Electrochemical studies of methyl-3-benzoyl indolizine carboxylates
Indolizine derivatives have been used in medicine and pharmacology due to their biological activity and therapeutical effects. Their capacity to form surface films and to be used as sensors in modern technologies makes them interesting to be studied. This work is devoted to the study of methyl-3-benzoyl indolizine carboxylates by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It is pursued the influence of concentration on CV and DPV curves and that of the scanning domain and rate on the CV curves. The CV and DPV results are in good agreement. There are established the number and characteristics of the redox processes for each compound. The common features and differences between their electrochemical behaviour were analyzed.
Electrochemical studies of biologically active indolizines
Abstract The electrochemical behavior of indolizine ethers, esters, tosylates, sulfonates and other indolizine and azaindolizine derivatives has been investigated by cyclic voltammetry and preparative electrolysis. The cyclic voltammetric data show that the E ° values, taken as the midpoints between the anodic and cathodic peak potentials, are sensitive to the identities of the substituents at C-1, C-2 and C-7 positions. The E ° values have been correlated with the Hammett substituent parameters. As expected, low E ° values are seen for electron donating substituents and higher E ° values are seen for electron withdrawing substituents. The cyclic voltammograms of indolizine derivatives with an oxygen atom connected to the C-1 position exhibit a one-electron reversible oxidation and a further, less well-defined, one-electron irreversible oxidation at higher E ° values. The cyclic voltammograms of indolizines with hydrogen atom or thienyl substituents connected to the C-1 position exhibit only a one-electron irreversible oxidation. Electrochemical bulk oxidations of indolizines with an oxygen atom at the C-1 position afforded oxoindolizinium salts in decent yields, whereas indolizines with a hydrogen atom at C-1 afforded 1,1′ dimers of indolizines as products in good yields. Bulk oxidation of 1-(α-hydroxybenzyl)-2,3-diphenylindolizine-7-carbonitrile afforded an unexpected ketone product in which the carbonyl group of the indolizine is connected at C-8 instead of at the C-1 position of the starting material. The findings described herein support our hypothesis that certain indolizine derivatives may inhibit lipid peroxidation by an electron transfer mechanism.
Background of the Hammett equation as observed for isolated molecules: meta- and para-substituted benzoic acids.
Fundamental model compounds for the Hammett equation, meta- and para-substituted benzoic acids, were investigated by the density functional theory at the B3LYP/6-311+G(d,p) level. Energies of 25 acids and of their anions were calculated in all possible conformations and from them the energies of the assumed mixture of conformers. Relative acidities correlated with the experimental gas-phase acidities almost within the experimental uncertainty, much more precisely than in the case of previous calculations at lower levels. Dissection of the substituent effects into those operating in the acid molecule and in the anion was carried out by means of isodesmic reactions starting from monosubstituted benzenes. Both effects are cooperating in the resulting effect on the acidity; those in the acid molecule are smaller but not negligible. They are also responsible for some deviations from the Hammett equation (through-resonance of para donor substituents) and for the weaker resonance in the acid molecule in meta derivatives; in the anions the inductive and resonance effects are almost equal. On the other hand, the cooperation of effects in the acid and in the anion makes the relative acidity more sensitive to electron withdrawing and is probably one of the reasons why the Hammett equation is so generally valid.