A computational mechanistic study of the deamination reaction of melamine

A detailed computational study of the deamination reaction of melamine by OH^–, n H₂O/OH^–, n H₂O (where n = 1, 2, 3), and protonated melamine with H₂O, has been carried out using density functional theory and ab initio calculations. All structures were optimized at M06/6‐31G(d) level of theory, as well as with the B3LYP functional with each of the basis sets: 6‐31G(d), 6‐31 + G(d), 6‐31G(2df,p), and 6‐311++G(3df,3pd). B3LYP, M06, and ω B97XD calculations with 6‐31 + G(d,p) have also been performed. All structures were optimized at B3LYP/6‐31 + G(d,p) level of theory for deamination simulations in an aqueous medium, using both the polarizable continuum solvation model and the solvation model based on solute electron density. Composite method calculations have been conducted at G4MP2 and CBS‐QB3. Fifteen different mechanistic pathways were explored. Most pathways consisted of two key steps: formation of a tetrahedral intermediate and in the final step, an intermediate that dissociates to products via a 1,3‐proton shift. The lowest overall activation energy, 111 kJ mol^?1 at G4MP2, was obtained for the deamination of melamine with 3H₂O/OH^?.     

核酸适配体生物传感器在三聚氰胺检测中的应用进展

三聚氰胺常被非法添加到食品中,以提高食品中蛋白质的含量。但是,三聚氰胺一旦进入体内,会对人们的健康造成伤害。因此,对三聚氰胺的检测十分必要。为了弥补传统仪器检测法和免疫检测法的不足,基于核酸适配体开发了一系列新的生物传感器,用于三聚氰胺的检测。按照与三聚氰胺的不同识别机制,把这些新的生物传感器分成了四类,分别为基于多聚胸腺嘧啶DNA链和三聚氰胺识别的生物传感器、基于无嘌呤位点的三链DNA结构和三聚氰胺识别的生物传感器、基于核酸适配体和三聚氰胺识别的生物传感器、基于三聚氰胺和汞离子/铜离子等配位识别的生物传感器。本文按照上述四类方法逐个展开,对核酸适配体生物传感器在三聚氰胺检测中的应用进行了综述,并对它们的优缺点进行阐述。     

二季戊四醇磷酸酯三聚氰胺盐的合成及阻燃性能测试

以磷酸、季戊四醇、三聚氰胺为原料,通过酸醇直接酯化和烘焙中和两步反应合成膨胀型阻燃剂二季戊四醇磷酸酯三聚氰胺盐,并对烘焙中和反应条件及其在聚乙烯中的阻燃性能进行了研究.确定最佳合成条件:n (二季戊四醇磷酸酯):n (三聚氰胺)=1:1;反应温度130-140℃;反应时间3-4h.将此阻燃剂添加到聚乙烯中,样品重量35...     

场放大进样-毛细管区带电泳法高灵敏检测三聚氰胺

建立了基于水塞联用场放大进样(FESI)的区带毛细管电泳(CZE)检测多种样品中三聚氰胺的分析方法。水塞组成为40%乙腈和60%水,水塞进入时间200 s,进水压力3 kPa。以120 mmol/L NaH2PO4缓冲液(pH 2.2)-10%甲醇为运行缓冲溶液,以0.10 mmol/L NaH2PO4(pH 2.2)-20%乙腈为样品基体溶液,进样电压20 kV,进样时间80 s,分离电压20 kV。在优化实验条件下,与普通的CZE法比较,三聚氰胺的紫外检测灵敏度提高了800倍,检出限(S/N=3)由2.0 mg/L降至2.5μg/L,线性范围为10～1 000μg/L。将该方法用于多种样品中三聚氰胺残留的检测,回收率为98%～106%,相对标准偏差(RSD,n=4)均不高于5.1%。该方法克服了紫外检测灵敏度低的缺陷,具有检测灵敏、简便易行、预处理简单、干扰少、经济环保和适用范围广等优点。     

High-Performance Liquid Chromatography Analysis of Hexamethylmelamine and its Demethylated and Hydroxylated Metabolites in Mice Plasma

Abstract

A selective assay of hexamethylmelamine and its metabolites in mice plasma has been developed. The method uses protein precipitation with acetonitrile in glass centrifuge tubes and analysis of the resulting supernatant by reverse-phase high performance liquid chromatography on a Lichrocart RP 18 column with a mobile phase acetonitrile-phosphate buffer containing n-propylamine (pH 7,5). The influence of various parameters on the separation (solvent composition, pH, n-propylamine content, temperature) has been examined.     

Surface‐enhanced Raman spectra of melamine and other chemicals using a 1550 nm (retina‐safe) laser

Many trace chemical analyses are being transitioned from the lab to the field, among which is surface‐enhanced Raman spectroscopy. Although initial portable Raman analyzers primarily employ 785 nm laser excitation, recent studies suggest longer wavelengths, with an appropriate surface‐enhanced Raman‐active substrate, may provide equal sensitivity. Furthermore, 1550 nm excitation may provide added safety for the user, in that permanent retina damage does not occur. Here, we show that a reasonable enhancement factor can be obtained for melamine using 1550 nm laser excitation that is nearly equivalent to those obtained using 785 and 1064 nm laser excitation. We also demonstrate that a number of other chemicals of interest can be measured by 1550 nm surface‐enhanced Raman scattering, albeit only modest sensitivity is achieved because of instrument limitations, not enhancement factors. Copyright © 2011 John Wiley & Sons, Ltd.     

Ag‐nanoparticle‐modified single Ag nanowire for detection of melamine by surface‐enhanced Raman spectroscopy

Silver nanowires synthesized by a solvothermal method were used as templates for fabricating silver‐nanoparticle‐decorated silver (AgNP/Ag) nanowires. The number density and particle size of Ag nanoparticles can be controlled by varying the concentration of Ag precursor. Single AgNP/Ag nanowire exhibited strong surface‐enhanced Raman scattering effect. Detection of melamine molecules at concentrations as low as 1.0 × 10⁻⁸ M was used as an example to show the possible applications of such AgNP/Ag nanowires. Their application in rapid detection of melamine in milk solution was further demonstrated. It was shown that melamine in milk solution at a low concentration of 5.0 × 10⁻⁸ M can be easily detected with little sample pretreatment. The results demonstrate the potential of single AgNP/Ag nanowire as a surface‐enhanced Raman scattering substrate for convenient and sensitive detection of trace amounts of melamine in a complex mixture. Copyright © 2012 John Wiley & Sons, Ltd.     

反应性挤出加工制备无卤阻燃高分子材料

聚合物反应性加工集聚合物加工与化学反应为一体,以聚合物加工装置为反应器,通过聚合物加工过程中的化学反应形成新物质和新结构,实现高分子材料的高性能化和功能化,是高分子材料科学的研究前沿之一.本文简要介绍了我们研究小组近年来采用反应性挤出加工制备高性能无卤阻燃高分子材料方面的研究进展.利用反应性挤出加工剪切力强、温度可控以及易于传质传热的特点实现了常规方法难以合成的高黏阻燃剂三聚氰胺磷酸盐季戊四醇酯（MPP）和三聚氰胺氰尿酸（MCA）的高效合成,制备了综合性能优良的聚丙烯/MPP、尼龙6/MCA等无卤阻燃高分子材料.研究所涉及的化学和物理方法,为聚合物无卤阻燃提供了高效、经济、环保和易于工业化的新技术,并拓宽了聚合物反应性加工的应用领域.     

气相色谱-质谱法测定鸡蛋中三聚氰胺

建立了气相色谱-质谱法测定鸡蛋中三聚氰胺的方法. 鸡蛋样品经三氯乙酸提取,乙酸铅沉淀蛋白后,过MCX阳离子交换固相萃取小柱除去样品基质干扰,用N,O-双三甲基硅基三氟乙酰胺(BSTFA)+三甲基氯硅烷(TMCS)(99+1)衍生,进行气相色谱-质谱分析. 在0.010~2.00 mg/L浓度范围内,线性关系良好(r=0.9996),检出限为0.01 mg/kg. 方法回收率为90.1%~94.7%,RSD为1.7%~5.3%. 方法准确、灵敏,适用于鸡蛋中三聚氰胺的检测.     

表面解吸常压化学电离质谱法直接测定奶粉中三聚氰胺

应用表面解吸常压化学电离(SDAPCI)质谱法,在无需样品预处理的情况下,直接测定了奶粉中三聚氰胺,并用串联质谱法对测定结果进行了鉴定.采用手动进样,单个样品测定时间少于0.5 min,回收率为86.7%～112.8%;相对标准偏差(RSD)为4.3%～10.3%;对奶粉中三聚氰胺的检出限为8.8 μg/kg.方法适用于批量样品的快速半定量检测.