PDF Publication Title:
Text from PDF Page: 005
M.A.N. Manaia et al. / Journal of Electroanalytical Chemistry 682 (2012) 83–89 87 Fig. 6. (A) 3D plots of second DP voltammograms base-line corrected in 10 lM curcumin; (B) Plot of (j) Ep3a vs. pH. Dotted line corresponds to 60 mV per pH unit. Fig. 5. DP voltammograms baseline corrected, in pH 6.9 0.1 M phosphate buffer: ( ) first and ( ) second scans in 10 lM (A) curcumin, (B) ferulic acid and (C) capsaicin; and (A) ( ) curcumin first scan in buffer. electrolyte, two consecutive DP voltammograms were recorded and from the second DP voltammogram the peak 3a potential was plot- ted vs. pH, Fig. 6A. Increasing the pH up to 9.0, peak 3a potential de- creased, Fig. 6B. The relationship was linear and the slope of the line, 60 mV per pH unit, shows that the mechanism of peak 3a oxi- dation process involves the same number of electrons and protons. Considering that W1/2 60 mV, for peak 3a, it was concluded that the oxidation reaction occurs with the transfer of two electrons and two protons. For pH > 9.0, peak 3a potential is pH-independent and the redox reaction involved only the transfer of electrons. 3.3. Square wave voltammetry SW voltammograms were obtained in 10lM curcumin in pH = 4.30.1 M acetate buffer, Fig. 7, oxidation peaks 1a and 2a occurring on the first scan, Fig. 7A, showing similar features to the results using CV and DP voltammetry. Since in SW voltammetry the current is sampled in both positive and negative-going pulses, peaks corresponding to the oxidation and reduction of the electroactive species at the elec- trode surface can be obtained in the same experiment. Thus, by plotting the forward and backward components of the total cur- rent, the irreversibility of peak 1a was observed since there was no backward peak current corresponding to the forward peak cur- rent. The reversible character of peak 2a was observed, since for- ward and backward components occurred with the same current and at the same potential. On the second SW voltammogram recorded in the same condi- tions without cleaning the electrode surface, Fig. 7B, peak 3a oc- curred, due to curcumin oxidation products formed during the first SW voltammetric scan. The deconvolution of the total current showed the reversible character of this redox reaction. 4. Discussion The electrochemical behaviour of curcumin, ferulic acid, capsaicin and dihydrocapsaicin was investigated using CV, DP and SW voltammetry. The CV study was very important as it enabled rapid screening of the electron transfer processes showing the formation of electroactive products. SW voltammetry was more sensitive than CV and allowed the clarification of the revers- ibility of the electron transfer processes. DP voltammetry enabled the study of the coupled electron/proton transfer reactions, the formation of electroactive products, and their pH dependence.PDF Image | Guaicolic spices curcumin and capsaicin electrochemical oxidation
PDF Search Title:
Guaicolic spices curcumin and capsaicin electrochemical oxidationOriginal File Name Searched:
170-curcumin-JEAC.PDFDIY PDF Search: Google It | Yahoo | Bing
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
Heat Pumps CO2 ORC Heat Pump System Platform More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)