Andrés Fernando Cardozo Perez

Carine Julcour-Lebigue

Laurie Barthe

Jean-François Blanco

Si Chen

Florence Gayet

Eric Manoury

Xuewei Zhang

Muriel Lansalot

Bernadette Charleux

Andrés F Cardozo

Carine Julcour
email: carine.julcour@ensiacet.fr

D ' Agosto

Rinaldo Poli

Henri Delmas

Aqueous phase homogeneous catalysis using core-shell nanoreactors: Application to rhodium-catalyzed hydroformylation of 1-octene

Keywords:

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Aqueous phase homogeneous catalysis using core-shell nanoreactors: Application to rhodium-catalyzed hydroformylation of 1-octene

Introduction

Biphasic catalysis is an elegant strategy of catalyst immobilization in which the catalyst is confined into a solvent slightly miscible or immiscible with the products, allowing fast separation of the catalytic phase by settling and easy recycling. Although there has been increasing research on the application of biphasic reaction media with innovative solvents-such as fluorous solvents [START_REF] Mathison | Recovery and Recycling, Chemistry and Process Design[END_REF] and ionic liquids [START_REF] Earle | Ionic Liquids in Synthesis[END_REF][START_REF] Doherty | Catalysis in Ionic Liquids: From Catalyst Synthesis to Application[END_REF]-yielding successful developments like the Difasol process [START_REF] Olivier-Bourbigou | [END_REF], use of water to solubilize the catalyst has the advantage of driving the system toward sustainability and diminishing costs. A well-established industrial application of the aqueous biphasic catalysis is the Ruhrchemie/Rhône Poulenc oxo process, in which propene is converted to butanal by a hydrosoluble rhodium complex. However, the same process cannot be applied to longer chain olefins (>C4), their poor solubility in water leading to poor reaction rates. Many strategies have been developed to overcome this issue, among which use of cosolvents [5][6][7] or phase transfer agents such as cyclodextrins [8,9] or activated carbons [10]. On the other hand, surfactants or amphiphilic ligands can also create organic substrate-rich nano-objects (micelles) within the aqueous catalyst phase. The latter yield more stable and more adequately tunable catalytic systems, but still the dynamic structure of the micelles results in catalyst loss at the interface and may also generate stable emulsions by excessive swelling of the micellar core [11,12]. In a novel approach recently introduced by us [13], both limitations have been removed by turning the self-organized and dynamic micellar architecture into a unimolecular polymeric core-shell nano-object by cross-linking the hydrophobic segments of self-assembled amphiphilic block copolymers. Hence, swelling of these particles is limited by the dimensions of the resulting macromolecule and the micellar equilibrium with the free arms is removed.

A few examples of unimolecular macrostructures that achieve a favorable environment for efficient catalysis in water are available in the open literature, yet with various architectures and levels of complexity. Using natural polyphenols as amphiphilic ligands, Mao et al. [14] could prepare noble metal complex and noble metal nanoparticle catalysts for the biphasic hydrogenation of cinnamaldehyde and quinoline. The authors observed some decrease of conversion upon recycling, whose extent depended on the content of polyphenols: from 61% to 97% of the original activity was retained after five runs. Gong et al. [15] synthesized four water-soluble dendritic phosphonated ligands starting from poly(amido amine) (PAMAM) dendrimers. The first ligand resulted from a partial functionalization of the dendritic surface with monophosphine moieties, the remaining amine functions enabling its dissolution into the aqueous phase. They also alternated phosphine and sulfonate functions to further increase phosphine loading while keeping enough water solubility. Finally, they grafted some long aliphatic chains to better interact with the olefin and enhance its solubilization into the aqueous phase. These various objects thus comprised a limited amount of phosphorus atoms (18 maximum per object), mainly located at the periphery. Their application to the hydroformylation of 1-octene led to relatively low turnover frequency (TOF) values (<25 h À1 ) and significant loss of rhodium, as indicated by the yellow coloring of the organic phase. Terashima et al. [16] proposed a different approach to incorporate monophosphine units into a star polymer, using controlled radical polymerization mediated by ruthenium. As the result of the simultaneous introduction of phosphine monomer, amphiphilic macroinitiator, and cross-linking agent, the phosphine ligands were here confined within the obtained polymer microgel core, entrapping ruthenium. These objects were successfully tested for Ru-catalyzed hydrogenation under a thermomorphic approach [17]. In a close strategy of catalyst confinement, Weck et al. [18] prepared shell cross-linked micelles containing catalytic Co(III) salen functions in the hydrophobic cores from amphiphilic triblock polymers. Applied to the hydrolytic kinetic resolution of epoxides, these catalysts exhibited substrate selectivity based on hydrophobicity, unlike their non-cross-linked analogs. They could also be successfully recycled eight times by ultrafiltration. L-Proline functionalized poly(methyl methacrylate) (PMMA) nanogel particles were also proposed by O'Reilly et al. [19] as catalysts for aldol reactions in water. An increase in the weight percentage of L-proline methacrylate incorporated in the nanogel particles from 2% to 10% strongly reduced their activity, while changes in the cross-linking density (CLD) in the 0.5-5 wt% range had only a minor effect. CLD as high as 50 wt% was indeed required to shut down the reaction. Moreover, the more hydrophobic the nanogel core, the higher the observed enantioselectivity. These examples prove that the performance and stability of such macrostructures require suitable loading and location of the catalytic moieties, as well as a good match between the hydrophobic character of the substrate and the polymer core.

In this study, triphenylphosphine(TPP)-functionalized core cross-linked micelles (TPP@CCM) were synthetized by a one-pot emulsion polymerization mediated by the reversible addition-fragmentation chain transfer (RAFT) technique, wherein the metal complex is located on the hydrophobic part of the polymer flexible arms. The method also allows great flexibility regarding the density of phosphine functions, their distribution within the object, the size of the core, and that of the hydrophilic layer. Our earlier contribution [13] has detailed the synthesis and characterization of these core-shell polymers and has provided indication of rapid mass transport of organic compounds across the hydrophilic barrier and into the hydrophobic core. It also proved them to be convenient ligands for the biphasic rhodium-catalyzed hydroformylation of 1octene. The present paper gives a fuller and more detailed account of the catalytic results obtained varying different reaction parameters, such as catalyst/ligand concentration, temperature, P/Rh ratio, as well as the density of phosphine within the objects and the molar mass of the hydrophobic segment, and discusses the driving mechanisms.

Materials and methods

Materials

[Rh(acac)(CO) 2 ] (99%, Alfa Aesar), 1-octene (99+%, Acros), nnonanal (>97%, Alfa Aesar), n-decanal (>96%, Alfa Aesar), and anisole (99.0%, Fluka) were used as received. Carbon monoxide and dihydrogen were obtained from Linde Gas. Syngas was prepared by introducing equimolar amounts of CO and H 2 into a monitored gas reservoir feeding the autoclave reactor at constant pressure. The reference core cross-linked micelle used for the parametric reaction study was prepared as described in our previous contribution [13] and stored under an inert atmosphere.

Fig. 1 exhibits the detailed structure of the TPP@CCM made by convergent synthesis in water. The thin hydrophilic shell (degree of polymerization (DP) = 30) was formed by RAFT copolymerization of methacrylic acid and poly(ethylene oxide) methyl ether methacrylate. The subsequent hydrophobic part consisted of a styrene (S)/4-diphenylphosphinostyrene (DPPS) copolymer, with 300 units and a DPPS:S ratio of 1:9. The resulting amphiphilic block copolymers self-assembled into ca. 70 nm micelles in water. Addition of (di(ethylene glycol) dimethacrylate) (DEGDMA) cross-linker, together with additional styrene in a DEGDMA/S ratio of 1:9, allowed generating the TPP@CCMs as a concentrated latex suspension (27.3% solid content), containing 0.128 mol L À1 of P. Slightly modified versions of the TPP@CCMs have now been synthesized by the same procedure with either longer hydrophobic chains (DP = 500) and the same DPPS:S ratio (1:9) or with the same DP for the hydrophobic chain (300) but different DPPS:S ratios (1:19 and 1:3). See the Supporting Information for the synthesis and characterization details.

Experimental procedure

Biphasic hydroformylation

A Hastelloy C276 autoclave equipped with a gas-inducing stirrer was used for the hydroformylation experiments. The volumetric ratio of organic to aqueous (including the TPP@CCM latex) phases was set to 3:1 (prior to swelling) for a total volume of 0.1 L. The organic phase consisted of a mixture of 1-octene (1.1 kmol m À3 uorg ) and n-decanal to mimic the conditions within a continuous stirred tank reactor, where the out-flowing organic phase stream should be mainly constituted of C9 aldehydes, while allowing precise quantification of these products.

Standard reaction tests.

First, Milli-Q water was introduced into a Schlenk tube and deoxygenated by nitrogen bubbling. The required quantity of TPP@CCM latex (according to desired P content) was added through a nitrogen-purged syringe, followed by stirring for 15 min. In order to swell the hydrophobic core of the nano-objects, 3 mL of n-decanal was added and the resulting mixture was stirred for an additional 15 min. Then, a separate solution containing [Rh(acac)(CO) 2 ] dissolved in 3 mL of n-decanal was added through a Teflon cannula, and the resulting mixture was stirred for 5 min. This colloidal suspension was then transferred into the autoclave, followed by the addition of the remaining ndecanal (56 mL) and 1-octene (81.6 mmol). The reactor was purged three times with 15 bar of nitrogen, checked for leak under N 2 pressure, and then purged four times with 15 bar of syngas (about 25 min for the whole procedure). It was subsequently heated under low syngas pressure (2 bar) and slow stirring speed (300 rpm, well under gas self-induction) to hinder significant gas dissolution and the start of the reaction. When the desired reaction temperature was achieved (after about half an hour), stirring was stopped and the autoclave was pressurized and constantly fed with syngas at the desired pressure (20 bar). A sample was withdrawn to evaluate the amount of products formed during the heating procedure. Then, the data acquisition was started, and the stirring speed was set to 1200 rpm. Both temperature and pressure of the reactor and the gas ballast were recorded online on a computer at a rate of 1 Hz. The instantaneous reaction rate was measured from the syngas consumption. After a few hours of reaction, a final sample of organic phase was taken for the chromatographic analysis. Acquisition and heating were stopped, and the autoclave was cooled slowly at low stirring speed (200 rpm). Once the autoclave was cold, stirring was stopped and the reactor was depressurized and purged four times with nitrogen. The whole reaction mixture was let overnight for settling under nitrogen atmosphere. Finally, the content of the autoclave was then taken out and separated. Rhodium leaching in the organic phase was measured by ICP/MS (cf. Section 2.2.2).

Recycling of the catalytic phase.

To perform recycling tests, the procedure was as described above, except that after cooling the reactor was kept under 2 bar of syngas and, after overnight settling, only the organic phase was withdrawn through a pipe placed above the interface with the help of the internal syngas pressure. Then, after venting the residual pressure, fresh 1-octene (81.6 mmol) and n-decanal (for a total volume of ca. 50 mL, corresponding to the withdrawn amount) were introduced into the autoclave through a dropping vessel pressurized with nitrogen. The reactor was subsequently purged four times with 15 bar of syngas. Heating period and reaction then proceeded as usual.

Analyses of the organic phase 2.2.2.1. Gas chromatography (GC).

The reactant and product concentrations were measured on a Thermo Fisher Trace GC 2000 chromatograph equipped with a CB-CP WAX 52 capillary column (25 m  0.25 mm; 0.2 lm film thickness) and a flame ionization detector (FID), using helium as carrier gas. A precise quantity of anisole (internal standard) was added before dilution with diethyl ether. The peak assignment was assisted by a separate GC/MS analysis.

High resolution inductively coupled plasma mass spectrometry (ICP/MS).

The rhodium catalyst leaching in the organic phase was quantified by high resolution ICP/MS on a XR Thermo Scientific Element. For the sample preparation, the recovered organic phase was diluted into water using a 10 5 volumetric dilution factor, high enough to insure complete dissolution. In practice, a 1-L volumetric flask was filled at $2/3 with Milli-Q water, then 10 lL of the organic product phase were introduced using a Gilson P20 preci-sion pipette. Borders were rinsed and the flask was introduced into an ultrasound bath for 30 min. The solution was left overnight and the dilution was then completed with Milli-Q water to the 1 L mark. Standards were prepared using [Rh(acac)(CO) 2 ] dissolved in n-decanal, attaining Rh concentrations in aqueous solution in the 1-1000 ppt range. The relative standard deviation on the measurements was less than 5%.

Results

Proof of concept: activity and stability of the reference TPP@CCM

The core cross-linked micelle depicted in Fig. 1 was first tested under the following conditions of biphasic hydroformylation: 1octene/Rh = 500, P/Rh = 4, 90 °C, 20 bar of syngas, and a stirring rate of 1200 rpm, further referred to as the ''standard conditions''. The pH of the aqueous phase was not adjusted, and a value of 4.3 was measured after the reaction.

As generally observed with usual convenient ligands based on triphenylphosphine, no hydrogenation and low isomerization (about 5%) were observed with the functionalized CCM, the main products being C9 aldehydes (about 90% yield after 3 h), mostly n-nonanal and its branched isomer, 2-methyloctanal. Conversely, the phosphine-free CCM gave very similar results as the homogeneous reaction without any ligand: after 4 h of reaction under standard conditions (except no P), and the aldehyde yield was 15% (vs. 23% for the homogeneous ligand-free process), while the internal octenes accounted for 35% of the initial substrate charge. This demonstrated that only the polymer-linked phosphine ligand can form the active complex with rhodium.

As shown in Table 1, the TOF obtained with the reference TPP@CCM was rather high (about 500 h À1 , see entries 1 and 2) confirming that 1-octene can easily enter the functionalized hydrophobic core of the polymer despite the hydrophilic shell [13].

The measured linear to branched aldehyde regioselectivity (l/b) was up to 5.0. For comparison, the homogeneous reaction performed with a star polymer made of Boltorn core and S/DPPS arms yielded TOF up to 1030 h À1 and l/b ratio between 4.0 and 5.6 under similar operating conditions (90 °C, 20 bar of syngas and 1.0 M of 1-octene) [20]. The uptake of the organic phase by the nanoobjects was confirmed from the weight gain of the aqueous phase. The rhodium loss in the organic phase accounted for about 1% of the amount introduced. A subsequent homogeneous hydroformylation with the recovered organic phase, mixed with fresh 1-octene, led to negligible reaction rate (less than 5 Á 10 À6 kmol m À3 uorg s À1 ). An additional proof of concept was performed by addition of a stronger water-soluble ligand (sulfoxantphos) to the latex aqueous phase to extract the rhodium initially coordinated to the CCM phosphines into the bulk of the aqueous phase. This experiment resulted in reaction inhibition (cf. [13], recalled in entry 3), thus excluding any interfacial catalysis mechanism [13]. This is opposite Fig. 1. Structure of the reference core cross-linked micelle (TPP@CCM), from Zhang et al. [13].

to what was reported with cationic surfactants [21] or polymer lattices [22] and should result from the lack of electrostatic interaction between the hydrophilic shell and the water-soluble catalytic complex. This result clearly shows that the reaction can only occur in the core of the TPP@CCM. The only role of the CCM shell is thus to confine the objects within the aqueous phase, yet allowing in and out migration of species according to their respective affinity, while catalysis actually occurs within the hydrophobic microenvironment combining catalyst and substrate.

The catalytic system stability was assessed through four successive recycles of the catalytic phase (entries 1r1 to 1r4 of Table 1). As explained in the experimental procedure, the catalytic phase was always kept under syngas atmosphere during these recycles, but it was previously shown that its exposure to air during a few days did not result in extensive deactivation [13]. Confirming our previous observations, the first recycle gave even higher activity than the first use, possibly because all the [Rh(acac)(CO) 2 ] precatalyst may not be fully activated during the first run. The small decrease under further recycles might be attributed to catalyst losses during the successive samplings (a small amount of aqueous phase being unavoidably withdrawn) and because of leaching in the organic phase. The rhodium leaching seemed to plateau to ca. 1.7 ppm after 3 runs. The possible cause for this leaching will be discussed more in detail below on the basis of additional evidence. Fig. 2 exhibits the evolution of the aldehyde production calculated from the syngas consumption during these successive cycles and during a repeat experiment with fresh catalyst run under the same conditions, showing reproducibility. In accordance with the narrow dispersion of the TOF values, all these profiles are very similar. The GC/FID analysis of the organic phase sample withdrawn prior to the gas induction showed that the preliminary heating period yields up to 6 mmol of aldehyde (7% conversion) and this sampling accounted for 5-10% of the total volume of organic phase. This explains the smaller measured amount of consumed syngas relative to theory (equivalent to 81.6 mmol of aldehyde) at complete conversion.

Influence of reaction parameters using the reference TPP@CCM

After confirmation that the TPP@CCM approach provides an efficient alternative for aqueous biphasic hydroformylation catalysis, additional kinetic studies were carried out to explore the effect of different operating conditions. Given that the organic phase is the continuous phase, that H 2 and CO have greater solubility in 1-octene than in water, and that 1-octene is essentially insoluble in water, the sequence of mass transfer events is probably as follows: the gaseous reactants are transported into the continuous organic phase, and all reagents migrate toward the TPP@CCM (external mass transfer) and finally diffuse within the polymer scaffold to reach the Rh catalytic sites (internal mass transfer) to be eventually transformed into products. The different operating parameters-catalyst and ligand concentrations, stirring speed, and temperature-were varied to check for mass transfer resistance, and their effects are detailed in Table 2.

Catalyst concentration

A common experimental test to evaluate external mass transfer limitations is to vary the catalyst concentration. If this transfer resistance is negligible and if all Rh atoms are working in the same way, the initial reaction rate should exhibit a first-order dependence with respect to the catalyst loading (or in other words the TOF should be unchanged). Starting from standard conditions (entry 2), two different procedures were applied: either the concentrations of both Rh precursor and latex were varied so as to keep the same P/Rh value of 4 (entries 4a and 4b) or only the concentration of Rh precursor was changed while maintaining the same TPP@CCM loading (entries 5a and 5b). Note that these procedures might have resulted in additional but different effects. In the first approach, the metal loading of each unimolecular nano-object is the same and the activity of Rh atoms should not be modified provided that the objects do not interact with each other. However, the properties of the aqueous phase (viscosity, surface tension) are altered, and consequently, the mobility of the objects and the available aqueous-organic interface (droplet size) will also change. In the second approach, the activity of the Rh atoms might be affected as the result of variations in the P/Rh ratio (from 2 to 8). It is therefore striking that in both cases, a fourfold increase in rhodium concentration resulted only in a threefold initial rate enhancement. This suggests that a weak resistance to external mass transfer is present, probably associated to gas-liquid transport limitations.

Regarding regioselectivity, the l/b ratio was slightly enhanced at the lowest concentrations of the catalytic objects but was almost unaffected by the P/Rh variation.

TPP@CCM concentration (at same Rh precursor concentration)

To better elucidate this effect, additional experiments were performed increasing the latex concentration, resulting in an increase of the P/Rh ratio up to 12 (entries 6a and 6b). No significant TOF or l/b variations were observed, showing that the aqueous phase properties did not significantly affect the physical transfers (if limiting) and that the Rh distribution within the objects played only a minor role on the whole catalytic activity for P/Rh P 4. This low effect of ligand concentration differs from the usual trends in homogeneous hydroformylation, where an excess of PPh 3 with respect to the [RhH(CO)(PPh 3 ) 3 ] complex led to a better selectivity toward the linear aldehyde (until a plateau was reached), with a complex effect on the reaction rate depending on the solvent nature [23]. Some homogeneous experiments were thus performed using the same composition of the organic phase and PPh 3 as a ligand, P/Rh being set at 4, 8, and 12, respectively (see details in the SI). Lower l/b ratios were achieved (less than 3), but the resulting TOF values were as high as 9000 h À1 . Nonetheless, no clear trends could be drawn on the effect of the P/Rh ratio, with TOF variations of less than 20% and only a slight l/b increase from 1.5 to 2.3 when increasing ligand excess.

Stirring speed

In order to enhance the external mass transfer (especially the gas absorption), the stirring speed was increased to 1400 and 1600 rpm (entries 7a and 7b). Slightly higher TOF values were observed, up to 580 h À1 as compared to a mean value of 460 h À1 at 1200 rpm, but also a significantly higher Rh leaching (about 5 times higher)-see Section 3.4. The organic phase obtained after the biphasic reaction at 1600 rpm showed little catalytic activity (about 5 Á 10 À5 kmol m À3 uorg s À1 ). Higher stirring speeds should thus be avoided in order to limit catalyst leaching with this type of CCM. During the course of the 1600 rpm reaction, the organic phase was regularly sampled and analyzed by GC in order to learn more about the time evolution of each individual reaction component. Fig. 3a exhibits the concentration-time profiles of all the reactants and products during this experiment. It confirms that isomerization was low (two different internal octenes being identified). No product other than the octenes and the aldehydes could be detected by GC, and the sum of all concentrations of these compounds yielded an excellent mass balance. Fig. 3b depicts the good agreement between the evolution of the amount of total produced aldehydes and that of the syngas consumption (as per stoichiometry). As expected from the low degree of isomerization, the l/b ratio was essentially constant during the course of the reaction.

Reaction temperature

Finally, the reaction was performed at two different temperatures, 343 and 353 K (entries 8a and 8b), in addition to the standard temperature (363 K, entry 2), keeping other parameters identical. Application of the Arrhenius equation yielded an activation energy of 22 kcal mol À1 . This value agrees well with those obtained in former studies on homogeneous and biphasic hydroformylation using monomeric ligands (PPh 3 or its trisulfonated analog) and operating in the kinetic regime: 28.0 and 13.7 kcal mol À1 for 1-hexene and 1dodecene in homogeneous system [24,25], 15.7 and 19.7 kcal mol À1 for 1-octene and 1-dodecene in biphasic aqueous system [26,27].

This high activation energy indicates that not only the exchange of reactants/products between the continuous organic phase and the nanoreactors but also their diffusion within the TPP@CCM structure was rapid.

Comparison between different macromolecular architectures

Table 3 summarizes the performance of different macromolecular ligands derived from the reference TPP@CCM, by varying either the size of the hydrophobic block or its functionalization degree. The essential characterization details of the new polymers are provided in the Supporting Information.

Effect of CCM size

The test was carried out with a nano-object built in the same way as the reference TPP@CCM, except for increasing the DP of the hydrophobic chain from 300 to 500, while maintaining the same DPPS:S ratio of 1:9. The initial reaction rate and l/b ratio were essentially unaffected by this increase in polymerization degree (entry 9), confirming that internal diffusion within the objects is not rate-limiting. Note, however, that leaching is reduced.

Effect of functionalization degree

To investigate the influence of the phosphine density within the polymer, two other TPP@CCMs were synthetized using DPPS:S ratios of 1:19 and 1:3 (see Supporting Information) and evaluated under standard conditions (entries 10 and 11a). The higher the functionalization degree of the hydrophobic core, the lower the resulting reaction rate. The l/b ratio increased upon rising the P concentration in the polymer core from 5% to 10% molar of the DPPS co-monomer, implying a possible shift to catalytic species with a higher number of coordinated phosphine ligands as these are less active and more regioselective [START_REF] Van Leeuwen | Homogeneous Catalysis: Understanding the Art[END_REF]. However, a subsequent increase of the DPPS co-monomer fraction from 10% to 25% molar had no further effect on the l/b ratio. With the most functionalized TPP@CCM, halving the catalyst concentration (entry 11b) resulted in a larger TOF increase (by 45%) than for the reference one (by 27%, cf. entries 2 and 4a in Table 2). Thus, additional mass transfer limitations could be also hypothesized. Nonetheless, the temperature effect was found as strong with this ligand (entry 11c), discarding such an explanation.

A greater functionalization degree implies a smaller number of nanoreactors at given C8/Rh and P/Rh ratios, and thus a higher density of Rh within the objects. In spite of the fact that the local Rh distribution did not apparently result in any significant activity change for the reference TPP@CCM (cf. Section 3.2.2), this might not be the case when the phosphine moieties are closer to each other: the formation of inactive dimeric Rh species could be promoted in this case as the result of the closer vicinity of the metal atoms [START_REF] Ro | [END_REF]. Another possible explanation would be that some Rh centers are not accessible due to steric hindrance caused by the high phosphine density.

Consideration on the rhodium leaching

It is possible in principle to imagine two basic mechanisms leading to Rh leaching into the organic product phase: either Rh escapes the polymer support and is transported into the organic phase by available small molecules as supporting ligands, or the polymer nanoreactor is partly transferred to the lipophilic phase during the catalytic procedure. On the basis of the known coordination chemistry of rhodium(I), leaching by rhodium extraction from the nanoreactor does not appear as a plausible explanation. Indeed, in order to extract the catalytically active hydride species from the polymer, the polymer-anchored TPP would have to be exchanged by another ligand available in the catalytic mixture. However, the only available donors are hard oxygen-based molecules (water, n-nonanal)-with much less affinity for Rh I than the softer TPP-and CO. However, [RhH(CO) 4 ] is a very elusive compound which could be observed (in the absence of TPP) only in small equilibrium amounts with [Rh 4 (CO) 12 ] and H 2 under a high pressure of H 2 and CO [30]. Hence, although Rh escape from the nanoreactor cannot be completely excluded at this stage, we assume that the metal is partially lost into the organic phase together with the polymer. In order to find conclusive evidence in support of this proposition, we attempted to carry out an ICP/ MS analysis of phosphorus in the product phase. This measurement, however, turned out inconclusive because of some interferences due to the presence of n-decanal. Thus, we turned to a DLS analysis of the organic phase.

We were particularly interested in analyzing the three organic phases recovered after the experiments run with different stirring speed (entries 2, 7a and 7b in Table 2), because of the prominent effect that this speed had on leaching. The DLS analysis results (see Fig. 4) show the presence of nano-objects, the size of which is comparable or greater than that of the CCMs in the starting latex (79 nm/0.18 in water, 175 nm/0.28 in THF) [13]. Incidentally, the absence of smaller size particles also shows that stirring has no destructive mechanical effect on the CCM. It is interesting to note that the size of the nano-objects increases with agitation speed. For the lower speed (1200 rpm, solid line), the D z /PDI values (90 nm/0.34) are quite comparable with those of the original latex.

The small increase in size can be attributed to slight core swelling by the organic medium, which is less prominent for n-decanal than for THF. Indeed, n-decanal was previously shown by a 1 H NMR analysis to have a small swelling power for the CCM at room temperature [13]. For the intermediate speed (1400 rpm, dashed line), the distribution remains narrow but the average size is increased (123 nm/0.18). Finally, at the highest speed (1600 rpm, dotted line), a bimodal size distribution is observed with the smaller mode centered at ca. 100 nm and the larger one at 300-400 nm.

The transport of nano-objects to the organic phase was confirmed by control experiments run by mixing the latex, either with or without rhodium, and n-decanal in the same proportions as in the catalytic experiment and vigorously stirring the mixture for the same time period as the catalytic run (2.5 h) and at the same temperature (90 °C). In the absence of rhodium, strong scattering resulted from the organic phase measured immediately after contact, yielding a broad particle-size distribution (PSD) with D z = 283 nm (PDI = 0.33) which extended to more than 1 lm (Fig. 5a, solid curve). After 1 week standing at room temperature (Fig. 5a, dashed curve), the PSD shifted to smaller dimensions (D z = 186 nm; PDI = 0.10) and became narrower. Hence, agglomerates were incontestably formed and transferred to the organic phase at high temperature, but they subsequently and slowly evolved toward monodispersed swollen particles upon cooling. Unfortunately, the DLS experiment does not provide quantitative information on the CCM concentration in the organic phase, and thus, it is not possible to extract a value for the partition coefficient, but a slight solubility of the TPP@CCM in decanal is qualitatively confirmed. The scenario was different when the polymer transport control experiment was carried out for the latex containing the Rh precatalyst [Rh(acac)(CO) 2 ] (P/Rh = 4). This time, the DLS signal of the freshly recovered n-decanal solution indicated a bimodal distribution, a minor one centered at slightly above 100 nm and a major one centered at ca. 650 nm, see Fig. 5b, solid curve. Upon standing for one week at room temperature, a slight shrinkage in average size was observed as expected from solvent release upon cooling, but the major distribution clearly persisted, see dashed curve in Fig. 5b. This bimodal pattern is similar to that observed after the catalytic experiment at high stirring. Note that the DLS experiments on the recovered organic phases were carried out several months after catalysis. In addition, prolonged heating (several hours) of the [Rh(acac)(CO) 2 ]/TPP@CCM latex at the reflux temperature resulted in precipitation of the polymer as an orange solid, which could no longer be dispersed in the aqueous phase. Quite evidently, the presence of rhodium favors the formation of stable aggregates that appear to be extracted into the organic phase more readily than the non-aggregated CCMs. A tentative explanation of this phenomenon is cross-linking of different poly-mer cores. Indeed, [Rh(acac)(CO) 2 ] is known to replace only one CO ligand upon interaction with triphenylphosphine at room temperature to yield [Rh(acac)(CO)(TPP)] [31], but heating induces also the exchange of the second CO ligand to yield [Rh(acac)(TPP) 2 ] [32]. Therefore, the same Rh atom has the possibility to be coordinated by two TPP ligands from two different CCM cores. Note that when the control experiment was performed at room temperature, no particles were detected in the organic phase. In the catalytic reaction, the metal complex is activated by syngas and transformed to a [RhH(CO) n (TPP) m ] species which, in the presence of a high CO pressure, probably favors the complex with m = 1 and therefore limits the extent of inter-particle cross-linking. While a complete understanding of the physical changes induced by the agitation to the nano-objects requires additional experiments, these preliminary results allow us to deduce that aggregation of CCMs occurs, one possible mechanism being related to inter-particle cross-linking through coordination of TPP ligands from different particle cores to the same Rh atom, that this phenomenon is favoured by heating and by a stronger agitation speed, and that the result of this aggregation is a greater extent of polymer transport into the organic phase.

Conclusions

Tailored catalytic nanoreactors for biphasic catalysis have shown promising results in the hydroformylation of 1-octene: high activity, low isomerization and good stability (Rh leaching of a few ppm), and recyclability. Independent variations of several process parameters have led to the same conclusion of an efficient transfer of the substrates into and within the nanoreactor hydrophobic core. Nevertheless, a moderate mass transfer limitation occurs for high rhodium concentrations, which is more likely due to rhodium interactions than to interfacial or internal mass transfer. A preliminary design study provided clues toward their optimization: a lower degree of functionalization leads to higher TOF. A Fig. 4. DLS analysis of the recovered organic phase after the catalytic runs 2, 7a and 7b in Table 2. Stirring speed (rpm): 1200 (solid), 1400 (dashed), and 1600 (dotted). kinetic modeling and the mass transfer mechanism are under investigation, which goes through the analysis of the microenvironment composition. Finally, leaching appears related to a particle aggregation phenomenon probably through particle cross-linking which appears accentuated by more vigorous stirring. In order to reduce or completely eliminate this phenomenon, we are currently investigating other polymer architectures that differ by either core cross-linking or shell chemical nature. The results of these investigations will be published in due course.

1 a

 1 Standard conditions: [Rh(acac)(CO) 2 ] = 6.5 Á 10 À3 kmol m À3 uaq , [1-octene] = 1.1 kmol m À3 uorg , P/Rh = 4 (based on P contained in TPP@CCM), V uorg = 75 mL (total volume of 1octene + n-decanal), V uaq = 25 mL (water + 1.4 g TPP@CCM, without swelling), T = 363 K, P syngas = 20 bar (CO/H 2 = 1), x = 1200 rpm. b Initial reaction rate (with respect to non-swollen aqueous phase) and corresponding turnover frequency calculated from the syngas consumption during the first 5 min following gas absorption. c Linear to branched aldehyde ratio determined from the GC/FID analysis of the final sample. d Rh concentration in the organic phase measured by ICP/MS. e Recalled from Zhang et al. [13]. f [Sulfoxantphos] = 0.033 kmol m À3 uaq (sulfoxantphos/Rh = 5).

Fig. 2 .

 2 Fig.2. Aldehyde production ⁄ during the consecutive cycles with the reference TPP@CCM in standard conditions. ⁄ Calculated from syngas consumption after gas induction (excluding the first 20 s corresponding to gas absorption).

a

  Standard conditions: [Rh(acac)(CO) 2 ] = 6.5 Á 10 À3 kmol m À3 uaq , [1-octene] = 1.1 kmol m À3 uorg , P/Rh = 4, V uorg = 75 mL, V uaq = 25 mL (without swelling), T = 363 K, P syngas = 20 bar (CO/H 2 = 1), x = 1200 rpm; n.a. = not available.

Fig. 3 .

 3 Fig. 3. Evolution of reactants and products during the reaction performed at 1600 rpm (other parameters set as per standard conditions): (a) evolution of the concentrations in the organic phase and overall mass balance, (b) comparison of the produced aldehydes from GC/FID analysis ⁄⁄ and from syngas consumption after gas induction and time evolution of the l/b ratio. ⁄⁄ Assuming a uniform composition of the organic phase (in the bulk and within the objects).

a

  Standard conditions: [Rh(acac)(CO) 2 ] = 6.5 Á 10 À3 kmol m À3 uaq , [1-octene] = 1.1 kmol m À3 uorg , P/Rh = 4, V uorg = 75 mL, V uaq = 25 mL (without swelling), T = 363 K, P syngas = 20 bar (CO/H 2 = 1), x = 1200 rpm; n.a. = not available.

Fig. 5 .

 5 Fig.5. DLS analysis of the recovered organic phase after stirring the TPP@CCM with n-decanal for 2.5 h at 90 °C (measurements carried out at room temperature): (a) without Rh and (b) with Rh (P/Rh = 4). In both cases, the solid curve was recorded immediately after recovery; the dashed curve was recorded after one week standing at room temperature.

Table 1

 1 First results of Rh/TPP@CCM complex for the biphasic 1-octene hydroformylation. a

	Entry	Ligand	Run	Initial rate b (kmol m À3 uaq s À1 )	TOF max b (h À1 )	l/b c (-)	Leaching d [Rh] uorg (ppm)
	1	Reference TPP@CCM (10% DPPS)	Original	8.5 Á 10 À4	473	4.4	2.5
	1r1		1st recycle	9.8 Á 10 À4	541	3.9	2.7
	1r2		2nd recycle	9.4 Á 10 À4	520	3.4	2.1
	1r3		3rd recycle	8.2 Á 10 À4	457	3.2	1.7
	1r4		4th recycle	7.3 Á 10 À4	402	3.6	1.7
	2 e		Repetition with fresh catalyst	8.0 Á 10 À4	441	5.0	2.0
	3 e	Reference TPP@CCM + sulfoxantphos f		2.3 Á 10 À5

Table 2

 2 Influence of reaction parameters on the biphasic hydroformylation of 1-octene catalyzed by the Rh/reference TPP@CCM complex.

	Entry	Parameter variation from std conditions a	Value	Initial rate (kmol m À3 uaq s À1 )	TOF max (h À1 )	l/b (-)	[Rh] uorg (ppm)
	2	No	Standard a	8.0 Á 10 À4	441	5.0	2.0
	4a	[Rh] and [TPP@CCM] (P/Rh = 4)	Cata/2 (C8/Rh = 1000)	5.1 Á 10 À4	562	5.5	n.a.
	4b		Cata  2 (C8/Rh = 250)	1.5 Á 10 À3	414	4.1	n.a.
	5a	[Rh] ([TPP@CCM] = const.)	[Rh]/2 (C8/Rh = 1000, P/Rh = 8)	4.4 Á 10 À4	484	4.6	2.7
	5b		[Rh] Â 2 (C8/Rh = 250, P/Rh = 2)	1.4 Á 10 À3	379	4.3	5.7
	6a	[TPP@CCM] ([Rh] = const.)	[TPP@CCM] Â 2 (P/Rh = 8)	9.2 Á 10 À4	507	4.4	n.a.
	6b		[TPP@CCM] Â 3 (P/Rh = 12)	8.2 Á 10 À4	454	4.8	n.a.
	7a	Stirring speed	x = 1400 rpm	1.0 Á 10 À3	557	3.4	6.5
	7b		x = 1600 rpm	1.0 Á 10 À3	579	3.5	11.6
	8a	Temperature	T = 343 K	1.3 Á 10 À4	72	3.8	1.3
	8b		T = 353 K	3.1 Á 10 À4

Table 3

 3 Influence of the macroligand architecture on its performance in the biphasic 1-octene hydroformylation.

	Entry	Investigated ligand	Operating conditions	Initial rate (kmol m À3 uaq s À1 )	TOF max (h À1 )	l/b (-)	[Rh] uorg (ppm)
	2	Reference TPP@CCM	Standard a	8.0 Á 10 À4	441	5.0	2.0
	9	TPP@CCM with DP P(S-co-DPPS) = 500	Standard	8.0 Á 10 À4	442	4.1	1.4
	10	TPP@CCM with DPPS:S = 1:19	Standard	1.3 Á 10 À3	695	3.3	1.8
	11a	TPP@CCM with DPPS:S = 1:3	Standard	3.5 Á 10 À4	191	4.7	1.4
	11b		Std, except cata/2 (C8/Rh = 1000)	2.5 Á 10 À4	278	4.1	3.3
	11c		Std, except T = 343 K	4.0 Á 10 À5

Acknowledgments

This work was carried out with the financial support of the Agence Nationale de la Recherche (ANR) under the Biphasnanocat Project (ANR-11-BS07-025-01). We thank J.L. Labat, I. Coghe, and M.L. Pern (LGC) for their technical support and F. Candaudap (GET Toulouse) for ICP/MS analyses.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcat.2015.01.009.


Mohamed-Ikbel Boulabiar
email: mohamed.boulabiar@telecom-bretagne.eu

Gilles Coppin
email: gilles.coppin@telecom-bretagne.eu

Franck Poirier
email: franck.poirier@univ-ubs.fr

Mashup Architecture for Connecting Graphical Linux Applications Using a Software Bus

Keywords: H.5.2 [Information interfaces and presentation]: User Interfaces; I.3.6 [Computer Graphics]: Methodology and Techniques Operating system, interaction, architecture, post-wimp, factorization, automation

Although UNIX commands are simple, they can be combined to accomplish complex tasks by piping the output of one command, into another's input. With the invasion of GUI applications, we have lost this ability to chain many small tools in order to accomplish a composite task or the possibility to script applications. As such we have become imprisoned into the interface as designed by the developer. Most applications are also designed to be used through a keyboard and a mouse even if the user has newer input devices. In this paper, we demonstrate how we can remove most of these limits and provide the possibility to script, adapt and automate GUI applications using a software bus in a Linux operating system. We provide implemented proof-of-concept cases in addition to conceptual scenarios showing the possibilities arising from the approach.

INTRODUCTION

The UNIX operating system has introduced the successful concept of building all the system experience by using small command-line tools which can be connected together through pipes. Unfortunately, this concept of "do one thing and do it well" is only available through the console and can not be applied to the GUI applications which have become more complex in each iteration. These applications are actually used as separated islands. They have some similar . functionalities and with different and redundant implementations that forced special users as designers to use a huge list of tools in order to accomplish a bigger task. In this paper we are trying to solve the problem of GUI application complexity, inability of the reuse of specific functionalities, and inflexibility by introducing a new concept of communicating between the GUI applications, and describing scenarios that show the importance of such a mechanism. The scenarios we are exposing show numerous cases where the possibilities exceed the communication with a single application.

Our contribution mainly lies in the use of a software bus to ensure the applications connection and the ideation of new scenarios offered by this technique. Scenarios are a ground point to rethink how application could be architected in a common open source platform like Linux and evaluate the approach by enumerating and testing the feasibility of scenarios. We target creative tools and graphical design software used mainly by designers, novice or advanced. First, we start by presenting the concept of reducing the use of creative applications to their canvas and presenting the reasons which led to such a decision. Then we start presenting scenarios sorted in terms of complexity.

APPLICATIONS AS CANVAS

Definition of a Software Bus

A Software Bus is an inter-process communication system which allows different applications to connect to a shared channel and then communicate information or invoke distant method calls. In the case of Linux systems, D-Bus is used to facilitate the communication of three message types: method calls, signals and properties. It is possible to call a method in a remote application, subscribe to signals events emitted or read variable properties shared on the bus. As defined by the standard, each application has an address and a list of methods which can be introspected by any application reading from the bus. The choice of D-Bus is suggested by the number of tools, libraries and applications that already support it.

Previous and Related work

When Linux developers have finished the work on supporting multi-touch events inside Linux kernel, they faced the problem of modifying a big list of software libraries and layers to support the event routing between the kernel and the application. A faster solution developed was Ginn, which is a Linux daemon that transforms multi-touch events into keyboard taps and mouse clicks. The transformation rules named "wishes", are loaded depending on the application currently in focus. The concept of transforming input events is similar to the one of the iCon project by Dragicevic [START_REF] Dragicevic | Support for input adaptability in the icon toolkit[END_REF]. A small piece of code enabled legacy applications to have a feeling that they react to the new events, without modifying the code of the legacy applications or soliciting the developers to do so. Ginn proposed a solution to adapt old applications to new ways of interaction, but it still needs to have the application in focus, and the old interface in which events are injected. From this case, we felt the importance of including pieces allowing applications to evolve in the future to support new means of interaction as referred by Chatty [START_REF] Chatty | Multiple input support in a model-based interaction framework[END_REF] than keyboard and mouse events. Ginn could do a better job if it were able to trigger, by a certain rule or wish, an internal function of the application. In this case, it would bypass the proposed GUI interface and only need the application canvas where the command response is shown as the case in Figure 1.

Reducing applications into their canvas

GUI applications have eliminated the need to memorize commands in order to accomplish tasks. Meanwhile, they have removed the possibility of scripting and intercommunication. Some attempts have tried to use software buses like TUIO [START_REF] Kaltenbrunner | Tuio: A protocol for table-top tangible user interfaces[END_REF] and IvyBus [START_REF] Buisson | Ivy: Un bus logiciel au service du développement de prototypes de systèmes interactifs[END_REF]. In the first case to transport input events which are more complex than the one standardized in the operating system, and in the second case to communicate between application to transport a generic type of information. Olivo et al. [START_REF] Olivo | Software requirements for a (more) manageable multi-touch ecosystem[END_REF] have pointed out this problem while trying to handle multi-touch events, but used network protocols. That does not completely solve the problem, especially when many applications do not use the same platform standard. We also present how we can reduce the dictatorship of the applications interface on what the user is able to do. This is different of what has been done by Stuerzlinger et al. [START_REF] Stuerzlinger | User interface façades: Towards fully adaptable user interfaces[END_REF] by trying to innovate at the interface level in order to reach the same goal. Minimizing the role of most of the applications into a visualization canvas of what is being done by accessing its internal functionalities from a software bus. It can also simplify the application migration into a new post-wimp paradigm because we will only need to connect new input events into these internal methods and need the canvas only for feedback. Contrary to model-viewcontroller pattern where frontiers of a single application are known, we are addressing a platform with multiple applications that can be used on multiple devices which is not limited to original developers intended use. In most of the upcoming scenarios, we target the vector drawing application Inkscape and show what are the new possibilities arising from it.

SCENARIOS

Scripting GUI Applications

Graphical applications can only be used through their interface, and using the input devices supported. When we want to handle a complex manipulation we are stuck in repeating input actions, especially when developers have not provided neither a macro recorder nor an app-internal scripting API like VBA or Gimp PDB (Procedural DataBase). Some of the solutions to this problem is to use an external daemon for input record and replay, or more complex ones like MIT Sikuli [START_REF] Yeh | Sikuli: Using gui screenshots for search and automation[END_REF] use computer vision to detect the position of graphical interface elements then generates clicks on them. Using computer vision for such operation means that we still need the graphical interface on the screen. This is more like a hack than a permanent solution, as the interface can change anytime between versions. In our case, by accessing the application methods exposed on a standardized software bus, we are able to script all needed actions using a simple python script executed from the outside of the application itself which is then transformed into a visualization canvas.

Interactive Programming

When we script application as we discussed, we also have the possibility to combine useful scripts, make them configurable and create a GUI for them. By taking the example of a drawing application like Inkscape, the application is divided into a canvas, where elements are drawn, and a default user interface. We can use floating windows in the same way of Magic Lenses by Bier et al. [START_REF] Bier | Toolglass and magic lenses: The see-through interface[END_REF] to add a new functionality to the application. The floating windows will internally contain a script to handle an object inside Inkscape as in Figure 3. The window can use sliders to configure the values to draw a complex shape, and generate the DBus commands in order to stream them to the application. From simple application methods like "draw line" or "draw circle ", we can write external plug-ins able to draw any shape. They will communicate with Inkscape using the software bus, developed in any selected language and are solely limited by the imagination of this plug-in developer. This new way of adding features to applications is very generic in terms of the programming language used or what is possible to, and can force the application to behave in newer ways. Figure 2 shows the use of C++ or python languages to add interactivity. For example we can make a drawing application to behave as a plotting tool by reading values from a file and transforming them into drawing commands to the app. We have even created an animated visualization by using the "move" method on a graphical element inside the plug-in internal loop which can export a frame each time then combined to create an video. Inkscape gained the animation ability just by plugging an external application that is based on its methods and compose them to create a new environment.

Factorization of applications development

In the previous example, we reached the level where we can make a normal application behave in new ways just by using external plug-ins that do not depend on the provided interface. This means that the important part of the application is changed. What are the limits if we push this concept into a new level by completely removing the default interface and providing new ones?

Any designer use many tools to create a mock-up or an animation. Tools he uses do not always come from a single company. Thus he needs to learn to use the interface of each of them. A beginner will find that these tools do not share the same icons, the same interaction design, even the same positioning of toolbar elements which is a problem of inconsistency in the actor platform. This problem can be solved when the developer of a platform can access internal functions through the installed software and provide by himself an interface which contain the same set of icons and based on a the same interaction design. And such an access can be done using a software bus between applications. We are proposing a resolution of a single platform inconsistency. But nowadays, applications now can be run on mobile phones, tablets, desktop computers and TVs. Even if the applications type can differ from one device to another, we still have a common space of functionalities used. In order to target all of these devices, a typical developer would create an application for each of them, with the proper in-terface and interaction, compile it and release a new version for each device. The problem here is that a lot of work and multiple skills from development to design are needed. When the person porting an application to another device is different, it becomes sometimes difficult to convince the main developer to create a new interface. This scenario applies the two levels of separation: Core functionalities including a visualization canvas, and a superposed interface. The core exports the internal functionalities into a software bus, and the interface connects to that bus, loads a selected interface and a "functionalities matching process" depending on the device. This concept is represented by Figure 4. The interfaces are created by main platform developers and the intellection will move from application level to platform level. The amount of work needed to adapt the application to a new device or modality is reduced to the creation of the interface and the matching. The core application role will be to show a canvas, and to export its internal methods into the bus. Here in addition to the proposed inconsistency resolution for single and multiple platform, we have factorized the application development into core functionalities which accelerate the development, and factorized also the interaction design which will be made by the designer for all the platforms. The link between the two layers is a component that matches the interaction to the functionality. Thinking about the platform and not the application itself, can push the thoughts into the solution of showing the canvas of the same application through many connected devices and being able to modify elements at the same time using the computer, the tablet and the phone, do part of the work on a device and finish it using another one. Events will be handled in each device and transformed into DBus method calls.

Figure 4: Concept of multi-device application development where the application will provide only a drawing canvas and export its functions through the bus

Applications Composer

In a platform where many applications get their internal methods exported and handled with the same way of thinking, we need a tool that is able to connect to any internal method of a chosen target application. Then run more complex tasks than what is provided by a single application. This tool capable for example to open a file inside an application as the "open file" is an exported method, apply operations on it and save it in a external file. Then, after completing with the first application, open these in a new one and so on. This tool will make GUI application as powerful as UNIX command line tools with a lot more possibilities. Since it looks like Apple Quartz Composer, but using applications as building blocks, let's call it "Applications Composer". This concept enables applications scripting, and simplifies complex tasks for the user. It reduces the meaning of having many alternative tools to do the same task inside a platform. If we have many drawing applications that do almost the same thing, the composer interface eclipses these applications the way of independent units they used to be. A simple user who wants to accomplish a task will load a script, provide the input files and get the output, with no need to look at how this is done in details and what applications will be used in the chain. Some developers can even develop small applications with no interface and no significance when used alone, but that are here to fill the gap when used inside the composer. We are speaking about interaction with application using tools, without being limited to a specific interface this is a way to rethink the interaction in a platform as multi-device and multi-application, but single interaction design [START_REF] Beaudouin-Lafon | Designing interaction, not interfaces[END_REF].

Interactive Documentation

The current way to create a documentation for a GUI application is either to write textual tutorials accompanied with pictures of the buttons where to click, screen-shots of the application windows, or to record a video of the author using the application directly. In both ways, the learning user should switch between the textual or video tutorial and the real application many times and to follow step by step what is shown. The switching is intensive and the user can easily lose focus and get lost as described by Laput et al. [START_REF] Laput | Tutorial-based interfaces for cloud-enabled applications[END_REF] Using the core model of a software bus, documentation can be built independently of the type of the current interface visible to the user, but on the core functions of the application instead. We have newer way to create documentation with DBus. For example, we can invoke an action, and we can also detect when a user does a specific step in a tutorial using signals. These can be used to show a part of the tutorial and go to the next step only when the user has done the previous required work. Using transparent windows, the user will no more switch between the application he is learning and the tutorial. The latter will be shown on top of the application step at-a-once that can even be written inside the learning document for a drawing application. Using this scenario, we have removed the switch between an application and its tutorial. The old forms of documentation can still be generated using a screen-shot taking or video recording script and will take into account the current interface according to the platform.

CONCLUSION AND LIMITS

In this paper we have presented many scenarios showing how the export of an application's internal methods can be beneficial for new platform design possibilities. Using the same concept we have also proposed solutions for problems like inconsistency in the interface and interactions of a platform. It also addresses the reduction of development time, multi-device deployment, unification of the documentation system. A side effect of our approach is the reducibility of creative creation GUI applications into their bare canvas. We have explained how this brings better interactions with computers for the developer who will write less code, as well as for the user who will get his task accomplished by writing small scripts. Developers do not want their tools eclipsed and hidden below a platform made, application composer. This also leads to the use of their applications in new, unintended way, which needs some standardization efforts like the MPRIS for video players.

Figure 1 :

 1 Figure 1: Connecting hand palm angle rotation events to control the movement of boxes inside inkscape, no modification to the target application code is needed

Figure 2 :

 2 Figure 2: Implementation of an interactive geometric shapes drawing. The user can select a value and visualize the change instantly on Inkscape while moving the slider.

Figure 3 :

 3 Figure 3: Implementation of a "magic lens" example. The completely separated application has a semitransparent window and can modify the elements color in Inkscape


Alaric Desmarchelier

Matthieu Raynal

Patrick Brocorens

Nicolas Vanthuyne

Laurent Bouteiller

Revisiting the assembly of amino ester-based benzene-1,3,5tricarboxamides: chiral rods in solution

Some benzene-1,3,5-tricarboxamide (BTA) monomers derived from (L) α-amino esters self-assemble into long rods at millimolar concentrations, and display a strong chiral amplification effect. These rods are in competition with dimeric species.

Synthetic helical macromolecules with a tunable chirality and rigidity in solution 1 have found applications as switchable chiral liquid crystalline materials 2 and asymmetric catalysts. 3 In this context, helical supramolecular polymers are particularly interesting, because the reversible nature of their backbone imparts an easy access to copolymers and to chirality amplification studies, as well as an improved stimuliresponsiveness. 4 Chiral supramolecular helices formed by the self-assembly of benzene-1,3,5-tricarboxamide (BTA) monomers constitute a platform of choice for that objective. 4d The self-assembly behaviour of BTAs bearing alkyl amide functions (alkyl BTAs) in alkanes is well understood: threefold hydrogen bonds between the amide functions and an aromatic interaction between the central rings of adjacent BTA monomers are the driving forces for the formation of long stacks (Chart 1, right). Moreover, the position of the stereogenic centre along the alkyl group with respect to the amide function has been shown to control the handedness of the helix 5 and mixtures of alkyl BTAs show strong "majority rules" and "sergeants-and-soldiers" effects. 6 Such a chiral amplification phenomenon expressed at the molecular level has been exploited for controlling racemization/deracemization processes 7 and for designing asymmetric catalysts. 8 Building BTA molecules from α-amino esters (ester BTAs) is a quite simple and potentially powerful strategy that can be used to incorporate a wide range of chiral pendants at the α-position of the amide functions. 9 BTAs derived from (L)-valine methyl ester, 9c (L)-methionine methyl ester, 9k and (L)-glutamic acid dimethyl ester 9a indeed self-assemble into chiral helical stacks in their crystalline states, similarly to alkyl BTAs. In contrast, little is known about the association behaviour of ester BTAs in solution, and the only two studies available hint at a poor selfassociation. van Esch et al. found that BTA derived from αamino octyl esters are poor gelators of organic solvents and attributed this effect to the steric bulkiness of the amino ester side-chain (Phe and Leu) and to interference of the ester moiety itself (Gly). 9e Meijer et al. showed that changing one alkyl chain of trioctyl BTA by one ester chain (amide function derived from (L)-phenylalanine octyl ester) prevents the cooperative formation of long stacks in methylcyclohexane. 9g They also studied the association behaviour of a BTA bearing three amide functions derived from (L)-phenylalanine octyl ester (closely related to BTA Phe, vide infra). No cooperative aggregation process was detected at the concentrations investigated (5-50 µM) and only "ill-defined aggregates" were formed. These disappointing results could suggest that ester BTAs are not suitable building blocks to prepare long chiral rods. In fact, we now report that long chiral rods can indeed be obtained by self-assembly of ester BTAs in solution by an appropriate choice of amino ester and concentration, and that these ester BTAs can efficiently impose their helical bias to rods of achiral BTAs. BTAs derived from (L)-methionine, (L)-norleucine and (L)-phenylalanine dodecyl ester (BTA Met, BTA Nle and BTA Phe, respectively, Chart 1) have been prepared in their pure form (ee>99%). † The self-assembly behaviour of these ester BTAs are compared with that of a trialkyl BTA, BTA C8*, known to form long chiral rods in bulk and in solution. 5 A first hint for the different self-assembly behaviour in solution of these ester BTAs was obtained by comparing their viscosity in cyclohexane. At 0.4 wt% (~ 4 mM) BTA Met and BTA Phe have relative viscosities of 7.3 and 1.4, respectively while solutions of BTA Nle are not viscous (Fig. S1). These differences in relative viscosity reveal the formation of large supramolecular objects for BTA Met and BTA Phe in cyclohexane. This observation was corroborated by small-angle neutron scattering (SANS) analyses in deuterated cyclohexane at 1 wt% (ca. 10mM) (Fig. S2). At 23°C, the scattering profiles of BTA Met and BTA Phe are characteristic of long fibrillar scatterers. The q -1 dependence observed at low angles is representative of rigid cylindrical objects that are longer than 200 Å. Fitting of the data using the form factor for rigid rods with a circular cross section 10 gave cross-section radii of 16.0 and 16.5 Å for BTA Met and BTA Phe, respectively. These values are close to that calculated for a monomer in a fully extended conformation (19.5 Å) and are thus consistent with a monomolecular cross-section of the objects. In sharp contrast, the scattering curve of BTA Nle exhibits no q -1 dependence. For that system, the scattering intensity, which is proportional to the mass of the object, is low. The data can be fitted using the form factor for a sphere 11 yielding a radius of 13.5 Å and a mass of 2000 g.mol -1 . These values suggest that BTA Nle exists as a dimeric species (M spherical object /M monomer = 1.9) in cyclohexane at 1 wt%. The stability of the rigid objects formed by BTA Met and BTA Phe was probed by heating to 70°C. For BTA Met, the scattering profile indicates that long cylindrical objects are still present but in a lower amount than at 23°C (Fig. S2). For BTA Phe, the scattering curve at 70°C is similar to that obtained for BTA Nle at 23°C, suggesting a transition from long objects to dimeric species. High-sensitivity differential scanning calorimetry (DSC) is well adapted to characterize such a transition. 12 DSC analyses (Fig. S3) of 1 mM cyclohexane solutions show relatively sharp endothermal peaks with maxima at T* = 37°C and T* = 29°C for BTA Met and BTA Phe, respectively. These features are consistent with the dissociation of the long objects upon increasing the temperature, as observed in the SANS analyses. Moreover, the stability of the assemblies to dilution was probed by isothermal titration calorimetry (ITC). The dilution of a 5 mM BTA solution into pure cyclohexane first yields a large endothermal signal characteristic for the dissociation of hydrogen-bonded assemblies (Fig. S4). As concentration increases in the cell, a sharp decrease of the heat evolved indicates that the assemblies become stable. Therefore, the concentration below which the rods disassemble (c*) is 0.28 mM and 0.44 mM for BTA Met and BTA Phe, respectively (Fig. S4). † † The sharpness of the heat decrease (in ITC) and of the endothermal peak (in DSC) are consistent with a cooperative transition between the long assemblies and the dimeric species. 13 In contrast, no significant heat effect has been observed for BTA Nle, in agreement with the absence of rods, and suggesting a very high stability of the dimeric aggregates (Figs. S3 andS4).

In order to gain more information on the local structure of these objects, we performed a series of spectroscopic IR, UV and circular dichroism (CD) measurements. First of all, the structure of the long assemblies formed by BTA Met and BTA Phe in cyclohexane above their c* (and below their T*) was probed. IR analyses confirm the formation of amide-bonded supramolecular polymers as the main species since the frequencies of the amide vibrations are characteristic of fully associated NH and amide CO moieties (Figs. S5 andS6). The UV absorption spectra (Fig. S7) show an absorption band at ~ 195 nm in cyclohexane, which is hypsochromically shifted (Δλ=14 nm) compared to ethanol (in which BTAs are molecularly dissolved). This blue shift is similarly observed for BTA C8* and can be assigned to rod-like Fig. 1 CD spectra of ester BTAs and BTA C8* in cyclohexane. The spectra were recorded at 0.125 mM (dimer, thin lines) and 2.0 mM (stacks, thick lines). The monomers are not CD active (Fig. S8). # At these concentrations BTA Met and BTA Phe predominantly exist as stacks but dimers are also present. † † objects that contain extended π-stacks of excitonically-coupled chromophores. 6a Finally, the shape and intensity of their CD spectra are similar to those of BTA C8* (molar ellipticity Δε ~ 55 L.mol -1 .cm -1 , λ max ~ 225 nm, Fig. 1). All together, these results confirm that BTA Met and BTA Phe do form amide-bonded helical stacks with a preferred handedness in cyclohexane. The positive Cotton effect observed in their CD spectra is indicative of a right-handed helix 14 consistent with the handedness of the helices formed by the BTA derived from (L)-methionine methyl ester in the crystalline state. 9k Interestingly, ester BTAs and BTA C8* exhibit opposite Cotton effects even though they all possess a S-configured centre at the α-position of the amide functions.

In a similar way, the molecular structure of the dimeric species was investigated. IR analyses of BTA Nle (Figs. S5 andS6) clearly demonstrate that the NH protons are bonded to the ester (rather than to the amide) functions in the dimer: i) the NH (3388 cm -1 ) and ester CO (1728 cm -1 ) frequencies are consistent with a NH proton being associated with an ester carbonyl, 15 and ii) amide CO groups are free (frequencies at 1675 cm -1 and 1530 cm -1 for the amide I and amide II region, respectively). The IR spectrum of BTA Nle does not vary over the range of concentrations (Fig. S9a) and temperatures (Fig. S10) investigated, providing another indication that that BTA does not form stacks. The UV absorption spectra of dimers are quite similar and resemble the spectra of their monomers (Fig. S7), as expected for species lacking extended aromatic interactions. Rather unexpectedly, dimers are strongly CD active (Fig. 1). The shape and intensity of their CD spectra significantly differ from those of the stacks: they exhibit three maxima (λ ‾ =205 nm, λ + =225 nm, λ ‾ =255 nm) and their molar ellipticity is higher (Δε ~ 85 L.mol -1 .cm -1 at 225 nm). We hypothesize that such a strong CD signal originates from a very rigid organization of the chromophores at the proximity of the chiral centres. The dimer is very stable and cannot be totally disrupted even by heating a 0.0125 mM cyclohexane solution to 70°C (Fig. S11)! The dimer can however be disrupted by adding a polar solvent (Fig. S14).

To account for all these data, we propose, on the basis of molecular modelling simulations, $ a molecular arrangement for the dimeric form of the ester BTAs (Fig. 2) in which the six-fold hydrogen bonds between the BTA monomers may explain the high stability of the dimer. The association behaviour of the investigated ester BTAs is summarized in Fig. 2. BTA Met and BTA Phe self-assemble into two competing forms: an ester-bonded dimer and an amidebonded helical polymer, both of which are CD active. BTA Nle only assembles into ester-bonded dimers, in these conditions. Our results explain why previous studies overlooked the formation of rods from ester BTAs: i) the assembly of ester BTAs is strongly dependent on the nature of the amino-ester side-group, and ii) at low concentrations (50 µM), BTA Phe exists as very stable CD-active dimeric species; stacks only form at concentrations ten times higher. 9g Despite their nearly isosteric structures, BTA Met forms helical stacks while BTA Nle does not. This difference points out the importance of weak non-covalent interactions (in addition to the hydrogen bond and aromatic interactions) to stabilize the rod-like architecture. Short-range contacts (e.g. Δε was monitored at ~ 235 nm (Fig. 3

Chart 1

 1 Ester BTAs studied in this work (left), reference alkyl BTA (middle) and structure of the stacks formed by alkyl BTAs in alkanes.

Fig. 2

 2 Fig. 2 Proposed molecular structures for the dimer and the long helical assemblies formed by ester BTAs in cyclohexane.

Fig. 3

 3 Fig. 3 Left: CD spectra of mixtures of BTA Phe:BTA C8. Total concentration = 2.0 mM, cyclohexane, 20 °C. Right: net helicity versus fraction of "sergeant" for mixtures of BTA Met:BTA C8 and BTA Phe:BTA C8. Net helicity = Δε measured/Δε max (Δε was determined at the isodichroic point for BTA Met and BTA Phe, at 2.0 mM (λ = 234 nm and 238 nm, respectively) or at 225 nm for BTA Phe, at 0.01 mM).

  3.5 Å between the sulfur of the methionine ester and an ester carbonyl) are present in the X-ray structure of a BTA derived from (L)-methionine methyl ester, 9k and we hypothesize that such contacts drive the formation of the long stacks over the dimers for BTA Met. Similarly, we propose that π-π interactions between the phenylalanine aromatic rings govern the formation of stacks for BTA Phe. A similar hypothesis was made by van Esch et al. to explain the better gelation of BTA Phe (with octyl instead of dodecyl ester side chains) compared to BTAs derived from glycine and valine. 9e Finally, "sergeants-and-soldiers" experiments were performed by mixing 2.0 mM cyclohexane solutions of the CD-active ester BTAs (BTA Met or BTA Phe) with the CD-silent alkyl BTA C8. CD spectra were recorded for different fractions (χ) of ester BTAs (Fig. 3 left for BTA Phe and Fig. S12 for BTA Met) and This journal is © The Royal Society of Chemistry [year]

  right). A very steep increase in the magnitude of the CD effect was observed upon addition of only 1 mol% of ester BTA. Both BTA Met and BTA Phe are thus able to induce a preferential helicity in aggregates mainly consisting of BTA C8, showing that the chirality present in ester BTAs can be efficiently transferred. This result is remarkable because, as previously reported, 9g and as shown on Figs.3 and S13, no amplification occurs at lower concentrations(10 µM). The formation of ester BTA : BTA C8 helical copolymers is evidenced by the presence of two regimes: i) the shape of the CD spectra at low χ values is similar to that of BTA C8* (with a maximum at ~ 220 nm and a strong shoulder at ~ 240 nm, regime I) indicating the incorporation of ester BTA within stacks of BTA C8, ii) at high χ values the CD spectra have the same shape as those displayed by pure stacks of ester BTAs (regime II). Interestingly, the handedness of the ester BTA : BTA C8 co-polymers is imposed by the ester BTA, even for very low proportions (χ = 0.01).In conclusion, ester BTAs are very accessible building blocks that can self-assemble into long rods or simple dimers at mM concentrations. The chosen amino acid residue introduced in ester BTAs not only dictates whether long rods or dimers are formed, but it also allows strong chirality amplification effects. Support from the French Agence Nationale de la Recherche is acknowledged (project ANR-13-BS07-0021 SupraCatal). We thank François Boué (LLB, Saclay) for assistance with SANS experiments. Aix Marseille Université, CNRS, iSm2, UMR 7313, 13397 Marseille cedex 20, France † Electronic Supplementary Information (ESI) available: general procedures, synthesis and characterization of ester BTAs and Figs. S1 to S14. See DOI: 10.1039/b000000x/ † † Despite the cooperative transition observed between dimers stacks, dimers are still present at mM concentrations in cyclohexane. 10 mM cyclohexane solutions of BTA Met and BTA Phe contain 5% and 7% of dimers, respectively, while 2 mM solutions contain 22% and 28% of dimers, respectively (see Figs. S5, S9 and S10). $ The relative stability of different hydrogen bond patterns in the dimer has been evaluated by molecular dynamics simulations using the Dreiding force field in the Materials Studio modelling package.

	Notes and references

a Sorbonne Université, UPMC Univ Paris 06, UMR 8232, IPCM, Chimie des Polymères, F-75005 Paris, France. laurent.bouteiller@upmc.fr b CNRS, UMR 8232, IPCM, Chimie des Polymères, F-75005 Paris, France c Service de Chimie des Matériaux Nouveaux, Université de Mons/Materia Nova, Place du Parc, 20, B-7000 Mons, Belgium d