Type I Photosensitized Oxidation of Methionine†

Methionine (Met) is an essential sulfur‐containing amino acid, sensitive to oxidation. The oxidation of Met can occur by numerous pathways, including enzymatic modifications and oxidative stress, being able to cause relevant alterations in protein functionality. Under UV radiation, Met may be oxidized by direct absorption (below 250 nm) or by photosensitized reactions. Herein, kinetics of the reaction and identification of products during photosensitized oxidation were analyzed to elucidate the mechanism for the degradation of Met under UV‐A irradiation using pterins, pterin (Ptr) and 6‐methylpterin (Mep), as sensitizers. The process begins with an electron transfer from Met to the triplet‐excited state of the photosensitizer (Ptr or Mep), to yield the corresponding pair of radicals, Met radical cation (Met^?+) and the radical anion of the sensitizer (Sens^??). In air‐equilibrated solutions, Met^?+ incorporates one or two atoms of oxygen to yield methionine sulfoxide (MetO) and methionine sulfone (MetO₂), whereas Sens^?? reacts with O₂ to recover the photosensitizer and generate superoxide anion (O₂^??). In anaerobic conditions, further free‐radical reactions lead to the formation of the corresponding dihydropterin derivatives (H₂Ptr or H₂Mep).     

Electrocatalytic Hydrogenation and Oxidation in Aqueous Conditions†

Water molecule contains one oxygen and two hydrogen atoms, making it a potential oxygen and hydrogen source. Electrocatalytic organic reduction and oxidation using water as oxygen and/or hydrogen donors provide an environmentally friendly and sustainable strategy to replace traditional chemical‐driven stoichiometric reactions that use sacrificial reagents. Furthermore, the development of electrochemical synthesis provides a potential application for low tension photoelectricity, which is not cost‐effective during boosted voltage and application. In the last decade, electrocatalytic redox reactions of organic molecules in aqueous media had shown progress owing to the development of electrode materials and water‐splitting technology. This paper highlights several electrocatalytic systems and corresponding mechanisms for both hydrogenation and oxidative transformation of representative compounds. The activation process of protons and water on the working electrode surface has received special focus. Furthermore, paired electrolysis using water as the oxygen and hydrogen source has been demonstrated. This paired system combines hydrogenation and oxidation half‐reactions in one cell using water as the hydrogen and oxygen source, resulting in high atomic and electron utilization rates.     

磁性壳聚糖去除水中腐殖酸的研究

采用高温水热法合成了磁性壳聚糖,并研究了其对水中腐殖酸(HA)的吸附、脱附行为。表征结果表明,磁性壳聚糖粒径大小为200～300nm,氨基含量1.29mmol·g-1,BET比表面积36.00m2·g-1,饱和磁化强度为38.78emu·g-1,易于磁性分离。HA在磁性壳聚糖上的吸附等温线可用Freundlich方程模拟,吸附动力学符合拟二级动力学方程。HA的吸附量随溶液pH值的升高而降低,随不同阳离子浓度增加而增加,不同类型的阳离子对HA吸附效果影响的大小顺序为:Ca2+Mg2+Na+K+。经5个脱附再生循环,磁性壳聚糖仍能保持79.8%的吸附量,表明该吸附剂再生性好,可循环使用。     

季铵型阳离子纤维素对水中腐殖酸的吸附

以异丙醇为分散剂,碱纤维与3-氯-2-羟丙基三甲基氯化铵反应,醚化接枝制得一种环境功能材料-季铵型阳离子纤维素（QACC）。用红外光谱、X-射线衍射和电镜扫描对材料的结构进行了表征：红外光谱中1644cm^-1处存在明显的季铵基的弯曲振动。经过改性的QACC结晶度下降,比表面积增加。研究了QACC对腐殖酸的吸附性能：pH=8、318K时,QACC对腐殖酸的饱和吸附容量为622mg·g^-1;其表观活化能为6.45kJ·mol^-1;吸附符合Lagergren二级动力学方程,吸附速率随温度升高而加快;吸附等温模型符合Langmuir等温式,为单分子层吸附;吸附腐殖酸的ΔH、ΔS、ΔG分别为：20.3kJ·mol^-1、77.8J·mol^-1·K-1、-4.44kJ·mol^-1,吸附主要为化学吸附。     

季铵型阳离子纤维素对水中腐殖酸的吸附

以异丙醇为分散剂,碱纤维与3-氯-2-羟丙基三甲基氯化铵反应,醚化接枝制得一种环境功能材料-季铵型阳离子纤维素(QACC)。用红外光谱、X-射线衍射和电镜扫描对材料的结构进行了表征:红外光谱中1 644 cm-1处存在明显的季铵基的弯曲振动。经过改性的QACC结晶度下降,比表面积增加。研究了QACC对腐殖酸的吸附性能:pH=8、318 K时,QACC对腐殖酸的饱和吸附容量为622 mg·g-1;其表观活化能为6.45 kJ·mol-1;吸附符合Lagergren二级动力学方程,吸附速率随温度升高而加快;吸附等温模型符合Langmuir等温式,为单分子层吸附;吸附腐殖酸的ΔH、ΔS、ΔG分别为:31.7 kJ·mol-1、119 J·mol-1·K-1、-5.34 kJ·mol-1,吸附主要为化学吸附。     

功能特异性杂多酸离子液体催化丁二酸水溶液直接酯化

将以磺化六亚甲基四胺([HMT-4PS])制备的阳离子与以杂多酸([HPA])制备的阴离子结合, 制备了一系列功能特异性离子液体催化剂([HMT-4PS][HPA]); 将其用于催化甲醇(MeOH)与丁二酸(SA)水溶液的直接酯化反应. 结果表明, 该系列离子液体在反应过程中以“乳状液”的形式均匀分散在体系中. 反应结束后, 通过降低体系极性即可实现催化剂的快速分离. 在合成的系列催化剂中, [HMT-4PS]₃[PW]₄表现出最佳的催化活性. 分别探讨了反应温度、 催化剂用量、 酸醇摩尔比和反应时间等因素对反应的影响, 确定了最优反应条件: 温度80 ℃, 催化剂用量5%(质量分数, 按丁二酸水溶液计), n(SA)∶n(MeOH)=1∶30, 反应时间8 h. 最优条件下丁二酸的转化率达到79.3%, 二酯选择性达到92.9%; 该催化剂重复使用5次后, 丁二酸转化率及二酯选择性仍分别保持在77%及90%以上.     

卟啉类化合物对生物分子的光敏化氧化

本文就光敏化氧化反应、光敏剂、生物小分子的光敏化氧化机制以及生物大分子的光敏氧化与切割进行了系统的介绍与评述。同时, 介绍了国内外有关生命分子的光敏化氧化反应的最新研究成果以及它们潜在的应用前景。     

Photosensitized DNA Damage: The Case of Fluoroquinolones†

This review focuses on DNA damage photosensitized by the fluoroquinolone (FQ) antibacterial drugs. The in vivo evidence for photocarcinogenesis mediated by FQs is presented in the introduction. The different methods employed for detection of DNA‐photodamage mediated by FQs are then summarized, including gel electrophoresis (with whole cells, with isolated DNA and with oligonucleotides) and chromatographic analysis (especially HPLC with electrochemical and MS/MS detection). The chemical mechanisms involved in the formation of the reported lesions are discussed on the basis of product studies and transient spectroscopic evidence. In general, the literature coverage is limited to the last decade, although some earlier citations are also included.     

Kinetics and Mechanism of Oxidation of Hydroquinone by Tetrabutylammonium Tribromide Ion in Aqueous Acetic Acid

The oxidation of hydroquinone by environmentally benign tetrabutyl ammonium tribromide (TBATB) was carried out in 50% V/V aqueous acetic acid medium under pseudo-first-order conditions, keeping a large excess of hydroquinone over the oxidant. The main reactive species of oxidant and substrate were found to be the Br₃^-\mathrm{Br}_{3}^{-} ion and hydroquinone, respectively. The reaction proceeds with prior complex formation between the reactants followed by its slow decomposition to generate semiquinone and bromine radicals. The complex formation was kinetically verified by its Michaelis–Menten plot. The solvent effect was verified by using Grunwald–Winstein equation which is consistent with an S_N2 mechanism. The formation constants for the complex and rate constant for the slow decomposition step were determined by studying the reaction at five different temperatures. The values of formation constant of the complex and the rate constant for its decomposition were determined at these temperatures. The activation parameters with respect to the slow step of the reaction have also been determined.     

Kinetics and Mechanism of the Autocatalyzed Oxidation of Theophylline by Permanganate in Aqueous Perchloric Acid Medium

The reaction kinetics for the oxidation of theophylline by permanganate ions have been investigated in perchloric acid medium using spectrophotometric techniques at 25?^°C, and at constant ionic strength 1.60 mol?dm^?3, under pseudo first order conditions. An autocatalyzed reaction is observed due to one of the products formed is Mn(II). The orders with respect to theophylline and Mn(VII) were both found to be unity, whereas fractional order is observed with respect to the autocatalyst, Mn(II). The rate of the reaction increases as the concentration of acid increases, but the order with respect to acid concentration is less than unity. The influence of temperature on the rate of reaction was studied. Based on the experimental results a suitable mechanism is proposed. The activation and thermodynamic parameters were determined with respect to slow reaction step.     

The Oxidation of Thiocyanate to Polythiocyanic Acid Using Peroxydisulfate in Aqueous Solution

Abstract

The oxidation of thiocyanate to polythiocyanic acid by peroxydisulfate was carried out in an aqueous solution at room temperature. The primary step is the decomposition of peroxydisulfate into sulfate-free radicals. At room temperature in the presence of peroxydisulfate as a oxidizing agent, HSCN polymerizes to (HSCN)_n. The oxidation of thiocyanate in an aqueous solution is often complicated, but here we obtained the polythiocyanic acid as a major product. The products were characterized by elemental analysis, IR, UV- visible, H-NMR spectroscopy, and X-ray powder diffraction.     

Mechanistic Study of Oxidation of Palladium(II) by Cerium(IV) in Aqueous Acid

The kinetics of oxidation of Pd^II by Ce^IV have been studied spectrophotometrically in HClO₄ media at 40 °C. The reaction is first order each in [Ce^IV] and [Pd^II] at constant [H⁺]. Increasing [H⁺] accelerates the reaction rate with fractional order in [H⁺]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At constant acidity, increasing the added chloride concentration enhances the rate of reaction. H₃Ce(SO₄)₄⁻ and PdCl₄²⁻ are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants involved have been determined.     

GC-MS法测定涂料中的四溴双酚A

建立了GC-MS法检测涂料中四溴双酚A的分析方法,并对样品前处理条件和GC-MS分析条件进行优化。采用二氯甲烷-丙酮(1∶1)混合溶剂超声提取样品,萃取液经硅胶小柱净化,平行蒸发定量浓缩后采用气相色谱-质谱法测定,外标法定量。结果显示,四溴双酚A标准溶液在1~50 mg/L范围内线性关系良好,相关系数大于0.999;方法的定量下限(LOQ)为2 mg/kg,加标回收率为83.2%~104%,相对标准偏差(RSD,n=8)为2.6%~4.7%。该方法操作简便、分析快速、结果准确,可满足涂料中四溴双酚A的定性定量分析要求。     

Kinetics of Oxidation of 4-Oxoacids by <Emphasis Type="Italic">N</Emphasis>-Chlorosaccharin in Aqueous Acetic Acid Medium

The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each of the 4-oxoacids, NCSA and H⁺. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA with 4-oxoacids.     

Catalytic Aerobic Oxidation of Biomass‐based Furfural into Maleic Acid in Aqueous Phase with Metalloporphyrin Catalysts

Catalytic oxidation of renewable furfural into valuable maleic acid in aqueous solutions using metalloporphyrin catalysts was investigated for the first time. The synthesized catalysts were characterized by FT‐IR , UV –vis, ¹H NMR , elemental analysis, and TGA . The catalysts varied in metal active sites and functional groups, which had different effects on their catalytic activity. Furthermore, the effects of temperatures, reaction time, catalyst loading, and oxygen pressure were studied in detail. Maleic acid could be achieved in 44% yield by using FeT (p‐Cl)PPCl as catalyst under optimal conditions. Finally, FeT (p‐Cl)PPCl could be reused in five consecutive runs without a significant loss of activity.     

Oxidation of Tyrosine Photoinduced by Pterin in Aqueous Solution

Pterins, heterocyclic compounds widespread in biological systems, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. Pterins have been previously identified as good photosensitizers under UV‐A irradiation. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the oxidation of tyrosine (Tyr) in aqueous solutions. Tyr is an important target in the study of the photodynamic effects of UV‐A radiation because it is oxidized by singlet oxygen (¹O₂) and plays a key role in polymerization and cross‐linking of proteins. Steady UV‐A irradiation of solutions containing Ptr and Tyr led to the consumption of Tyr and dissolved O₂, whereas the Ptr concentration remained unchanged. Concomitantly, hydrogen peroxide (H₂O₂) was produced. By combining different analytical techniques, we could establish that the mechanism of the photosensitized process involves an electron transfer from Tyr to the triplet excited state of Ptr. Mass spectrometry, chromatography and fluorescence were used to analyze the photoproducts. In particular, oxygenated and dimeric compounds were identified.     

Kinetics of Polyol Oxidation by Ozone in Aqueous Solutions

Spectrophotometry is applied to study the oxidation of ethylene glycol, triethylene glycol, glycerol, etriol, pentaerithritol and mannitol by ozone in aqueous solutions at 277–304 K. Rate constants and activation parameters of the reaction are measured. It is proposed that the oxidation of these alcohols by ozone occurs via the same mechanism. The formation of an intermediate complex is a rate-limiting step in the case of diols; the decomposition of the complex is a rate-limiting step for tri- to hexatomic alcohols.     

Kinetics of Oxidation of Reduced Phosphorus-Molybdenum-Vanadium Heteropoly Acid Species with Dioxygen in Aqueous Solutions

The kinetics of dioxygen oxidation of the reduced heteropoly acid H_{7 + m} PV _m ^IV V _{4 − m} ^V Mo₈O⁴⁰ (H_mHPA-4) in aqueous solutions at atmospheric pressure and 313–363 K was studied, and a rate equation was proposed for this reaction. The reaction was of first order with respect to dioxygen. However, the order of the reaction with respect to H_mHPA-4 was close to 1 at [H_mHPA-4] > 0.20 mol/l but increased to ≈2.8 at [H_mHPA-4] < 0.20 mol/l. Variable orders of reaction with respect to H⁺ ions with high negative values were observed. The introduction of overstoichiometric VO²⁺ cations into H_mHPA-4 accelerated the oxidation of the solution. The apparent activation energy of the reaction dramatically increased as the degree of reduction of H_mHPA-4 decreased. This can be explained by the fact that the heats of endothermic preequilibrium steps of the disproportionation of weakly reduced heteropoly anions are added to the true activation energy of formation of an active intermediate complex of the heteropoly anion with O₂.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 380–389.Original Russian Text Copyright © 2005 by Zhizhina, Odyakov, Simonova, Matveev.     

Effect of Humic Acids on the State of Disperse,Acid, and Vat Dyes in Aqueous Solutions

Effect of humic acids (biopolymeric compounds of anionic type recovered from peat) on the state of disperse, acid, and vat dyes in aqueous solutions was studied; vat dye was studied in the form of water-soluble sodium salt of leuco acid.