A D-Carnitine Dehydrogenase Electrode For The Assessment Of Enantiomeric Purity Of L-Carnitine Preparations

ABSTRACT

The enantiomeric purity of pharmaceutical L-carnitine preparations can be assessed within 60 seconds using a highly selective bienzyme electrode. D-carnitine dehydrogenase from Agmbacterium is highly specific for the non-physiological D-enantiomer and was therefore used as the recognition element. NADH produced in the primary reaction was oxidized by salicylate hydroxylase (EC 1.14.13.1) in an oxygen and salicylate dependent reaction. The consumption of oxygen was monitored with a miniature Clark-electrode. A linear calibration graph from 0.01 mM through 0.6 mM D-carnitine was obtained in phosphate buffer pH 8 comprising 0.5 mM concentrations of the cosubstrates NAD and salicylate. The sensitivity for DL-carnitine was exactly 50% of the respective value for pure D-carnitine, while L-carnitine and ascorbic acid, a common interferent, gave no response at all. Mixtures of both enantiomers containing 1% and 3% D-carnitine, respectively, could be distinguished from each other and from pure (i.e. >98 %) L-carnitine preparations with the new sensor. The biosensor method is faster and less laborious than established HPLC and ¹H-NMR methods since it requires no chemical derivatization. The lower detection limit was 10-fold reduced as compared with a recently published enzymatic assay.     

一种新型基底上右旋肉碱的表面增强拉曼光谱研究

在聚乙烯吡咯烷酮(PVP)存在下,用多元醇还原硝酸银,Cu(NO₃)₂作为保护剂,快速有效的合成大量银纳米线,并优化了反应条件,得到结构均一、分散性较好的银纳米线。以罗丹明B为探针分子检测了该银纳米基底的表面增强效应,结果表明该基底对罗丹明B的表面增强效果明显,其表面增强因子可达6.4×105。文中利用这种基底得到了右旋肉碱的表面增强拉曼光谱(SERS),与其固体常规拉曼光谱(NRS)和10-3 mol·L-1水溶液的拉曼光谱对比,并对各自的峰位进行了归属。右旋肉碱固体在3 100～2800和1 700～200 cm-1处有明显拉曼振动峰,在右旋肉碱的表面增强拉曼光谱中,1700～200 cm-1处的峰得到了明显的增强。经分析,右旋肉碱分子与银纳米基底呈180°。本文还用合成的纳米银基底得到了不同浓度右旋肉碱溶液的表面增强拉曼光谱,其最低检测浓度为10-6 mol·L-1。右旋肉碱是一种重要的心血管药物,本文为其研究提供了较全面的拉曼光谱信息,为右旋肉碱的快速、特征、痕量监测提供了有力依据,也为进一步研究右旋肉碱的药理学提供了重要参考。