Electro‐induced polymerization of acrylamide initiated by the potassium permanganate–titriplex VI redox system

The polymerization of acrylamide (AAm) was carried out with a potassium permanganate–Titriplex VI redox initiator system with and without electrolysis. Because of the high metal‐ion concentration in general, low‐molecular‐weight polymers were obtained (weight‐average molecular weight = 2600–4000). The effect of potassium permanganate and AAm concentrations and temperature on the polymerization yield was studied and compared with results obtained under the same experimental conditions used for electrolysis. The results of Fourier transform infrared spectroscopy, atomic absorption spectrometry, and scanning electron microscopy (SEM) results are given. SEM micrographs of the polymer obtained by electrochemical methods exhibited smoother surfaces than those obtained by nonelectrolytic methods. In the absence of potassium permanganate, there was no polymerization under experimental conditions. A possible reaction mechanism is suggested. The electro‐induced system resulted in about a 50% increase in the yield. Manganese content in the electro‐induced and chemical polymerization systems were 2.7 and 8.2%, respectively, supporting the yield increase in the electro‐induced system. A graphite electrode was used and resulted in a high yield and a fibrous polymeric structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1526–1534, 2001     

The competitive interactions between the anion-receptor, anions and neutral solvent species

In this article, studies on coordinative properties of 5,11,17,23-tetra-p-tert-butyl-25,27-bis(N-p-nitrophenylureido-butoxy)-26,28-dipropoxycalix[4]arene (Cx2) are presented. Since this anion-receptor was previously used as an additive to solid polymer electrolytes, the correlation of the data presented here and the role of anion-receptors in this type of electrolytes is discussed. The formation constants of salt-receptor complexes and receptor self-complexation (dimer formation) are estimated in the solution in the non-interacting solvent using ¹H and ¹⁹F NMR titration. Independently, the affinity of the Cx2 to low molecular weight analogs of PEO and some other organic solvents in this system was tested using the same technique. The estimated values of the formation constants are used in the discussion the role of the anion-receptor in the changes of concentration of ions, ionic agglomerates and complexes of Cx2 in the system comprising salt, solid or liquid matrix and anion-receptor.     

中和滴定法在生产中的应用

在强酸与弱酸、强碱与弱碱的生产中利用中和滴定法测定其含量的方法简捷、实用 ,测定的结果比较精确 ,应用范围广     

硼酸测定中强化试剂效果比较

考察了几种不同的多元醇作为强化试剂,对硼酸强化后进行对比测试,从中筛选出较为合适的强化试剂和合理的用量,结果表明,几种多元醇均可很好地强化硼酸,滴定终点颜色变化灵敏,结果准确,该方法操作简单、快速、测定重现性好,获得了满意的结果,为拓宽硼酸测定的方法提供了可靠的理论依据.     

Cloning,Expression and Purification of Cindoxin,an Unusual Fmn‐Containing Cytochrome P450 Redox Partner

Cytochromes P450 (P450s) belong to a superfamily of haemoproteins that catalyse a remarkable variety of oxidative transformations. P450 catalysis generally requires that cognate redox proteins transfer electrons, derived ultimately from NAD(P)H, to the P450 for oxygen activation. P450_cin (CYP176A1) is a bacterial P450 that is postulated to allow Citrobacter braakii to live on cineole as its sole carbon source by initiating cineole biodegradation. Here we report the cloning, expression, purification and characterisation of one of its postulated redox partners, cindoxin (Cdx), which has strong similarity to the FMN domain of cytochrome P450 reductase. Cindoxin reductase (CdR), which displays strong similarity to NADPH‐dependent ferredoxin reductases, was unable to be expressed in a functional form. Mass spectrometric and HPLC analyses confirmed that the flavin cofactor of cindoxin was FMN. Redox potentiometric titrations were performed with cindoxin within the range 6<pH<8; this enabled the quinone/semiquinone (E₁) and semiquinone/hydroquinone (E₂) redox potentials to be determined. Our results show that cindoxin might be somewhat different to other flavodoxins that interact with P450s, in which generally only one couple is important. Both redox states of cindoxin could be catalytically relevant. A catalytically active system was reconstituted in vitro with E. coli flavodoxin reductase (Fpr) acting as the terminal redox partner in the absence of CdR. Our results show that Cdx and Fpr support regio‐ and stereoselective P450_cin‐catalysed cineole oxidation to (1R)‐6β‐hydroxycineole with turnover rates up to 1500 min^?1. This system is tightly coupled with 80 % of NADPH reducing equivalents funnelled into substrate oxidation.     

Controlled band dispersion for quantitative binding determination and analysis with electrospray ionization‐mass spectrometry

This review discusses recent emerging techniques that have been used to couple flow‐injection analysis (FIA) and electrospray ionization‐mass spectrometry (ESI‐MS) for the quantitation of noncovalent binding interactions. Focus is placed predominantly on two such methods. Diffusion‐based measurements, developed by Konermann and co‐workers, uses controlled‐band dispersion prior to ESI‐MS to determine diffusion constants and binding constants based on the temporal variation of ligand signal measured in the mass spectrum (an indirect technique). Dynamic titration, developed by Schug and co‐workers, is a direct method, where a temporal compositional gradient of a guest molecule is induced in the presence of host in solution to monitor the concentration dependence of complex formation as a function of observed complex ion abundance after ESI‐MS. Further discussion places these techniques in the context of a variety of other direct and indirect ESI‐MS‐based binding determination methods, and highlights advantages, disadvantages, and practical considerations for their proper use to investigate a broad range of macromolecular and small‐molecule interaction systems. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:806–829, 2010     

Enhanced transformation of triclosan by laccase in the presence of redox mediators

Triclosan (TCS), an antimicrobial agent, is an emerging and persistent environmental pollutant that is often found as a contaminant in surface waters and sediments; hence, knowledge of its degradability is important. In this study we investigated laccase-mediated TCS transformation and detoxification, using laccase (from the fungus Ganoderma lucidum) in the presence and absence of redox mediators. Transformation products were identified using HPLC, ESI-MS and GC-MS, and transformation mechanisms were proposed. In the absence of redox mediator, 56.5% TCS removal was observed within 24 h, concomitant with formation of new products with molecular weights greater than that of TCS. These products were dimers and trimers of TCS, as confirmed by ESI-MS analysis. Among the various mediators tested, 1-hydroxybenzotriazole (HBT) and syringaldehyde (SYD) significantly enhanced TCS transformation (∼90%). The presence of these mediators resulted in products with lower molecular weights than TCS, including 2,4-dichlorophenol (2,4-DCP; confirmed by GC-MS) and dechlorinated forms of 2,4-DCP. When SYD was used as the mediator, dechlorination resulted in 2-chlorohydroquinone (2-CHQ). Bacterial growth inhibition studies revealed that laccase-mediated transformation of TCS effectively decreased its toxicity, with ultimate conversion to less toxic or nontoxic products. Our results confirmed the involvement of two mechanisms of laccase-catalyzed TCS removal: (i) oligomerization in the absence of redox mediators, and (ii) ether bond cleavage followed by dechlorination in the presence of redox mediators. These results suggest that laccase in combination with natural redox mediator systems may be a useful strategy for the detoxification and elimination of TCS from aqueous systems.     

Reconstructing a Flavodoxin Oxidoreductase with Early Amino Acids

Primitive proteins are proposed to have utilized organic cofactors more frequently than transition metals in redox reactions. Thus, an experimental validation on whether a protein constituted solely by early amino acids and an organic cofactor can perform electron transfer activity is an urgent challenge. In this paper, by substituting “late amino acids (C, F, M, T, W, and Y)” with “early amino acids (A, L, and V)” in a flavodoxin, we constructed a flavodoxin mutant and evaluated its characteristic properties. The major results showed that: (1) The flavodoxin mutant has structural characteristics similar to wild-type protein; (2) Although the semiquinone and hydroquinone flavodoxin mutants possess lower stability than the corresponding form of wild-type flavodoxin, the redox potential of double electron reduction E_m,7 (fld) reached −360 mV, indicating that the flavodoxin mutant constituted solely by early amino acids can exert effective electron transfer activity.     

EDTA滴定法测定铝土矿石中氧化铝含量的不确定度评定

不确定度可用于对试样加工质量的评估、内检和外检质量评估以及不同分析方法等的质量评估。通过对EDTA滴定法测定铝土矿石中氧化铝的不确定度来源进行分析识别，并对影响不确定度的各分量进行量化，计算合成标准不确定度和扩展不确定度并给出不确定度报告。结果表明，分取试样溶液的体积是最大的不确定度来源。     

土壤腐殖酸的质子解离平衡研究

本文用电位滴定法对提纯了土壤胡敏酸ＨＡ，富啡酸ＦＡ的质子解离子平衡进行了研究，并根据离子散模和连续亲和谐模型对实验数据进行了分析，得知ＨＡ和ＦＡ均含有三类酸性基团，