title: Electrochemical and theoretical analysis of the reactivity of shikonin derivatives: dissociative electron transfer in esterified compounds.
abstract: An electrochemical and theoretical analysis of a series of shikonin derivatives in aprotic media is presented. Results showed that the first electrochemical reduction signal is a reversible monoelectronic transfer, generating a stable semiquinone intermediate; the corresponding E(I)⁰ values were correlated with calculated values of electroaccepting power (ω(+)) and adiabatic electron affinities (A(Ad)), obtained with BH and HLYP/6-311++G(2d,2p) and considering the solvent effect, revealing the influence of intramolecular hydrogen bonding and the substituting group at position C-2 in the experimental reduction potential. For the second reduction step, esterified compounds isobutyryl and isovalerylshikonin presented a coupled chemical reaction following dianion formation. Analysis of the variation of the dimensionless cathodic peak potential values (ξ(p)) as a function of the scan rate (v) functions and complementary experiments in benzonitrile suggested that this process follows a dissociative electron transfer, in which the rate of heterogeneous electron transfer is slow (~0.2 cm s(-1)), and the rate constant of the chemical process is at least 10(5) larger.
authors.affiliation: Subdirección de Investigación, Centro de Investigación y Desarrollo Tecnológico en Electroquímica, SC, Parque Tecnologico Queretaro SN, Sanfandila, Pedro Escobedo, Queretaro, Mexico. ultrabuho@yahoo.com.mx.
authors.forename: Georgina
authors.initials: G
authors.lastname: Armendáriz-Vidales
authors.forename: Carlos
authors.initials: C
authors.lastname: Frontana
mesh_terms: D055664:Electrochemical Techniques; D004579:Electron Transport; D004952:Esters / Q000737:chemistry*; D015394:Molecular Structure; D009285:Naphthoquinones / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D004952:Esters; D009285:Naphthoquinones; C016101:shikonin