Design and Synthesis of 3-Triazolo-coumarins and Their Applications in Scavenging Radicals and Protecting DNA

In this study, we synthesized a series of 3-triazolo-coumarins and evaluated their antioxidant activities respectively by two methods: trapping 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical(ABTS^+·) and oxidation of DNA which was induced by Cu²⁺/glutathione(GSH), ·OH and 2,2'-azobis(2-amidinopropane hydrochloride)(AAPH). Among the nine 3-triazolo-coumarins, compounds 6c and 6f―6i were synthesized for the first time, which exhibited the capability of terminating radical propagation-chains in oxidation of DNA induced by AAPH. In this study, we found that phenethylamine moiety, hydroxyl and ortho-methoxy are the key groups to enhance the antioxidant activities of compounds.     

Scavenging Effects of Plant Antioxidants on Gas-Phase Free Radicals in Mainstream Cigarette Smoke

Cigarette smoke contains free radicals that are considered to be a major group of carcinogens. In the present study, we used plant antioxidants to treat cigarette filters for scavenging gas phase free radicals in cigarette smoke. The scavenging activities of four antioxidants against gas phase free radicals were analyzed using an improved spin trap protocol. The scavenging rates ranked as lycopene > grape seed extract > pycnogenol > tomato powder. A scavenging rate of 62% (p < 0.001) was obtained from the lycopene treatment. The use of plant antioxidants as potential scavengers for reducing free-radicals in cigarette smoke is discussed.     

Oxidation of DNA Bases Influenced by the Presence of Other Bases

Electrochemical detection of DNA is a highly important topic. Here we show that the electrochemical responses of one DNA base (guanine, adenine, cytosine or thymine), in terms of oxidation potential, current intensity, peak width and resolution can be highly influenced by the presence of other DNA bases at electrochemically reduced graphene oxide (ER‐GO) as well as standard glassy carbon electrode. We have observed that the effects were more significant for adenine base on ER‐GO and cytosine base on glassy carbon (GC) electrode. Differences in responses were generally low in a mixture of four different DNA bases but interestingly, deviations become significantly larger when only one or two other bases were present. Our findings are of paramount importance for future developments in DNA detection and analysis since individual DNA bases are not present in isolation in nature or in typical biosensing systems.     

硫酸存在时N-溴代苯二甲酰亚胺对甘露糖的胶束催化氧化

The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.     

Metal free in situ formation of phthalimide N-oxyl radicals by light-induced homolysis of N-alkoxyphthalimides

Irradiation of N-triphenylmethyloxy- or N-diphenylmethyloxy phthalimide is reported to result in the formation of phthalimide N-oxyl radical (PINO), which is able to initiate and propagate oxidative radical chain reactions of hydrocarbons.     

Oxidation of caffeine by phosphate radical anion in aqueous solution under anoxic conditions

The photooxidation of caffeine in presence of peroxydiphosphate (PDP) in aqueous solution at natural pH (∼7.5) has been carried out in a quantum yield reactor using a high-pressure mercury lamp. The reactions were followed spectrophotometrically by measuring the absorbance of caffeine at λ_max (272 nm). The rates of reaction were calculated under different experimental conditions. The quantum yields were calculated from the rates of oxidation of caffeine and the intensity of light at 254 nm which was measured by using peroxydisulphate solution as a standard chemical actinometer. The reaction rates of oxidation of caffeine by PDP increase with increase in [PDP] as well as with increase in light intensity, while they are independent of [caffeine]. The quantum yields of oxidation of caffeine by PDP are independent of [PDP] as well as light intensity. However, quantum yields of oxidation of caffeine by PDP increase with increase in caffeine concentration. On the basis of these experimental results and product analysis, a probable mechanism has been suggested in which PDP is activated to phosphate radical anions (PO₄ ^·2−) by direct photolysis of PDP and also by the sensitizing effect of caffeine. The phosphate radical anions thus produced react with caffeine by electron transfer reaction, resulting in the formation of caffeine radical cation, which deprotonates in a fast step to produce C8-OH adduct radicals. These radicals might react with PDP to give final product 1,3,7-trimethyluric acid and PO₄ ^·2− radicals, the latter propagates the chain reaction.     

Design and Synthesis of 1,4-Dihydropyridine and Cinnamic Acid Esters and Their Antioxidant Properties

In this study, cinnamic acid derivatives with pyridine ring were synthesized via Hantzsch reaction in order to expand conjugation system and their antioxidant abilities were tested. According to the evaluation results of their antioxidant properties, compounds 2 and 3 have similar antioxidant activity to prevent DNA from ^·OH^- and Cu²⁺/GSH induced oxidation, demonstrating that 1,4-dihydropyridine and pyridine nucleus exhibit good resistance to oxidation while the substituents have little effect. In the meantime, the AAPH-induced oxidative DNA damage[AAPH=2,2'-azobis(2-methylpropionamidine)dihydrochloride] and trapping ABTS^+· test show that N—H bond and large conjugation systems are the pivotal parts to improve the activities of antioxidant.     

水为洗脱液在表面活性剂胶束涂层固定相上分离手性药物

讨论了手性固定相稳定的条件，以表面活性剂胶束涂层为固定相，纯水作流动相，对氨氯地平，麻黄碱，伪麻黄碱，芬必得，美西律平和扑尔敏等外消旋药物进行了手性拆分，探索了手性药物氨地平及麻黄碱，伪麻黄碱的分离条件，当流动相的PH值为5．5时分离效果最佳，在流动相中加入2.5-5mmol/L硼酸时分离因子较大。     

氢醌对胆红素氧化过程的促进作用及其分析意义

研究了氢醌与胆红素的作用过程，发现氢醌在碱性条件下可促使胆红素氧化，且胆红素被氧化成胆绿素，此反应过程被证实为自由基反应，考察了介质条件，抗氧化剂等反应过程的影响及其它酚类物质对胆红素氧化的作用情况。     

Micelle formation of a cationic surfactant in the presence of 1,n-alkanediol and the miscibility of alcohols in micelles

Micelle formation of dodecyltrimethylammonium bromide (DTAB) was examined in the presence of α,ω-alkanediols applying conductivity measurements. Octanediol and hexanediol promoted the formation of mixed micelles of DTAB and the alcohol, but butanediol interfered with micellization. Analysis of the critical micelle concentration (cmc) based on the lattice model for mixed solution with the Bragg–Williams approximation indicated an unfavorable interaction between alcohol and water and a favorable interaction between the alcohol and surfactant, with the exception of butanediol. The exchange energy between alcohol and water was 0.5kT higher for alkanediol (C_2n(OH)₂) than for the corresponding regular alcohol (C_nOH), which is believed to have resulted from the smaller mixing entropy for the alkanediol than for the corresponding regular alcohol. It was inferred from the analysis that the cmc increase for C₄(OH)₂ was caused by favorable interaction with water but unfavorable interaction with the micellar surfactant.     

杂多钼酸盐中心原子(P,As)对催化氧化性能的影响

合成了具有不同中心原子Keggin阴离子结构的杂多钼酸盐M₃(XMo₁₂O₄₀)(M=K⁺,NH₄⁺,X=P,As)。利用FTIR、TPD、ESR和CV等手段考查了各化合物的氧化还原性质和酸性。比较两种不同中心原子的杂多钼酸盐,其中砷为中心原子的更容易被还原及有较低的酸强度,这类催化剂对异丁醛氧化脱氢活性较低,而对异丁醛氧化为甲基丙烯酸有较高的选择性,中心原子对活性和选择性的影响分别与它们氧化还原电位的升高关联,也与更易给出轿式氧有关。     

Vitamin K脉冲辐解与激光光解的研究(Ⅱ)——VK3水溶液氧化反应时间分辨的研究

Vitamin K3(VK3)是很好的电子载体,文献[1,2]利用微秒级脉冲辐解研究了VK3水溶液体系,测定了一些自由基与VK3进行的单电子氧化还原反应及相关动力学参数.     

声发射和激光拉曼研究镍氧化机制中的稀土元素效应

对纯镍及其表面离子注钇样品在1000℃空气中的恒温氧化和循环氧化行为进行了研究。用扫描电镜(SEM)和透射电镜(TEM)对氧化膜的表面形貌及结构进行了观测。研究表明离子注钇极大地提高了金属镍的抗氧化性能。此外,用声发射(AE)技术研究了氧化膜／基体界面上缺陷的分布情况,并用激光拉曼(Raman)谱对注钇引起的膜内应力变化进行了测量。结果表明,离子注钇降低了NiO氧化膜的生长速率,减小了表面NiO的晶粒尺寸,降低了膜内压应力水平。同时,离子注钇还减小了氧化膜／基体界面缺陷的平均尺寸和数目,因此,极大地提高了镍表面NiO氧化膜的粘附性和保护性。     

Efficient Oxidation of Alcohols with KBrO 3 in the Presence of Silica Chloride and Wet SiO 2

Alcohols were oxidized to their corresponding carbonyl compounds with KBrO 3 in the presence of silica chloride and wet SiO 2 , in solution and under solvent free conditions.     

SO4●－自由基氧化酪氨酸反应中的溶剂效应

研究了水-乙腈混合溶液中SO4●－自由基氧化酪氨酸的反应.实验结果表明，SO4●－自由基氧化酪氨酸的反应机制不因乙腈的加入而改变，但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加，SO4●－的衰变速率减慢而酪氨酸中性自由基（TyrO●）的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加，SO4●－氧化酪氨酸的反应速率减慢.这一实验结果意味着，在有机溶剂存在的情况下TyrO●/ TyrOH的氧化还原电势可能发生了变化，从而旁证了关于TyrO●/ TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测.     

SO·4-自由基氧化酪氨酸反应中的溶剂效应

研究了水-乙腈混合溶液中SO·4-自由基氧化酪氨酸的反应.实验结果表明,SO·4-自由基氧化酪氨酸的反应机制不因乙腈的加入而改变,但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加,SO·4-的衰变速率减慢而酪氨酸中性自由基(TyrO·)的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加,SO·4-氧化酪氨酸的反应速率减慢.这一实验结果意味着,在有机溶剂存在的情况下TyrO·/TyrOH的氧化还原电势可能发生了变化,从而旁证了关于TyrO·/TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测.     

Phase behavior of DNA in the presence of cetyltrimethylammonium bromide / alkyl polyglucoside surfactant mixture

Interaction of DNA with a CTAB/APG mixture was studied by determining its phase behavior. Results showed that, at low DNA concentration, the addition of APG could lead to earlier turbidity, indicating that APG can strengthen the interaction between CTAB and DNA. At high DNA concentration, however, APG had little influence on the turbidity boundary. We found that addition of salt could also lead to such an asymmetry of the phase map. Two mechanisms were presented to account for the asymmetry of the phase behavior. At the lower DNA concentration, it was assumed that the surfactant was bound to DNA in a way similar to that of micelle formation. That is, the binding is dominated by hydrophobic association processes. APG can facilitate this process by forming a surfactant mixture with CTAB, and salt facilitates this process by salting out effects. At high DNA concentrations, surfactants bind to DNA mainly through random electrostatic interaction. Addition of salt screens this interaction and therefore delays the turbidity. APG, however, exerts little influence on this process. Viscosity measurements at low DNA concentration showed that the complex with APG is more compact than that of CTAB alone with DNA.     

Direct Electrochemical Oxidation of DNA on Polycrystalline Gold Electrodes

Electrochemical CV and SWV studies were performed with double stranded DNA from salmon testes (dsDNA) and single stranded DNAs, containing 25 nucleotides (ssDNA) directly adsorbed at polycrystalline Au electrodes. A distinct oxidation peak at +730 mV (SWV, scan rate 0.248 V s^?1) or at +730 – +780 mV (CV, scan rate from 0.3 to 1 V s^?1) was obtained with DNA‐modified Au electrodes after a time‐dependent prepolarization step at a positive potential value, i.e., at +500 mV (vs. Ag|AgCl), performed with the DNA‐modified Au electrodes dipped in a blank buffer solution. No electrochemical activity was detected when ssDNA, containing no guanines, was used for adsorptive modification of the Au electrodes. Electrochemical impedance measurements registered a possible reorganization of the adsorbed DNA layer in the course of the prepolarization, accompanied by decreasing in‐phase impedance. The results enable us to relate the oxidation process observed at the DNA‐modified Au electrodes with the oxidation of guanine residues in DNA.