铜（Ⅱ）－4－（吡啶－2′－甲基）－1，4，7，10－四氮杂环十三烷－11，13－二酮－α－氨基酸（5－取代邻菲罗啉）三元配合物的稳定性研究

用ｐＨ法在２５．０±０．１℃，Ｉ＝０．１ｍｏｌ·ｄｍ－３ＫＮＯ３条件下，测定铜（Ⅱ）－４－（吡啶－２′－甲基）－１，４，７，１０－四氮杂环十三烷－１１，１３－二酮－α－氨基酸（５－取代邻菲罗啉）三元配合物的稳定常数；比较了带吡啶甲基二氧四胺大环配体和二氧四胺大环配体与Ｃｕ（Ⅱ）的配位能力、配位方式；研究了该三元体系配合物稳定性与配体α－氨基酸酸碱强度之间的直线自由能关系；探讨了Ｃｕ（Ⅱ）和５－取代邻菲罗啉之间的ｄ－ｐ反馈π键以及邻菲罗啉取代基Ｈａｍｍｅｔｔ诱导效应与该三元配合物稳定性之间的关系。讨论了４－（吡啶－２′－甲基）－１，４，７，１０－四氮杂环十三烷－１１，１３－二酮和４－（喹啉－２′－甲基）－１，４，７，１０－四氮杂环十三烷－１１，１３－二酮与Ｃｕｘｐｈｅｎ所形成配合物的不同空间结构及其对配合物稳定性产生的影响。     

酞菁（H_2TAP）的X－射线光电子能谱（XPS）

酞菁（Ｈ_２ＴＡＰ）的Ｘ－射线光电子能谱（ＸＰＳ）朱志昂，卜显和，刘月霞（南开大学化学系天津３０００７１）ＰａｕｌＧ．Ｇａｓｓｍａｎ（美国明尼苏达大学化学系）关键词酞青，ＸＰＳ，Ｃ１ｓ电子结合能，Ｎ１ｓ电子结合能酞菁及其金属配合物作为叶绿素，血红素的?..     

Single-Molecule single crystals of isotactic polystyrene

Single-molecule single crystals were grown from amorphous droplets of fractionated isotactic polystyrene. The crystals were analyzed by electron microscopy and electron diffraction. The molecular mass distribution could be matched with a statistical analysis of single-molecule particles (amorphous and crystals). Proof was brought that single molecules of isotactic polystyrene do not reach equilibrium dimensions on crystallization, rather assume the lamellar morphology with chain-folded macroconformation, also known from crystallization of polymolecular crystals. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America. US Government contract No. DE-AC05-840R-21400.

     

Improved hygrothermal durability of flax/polypropylene composites after chemical treatments through a hybrid approach

There are growing research interests in flax fibers due to their renewable ‘green’ origin and high strength. However, these natural fibers easily absorb moisture and have poor adhesion with polymer matrix leading to low interfacial strength for the composites. A hybrid chemical treatment technique combining alkali (sodium hydroxide) and silane treatments is adopted in the current study to modify flax fibers for improved performances of flax/polypropylene composites. Changes in chemical composition, microstructure, wettability, surface morphology, crystallinity and tensile properties of single flax fiber before and after chemical treatments were comprehensively characterized using techniques including SEM, FTIR, AFM, XRD, micro-fiber tester, etc. It was found that hemicellulose and lignin at the fiber surface were removed due to alkali treatment, which helped to reduce moisture absorption of the composites. Alkali-treated flax fibers were later subjected to silane treatment, which helped to improve the compatibility between flax fiber and polypropylene matrix. After alkali-silane hybrid chemical treatment, moisture absorption of the composites was further decreased. At the same time, the interfacial bonding strength between flax and polypropylene is significantly enhanced. All these results validate the great advantage of the hybrid chemical treatment approach for flax/polypropylene composites, which has the potential to promote the application of chemical treatment techniques in the plant fiber composite industry.

Graphic abstract

     

Hydrothermal synthesis, crystal structures and luminescent properties of two new Ln(III)–succinate (Ln=Eu, Tb) complexes exhibiting three dimensional networks

Two new coordination polymers, [Eu₂(L)₃(H₂O)₂]_n 1 and {[Tb₂(L)₃(H₂O)₂]·H₂O}_n 2, (H₂L=succinic acid) have been synthesized by the reaction of H₂L with nitrate salts of Eu(III) or Tb(III) under hydrothermal conditions. The X-ray diffraction analysis reveals that the two complexes are constructed by L bridging the chains of edge-sharing EuO₈(H₂O) or TbO₈(H₂O) polyhedra to form 3D network structure. 1 and 2 possess different topological structures due to the difference in the conformations of L. The solid photoluminescence of 1 and 2 was also investigated in room temperature.     

One-dimensional coordination polymers containing penta-supertetrahedral sulfide clusters linked by dipyridyl ligands

Three new one-dimensional coordination polymers [Zn8S(SC6H5)14.C12H10N2](1), [Zn7CoS(SC6H5)14.C13H14N2](2) and [Zn8S(SC6H5)14.C13H14N2](3) have been prepared containing penta-supertetrahedral clusters and linear crosslinking dipyridyl ligands; the two complexes show optical transitions with band gaps of approximately 3.44 eV (1) and approximately 3.54 eV (2).     

Theoretical prediction of the contact distance dependence of the electron transfer reactivity of the ClO/ClO− coupling system

On the basis of the structures and properties of the ClO/ClO^? system obtained at the density functional theory (DFT) (UB3LYP) level, employing the 6‐311+G(3df) standard basis set, the electron transfer reactivity of this system is investigated. The results indicate that there are five possible stable coupling complexes that correspond to the generous minima on the global potential energy surfaces (PES). The most stable coupling complex is planar EC4, in which there is a O? O linkage with two trans‐Cl atoms. Their stabilization energies are calculated to be 20.57 (EC1: C₁), 20.54 (EC2: C₂, ²B), 20.69 (EC3: C₁), 20.70 (EC4: C_s, ²A′), and 20.69 (EC.5: C_2h, ²B_u) kcal/mol at the B3LYP/6‐311+G(3df) level; with the correction of the basis set superposition error (BSSE), the stability order of these encounter complexes is EC4 > EC.5 > EC3 > EC1 > EC2. Based on the five encounter complexes, five coupling modes are designed for the study of the electron transfer reactivity of this system. The dissociation energy curves at the activated states and the corresponding activation energies of these five coupling modes are obtained and are compared at the B3LYP/6‐311+G(3df) and MP2/6‐311+G* levels. The inapplicability of DFT methods has also been discussed in this article in predicting the energy curves, especially with a long contact distance, in which DFT methods give the abnormal behavior for the dissociations of the complexes caused by the “inverse symmetry breaking” problem. On the basis of the golden rule of the time‐dependent perturbation theory, the electron transfer reactivity and the contact distance dependence of the various electron transfer kinetics parameters (e.g., activation energy, coupling matrix element) have been analyzed at the UMP2(full)/6‐311+G* level. The electron transfer can take place over a range of contact distances, but the most effective coupling distance corresponds to only a small range. The coupling orientation analyses also indicate that the most favorable coupling mode to the electron transfer does not always correspond to the most stable encounter complex mechanism. Some highly energetic coupling modes are more favorable for the electron transfer. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Synthesis of gramicidin S and its analogues via an on-resin macrolactamization assisted by a predisposed conformation of the linear precursors

A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance.