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51.
A protocol is described for the treatment of molecular polarization in force field calculations. The resulting model is consistent in that both inter- and intramolecular polarization are handled within a single scheme. An analytical formula for removing intramolecular polarization from a set of atomic multipoles for an arbitrary static structure or conformation is given. With the help of the intramolecular polarization, these permanent atomic multipoles can then be applied in modeling alternative conformations of a molecule. Equipped with this simple technique, one can derive transferable electrostatic parameters for peptides and proteins using flexible model compounds such as dipeptides. The proposed procedure is tested for its ability to describe the electrostatic potential around various configurations of the N-methylacetamide dimer. The effect of different intramolecular polarization schemes on the accuracy of a force field model of the electrostatic potential of alanine dipeptide is investigated. A group-based scheme for including direct intramolecular polarization is shown to be most successful in accounting for the conformational dependence of electrostatic potentials. 相似文献
52.
53.
Li Yan Liang Shao Ping Ren Yi Quan Zheng Man Geng Lu Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Key Laboratory of Polymer Materials for Electronics Guangdong China Graduate School of the Chinese Academy of Sciences Beijing China 《中国化学快报》2007,18(2):225-228
A series of novel liquid crystalline epoxides with lateral substituents were cured with anhydrides and the cure kinetics was investigated by non-isothermal DSC technique. The results showed that the lengths of lateral substituents have great effect on the value of Ea. The curing reaction became less active, when the liquid crystalline epoxides have long lateral substituents and were controlled by diffusion at the late stage of cure. A nematic structure was observed by POM and XRD. 相似文献
54.
Diglycidyl ether of 4,4′-dihydroxybiphenol (BPDGE) is a liquid crystalline epoxy. The biphenyl epoxy (diglycidyl ether of 3,3′,5,5′-tetramethyl-4,4′-biphenyl, TMBPDGE) has found great applications in plastic encapsulated semiconductor packaging. Phenol novolac (PN) was used as curing agent. The reaction kinetics of BPDGE/PN and TMBPDGE/PN systems in the presence of triphenylphosphine (TPP) were characterized by an isoconversional method under dynamic conditions using differential scanning calorimetry (DSC) measurements. The results showed that the curing of epoxy resins involves different reaction stages and the values of activation energy are dependent on the degree of conversion. The effects of curing temperature on their phase structure have been investigated with polarized optical microscopy and Wide-angle X-ray diffraction. With proper curing process, BPDGE showed a nematic phase when cured with PN. 相似文献
55.
The guaianolide ester is a potent inhibitor of cancer cells. Lactucopicrin, a guaianolide, shows analgesic, antitussic, and sedative activities. In order to investigate its structure, 1H and 13C NMR and 2D NMR have been carried out at a proton field strength of 400 MHz and a carbon field strength of 100 Mhz in DMSO-d
6 at 20°C. Resonances for all protons and carbons have been assigned. The results of HMQC and HMBC experiments suggest that the structure of lactucopicrin is as shown in Fig. 1. Its stereostructure is verified by the X-ray experiment. 1H and 13C NMR of lactucopicrin are reported. Its 2D NMR and X-ray are reported for the first time. 相似文献
56.
Anna Worobiec Lucyna Samek Zoya Spolnik Velichka Kontozova Elzbieta Stefaniak René Van Grieken 《Mikrochimica acta》2006,156(3-4):253-261
The St. Michael Archangel’s Church in Szalowa, Poland, was selected for closer investigation with respect to the indoor/outdoor
air exchange and its influence on the air quality and work arts preservation. Chemical composition, size and abundance of
particulate matter and concentration of gases NO2, SO2, O3 inside and outside the church were determined. To study seasonal variation of the weather condition (temperature, inversion
level, wind direction) and the influence of seasonal sources of the air pollution (like heating of the nearby houses), samples
were collected in winter and summer time. It was stated that suspended particulate matter inside the wooden church has in
general an outdoor source. Several groups of particles were distinguished such as the organic ones, soil dust, nitrates and
sulphates. In case of organic and soil dust particles, the concentration inside was higher than outside. From the results,
in comparison to literature data, one can conclude that accumulation of particulate suspended matter in the church is more
intense than in other types of buildings. Gaseous pollutants were detected but their concentration was negligible. 相似文献
57.
PengWANG ShuRenJIANG ZhiQiangZHOU 《中国化学快报》2004,15(12):1457-1460
Cellulose-tris(3,5-dimethylphenylcarbamate)(CDMPC) were synthesized as highperformance liquid chromatography (HPLC) chiral stationary phase(CSP). The successful resolution of four chiral pesticides on the CSP was realized and the influence of the temperature on the separation was studied. 相似文献
58.
Within a second virial theory, we study bulk phase diagrams as well as the free planar isotropic-nematic interface of binary mixtures of nonadditive thin and thick hard rods. For species of the same type, the excluded volume is determined only by the dimensions of the particles, whereas for dissimilar ones it is taken to be larger or smaller than that, giving rise to a nonadditivity that can be positive or negative. We argue that such a nonadditivity can result from modeling of soft interactions as effective hard-core interactions. The nonadditivity enhances or reduces the fractionation at isotropic-nematic (IN) coexistence and may induce or suppress a demixing of the high-density nematic phase into two nematic phases of different composition (N(1) and N(2)), depending on whether the nonadditivity is positive or negative. The interfacial tension between coexisting isotropic and nematic phases shows an increase with increasing fractionation at the IN interface, and complete wetting of the IN(2) interface by the N(1) phase upon approach of the triple-point coexistence. In all explored cases bulk and interfacial properties of the nonadditive mixtures exhibit a striking and quite unexpected similarity with the properties of additive mixtures of different diameter ratio. 相似文献
59.
It is proposed that in molecular mechanics calculation points belonging to various stable or meta-sta-ble conformtrs are mixed up and form fractal structures in conformation space.The calculation results show the following two phenomena:(i)Two levels of structure with fractal feature were observed.Around the conformer without mirror symmetry points belonging to the conformer and its enantiomer are mixed up and form the first level of fractal structure; on the boundary of the attractive basin o{ each atlractor,points belonging to different attractors form the second level of fractal structure.(ii) The variation of molecular mechanics parameters will influence the structure and area of each attractive basin significantly The above phenomena may become the basis of a new method for solving the troublesome multi-minimum-point problem in molecular mechanics calculation. 相似文献
60.
用TRP技术研究了以全硅MCM-41(Si-MCM-41)和HNO3交换的全硅MCM-41(H-MCM-41)为载体制备的Ni-Mo、Co-Mo和Ni-W加氢脱硫(HDS)催化剂的还原性能,并以0.8(wt)%二苯并噻吩(DBT)的十氢萘溶液为模型化合物,在高压固定床反应器上考察了上述催化剂的加氢脱硫(HDS)反应性能。结果表明,Si-MCM-41经稀HNO3交换后,所担载的Ni-Mo和Ni-W催化剂还原性能、HDS活性和加氢活性有显著变化,但对Co-Mo催化剂影响不大。这说明在Ni-Mo/H-MCM-41和Ni-W/H-MCM-41中可能存在氢溢流现象,DBT的HDS活性与载体表面酸性和氢溢流有关。 相似文献