Decomposition of 1-(ω-aminoalkanoyl)guanidines under alkaline conditions

The decomposition of some N^G-(ω-aminoalkanoyl)argininamides, which are key intermediates for the preparation of radiolabeled and fluorescent neuropeptide Y receptor ligands, prompted us to synthesize a small series of simple 1-(ω-aminoalkanoyl)guanidines, and to investigate these model compounds for stability in alkaline buffers. The degradation of acylguanidines was monitored by time resolved UV spectroscopy. The most labile compound, 1-(5-aminopentanoyl)guanidine, decomposed with a half life of 19 s to yield piperidin-2-one (pH 10.4 at 25 °C). In contrast the half life of 1-(6-aminohexanoyl)guanidine is 7.7 h, which is comparable to the hydrolysis of acetylguanidine (t_1/2 = 9.6 h) in alkaline solution.     

Drift tube investigations on the reactions of O 2 + with CH4 and of CO 2 + with NO in various buffer gases

The influence of internal excitation on the reactions of O ₂ ⁺ + CH₄ and of CO ₂ ⁺ + NO has been investigated using a slow flow drift tube. The rate coefficients for these reactions obtained as a function of relative kinetic energy in various buffer gases like He, Ne, Ar, and Kr showed higher values under conditions where the internal excitation of the reactant ions was enhanced. For both reactions the lowest reactivity at all kinetic energies was observed to occur in He, indicating that He is the least effective buffer for collisionally inducing internal excitation of molecular ions.     

Pulse radiolysis study of I− oxidation with radical anions Cl2 ⋅− in an aqueous solution

Radiation-chemical transformations of chloride solutions in the presence of iodide additives were studied by pulse radiolysis. Radical anion Cl₂ ^⋅− oxidize I⁻ ion, while in the secondary reactions Cl₂ reacts with I⁻ to form a mixed trihalide ion ICl₂ ⁻. A reaction model that satisfactorily describes the experimental data was proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1336–1340, June, 2005.     

Improvement of some pharmaceutical properties of nocloprost by β- and γ-Cyclodextrin Complexation

Inclusion complexation of nocloprost, a potent antiulcer prostaglandin derivative, with -, -, and -cyclodextrins (CyDs) in aqueous solutions has been studied by the solubility method and¹³C-NMR spectroscopy. The steric requirement of host-guest interaction was reflected in the magnitude of the stability constants and the thermodynamic parameters of the inclusion complexes. Solid complexes of nocloprost with - and -CyDs in a molar ratio of 1 : 2 were obtained on the basis of aBs-type phase solubility diagram. The X-ray diffraction data suggested that nocloprost is included in the cylindrical channel formed by coaxial alignment of -CyD molecules to give a channel type structure. Release and thermal behavior of the solid complexes was examined and compared with nocloprost itself. The results indicated that the -CyD complex may have great utility among the three CyDs, being a rapid dissolving form of nocloprost with improved thermal stability.     

H原子与CH3NH2抽氢反应的动力学计算

用QC ISD(T)/6-311 G(3DF,3PD)/MP2/6-311G(D,P)方法研究了H原子与CH3NH2的抽氢反应过程。该反应包含两个反应通道:H分别从CH3基团(R1)和NH2(R2)基团上抽氢。R1势垒比R2势垒低3.42kJ/mol,表明R1是主反应通道。在从头算的基础上,用变分过渡态理论(CVT)加小曲率隧道效应(SCT)研究了各反应温度范围为200~4000K内的速率常数,所得结果与实验值符合的很好。动力计算表明,在所研究的温度范围内,变分效应对速率常数的计算影响不大,而在低温范围内,隧道效应起了很重要的作用。     

Effect of deacetylation rate on gelation kinetics of konjac glucomannan

Effect of deacetylation rate on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a degree of acetylation (DA) range of 1.38-10.1 wt.% synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (C(Na)), both the critical gelation times (t(cr)) and the plateau values of storage moduli (G'(sat)) of the KGM gels increased with increasing DA. While at a fixed ratio of alkaline concentrations to values of DA (C(Na)/DA), the similar t(cr) and (G'(sat)) values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the C(Na)/DA on the gelation kinetics of the KGM samples were discussed.     

应变速率和电位对应力腐蚀裂纹扩展的影响

以滑移-溶解-再钝化模型为基础,推导出应力腐蚀裂纹扩展速率与裂尖应变速率和电位之间的理论公式.计算表明,在裂纹扩展速率与裂尖应变速率的关系曲线中有两个特征区域.裂纹扩展速率在区域I随裂尖应变速率增加而增大,而在区域II不随裂尖应变速率的改变而变化.用慢应变速率拉伸技术（SSRT）测量了304L不锈钢的裂纹增长速率.当电位控制在区域II的阳极区时,理论计算的裂纹扩展速率与实验得到的结果比较吻合.     

Methyl cellulose-based edible films and coatings I. Effect of plasticizer content on water and 1-octen-3-ol sorption and transport

Edible films were prepared from methyl cellulose with various concentrations of poly(ethylene glycol) 400 (PEG400) used as a plasticizer. Water vapour and 1-octen-3-ol (an aroma compound) were selected as hydrophilic and hydrophobic volatile penetrants respectively. Their solubility and permeability through methyl cellulose-based edible films were studied using gas chromatography methods. Whatever penetrant was used, the flux increased with the PEG400 content. Transfer behaviour, i.e., the order of increased magnitude of the transfer rate, strongly depends on the nature of the volatile compound. However, water sorption only depends on the PEG400 content whereas the aroma compound sorption is affected by both the water and the PEG400 concentrations. Relationships between solubility and permeability can be partially explained by the plasticization phenomenon.     

纳米级碳导电剂的种类对licoo2电化学性能的影响

碳纳米管;锂离子电池;正极;倍率容量;导电剂     

Growth transition and morphology change in polypropylene

The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 C and interpreted as a Regime III Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II Regime I transition is also theoretically predicted at 155 C, i. e. at a temperature outside the investigated temperature range. The Regime III Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae atT _c < 138 C (Regime III) and preferentially radiating lamellae atT _c > 138 C (Regime II). It is suggested that such a morphological change could be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites.