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951.
More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Gō-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T(opt). The optimal folding temperature T(opt) is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T(opt) and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T(opt) and start to diverge when the temperature is lower than T(opt). The distribution of FPT is close to a log-normal-like distribution at T > or = T(opt). At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations. 相似文献
952.
Separation of ephedrine stereoisomers by molecularly imprinted polymers was performed to study the factors that affect the selectivity and column efficiency. The polymer synthesized with pentaerythritol triacrylate as the cross-linker and chloroform as the porogen was found to have the best overall separation performance. Investigation of the recognition mechanism by NMR and chromatographic analysis revealed that the major binding forces between the polymer stationary phase and ephedrine are the ionic and hydrogen bonding interactions. Studies of the influence of mobile phase compositions on the HPLC analysis have shown that a methanol-aqueous buffer was the suitable mobile phase for the separation in which pH, ionic strength and water content can be adjusted to optimize the chromatographic analysis. 相似文献
953.
合成了γ-氨丙基七甲基环四硅型氧烷和γ-氨丙基甲基二乙氧基硅烷。研究了它们与八甲基环四硅氧烷在阳离子乳化剂及阴离子型乳化剂存在下的乳液共聚合反应。探讨了催化剂量、单体浓度、氨丙基含量及温度等对聚合的影响。 相似文献
954.
Zhou YanXia Tan HongWei Yang ZuoYin Jia ZongChao Liu RuoZhuang Chen GuangJu 《中国科学B辑(英文版)》2007,50(2):266-271
The insect spruce budworm(Choristoneura fumiferana) produces antifreeze protein(AFP) to assist in the protection of the over-wintering larval stage and contains multiple isoforms. Structures for two isoforms,known as CfAFP-501 and CfAFP-337,show that both possess similar left-handed β-helical structure,although thermal hysteresis activity of the longer isoform CfAFP-501 is three times that of CfAFP-337. The markedly enhanced activity of CfAFP-501 is not proportional to,and cannot be simply accounted for,by the increased ice-binding site resulting from the two extra coils in CfAFP-501. In or-der to investigate the molecular basis for the activity difference and gain better understanding of AFPs in general,we have employed several different computational methods to systematically study the structural properties and ice interactions of the AFPs and their deletion models. In the context of intact AFPs,a majority of the coils in CfAFP-501 has better ice interaction and causes stronger ice lattice disruption than CfAFP-337,strongly suggesting a cooperative or synergistic effect among β-helical coils. The synergistic effect would play a critical role and make significant contributions to the anti-freeze activity β-helical antifreeze proteins. This is the first time that synergistic effect and its implica-tion for antifreeze activity are reported for β-helical antifreeze proteins. 相似文献
955.
噻吩及衍生物的微波反应机理研究 总被引:5,自引:0,他引:5
应用量子化学理论,初步探讨了苯-噻吩协同分离的可能性,利用微波诱导反应提高了选择性,介绍了在复合催化作用下,对Diels-Alder,acylacylation,HydrogenExchange几个基元反应的机理。 相似文献
956.
957.
The title compound, the Tl-richest in the K-Tl system, has been synthesized in Ta containers via direct reaction of the elements at 400 degrees C followed by quenching to room temperature and subsequent annealing at 150 degrees C for 4 weeks. It crystallizes in the orthorhombic space group Cccm (No. 66) with a = 16.625(1) A, b = 23.594(2) A, c = 15.369(2) A (22 degrees C), and Z = 8. Two different Tl(12) units consisting of augmented tetrahedral stars are condensed into layers of such tetrahedra, and further Tl(2) dumbbells and the potassium cations also interconnect the stars and layers into a three-dimensional network. The former anionic Tl(8) subunits clearly resemble those in the heteroatomic 3-D structure of cubic Cr(3)Si before their augmentation with bridging atoms. The compound is metallic (rho(270) = 22.6 micro omega x cm, alpha = 0.0023 K(-)(1)) and shows Pauli-like paramagnetic susceptibility (chi(296) = 1.1 x 10(-4) emu/mol). EHTB calculations illustrate the importance of Tl p-orbital bonding, the positive Tl-Tl overlap populations up to E(F), and greater strengths of the Tl-Tl bonding between and about the surface of the augmented Tl(12) units. Cations between the thallium layers play specific and important roles in the structure. 相似文献
958.
The m6A‐RNA modification is a dynamic and reversible process, which has emerged as a new RNA code for the regulation of gene expression. The functional network of methyltransferases (writers), demethylases (erasers), and binding proteins (readers) modulate the level of m6A modification. Dysfunction of RNA methylation has been associated with various fundamental biological processes and human diseases. Herein, we briefly introduce an understanding‐enabled manipulation on m6A‐RNA modification with an emphasis on the use of small‐molecule intervention. 相似文献
959.
960.
Shao-Min Zhou Xiang-Min Meng Xia Fan Shuit-Tong Lee Shi-Kang Wu 《Journal of solid state chemistry》2005,178(1):399-403
Based on sonochemical technique, large-scale PbS nanobelts are successfully synthesized in the mixed solution of PbCl2 and Na2S2O3. These nanobelts are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), selected area electronic diffraction, energy dispersive X-ray spectroscopy, and high-resolution TEM. The as-synthesized PbS nanobelts have width of about 80 nm, length up to several millimeters, and width-to-thickness ratio of about 5. In addition, the growth mechanism of PbS nanobelts is suggested. 相似文献