Voltammetric determination of total alkannin using a glassy carbon electrode

Electrochemical and theoretical analysis of the reactivity of shikonin derivatives: dissociative electron transfer in esterified compounds

“…Simulated voltammograms indicate that k f is at least 10 5 times greater than the electron transfer process, being the latter the rate determining step. A proposal for this coupled chemical process was made by Chaisuksant and co-workers, 10 who explained that the irreversible second reduction process in esterified Alkannin derivatives (stereoisomers of Shikonin) is attributed to proton addition from the solvent, following the reaction…”

“…In the case of the studied intermediates, this nucleophile could be the same electrogenerated dianion, thus forming products resembling dimers, as has been reported during the reduction of Alkannin derivatives. 10 From an electrochemical point of view, the observed mechanism can be described as a dissociative electron transfer, 12 where the relative rates between the coupled chemical reaction and the electron transfer process suggest that it is also possible to consider a concerted route, rather than a stepwise formation of the final product. 28 This result is important, as ester-substituted Shikonin derivatives can function as bioreductive alkylating agents, generated during the reductive elimination sequence, acting as Michael acceptors with cellular nucleophiles, inducing apoptosis.…”

“…9 In another work by Chaisuksant and collegues, a voltammetric description of some Shikonin derivatives in aprotic media is presented; results showed that the second reduction process of esterified derivatives is always irreversible. 10 Unfortunately, there are no indications on the reaction sequence taking place experimentally, significant variations in the voltammograms and there is no description on the mechanistic pathway occurring. Therefore, a molecular-based description on the above referred variations in reactivity between molecules is required, particularly for esterified compounds.…”

Insights into dissociative electron transfer in esterified shikonin semiquinones by in situ ESR/UV-Vis spectroelectrochemistry

“…These results can be explained considering the highly reactive character of the species involved. 23 In order to correlate the results from spectral analysis with the electrochemical behaviour of signal IIc/IIa, a theoretical analysis of the DET process taking place was performed.…”

Naphthoquinone colorants from Arnebia nobilis Rech.f

“…75530) and their isohexenylnaphthazarin derivatives. Biological investigations over the last decades have proved these colorants to be potent pharmaceutical substances with a wellestablished and wide spectrum of medicinal properties [12][13][14][15][16][17][18][19][20][21][22][23]. The colour-yielding property and therapeutic efficacy of this plant is attributed to the presence of these napthoquinones [17].…”