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991.
A new guaiane-type diterpenoid, (1alpha,5beta,7alpha)-3,10(18),11-dictytriene-19-acid, was obtained from the roots of Euphorbia wallichii. This is the first isolation of guaiane diterpene from this genus of Euphorbia. The structure was elucidated by spectral methods. And the compound was tested for the cytotoxicities on the cancer cell line P-388 and A-549 in vitro. 相似文献
992.
alpha-Helix formation is known to be opposed by the entropy loss due to the folding and favored by the energy of molecular interactions. However, the underlying mechanism of these factors is still being discussed. Here we have used the experimental and calculation data for short alanine-based peptides embedded in water to model the mechanism of helix folding and unfolding and to calculate microscopically the free energy factors of alanine in the frame of helix coil conformational integrals. Classical helix-coil transition theories take into account the interactions in a peptide chain only if the i, i + 3 peptide bond participates in hydrogen bonding. But quantum mechanical calculations showed that interactions of the i, i + 2 peptide bond play an important role in helix folding too. We also included the short-range repulsive interactions due to molecular steric clashes and the end effects due to polar/hydrogen-bonding interactions at the N and C termini. The helix and coil regions of peptide conformational space were defined using an experimental steric criterion for hydrogen bonding. Arginine helix propensity was discussed and estimated. Monte Carlo numerical simulations of thermodynamics and kinetics for the 21 amino acid alpha-helical polypeptide Ac-A5(AAARA)3A-NMe were carried out and found to be in an agreement with the experimental results. 相似文献
993.
Gao D Tian Y Ding L Liang F Bi S Chen Y Yu A Zhang H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,64(2):430-434
Based on the interaction between human complement factor C4 (human C4) and sodium dodecylbenzene sulphonate (SDBS) and the resonance light-scattering (RLS) technique, a highly sensitive assay for human C4 using resonance light-scattering technique was developed. At pH 2.8 Na2HPO4-citric acid buffer solution, the RLS intensities of SDBS system at 283, 503 and 600 nm were obviously enhanced in the presence of human C4. The effects of surfactant, pH, incubation time, concentration of SDBS and foreign substances on the enhanced RLS intensity of system were investigated. Under the optimum conditions, the enhanced RLS intensity is directly proportional to the concentration of human C4 in the range of (0.5-120)x10(-6)gl-1 and the linear regression equation was obtained with high correlation coefficient. This RLS technique was applied to the determination of human C4 in some synthetic samples with good recovery. Moreover, it was found that the electrostatic interaction is the main binding force between SDBS and human C4. 相似文献
994.
995.
996.
997.
Angular distributions of the ^7Li(^6Li, ^6Li)^7Li elastic scattering and the ^7Li(^6Li, ^7Lig.s.)^6Li, ^7Li(^6Li, ^7Li0.48)^6Li transfer reactions at Ec.m. = 23.7 MeV are measured with the Q3D magnetic spectrograph. The optical potential of ^6Li + ^7Li is obtained by fitting the elastic scattering differential cross sections. Based on the distorted wave Born approximation (DWBA) analysis, spectroscopic factors of ^7Li =^6Li n are determined to be 0.73 ± 0.05 and 0.90 ± 0.09 for the ground and first exited states in ^7Li, respectively. Using the spectroscopic factors, the cross sections of the ^6 Li(n, γ0,1)^7 Li direct neutron capture reactions and the astrophysical ^6Li(n, γ)^7 Li reaction rates are derived. 相似文献
998.
Weiwei Ling Huaiwu Zhang Ying He Yang Wu Kai Yang Yuanxun Li Sheng Li 《Journal of magnetism and magnetic materials》2010,322(7):819-823
The Ni-Cu-Zn ferrites with different contents of Bi4Ti3O12 ceramics (1-8 wt%) as sintering additives were prepared by the usual ceramic technology and sintered at 900 °C to adapt to the low temperature co-fired ceramic (LTCC) technology. The magnetic and dielectric properties of the ferrite can be effectively improved with the effect of an appropriate amount of Bi4Ti3O12. For all samples, the ferrite sintered with 2 wt% Bi4Ti3O12 has relatively high density (98.8%) and permeability, while the ferrite with 8 wt% Bi4Ti3O12 has relatively good dielectric properties in a wide frequency range. The influences of Bi4Ti3O12 addition on microstructure, magnetic and dielectric properties of the ferrite have been discussed. 相似文献
999.
1000.
Benjamin M. O’Brien Emilio P. Calius Tokushu Inamura Sheng Q. Xie Iain A. Anderson 《Applied Physics A: Materials Science & Processing》2010,100(2):385-389
Some of the most exciting possibilities for dielectric elastomer artificial muscles consist of biologically inspired networks
of smart actuators working towards common goals. However, the creation of these networks will only be realised once intelligence
and feedback can be fully distributed throughout an artificial muscle device. Here we show that dielectric elastomer artificial
muscles can be built with intrinsic sensor, control, and driver circuitry, bringing them closer in capability to their natural
analogues. This was achieved by exploiting the piezoresistive behaviour of the actuator’s highly compliant electrodes using
what we have called the dielectric elastomer switch. We developed suitable switching material using carbon loaded silicone
grease and experimentally demonstrated the primitives required for self-sensing actuators and digital computation, namely
compliant electromechanical NAND gates and oscillator circuits. We anticipate that dielectric elastomer switches will reduce
the need for bulky and rigid external circuitry as well as provide the simple distributed intelligence required for soft,
biologically inspired networks of actuators. Examples include many-degree-of-freedom robotic hearts, intestines, and manipulators;
wearable assistive devices; smart sensor skins and fabrics; and ultimately new types of artificial muscle embedded, electromechanical
computers. 相似文献