温控分子动力学研究微管蛋白活性肽链的折叠机制

运用温控和常温分子动力学方法, 研究了微管蛋白活性部位Pep1-28肽链的折叠机制, 总模拟时间为380.0 ns. 对于温控分子动力学, 逐渐降温可以清晰显示Pep1-28肽链的折叠途径, 发生明显折叠的温度约为550 K, 其折叠和去折叠可逆机制为U(>1200 K)←→I1(1200-1000 K)←→I2(800 K)←→I3(600 K)←→I4(450 K)←→F1(400 K)←→F2(300 K), 其中U为去折叠态构象, I1、I2、I3和I4是折叠过程中的四个重要的中间态构象, F1和F2是两个结构相近的折叠态构象. 对于常温(300 K)分子动力学, 其构象转变和折叠过程相当迅速, 很难观察到有效、稳定的中间态构象. 尤其引人注意的是, 其折叠态结构陷入了能量局域极小点, 与温控(300 K)的有较大差异, 两者能量差高达297.53 kJ·mol-1. 可见, 温控分子动力学方法不仅清晰地显示多肽和蛋白质折叠过程的重要中间态构象, 为折叠和去折叠机制提供直接、可靠的依据, 而且还有助于跨越较高的构象能垒, 促使多肽和蛋白质折叠以形成全局能量最低的稳定结构.     

Nucleation of crystallization in molten isotactic polybutene-1

Droplet experiments have been performed on polybutene-1. It was found that this polymer can be cooled to room temperature without homogeneous nucleation of crystallization. It was also found that when the polymer was heterogeneously nucleated, form I (as well as form II) could be crystallized directly from the melt. The melting point of droplets crystallized in form I near room temperature decreased with increasing crystallization temperature, while the melting point of the droplets crystallized in form I at the highest temperatures increased with increasing crystallization temperature. There was a broad minimum at about 60°C. in the melting point versus crystallization temperature curve.     

DSC and adiabatic calorimetry study of the polymorphs of paracetamol

Monoclinic (I) and orthorhombic (II) polymorphs of paracetamol were studied by DSC and adiabatic calorimetry in the temperature range 5 - 450 K. At all the stages of the study, the samples (single crystals and powders) were characterized using X-ray diffraction. A single crystal → polycrystal II→ I transformation was observed on heating polymorph II, after which polymorph I melted at 442 K. The previously reported fact that the two polymorphs melt at different temperatures could not be confirmed. The temperature of the II→I transformation varied from crystal to crystal. On cooling the crystals of paracetamol II from ambient temperature to 5 K, a II→ I transformation was also observed, if the 'cooling-heating' cycles were repeated several times. Inclusions of solvent (water) into the starting crystals were shown to be important for this transformation. The values of the low-temperature heat-capacity of the I and II polymorphs of paracetamol were compared, and the thermodynamic functions calculated for the two polymorphs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal characterization of iron oxide powders by emanation thermal analysis

Emanation thermal analysis (ETA) using a surface-impregnation method of Ra-226 nuclide was applied for the thermal characterization of near-surface of iron oxide powders with various preparation histories in the heating and grinding treatments. Peaks I and II appeared at the temperature regions lower and higher than 0.4 – 0.5 T_m, respectively, where T_m is a melting temperature (K) of powders. Further, peak I′ appeared at the temperature region of 0.4 – 0.5 T_m. The appearance of peak I was explained by the mechanochemical effects due to the grinding treatment, and it disappeared in the repeated run. The shift of peak II 900°C to 1000°C in the repeated run was explained by the orderingeffect of crystal lattice due to the heating treatment. The behavior of peak I′ was complicated.     

Microscopic inhomogeneities in weakly-charged temperature sensitive polymer gels and solutions

A comparison of small-angle neutron scattering (SANS) intensity functions, I(q), was made between gels and solutions of poly(N-isopropyl acrylamide-co-acrylic acid) (NIPA/AAc), where q is the magnitude of the scattering vector. I(q)'s were strongly dependent on polymer concentration as well as temperature. At low temperatures, I(q)'s for both gels and solutions were similar to each other and were monotonous decreasing functions. However, at high temperatures above θ, the so-called theta temperature of poly-NIPA in aqueous solution, both had a distinct peak and a significant difference appeared in I(q) due to the presence or absence of crosslinks. Origins of the peak and the differences in I(q) are discussed.     

镍负载硅酸铝催化剂上丙烯齐聚反应 3: 镍离子与丙烯分子的相互作用

为了探明在Ni(II)/SiO2-Al2O3催化剂上丙烯齐聚反应诱导期的成因及活性中心的本质, 考察了反应过程中镍离子与丙烯分子的相互作用, 发现反应诱导期随着催化剂预抽空温度的升高而缩短, 也随着丙烯预处理及反应温度的升高而缩短。用ESR、XPS法跟踪考察发现, 随着丙烯在催化剂上反应的进行, 首先Ni(II)被丙烯还原成Ni(I)离子。之后, 丙烯与Ni(I)配位形成不饱和配位离子, 形成齐聚反应表面活性中间体, 并且在反应过程中, 二、三聚产物也可与Ni(I)离子配位, 形成三、、四聚反应面活性中间体。结果表明在Ni(II)/SiO2-Al2O3催化剂上Ni(I)离子是丙烯齐聚反应的活性中心。     

A dynamic covalent, luminescent metallopolymer that undergoes sol-to-gel transition on temperature rise

The condensation of linear diamine and dialdehyde subcomponents around copper(I) templates in the presence of bulky trioctylphosphine ancillary ligands gave a linear, conjugated polymeric material in DMSO solution. This polymer solution was observed to undergo sol-to-gel transition as the temperature was raised to 140 °C, in contrast with the behavior of most gel-forming polymers, which do so upon cooling. We attribute the sol-to-gel transition to the formation of Cu(I)N(4) cross-links as the equilibria 2[Cu(I)N(2)P(2)] ? [Cu(I)N(4)] + [CuP(n)](+) + (4 - n)P favor the right-hand side at higher temperatures. The material was also observed to exhibit thermochromism and photoluminescence, with the color and intensity of both absorption and emission exhibiting temperature dependence. This material thus responds predictably to combinations of stimuli (heat, light, mechanical shear) in an interconnected way, as is required to generate complex function.     

Subject index

Thermal decomposition of an intimate mixture of thallium(I) perchlorate and chromium(III) oxide revealed that chromium(III) oxide lowers the decomposition temperature of thallium(I) perchlorate and is oxidized into hexavalent state to give thallium(I) dichromate. The thermal decomposition was followed by constant temperature heating, thermogravimetry and differential thermal analysis. The reaction products were characterized by chemical analysis, X-ray diffraction and infrared spectral measurements.     

Diiron carbonyl complexes possessing a {Fe(II)Fe(II)} core: synthesis, characterisation, and electrochemical investigation

Two diferrous complexes, [Fe(2)(μ-SCH(2)CH(3))(3)(CO)(5)I] and [Fe(2)(μ-SCH(2)CH(2)CH(3))(3)(CO)(5)I] were synthesised via reaction of a monoiron carbonyl precursor, [Fe(CO)(4)I(2)], with ethanethiolate and propanethiolate, respectively. The complexes were fully characterised using spectroscopic techniques, for instance, FTIR and NMR. Their crystal structures were determined using single crystal diffraction analysis. Electrochemical reduction of these complexes are temperature-dependent. At room temperature, the diferrous complexes undergo one-electron reduction. The reduction-initiated cleavage of one bound thiolate and one iodide as a radical, takes the oxidation states of the diiron core from {Fe(I)Fe(II)} to {Fe(I)Fe(I)}. This reduction-initiated transformation can be suppressed by lowering the temperature to 195 K, further reduction of the monoanion was observed at a potential very close to that of the first reduction, which is analogous to the mechanism observed for diiron complexes with a core of {Fe(I)Fe(I)}.     

Plastic and glassy crystal states of caffeine

The present paper focuses on the high temperature form I of caffeine and on its low temperature metastable form. Structural, dynamic, and kinetic information has been obtained by X-ray, dielectric, and calorimetric investigations. This study shows the following features: (1) The high temperature phase (I) of caffeine is in a state of dynamically orientationally disordered crystalline state (so-called "plastic, or rotator, phase"). (2) This high-symmetry hexagonal phase can be maintained at low temperature in a metastable situation. (3) Under deep undercooling of form I a glass transition occurs in the disordered crystalline state near room temperature. It is associated with the orientational freezing in of the molecular motions. Otherwise stated, the metastable state I enters into a nonergodic unstable state, so-called "glassy crystal" state. These findings rationalize the difficulties seen with caffeine in pharmaceutical science.     

Identification of radical structures on 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5‐dimethylbenzimidazoliumsilver(I)bromide exposed to gamma rays: an EPR study

1‐Pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide and their Ag⁺ complexes were synthesized and their polycrystal forms were produced by recrystallization in dichloromethane/Et₂O solvent system. Structural determinations were carried out by ¹H NMR and ¹³C NMR with a Varian 400 NMR system using tetramethylsilane as internal standard and CDCl₃ as solvent. The disappearance of acidic N‐heterocyclic carbene proton showed the formation of Ag(I) complexes. Also, elemental analyses were carried out. Electron paramagnetic resonance (EPR) measurements were performed to determine the formed radical structure on the samples irradiated at the room temperature for 72 h by using ⁶⁰Co‐source with dose rate of 0.680 kGy. The EPR measurements were carried out in the temperature range of 200 K–450 K. Identical radicals were determined on the irradiated compounds. It was observed that the shapes of the spectra of the samples were independent of the temperature but, the resonance line intensities changed linearly with the temperature. Also, it was detected that the free radical on the 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide is not stable compared to that on the 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide. Copyright © 2016 John Wiley & Sons, Ltd.     

钙离子和PH值对海藻酸钠液流变性能影响

海藻酸钠溶液是假塑性体系, 它的粘度与体系的浓度、温度、PH值和外加盐类的浓度等有密切关系, 并有一定触变性, 在某个钙离子浓度范围内, 体系出现了负触变性,对此用配离子的"屏蔽"现象进行了解释。     

On the temperature dependence of amide I frequencies of peptides in solution

The temperature dependence of the amide I vibrational frequencies of peptides in solution was investigated. In D2O, the amide I' bands of both an alpha-helical oligopeptide, the random-coil poly(L-lysine), and the simplest amide, N-methyl acetamide (NMA), exhibit linear frequency shifts of approximately 0.07 cm(-1)/degrees C with increasing temperature. Similar amide I frequency shifts are also observed for NMA in both polar (acetonitrile and DMSO) and nonpolar (1,4-dioxane) organic solvents, thus ruling out hydrogen-bonding strength as the cause of these effects. The experimental NMA amide I frequencies in the organic solvents can be accurately described by a simple theory based on the Onsager reaction field with temperature-dependent solvent dielectric properties and a solute molecular cavity. DFT-level calculations (BPW91/cc-pVDZ) for NMA with an Onsager reaction field confirm the significant contribution of the molecular cavity to the predicted amide I frequencies. Comparison of the computations to experimental data shows that the frequency-dependent response of the reaction field, taken into account by the index of refraction, is crucial for describing the amide I frequencies in polar solvents. The poor predictions of the model for the NMA amide I band in D2O might be due, in part, to the unknown temperature dependence of the refractive index of D2O in the mid-IR range, which was approximated by the available values in the visible region.     

丙烯腈与衣康酸的溶液共聚合

为了获得性能优越的碳纤维,聚丙烯腈（ＰＡＮ）纤维已经成为应用最广泛的前驱体之一［１］．事实表明,碳纤维的性能在很大程度上依赖于前驱体纤维的性能［１］,利用丙烯腈与少量其它单体进行共聚,可使聚合物的力学性能（机械强度、弹性、塑性等）得到明显的改善．由已报道的文章可知,与丙烯腈共聚时所采用的其它单体主要有丙烯酸、甲基丙烯酸、丙烯酸酯、丙烯酰胺、衣康酸等［２～７］,所采用的溶剂主要为二甲基甲酰胺（ＤＭＦ）．对在二甲基亚砜（ＤＭＳＯ）为溶剂中的聚合条件,并未见详细报道．本文以ＤＭＳＯ为溶剂,用偶氮二异丁…     

Structure and some reactions of coriose

Coriose was obtained in a higher yield from the root of Coriaria japonica. The structure, -altro-3-heptulose (I) was determined by the sodium borohydride reduction which yielded volemitol (II) and -glycero- -altro-hepitol (IV). Other reactions in agreement with this structure (I) were also carried out: The oxidative degradation of coriose in cold alkali produced a pentanolactone syrup which was reduced to ribose, while the degradation at elevated temperature gave a hexanolactone syrup which yielded ribose on treatment with ferric acetate-hydrogen peroxide. The rearrangement of coriose in alkali at room temperature to 2-heptuloses was investigated. Lead tetraacetate oxidation of coriose produced -glyceraldehyde and -glyceric acid.     

Simultaneous determination of bifonazole and tinctures of calendula flower in pharmaceutical creams by reversed-phase liquid chromatography

The aim of this research was to develop and validate a sensitive, rapid, easy, and precise reversed-phase liquid chromatography (LC) method for stability studies of bifonazole (I) formulated with tinctures of calendula flower (II). The method was especially developed for the analysis and quantitative determination of I and II in pure and combined forms in cream pharmaceutical formulations without using gradient elution and at room temperature. The influence on the stability of compound I of temperature, artificial radiation, and drug II used for the new pharmaceutical design was evaluated. The LC separation was carried out using a Supelcosil LC-18 column (25 cm x 4.6 mm id, 5 microm particle size); the mobile phase was composed of methanol-0.1 M ammonium acetate buffer (85 + 15, v/v) pumped isocratically at a flow rate of 1 mL/min; and ultraviolet detection was at 254 nm. The analysis time was less than 10 min. Calibration graphs were found to be linear in the 0.125-0.375 mg/mL (rI = 0.9991) and 0.639-1.916 mg/mL (rII = 0.9995) ranges for I and II, respectively. The linearity, precision, recovery, and limits of detection and quantification were satisfactory for I and II. The results obtained suggested that the developed LC method is selective and specific for the analysis of I and II in pharmaceutical products, and that it can be applied to stability studies.     

Preparation of 1H‐1,2,3‐Triazoles by Cuprous Ion Mediated Cycloaddition of Terminal Alkyne and Sodium Azide

1H‐1,2,3‐triazoles can be prepared in good yield by the reaction of terminal alkyne and sodium azide in the presence of cuprous chloride at a temperature higher than 70°C. The alkyne is unactivated and the reaction has to be carried out under inert gas. At room temperature, the reaction first gives a Cu(I)‐azide complex which is converted to a Cu‐alkyne complex when the temperature is raised to higher than 70°C. The reaction of Cu(I)‐alkyne complex and azide ion dissociated from or coordinated to Cu(I) then gives 1H‐1,2,3‐triazoles.     

Minimum in the temperature dependence of the Kováts retention indices of nitroalkanes and alkanenitriles on an apolar phase

The Kováts retention indices (I) of 1-nitroalkanes and alkanenitriles were determined on polydimethylsiloxane and Innowax (polyethylene glycol) columns in a wide temperature range. The temperature dependence of the retention indices exhibits a definite minimum for the early members of the homologous series. The position of the minimum shifts to lower temperatures with increasing carbon atom number of the solute. The thermodynamic explanation of an extreme in the I vs. T function is the higher solvation heat capacities of nitroalkanes and alkanenitriles relative to those of the reference n-alkanes, owing to the deviation from the ideal state in the solution. A novel equation was derived which describes the minimum in the I vs. T function, too.     

Electrical conducting and magnetic properties of (ethylenedithiotetrathiafulvalenothioquinone-1,3-diselenolemethide)2.FeBr4 (GaBr4) crystals with two different interlayer arrangements of donor molecules

Two donor molecules newly synthesized, dimethylthio- and ethylenedithio-tetrathiafulvalenothioquinone-1,3-diselenolemethides (1 and 2), were used to prepare their charge-transfer (CT) salts with a magnetic FeBr(4)(-) counteranion. For 1, a low electrical conducting 1:1 salt (1.FeBr(4)) was obtained, in which molecules of 1 are tightly dimerized in a one-dimensional (1D) stacking column. On the other hand, 2 gave a 2:1 salt (2(2).FeBr(4)) as two different kinds of plate crystals (I and II). Both I and II possess similar stacking structures of molecules of 2 in each 1D column with a half-cut pipelike structure along the c axis. However, for I, the stacking columns are aligned in the same direction along the a and b axes, while for II they are in the same direction along the a axis, but in the reverse direction along the b axis, resulting in the difference in the relative arrangement of molecules of 2 and FeBr(4)(-) ions between the two crystals. The room-temperature electrical conductivities of the single crystals of I and II were 13.6 and 12.7 S cm(-)(1), respectively. The electrical conducting behavior in I was metallic above 170 K but changed to be semiconducting with a very small activation energy of 7.0 meV in the temperature range 4-170 K. In contrast, II showed the semiconducting behavior in the whole temperature range 77-285 K. The corresponding nonmagnetic GaBr(4)(-) salts with almost the same crystal structure as I and II showed definitively different electrical conducting properties in the metal to semiconductor transition temperature in I as well as in the magnitude of activation energy in the semiconducting region of I and II. The interaction between the d spins of FeBr(4)(-) ions was weak and antiferromagnetic in both I and II, but the magnitude of the spin interaction was unexpectedly larger compared with that in the FeBr(4)(-) salt of the corresponding sulfur derivative of 2 with closer contact between the neighboring FeBr(4)(-) ions. These electrical conducting and magnetic results suggest a significant interaction between the conducting pi electrons and the d spins of FeBr(4)(-) ions located near the columns or layers.