An investigation into the construction of molecular models by the template joining method

Summary The results of a wide-ranging investigation into some of the different methods available for performing the joining of templates to build molecular models show that the choice of algorithm can significantly affect the quality of the results obtained, and different algorithms are most suited to particular categories of join.     

Thermotropic gelation of ovalbumin 1. Viscoelastic properties of gels as a function of heating conditions and protein concentration at various pH values

A study has been undertaken of stress relaxation in ovalbumin thermotropic gels with a concentration of 8–20%, depending on time and temperature of heating (respectively, 20–60 min, 70°–110°C), at pH 2.5–10.0. In all instances, the dependence of the initial gel elasticity modulus on heating has a single maximum. Gelation conditions corresponding to this maximum are considered optimal. Optimal gelation time is 30 min, regardless of pH. On the other hand, the optimal heating temperature depends on pH. To the right and left of the isoelectric point of protein (2.5pH<4.0 and 5.5G) of gels on heating conditions, pH and protein concentration (X ₁,X ₂,X ₃,X ₄), as well as on time of relaxation (t) may be generally described asG(X ₁,X ₁,X ₁,X ₁,t)=G _e(X ₁,X ₂,X ₃,X ₄)f(t), whereG _e is the equilibrium value of the elasticity modulus, and f(t) the relaxation function. Thus, a change in the parameters only affects the value of the equilibrium elasticity modulus, and exerts no effect on the relaxation time spectrum. For this reason, all the relaxation curves obtained may be transformed into two normalized relaxation functions:f(t)=f(t)/f(1)=G(X ₁,X ₂,X ₃,X ₄,t)/G(X ₁,X ₂,X ₃,X ₄, 1)Each of these normalized functions corresponds to one of the homologous groups. Rheological similarity of gels in each homologous group evidently points to their structural similarity. Invariance of the gel relaxationproperties with regard to protein concentration, leads to a concentration dependence of the equilibrium modulus at various pH values. These dependences are curvilinear on a double logarithmic scale. The slope of the curve exceeds 2 in the entire concentration interval studied. In other words, the dependences obtained cannot be described by the usual law of squares. On the other hand, they adequately match Hermans theoretical relation for a network formed by random association of identical polyfunctional particles without cyclization. This simple model evidently gives a true picture of the major regularities of thermotropic gelation for ovalbumin. An agreement between this theory and experiment was achieved for a protein concentration ofC ^*=6.0±1.0% at the gel point regardless of pH. Invariance of gelpoint position with regards to pH demands further confirmation.List of symbols T _h,t _h heating temperature and time - T _h ^* ,t _h ^* optimal heating temperature and time - C protein concentration - C ^* protein concentration in gel-point - G relaxation modulus - G _e equilibrium modulus - f(t) relaxation function - t time of relaxation - f(t) normalized relaxation function - fT _A (t), f _B (t) normalized relaxation functions of groups A and B - G ₁ T _h,t _h-reduced modulus - G ₂ T _h,t _h, pH-reduced modulus - G ₃ C-reduced modulus - b ₁ T _h, t_h reduction parameter of modulus - b ₂ pH reduction parameter of modulus - b ₃ C reduction parameter of modulus - W_g gel-fraction     

水热法合成K0.5Bi0.5TiO3纳米陶瓷粉体

K_0.5Bi_0.5TiO₃(KBT)nanocrystalline particles were hydrothermally synthesized from Bi(NO₃)₃·5H₂O, TiO₂ and KOH. The crystal phase, chemical composition and microstructure were characterized by XRD, XRF, Raman scattering spectroscopy and TEM. The results indicated that the products were pure perovskite structured K_0.5Bi_0.5TiO₃ with chemical stoichiometry and perovskite structure. The TEM observation revealed that the particles possessed a feature of cubic shape and a nano-scale of about 40 nm. The KBT ceramics sintered at 1 040 ℃ from hydrothermal powders show higher density and better electric properties than that prepared by a solid-state reaction method.     

土壤重金属生物有效性的评价方法

土壤重金属污染已成为人们广泛关注的全球性的环境问题之一。重金属生物有效性已成为污染生态学研究的前沿。对国内外土壤重金属生物有效性评价方法的研究进展作了简要综述，并对今后的研究作了展望。     

Au/Ag复合纳米笼在表面增强拉曼光谱中的应用

表面增强拉曼光谱（SERS）技术是一种基于贵金属纳米结构基底对被检测物进行高灵敏度检测的一种方法.具有特殊纳米结构的贵金属表面受到激光的照射时，金属表面的自由电子会受到极大的振荡，当入射光频率与振荡频率相近时，则会发生表面等离子体共振现象（SPR），使金属表面的局域电场强度极大增强，入射光强度和散射光强度都得到成倍的放大，从而使吸附在贵金属纳米结构表面的分子的拉曼散射信号得到有效的增强.使用NaBH₄还原-酸刻蚀模板法，制备了八面体Au/Ag复合纳米笼，其形貌规整，尺寸均匀约为600 nm，无Cu₂O模板的残留，Au元素均匀负载在Ag纳米笼上，质量分数约为16.8%；Au/Ag复合纳米笼的紫外可见吸收峰相对于Ag纳米笼发生了红移，更重要的是，Au和Ag元素协同赋予了复合纳米笼超高的SERS灵敏度和重复性，Au/Ag复合纳米笼实现了对罗丹明6G的痕量检测（5×10^-14 mol/L），通过时域有限差分法（FDTD）模拟证实：这主要归因于等离子共振作用产生的高电磁场强度；此外，Au元素的加入使Au/Ag复合纳米笼具有优异的抗氧化性和化学稳定性，即使在1%的H₂O₂溶液中浸泡3 h，仍然能够保持优异的SERS性能.八面体Au/Ag复合纳米笼有望成为一种具有应用前景的高灵敏度、高稳定性的SERS基底.     

Crystal structure of hexagonal SrAl2O4 at 1073 K

The crystal structure of SrAl₂O₄ at 1073 K was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was hexagonal (space group P6₃, Z=6) with a=0.89260(3) nm, c=0.84985(2) nm and V=0.58639(3) nm³. Final reliability indices were R_wp=7.87%, R_p=5.87% and R_B=4.19%. The [AlO₄] tetrahedra are linked to form trigonally distorted rings and they are joined in layers. These layers are stacked with a two-layer repeat and connected by the tetrahedral apices. All of the Sr atoms occupy the centers of the rings when viewed along the c-axis. The structure is described as a stuffed derivative of tridymite.     

丙烯环氧化制环氧丙烷Fe-Al-P-O催化剂的研究

用溶胶-凝胶法制得了Fe-Al-P-O催化剂，采用IR、XRD、TEM、BET、TPR和微反等技术研究了催化剂的物化性质和反应性能。实验结果表明，Fe1/2-Al1/2-PO4由10 nm左右 FePO4和AlPO4微晶组合而成，其晶格氧的活泼性大于单纯FePO4，AlPO4在Fe1/2-Al1/2-PO4中起到分散FePO4微晶的作用；Fe1/2-Al1/2-PO4的反应性能与原料气组成密切相关，丙烯与O2的选择氧化产物主要是丙烯醛，原料气中加入H2后，反应产物以环氧丙烷为主，同时还有部分丙烯醛，原料气中引入水蒸气后，可进一步增加环氧丙烷的选择性及减少丙烯醛的产率；在0.1 MPa、200 ℃、C3H6/O2/H2/H2O/N2=1∶1∶1∶1∶6（mol比）和空速1 200 h－1条件下，丙烯的转化率为8.9％，环氧丙烷的选择性为81.0％。     

相转移催化法合成糖苷化合物

糖苷化合物广泛存在于生物体内，中草药和天然药物中的许多抗病活性化合物也是糖苷化合物。根据糖苷化合物分子结构中的配糖体与糖环碳原子相连的原子类型可把糖苷化合物分为氧苷、氮苷、硫苷和碳苷等。未作特殊说明的糖苷化合物均指氧苷，且配糖体为羧酸的糖苷化合物亦称为糖酯。有关糖苷（酯）化合物和其合成方法的研究很多，其中应用相转移催化法较为常见。我们曾用相转移催化法合成过许多糖酯化合物并对其生理活性进行研究报道。本文在原合成糖酯的基础上通过相转移催化法，选用不同于文献报道催化剂及溶剂体系，     

Quantum scattering LCAC-SW theory studies on reaction probabilities of three-dimensional H + H2 (v, j) → H2 (v′, j′) + H reaction

Upon the Liu, Siegbahn, Truhlar, Horowitz (LSTH) potential energy surface, the reaction probabilities of the three-dimensional (3-D) state-to-state H + H₂ (v, j) →H ₂(v′, j′) + H reaction are calculated with the linear combination of arrangement channels-scattering wavefunction (LCAC-SW) method. In the calculation, the vibration function of H₂ and the radial propagating wave functions are expanded by the real Gauss functions. The calculated threshold energy and the resonating structure are consistent with the results of the accurate quantum scattering calculations, which shows the accuration, simplicity and practicability of the LCAC-SW method. Project supported by the National Natural Science Fondation of China and the Doctoral Foundation of the State Education Commission of China.     

均三氮苯类除草剂结构与活性的理论研究

利用Gaussian03程序包中的B3LYP方法,选择6-31G基组对均三氮苯类除草剂及类似衍生物2-(4-溴苄氨基)-4-甲基-6-三氟甲基-1,3,5-三氮苯进行了量子化学计算,从理论上讨论了它们的空间结构、电子结构特征与活性的关系.计算结果表明:三氮苯环与N(7)和N(8)原子形成了共轭结构,分子活性大小与LUMO轨道的得电子能力以及在LUMO轨道中占主要成分的原子有重要关系.N(7)和N(8)连接单个具有推电子能力的基团,有利于生物活性的提高.对于2-(4-溴苄氨基)-4-甲基-6-三氟甲基-1,3,5-三氮苯中,N(8)和C(9)是重要的活性部位,和传统的均三氮苯类除草剂分子相比,与D1蛋白上不同的氨基酸残基发生了键合作用.