| The electroreduction behavior of three kinds of nitrogen-containing organic medicines, and the electrochemical behaviors of eleven kinds of polyphenols, as well as the electrocatalytic activity of two kinds of polyphenols to the electrooxidation of hydrazine or hydroxylamine were investigated using electrochemical methods. Besides, the small oscillographic chronopotentiometry was proposed. These studies are significant to interpreting the electrochemical mechanism, establishing the determination methods, elucidating pharmacological effect, developing organic molecule electrochemical sensor of these compounds, and further broadening the application range of electroanalysis. The thesis consists of five chapters. The main contributions are summarized and presented as follows:1. The electrochemical reductive or oxidative behavior and the antioxidative effect of eleven kinds of polyphenols were studied. The experimental results support the following four conclusions. Firstly, the reduction wave of ionized polyphenols would present at more positive potential than the reduction wave of the neutral molecule. Secondly, the electroreductive products of flavonoids adsorb strongly at the mercury electrode surface and usually produce adsorption prewave on the voltammogram. Thirdly, the antioxidation ability of resveratrol was the strongest in the three studied polyphenols, chrysin and methylhesperidine exhibits similar antioxidation effect. Finally, the electrochemical oxidation of the polyphenols proceeds in sequential steps, related with the hydroxyl groups in the three aromatic rings. When the oxidation potential shifts from negative to positive values, the reversible oxidation of the dihydroxy moiety at A or B ring of polyphenols occurs first, the small oxidative peak of hydroxyl group at C ring follows, and the other hydroxyl groups at B ring and A ring are oxidized at more positive potentials. These conclusions could complement the electrochemical mechanism and establish the new determination methods, also offer techniques to the study of antioxidative activity of these polyphenols.2. The electroreductive behavior and mechanism of three nitrogen-containing compounds, miconazole, propafenone and camptothecin, were investigated using electrochemical methods favored by spectrometry, and the new determination methods of the three medicines in pharmaceutical preparations, serum or plant resource were founded. The experimental results indicate that the reduction waves of nitrogen-containing compounds could be divided into two types, one is the reduction wave of the reductive bond in the molecule, and the other is the catalytic hydrogen wave. Under the same experimental conditions, the catalytic hydrogen wave displays better sensitivity than the reduction wave of the compound itself. The conclusion was deduced by the low detection limit of 2×10-9 mol·L-1 for miconazole and 5×10-8 mol·L-1 for propafenone when the determination of the two medicines was carried out utilizing the catalytic hydrogen wave. In this part, the analysis methods of the three nitrogen-containing compounds with excellent sensitivity and selectivity were founded based on their electrochemical mechanism.3. Rutin and baicalin were selected to study the electrocatalytic activity of polyphenols. The electrochemical properties and the electrocatalysis effect of the two modified electrodes (Rt/MWNT/GC and Bc/MWNT/GC), prepared by drop-coating combined adsorption methods, were investigated. At the modified electrodes, the sensitive determination of hydrazine and hydroxylamine at low overvoltage was realized. The experimental results showed that hydrazine could be detected at 260 mV and the detection limit is 5×l0-7 mol·L-1 using the Rt/MWNT/GC electrode, while hydroxylamine could be detected at 120 mV and the detection limit is 1×10-7 mol·L-1 using the Bc/MWNT/GC electrode. The two modified electrodes give several distinct advantages, including good stability, extraordinary response time and good limit of detection for hydrazine or hydroxylamine. In addition, the preparation of the modified electrode is simple. 4. A small oscillogram and a new method of oscillographic determination based on it were presented. In oscillographic chronopotentiometry employed Hg working electrode, oscillographic chronopotentiogram formed after classical oscillogram was incised by end depolarizer was called a small oscillogram. Three types of small oscillogram could be obtained when different end depolarizer was applied to incise the classical oscillogram. Here the end depolarizer is a depolarizer that the top ends of its reversible incision could form to the end of a small oscillogram. The theory formula of the small oscillogram was deduced and the adjustment method of the small oscillogram was discussed. Then the oscillogram was applied to the determination of several medicines. Experimental results showed that the oscillographic determination with the small oscillogram not only could be used to the determination of substance whose incision produces near the end of classical oscillogram, but also could be used to the convenient, stable, sensitive and selective determination of many substances in a broad potential windows. Thus, oscillographic analysis with the small oscillogram is an important supplement and development for oscillographic analysis with classical oscillogram. |
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