Oxidation of capsaicin in acetonitrile in dry and wet conditions
An electrochemical study of the phenol capsaicin (CAPH), the active ingredient in chilli pepper, was performed in dried and wet acetonitrile on a glassy carbon electrode. Under dried conditions, two oxidation peaks at ca. 0.7 vs. (Fc/Fc+)/V (labelled E1) and 1.0 vs. (Fc/Fc+)/V (labelled E2) and two...
| Main Authors: | , , |
|---|---|
| Other Authors: | |
| Format: | Journal Article |
| Language: | English |
| Published: |
2022
|
| Subjects: | |
| Online Access: | https://hdl.handle.net/10356/160247 |
| _version_ | 1811687147513577472 |
|---|---|
| author | Chan, Kwok Kiong Muhammad Shafique Hamid Webster, Richard David |
| author2 | School of Physical and Mathematical Sciences |
| author_facet | School of Physical and Mathematical Sciences Chan, Kwok Kiong Muhammad Shafique Hamid Webster, Richard David |
| author_sort | Chan, Kwok Kiong |
| collection | NTU |
| description | An electrochemical study of the phenol capsaicin (CAPH), the active ingredient in chilli pepper, was performed in dried and wet acetonitrile on a glassy carbon electrode. Under dried conditions, two oxidation peaks at ca. 0.7 vs. (Fc/Fc+)/V (labelled E1) and 1.0 vs. (Fc/Fc+)/V (labelled E2) and two reduction peaks at ca. 0.1 and −0.5 vs. (Fc/Fc+)/V when the scan direction was reversed were observed. Rotating disk electrode experiments indicated that the two oxidation processes occur by same number of electrons and it is proposed they occur in two one-electron steps. As water was added to the acetonitrile, hydrogen bonding interactions between the water and the phenolic groups led to the E1 and E2 potentials shifting progressively more negatively. The shift in E2 as water was added was greater than the shift in E1, so that after the addition of approximately 0.2 M H2O, only one voltammetric wave was observed (labelled as E1′) corresponding to a two-electron oxidation, that continued to shift more negatively as more water was added. Under very wet conditions ([H2O] > 1 M), only one chemically irreversible oxidation peak was observed (E1′) at ca. > 0.5 vs. (Fc/Fc+)/V with one reduction peak at ca. −0.1 vs. (Fc/Fc+)/V upon reversal of the scan direction. Controlled-potential electrolysis under wet conditions indicated a total of two-electrons per molecule were transferred with the overall mechanism interpreted as a −2e–/−H+ oxidation, followed by a hydrolysis reaction and loss of a methoxy group to form a 1,2-benzoquinone moiety. |
| first_indexed | 2024-10-01T05:11:41Z |
| format | Journal Article |
| id | ntu-10356/160247 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T05:11:41Z |
| publishDate | 2022 |
| record_format | dspace |
| spelling | ntu-10356/1602472022-07-18T05:33:58Z Oxidation of capsaicin in acetonitrile in dry and wet conditions Chan, Kwok Kiong Muhammad Shafique Hamid Webster, Richard David School of Physical and Mathematical Sciences Science::Chemistry Hydrogen-Bonding Karl-Fischer Titration An electrochemical study of the phenol capsaicin (CAPH), the active ingredient in chilli pepper, was performed in dried and wet acetonitrile on a glassy carbon electrode. Under dried conditions, two oxidation peaks at ca. 0.7 vs. (Fc/Fc+)/V (labelled E1) and 1.0 vs. (Fc/Fc+)/V (labelled E2) and two reduction peaks at ca. 0.1 and −0.5 vs. (Fc/Fc+)/V when the scan direction was reversed were observed. Rotating disk electrode experiments indicated that the two oxidation processes occur by same number of electrons and it is proposed they occur in two one-electron steps. As water was added to the acetonitrile, hydrogen bonding interactions between the water and the phenolic groups led to the E1 and E2 potentials shifting progressively more negatively. The shift in E2 as water was added was greater than the shift in E1, so that after the addition of approximately 0.2 M H2O, only one voltammetric wave was observed (labelled as E1′) corresponding to a two-electron oxidation, that continued to shift more negatively as more water was added. Under very wet conditions ([H2O] > 1 M), only one chemically irreversible oxidation peak was observed (E1′) at ca. > 0.5 vs. (Fc/Fc+)/V with one reduction peak at ca. −0.1 vs. (Fc/Fc+)/V upon reversal of the scan direction. Controlled-potential electrolysis under wet conditions indicated a total of two-electrons per molecule were transferred with the overall mechanism interpreted as a −2e–/−H+ oxidation, followed by a hydrolysis reaction and loss of a methoxy group to form a 1,2-benzoquinone moiety. Ministry of Education (MOE) This work was partially supported by a Singapore Government MOE Academic Research Fund Tier 1 Grant (RG3/19) . 2022-07-18T05:33:58Z 2022-07-18T05:33:58Z 2021 Journal Article Chan, K. K., Muhammad Shafique Hamid & Webster, R. D. (2021). Oxidation of capsaicin in acetonitrile in dry and wet conditions. Journal of Electroanalytical Chemistry, 903, 115838-. https://dx.doi.org/10.1016/j.jelechem.2021.115838 1572-6657 https://hdl.handle.net/10356/160247 10.1016/j.jelechem.2021.115838 2-s2.0-85118710193 903 115838 en RG3/19 Journal of Electroanalytical Chemistry © 2021 Elsevier B.V. All rights reserved. |
| spellingShingle | Science::Chemistry Hydrogen-Bonding Karl-Fischer Titration Chan, Kwok Kiong Muhammad Shafique Hamid Webster, Richard David Oxidation of capsaicin in acetonitrile in dry and wet conditions |
| title | Oxidation of capsaicin in acetonitrile in dry and wet conditions |
| title_full | Oxidation of capsaicin in acetonitrile in dry and wet conditions |
| title_fullStr | Oxidation of capsaicin in acetonitrile in dry and wet conditions |
| title_full_unstemmed | Oxidation of capsaicin in acetonitrile in dry and wet conditions |
| title_short | Oxidation of capsaicin in acetonitrile in dry and wet conditions |
| title_sort | oxidation of capsaicin in acetonitrile in dry and wet conditions |
| topic | Science::Chemistry Hydrogen-Bonding Karl-Fischer Titration |
| url | https://hdl.handle.net/10356/160247 |
| work_keys_str_mv | AT chankwokkiong oxidationofcapsaicininacetonitrileindryandwetconditions AT muhammadshafiquehamid oxidationofcapsaicininacetonitrileindryandwetconditions AT websterricharddavid oxidationofcapsaicininacetonitrileindryandwetconditions |