排序方式: 共有101条查询结果,搜索用时 31 毫秒
91.
Souvik Mondal Durga Sankar Chowdhuri Soumen Ghosh Ajay Misra Sudipta Dalai 《Journal of Molecular Structure》2007,810(1-3):81-89
DFT calculations has been done applying 6-31G* basis set on a series of dipeptides where the N-terminus position is fixed with phenylalanine and the C-terminus is varied with eight different amino acids. Different geometrical parameters (bond angle, bond length, geometry around -carbon atom) are thoroughly investigated to study the effect of amino acid sequence on dipeptide. Dihedral angle data analysis shows the deviation of amide plane from planarity, which is due to the combined effect of the steric hindrance of –R group and hydrogen bonding. The λmax value for phenylalanine has been calculated, which shows good agreement with the experimental value. A rigid potential energy scan is performed on phenylalanine by rotating –CH2Ph, –COOH and –NH2 groups separately to get some idea about the conformational stability. 相似文献
92.
Madhan Vinu Souvik Pal Jia‐Dian Chen Yi‐Feng Lin Yu‐Lun Lai Cheng‐Shiuan Lee Chia‐Her Lin 《中国化学会会志》2019,66(9):1165-1171
An aluminum metal–organic framework (Al‐MOF), [Al(OH)(BPDC)] (DUT‐5; BPDC = Biphenyl‐4,4′‐dicarboxylate), was synthesized using solvothermal reactions. The high surface area and micropores (approximately 1.2 nm) of DUT‐5 were characterized using N2 gas sorption measurements. The thermal stability of DUT‐5 and its phase purity were also investigated. The different amounts of DUT‐5 (0.1, 0.15, and 0.2 wt%) were successfully incorporated into the chitosan (CS) polymer to prepare a mixed matrix membrane (MMM) for the pervaporation of water/ethanol at 25°C. In particular, when 0.15 wt% of DUT‐5 was loaded, the DUT‐5@CS MMMs displayed excellent permeability and selectivity in ethanol/water separation. The results indicated that compared with pristine chitosan membranes, the flux of DUT‐5@CS membranes with 0.15 wt% loading significantly increased from 315 to 378 (g/m2 h?1) and the separation factor from 347 to 3,429. These promising results of the microporous Al‐MOF doped into chitosan MMMs reveal its good application potential for the bio‐ethanol separation processes. 相似文献
93.
A two region conduction-controlled rewetting model of hot vertical surfaces with internal heat generation and boundary heat
flux subjected to constant but different heat transfer coefficient in both wet and dry region is solved by the Heat Balance
Integral Method (HBIM). The HBIM yields the temperature field and quench front temperature as a function of various model
parameters such as Peclet number, Biot number and internal heat source parameter of the hot surface. Further, the critical
(dry out) internal heat source parameter is obtained by setting Peclet number equal to zero, which yields the minimum internal
heat source parameter to prevent the hot surface from being rewetted. Using this method, it has been possible to derive a
unified relationship for a two-dimensional slab and tube with both internal heat generation and boundary heat flux. The solutions
are found to be in good agreement with other analytical results reported in literature. 相似文献
94.
Dasgupta A Das PK Dias RS Miguel MG Lindman B Jadhav VM Gnanamani M Maiti S 《The journal of physical chemistry. B》2007,111(29):8502-8508
The interaction behavior of DNA with different types of hydroxylated cationic surfactants has been studied. Attention was directed to how the introduction of hydroxyl substituents at the headgroup of the cationic surfactants affects the compaction of DNA. The DNA-cationic surfactant interaction was investigated at different charge ratios by several methods like UV melting, ethidium bromide exclusion, and gel electrophoresis. Studies show that there is a discrete transition in the DNA chain from extended coils (free chain) to a compact form and that this transition does not depend substantially on the architecture of the headgroup. However, the accessibility of DNA to ethidium bromide is preserved to a significantly larger extent for the more hydrophilic surfactants. This was discussed in terms of surfactant packing. Observations are interpreted to reflect that the surfactants with more substituents have a larger headgroup and therefore form smaller micellar aggregates; these higher curvature aggregates lead to a less efficient, "patch-like" coverage of DNA. The more hydrophilic surfactants also presented a significantly lower cytotoxicity, which is important for biotechnological applications. 相似文献
95.
We report a new catalytic protocol for highly selective C-H arylation of pyridines containing common and synthetically versatile electron-withdrawing substituents (NO(2), CN, F and Cl). The new protocol expands the scope of catalytic azine functionalization as the excellent regioselectivity at the 3- and 4-positions well complements the existing methods for C-H arylation and Ir-catalyzed borylation, as well as classical functionalization of pyridines. Another important feature of the new method is its flexibility to adapt to challenging substrates by a simple modification of the carboxylic acid ligand or the use of silver salts. The regioselectivity can be rationalized on the basis of the key electronic effects (repulsion between the nitrogen lone pair and polarized C-Pd bond at C2-/C6-positions and acidity of the C-H bond) in combination with steric effects (sensitivity to bulky substituents). 相似文献
96.
We show that the steady states of the classical Heisenberg XXX spin-chain in an external magnetic field can be found by iterations of a quaternionic map. A restricted model, e.g., the xy spin-chain is known to have spatially chaotic steady states and the phase space occupied by these chaotic states is known to go through discrete changes as the field strength is varied. The same phenomenon is studied for the xxx spin-chain. It is seen that in this model the phase space volume varies smoothly with the external field. 相似文献
97.
We report the formation of a hybrid RNA2-PNA2 i-motif comprised of two RNA and two PNA strands based on the sequence specific self assembly of RNA, with potential as a building block for structural RNA nanotechnology. 相似文献
98.
99.
Using UV melting and CD spectroscopy, we show that alpha-l-LNA-modified oligonucleotides possess the ability to form triplexes at pH 6.8 with significantly increased thermostability relative to DNA triplexes. 相似文献
100.
JPC – Journal of Planar Chromatography – Modern TLC - A simple and rapid high-performance thin-layer chromatographic (HPTLC) determination of ursolic acid (UA) in tissue is necessary... 相似文献