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Vasudev PG Ananda K Chatterjee S Aravinda S Shamala N Balaram P 《Journal of the American Chemical Society》2007,129(13):4039-4048
The crystal structure of 12 peptides containing the conformationally constrained 1-(aminomethyl)cyclohexaneacetic acid, gabapentin (Gpn), are reported. In all the 39 Gpn residues conformationally characterized so far, the torsion angles about the Calpha-Cbeta and Cbeta-Cgamma bonds are restricted to the gauche conformation (+/-60 degrees ). The Gpn residue is constrained to adopt folded conformations resulting in the formation of intramolecularly hydrogen-bonded structures even in short peptides. The peptides Boc-Ac6c-Gpn-OMe 1 and Boc-Gpn-Aib-Gpn-Aib-OMe 2 provide examples of C7 conformation; peptides Boc-Gpn-Aib-OH 3, Boc-Ac6c-Gpn-OH 4, Boc-Val-Pro-Gpn-OH 5, Piv-Pro-Gpn-Val-OMe 6, and Boc-Gpn-Gpn-Leu-OMe 7 provide examples of C9 conformation; peptide Boc-Ala-Aib-Gpn-Aib-Ala-OMe 8 provides an example of C12 conformation and peptides Boc-betaLeu-Gpn-Val-OMe 9 and Boc-betaPhe-Gpn-Phe-OMe 10 provide examples of C13 conformation. Gpn peptides provide examples of backbone expanded mimetics for canonical alpha-peptide turns like the gamma (C7) and the beta (C10) turns. The hybrid betagamma sequences provide an example of a mimetic of the C13 alpha-turn formed by three contiguous alpha-amino acid residues. Two examples of folded tripeptide structures, Boc-Gpn-betaPhe-Leu-OMe 11 and Boc-Aib-Gpn-betaPhg-NHMe 12, lacking internal hydrogen bonds are also presented. An analysis of available Gpn residue conformations provides the basis for future design of folded hybrid peptides. 相似文献
34.
The extensive band system belonging to the C2Πr–X2Σ+ transition of boron monoxide (BO) molecule lying in the vacuum ultraviolet region (150–230 nm) has been recorded in emission in a hollow cathode glow. A few new bands involving high v′ levels of C state have been observed. The Franck–Condon factors and r‐centroids were computed for the C–X system. By correlating the measured intensities to theory, the (relative) variation of the C–X electronic transition moment with internuclear separation was examined. 相似文献
35.
Don Galagedera George Woodward Sunanda Degamboda 《International Journal of Mathematical Education in Science & Technology》2013,44(5):679-689
This study investigates the effects of perceived mathematics ability (PMA) on the learning process with special reference to 147 undergraduates following an elementary statistics (ES) course. A model incorporating PMA together with aptitude, effort put in, expected grade, motivation to do well and interest in the subject, which are deemed to be either directly or indirectly associated with performance, is developed. PMA itself is not a good predictor of ES performance, rather its effect may be channelled through interest, expected grade and motivation to do well in ES. Low perception in mathematics ability impedes effort put forth when learning ES. The influence of PMA on ES performance is likely to be the consequence of the belief that mathematics is essential to learn ES. 相似文献
36.
The spectrum of B2Σ+-X2Σ+ system of AlO has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.05 cm−1. Nineteen bands of the Δv = 1, 0, −1, and −2 sequences of this band system have been analyzed for the rotational structure. Out of which seven bands, viz. 3-2, 4-3, 2-3, 3-4, 4-5, 5-6 and 6-7 have been analyzed for the first time. The rotational lines of these 19 bands along with 20 earlier analyzed bands, a total of 7200 lines, have been fitted in a simultaneous least squares fit. The study has resulted in determining more precise vibrational and rotational constants of the two states. Because of the high resolution employed it became necessary to invoke H0 and H1 coefficients, and a fifth order term to explain the anomalous spin-doubling observed in the v″ = 5, 6 and 7 levels of the X2Σ+ state. 相似文献
37.
Raghvendra S. Yadav Avinash C. Pandey Sharda Sundaram Sanjay 《Structural chemistry》2007,18(6):1001-1004
ZnO porous structures have been fabricated by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process. X-ray diffraction
(XRD) pattern indicated that the synthesized ZnO porous structures were hexagonal. It is found that CTAB influences the morphology
of ZnO structures. On the basis of structural information provided by XRD, SEM, and TEM, a growth mechanism is proposed for
the formation of ZnO porous structures. 相似文献
38.
Hans R. Kricheldorf Sharda V. Joshi William E. Hull 《Journal of polymer science. Part A, Polymer chemistry》1982,20(10):2791-2807
Alternating copolyamides of various ω-amino acids were synthesized by base-catalyzed polycondensation of N-isothiocyanatoacyl ω-amino acids in solution. Derivatives of the following amino acids were used: glycine, β-alanine, γ-aminobutyric acid, δ-aminovaleric acid, ε-aminocaproic acid, D ,L -β-aminobutyric acid, trans-4-aminocyclohexane 1-carboxylic acid, 4-aminophenyl acetic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, 3-amino-4-methyl benzoic acid, and 4-amino-3-methyl benzoic acid. The base-catalyzed polycondensation at lower temperatures gave purer products than the bulk condensation at 180–200°C. 13C-NMR and natural-abundance 15N-NMR spectra measured in trifluoroacetic acid demonstrate that in most cases undisturbed alternating sequences were obtained. Strong neighboring residue effects and long-range sequence effects were found in the 15N-NMR spectra, and structure/shift relationships are discussed. The sequences of copolyamides obtained by copolymerizations of lactams or β-amino acid N-carboxyanhydrides were investigated by both 15N-NMR and 13C-NMR spectroscopy. 13C-NMR spectroscopy was found to be more useful if the copolyamides consist of ω-amino acid units of different chain length. However, 15N-NMR spectroscopy is more suited if the monomer units differ exclusively by their substituents. 相似文献
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The use of crosslinked polystyrene anion-exchange resin as a support for borohydride ions made it possible to reduce conjugated olefinic bonds selectively under very mild conditions. The isolation of the reduced products by a simple filtration and evaporation process is another interesting feature of this reaction. 相似文献