Effect of hydrocolloids on starch thermal transitions,as measured by DSC

Differential scanning calorimetry (DSC) was used to analyze the influence of different hydrocolloids (xanthan, guar, and locust bean gums, carboxymethylcellulose and sodium alginate) on the gelatinization of corn starch in systems with starch concentration ranging between 0.1 and 0.7 g starch/g mixture. The reduction of available water produced a shift in gelatinization temperature, especially of the conclusion temperature. The effect was more marked for ionic hydrocolloids. The influence of hydrocolloids on glass transition temperature (T _g) of gelatinized starch suspensions and on the glass transition temperature of the maximally freeze-concentrated solute/unfrozen water matrix (T _g) was also studied.T _g onset values ranged between –4.5 and –5.5C for corn starch pastes with and without hydrocolloids. Those hydrocolloids that increased the viscosity of the unfrozen matrix inhibited additional ice formation during thawing (devitrification).Starch concentration and final heating temperature were found to be relevant factors affecting the kinetics of amylopectin retrogradation during frozen storage at –4C. Xanthan gum failed to prevent amylopectin retrogradation; this observation could be attributed to the fact that gums act outside the starch granule, while amylopectin retrogradation takes place within the granule.     

SNAP-tag蛋白标签技术与荧光分析法在蛋白原位分析中的联合应用

为将生物体内微观的蛋白行为可视化并以宏观信号呈现出来对蛋白进行实时、动态分析，借助SNAP-tag蛋白标签技术与有机小分子荧光染料，构建了一系列用于活细胞内实时监测目标蛋白的免洗荧光探针。标签蛋白SNAP-tag能够特异性识别探针中的苄基鸟嘌呤，从而使目标蛋白共价连接上荧光团（萘酰亚胺），携带上荧光信使。此外，由于萘酰亚胺从水环境中被牵引至SNAP-tag蛋白的疏水空腔，其荧光信号呈现出2~13倍的增强。通过SNAP-tag标签蛋白与目标蛋白的融合，该荧光探针实现了对活细胞内线粒体蛋白CoX8A及核内蛋白H2B特异性识别，在免洗条件下完成了对目标蛋白的实时追踪及原位分析。     

Surface cavities produced by high‐dose nitrogen ion implantation into silicon

Nitrogen ion implantation (24 keV, 4.6 × 10¹⁷ cm^?2) into (100) a p‐type silicon wafer material and a subsequent electron beam annealing at 1100 °C for 15 s under high vacuum conditions leads to the formation of an uneven surface in the implanted region caused by nitrogen bubbles beneath the surface. Annealing at 1200 °C for 300 s results in surface cavities with a mean diameter of 350 nm and a surface coverage of 3–4% and an average depth of ～60 nm. Nuclear reaction analysis reveals that the nitrogen concentration in the as‐implanted state exceeds 57 at%, the value of stoichiometric Si₃N₄. Annealing at 1100 °C for 15 s slightly reduces the nitrogen peak concentration, whereas annealing at 1200 °C for 300 s induces a significant alteration to the shape of the nitrogen depth profile coupled with the lowering of the concentration close to the stoichiometry of Si₃N₄. The results present a new method of producing sub‐micrometre cavities embedded in a thin silicon nitride film on wafer silicon which may lead to novel micro‐electronic and biotechnology applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Time and temperature-based study for the production of high T C phase by sol-gel technique in Pb-bscco system

The high T_C superconducting phase Bi₂Sr₂Ca₂Cu₃Ox (2223) in the Pb-BSCCO system has been produced by EDTA-gel processing using nitrate solutions. The precursor has heated in two stages, at 300 and 800°C each for 2 h, to avoid the burning of the important species involved in the final product. The effects of time (6 to 48 h) and temperature (845 and 855°C) on the formation of the 2223 phase have been studied by sintering the samples in air. Thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and a vibrating sample magnetometer (VSM) have been employed to investigate the powder produced at different stages of decomposition, oxidation and formation of sintered materials from the powders. The volume-fraction of the 2223 phase at 845°C increases with time, the maximum value of the 2223 phase was obtained at 120 h. It has been observed that the formation of the high T_C phase is remarkably enhanced at the temperature of the endothermic peak of the DTA curve. The best result has been obtained in the sample sintered for 24 h at the temperature 855°C (endothermic peak). This also indicated that at 855°C, the large volume-fraction of 2223 phase with T_C 113 K grew in short time and as the sintering time increased, it decomposed into the Bi₂Sr₂CaCu₂Ox (2212) phase and other phases.     

手性锌卟啉对咪唑类客体分子识别的构象研究

Chiral recognition is an attractive subject in the area of host-guest chemistry. Conformation study is performed to understand chiral recognition of zinc(Ⅱ) porphyrin with imidazole derivatives on a molecular level. The molecular recognition of three novel chiral zinc porphyrin(1-3) with four types of imidazole derivatives was studied. The conformation searching of this host-guest system was studied by using simulated annealing method on the basis of Tripos force field. The different minimal energy conformation of imidazole combind with porphyrin was studied. The quantum chemistry calculation was performed to calculate the single-point energies of the host-guest system. The minimal energy conformation of ZnT(o-BocAla)APP (3)-Im showed that Im attaching from the single-side chain of the host had the reasonable configuration than that from the three-side chain. The former also had the lower energy than the latter. And the quantum chemistry calculation results of orbital energy, ΔE_L-H, and atomic net charge revealed the same way. The results illumate that combination oriention of the host-guest system is the single chain of the hosts.     

Cathodoluminescence Depth Profiling in SiO2:Ge Layers

 For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary electron energy E ₀ = 2…30 keV. Applying a constant incident power regime (E ₀·I ₀ = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx. Thermally grown SiO₂ layers of thickness d = 500 nm have been implanted by Ge⁺-ions of energy 350 keV and doses (0.5–5)10¹⁶ ions/cm². Thus Ge profiles with a concentration maximum of (0.4 – 4) at% at the depth of d_m≅240 nm are expected. Afterwards the layers have been partially annealed up to T _a = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (λ = 400 nm) of the Ge centers is strongly increased but also the luminescent center profiles are shifted from about 250 nm to 170 nm depth towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm.     

蒙特卡洛模拟退火与距离限制相结合的方法在多肽溶液构象分析中的应用

多维核磁共振技术的飞速发展议得其在生物大分子结构测定方面的应用已经达到可以与【射线晶体学并驾齐驱的地步．蛋白质结构堆积紧密，较适合于用核磁共振方法给出确定的结构．与蛋白质不同的是多肽的柔性较大，在溶液中可能存在多种构象，核磁共振实验给出的只是平均信息＊．利用核磁，（振数据构建分子结构模型常用的方法有距离几何、分子动力学等，在由核磁共振NOESZ得到的距离信息足够多时可以给出较好的结果问．由于多肽本身的特点：柔性较大，由核磁共振得到的距离信息较少等，利用距离几何、分子动力学方法进行构象搜索时容易陷入…     

非水溶剂中铁酞菁的“in—situ”可见紫外光谱电化学

用循环伏安与现场可见紫外光谱电化学方法研究了氯化４－特丁基苯氧基铁酞菁［（ＴｂＰｃ）Ｆｅ（Ⅲ）Ｃｌ］电化学行为．结果表明，在四氢呋喃溶剂中其正电位区经历了两步氧化过程，对应于Ｆｅ（Ⅲ）／Ｆｅ（Ⅳ）以及Ｆｅ（Ⅳ）／阳离子自由基的生成反应，负电位区还原过程经历了Ｆｅ（Ⅲ）／Ｆｅ（Ⅱ），Ｆｅ（Ⅱ）／Ｆｅ（Ⅰ）和Ｆｅ（Ⅰ）／阴离子自由基生成的３个步骤，阐述了配位效应对氧化还原机理的影响．指出Ｆｅ（Ⅳ）不寻常价态的出现，是阴离子Ｃｌ－的轴向配位对超常价态起到稳定作用的结果．     

烟碱型乙酰胆碱受体吡啶基胺类配体的构效关系研究

采用分子动力学模拟退火技术寻找了一类新型烟碱型乙酰胆碱受体吡啶基胺类配体分子的优势构象，用分子力学方法进行了结构优化，再用半经验量子化学方法中的AM1方法进一步优化，并做了电子结构计算.用计算所得物化参数对配体亲和性进行多元线性回归分析，回归结果表明：化合物pKi值与分子最低空轨道能量(ELUMO)、吡啶基所带总电荷(Qp)及分子构象相关.根据计算结果对该类化合物与受体的作用机制和作用位点进行了讨论.     

Singular perturbed Markov chains and exact behaviors of simulated annealing processes

We study asymptotic properties of discrete and continuous time generalized simulated annealing processesX(·) by considering a class of singular perturbed Markov chains which are closely related to the large deviation of perturbed diffusion processes. Convergence ofX(t) in probability to a setS ₀ of desired states, e.g., the set of global minima, and in distribution to a probability concentrated onS ₀ are studied. The corresponding two critical constants denoted byd and withd are given explicitly. When the cooling schedule is of the formc/logt, X(t) converges weakly forc>0. Whether the weak limit depends onX(0) or concentrates onS ₀ is determined by the relation betweenc, d, and . Whenc>, the expression for the rate of convergence for each state is also derived.