贮氢材料电极循环寿命的定量预测定时放电半衰期法的应用

贮氢材料电极循环寿命的定量预测定时放电半衰期法的应用韩剑文，袁满雪，周作祥，赖城明（南开大学化学系天津３０００７１）关键词：贮氢电极，循环寿命，半衰期。前文￣［１］讨论了应用定终点电位放电半衰期法来预测贮氢材料电极循环寿命的问题。本文讨论如何采用定时...     

反相液相色谱中固定相和流动相对柱相比的贡献

依据柱相比的热力学定义和反相液相色谱中溶质的计量置换保留理论(the stoichiometric dispheement heory of solute for retention，SDT-R)，对反相液相色谱中固定相和流动相性质、温度对柱相比的影响进行了研究。结果表明：固定相的种类和配基的疏水性对柱相比影响较大，而流动相中有机溶剂的种类，特别是脂肪酸作为置换剂时，对柱相比的影响更大，而柱相比受温度的影响较小。此外，通过用27种小分子溶质对柱相比的测定，其logI和Z良好的线性关系，进一步证明柱相比是一个与溶质性质无关的常数。     

A Density Functional Study of Substituent Effects on the O-H and O-CH(3) Bond Dissociation Energies in Phenol and Anisole

The substituent effects on O-H and O-CH(3) bond dissociation energies for a series of 18 para-substituted phenols (p-XC(6)H(4)OH) and 11 para-substituted anisoles have been studied using the density functional method in order to understand the origin of these effects. The calculated substituent effects agree well with experimental measurements for phenols but are substantially larger than the reported values for anisoles. Both ground-state effect and radical effect contribute significantly to the overall substituent effect. An electron-donating group causes a destabilization in phenols or anisoles (ground-state effect) but a stabilization in the phenoxy radicals (radical effect), resulting in reduced O-R bond dissociation energy. An electron-withdrawing group has the opposite effect. In most cases, the radical effect is more important than the ground-state effect. There is a good correlation between the calculated radical effects and calculated variations in charge and spin density on the phenoxy oxygen. This supports the concept that both polar and spin delocalization effects influence the stability of the phenoxy radical. While almost every para-substituent causes a stabilization of the phenoxy radical by spin delocalization, electron-donating groups stabilize and electron-withdrawing groups destabilize the phenoxy radical by the polar effect.     

Dependence of Elution Curve and Adsorption Isotherms of Insulin on composition of Mobile Phase of Frontal Analysis in Reversed Phase Liquid Chromatography

With frontal analysis(FA),the dependence of adsorption isotherms of insulin on the composition of mobile phase in reversed phase liquid chromatography (RPLC) has been investigated,This is also a good example to employ the stoichiometric displacement theory (SDT) for ivestigating solute adsorption in physical chemistry.Six kinds of mobile phase in RPLC were employed to study the effects on the elution curves and adsorption isotherms of insulin.the key points of this paper are:(1) the stability of insulin due to delay time after preparing,the organic solvent concentration,the kind and the concentration of ion-pairing agent in mobile phase were found to affect both elution curve and adsorption isotherm very seriously.(2)To obtain a valid and comparable result,the composition of the mobile phase employed in FA must be as same as possible to that in usual RPLC of either analytical scale or preparative purpose.(3)Langmuir Equation and the SDT were employed to imitate these obtained adsorption isotherms.The expression for solute adsorption from solution of the SDT was found to have a better elucidation to the insulin adsorption from mobile phase in RPLC.     

Carbon nanohorns grown from ruthenium nanoparticles

A nanoscale ruthenium/gold bimetallic cluster of clusters has been used as a molecular precursor to produce pure ruthenium nanoparticles (seeds) as catalysts for the growth of carbon nanohorns (CNHs).     

Studies on the refolding of the reduced-denatured insulin with size exclusion chromatography

The refolding of the reduced-denatured insulin from bovine pancreas was investigated with the size exclusion chromatography (SEC). It was shown that the reduced-denatured insulin originally denatured with 7.0 mol L^?1 guanidine hydrochloride (GuHCI) or 8.0 mol L^?1 urea could not be refolded with a non-oxidized mobile phase. Although the oxidized and reduced glutathione (GSSG and GSH) were employed in the oxidized mobile phase, the reduced-denatured insulin still could not be renatured. However, in the presence of 2.0 mol L^t-1 urea in the oxidized mobile phase employed, the reduced-denatured insulin can be refolded with SEC, and the aggregation of denatured insulin can be diminished by urea. In addition, the disulfide exchange of reduced-denatured insulin also can be accelerated with GSSG/GSH in the oxidized mobile phase. The three disulfide bridges of insulin were formed correctly and the reduced-unfolded insulin can be renatured completely. The results were further tested with reversed-phase liquid chromatography (RPLC) and hydrophobic interaction chromatography (HIC).     

Density functional study of HO(H2O)n (n = 1–3) clusters

The hydrogen bonding complexes HO(H₂O)_n (n = 1–3) were completely investigated in the present study using DFT and MP2 methods at varied basis set levels from 6‐31++G(d,p) to 6‐311++G(2d,2p). For n = 1 two, for n = 2 two, and for n = 3 five reasonable geometries are considered. The optimized geometric parameters and interaction energies for various complexes at different levels are estimated. The infrared spectrum frequencies and IR intensities of the most stable structures are reported. Finally, thermochemistry studies are also carried out. The results indicate that the formation and the number of hydrogen bonding have played an important role in the structures and relative stabilities of different complexes. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Pharmacokinetic study of free mangiferin in rats by microdialysis coupled with microbore high-performance liquid chromatography and tandem mass spectrometry

Mangiferin (2-beta-D-glucopyranosyl-1,3,6,7-tetrahydroxyxanthen-9-one) has been isolated from the herbal root of Anemarrhena asphodeloides Bung showing antioxidative, antiviral, and anticancer effect. An in vivo microdialysis sampling method coupled to microbore high-performance liquid chromatography (HPLC) was employed for continuous monitoring of free mangiferin in rat blood. Microdialysis probes were inserted into the jugular vein/right atrium and brain striatum of Sprague-Dawley rats, and mangiferin at doses of 10, 30 or 100 mg/kg were then administered via the femoral vein. Dialysates were collected every 10 min and injected directly into a microbore HPLC system. Mangiferin was separated by a reversed-phase C18 microbore column (150 x 1 mm) from dialysate within 10 min. The mobile phase consisted of acetonitrile-0.05% phosphoric acid-tetrahydrofuran (10:75:15, v/v/v) with a flow-rate of 0.05 ml/min. The wavelength of the UV detector was set at 257 nm. The limit of quantification for mangiferin was 0.05 microg/ml and in vivo recovery of mangiferin at concentrations of 1, 5 and 10 microg/ml was in range of 37.7-39.8%. The results indicate that the pharmacokinetics of mangiferin at doses of 10-30 mg/kg reveals a linear relation, while doses of 30-100 mg/kg show a nonlinear pharmacokinetic phenomenon. Mangiferin was undetectable in brain dialysate. The proposed method provides a technique for rapid and sensitive analysis of free mangiferin in rat blood and further application in pharmacokinetic study. Furthermore, the metabolites of mangiferin in the rat bile were confirmed by LC electrospray ionization (ESI) tandem mass spectrometry (MS-MS).     

3-Aminooxetanes: versatile 1,3-amphoteric molecules for intermolecular annulation reactions

Despite the versatility of amphoteric molecules, stable and easily accessible ones are still limitedly known. As a result, the discovery of new amphoteric reactivity remains highly desirable. Herein we introduce 3-aminooxetanes as a new family of stable and readily available 1,3-amphoteric molecules and systematically demonstrated their amphoteric reactivity toward polarized π-systems in a diverse range of intermolecular [3 + 2] annulations. These reactions not only enrich the reactivity of oxetanes, but also provide convergent access to valuable heterocycles.

Despite the versatility of amphoteric molecules, stable and easily accessible ones are still limitedly known.

Amphoteric molecules, which bear both nucleophilic and electrophilic sites with orthogonal reactivity, represent an attractive platform for the development of chemoselective transformations.¹ For example, isocyanides are well-established 1,1-amphoteric molecules, with the terminal carbon being both nucleophilic and electrophilic, and this feature has enabled their exceptional reactivity in numerous multi-component reactions.² In the past few decades, substantial effort has been devoted to the search for new amphoteric molecules.^1–5 Among them, 1,3-amphoteric molecules proved to be versatile. The Yudin and Beauchemin laboratories have independently developed two types of such molecules, α-aziridine aldehydes and amino isocyanates, respectively.^4,5 With an electrophilic carbon and a nucleophilic nitrogen in relative 1,3-positions, these molecules are particularly useful for the chemoselective synthesis of heterocycles with high bond-forming efficiency without protective groups (Fig. 1). However, such elegant amphoteric systems still remain scarce. Therefore, the development of new stable amphoteric molecules with easy access remains highly desirable.Open in a separate windowFig. 1Representative [1,3]-amphoteric molecules versus 3-aminooxetanes.In this context, herein we introduce 3-aminooxetanes as a new type of 1,3-amphoteric molecules and systematically demonstrate their reactivity in a range of [3 + 2] annulations, providing rapid access to diverse heterocycles. Notably, 3-aminooxetanes are bench-stable and either commercially available or easily accessible. However, their amphoteric reactivity has not been appreciated previously.Oxetane is a useful functional group in both drug discovery and organic synthesis.^6–9 Owing to the ring strain, it is prone to nucleophilic ring-opening, in which it serves as an electrophile (Scheme 1A).^6–8 We envisioned that, if a nucleophilic group is installed in the 3-position (e.g., amino group), such molecules should exhibit 1,3-amphoteric reactivity due to the presence of both nucleophilic and electrophilic sites (Scheme 1B). Importantly, the 1,3-relative position is crucial for inhibiting self-destructive intra- or intermolecular ring-opening (i.e. the 3-nucleophilic site attack on oxetane itself) due to high barriers. Thus, such orthogonality is beneficial to their stability. In contrast, the nucleophilic site is expected to react with an external polarized π bond (e.g., X = Y, Scheme 1B), which enables a better-positioned nucleophile (Y) to attack the oxetane and cyclize. Thus, a formal [3 + 2] annulation should be expected. Unlike the well-known S_N2 reactivity of oxetanes with simple bond formation, this amphoteric reactivity would greatly enrich the chemistry of oxetanes with multiple bond formations and provide expedient access to various heterocycles. In contrast to the conventional approaches that require presynthesis of advanced intermediates (e.g., intramolecular ring-opening),⁸ the exploitation of such amphoteric reactivity in an intermolecular convergent manner from simple substrates would be more practically useful. Moreover, more activation modes could be envisioned in addition to oxetane activation. In 2015, Kleij and coworkers reported an example of cyclization between 3-aminooxetane and CO₂ in 55% yield, which provided a pioneering precedent.¹⁰ However, a systematic study to fully reveal such amphoteric reactivity in a broad context remains unknown in the literature.Open in a separate windowScheme 1Typical oxetane reactivity and the new amphoteric reactivity.To test our hypothesis, we began with the commercially available 3-aminooxetanes 1a and 1b as the model substrates. Phenyl thioisocyanate 2a and CS₂ were initially employed as reaction partners, as they both have a polarized C S bond as well as a relatively strong sulfur nucleophilic motif. Moreover, the resulting desired products, iminothiazolidines and mercaptothiazolidines, are both heterocycles with important biological applications (Fig. 2).¹¹ To our delight, simple mixing these two types of reactants in DCM resulted in spontaneous reactions at room temperature without any catalyst. The corresponding [3 + 2] annulation products iminothiazolidine 3a and mercaptothiazolidine 4a were both formed with excellent efficiency (Scheme 2). It is worth mentioning that catalyst-free ring-opening of an oxetane ring is rarely known, particularly for intermolecular reactions.^6–9 In this case, the high efficiency is likely attributed to the suitable choice and perfect position of the in situ generated sulfur nucleophile.Open in a separate windowFig. 2Selected bioactive molecules containing iminothiazolidine and mercaptothiazolidine motifs.Open in a separate windowScheme 2Initial results between 3-aminooxetanes and thiocarbonyl compounds.The catalyst-free annulation protocol is general with respect to various 3-aminooxetanes and isothiocyanates. A range of iminothiazolidines and mercaptothiazolidines were synthesized with high efficiency under mild conditions (Scheme 3). Many of them were obtained in quantitative yield. Quaternary carbon centers could also be generated from 3-substituted 3-aminooxetanes (e.g., 3j). The structure of product 3b was unambiguously confirmed by X-ray crystallography.Open in a separate windowScheme 3Formal [3 + 2] annulation with isothiocyanates and CS₂. Reaction conditions: 1 (0.3–0.4 mmol), 2 (1.1 equiv.) or CS₂ (1.5 equiv.), DCM (2 mL), RT, 3 h for 3 and 36 h for 4. Yields are for the isolated products.With the initial success of thiocarbonyl partners, we next turned our attention to isocyanates, in which the carbonyl group serves as the [3 + 2] annulation motif. Compared with sulfur as the nucleophilic site in the above cases, the oxygen atom is less nucleophilic. As expected, initial tests of the reactivity by mixing 1b and 5a resulted in no desired annulation product 6a in the absence of a catalyst (Table 1, entry 1). Next, Brønsted acids, including TsOH and the super acid HNTf₂, were examined as catalysts, but with no success (entries 2 and 3). We then resorted to various Lewis acids, particularly those oxophilic ones, in hope of activating the oxetane unit. Unfortunately, many of them still remained ineffective (e.g., ZnCl₂, AuCl, and FeCl₃). However, to our delight, further screening of stronger Lewis acids helped identify Sc(OTf)₃, Zn(OTf)₂, and In(OTf)₃ to be effective at room temperature, leading to the desired iminooxazolidine product 6a in good yield (entries 7–9). Its structure was confirmed by X-ray crystallography. Nevertheless, aiming to search for a cheaper catalyst, we continued to optimize this reaction at a higher temperature using previous ineffective catalysts. Indeed, FeCl₃ was found to be effective at 80 °C (61% yield, entry 10), while Brønsted acid TsOH remained ineffective at this temperature (entry 11). Notably, decreasing the loading of FeCl₃ to 1 mol% led to a higher yield (89% yield, entry 12). However, further decreasing to 0.5 mol% resulted in slightly diminished efficiency (entry 13).Reaction conditions for annulation with isocyanates^a

蛋白质-蛋白质相互作用界面统计分析

以作者开发的从蛋白质结合部位推导出其界面所具有的疏水性质和氢键性质的计算程序PP_SITE为基础,利用蛋白质结构数据库(PDB),对蛋白质-蛋白质相互作用界面进行了统计分析.从PDB中挑出非冗余的链间相互作用对,计算出这个数据集中所有链间界面的疏水和氢键相互作用特征.对得到的界面特征进行统计分析,寻找能够明显聚类的界面特征.结果表明，界面大小、氢键和疏水相互作用在界面所占比例以及疏水相互作用的集中程度可以作为分类的依据.