EEDF at position r in the sheath probe. When r→∞ , f(ε e ,r)=f 0 (ε e ) which is the undisturbed EEDF within the plasma bulk.

The electron flow

) ( e d ε φ corresponding to electrons from energy ranging from ε e to ε e +d ε e , is given by [START_REF] Swift | Proc. Phys. Soc[END_REF],

∂ - = ) ) , ( ( ) ( ) ( ) ( ) ( ε ε ε ε ε ε φ . EQ (2)
The change of EEDF due to the electron diffusion through the sheath can be written,

[ ] ( ) ( ) ∫ ∫ = - = -
0 0 0 ) ( ) ( ) ( ) ( ε ε ε ε φ ε ε ε EQ(3)
S is the collecting probe area, dj e (ε e )=-eSdφ(ε e ) is the electron current due to electron energy ranging from ε e to ε e +d ε e .

From EQ(3), it can be seen that the larger diffusion coefficient value the lower is the change in EEDF. Using the Langmuir law, the electron current collected by a probe biased at a negative potential V is written in position r within the sheath,

ε ε ε ε ε       - = 1 ) ( 2 / 1
, where g is a constant.

Using this equation and EQ(3), we obtain for the total electron current collected by a negatively biased probe, the equation first proposed by Swift [START_REF] Swift | Proc. Phys. Soc[END_REF], . These equations show that the electron current collected by the negatively biased probe depends on the parameter Ψ(ε e ) , called the electron diffusion parameter (or electron sink parameter). This parameter is function of the electron diffusion coefficient through the sheath.

( ) ( ) ∫ ∞ -       Ψ         - + - =
Arslanbekov [6] has shown that the knowledge of the distribution potential profile through the sheath is required to calculate the diffusion parameter in condition of collisional-probe space charge layer. However the determination of this parameter becomes very difficult without hypothesis on the potential profile. Different authors have attempted to model the electron diffusion within the sheath to determine an analytical equation for the diffusion parameter.

However, these models need hypothesis and approximations and until now, they give erroneous results in the case of cold plasmas [5,6,[START_REF] Swift | Proc. Phys. Soc[END_REF].

In a previous work, we have developed a numerical method to directly determine the diffusion parameter values from experimental data without model or hypothesis [START_REF] Jauberteau | [END_REF].

In this method we use of EQ(4) and of its first derivative function with respect to V,

∫ ∞ -       Ψ         - + - = ∂ ∂
d f eV g V j A ε ε ε ε ε ε ε ε ε ∂ ∂ ∂ ∂ =       Ψ         - + - = ∂ ∂ = - ) ( ) ( 1 ) ( ) ( 0 2 / 1
and using the first derivative function of EQ(4) versus V we have,

d f e g V V j B ε ε ε ε ε ε ε ε ∂ ∂ ∂ ∂ =       Ψ         - + - = ∂       ∂ ∂ ∂ = - 2 2 2 0 2 1 ) ( ) ( 1 ) ( ) (
      + - = Ψ 1 , EQ (5) with 2 2
) ( Using this numerical method, we have calculated the value of the diffusion parameter under different experimental conditions and study the change of this value with plasma parameters.

) ( V V j V V j B A X

Experiments and discussion.

Experiments have been performed by means of a cylindrical Langmuir probe (diameter 0.5mm, length 6mm) located in the middle of a cylindrical reactor made of OFHC copper (diameter 90mm, length 97mm) along the cylinder axis. Microwave plasma working at 2.45GHz with powers ranging from 1500W to 1800W is maintained in hydrogen at 0.19Pa. A magnetic field intensity ranging from 80mT to 120mT is applied by means of four coils. It is parallel to the reactor axis and to the probe collector. More details of the experimental set up and a scope of the reactor are given in [10]. The ion current collected by the probe at saturation is determined at large negative biased voltage ranging from -150V to -100V, when all electrons are repelled. The electron current is calculated by substracting the ion current at saturation to the measured total current. Experiments have been performed in different positions along the reactor axis. The magnetic field is determined by means of a Hall probe with error bellow 2%. Figure 1 shows the magnetic field profile along the reactor axis with a simplified view of the reactor in the inset. The plasma chamber is located between z=0mm to z=97mm. Figure1. The magnetic field profile along the z axis and a simplified set up of the reactor.

Figure2 shows the evolution of the diffusion parameter value versus E e =ε e -eV. It is calculated using EQ(5) for different applied voltage V app , which correspond to a bias voltage V=V P -V app ,

V P is the plasma potential equal to 42,08V. The derivative functions of je(V) versus V are obtained using the numerical differentiation method for noisy signal proposed in ref [11,12].

Measurements have been performed at 43mm from the wave launcher exit on the z-axis, using a microwave power equal to 1500W. It can be seen that the diffusion parameter depends on the biased voltage and is strongly decreasing with increasing electron energy.

Whatever the applied bias voltage, the diffusion parameter value versus electron energy ε e can be fitted using a function ( )

α ε ε - = Ψ e e A
, with α ranging from 0.8 to 1.4 and "A" ranging from 80 to 500 for an hydrogen pressure of 0.2Pa, a power ranging from 1500W to 1800W and a magnetic field intensity ranging from 70mT to 100mT. A typical fit of experimental diffusion parameter values using this function is shown on Figure 3. Figure3. Fit of the diffusion parameter versus electron energy, in the case of hydrogen pressure of 0.2Pa, power of 1800W and magnetic field of 85mT. Measurements are performed along the reactor axis at a biased voltage of 0,1V.

Using EQ(5) and comparing the diffusion parameter corresponding to two different values of biased voltage V 1 and V 0 , we have,

( ) ( ) ( ) (
)

0 1 0 1 0 1 1 1 eV E eV E X E e X E e E E e e e e e V e V + +       +               +         = Ψ Ψ EQ(6)
Figure4 shows the change of Ψ V1 (E e )/ Ψ V0 (E e ), X 1 /X 0 , dI/dV and d 2 I/dV 2 versus biased voltage V p -V, corresponding to measurements performed at 43mm on the z-axis from the wave launcher exit and using a microwave power equal to 1500W. Calculations of Ψ V1 (E e )/ Ψ V0 (E e ) have been performed at E e =10 -5 eV. This figure shows the strong dependence of Ψ V (E e ) with X.

Figure4. Comparison of the first and second derivative of the I-V probe characteristic and of

X and Ψ/Ψ 0 , versus V p -V; Measurements are performed at 1500W, 0.2Pa H 2 and at 43mm of the wave launcher exit on the Z-axis in the middle of the reactor and for E e =10 -5 eV.

According to Dote [13], in the case of a cylindrical probe parallel to the magnetic field and when ω 2 τ 2 >>1, the ratio

( ) ( ) ( ) [ ] 1 2 2 1 2 2 0 1 1 log 1 - - + =         +         + + = τ ω τ ω λ ε ε A r d r
Where, A is a constant, ω and τ=λ e /v e are the angular frequency and the time between two electron-neutral collisions, respectively. λ e and v e are the electron mean free path and the electron velocity at the probe sheath entrance. It is worth noting that in EQ(7), Dote considers a monokinetic electron current of energy ε e .

Considering the Langmuir law for the electron current I e0 collected when no magnetic field is applied and considering EQ(4) for the electron current I e collected when a magnetic field is The comparison with EQ(7) gives,

( ) ( ) [ ] 1 2 2 1 1 1 3 4 - - + =       Ψ - + τ ω ε ε ε γ A eV e e e .
This equation shows that Ψ(ε e ) is proportional to ω 2 τ 2 and consequently to B 2 This confirms the previous experimental results obtained using EQ(5) and shown in Figure2 and Figure3. The electron diffusion parameter depends on ε e -1 .

Based on the work of Mal'kov [START_REF] Mal'kov | [END_REF], who has calculated the electron current under the conditions of a collisional near-probe space-charge layer, authors [5,6] obtained Ψ(ε e )

proportional to ωτ, i.e. to Bε e -1/2 . These results disagree with our results, with Swift model [START_REF] Swift | Proc. Phys. Soc[END_REF] and with Dote et al theory [13]. Based on their models these authors [START_REF] Mal'kov | [END_REF]5,6] overestimate

( ) e ε
Ψ by a factor 100, in such cold plasma. [START_REF] Jauberteau | [END_REF] As previously shown, ( )

∫ ∞ = Ψ rp r e e eS D dr g 2 / 1 ε ε
Where D r is the normal component of the electron diffusion coefficient, which in a magnetic field parallel to the probe is equal to ( )

2 2 1 τ ω + = D D r
, where D is the electron diffusion coefficient without magnetic field.

ν λ 2 e D =
, ν is the electron collision frequency [START_REF] Shkarofsky | the particle kinetics of plasmas[END_REF].

The electron diffusion parameter depends on the sheath thickness, on the potential profile through the sheath, on the diffusion coefficient and consequently on the Larmor radius and the electron energy incoming in the probe sheath. So, it depends on plasma parameters as the electron mean energy and density, <ε e > and n e , respectively and on the magnetic field intensity B.

We assume in a first approximation a constant diffusion coefficient through the sheath. This , if ω 2 τ 2 >>1.

In the case of a cylindrical probe with length L and radius r p , ( ) e ε Ψ can be written, ( ) integrating the EEDF which is determined using the method described in ref [START_REF] Jauberteau | [END_REF]. The plasma and the floating potential are determined at the inflection point of the I-V curve and at the crossing point with the x axis, respectively.

        = = Ψ - ∞ ∫ p d e e
It can be seen that the electron density and the plasma and floating potentials increase with increasing B. However, the mean electron energy decreases with increasing B, probably because of the decrease of the Larmor radius and the increase of the electron neutral collision frequency with increasing B. The phenomena produced under such experimental conditions cannot be correlated by a simple model. So another attempt to correlate the electron diffusion parameter to the magnetic field is given as follows.

The diffusion parameter has been previously shown to be fitted by the function ( )

α ε ε - = Ψ e e A .
Using diffusion parameter values calculated with the experimental method for series a, b, c and d, we have determined an equation ( )

B n V f A e e , , , ε =
. In this equation, V, n e , <ε e > and B are the biased voltage of the probe, the electron density, the mean energy and the magnetic field intensity, respectively. Figure 9 shows the change of

Conclusion.

This work is devoted to the study of the electron diffusion parameter in magnetized plasma.

Experiments are performed in a cylindrical reactor, in microwave magnetized plasma working at 2,45GHz. We have shown that the diffusion parameter depends strongly on the ratio of the first to the second derivative function versus V of the probe characteristic I-V. The diffusion parameter can be fitted using the general law ( ) n e A - = Ψ ε ε with n ranging from 0.8 to 1.4 and A ranging from 80 to 500 according to the experimental condition at 0.19Pa and for a microwave power ranging from 1500W to 1800W and a magnetic field intensity ranging from 80mT to 120mT. These results agree with Dote and Swift model [7,10] and show that the diffusion parameter is proportional to ε e -1 . It disagrees with Mal'kov, Arslanbekov or Popov model [START_REF] Mal'kov | [END_REF][5][6] model which obtain a diffusion parameter proportional to ε e -1/2 . Until now none model is really efficient to calculate the diffusion parameter, probably because of the real potential profile and the electron motion within the sheath formed around the probe collector are unknown or because of a wrong estimation of the sheath thickness. According to Rozhansky [7] in presence of magnetic field, the anomalous diffusion can have an effect on the charged particles density profile near the probe and there can be a significant expansion of the sheath.

However, we have obtained a linear regression for

.

  The diffusion parameter can be deduced from the ratio A/B,

  directly using the first and second derivative functions with respect to the applied voltage V of the I-V probe characteristic. Only experimental results are used and no model is needed. It can be seen that for E e constant the change of Ψ(ε e ) is proportional to the product VX of the biased voltage with the ratio X of the first to the second derivative of the electron current with respect to V.

  Figure2. ( )e ε Ψversus Ee=ε e -eV, in the case of different biased voltages.

  current collected with magnetic field on the electron current collected without magnetic field, is given by,

  in the case of a mono kinetic electron current,

  assumption has been used in previous work to determine( )

  is the sheath thickness formed around the probe. Assuming in a first approximation that e > and n e are the electron mean energy and density, respectively. Under these conditions and if x d <<r p , Ψ(ε e ) should be proportional to B 2 λ e ε e -1 λ D .This model (EQ(8)) has been applied to experimental data obtained within four series a, b, c and d. The incident power and the pressure are equal to 1500W and 0.19Pa, respectively for the series a, b and c, 1800W and 0.2Pa, respectively for the series d. In the case of the series b, measurements are performed in a region corresponding to electron cyclotron resonance (ECR) conditions. Figure5shows the change of the case of the four series. The electron density and mean energy value needed to calculate λ d have been calculated integrating the measured EEDF using the method described in[START_REF] Jauberteau | [END_REF].The correlation factor of the linear regression with experimental data remains low for most of the series and the slope of the linear regression changes according to the series .i.e. with the experimental conditions (pressure, microwave incident power, position and magnetic field intensity). The results show that the ratio on Figure3) slightly increases with increasing magnetic field intensity. However, this simple model is inefficient to describe the phenomena because of the low correlation between theory and experiment. This can be ascribed to the rough assumptions concerning the sheath thickness and the diffusion coefficient but also to the strong dispersion in experimental values depending on plasma conditions. The change in plasma parameters leads to change in electron motion, sheath thickness or potential profile within the sheath and consequently in the values of the electron diffusion parameters. Figure6, 7 and 8 show the values of plasma parameters along the z axis of the reactor and between the different series. In the sake of clarity we use "spline interpolation" between the points of the different series. The values of the electron density and mean energy are calculated

  Figure5. Change of

Figure6.

  Figure6. Electron density and magnetic field intensity versus the position along the longitudinal reactor axis, in the case of the four previous series a, b, c, d used in Figure5.

Figure7.Figure8.

  Figure7. Mean electron energy versus the position along the longitudinal reactor axis, in the case of the four previous series a, b, c, d used in Figure5.

  Figure9. Linear regression of

  a biased voltage V=0.1V. The best agreement with experimental data is obtained for x=4,3 and y=-1,67 and corresponds to a correlation factor equal to 0.75. Such linear regression can be used to measure the magnetic field intensity within the reactor, with a more or less large error according to the correlation factor.