铂电极上二茂铁甲基季铵盐电催化氧化异烟肼的电化学及其动力学性质研究

在0.1 mol·L-1Na2SO4水溶液中,二茂铁甲基季铵盐对异烟肼的电化学氧化具有很好的催化作用。运用循环伏安法研究了二茂铁甲基季铵盐和异烟肼的浓度、扫描速率分别对该电催化氧化体系的影响,同时运用循环伏安法和计时电流法探讨了该电催化氧化反应体系的电化学动力学规律,由电化学动力学测定并计算出了该催化体系的电子转移系数α、反应级数、催化反应速率常数k值。     

甲基红-H2O2-HRP伏安酶联免疫分析法测定HRP及其标记物

提出了一种新的辣根过氧化物酶的底物-甲基红,它本身具有电化学活性,能够在静汞电极上发生还原反应,产生灵敏的伏安电流信号.以H2O2为氧化剂,HRP能催化氧化还原反应的发生,使甲基红被氧化分解,其平衡浓度降低,对应的还原峰电流降低,峰电流的降低值与HRP的质量浓度在5.0×10-8～5.0×10-7g/mL之间呈线性关系,对2.0×10-7g/mL HRP进行11次测定的相对标准偏差为4.6%,方法的检出限为1.8×10-8g/mL.应用于IgG-HRP和Avidin-HRP的测定.     

新型二茂铁甲基季铵盐离子液体的合成与表征

以二茂铁与二甲胺为原料合成了碘化二茂铁甲基季铵盐,再经复分解反应得到乙酸二茂铁甲基季铵盐离子液体;表征了离子液体的结构,测定了其熔点和溶解性.结果表明,合成的乙酸二茂铁甲基季铵盐离子化合物熔点低于100℃,是一种新型的二茂铁甲基季铵盐离子液体.     

α，β-不饱和酮的绿色环氧化

以过氧化氢为氧源,磷钨杂多酸季铵盐为催化剂,研究了α,β-不饱和酮的环氧化反应,考察了溶剂、温度、催化剂用量、反应时间以及底物浓度等因素对环氧化反应的影响. 结果表明,在适宜反应条件下,过氧化氢/磷钨杂多酸季铵盐催化体系可以催化α,β-不饱和酮环氧化,得到相应的环氧化合物,并能取得较好的结果. 其中, 4-甲基-3-戊烯-2-酮的环氧化合物的产率达到了87%.     

肿瘤标记物1-甲基鸟苷的微分脉冲伏安法的研究

建立一种灵敏的测定修饰核苷1 甲基鸟苷(1 MG)的电化学分析方法.在pH为2.00的BR缓冲液中,用循环伏安法(CV),线性扫描伏安法(LSV),方波伏安法(SWV),微分脉冲伏安法(DPV)等现代电化学技术研究了肿瘤标记物1 甲基鸟苷在玻碳电极(GCE)上的伏安行为.实验结果表明,pH为2.00的BR缓冲液中,1 甲基鸟苷在+1.16V(vs.甘汞)电位处产生一个灵敏的微分脉冲阳极氧化峰,该氧化峰的峰电流值与1 甲基鸟苷的浓度在4.0×10-7～1.0×10-5mol/L范围内呈良好的线性关系,最低检测限达(定义为D=2σ/K)6.6×10-8mol/L.将该法应用于兔血清及尿样中1 甲基鸟苷的测定,回收率在96.0%～102.0%之间,5次测定的相对标准偏差(RSD)均小于3 5%.并初步研究了1 甲基鸟苷的电化学机理.     

嵌入式超薄碳糊膜电极伏安法同时测定黄嘌呤和次黄嘌呤

以镍铬合金为基体制备了嵌入式超薄碳糊膜电极,研究了黄嘌呤(Xa)和次黄嘌呤(Hxa)在该电极上的电化学行为。该电极对Xa和Hxa具有良好的电化学催化特性。两峰电位相差320mV。其氧化峰电流与Xa和Hxa的浓度在5.0×10-8～8.0×10-5mol/L和7.0×10-8～7.0×10-5mol/L范围内呈良好线性关系;检出限为2.0×10-10mol/L。电极制备简单,有良好的灵敏度、选择性和稳定性。该方法可用于人尿中Xa和Hxa的同时测定。     

抗坏血酸在β-环糊精/二茂铁甲酸修饰电极上的电化学行为及测定

利用主客体化学反应将二茂铁甲酸包络在β-环糊精聚合物的空穴中,用新鲜蛋清作交联剂制成β-环糊精聚合物/二茂铁甲酸化学修饰玻碳电极,用电化学阻抗法和循环伏安法研究了修饰电极的电化学性能。在pH 7.0的磷酸盐缓冲溶液中,该修饰电极对抗坏血酸的电化学氧化有很好的催化活性,氧化峰电流与其浓度在6.2×10-6~5.0×10-3mol/L范围内呈良好的线性关系,线性回归方程为ip=0.4375+0.0301C(ip:μA,C:μmol/L),相关系数r=0.9982,检出限为1.0×10-6mol/L。抗坏血酸和多巴胺在修饰电极上于不同的电位(ΔE=490 mV)被氧化,可用于多巴胺存在下选择性测定抗坏血酸。     

二茂铁/L-半胱氨酸修饰电极的电化学行为及电催化性能

利用配对试剂将二茂铁酰胺键合在L-半胱氨酸自组装单层膜(SAM)表面, 制成稳定的二茂铁/L-半胱氨酸修饰电极, 该电极在pH 7.0的磷酸盐缓冲液中有一对很好的氧化还原峰. 运用循环伏安法和交流阻抗谱详细研究了修饰电极的电化学行为, 测得电子转移系数为0.66, 表观电极反应速率常数为6.86 s-1. 该修饰电极对肾上腺素有很好的催化作用, 峰电流与肾上腺素浓度在2.0×10-7～1.0×10-5 mol·dm-3范围内呈现良好的线性关系.     

P2W18杂多酸-萘胺修饰电极研制及应用

研制了Dawson型杂多酸P2W18-1_萘胺化学修饰电极 ,采用循环伏安法等方法研究了聚合膜电极的电化学特性。在弱酸性介质中 ,电极对亚硝酸根的氧化有电催化作用。亚硝酸盐的浓度在1×10 -6～1×10-4mol/L范围内 ,催化电流与亚硝酸根浓度成线性关系。电极用于水样中NO2- 含量测定 ,结果令人满意     

美索巴莫在［BnMIM］PF6修饰碳糊电极上的电催化氧化及电分析方法

研究了美索巴莫（MET）在离子液体1-苄基-3-甲基咪唑六氟磷酸盐［BnMIM］PF6修饰碳糊电极（［BnMIM］PF6/CPE）上的电催化氧化行为和电化学动力学性质,并用循环伏安法（CV）、计时电流法（CA）测得MET在［BnMIM］PF6/CPE上的电极反应过程动力学参数。实验结果表明,MET在［BnMIM］PF6/CPE上发生了受扩散控制的不可逆电化学氧化过程。用方波伏安法（SWV）测得MET氧化峰电流（Ipa）与其浓度在3.0×10-5~1.0×10-2 mol?L-1范围内呈良好线性关系,检出限（S/N=3）为3.3×10-6 mol?L-1。同时运用SWV法对市售美索巴莫片进行电化学定量测定,RSD为1.5%~2.5%,加标回收率为98%~99%。     

Enantiomer separation by CEC——Enantiomer separation by packed-capillary electrochromatography

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (β-CD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R_s) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2 cm packed length. Efficiency of 45 000 theoretical plates per meter and R_s of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R_s of 2.60. (ⅱ) 75 μm I.D. capillary was packed with octadecylsilica particles (ODS). Chiral separat     

Regioselectivity of olefin oxidation by iodosobenzene catalyzed by metalloporphyrins : control by the catalyst

The regioselectivity of the oxidation of three monosubstituted olefins, 6-phenoxyhex-1-ene, hex-1-ene and styrene, by iodosobenzene in the presence of various Fe-, Mn- or Cr-tetraaryl-porphyrins, was studied. It was found that, besides epoxides, known products from such systems, allylic alcohols and aldehydes were formed, the latter not being derived from the corresponding epoxides. The relative importance of these reactions greatly depends upon both the metal and porphyrin constituents of the catalyst. More particularly, the competition between epoxidation and allylic hydroxylation can be efficiently controlled by non-bonded interactions between the olefin and porphyrin substituents. No hydroxylation of the aromatic rings and no oxidative dealkylation of the ether function was detected.     

Glycosidase inhibition by macrolide antibiotics elucidated by STD-NMR spectroscopy

A glycosynthase approach was attempted to glycodiversify macrolide antibiotics, using DesR, a family-3 retaining beta-glucosidase involved in the self-resistance mechanism of methymycin production. STD-NMR was used to probe enzyme-substrate interactions. Analysis of competitive STD-NMR experiments between erythromycin A and a chromogenic substrate (pNP-beta-d-glucose) with the hydrolytically inactive nucleophile mutants led us to discover a family of unprecedented glycosidase inhibitors. Analysis of kinetic data with wild-type DesR determined that erythromycin is a competitive inhibitor of the glucosidase (IC50 = 2.8 +/- 0.3 microM and Ki = 2 +/- 0.2 microM) with respect to the hydrolysis of pNP-beta-d-glucose. Comparable inhibitory data was obtained for clarithromycin; however, the inhibitory effect of azithromycin was weak and no significant inhibition was observed with methymycin or d-desosamine. This report documents significant inhibition of glycosidases by macrolide antibiotics and provides insight into the design of novel glycosidase inhibitors based on the macrolactone ring of macrolide antibiotics.     

Membrane solubilization by detergent: resistance conferred by thickness

The commonly held model for membrane dissolution by detergents/surfactants requires lipid transport from the inner to the outer bilayer leaflet ('flip-flop'). Although applicable to many systems, it fails in cases where cross-bilayer transport of membrane components is suppressed. In this paper we investigate the mechanism for surfactant-induced solubilization of polymeric bilayers. To that end, we examine the dissolution of a series of increasingly thick, polymer-based vesicles (polymersomes) by a nonionic surfactant, Triton X-100, using dynamic light scattering. We find that increasing the bilayer thickness imparts better resistance to dissolution, so that the concentration required for solubilization, after a fixed amount of time, increases nearly linearly with membrane thickness. Combining our experimental data with a theoretical model, we show that the dominant mechanism for the surfactant-induced dissolution of polymeric vesicles, where polymer flip-flop across the membrane is suppressed, is the surfactant transport through the bilayer. This mechanism is different both qualitatively and quantitatively from the mechanisms by which surfactants dissolve pure lipid vesicles.     

Antibiotic recognition by binuclear metallo-beta-lactamases revealed by X-ray crystallography

Metallo-beta-lactamases are zinc-dependent enzymes responsible for resistance to beta-lactam antibiotics in a variety of host bacteria, usually Gram-negative species that act as opportunist pathogens. They hydrolyze all classes of beta-lactam antibiotics, including carbapenems, and escape the action of available beta-lactamase inhibitors. Efforts to develop effective inhibitors have been hampered by the lack of structural information regarding how these enzymes recognize and turn over beta-lactam substrates. We report here the crystal structure of the Stenotrophomonas maltophilia L1 enzyme in complex with the hydrolysis product of the 7alpha-methoxyoxacephem, moxalactam. The on-enzyme complex is a 3'-exo-methylene species generated by elimination of the 1-methyltetrazolyl-5-thiolate anion from the 3'-methyl group. Moxalactam binding to L1 involves direct interaction of the two active site zinc ions with the beta-lactam amide and C4 carboxylate, groups that are common to all beta-lactam substrates. The 7beta-[(4-hydroxyphenyl)malonyl]-amino substituent makes limited hydrophobic and hydrogen bonding contacts with the active site groove. The mode of binding provides strong evidence that a water molecule situated between the two metal ions is the most likely nucleophile in the hydrolytic reaction. These data suggest a reaction mechanism for metallo-beta-lactamases in which both metal ions contribute to catalysis by activating the bridging water/hydroxide nucleophile, polarizing the substrate amide bond for attack and stabilizing anionic nitrogen intermediates. The structure illustrates how a binuclear zinc site confers upon metallo-beta-lactamases the ability both to recognize and efficiently hydrolyze a wide variety of beta-lactam substrates.