Electrochemical And In-situ FTIR Spectroelectrochemical Studies Of Catechol,Hydroquinone And Melatonin

The method, the applications of in-situ FTIR spectroelectrochemistry (FTIRS) and the development of IR spectroelectrochemical cell were reviewed. A double transparent windows, double-walled IR reflected thin layer electrochemical cell was designed and characterized. A systematic investigation of the behavior of phenol and bioactive material, melatonin, was undertaken by electrochemistry and in-situ FTIR spectroelectrochemistry. The dissertation focuses on the following aspects: the mechanism of electrochemical redox reactions of catechol and hydroquinone and the mechanism of electrochemical oxidation of melatonin in aqueous system and non-aqueous system. These studies provide useful information at molecular level for understanding of the reaction pathways of these important species.1, A double transparent windows, double-walled IR reflected thin layer electrochemical cell was designed and characterized. The design of double-walled can make the cell use in the experiment of different temperature. Furthermore, the design of double transparent windows can make it carry out low-temperature experiment. The results of electrochemistry and spectroelectrochemistry showed that the cell had satisfactory performances and is suitable to be applied to in-situ IR spectroelectrochemical studies.2, Electrochemical redox process of catechol and hydroquinone in acetonitrile solution v/ere studied. The results indicated that the redox of catechol and hydroquinone at the Pt electrode were both EC process at room temperature. In oxidation process, catechol and hydroquinone are firstly oxidized by the loss of twoelectrons and then followed by the loss of two protons to generate quinone. In reduction process, quinone are firstly reduced by the gain of two electrons and then followed by the gain of two protons to generate phenol. Meanwhile, the mechanism of the redox process of hydroquinone at -40C by the use of cold N2 as cryogen was also studied. The results showed that the mechanism was the same as that of room temperature.3, The electrochemical oxidation of melatonin in PBS under different pH condition and the mutual effect between melatonin and Se were studied by cyclic voltammetry. The results indicated that melatonin was firstly oxidized by the loss of one electron to a radical cation. This was further oxidized by the loss of a second electron and proton to a very reactive quinoneimine which was susceptible to nucleophilic attack. Hence the attack by water yield 4,5-dihydroxy indolic derivative which was further oxidized to give quinone. Meanwhile, the electrochemical oxidation of melatonin in acetonitrile solution was studied by cyclic voltammetry, differential pulse voltammetry and in-situ FTIR spectroelectrochemistry. The initial step leads to the formation of a radical cation , followed by coupling of this radical with melatonin to yield a dimer radical cation which is oxidized at more anodic. The experiment of the mutual effect of melatonin and Se has not obtained satisfactory result. It may be due to improper experimental condition and/or some other cause. Further experiments should be carried out to understand the mutual effect of melatonin and Se.