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1.
Solvent Influence on Cellulose 1,4‐β‐Glycosidic Bond Cleavage: A Molecular Dynamics and Metadynamics Study 下载免费PDF全文
Claudia Loerbroks Eliot Boulanger Prof. Dr. Walter Thiel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(14):5477-5487
We explore the influence of two solvents, namely water and the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EmimAc), on the conformations of two cellulose models (cellobiose and a chain of 40 glucose units) and the solvent impact on glycosidic bond cleavage by acid hydrolysis by using molecular dynamics and metadynamics simulations. We investigate the rotation around the glycosidic bond and ring puckering, as well as the anomeric effect and hydrogen bonds, in order to gauge the effect on the hydrolysis mechanism. We find that EmimAc eases hydrolysis through stronger solvent–cellulose interactions, which break structural and electronic barriers to hydrolysis. Our results indicate that hydrolysis in cellulose chains should start from the ends and not in the centre of the chain, which is less accessible to solvent. 相似文献
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3.
Thierry Boulanger Daniel P. Vercauteren Guy Evrard François Durant 《Journal of chemical crystallography》1987,17(5):561-573
The crystal structure of 2-(carboxy-3-propyl)-3-amino-6-cyclohexylpyridazinium bromide has been determined by single-crystal X-ray diffraction techniques and refined by full-matrix least squares. The compound crystallized in the tri-clinic space groupP ¯1 witha=10.275(1),b=11.215(1),c=7.082(1) Å,=91.84(1),=102.21(1), =106.77(1)°, andZ=2. FinalR-factor is 0.045. The main structural results are very similar to the ones observed for the 6-phenyl analog. These two compounds are GABA-A antagonists.Ab initio molecular orbital calculations, with STO-3G and 4-31G basis sets, suggest that the exocyclic nitrogen accurately mimics the nitrogen atom of GABA. 相似文献
4.
Commodari F Sclavos G Ibrahimi S Khiat A Boulanger Y 《Magnetic resonance in chemistry : MRC》2005,43(6):444-450
The NMR-derived structure of estrogen (17beta-estradiol, E2), the drug of choice for postmenopausal women, was compared with a recent literature crystal x-ray structure of Fab-bound E2. 1H and 13C NMR spectra of E2 were acquired in DMSO-d6. Assignments were obtained from an analysis of DQF-COSY, TOCSY, HETCOR, HMQC and HMBC 2D NMR spectra. The 1H and 13C NMR assignments are the first reported for E2 in DMSO-d6. Two solution structures, S1 and S2, were obtained with molecular modeling using NOE constraints. S1 overlaps with the crystal structure for all rings. S2 shows prominent differences in the C-ring (C9--C11--C12--C13) segment, which deviates from a chair conformation, and excellent overlap in the A-, B- and D-rings of E2. The C-ring in S2 adopts a boat conformation as opposed to a chair conformation in the x-ray and S1 structures. The S2 structure is about 6 degrees more twisted than the bound x-ray and S1 models. The S1, S2 and x-ray structures had ring bowing values of 10.1 +/- 0.3, 11 +/- 1 and 10.37 degrees , respectively. Of the 100 solution conformers generated, 83 had S1 conformation and 17 had S2 conformation, with average internal energies of 112 +/- 2 and 141 +/- 2 kcal mol(-1), respectively. The 100 S1- and S2- derived conformers showed a r.m.s.d. of 0.72 A for all atoms. The x-ray, S1 and S2 C18--O17 distances were 2.93, 2.92 +/- 0.01 and 2.93 +/- 0.01 A, respectively, and the O3--O17 distances were 11.06, 11.18 +/- 0.12, and 10.89 +/- 0.05 A, respectively. 相似文献
5.
Persephone Canonne Raynald Boulanger Bernard Chantegrel 《Journal of heterocyclic chemistry》1989,26(1):113-117
A one-step synthesis of spiro[cycloalkane-1,4′-2H-3′,1-benzoxazin]-2′-ones and spiro[cycloalkane-1,4′-1H-pyrido[2′,3′-d][1,3′]oxazin]-2′-ones, obtained in good yield from the corresponding 1-(o-aminophenyl) and 1-(2′-amino-3′-pyridinyl)cycloalkanols is described using ethyl carbonate in presence of n-butyllithium. 相似文献
6.
Thierry Boulanger Christine Evrard Daniel P. Vercauteren Guy Evrard François Durant 《Journal of chemical crystallography》1991,21(3):287-295
The crystal structures ofp-methoxyphenyl-3-triazolo [4,3-a] isoquinoline (SR95926),p-methoxyphenyl-3-triazolophtalazine (CMW1842), andp-methoxyphenyl-3-N-dimethoxyethylamino-6-triazolophtalazine (L16317) have been solved by direct methods from single-crystal X-ray diffraction data, and refined by full-matrix least squares. SR95926: monoclinic,P21/n,a=20.950(3),b=6.769(1),c=9.465(2) Å,=100.90(1)°. CMW1842: triclinic,P¯1,a=8.784(1),b=9.160(4),c=8.555(1) Å,=99.10(2),=93.90(1), =106.77(1)°. L16317: monoclinic,P21/n,a=20.124(3),b=9.586(1),c=10.788(1) Å,=91.91(1)°. FinalR factors are 0.034, 0.037, and 0.053, respectively. Experimental geometries were used to perform STO-3Gab initio molecular-orbital calculations. A relationship between the electronic pattern within the molecules and the affinity of the benzodiazepine receptor sites is pointed out. 相似文献
7.
We develop a mechanical theory for systems of rod-like particles. Central to our approach is the assumption that the external power expenditure for any subsystem of rods is independent of the underlying frame of reference. This assumption is used to derive the basic balance laws for forces and torques. By considering inertial forces on par with other forces, these laws hold relative to any frame of reference, inertial or noninertial. Finally, we introduce a simple set of constitutive relations to govern the interactions between rods and find restrictions necessary and sufficient for these laws to be consistent with thermodynamics. Our framework provides a foundation for a statistical mechanical derivation of the macroscopic balance laws governing liquid crystals. 相似文献
8.
Working on a state space determined by considering a discrete system of rigid rods, we use nonequilibrium statistical mechanics to derive macroscopic balance laws for liquid crystals. A probability function that satisfies the Liouville equation serves as the starting point for deriving each macroscopic balance. The terms appearing in the derived balances are interpreted as expected values and explicit formulas for these terms are obtained. Among the list of derived balances appear two, the tensor moment of inertia balance and the mesofluctuation balance, that are not standard in previously proposed macroscopic theories for liquid crystals but which have precedents in other theories for structured media. 相似文献
9.
William A. Boulanger 《合成通讯》2013,43(12):2201-2210
We report novel procedures for the efficient resolution of (±)-cis-2 -hydroxy-5, 9-dimethyl-6, 7-benzomorphan via the (-)-N-acetyl-L-glutamate and (+)-α-bromocamphor-φ-sulfonate salts, the direct N-substitution of the (+)-α-bromocamphor-φ-sulfonate salts, and the use of these methods for the synthesis of racemic, (+)-, and (-)-cyclazocine. 相似文献
10.
Hans Eliot Edling Matthew Vincent Herv Marand Samantha J. Talley Kevin Barr Robert B. Moore S. Richard Turner 《Journal of Polymer Science.Polymer Physics》2019,57(15):973-980
Structurally rigid copolyester thermoplastics were synthesized from 1,4‐cyclohexanedimethanol and the diesters dimethyl biphenyl‐4,4′‐dicarboxylate and dimethyl 2,6‐naphthalenedicarboxylate (DMN) via conventional melt transesterification. Conventional differential scanning calorimetry (CDSC) showed all compositions to exhibit multiple endotherms upon heating. Wide‐angle X‐ray diffraction analysis showed copolyester compositions to exhibit the crystalline structure of either the homopolyester Poly(1,4‐cyclohexylenedimethylene 2,6‐naphthalate) (PCN) or the homopolyester Poly(1,4‐cyclohexylenedimethylene 4,4′‐bibenzoate) (PCB), but not both simultaneously. Further thermal analysis using CDSC and fast DSC investigated the origin of the multiple endotherm behavior. While three endotherms are observed for low heating rates, the upper two endotherms appear to merge at heating rates about 1–5 °C s?1 and a single endotherm remains above heating rates about 10–50 °C s?1. While the behavior of the upper two endotherms is undeniably consistent with the mechanism of melting–recrystallization–remelting (MRR), we suggest that the low endotherm is likely associated with the melting of constrained secondary crystals, although MRR effects cannot be ruled out. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 973–980 相似文献