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Carlo Rosini - One of the best experts on this subject based on the ideXlab platform.
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assignment of the absolute configuration of diplopyrone the main phytotoxin produced by diplodia mutila the pathogen of the cork oak decline by a nonempirical analysis of its chirOptical properties
Journal of Organic Chemistry, 2005Co-Authors: Egidio Giorgio, Lucia Maddau, Emanuela Spanu, Antonio Evidente, Carlo RosiniAbstract:The nonempirical assignment of the absolute configuration of (+)-diplopyrone, the main phytotoxin of Diplodia mutila, i.e., an endophytic fungus, widespread in Sardinian oak forests, and considered one of the main causes of cork oak decline, has been approached by two different methods: (a) the exciton analysis of the circular dichroism (CD) spectrum and (b) the ab initio calculation of the Optical Rotatory Power. Both methods indicate that (+)-diplopyrone is 6-[(1S)-1-hydroxyethyl]-2,4a(S),6(R),8a(S)-tetrahydropyrano[3,2-b]pyran-2-one, so the stereostructure of this important biomolecule is safely determined for the first time. A comparison of advantages and limitations of the two methods of analysis is also presented.
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ab initio calculation of Optical Rotatory dispersion ord curves a simple and reliable approach to the assignment of the molecular absolute configuration
Journal of the American Chemical Society, 2004Co-Authors: Egidio Giorgio, Rosario G Viglione, Riccardo Zanasi, Carlo RosiniAbstract:In this paper, both Hartree−Fock (HF) and density functional theory (DFT) methods have been used to make ab initio calculations of the Optical Rotatory Power of selected molecules at several wavelengths; that is, part of the Optical Rotatory dispersion (ORD) curve has been predicted. This approach constitutes a new, simple, and reliable method to assign the molecular absolute configuration, at least for rigid molecules such as those studied in the present work. In fact, in this way, it is possible to overcome the difficulties connected to some relevant cases, in particular that of (−)-β-pinene, for which even a very high-level (DFT/B3LYP/6-311++G(2d,2p)) calculation affords the wrong sign of the Optical rotation at 633 nm. On the contrary, the predicted ORD curve, even using small basis sets, reproduces (below 400 nm) the experimental trend well, allowing for the correct configurational assignment. This result clearly shows that to have a reliable configurational assignment the comparison between experime...
Egidio Giorgio - One of the best experts on this subject based on the ideXlab platform.
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assignment of the absolute configuration of diplopyrone the main phytotoxin produced by diplodia mutila the pathogen of the cork oak decline by a nonempirical analysis of its chirOptical properties
Journal of Organic Chemistry, 2005Co-Authors: Egidio Giorgio, Lucia Maddau, Emanuela Spanu, Antonio Evidente, Carlo RosiniAbstract:The nonempirical assignment of the absolute configuration of (+)-diplopyrone, the main phytotoxin of Diplodia mutila, i.e., an endophytic fungus, widespread in Sardinian oak forests, and considered one of the main causes of cork oak decline, has been approached by two different methods: (a) the exciton analysis of the circular dichroism (CD) spectrum and (b) the ab initio calculation of the Optical Rotatory Power. Both methods indicate that (+)-diplopyrone is 6-[(1S)-1-hydroxyethyl]-2,4a(S),6(R),8a(S)-tetrahydropyrano[3,2-b]pyran-2-one, so the stereostructure of this important biomolecule is safely determined for the first time. A comparison of advantages and limitations of the two methods of analysis is also presented.
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ab initio calculation of Optical Rotatory dispersion ord curves a simple and reliable approach to the assignment of the molecular absolute configuration
Journal of the American Chemical Society, 2004Co-Authors: Egidio Giorgio, Rosario G Viglione, Riccardo Zanasi, Carlo RosiniAbstract:In this paper, both Hartree−Fock (HF) and density functional theory (DFT) methods have been used to make ab initio calculations of the Optical Rotatory Power of selected molecules at several wavelengths; that is, part of the Optical Rotatory dispersion (ORD) curve has been predicted. This approach constitutes a new, simple, and reliable method to assign the molecular absolute configuration, at least for rigid molecules such as those studied in the present work. In fact, in this way, it is possible to overcome the difficulties connected to some relevant cases, in particular that of (−)-β-pinene, for which even a very high-level (DFT/B3LYP/6-311++G(2d,2p)) calculation affords the wrong sign of the Optical rotation at 633 nm. On the contrary, the predicted ORD curve, even using small basis sets, reproduces (below 400 nm) the experimental trend well, allowing for the correct configurational assignment. This result clearly shows that to have a reliable configurational assignment the comparison between experime...
Huber Patrick - One of the best experts on this subject based on the ideXlab platform.
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A ferroelectric liquid crystal confined in cylindrical nanopores : reversible smectic layer buckling, enhanced light rotation and extremely fast electro-Optically active Goldstone excitations
Royal Society of Chemistry (RSC), 2017Co-Authors: Busch Mark, Kityk Andriy, Piecek Wiktor, Hofmann Tommy, Wallacher Dirk, Calus Sylwia, Kula Przemyslaw, Steinhart Martin, Eich Manfred, Huber PatrickAbstract:The orientational and translational order of a thermotropic ferroelectric liquid crystal (2MBOCBC) imbibed in self-organized, parallel, cylindrical pores with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are explored by high-resolution linear and circular Optical birefringence as well as neutron diffraction texture analysis. The results are compared to experiments on the bulk system. The native oxidic pore walls do not provide a stable smectogen wall anchoring. By contrast, a polymeric wall grafting enforcing planar molecular anchoring results in a thermal-history independent formation of smectic C* helices and a reversible chevron-like layer buckling. An enhancement of the Optical Rotatory Power by up to one order of magnitude of the confined compared to the bulk liquid crystal is traced to the pretransitional formation of helical structures at the smectic-A*-to-smectic-C* transformation. A linear electro-Optical birefringence effect evidences collective fluctuations in the molecular tilt vector direction along the confined helical superstructures, i.e. the Goldstone phason excitations typical of the para-to-ferroelectric transition. Their relaxation frequencies increase with the square of the inverse pore radii as characteristic of plane-wave excitations and are two orders of magnitude larger than in the bulk, evidencing an exceptionally fast electro-Optical functionality of the liquid-crystalline-AAO nanohybrids
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A ferroelectric liquid crystal confined in cylindrical nanopores: Reversible smectic layer buckling, enhanced light rotation and extremely fast electro-Optically active Goldstone excitations
'Royal Society of Chemistry (RSC)', 2017Co-Authors: Busch Mark, Kityk Andriy, Piecek Wiktor, Hofmann Tommy, Wallacher Dirk, Calus Sylwia, Kula Przemyslaw, Steinhart Martin, Eich Manfred, Huber PatrickAbstract:The orientational and translational order of a thermotropic ferroelectric liquid crystal (2MBOCBC) imbibed in self-organized, parallel, cylindrical pores with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are explored by high-resolution linear and circular Optical birefringence as well as neutron diffraction texture analysis. The results are compared to experiments on the bulk system. The native oxidic pore walls do not provide a stable smectogen wall anchoring. By contrast, a polymeric wall grafting enforcing planar molecular anchoring results in a thermal-history independent formation of smectic C* helices and a reversible chevron-like layer buckling. An enhancement of the Optical Rotatory Power by up to one order of magnitude of the confined compared to the bulk liquid crystal is traced to the pretransitional formation of helical structures at the smectic-A*-to-smectic-C* transformation. A linear electro-Optical birefringence effect evidences collective fluctuations in the molecular tilt vector direction along the confined helical superstructures, i.e. the Goldstone phason excitations typical of the para-to-ferroelectric transition. Their relaxation frequencies increase with the square of the inverse pore radii as characteristic of plane-wave excitations and are two orders of magnitude larger than in the bulk, evidencing an exceptionally fast electro-Optical functionality of the liquid-crystalline-AAO nanohybrids.Comment: 14 pages, 13 figures, 2 ancillary files, as submitted, Nanoscale (in press
Mylène Potier - One of the best experts on this subject based on the ideXlab platform.
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Comparative Effects of R- and S-equol and Implication of Transactivation Functions (AF-1 and AF-2) in Estrogen Receptor-Induced Transcriptional Activity
Nutrients, 2010Co-Authors: Svitlana Shinkaruk, Charlotte Carreau, Gilles Flouriot, Catherine Bennetau-pelissero, Mylène PotierAbstract:Equol, one of the main metabolites of daidzein, is a chiral compound with pleiotropic effects on cellular signaling. This property may induce activation/inhibition of the estrogen receptors (ER) a or b, and therefore, explain the beneficial/deleterious effects of equol on estrogen-dependent diseases. With its asymmetric centre at position C-3, equol can exist in two enantiomeric forms (R- and S-equol). To elucidate the yet unclear mechanisms of ER activation/inhibition by equol, we performed a comprehensive analysis of ERa and ERb transactivation by racemic equol, as well as by enantiomerically pure forms. Racemic equol was prepared by catalytic hydrogenation from daidzein and separated into enantiomers by chiral HPLC. The configuration assignment was performed by Optical Rotatory Power measurements. The ER-induced transactivation by R- and S-equol (0.1–10 µM) and 17b-estradiol (E2, 10 nM) was studied using transient transfections of ERa and ERb in CHO, HepG2 and HeLa cell lines. R- and S-equol induce ER transactivation in an opposite fashion according to the cellular context. R-equol and S-equol are more potent in inducing ERa in an AF-2 and AF-1 permissive cell line, respectively. Involvement of ERa transactivation functions (AF-1 and AF-2) in these effects has been examined. Both AF-1 and AF-2 are involved in racemic equol, R-equol and S-equol induced ERa transcriptional activity. These results could be of interest to find a specific ligand modulating ER transactivation and could contribute to explaining the diversity of equol actions in vivo.
Gharbi Abdelhafidh - One of the best experts on this subject based on the ideXlab platform.
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Influence de la chiralité dans les cristaux liquides smectiques chiraux (ferroélectricité induite sous champ électrique et propriétés optiques)
2009Co-Authors: Bitri Nabila, Marcerou Jean-paul, Gharbi AbdelhafidhAbstract:Dans une première partie de cette thèse, nous avons étudié le comportement sous champ électrique de la séquence de phases des "cristaux liquides smectiques chiraux" en développant une étude sous champ électrique (E) et en fonction de la température (T) qui sont deux variables thermodynamiques indépendantes. Les résultats de mesures ont conduit au tracé des diagrammes de phase Champ électrique-Température (E-T). Ces diagrammes peuvent dans certains cas révéler l'induction sous champ électrique de nouvelles phases n'existant pas à champ nul. D'autre part, suite à l'étude de certains composés présentant la phase ferroélectrique SmC* dans leur séquence de phase à champ nul. Le tracé de leurs diagrammes de phases (E-T) a permis de mettre en évidence un problème de coexistence entre une phase paraélectrique et une autre ferroélectrique. Pour bien localiser cette séquence de phases sans rencontrer ce phénomène de démixtion, on a fait appel à une nouvelle étude optique sans champ électrique basée sur la méthode de conoscopie à balayage. L'analyse de l'ellipticité de la lumière transmise en fonction de la rotation de l'échantillon a donné accès aux deux indices de réfraction (ne et no) séparément, à la biréfringence (?n), au pouvoir rotatoire optique (PRO) et à la gyrotropie. Ces études que nous avons développé avec succès nous permettent une mise au point robuste et efficace des comportements des différentes phases de cristaux liquides smectiques chiraux sous et en absence du champ électrique.In the first part of this thesis, we studied the behavior of the phase sequence of "smectic chiral liquid crystals" in order to develop a study under electric field (E) and as a function of tempertaure (T) which are two independent thermodynamic variables. The measurement results allow us to establish the electric field versus temperature phase diagram (E-T). In some cases, the phase diagram, under electric field, can reveal the induction of new phase which is not existing at zero field. On the other hand, we investigated certain compounds with ferroelectric phase SmC* in their phase sequence at zero field. The delimitation of phase diagrams (E-T) helped to highlight a coexistence problem between a paraelectric phase and a ferroelectric one. To locate this phase sequence without encountering this demixing phenomenon, we used a new Optical study without electric field based on scanning conoscopy method. The analysis of the ellipticity of the transmitted light depending on the rotation of the sample gave access to the two refractive indices (ne and no) seperately, the birefringence (?n), the Optical Rotatory Power (ORP) and the gyrotropy. These studies that we have successfully developed enable us to develop a robust and effictive behavior of different phases of chiral smectic liquid crystals under and without electric field.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF