5- Hydroxytryptamine electrochemical oxidation

Figure 3. Cyclic voltammogram at the PGE after exhaustive electrochemical oxidation of 30 5-hydroxytryptamine in 0,01 M HCl, Controlled potential electrolysis was performed at 0.52 V (Ep/2 for peak la). Sweep rate 200 mVs i. (Reprinted by permission of the American Chemical Society from M.Z. Wrona and G. Dryhurst,...

Figure 8. Mechanism proposed for the electrochemical oxidation of 5-hydroxytryptamine at low pH,... 

The problem of selectivity is the most serious drawback to in vivo electrochemical analysis. Many compounds of neurochemical interest oxidize at very similar potentials. While this problem can be overcome somewhat by use of differential waveforms (see Sect. 3.2), many important compounds cannot be resolvai voltammetrically. It is generally not possible to distinguish between dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) or l tween 5-hydroxytryptamine (5-HT) and 5-hydroxyindolacetic acid (5-HIAA). Of even more serious concern, ascorbic acid oxidizes at the same potential as dopamine and uric acid oxidizes at the same potential as 5-HT, both of these interferences are present in millimolar concentrations... 

Sensitive electrochemical techniques have also been developed to directly measure the release of oxidizable neurotransmitters such as catecholamines (CAs) and serotonin (5-hydroxytryptamine, 5-HT). Current flows in the circuit when the potential of the electrode is positive enough to withdraw electrons from, i.e. oxidize, the released neurotransmitter. The technique is very sensitive and readily detects the release of individual quanta of neuro transmitter resulting from the fusion of single secretory vesicles to the plasmalemma (Fig. 10-2). 

Because they mimic the chemical synapse by replacing the receptor cell by a UME, electrochemical techniques involving the artificial synapse configuration are suitable for the real-time monitoring of exocytosis at the single-cell level (see Section 12.1.1) and most particularly because the common neurotransmitters (serotonin [5-hydroxytryptamine] and catecholamines like dopamine, noradrenaline, and adrenaline) can be easily oxidized at carbon surface (E=650 mV versus Ag/AgCl). 

Polycrystalline boron-doped diamond (pBDD) is inherently heterogeneous due to variations in dopant density across different facets. Figure 19.5a shows an example of an SECCM reactivity map of oxygen-terminated pBDD for a complex multistage reaction, the oxidation of the neurotransmitter serotonin (5-hydroxytryptamine) in aqueous solution. The advantage of a confined electrochemical... 

Wrona, M. Z. Dryhurst, G. 1990. Oxidation chemistry of 5-hydroxytryptamine Part II. Mechanisms and products formed at millimolar concentrations in acidic aqueous solution. J. Electroanal. Chem. Interf. Electrochem., 278, 249-267. 

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