New voltammetric method useful for water insoluble or weakly soluble compounds: application to pKa determination of hydroxyl coumarin derivatives
- 142 Downloads
Here, we reveal a different way of doing the voltammetric experiments that considers the electroactive species packaged in the electrodic phase instead of dissolved in solution. In this way, it is possible to obtain voltammograms of insoluble species. In this work, the method is exemplified by obtaining voltammograms for weakly soluble coumarins but it could be extrapolated to other weakly soluble compounds. We have studied a comprehensive series of 3-acetyl-hydroxycoumarins derivatives which are insoluble in aqueous medium but capable of being trapped in a three-dimensional multi-walled carbon nanotubes (MWCNT) network. Consequently, an electrodic phase composed of an MWCNT modified glassy carbon electrode (GCE) containing the coumarin derivative is prepared. The voltammetric experiment is performed with the above electrodic phase and an aqueous medium as the solution phase. All the coumarin derivatives show one anodic peak due to the oxidation of the hydroxyl group in the phenyl ring. The oxidation peaks follow a one-electron, one-proton irreversible, pH-dependent process for all monohydroxylated compounds. The Ep values are closely dependent of the substituent effect being the 7,8-cum derivative more easily oxidized due to both the electron donor effect of neighboring hydroxyls groups and hydrogen bonding interaction between them. On the other hand, the hydroxyl of the 7-cum derivative is the most difficult to oxidize due to the electron-attracting effect of the lactone carbonyl group at position 2 and acetyl carbonyl at position 3 which is conjugated with OH at 7 positions. From the breaks in the graphs Ep versus pH, we estimate the voltammetric pKa values for all the studied coumarin derivatives.
KeywordsCoumarin derivatives MWCNT Modified electrode
The authors thank the financial support from FONDECYT project N° 1170054.
- 2.Han J (2005) In: Meyyappan M (ed) Carbon nanotubes: science and applications. CRC Press, London, p 1Google Scholar
- 3.Mercè Pacios Pujadó, (eds)(2011) Carbon nanotubes as platforms for biosensors with electrochemical and electronic transduction. Springer, p.9Google Scholar
- 9.Moscoso R, Inostroza E, Squella J.A. (2017) A non-conventional way to perform voltammetry. Electrochem Commun 81:61–64Google Scholar
- 11.Gupta JK, Sharma PK, Dudhe R, Chaudhary A, Verma PK (2010) Synthesis, analgesic and ulcerogenic activity of novel pyrimidine derivative of coumarin moiety. Analele Universitătii Bucuresti 19(2):9–21Google Scholar
- 12.Tasqeerudin S, Abdullah S, Al-Arifi and Dubey PK (2013) An efficient solid-phase green synthesis of chromen-2-one derivatives. Chem Asian J 25(12):6885–6887Google Scholar
- 13.Baghernejad B (2016) A new strategy for the synthesis of 3-Acyl-coumarin using nano ZnO as an efficient catalyst. Der Pharma Chem 8(2):109–113Google Scholar
- 16.Carneiro K, Torres L, Ferreira L, Garcia S, de Oliveira-Neto J, Marques F, Alves T, Verly R, dos Santos W, de Souza E (2015) Eletrochemical characterization of scopoletin, a 7-hydroxy-6- methoxy-coumarin. Int J Electrochem Sci 10:5714–5725Google Scholar
- 21.Sabnis RW (2015) Handbook of fluorescent dyes and probes. John Wiley & Sons, Inc, Chap.82, p. 246Google Scholar