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Philippe Lesot - One of the best experts on this subject based on the ideXlab platform.
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Determination of the natural deuterium distribution of fatty acids by application of 2H 2D-NMR in liquid crystals: fundamentals, advances, around and beyond
Liquid Crystals, 2020Co-Authors: Philippe LesotAbstract:Based on pionneering work reported in the 1980’s by Martin and co-workers, experimental investigation of the site-specific, natural (2H/1H) isotope fractionation in bioproducts by natural abundance deuterium 1D-NMR (NAD 1D-NMR) spectroscopy is the method of choice to understand the enzymatic mechanisms leading to their synthesis or transformation, but also to determine their geographical or botanical origins. This approach, known as 2H-SNIF-NMRTM method, is also an effective tool in the fight against the counterfeiting of molecules of economical interests. However, the use of achiral Isotropic solvents has two significant disadvantages that reduce accessible isotopic information: a rate of overlap of signals generally too high for complex analytes and the absence of spectral discrimination of enantiotopic directions in prochiral compounds. Both drawbacks can be overcome by replacing liquid solvents with chiral liquid cristals (CLC). In this review, we overview the theoretical basis and the analytical advantages of anIsotropic NAD (ANAD) 2D-NMR using polypeptide-based, lyotropic CLCs as enantiodiscriminating ordered NMR solvents. We discuss how and why ANAD 2D-NMR can provide a robust alternative to the conventional method of determining isotopic ratios, (2H/1H)i, particularly when applied to long-chain fatty acids or homogeneous triglycerides. Various applicative aspects are presented.
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Analytical contribution of deuterium 2D-NMR in oriented media to H-2/H-1 isotopic characterization: the case of vanillin
Flavour and Fragrance Journal, 2018Co-Authors: Tristan Texier-bonniot, Philippe Berdague, Richard J. Robins, Gerald Remaud, Philippe LesotAbstract:The evaluation of intramolecular H-2 or C-13 isotopic composition of vanillin by liquid-state nuclear magnetic resonance (NMR) is an illustrative example of the analytical challenges associated with molecular authenticity/traceability investigations in food products, and the determination/understanding of metabolic/synthetic pathways. Although isotopic ratio monitoring by C-13 NMR (irm-C-13 NMR) provides a valuable new source of isotopic information, the analysis of position-specific (H-2/H-1) isotopic fractionation of vanillin remains incomplete because of the overlap of two aromatic H-2 resonances, and the impossibility of separating these fortuitous isochronous nuclei by Isotropic NMR. Exploiting the analytical potential of H-2 2D-NMR in media containing polypeptide-based liquid crystals, we show that all aromatic monodeuterated isotopomers can be spectrally discriminated on the basis of H-2 residual quadrupolar couplings, (Q)(H-2), thus enabling the determination of their relative proportions for the first time. After discussing the multiple relevant cofactors leading to the best discrimination and optimization of experimental conditions for reliable quantitative measurements by anIsotropic 2D-NMR, a comparative analysis of six vanillin samples from diverse origins is reported. How the H-2 distribution might relate to the biosynthesis of vanillin is discussed.
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Natural Abundance Deuterium NMR Spectroscopy
2016Co-Authors: Philippe Lesot, Olivier LafonAbstract:Compared to 1H nuclear magnetic resonance (NMR), natural abundance deuterium (NAD) NMR spectroscopy benefits from specific advantages. In particular, NAD NMR spectra provide key information on molecular orientation and dynamics and are not obscured by homonuclear couplings. The use of 2H NMR is often limited by its low gyromagnetic ratio and its low natural isotopic abundance (Vienna standard mean ocean water = 0.0155%). Nevertheless, thanks to the instrumental and methodological developments, NAD NMR is nowadays possible for a large number of samples, including Isotropic liquids, liquid crystals, and solids. We review here the major applications of NAD NMR and notably the isotope fractionation and stereochemical analysis using chiral orienting media.
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(D/H) Isotopic Fractionation by AnIsotropic NAD 2D-NMR Spectroscopy: Exploiting the Analytical Wealth of Oriented Solvents to Investigate Molecules of Interest
2016Co-Authors: Philippe Lesot, Philippe Berdague, Jérémy JacobAbstract:The deuterium/hydrogen (D/H)i ratio measurement by quantitative 2H-{1H} NMR spectroscopy is a method of choice in numerous analytical fields such as the study of biosynthetic pathway or kinetic isotopic effects associated with enzyme-catalyzed reaction, the determination of botanical or geographical origin of biocompounds, and last by not least, the authentication of molecules in the frame of the fight against counterfeigthing [1,2]. As the solvent used in the « SNIF-NMR » protocol is both Isotropic (liquid) and achiral, the efficiency of the current protocol is basically limited for two reasons : i) the small 2H chemical shift dispersion of deuterium nuclei (expressed i Hz); ii) the impossibility of spectrally discriminating enantiotopic sites (methylene prostereogenic sites) in prochiral molecules or enantiomers of chiral molecules, hence precluding the quantification of isotopic fractionation on methylene prostereogenic sites or mirror-image isomers [3]. To overcome these drawbacks, the natural abundance deuterium bidimensional NMR (NAD 2D-NMR) using chiral oriented phases is a powerful way to separate deuterium signals of monodeutero-isotopomers on the basis of the quadrupolar interaction, not longer averaged to zero as in Isotropic NMR. The distribution of quadrupolar doublets on the 2D maps significantly facilitates the analysis of overcrowded NAD 1D-NMR spectra obtained in liquid state, thus providing a real original and robust approach to classical tool [2-5]. To illustrate the analytical potential of the method, various illustrative examples of (pro)chiral molecules of interest are presented. Among them, the case of miliacin of a triterpenic chiral molecular biomarker found in sedimentary archives is examined [6,7]. Among perspectives, this approach has the potential to permit predicting isotopic natural fractionations during pentacyclic triterpene diagenesis. References: [1] G. J. Martin, M.L. Martin, Tet. Lett., 22, 3525, (1981). [2] P. Lesot, Encyclopedia of Magnetic Resonance (eMagRes), 2 (3), 315, (2013). [3] P. Lesot, C. Aroulanda, H. Zimmermann, Z. Luz Chem. Soc. Rev., 44, 230, (2015). [4] P. Lesot, Z. Serhan, I. Billault, Anal. Bioanal. Chem., 399, 1187, (2011). [5] Z. Serhan, I. Billault, A. Borgogno, A. Ferrarini, P. Lesot, Chem. Eur. J., 18, 117, (2012). [6] P. Berdagué, P. Lesot, J. Jacob, V.-J. Terwilliger, C. Le Milbeau, Geochim. Cosmochim. Acta, 173, 337, (2016). [7] http://www.cnrs.fr/inc/communication/direct_labos/lesot2.htm http://www.insu.cnrs.fr/environnement/actualites
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Recent advances in the analysis of the site-specific isotopic fractionation of metabolites such as fatty acids using anIsotropic natural-abundance ^2H NMR spectroscopy: application to conjugated linolenic methyl esters
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Philippe Lesot, Zeinab Serhan, Isabelle BillaultAbstract:The full elucidation of the enzymatic mechanisms leading to polyunsaturated ω-3 to ω-5 fatty acids (PUFAs) occurring in plants or microorganisms by analyzing their site-specific isotopic fractionation profiles is a challenging task. Isotropic SNIF-NMR® method is an historical, powerful tool for the determination of (^2H/^1H) ratios. However, the absence of accessible isotopic data on the enantiotopic hydrogen sites (CH_2 groups) prevents the study of the enzymatic reaction stereoselectivity. Natural-abundance deuterium (NAD) 2D NMR experiment using chiral liquid crystals (CLC) as solvent is a new tool in this field, overcoming this limitation. In this work, we have explored various possibilities for optimizing the enantio-discrimination properties of CLC by changing the nature of the polypeptide and/or increasing the polarity of the organic co-solvents. We report also the first applications of TMU as co-solvent for preparing enantio-discriminating, homogenous polypeptide mesophases. The various experimental NAD NMR results recorded at an optimal sample temperature are discussed and compared in terms of number of discriminated ^2H sites and magnitude of spectral separation for different PUFAs such as the linoleic and linolenic acids. The comparison of all NMR results shows that optimal results are obtained when CLC mixtures made of poly-γ-benzyl- l -glutamate (PBLG) and high polarity co-solvents are used. As new challenging examples of applications, we report the preliminary analytical results obtained from two ω-5 conjugated linolenic acids: the α-eleostearic acid (9 Z , 11 E , 13 E ) and the punicic acid (9 Z , 11 E , 13 Z ). NMR data are discussed in terms of molecular orientational ordering parameters and isotopic distribution. Figure The new challenges of the site-specific isotopic fractionation analysis of fatty acids using the natural-abundance deuterium NMR in polypeptide aligned media
Isabelle Billault - One of the best experts on this subject based on the ideXlab platform.
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Recent advances in the analysis of the site-specific isotopic fractionation of metabolites such as fatty acids using anIsotropic natural-abundance ^2H NMR spectroscopy: application to conjugated linolenic methyl esters
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Philippe Lesot, Zeinab Serhan, Isabelle BillaultAbstract:The full elucidation of the enzymatic mechanisms leading to polyunsaturated ω-3 to ω-5 fatty acids (PUFAs) occurring in plants or microorganisms by analyzing their site-specific isotopic fractionation profiles is a challenging task. Isotropic SNIF-NMR® method is an historical, powerful tool for the determination of (^2H/^1H) ratios. However, the absence of accessible isotopic data on the enantiotopic hydrogen sites (CH_2 groups) prevents the study of the enzymatic reaction stereoselectivity. Natural-abundance deuterium (NAD) 2D NMR experiment using chiral liquid crystals (CLC) as solvent is a new tool in this field, overcoming this limitation. In this work, we have explored various possibilities for optimizing the enantio-discrimination properties of CLC by changing the nature of the polypeptide and/or increasing the polarity of the organic co-solvents. We report also the first applications of TMU as co-solvent for preparing enantio-discriminating, homogenous polypeptide mesophases. The various experimental NAD NMR results recorded at an optimal sample temperature are discussed and compared in terms of number of discriminated ^2H sites and magnitude of spectral separation for different PUFAs such as the linoleic and linolenic acids. The comparison of all NMR results shows that optimal results are obtained when CLC mixtures made of poly-γ-benzyl- l -glutamate (PBLG) and high polarity co-solvents are used. As new challenging examples of applications, we report the preliminary analytical results obtained from two ω-5 conjugated linolenic acids: the α-eleostearic acid (9 Z , 11 E , 13 E ) and the punicic acid (9 Z , 11 E , 13 Z ). NMR data are discussed in terms of molecular orientational ordering parameters and isotopic distribution. Figure The new challenges of the site-specific isotopic fractionation analysis of fatty acids using the natural-abundance deuterium NMR in polypeptide aligned media
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recent advances in the analysis of the site specific isotopic fractionation of metabolites such as fatty acids using anIsotropic natural abundance 2h nmr spectroscopy application to conjugated linolenic methyl esters
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Philippe Lesot, Zeinab Serhan, Isabelle BillaultAbstract:The full elucidation of the enzymatic mechanisms leading to polyunsaturated ω-3 to ω-5 fatty acids (PUFAs) occurring in plants or microorganisms by analyzing their site-specific isotopic fractionation profiles is a challenging task. Isotropic SNIF-NMR® method is an historical, powerful tool for the determination of (2H/1H) ratios. However, the absence of accessible isotopic data on the enantiotopic hydrogen sites (CH2 groups) prevents the study of the enzymatic reaction stereoselectivity. Natural-abundance deuterium (NAD) 2D NMR experiment using chiral liquid crystals (CLC) as solvent is a new tool in this field, overcoming this limitation. In this work, we have explored various possibilities for optimizing the enantio-discrimination properties of CLC by changing the nature of the polypeptide and/or increasing the polarity of the organic co-solvents. We report also the first applications of TMU as co-solvent for preparing enantio-discriminating, homogenous polypeptide mesophases. The various experimental NAD NMR results recorded at an optimal sample temperature are discussed and compared in terms of number of discriminated 2H sites and magnitude of spectral separation for different PUFAs such as the linoleic and linolenic acids. The comparison of all NMR results shows that optimal results are obtained when CLC mixtures made of poly-γ-benzyl-l-glutamate (PBLG) and high polarity co-solvents are used. As new challenging examples of applications, we report the preliminary analytical results obtained from two ω-5 conjugated linolenic acids: the α-eleostearic acid (9Z, 11E, 13E) and the punicic acid (9Z, 11E, 13Z). NMR data are discussed in terms of molecular orientational ordering parameters and isotopic distribution.
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Combined analysis of C-18 unsaturated fatty acids using natural abundance deuterium 2D NMR spectroscopy in chiral oriented solvents
Analytical Chemistry, 2008Co-Authors: Philippe Lesot, Vincent Baillif, Isabelle BillaultAbstract:The quantitative determination of isotopic ((2)H/(1)H)(i) ratios at natural abundance using the SNIF-NMR protocol is a well-known method for understanding the enzymatic biosynthesis of metabolites. However, this approach is not always successful for analyzing large solutes and, specifically, is inadequate for prochiral molecules such as complete essential unsaturated fatty acids. To overcome these analytical limitations, we use the natural abundance deuterium 2D NMR (NAD 2D NMR) spectroscopy on solutes embedded in polypeptide chiral liquid crystals. This approach, recently explored for measuring ((2)H/(1)H)i ratios of small analytes (Lesot, P.; Aroulanda, C.; Billault, I. Anal Chem. 2004, 76, 2827-2835), is a powerful way to separate the (2)H signals of all nonequivalent enantioisotopomers on the basis both of the 2H quadrupolar interactions and of the 2H chemical shift. Two significant advances over our previous work are presented here and allow the complete isotopic analysis of four mono- and polyunsaturated fatty acid methyl esters: methyl oleate (1), methyl linoleate (2), methyl linolenate (3), and methyl vernoleate (4). The first consists of using NMR spectrometers operating at higher magnetic field strength (14. 11) and equipped with a selective cryoprobe optimized for deuterium nuclei. The second is the development of Q-COSY Fz 2D NMR experiments able to produce phased (2)H 2D maps after a double Fourier transformation. This combination of modern hardware and efficient NMR sequences provides a unique tool to analyze the ((2)H/(1)H)(i) ratios of large prochiral molecules (C-18) dissolved in organic solutions of poly(gamma-benzyl-L-glutamate) and requires smaller amounts of solute than previous study on fatty acids. For each compound (1-4), all (2)H quadrupolar doublets visible in the 2D spectra have been assigned on the basis of (2)H chemical shifts, isotopic data obtained from Isotropic quantitative NAD NMR, and by an interspectral comparison of the anIsotropic NAD spectra of four fatty acids. The NMR results are discussed in terms of ((2)H/(1)H)(i) isotopic distribution and molecular orientation in the mesophase. For the first time, we show that the investigation of natural isotopic fractionation of complete fatty acids is possible without the need of chemical modifications, hence providing an alternative method to probe the mechanisms of enzymes implied in the biosynthetic pathway of unsaturated fatty acids.
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Exploring the Analytical Potential of NMR Spectroscopy in Chiral AnIsotropic Media for the Study of the Natural Abundance Deuterium Distribution in Organic Molecules
Analytical Chemistry, 2004Co-Authors: Philippe Lesot, Christie Aroulanda, Isabelle BillaultAbstract:The deuterium/hydrogen (D/H)i ratio measurement by quantitative 2H NMR spectroscopy is a method of choice for the analysis of kinetic isotopic effects associated with enzyme-catalyzed reactions during a biosynthetic pathway. However, the efficiency of the current Isotropic 2H-{1H} NMR can be limited by the rather small chemical shift dispersion of deuterium nuclei. In addition, this method does not allow the enantiotopic deuterons in prochiral molecules to be spectrally discriminated, hence preclud-ing the quantification of isotopic fractionation on methyl-ene prostereogenic sites. In this work, we explore another analytical strategy able to circumvent these disadvantages. This approach is based on the use of natural abundance 2H 2D NMR experiments on solutes embedded in polypep-tidic, chiral liquid crystalline solvent. Thus, we show that NMR in these oriented phases is a powerful way to separate deuterium signals on the basis of the quadru-polar interactions, providing a promising alternative to overcrowded 2H NMR spectra obtained in liquid state. To illustrate our purpose, we have experimentally investigated the case of 1,1′-bis(phenylthio)hexane derived by cleavage from methyl linoleate of safflower. The 2H NMR results in chiral liquid crystals are presented and dis-cussed. We show, for the first time, that (D/H)pro-R and (D/H)pro-S can be measured at the same methylene position of a fatty acid chain.
Prabir K. Mukherjee - One of the best experts on this subject based on the ideXlab platform.
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Dielectric permittivity in the Isotropic phase above the Isotropic to smectic-E transition
Journal of Molecular Liquids, 2014Co-Authors: Prabir K. MukherjeeAbstract:Abstract The Landau theory of phase transition is applied to calculate the temperature dependence of the static dielectric permittivity in the Isotropic phase above the Isotropic to smectic-E transition. A comparison is made with experimental data available in the Isotropic phase above the Isotropic to smectic-E transition. The theory provides a good description of all known features of the static dielectric permittivity in the Isotropic phase above the transition.
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Dielectric permittivity in the Isotropic phase above the Isotropic to smectic-A phase transition
Physics Letters A, 2013Co-Authors: Prabir K. MukherjeeAbstract:Abstract We use a phenomenological model to find theoretically the temperature dependence of the static dielectric permittivity at the Isotropic to smectic-A phase transition. The temperature dependence of the static dielectric permittivity is presented for the Isotropic and smectic-A phases of the transition. Eventually, a comparison is made with experimental data available in the Isotropic phase above the Isotropic to smectic-A phase transition. We finally conclude that the model provides a good description of all known features of the static dielectric permittivity in the Isotropic phase above the phase transition.
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Non-linear dielectric effect in the Isotropic phase above the Isotropic-cholesteric phase transition
2011Co-Authors: Prabir K. Mukherjee, Sumanta Chakraborty, Sylwester J. RzoskaAbstract:Abstract Using the Landau-de Gennes theory, the temperature, pressure and frequency dependence of the non-linear effect in the Isotropic phase above the Isotropic–cholesteric phase transition is calculated. The influence of pressure on the Isotropic–cholesteric phase transition is discussed by varying the coupling between the orientational order parameter and the macroscopic polarization of polar cholesterics. Comparing the results of the calculations with existing data, we finally conclude that the model provides a description of the Isotropic–cholesteric transition that takes all experimentally known features of the unusual negative and positive pretransitional effect in the Isotropic phase of the system into account in a qualitatively correct way.
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Non-linear dielectric effect in the Isotropic phase above the Isotropic–cholesteric phase transition
Chemical Physics, 2011Co-Authors: Prabir K. Mukherjee, Sumanta Chakraborty, Sylwester J. RzoskaAbstract:Using the Landau-de Gennes theory, the temperature, pressure and frequency dependence of the non-linear effect in the Isotropic phase above the Isotropic-cholesteric phase transition is calculated. The influence of pressure on the Isotropic-cholesteric phase transition is discussed by varying the coupling between the orientational order parameter and the macroscopic polarization of polar cholesterics. Comparing the results of the calculations with existing data, we finally conclude that the model provides a description of the Isotropic-cholesteric transition that takes all experimentally known features of the unusual negative and positive pretransitional effect in the Isotropic phase of the system into account in a qualitatively correct way
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landau model of the smectic c Isotropic phase transition
Journal of Chemical Physics, 2002Co-Authors: Prabir K. Mukherjee, Harald Pleiner, Helmut R BrandAbstract:We propose a Landau model to describe the smectic C–Isotropic phase transition. A general Landau theory for the coupled orientational and translational order parameters and including the tilt angle is developed. The conditions for the smectic C–Isotropic phase transition and the stability conditions of the smectic C phase are calculated. On the basis of this model it is argued that the smectic C–Isotropic phase transition is always first order. We present a detailed analysis of the question under which conditions a direct smectic C–Isotropic phase transition prevails in comparison to smectic A–Isotropic and nematic–Isotropic transitions. The theoretical results are found to be in qualitative agreement with all published experimental results.
Graeme M. Day - One of the best experts on this subject based on the ideXlab platform.
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Powder crystallography of pharmaceutical materials by combined crystal structure prediction and solid-state H-1 NMR spectroscopy
Physical Chemistry Chemical Physics, 2013Co-Authors: Maria Baias, M. Widdifield Cory, Jean-nicolas Dumez, Hugh P. G. Thompson, Timothy G. Cooper, Elodie Salager, Sirena Bassil, Robin S. Stein, Anne Lesage, Graeme M. DayAbstract:A protocol for the ab initio crystal structure determination of powdered solids at natural isotopic abundance by combining solid-state NMR spectroscopy, crystal structure prediction, and DFT chemical shift calculations was evaluated to determine the crystal structures of four small drug molecules: cocaine, flutamide, flufenamic acid, and theophylline. For cocaine, flutamide and flufenamic acid, we find that the assigned H-1 Isotropic chemical shifts provide sufficient discrimination to determine the correct structures from a set of predicted structures using the root-mean-square deviation (rmsd) between experimentally determined and calculated chemical shifts. In most cases unassigned shifts could not be used to determine the structures. This method requires no prior knowledge of the crystal structure, and was used to determine the correct crystal structure to within an atomic rmsd of less than 0.12 angstrom with respect to the known reference structure. For theophylline, the NMR spectra are too simple to allow for unambiguous structure selection
Kumbakonam R. Rajagopal - One of the best experts on this subject based on the ideXlab platform.
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Wave propagation in elastic solids infused with fluids
International Journal of Engineering Science, 1992Co-Authors: Kumbakonam R. RajagopalAbstract:Abstract We study the propagation of waves in homogeneous Isotropic and transversely Isotropic elastic solids infused with fluids, within the context of the Theory of Mixtures. We show that our theory reduces to that proposed by Biot, when appropriate assumptions are made. We analyze the propagation of transverse plane waves, longitudinal waves and spherical waves in both Isotropic and transversely Isotropic elastic solids infused with a fluid.
