Microbial manganese oxide formation and interaction with toxic metal ions

Diverse bacteria and fungi oxidize Mn(II) enzymatically and produce insoluble Mn(III, IV) oxides, and these organisms are considered to be the primal agents for the occurrence of natural Mn oxide phases in most environments. Biogenic Mn oxides have a high sorption capacity for metal cations and an ability to oxidize numerous inorganic and organic compounds, owing to their structural and redox features. Thus, the microbial process is of significance in both biogeochemical and biotechnological contexts. In this article we summarize the enzymatic Mn(II) oxidation and interactions of biogenic Mn oxides with toxic metal and metalloid ions. Although Mn oxide formation by fungi has not been fully characterized yet, recent researches with ascomycetes emphasize the similarity between the bacterial and fungal Mn(II) oxidation with respect to the involved catalyst (i.e., multicopper oxidase-type enzymes) and the reaction product [i.e., layer-type Mn(IV) oxides]. Laboratory cultures of bacterial and fungal Mn oxidizers are expected to provide fundamental knowledge in their potential use for remediation of environments and effluents contaminated with toxic metal(loid) ions.     

柚皮苷-金属配合物的抗氧化活性研究

采用二苯代苦味肼基自由基(DPPH)法和硫代巴比妥酸法(TBA)对3种柚皮苷-金属配合物的抗氧化活性进行了测定.结果显示,3种柚皮苷-金属配合物对DPPH自由基均具有清除作用,其清除能力大小依次为:柚皮苷-铁(Ⅲ)配合物、柚皮苷-锌(Ⅱ)配合物和柚皮苷-铜(Ⅱ)配合物;柚皮苷-铁配合物和柚皮苷-锌配合物对亚油酸的过氧化反应均表现出抑制作用,其中柚皮苷-铁配合物的抗氧化活性高于抗坏血酸,而柚皮苷-铜配合物对亚油酸过氧化反应表现出较大的促进作用.柚皮苷与铁盐或锌盐形成金属配合物后其抗氧化活性得到提高,不同柚皮苷-金属配合物具有不同的抗氧化活性.     

Werner-type metal complexes of potato starch

It was shown that potato starch formed Werner‐type complexes. In these complexes a metal atom is ligated by the lone electron pairs of hydroxyl groups from d ‐glucose units and phosphate groups in starch. Acetate, chloride and nitrate were counter‐ions to the transition metal atoms. The metal cations bound preferentially to the phosphoric acid moiety of amylopectin, but secondarily they were co‐ordinated by the hydroxyl groups of the d ‐glucose units. This resulted in the formation of clathrate cages in which a significant number of the water molecules were trapped. Such structures were able to co‐ordinate further metal cations. Only Mn(II) and Co(II) ions, with acetate counter‐ions, neither formed clathrate cages nor were co‐ordinated by the hydroxyl groups of the d ‐glucose of starch.     

壳聚糖与DNA相互作用的研究

采用循环伏安法、紫外吸收光谱和荧光光谱研究了壳聚糖与DNA的相互作用。结果表明,壳聚糖与DNA分子之间发生了相互作用;DNA的紫外吸收光谱随壳聚糖浓度的增加表现出明显的增色效应和较小的红移。同时发现,随着壳聚糖浓度的增加,NaH2PO4-Na2HPO4、DNA和溴化乙锭(EB)混合溶液的荧光强度值下降,说明了壳聚糖和EB与DNA之间的结合存在竞争性;随着NaH2PO4-Na2HPO4离子浓度的增加,壳聚糖-EB-DNA三者形成的平衡体系整体荧光强度不断减弱,表明壳聚糖是以静电与DNA相互作用的。     

肉类香精的研究概况及其应用

简述了肉类香精的理论基础研究发展历程及其分类;重点介绍了肉类香精在方便面及熟肉制品中的应用,并展望了肉类香精的研究开发前景。     

芦丁金属配合物的制备及抑菌活性研究

研究了芦丁与Cu(Ⅱ)、Zn(Ⅱ)、Mn(Ⅱ)形成的金属离子配合物的合成、初步表征及其抑菌活性.结果表明,配合物的组成为[M3L2(H2O)n](CH3COO)2(n=1,2,3…),配体不饱和环的3个羟基参与了金属离子的配位作用;测定其摩尔电导率和红外光谱,对其抑菌活性较为显著.     

金属离子配合物的水解作用研究进展

金属离子配合物的水解作用正受到越来越多人的关注。相对于酶和化学试剂的水解作用,金属离子配合物的水解具有条件温和、易于实现和成本低廉的优点。综述了金属离子同环糊精、碳氮杂环、多聚糖和高分子支持物形成的配合物对肽键和磷酸键的水解作用的最新研究进展。     

A review on DNA interaction with synthetic phenolic food additives

Synthetic phenolic food additives occupy an important place in food industry. Among the various food additives butylated hydroxyanisol (BHA), tertiary butylhydroquinone (TBHQ), 2-tert-butyl-4-methylphenol (TBMP) and propyl gallate (PG) have potential to form molecular complexes with nucleic acid structure and have attracted recent attention for their prospective industrial utility. This review highlights the properties of these synthetic phenolic food additives and their interactions with calf thymus DNA (CT-DNA) reported by several research groups. Various analytical techniques were employed including absorbance and fluorescence spectroscopies, viscosity, voltammetry and thermodynamic studies to provide more details about binding mechanism of these food additives with DNA.     

Autoinducer-2-like activity associated with foods and its interaction with food additives

The autoinducer-2 (AI-2) molecule produced by bacteria as part of quorum sensing is considered to be a universal inducer signal in bacteria because it reportedly influences gene expression in a variety of both gram-negative and gram-positive bacteria. The objective of this study was to determine whether selected fresh produce and processed foods have AI-2-like activity and whether specific food additives can act as AI-2 mimics and result in AI-2-like activity. The luminescence-based response of the reporter strain Vibrio harveyi BB170 was used as the basis for determining AI-2 activity in the selected foods and food ingredients. Maximum AI-2 activity was seen on the frozen fish sample (203-fold, compared with the negative control) followed by tomato, cantaloupe, carrots, tofu, and milk samples. Interestingly, some samples were capable of inhibiting AI-2 activity. Turkey patties showed the highest inhibition (99.8% compared with the positive control) followed by chicken breast (97.5%), homemade cheeses (93.7%), beef steak (90.6%), and beef patties (84.4%). AI-2 activity was almost totally inhibited by sodium propionate, whereas sodium benzoate caused 93.3% inhibition, compared with 75% inhibition by sodium acetate. Sodium nitrate did not have any appreciable effect, even at 200 ppm. Understanding the relationships that exist between AI-2 activity on foods and the ecology of pathogens and food spoilage bacteria on foods could yield clues about factors controlling food spoilage and pathogen virulence.     

Contribution of partially labile complexes to the DGT metal flux

Penetration of complexes into the resin layer can dramatically increase the contribution of complexes to the metal flux measured with a DGT (diffusive gradients in thin films) sensor, but equations to describe this phenomenon were not available. Here, simple approximate analytical expressions for the metal flux, the lability degree and the concentration profiles in a DGT experiment are reported. Together with the thickness of the reaction layer in the gel domain, the effective penetration distance into the resin layer that would be necessary for full dissociation of the complex (λ(ML)) plays a key role in determining the metal flux. An increase in the resin-layer thickness (r) effectively increases the metal flux and the lability degree until r ≈ 3λ(ML). For the usual DGT configuration, where the thickness of the gel layer exceeds that of the resin layer, the complex is labile if r > (D(ML)/k(d))?, where D(ML) is the diffusion coefficient of the metal complex and k(d) its dissociation rate constant. A general procedure for estimating the lability of any complex in a standard DGT configuration is provided.     

Co-transport of metal complexes by the green mussel Perna viridis

We examined the uptake of ligand-bound metals (Cd and Zn) by the green mussel Perna viridis using defined artificial seawater. Different free ion concentrations (1 pM to 10 microM) in uptake solutions were created by adding different amounts of total metals (Cd 0.1 nM to 0.1 mM; Zn 0.5 nM to 0.05 mM) and ligands (EDTA, NTA, citric acid). Our results showed that Cd and Zn uptake could not be fully explained by the free Cd and Zn concentrations in the presence of different ligands, indicating that metal-ligand complexes were at least partially available for uptake by the mussels. Total Zn concentrations appeared to be a better predictor of metal uptake than the free Zn ion concentrations in the presence of different ligands. Uptake of lipophilic organic metal complexes was substantially greater than the hydrophilic metal complexes, even though the free ion concentration was comparable or lower. Moreover, the radiolabeled ligand compounds were directly accumulated by the mussels. The accumulation of metal complexes may explain the increased metal uptake with increasing ligand and total metal concentration, even though the free ion metal concentration was constant. Overall, our experimental results indicated that free metal ion cannot fully explain metal uptake since metal complex species were also available to the mussels to some extent, apparently through a co-transport process.     

Sensory interaction of umami substances with model food matrices and its hedonic effect

Palatability changes in seven model foods (soups and mashed potato) evoked by various combinations of monosodium glutamate (MSG) and disodium inosinate and guanylate (I + G) were studied. Flavour enhancers were added to each food matrix according to the same factorial design. The magnitude, direction and regularity of hedonic responses were highly product-dependent. Contribution of MSG and I + G to palatability-enhancement also varied for different model product: in chicken broth and vegetable soup MSG played the leading role; in mushroom, red beets and asparagus soups contribution of I + G was considerable. In green peas cream soup the supplementation by MSG/I + G evoked mostly negative hedonic effect. Analysis of naturally present free amino acids revealed considerable differences in their amount and composition. The interaction of naturally present glutamates and added umami substances (and probably other sensory-active compounds) might be at least partially responsible for observed diversity of hedonic responses.     

休闲食品和谷物制品包装系统的演进

<正> 休闲食品和谷物制品是目前市场上相当受欢迎的食品,这不仅由于产品本身美味可口,食用方便,还与其包装有莫大的关系,这要归功于其包装系统的不断革新与进步。事实上,休闲食品和谷物制品的发展历史并不悠久,但因市场迅速膨胀,用以包装这些食品的方法因而发生了巨大的变化。本文将探讨这两种食品包装技术的发展情况。     

Metribuzin degradation by membrane anodic Fenton treatment and its interaction with ferric ion

Metribuzin, a widely used herbicide and a frequently detected pollutant in the environment, was studied as a target compound for membrane anodic Fenton treatment (AFT), a Fenton technology with application potential for on-site treatment of pesticide wastewater. It was found that the degradation kinetics of metribuzin do not obey the AFT model, a previously developed model that fit AFT degradation kinetics of all previously investigated pesticides. The lack of fit for metribuzin data was determined to result from a weak interaction between metribuzin and the ferric ion, resulting in a significant reduction in availability of metribuzin for reaction with hydroxyl radicals during AFT, thus slowing degradation. A revised kinetic model was developed based on the original AFT model with the addition of this interaction. Results demonstrate that the new kinetic model fits metribuzin degradation data quite well at different delivery rates of Fenton reagent and at different temperatures. This weak interaction is also found to exist between ferric ion and several other triazinone/triazine herbicides during membrane AFT. The interaction intensity correlates with the electron-withdrawing/-donating property of substituents on the triazine/triazinone ring. The stronger the electron-donating ability of substituents, the stronger the interaction.     

The interaction of sesamol with DNA and cytotoxicity,apoptosis, and localization in HepG2 cells

Sesamol, a nutritional antioxidant phenolic compound present in sesame seed, has a potential therapeutic molecule effect against cancers. In this study, the interaction between sesamol and DNA was investigated by employing ultraviolet/visible (UV/Vis), fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR), and molecular modeling. The fluorescence analysis indicated that the fluorescence quenching mechanism of sesamol by calf thymus DNA (ctDNA) occurred through static quenching. The UV/Vis, CD, FT-IR spectra and molecular docking results implied that the primary binding mode was minor groove binding. Furthermore, the intracellular interaction of sesamol with DNA and its bioactivity effect were explored. The cell activity results demonstrated that sesamol induced hepatic cell line (HepG2) death. The acridine orange (AO)/ethidium bromide (EB) staining assay and DNA fragmentation confirmed that sesamol could efficiently induce the apoptosis of HepG2 cells. Moreover, addition of sesamol to HepG2 cells resulted in nuclear localization, as visualized by confocal microscopy.     

Trace metal distribution coefficients in the Mersey Estuary,UK: evidence for salting out of metal complexes

An examination of partition data for trace metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) from a number of independent studies conducted in a highly contaminated, organic-rich estuary (Mersey, UK) indicates an increase in the sediment-water distribution coefficient, KD, with increasing salinity for all metals with the excepton of Cd. This behavior is not consistent with inorganic speciation calculations or empirical modeling studies in other estuaries, which predict an inverse relationship between KD and salinity due to competitive adsorption and complexation with seawater ions. The data are, however, well-defined by an empirical model based on the salting out of neutral organic chemicals and yield salting constants in the range 0.7-2.0 L mol(-1). It is suggested that trace metals are complexed by and, subsequently, neutralize organic ligands, and that the resulting neutral assemblages are salted out, possibly via electrostriction. Examination of sorption date from other environments suggests that the effect may be more general in highly contaminated or organic-rich estuaries, and that a specific pool of relatively large, but undefined ligands, is mainly responsible.     

金属硫蛋白及其重金属解毒功能研究进展

近年来,全球范围内重金属污染日益严重,大量重金属元素进入人体并产生蓄积,严重威胁到人类健康,因此寻找安全、高效的重金属解毒天然产物引起国内外学者越来越多的重视。金属硫蛋白是一种低分子量、富含半胱氨酸的胞内蛋白质,根据不同的蛋白质结构可将金属硫蛋白分为MT-Ⅰ、MT-Ⅱ、MT-Ⅲ和MT-Ⅳ四种异构形式。金属硫蛋白含有大量巯基,这一特殊结构赋予了其螯合重金属离子及重金属解毒功能。本文综述了目前通用金属硫蛋白定义及其构型分类方式;阐述了不同构型金属硫蛋白的蛋白质结构;重点归纳了金属硫蛋白解除重金属毒性机制及其在重金属解毒产品中的应用。本文同时指出了我国在金属硫蛋白研究与应用方面存在的不足,旨在为金属硫蛋白在重金属解毒方面的研究与应用提供参考依据。     

通信卫星金属网状天线及其编织技术

从民用通信的需求出发,对通信卫星金属网状天线的性能要求进行阐述,分析金属丝编织网的编织方法,提出通信卫星金属网状天线用金属丝编织网材料今后的研究方向。