Depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) under oxidative conditions

Depolymerization of an engineering plastic, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), was accomplished by using 2,6-dimethylphenol (DMP) under oxidative conditions. The addition of an excess amount of DMP to a solution of PPO in the presence of a CuCl/pyridine catalyst yielded oligomeric products. When PPO (M(n)=1.0x10(4), M(w)/M(n)=1.2) was allowed to react with a sufficient amount of DMP, the molecular weight of the product decreased to M(n)=4.9x10(2) (M(w)/M(n)=1.5). By a prolonged reaction with the oxidant, the oligomeric product was repolymerized to produce PPO essentially identical to the starting material, making the oligomer useful as a reusable resource. During the depolymerization reaction, an intermediate phenoxyl radical was observed by ESR spectroscopy. Kinetic analysis showed that the rate of the oxidation of PPO was about 10 times higher than that of DMP. These results show that a monomeric phenoxyl radical attacks the polymeric phenoxyl to induce the redistribution via a quinone ketal intermediate, leading to the substantial decrease in the molecular weight of PPO, which is much faster than the chain growth.     

食品中化学性有害物的质谱软电离裂解规律及筛查技术研究进展

食品中化学性有害物是导致食品安全问题的重要原因，质谱是对食品中化学性有害物进行定性定量分析的有效方法。该文按照化合物结构类别，综述了食品中重要化学性有害物的质谱软电离裂解机理，包括农药、兽药、真菌毒素，以及其他化学污染物。对于每类化合物，重点综述化合物质谱裂解产生的特征碎片、中性丢失等，以及这些质谱软电离裂解机理在食品中化学性有害物筛查及发现中的应用。研究化合物的质谱裂解机理可以帮助研究者对化合物进行结构解析和结构确证，为食品中同类结构新型化学性有害物的发掘提供理论依据。     

Reactions of Sulphate Radicals with Substituted Pyridines: A Structure–Reactivity Correlation Analysis

The kinetics of the oxidation of pyridine, 3‐chloropyridine, 3‐cyanopyridine, 3‐methoxypyridine and 3‐methylpyridine mediated by SO₄ ^{< M ‐>} radicals are studied by flash photolysis of peroxodisulphate, S₂O₈^2?, at pH 2.5 and 9. The absolute rate constants for the reactions of both, the basic and acid forms of the pyridines, are determined and discussed in terms of the Hammett correlation. The monosubstituted pyridines react about 10 times faster with sulphate radicals than their protonated forms, the pyridine ions. The organic intermediates are identified as the corresponding hydroxypyridine radical adducts and their absorption spectra compared with those estimated employing the time‐dependent density functional theory with explicit account for bulk solvent effects. A reaction mechanism which accounts for the observed intermediates and the pyridinols formed as products is proposed.     

A theoretical investigation of the gas-phase oxidation reaction of the saturated tert-butyl radical.

The radical-radical reaction mechanisms and dynamics of ground-state atomic oxygen [O(3P)] with the saturated tert-butyl radical (t-C4H9) are investigated using the density functional method and the complete basis set model. Two distinctive reaction pathways are predicted to be in competition: addition and abstraction. The barrierless addition of O(3P) to t-C4H9 leads to the formation of an energy-rich intermediate (OC4H9) on the lowest doublet potential energy surface, which undergoes subsequent direct elimination or isomerization-elimination leading to various products: C3H6O + CH3, iso-C4H8O + H, C3H7O + CH2, and iso-C4H8 + OH. The respective microscopic reaction processes examined with the aid of statistical calculations, predict that the major addition pathway is the formation of acetone (C3H6O) + CH3 through a low-barrier, single-step cleavage. For the direct, barrierless H-atom abstraction mechanism producing iso-C4H8 (isobutene) + OH, which was recently reported in gas-phase crossed-beam investigations, the reaction is described in terms of both an abstraction process (major) and a short-lived addition dynamic complex (minor).     

Electron Transfer and Charge Transfer: Twin Themes in Unifying the Mechanisms of Organic and Organometallic Reactions

The broad varieties of organic and organometallic reactions merge into a common unifying mechanism by considering all nucleophiles and electrophiles as electron donors (D) and electron acceptors (A), respectively. Comparison of outer-sphere and inner-sphere electron transfers with the aid of Marcus theory provides the thermochemical basis for the generalized free energy relationship for electron transfer (FERET) in Equation (37) and its corollaries in Equations (43) and (44) that have wide predictive applicability to electrophilic aromatic substitutions, olefin additions, organometallic cleavages, etc. The FERET is based on the conversion of the weak nucleophile–electrophile interactions extant in the ubiquitous electron donor—acceptor (EDA) precursor complex [D, A] to the radical ion pair [D^⊕, A^?], for which the free energy change can be evaluated from the charge-transfer absorption spectra according to Mulliken theory. FERET analysis thus indicates that the charge-transfer ion pairs [D^⊕, A^?] are energetically equivalent to the transition states for nucleophile/electrophile transformations. The behavior of such ion pairs can be directly observed immediately following the irradiation of the charge-transfer bands of various EDA complexes with a 25-ps laser pulse. Such studies confirm the radical ion pair [Arene^⊕, NO₂] as a viable intermediate in electrophilic aromatic nitration, as presented in the electron-transfer mechanism between arenes and the nitryl cation (NO) electrophile.     

Chemo- and periselectivity in the addition of [OsO2(CH2)2] to ethylene: a theoretical study

Quantum chemical calculations by using density functional theory at the B3LYP level have been carried out to elucidate the reaction course for the addition of ethylene to [OsO2(CH2)2] (1). The calculations predict that the kinetically most favorable reaction proceeds with an activation barrier of 8.1 kcal mol(-1) via [3+2] addition across the O=Os=CH2 moiety. This reaction is -42.4 kcal mol(-1) exothermic. Alternatively, the [3+2] addition to the H2C=Os=CH2 fragment of 1 leads to the most stable addition product 4 (-72.7 kcal mol(-1)), yet this process has a higher activation barrier (13.0 kcal mol(-1)). The [3+2] addition to the O=Os=O fragment yielding 2 is kinetically (27.5 kcal mol(-1)) and thermodynamically (-7.0 kcal mol(-1)) the least favorable [3+2] reaction. The formal [2+2] addition to the Os=O and Os=CH2 double bonds proceeds by initial rearrangement of 1 to the metallaoxirane 1 a. The rearrangement 1-->1 a and the following [2+2] additions have significantly higher activation barriers (>30 kcal mol(-1)) than the [3+2] reactions. Another isomer of 1 is the dioxoosmacyclopropane 1 b, which is 56.2 kcal mol(-1) lower in energy than 1. The activation barrier for the 1-->1 b isomerization is 15.7 kcal mol(-1). The calculations predict that there are no energetically favorable addition reactions of ethylene with 1 b. The isomeric form 1 c containing a peroxo group is too high in energy to be relevant for the reaction course. The accuracy of the B3LYP results is corroborated by high level post-HF CCSD(T) calculations for a subset of species.     

短波段光学减反膜的溶胶-凝胶法制备及性能分析

 随着大型激光器的发展，对短波段减反膜的要求日益提高，其中钕玻璃激光三倍频（355nm）的减反射成为新的技术要点。采用溶胶-凝胶工艺合成SiO₂溶胶，采用提拉镀膜法制备纳米多孔SiO₂薄膜，薄膜厚度为75nm，折射率控制在1.22，镀制在石英基底上的薄膜其355nm波长的反射率仅为0.2%。通过氨处理工艺和薄膜的表面修饰，薄膜的抗磨擦性能和疏水性能大大提高，薄膜经过蘸有灰尘、乙醇的棉花球擦洗20次和50次后，透射率最大值仅分别降低0.13% 和 0.39%，与水珠的接触角达到110°。     

Exploring the Potential of Metallodrugs as Chemotherapeutics for Triple Negative Breast Cancer

This review focuses on studies of coordination and organometallic compounds as potential chemotherapeutics against triple negative breast cancer (TNBC) which has one of the poorest prognoses and worst survival rates from all breast cancer types. At present, chemotherapy is still the standard of care for TNBC since only one type of targeted therapy has been recently developed. References for metal-based compounds studied in TNBC cell lines will be listed, and those of metal-specific reviews, but a detailed overview will also be provided on compounds studied in vivo (mostly in mice models) and those compounds for which some preliminary mechanistic data was obtained (in TNBC cell lines and tumors) and/or for which bioactive ligands have been used. The main goal of this review is to highlight the most promising metal-based compounds with potential as chemotherapeutic agents in TNBC.