Assessment of enveloping distribution sampling to calculate relative free enthalpies of binding for eight netropsin-DNA duplex complexes in aqueous solution

The performance of enveloping distribution sampling (EDS) simulations to estimate free enthalpy differences associated with seven alchemical transformations of A-T into G-C base pairs at the netropsin binding site in the minor groove of a 13-base pair DNA duplex in aqueous solution is evaluated. It is demonstrated that sufficient sampling can be achieved with a two-state EDS Hamiltonian even for large perturbations such as the simultaneous transformation of up to three A-T into three G-C base pairs. The two parameters required to define the EDS reference state Hamiltonian are obtained automatically using a modified version of a scheme presented in earlier work. The sensitivity of the configurational sampling to a variation of these parameters is investigated in detail. Although for relatively small perturbations, that is, one base pair, the free enthalpy estimate depends only weakly on the EDS parameters, the sensitivity is stronger for the largest perturbation. Yet, EDS offers various convenient measures to evaluate the degree of sampling and thus the reliability of the free enthalpy estimate and appears to be an efficient alternative to the conventional thermodynamic integration methodology to obtain free energy differences for molecular systems.     

治疗胆石症蒙药苏斯—12中多种元素的ICP-AES法测定及分析

通过分析治疗胆囊炎、胆石症的蒙药苏斯—12中微量元素含量,探讨蒙药苏斯—12的药效与微量元素含量的关系。应用高压密封微波消解、电感耦合等离子体原子发射光谱法(ICP-AES)对蒙药苏斯—12进行微量元素含量分析。在蒙药的配制及整体研究工作中发现它们含有多种氨基酸和丰富的微量元素,实验结果表明：苏斯—12中含有丰富的微量元素,尤其Ca,Al,Mg,Fe,Sr,Mn,Zn,Cu等元素的含量比较高,而Pb,Cd,As等元素含量相对低,都低于国家限定值。加标回收率在94.63%～106.40% 之间,相对标准偏差RSD≤3.35 %,检出限在≤0.009 μg·L-1。蒙药苏斯—12有效控制和治疗胆囊炎、胆石症,总有效率达91.2%和100%,蒙药苏斯—12中的微量元素与药效之间有密切的关系。     

四川泸定县泥石流灾害成因、特征与防治建议

泸定县地处川西高原与四川盆地的过渡地带,地质环境条件复杂,分布泥石流沟127条,发育密度054条·10km-2。在遥感解译和地面调查基础上,论述了泸定县泥石流灾害成因、发生特征、危害和发展趋势,提出了相关防治建议。(1)成因表现为复杂的断裂构造导致流域内松散物源丰富,较大的相对高差提供了良好势能条件,而汛期集中强降雨则提供了动能条件,且雨量条件中当日雨量与前期有效降雨量之间具有幂函数关系; (2)发生特征表现出典型的空间群发性(包括2005-06-30群发性泥石流、2005-08-11群发性泥石流和2006-07-14群发性泥石流)与时间的夜发性; (3)危害方式主要包括淤埋、冲毁、侵蚀、堵河4种,泥石流已造成74人死亡; (4)发展趋势表现为泥石流沟多处于形成期和发展期(113条,占89%),发生的年际准周期由20a缩短至不足10a,且发生条(次)由4条(次)增加至44条次(2005年); (5)泸定县泥石流防治的突出问题表现为城镇泥石流问题、泥石流堵塞主河问题、风景区泥石流问题与冲沟泥石流问题,建议通过科学规划、风险防御体系构建、土木工程治理、监测预警等措施予以防御。     

Monte Carlo模拟研究抗体-抗原复合物生长的标度行为

通过Monte Carlo模拟方法对抗体-抗原复合物在等活性和非等活性条件下生长的标度行为进行了研究. 模拟所用算法的有效性通过在等活性条件下的模拟结果与解析结果之间的一致性得以证明. 在模拟中, 主要考察了抗体-抗原复合物的数量分布函数、重均聚合度以及特征关联长度在临界点附近的标度行为, 给出相应的标度指数, 并以其检验溶胶-凝胶相变的广义标度律. 研究结果表明, 非等活性对抗体-抗原复合物的生长具有显著影响, 可为临床免疫分析提供相应的理论线索.     

Resonance estimates of \mathcal{O}(p^6) low-energy constants and QCD short-distance constraints

Starting from the study of the low-energy and high-energy behaviors of the QCD three-point functions , and , several low-energy constants of the chiral Lagrangian are evaluated within the framework of the lowest meson dominance (LMD) approximation to the large- limit of QCD. In certain cases, values that differ substantially from estimates based on a resonance Lagrangian are obtained. It is pointed out that the differences arise through the fact that QCD short-distance constraints are in general not correctly taken into account in the approaches using resonance Lagrangians. We discuss the implications of our results for the counterterm contributions to the vector form factor of the pion and to the decay , and for the pion–photon–photon transition form factor. Received: 4 June 2001 / Published online: 31 August 2001     

二茚基稀土胺化物催化丙烯腈聚合

用二茚基稀土胺化物Ind2LnN(i-Pr)2(Ln=Y,Yb)作为单组分催化剂催化丙烯腈聚合,研究了催化剂用量、单体浓度及聚合温度对标题化合物的催化活性和所得聚丙烯腈的分子量的影响。提高聚合发应温度可明显提高催化活性,当聚合温度达50℃,单体浓度为5.1mol     

A Study of the Probe Effect on the Apparent Image of Biological Atomic Force Microscopy

The atomic force microscopy (AFM) possesses high spatial resolution and it is compatible with liquid environments. AFM can provide possibility to study a wide range of biological problems at the molecular level and acquire topological information at nanometre resolution under physiological conditions1,2. However, a major problem for image reconstruction of biological specimens is that structures of most biological molecules are very soft and delicate, which could be easily deformed and dama…     

二茚基钇-铝双金属配合物催化丙烯腈聚合

丙烯腈 (AN)聚合通常采用自由基和阴离子聚合两种 .它们存在催化剂活性低 ,用量大等缺点 .关于丙烯腈的配位聚合研究报道则较少 .最近 ,有报道发现二价稀土化合物可以催化丙烯腈聚合 ,但催化活性较低[1 ,2 ] .本文以二茚基钇 -铝双金属配合物 (C9H7) 2 Y(μ- Et) 2 Al Et2(以下以 Y- Al代表 )为 AN聚合催化剂 ,发现它单独可以催化 AN聚合 .当外加酚钠(Ph ONa)时 ,可以大大提高聚丙烯腈 (PAN)的产率及分子量 .研究了单体浓度、催化剂浓度、温度、时间等对 AN聚合的影响 ,并对其引发机理进行了研究 .Y- Al的合成及聚合方法见文献 [3…     

非线性Af—Bg型自由基交替共聚反应的固化理论

利用高分子反应统计理论,给出了非线性Ａｆ－Ｂｇ型自由基交替共聚反应的溶胶－凝胶分配方程和反应体系的凝凝胶化条件,这些结果是进一步研究与凝胶网络性能相关的网络结构参数的基础。     

非线性A_f-B_g型自由基交替共聚反应的固化理论

利用高分子反应统计理论 ,给出了非线性Af-Bg 型自由基交替共聚反应的溶胶 -凝胶分配方程和反应体系的凝胶化条件 ,这些结果是进一步研究与凝胶网络性能相关的网络结构参数的基础