人尿中氟含量的测定及其意义

采用氟离子选择电子法对右江民族医学院28名≥19岁的成年健康学生(其中男生18名,女生10名)早上和晚上尿样分别进行了氟含量测定。结果表明,早上和晚上尿样尿氟含量有一定差异,而早上尿样中的氟含量小于晚上尿样。可认为从早到晚的时段内,人体从食物、水源或其它途径摄入了氟,从而出现了差异;样品氟含量的最大值0.959 mg/L在百色地区正常人尿氟百分位数法(P25～P97.5)正常值范围0.589～2.268 mg/L内,可认为右江民族医学院的人员未出现氟中毒,处于一个氟安全的地区。     

气相色谱法测定饮料酒中的低沸点有机酸

在非质子极性溶剂-二甲基乙酰胺中,室温下用碘乙烷与C_1—C_6脂肪酸及乳酸的四甲基铵盐反应制备各酸相应的乙酯。乙酯在15%的邻苯二甲酸二壬酯与6%的土温-80混合固定液填充柱上获得满意分离。用本法测定饮料酒中的低沸点有机酸含量,简便、快速、准确。     

Simultaneous kinetic determination of thiocyanate and sulfide using eigenvalue ranking and correlation ranking in principal component-wavelet neural network

In this work, two toxic compound, sulfide and thiocyanate were determined simultaneously using kinetic spectrophotometry. These anions have shown the catalytic effects on the reaction between iodine and azide. Since the system was nonlinear, a nonlinear model, principal component-wavelet neural network (PC-WNN) was used as the multivariate calibration method. The principal component analysis was used to decrease the dimension of the original matrix. In other words, the scores of the PCs, 5, instead of the original variables, 301, were used as the input for the model. Two methods were used to select the most relevant principal components: eigenvalue ranking and correlation ranking. In this work, eigenvalue and correlation ranking methods have shown better results for thiocyanate and sulfide, respectively, and it can be concluded that these methods are complementary. The WNN has several advantages relative to other types of neural network such as better convergence ability. The data set was divided to calibration, prediction and validation sets. Each set was selected so that the concentrations of the analytes were approximately covered the entire ranges of the analytes. Mean relative error for thiocyanate and sulfide in validation set were 8.5 and 10.6, respectively. Thiocyanate and sulfide can be determined in the range of 60–700 ng ml⁻¹ and 20–400 ng ml⁻¹, respectively. The proposed method was applied for the determination of sulfide and thiocyanate in real samples such as tap, waste and river waters with satisfactory results.     

A Zn(Ⅱ) 5-Aminoisophthalate Coordination Polymer

The title compound, [Zn(AIP)(4,4-bipy)0.5(H2O)]n·0.75nH2O 1, was synthesized via the hydrothermal reaction of Zn(OAc)2 with 5-aminoisophthalic acid (H2AIP) and characterized by elemental analysis and infrared spectra. The complex crystallizes in monoclinic system, space group P21/c with a = 12.672(1), b = 7.6557(4), c = 16.181(1) (A),β = 109.187(2)o, V = 1482.6(2) (A)3, Z = 1, C52H52N8O23Zn4, Mr = 1418.58, Dc = 1.589 g/cm3, F(000) = 724 and μ(MoKα) = 1.685mm-1. The final R = 0.0702 and wR = 0.1524 for 1847 observed reflections with Ⅰ ＞ 2σ(I), and R = 0.0873 and wR = 0.1664 for all data. X-ray diffraction studies reveal that the title compound has an interesting 2D microporous architecture with guest water molecules inside the channel.     

GABAA五种亚型受体与BZ配基的3D-QSAR研究

GABAA受体是中枢神经系统内重要的抑制性受体,有广泛的神经生理活性.由于镇静/抗惊厥药物在临床上的广泛应用,使得其中苯并二氮杂作用位点尤为重要.我们用比较分子场法(CoMFA)对一系列咪唑苯并二氮杂类化合物（BZ）与五种重组受体亚型的亲和力进行了结构活性关系研究,得到的一组模型都有较高的交叉验证系数.并在此基础上,建立了非交叉验证的一组PLS模型.用该组模型对随机选择的6个化合物组成的测试集进行了预测,都得到了相当满意的结果,表明所建立的一组模型具有良好的预测能力.本研究对于设计高亲和力的BZ受体的配基和研究GABAA受体的模型有指导意义.     

Flexibility and Rigidity of Proteins and Protein–Pigment Complexes

Proteins may be rigid or flexible to various degrees as required for optimal function. Flexibility of large parts of a protein, which rearrange or move, is particularly interesting and will be discussed in this article. We differentiate between several categories, although the boundaries between them are diffuse: flexibility of peptide segments, order–disorder transitions of spatially contiguous regions, and domain motions. The domains may be flexibly linked to allow rather unrestricted motions or the motions may be constrained to certain modes. The various categories of large-scale flexibility will be illustrated with the following examples: (1) Small protein proteinase inhibitors are rather rigid molecules which provide binding surfaces complementary to their cognate proteases but show also limited segmental flexibility and adaptation. (2) Large plasma proteinase inhibitors exhibit large conformational changes after interaction with proteases probably for regulatory purposes. (3) Pancreatic serine proteases employ a disorder–order transition of their activation domain as a means to regulate enzymic activity. (4) Immunoglobulins show rather unrestricted and also hinged domain motions in different parts of the molecule probably to allow binding to antigens in different arrangements. (5) Citrate synthase adopts open and closed forms by a hinged domain motion to bind substrates and release products and to perform the catalytic condensation reaction, respectively. (6) Riboflavin synthase, a bifunctional multienzyme complex, catalyzes two consecutive reactions by means of two subunits, α and β. The β-subunits form a shell, in which the α-subunits are enclosed. Diffusional motion of the catalytic intermediates is therefore restricted. In addition, rearrangement of the N-terminal segment occurs during the assembly of the β-subunit. In contrast, rigidity is dominant in the structures of the light-harvesting complexes and the photosynthetic reaction centers involved in photosynthetic light reactions. These are large protein–pigment complexes in which the proteins serve as matrices to hold the pigments in the appropriate conformation and relative arrangement. Since motion would contribute to deactivation of the photoexcited states of the pigments and diminish the efficiency of light-energy and electron transfer, the functional role of rigidity is easy to rationalize for these proteins.     

HRGC of wine free amino acids as a tool for elementary wine characterization

In this paper we show that wine free amino acids derivatized as isopropyl N-heptafluorobutyryl esters can be used as a tool for wine characterization. Elementary wines of eight Vitis vinifera varieties were studied during a seven year period. The characteristic wine amino acids for each variety were assessed by means of pattern recognition techniques. A “star symbol plot” was used for graphic representation.     

Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products

Carotenoids have been implicated in protection of the eye from light-mediated photo-toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O-ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI-MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC-UV and fluorescence absorption methods. Protonated molecules [M + H](+) of carotenoids upon collision-induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH(2))and 26 (C(2)H(2))Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3-hydroxy-beta-ionone and 3-hydroxy-14'-apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample.     

安眠镇静药物的串联质谱分析方法

气相色谱以及气相色谱／质谱联用经常被用来分析生物体液样品中的药物。用这些方法分析时，需要在色谱分析前，进行长时间的样品制备和衍生化过程。本文描述了用地识别１６安眠镇静药物的ＥＩ／ＭＳ／ＭＳ过程，并且对两例服毒自杀者的尿样进行了检测。     

Thermogravimetric analysis of poly(alkyl methacrylates) and poly(methylmethacrylate-g-dimethyl siloxane) graft copolymers

The thermal stabilities of various poly(alkyl methacrylate) homopolymers and poly(methyl methacrylate-g-dimethyl siloxane) (PMMA-g-PSX) graft copolymers have been determined by thermogravimetric analysis (TGA). As expected, the thermal stabilities of poly(alkyl methacrylates) were a function of the ester alkyl group, and polymerization mechanism. In particular, thermally labile linkages, which result from termination during free radical or nonliving polymerization mechanisms, decrease the ultimate thermal stabilities of the polymers. However, graft copolymers, which were prepared by the macromonomer technique with free radical initiators, exhibited enhanced thermal stability compared to homopolymer controls. A more complex free radical polymerization mechanism for the macromonomer modified polymerization may account for this result. © 1994 John Wiley & Sons, Inc.