Study On The Electrochemistry Of Melatonin And Its Related Derivatives

The study on the melatonin and its-related derivatives (5-methoxyl indole-3-acetic acid(MIAA),N-acetyl serotonin (NAHT), 6-hydroxyl melatonin(HMT), serotonin(HT), 5-hydroxyl indole-3-acetic acid(HIAA) and 5-methoxyl tryptamine (5-MT)) (be comprehensively termed as MTS) is an advancing topic for the neurophysiology, pharmacology and clinical fields. As the MTS levels in mammalian species represent an important index of circadian rhythms and pineal function, therefore the development of accurate, simple and sensitive methods for the analysis and clinical studies of MTS is of great consequence.This thesis includes four parts. The first part is the review of the present knowledge on the biochemistry, physiology, pharmacology and current analytical methods of MTS. The second part is focused on the investigation of electrochemical behavior, separation and electroanalysis methods for MTS. Simple and sensitive methods, with a low detection limit in the sub nM range, were developed for the determination of MT, HIAA or HMT respectively in medical, clinical examination and pharmacokinetics research fields by using voltammetry and chemical modification technique. By means of voltammetry, chronocoulometry and related electrochemical techniques, the electrochemical reaction mechanisms of MTS was proposed to be an irreversible (or quasi-reversible), proton-concerned and adsorption-controlled oxidation process respectively. A method based on micellar electrokinetic capillary chromatography with end-column amperometric detection (MECC-AD) was developed for the determination of MTS in the pineal gland of rat and human urine. The investigated compounds can be well separated within 15 minutes with the detection limits of nM range. All these results provide important information and firm foundation for the investigation of neuroendocrine physiology and clinical diagnosis.The third part presents the preparation, characterization and application of poly-MT modified glassy carbon electrode (PMT-GCE). PMT-GCE was obtained byanodic electropolymerazation of MT monomer on glassy carbon electrode in aqueous solutions. Cyclic voltammetry and chronocoulometry measurements suggested that the electrode reaction was redox quasi-reversible process with 2n proton and electron. Structural analysis of PMT were performed by scanning electron microscope (SEM) and reflected IR measurements, and results showed that a stable electric polymer film formed on the GCE was largely composed of dimer and multipolymer, which suggested the C2,C4 - polymerization dominant mechanism of MT. Via the electrochemical and SEM techniques, it was found that the poly-MT film with micropore is capable of binding and embedding calcium ion, and producing a sensitive electrochemical responses upon chelation-adsorption. Based on this characteristic, a strategy to develop a sensitive responsing system of Ca2+ with a low detection limit of 4.5 10-7 mol/L towards the fabrication of ion sensor was described. The analytical application of PMT-GCE for Ca2+ in body fluid is also presented.The fourth part is the studies of the electrogenerated chemiluminescences(ECL) of MTS. By using the cyclic voltammetry, fluorescence spectrum and ECL spectrum analysis, it is showed that the excited state of Ru(bpy)32+, the reaction product of the radical or radical ion of MTS and Ru(bpy)33+ under applied oxidation potential, is responsible for the ECL of system. The ECL intensity and mechanism depends on the type of substituent in indole ring. Based on the enhancement in ECL of Ru(bpy)32+ by MT, a simple method for the determination of MT in medicines with an extraordinarily low detection limit of 1.0 10-10 mol/L is presented. All these work provide important information for the theoretical and analytical studies of heterocyclic compounds.