Electrochemical Oxidation of 5-Hydroxytryptophan in Acid Solution

Humphries, Keith A.; Dryhurst, Glenn

doi:10.1002/jps.2600761019

Cited by 30 publications

(23 citation statements)

References 22 publications

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“…When the results obtained for electrolyses at pH 2.6 and 7.2 were compared, it was noted that the abundance of the dione relative to the dimers was greater at pH 2.6 than at pH 7.2. These results are comparable to those reported for electrolyses at a pyrolytic graphite electrode (PGE) except that at a PGE the oxygen-linked dimer was not significant at pH 2.6 [25,28]. …”

Section: Resultssupporting

confidence: 87%

Oxidation and flow-injection amperometric determination of 5-hydroxytryptophan at an electrode modified by electrochemically assisted deposition of a sol–gel film with templated nanoscale pores

Ranganathan

Zamponi

Mehdi

et al. 2010

Talanta

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The oxidation of 5-hydroxytryptophan (5-HTPP) yielded a passivating polymeric film at an indium tin oxide (ITO) electrode. Coating ITO with a nanoscale sol-gel film with a mesoporous structure was shown to change the pathway of the chemical reaction coupled to the electron transfer. The sol-gel film was deposited by an electrochemically assisted process, and the mesoporosity was imparted by including generation-4 poly(amidoamine) dendrimer in the precursor solution. The dendrimer was removed subsequently with an atmospheric oxygen plasma. This electrode remained active during cyclic voltammetry and controlled potential electrolysis of 5-HTPP, which was attributed to dimer, rather than polymer, formation from the oxidation product. Mass spectrometry confirmed this hypothesis. The anodic current was limited by the electron-transfer kinetics. Modification of the sol-gel film by inclusion of cobalt hexacyanoferrate, which catalyzes the oxidation, resulted in a diffusion-limited current. Determination of 5-HTPP by flow-injection amperometry had a detection limit of 17 nM.

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Section: Resultssupporting

confidence: 87%

Oxidation and flow-injection amperometric determination of 5-hydroxytryptophan at an electrode modified by electrochemically assisted deposition of a sol–gel film with templated nanoscale pores

Ranganathan

Zamponi

Mehdi

et al. 2010

Talanta

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“…It is assumed that oxidation occurs first on the nitrogen atom in the indole ring of the molecule, which is electroactive in both acidic and basic media, leading finally to hydroxylation of the benzene ring [8,20,21]. A comparative study of 5-hydroxyindole and indole-3-acetic acid was performed by cyclic voltammetry at the glassy carbon electrode, as a function of pH, to investigate the oxidation of fluvastatin, taking into account that the cyclic voltammogram of indole-3-acetic acid and 5-hydroxyindole closely matches the voltammogram of fluvastatin.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical study of fluvastatin sodium – analytical application to pharmaceutical dosage forms, human serum, and simulated gastric juice

Özkan

Uslu

2002

Anal Bioanal Chem

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The oxidation of fluvastatin sodium on a glassy carbon electrode has been studied by use of a variety of voltammetric techniques. Different conditions were investigated to optimize the determination of fluvastatin sodium. The dependence of the intensities of currents and potentials on pH, concentration, scan rate, and nature of the buffer was investigated. Oxidation of fluvastatin sodium was found to be diffusion-controlled and irreversible. The best results for the determination of fluvastatin sodium were obtained by using differential pulse and square-wave voltammetric techniques in Britton-Robinson buffer at pH 10.04. Differential pulse and square-wave voltammetry at a glassy carbon electrode resulted in linear calibration in the range 8x10(-6) to 6x10(-4) mol L(-1) and detection limits of 1.07x10(-6) and 7.99x10(-7) mol L(-1), respectively. The proposed methods were successfully applied to the determination of the drug in capsules and biological fluids. Excipients did not interfere with the determination. Statistical validation revealed that the methods were free from significant systematic errors.

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“…Musser, FDA, personal communication) or with potassium nitrosodisulfonate (Teuber and Staiger, 1954;Klarskov et al, 2003). Formation of tryptophan-4,5-dione proceeds via a reversible intermediate, tryptophan-4,5-diol (Humphries and Dryhurst, 1987;Dryhurst, 1998). This initial formation of a diol is in agreement with the classical Raper-Mason scheme of melanogenesis, wherein dihydroxyindole precedes indolequinone (Raper, 1928;Arnow, 1938;Mason, 1948;Pawalek and Körner, 1982).…”

Section: Analytical Search For Toxic Impurities In 5-htpmentioning

confidence: 51%

“…Tryptophan-4,5-dione could be generated from 5-HTP in vitro by oxidation electrochemically (Humphries and Dryhurst, 1987), with H 2 O 2 (S.M. Musser, FDA, personal communication) or with potassium nitrosodisulfonate (Teuber and Staiger, 1954;Klarskov et al, 2003).…”

Section: Analytical Search For Toxic Impurities In 5-htpmentioning

confidence: 98%

“…However, the so-called abnormal oxidation products of biogenic amines suspected of neurotoxicity (e.g., tryptophan-4,5-dione and tryptophan-4,5-diol) are believed to be endogenous to the serotonergic neurons of patients with inherent faulty metabolism (Humphries and Dryhurst, 1987;Dryhurst, 1998). There is no known physiological mechanism by which unstable intermediates could be delivered into the neurons from an exogenous source (ingested nutritional supplements, in this case).…”

Section: Analytical Search For Toxic Impurities In 5-htpmentioning

confidence: 98%

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