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Featured researches published by Dominique Cavagnat.


Journal of Physical Chemistry A | 2009

New Interpretation of the CH Stretching Vibrations in Imidazolium-Based Ionic Liquids

Jean-Claude Lassegues; Joseph Grondin; Dominique Cavagnat; Patrik Johansson

In ionic liquids composed of alkyl-substituted imidazolium cations and weakly coordinating anions such as bis(trifluoromethanesulfonyl)imide, (CF(3)SO(2))(2)N(-), the stretching vibrations of the imidazolium CH groups are shown to interact by Fermi resonance with the overtones and the combination of two in-plane ring vibrations. This new assignment, based on isotopic substitutions and anharmonic frequency calculations for gas phase cations, implies that these imidazolium cations do not establish any strong and directional C-H...anion hydrogen bond.


Chemistry: A European Journal | 2009

Enantiopure dendritic polyoxometalates: chirality transfer from dendritic wedges to a POM cluster for asymmetric sulfide oxidation.

Claire Jahier; Martine Cantuel; Nathan D. McClenaghan; Thierry Buffeteau; Dominique Cavagnat; Francine Agbossou; Mauro Carraro; Marcella Bonchio; Sylvain Nlate

The quest for new catalytic and highly enantioselective processes is currently one of the most intensively studied areas in chemical synthesis. In this context, chiral polyoxometalates (POMs) have become a topic of recent interest owing to their potential application in medicine and asymmetric catalysis. Among numerous applications of POMs, catalysis is by far the most studied, owing to the enormous versatility that POMs offer in the clean synthesis of fine chemicals. However, few chiral POM compounds for asymmetric catalysis are known. Of those reported, none are based on dendritic structures, although dendritic counter cations are known to play a critical role in determining the properties of anionic POMs. Two main approaches have been developed for the synthesis of chiral POM-based frameworks. The first involves the use of a chiral species (organic moieties or metal complexes) as a chirality transfer agent. The second strategy is based on spontaneous resolution upon crystallization in the absence of any chiral auxiliary, which yields conglomerates. For example, enantiopure hafnium-substituted POMs, which are obtained by spontaneous resolution upon crystallization in the absence of any chiral source have been reported. Recently, two enantiomerically pure 3D chiral POM-based architectures were developed from achiral moieties without any chiral auxiliaACHTUNGTRENNUNGry.[6b–c] However, despite their potential applications in catalysis and separation, enantiopure POM frameworks are still under represented. The search for suitable enantiomerically pure POM-based hybrid materials remains a challenging issue in synthetic chemistry and materials science. To date, chiral dendritic POM systems, as well as the study of chiroptical activity of enantiopure POM-based frameworks in asymmetric catalysis have, to the best of our knowledge, never been reported. Herein, we report the synthesis and characterization of four enantiopure polyoxometalate-cored dendrimers, which contain n-propyl [(R)-(+)-6 and (S)-( )-6] and epoxy [(R)(+)-7 and (S)-( )-7] groups, based on electrostatic interactions between enantiopure dendritic quaternary ammonium ions and an achiral trianionic POM. To the best of our knowledge, these compounds represent the first examples of optically active dendritic POM systems. Importantly, the POM cluster displays chiroptical effects, indicating chirality transfer from the enantiopure dendritic ammonium ions. The optical and chiroptical properties of the n-propyl-terminated POM-cored dendrimers (R)-(+)-6 and (S)-( )-6 have been demonstrated in solution by UV/Vis spectroscopy, circular dichroism (CD) and vibrational circular dichroism (VCD) spectroscopy, as well as fluorimetry. In addition, the use of 6 as a catalyst in the asymmetric oxidation of thioanisole with aqueous H2O2 provides the corresponding optically active sulfoxide with up to 14% enantiomeric excess (ee) as a result of a chirality transfer process from the dendritic wedge to the catalytically active POM unit. Despite the modest enantioselectivity, this proof-of-principle catalytic experiment demonstrates and confirms the transfer of chiroptical properties from organic moieties to a catalytically active POM unit. Interestingly, the catalyst was recovered and reused in three successive cycles without discernable [a] C. Jahier, Dr. M. Cantuel, Dr. N. D. McClenaghan, Dr. T. Buffeteau, Dr. D. Cavagnat, Dr. S. Nlate ISM, UMR CNRS No. 5255, Universit Bordeaux I 351 Cours de la Lib ration, 33405 Talence Cedex (France) Fax: (+33)5-4000-6994 E-mail : [email protected] [b] Dr. F. Agbossou UCCS UMR CNRS N8 8181, Universit de Lille 59652 Villeneuve d’Asq Cedex (France) [c] Dr. M. Carraro, Prof. M. Bonchio Department of Chemical Sciences and ITM-CNR University of Padova, Via Marzolo, 1 35131 Padova (Italy) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200901512.


Journal of Organic Chemistry | 2011

Enantioselective Complexation of Chiral Propylene Oxide by an Enantiopure Water-Soluble Cryptophane

Aude Bouchet; Thierry Brotin; Hans Ågren; Dominique Cavagnat; Thierry Buffeteau

ECD and NMR experiments show that the complexation of propylene oxide (PrO) within the cavity of an enantiopure water-soluble cryptophane 1 in NaOH solution is enantioselective and that the (R)-PrO@PP-1 diastereomer is more stable than the (S)-PrO@PP-1 diastereomer with a free energy difference of 1.7 kJ/mol. This result has been confirmed by molecular dynamics (MD) and ab initio calculations. The enantioselectivity is preserved in LiOH and KOH solutions even though the binding constants decrease, whereas PrO is not complexed in CsOH solution.


Chirality | 2008

C3-symmetrical self-assembled structures investigated by vibrational circular dichroism.

Maarten M. J. Smulders; Thierry Buffeteau; Dominique Cavagnat; Martin Wolffs; Albertus P. H. J. Schenning; E. W. Meijer

We demonstrate by using vibrational circular dichroism (VCD) spectroscopy that it is possible to investigate the chirality of a supramolecular polymeric system in relatively dilute solutions. Chiral C(3)-symmetrical discotic molecules, based on a trialkylbenzene-1,3,5-carboxamide, form supramolecular columnar stacks with a right-handed helical structure in solution due to intermolecular hydrogen bonds. The handedness of the supramolecular chirality is determined using electronic spectroscopy measurements. Under dilute conditions (at 10(-3) M concentrations), it was also possible to probe the hydrogen bonding moieties with IR and VCD spectroscopy on these self-assembled structures. In combination with density functional theory (DFT) calculations, we could verify the preference for a right-handed chirality in the helical stacks and the nonplanar orientation of the carbonyl groups present in the molecule. This chiral arrangement is in agreement with the structure determined for a related benzene-1,3,5-tricarboxamide by X-ray diffraction. Chirality, 2008. (c) 2008 Wiley-Liss, Inc.


Journal of Organic Chemistry | 2011

Conformational Effects Induced by Guest Encapsulation in an Enantiopure Water-Soluble Cryptophane

Aude Bouchet; Thierry Brotin; Hans Ågren; Dominique Cavagnat; Thierry Buffeteau

A new water-soluble cryptophane 1 derivative (penta-hydroxyl cryptophane-A) has been synthesized from cryptophanol-A and the chiroptical properties of its two enantiomers MM-1 and PP-1 have been studied by polarimetry, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD). Cryptophane 1 shows specific circular dichroism responses upon complexation that depend on the size of the guest and on the nature of the counterion (Li(+), Na(+), K(+), Cs(+)) present in the solution. In LiOH and NaOH solutions, chiroptical changes induced by the encapsulation of guests and by the presence of cations in the vicinity of hosts can be interpreted from molecular dynamics (MD) and ab initio calculations by subtle conformational changes of the bridges. In KOH solution, the exchange dynamics is dependent on the size of the guest molecules, whereas in CsOH solution no encapsulation effect is observed whatever the size of the guest molecule. This last behavior comes from the fact that host 1 exhibits a very high affinity for cesium cations.


Chemistry: A European Journal | 2010

Induced Chiroptical Changes of a Water‐Soluble Cryptophane by Encapsulation of Guest Molecules and Counterion Effects

Aude Bouchet; Thierry Brotin; Dominique Cavagnat; Thierry Buffeteau

We report the synthesis of the water-soluble cryptophanol derivative 1 and the study of the chiroptical properties of its two enantiomers (>99 % ee) by polarimetry, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD). We show that cryptophanol 1 exhibits unusual chiroptical properties in water under basic conditions (pH>12). For instance, the shapes of the ECD and VCD spectra of 1 in water were strongly dependent on the nature of the alkali metal ions (Li(+), Na(+), K(+), Cs(+)) surrounding the cryptophane and whether or not a guest molecule is present inside the cavity of the host. To the best of our knowledge, this is the first example in which the nature of these counterions governs the chiroptical properties of a host molecule. Moreover, specific ECD spectra were obtained depending on the size of the guest molecules. This makes 1 a good sensor for small neutral molecules in aqueous solvent. Finally, VCD experiments associated with DFT calculations show that the chiroptical changes can be directly correlated to the presence of charges close to the aromatic rings and with a conformational change of the alkyl chains upon encapsulation.


Chirality | 2009

Molecular and supramolecular chirality in gemini-tartrate amphiphiles studied by electronic and vibrational circular dichroisms†

Aurélie Brizard; Damien Berthier; Carole Aimé; Thierry Buffeteau; Dominique Cavagnat; Laurent Ducasse; Ivan Huc; Reiko Oda

This contribution presents an application of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) to study the molecular and supramolecular chirality in assemblies of gemini-tartrate amphiphiles. Nonchiral dicationic n-2-n amphiphiles (n = 14-20) can self-organize into right- or left-handed structures upon interacting with chiral tartrate counterions. Micellar solutions can also be obtained for shorter alkyl chains (n = 12). First, the conformation of tartrate counterions has been investigated in various environments (micellar solutions and chiral ribbons). ECD and VCD spectra recorded in micellar solutions are independent from the solvent and from the nature of the cations (sodium, cetyl-trimethylammonium, or dimeric surfactant 12-2-12) used and are representative of the anticonformation of the tartrate dianions. On the other hand, drastic changes in the ECD and VCD spectra have been observed in multilayered chiral assemblies of 16-2-16 tartrate. These strong spectral modifications are associated with the chiral arrangement of the tartrate molecules at the surface of the bilayers. Moreover, chirality transfer from counterions to achiral amphiphiles has been clearly evidenced by VCD since circular dichroism has been observed on vibrations related to alkyl chains and gemini headgroups. Finally, ECD and VCD experiments were performed varying the enantiomeric excess of the tartrate. The ECD and VCD intensities do not vary linearly with the enantiomeric excess of the anion and different behaviors have been observed from the two spectroscopic methods: ECD intensities are correlated to the pitch of the ribbons, whereas the VCD intensities are correlated to the dimension of the chiral ribbons.


Journal of Physical Chemistry A | 2008

Conformational Changes in Cryptophane Having C1-Symmetry Studied by Vibrational Circular Dichroism

Thierry Brotin; Dominique Cavagnat; Thierry Buffeteau

Vibrational circular dichroism (VCD) measurements and density functional theory (DFT) calculations were used to obtain the absolute configuration of a cryptophane molecule having C1-symmetry (labeled cryptophane-H). This molecule exhibits chiroptical properties different from those published for cryptophane-A having D3-symmetry [Brotin et al. J. Am. Chem. Soc. 2006, 128, 5533-5540]. In particular, we have shown that the conformation of the aliphatic linkers is very dependent on the solvent used and its ability to enter (CDCl3 solution) or not (C2D2Cl4 solution) in the cryptophane cavity. Calculations performed at the DFT (B3PW91/6-31G*) level establish, besides the absolute configuration, the preferential anti and gauche conformations of the aliphatic linkers of the chloroform@cryptophane-H complex and the empty cryptophane-H molecule, respectively. Polarimetric measurements performed in several solvents reflect also the change of conformation of the bridges upon guest encapsulation.


Journal of Organic Chemistry | 2012

High Affinity of Water-Soluble Cryptophanes for Cesium Cations

Thierry Brotin; Roland Montserret; Aude Bouchet; Dominique Cavagnat; Thierry Buffeteau

Exceptionally high affinity for cesium cations was achieved in aqueous solution using two enantiopure cryptophanes. Complexation of cesium was evidenced by (133)Cs NMR spectroscopy and by electronic circular dichroism (ECD). Binding constants as high as 6 × 10(9) M(-1) have been measured by isothermal titration calorimetry (ITC). Very strong complexation of rubidium cations (K ~10(6) M(-1)) has also been measured. Chiral hosts allowed the detection of the two cations at low concentrations (μM) using ECD.


Journal of Chemical Physics | 1993

Methyl rotational potentials and transferable pair potentials in toluene

M. Prager; M. Monkenbusch; Richard M. Ibberson; W. I. F. David; Dominique Cavagnat

The crystal structure of α‐phase toluene at 5 K has been refined from high resolution neutron powder diffraction data and the charge distribution in the molecule calculated ab initio. From these data, methyl rotational potentials of the two inequivalent methyl groups have been calculated for various parametrizations of transferable pair potentials and compared with potentials derived from tunneling and librational transitions. The results demonstrate that the inclusion of Coulomb interactions is necessary to reproduce the equilibrium orientations of the methyl groups. However, none of the model pair potentials yield the very strong sixfold contribution of the rotational potential of methyl group 1. The best approximation to the experimentally determined values is obtained with the pair potential parameters of Kitaigorodskii [Acta Crystallogr. 18, 585 (1965)]. However, by the inclusion of existing results on p‐xylene, the average agreement obtained with the parametrization of Claverie [Acta Crystallogr. Pa...

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L. Lespade

University of Bordeaux

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Thierry Brotin

École normale supérieure de Lyon

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Aude Bouchet

Technical University of Berlin

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C. Lapouge

University of Bordeaux

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