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Biomedical subjects

Michel Vaultier

Publications and source records attributed to Michel Vaultier.

16 recordsLinked to original sources
PubMed2006

Chemoenzymatic dynamic kinetic resolution of rac-1-phenylethanol in ionic liquids and ionic liquids/supercritical carbon dioxide systems.

Continuous dynamic kinetic resolution processes in different ionic liquid/supercritical carbon dioxide biphasic systems were carried out by simultaneously using both immobilized Candida antarctica lipase B (Novozym 435) and silica modified with benzenosulfonic acid (SCX) catalysts at 40 degrees C and 10 MPa. SCX was seen to act as an efficient heterogeneous chemical catalyst for the racemization of (S)-1-phenylethanol in different ionic liquid media ([emim][NTf(2)], [btma][NTf(2)] and [bmim][PF(6)]). Coating both chemical and enzymatic catalysts with ILs greatly improved the efficiency of the process, providing a good yield (76%) of (R)-1-phenylethyl propionate product with excellent enantioselectivity (ee = 91-98%) in continuous operation.

Benzyl Alcohols↗
PubMed2006

Ionic liquid droplet as e-microreactor.

A powerful approach combining a droplet-based, open digital microfluidic lab-on-a-chip using task-specific ionic liquids as soluble supports to perform solution-phase synthesis is reported as a new tool for chemical applications. The negligible volatility of ionic liquids enables their use as stable droplet reactors on a chip surface under air. The concept was validated with different ionic liquids and with a multicomponent reaction. Indeed, we showed that different ionic liquids can be moved by electrowetting on dielectric (EWOD), and their displacement was compared with aqueous solutions. Furthermore, we showed that mixing ionic liquids droplets, each containing a different reagent, in "open" systems is an efficient way of carrying supported organic synthesis. This was applied to Grieco's tetrahydroquinolines synthesis with different reagents. Analysis of the final product was performed off-line and on-line, and the results were compared with those obtained in a conventional reaction flask. This technology opens the way to easy synthesis of minute amounts of compounds ad libitum without the use of complex, expensive, and bulky robots and allows complete automation of the process for embedded chemistry in a portable device. It offers several advantages, including simplicity of use, flexibility, and scalability, and appears to be complementary to conventional microfluidic lab-on-a-chip devices usually based on continuous-flow in microchannels.

Ions↗
PubMed2005

Antioxidative properties of natural polyamines and dimethylsilane analogues.

Structural analogues of natural polyamines, which contain a -Si(CH3)2 group in the central carbon chain, have previously been found to be cytotoxic to various tumor cell lines in vitro and to inhibit tumor cell growth in experimentally grafted animals. In the present study, the antioxidative properties of dimethylsilane polyamine analogues were analyzed in comparison with the natural polyamines. Reactivities of these various polyamines against superoxide anions (generated from the hypoxanthine/xanthine oxidase reaction) and peroxyl radicals (produced from the thermal decomposition of water-soluble 2,2'-azo-bis-[2-amidinopropane] hydrochloride) were investigated. The dimethysilane analogues, and more particularly the hexamine derivative, exhibited the highest scavenging efficiency towards these two reactive oxygen species (ROS). Furthermore, analysis of their ability to prevent hydroxyl radical formation and to trap this ROS showed that the efficiency of the hexamine as a metal chelator and hydroxyl radical scavenger is similar to that of spermine. The higher antioxidant efficiency of the dimethylsilane polyamine analogues with respect to spermidine, together with their ability to displace this polyamine, essential for the promotion of cell growth, from its cellular anionic binding sites that are particularly prone to oxidation, could be biologically relevant and contribute to their in vivo cytotoxic effect and anti-tumor activity. Further experiments will be necessary to demonstrate clearly the relationship between their antioxidant properties and their antiproliferative effects.

Antioxidants↗
PubMed2004

Fluorescence and CD spectroscopic analysis of the alpha-chymotrypsin stabilization by the ionic liquid, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide.

The stability of alpha-chymotrypsin in the ionic liquid, 1-ethyl-3-methyl-imidizolium bis[(trifluoromethyl)sulfonyl]amide ([emim][NTf2]), was studied at 30 and 50 degrees C and compared with the stability in other liquid media, such as water, 3 M sorbitol, and 1-propanol. The kinetic analysis of the enzyme stability pointed to the clear denaturative effect of 1-propanol, while both 3M sorbitol and [emim][NTf2] displayed a strong stabilizing power. For the first time, it is shown that enzyme stabilization by ionic liquids seems to be related to the associated structural changes of the protein that can be observed by differential scanning calorimetry (DSC) and fluorescence and circular dichroism (CD). The [emim][NTf2] enhanced both the melting temperature and heat capacity of the enzyme compared to the other media assayed. The fluorescence spectra clearly showed the ability of [emim][NTf2] to compact the native structural conformation of alpha-chymotrypsin, preventing the usual thermal unfolding which occurs in other media. Changes in the secondary structure of this beta/beta protein, as quantified by the CD spectra, pointed to the great enhancement (up 40% with respect to that in water) of beta-strands in the presence of the ionic liquid, which reflects its stabilization power.

Chymotrypsin↗
PubMed2004

Superoxide-stable ionic liquids: new and efficient media for electrosynthesis of functional siloxanes.

The electrogeneration of diorganylsilanones from difunctional precursors Y(CH(2))(3)(Me)SiX(2) and Ph(2)SiX(2)(Y = NH(2), CF(3), CN; X = Cl, OEt, OMe), performed in the presence of hexamethyldisiloxane or hexamethylcyclotrisiloxane (D(3)) in the ionic liquids [C(5)H(5)NC(8)F(18)].NTf(2), [C(5)H(5)NC(18)H(38)].NTf(2) and Me(3)BuN.NTf(2), which reveal high solubility of oxygen and are inert toward superoxide anion, allows functionalized siloxanes to be produced selectively in good isolated yields.

Journal Article↗
PubMed2004

Kinetic resolution of rac-2-pentanol catalyzed by Candida antarctica lipase B in the ionic liquid, 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide.

The ionic liquid, l-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide ([Bmim] [NTf2]), was used as a reaction medium for the kinetic resolution of rac-2-pentanol catalyzed by free Candida antarctica lipase B, using vinyl propionate at 2% (v/v) water content. The synthetic activity of lipase in [Bmim] [NTf2] was up 2.5-times greater than in hexane, and showed high enantioselectivity (ee > 99.99%). The optimal temperature and pH were 60 degrees C and 7, respectively. A decrease in water activity (aw) produced a decay in synthetic activity, and an exponential increase in selectivity.

Biotechnology↗
PubMed2003

Improved transparency--nonlinearity trade-off with boroxine-based octupolar molecules.

A series of octupolar molecules derived from the boroxine framework were designed and their optical nonlinearities were investigated by performing harmonic light scattering experiments in solution; the molecules were found to combine excellent transparency in the near UV-visible region (lambdamax < or = 280 nm) and significant first-order hyperpolarisabilities (up to beta(0) = 56 x 10(-30) esu).

Journal Article↗
PubMed2003

Activation of bismuth(III) derivatives in ionic liquids: novel and recyclable catalytic systems for Friedel-Crafts acylation of aromatic compounds.

The activity of four bismuth(III) derivatives when employed as Friedel-Crafts catalysts for the acylation of aromatics was found to increase dramatically when dissolved in ionic liquids. Solutions of bismuth oxide or triflate in [emim][NTf(2)] and [bmim][NTf(2)] are the most efficient catalytic systems, with catalyst loading as low as 1% leading to clean, high-yielding acylation of a variety of benzene derivatives. These improved Friedel-Crafts catalytic systems can also be efficiently recycled as opposed to traditional systems. [reaction: see text]

Journal Article↗
PubMed2003

Evidence for the intermediacy of arylbenzylnitrenium ions in the thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile.

In contrast to the diaryl, dialkyl, alkylaryl, and parent series, nothing is known about the generation and chemical behavior of arylbenzylnitrenium ions. Herein, we report that these species can be generated by a process involving an unprecedented thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile. The products from these reactions are dramatically dependent upon the nature of the nitrone. Most of the observed chemistry originates from the singlet state.

Journal Article↗
PubMed2003

Interaction of natural polyamines and dimethylsilyl analogues with a phospholipid monolayer: a study by Brewster angle microscopy and PM-IRRAS.

This work presents an analysis of the physicochemical interactions of natural and dimethylsilyl polyamines with an anionic deuterated phospholipid monolayer, d(62)DPPG (dipalmitoyl phosphatidyl glycerol), at the air-water interface. It was motivated by previous studies, which suggested an antitumour strategy based on the accumulation of derivatives such as bis(7-amino-4-azaheptyl) dimethylsilyl (azhepSi), in order to diminish the concentration of natural polyamines (spermine and putrescine) whose metabolism is strongly activated in tumour cells. Our results, obtained by the surface-pressure technique, Brewster angle microscopy (BAM) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), support the idea of an interaction between the polar head groups of d(62)DPPG and amino groups followed by an adsorption of polyamines up to the carbonyl group. Moreover, an insertion of the dimethylsilyl group up to the alkyl chains occurs with azhepSi, in agreement with the observation that the cohesion of the alkyl chain is lower in this case, as compared with the effect of natural polyamines.

Adsorption↗
PubMedDate not supplied

Understanding structure-stability relationships of Candida antartica lipase B in ionic liquids.

Two different water-immiscible ionic liquids (ILs), 1-ethyl-3-methylimidizolium bis(trifluoromethylsulfonyl)imide and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, were used for butyl butyrate synthesis from vinyl butyrate catalyzed by Candida antarctica lipase B (CALB) at 2% (v/v) water content and 50 degrees C. Both the synthetic activity and stability of the enzyme in these ILs were enhanced as compared to those in hexane. Circular dichroism and intrinsic fluorescence spectroscopic techniques have been used over a period of 4 days to determine structural changes in the enzyme associated with differences in its stability for each assayed medium. CALB showed a loss in residual activity higher than 75% after 4 days of incubation in both water and hexane media at 50 degrees C, being related to great changes in both alpha-helix and beta-strand secondary structures. The stabilization of CALB, which was observed in the two ILs studied, was associated with both the maintenance of the 50% of initial alpha-helix content and the enhancement of beta-strands. Furthermore, intrinsic fluorescence studies clearly showed how a classical enzyme unfolding was occurring with time in both water and hexane media. However, the structural changes associated with the incubation of the enzyme in both ILs might be attributed to a compact and active enzyme conformation, resulting in an enhancement of the stability in these nonaqueous environments.

Amino Acid Sequence↗
PubMedDate not supplied

Lipase catalysis in ionic liquids and supercritical carbon dioxide at 150 degrees C.

Free and immobilized Candida antarctica lipase B dispersed in ionic liquids (1-ethyl-3-methylimidazolium bistriflimide and 1-buthyl-3-methylimidazolium bistriflimide) were used as catalyst for the continuous kinetic resolution of rac-1-phenylethanol in supercritical carbon dioxide at 120 and 150 degrees C and 10 MPa. Excellent activity, stability and enantioselectivity levels were recorded in continuous operation.

Bioreactors↗
PubMedDate not supplied

Criteria to design green enzymatic processes in ionic liquid/supercritical carbon dioxide systems.

Five different ionic liquids (ILs) based on quaternary ammonium cations, with functional side chains ((3-hydroxypropyl)-trimethyl-, (3-cyanopropyl)-trimethyl-, butyl-trimethyl-, (5-cyanopentyl)-trimethyl- and hexyl-trimethyl-) associated with the same anion (bis(trifluoromethane)sulfonyl amide)), were synthesized, and their suitability for Candida antarctica lipase B (CALB)-catalyzed ester synthesis in IL/supercritical carbon dioxide (scCO(2)) biphasic systems was assayed. Catalytic efficiency of the system has been analyzed as a function of both enzyme properties and mass-transfer phenomena criteria. First, the suitability of these ILs as enzymic reaction media was tested for the kinetic resolution of rac-phenylethanol. All ILs were found to be suitable media for enzyme catalysis, the best catalytic parameter (5.3 U/mg specific activity, 94.9% selectivity) being obtained for the (5-cyanopentyl)-trimethylammonium. Second, enzyme stability in all of the ILs was studied at 50 degrees C over a period of 50 days, and data were analyzed by a two-step kinetic deactivation model. All of the ILs were shown to act as stabilizing agents with respect to hexane, producing an increase in the free energy of deactivation (to 25 kJ/mol protein) and an improvement in the half-life time of the enzyme (2000-fold), which agrees with the observed increased hydrophobicity of the cation alkyl side chain (measured by Hansen's solubility parameter, delta). By using two different CALB-IL systems with different hydrophobicity in the cation, continuous processes to synthesize six different short chain alkyl esters (butyl acetate, butyl propionate, butyl butyrate, hexyl propionate, hexyl butyrate, and octyl propionate) in scCO(2) at 10 MPa and 50 degrees C were carried out. Both rate-limiting parameters (synthetic activity and scCO(2)-ILs mass-transfer phenomena) were related with the delta-parameter of the ILs-alkyl chain and reagents.

Carbon Dioxide↗