Direct Characterization of Radical Species Generated on One-Electron Oxidation of 3,6-Diamino-10-methylacridan

Abstract

Sequential electron−proton−electron transfer processes in the oxidation of 3,6-diamino-10-methylacridan, an uncharged precursor of acriflavine, were studied. Transient products, i.e., radical cations and radicals, were spectroscopically characterized by pulse radiolysis and laser flash photolysis.

Benzopinacol Radical Cation

“…It is very likely that the shift observed in the radical cation spectrum is due to relaxation of the molecule geometry upon softening of the matrix. Such an influence of the matrix on the structure of a radical cation is often observed for large organic molecules which undergo significant structural relaxation on ionization . The potential energy surface for relaxation can be very flat and hence susceptible to distortion by cage effects.…”

Transient Species in the Stepwise Interconversion of NADH and NAD+

“…In the case of 1,4-dihydropyridines, the geometry changes are very subtle. However, in the case of 9,10-dihydroanthracenes, geometry relaxation accompanied by the changes in the spectra can be comfortably observed. , …”

“…On ionization, the dihedral angle increases to 162°in 4H •+ . 20 The calculated energy for the relaxation of 4H •+ from the neutral geometry is only 3.4 kcal/mol. This means that the potential energy surface for the relaxation is so flat that the process may be significantly inhibited in a solid matrix.…”

“…However, in the case of 9,10dihydroanthracenes, geometry relaxation accompanied by the changes in the spectra can be comfortably observed. 19,20 10-Methylacridan (4H), a compound that is frequently used to model the reactivity of NADH and its derivatives, is not planar (the B3LYP/6-31G* method predicts that the dihedral angle, Φ, between two aromatic rings is 148°). On ionization, the dihedral angle increases to 162°in 4H •+ .…”

“…33 On the other hand, its reduced form, 3,6-diamino-10-methylacridan (6H), is not an efficient DNA intercalator because it is not planar. 20 However, being an uncharged, hydrophobic acriflavine precursor it readily penetrates cell membranes. It was in fact found that 6H possesses much better antimicrobial properties (against bacteria, fungi, and viruses) than acriflavine itself.…”