A special hybrid quantum mechanics/molecular mechanics forcefield is defined, parameterized and validated for studying the photoisomerization path of the retinal chromophore in the rhodopsin protein. It couples a multireference ab initio Hamiltonian (CASSCF and second-order multireference many-body perturbation theory using a CASSCF reference) to describe the chromophore while the rest of the protein is approximated with the Amber forcefield. The frontier has been carefully parameterized in order to reproduce full quantum mechanics torsional energy profiles, for both the ground state and the first excited state. It is also shown that replacing the chromophore counterion with point charges is a valid approximation. This result is interpreted in terms of a cancellation effect for which a possible explanation is given. 相似文献
In the course of this investigation, a method for the characterization and differentiation of paper pulps was developed. After hydrolyzation of the papers and the respective raw pulps with trifluoroacetic acid, the hydrolyzates were analyzed with respect to their carbohydrate composition using ion exchange chromatography. The variations in carbohydrate composition mainly arise from the various hemicelluloses of the papers and pulps. The chromatographic results were then further processed using principal component analysis which allows correlating the various papers to different pulp materials. 相似文献
The Mitsunobu inversion reaction of 3-methoxyestra-1,3,5(10)-trien-17-ol is dramatically influenced by the acidic component. There appears to be a relationship between the dissociation constant of the electron-withdrawing substituent on the aryl acid and the overall effectiveness of the reaction, with more acidic species generally providing a higher yield of inverted product. 相似文献
Nudix hydrolases form a protein family whose function is to hydrolyse intracellular nucleotides and so regulate their levels
and eliminate potentially toxic derivatives. The genome of the radioresistant bacterium Deinococcus radiodurans encodes 25 nudix hydrolases, an unexpectedly large number. These may contribute to radioresistance by removing mutagenic
oxidised and otherwise damaged nucleotides. Characterisation of these hydrolases is necessary to understand the reason for
their presence. Here, we report the cloning and characterisation of the DR0975 gene product, a nudix hydrolase that appears
to be unique to this organism. 相似文献
The relative rates for the addition reactions of tert-butyl radical to 2-substituted ally chlorides I have een determined. The correlation of log k/k0, vs. σm gives a ρ mvalue of 3.59 with correlation coefficient of 0.930. When the substituent CH2Cl is excluded, correlation coefficient raises to 0.990 and ρ value becomes 3.39. The large p value and the deviation of relative rate of substituent CH2C1 are discussed. 相似文献
The covalent conjugation of a 20-mer peptide belonging to the VP3 capsid protein of hepatitis A virus to the surface of preformed liposomes was investigated. Three different bonds (disulfide, thioether and amide) were established between the peptide sequence and liposomes bearing at their surface appropriate reactive groups. The effect of the relative concentration of the N-[4-(p-maleimidophenyl)butyryl]dipalmitoylphosphatidylethanolamine anchor in liposomes on stability during coupling of the peptide sequence was studied. The interaction of the three liposomal preparations with phospholipids in a biomembrane model system, monolayers at the air-water interface, is also reported. The results showed that although the peptides associate with liposomes in similar yields for the three strategies studied, differences can be observed when their interaction with phospholipid monolayers composed of dipalmitoylphosphatidylcholine is analysed. 相似文献
The cover picture shows a typical building within the Campus of Xiamen University displaying Chen Jiageng (Tan Kah Kee)'s style. Just like many beautiful buildings designed and constructed by human, Nature “designs and constructs” a huge number of useful molecules with fascinating structures called natural products. Many natural products possess a fused six or seven‐membered carbocyclic unity. On page 315–322, the Huang's group disclosed a three‐step “[2+n]” annulation method for the construction of fused six and seven‐membered carbocyclic enimines and enones. The method starts from simple cyclic ketones and terminal olefinic amides, and relies on both the Suzuki coupling reaction and the olefin‐amide based Friedel‐Crafts type acylating reaction, a method developed by Huang and coworkers.