The strong influence of the solvent on the electron spin resonance spectra of semiquinone radical anions I. A theoretical investigation of the hyperfine constants of 1,2- and 1,4-benzosemiquinone by using density functional theory and polarizable continuum solvation models

Anodic oxidation of selenadiazoloquinolones in alkaline media

“…Moreover, the contribution of the selenadiazole nitrogen nuclei (N‐1 and N‐3; Table 1) was not evident in the simulated spectra. In order to explain the observed EPR splitting pattern, we needed to consider the replacement of selenadiazole ring via interaction of the radical cations with solvent, forming such paramagnetic species analogous to ortho semiquinone radical anion 28–32. This structure is in agreement with our calculated distribution of the unpaired spin density presented in Table 2 for Q1 and Q2 derivatives.…”

Chrysazin semiquinone radical anion. A theoretical study of the influence of the solvent on the electron spin resonance spectrum

“…Taken at face value, the IPCM approximates the effect of a protic solvent by a suitable choice of the parameters IsoD and ε, without an explicit representation of hydrogen-bonded complexes between solute and solvent molecules. This supports the assumption that the rapidly changing formation and breaking of complexes can be considered as giving rise to an average electrostatic reaction field at the position of the solute species [7]. It is noteworthy that semiempirical procedures with simple electrostatic effective solvent field (ESF) models account adequately for the hyperfine data for benzosemiquinones in alcoholic and aqueous solvents [5,6].…”

“…Different input parameters are appropriate for different solute-solvent systems. In a previous investigation on benzosemiquinones [7], calculations were performed with IsoD values between 0.001 and 0.003. The present calculations were carried out with an isodensity of 0.0015 and with dielectric constants ε ranging from 1 to 30.…”

“…But the analysis of the observed ESR spectra is frequently complicated by a strong interaction with the solvent. The relative values of the hyperfine constants may thus be rearranged by the impact of the solvent, as observed for example for a number of benzosemiquinones, leading to conflicting assignments in the literature of the constants to distinct positions in the radicals [2][3][4][5][6][7].…”

Conformational Analysis of Quinone Anion Radicals in Photosystem II and Photosynthetic Bacteria

“…Of previous theoretical studies of properties of quinones, we in particular mention the recent accurate hybrid Hartree−Fock density functional theory (HF-DFT) work by O'Malley et al. − and Spanget-Larsen, exploring the effects of different solvents, either as polarizable continuum models or via direct formation of hydrogen bonds to the quinoid oxygens, on the hyperfine properties of benzoquinone anions and related model compounds. Nonelli has investigated the orientation of the methoxy groups in ubiquinone models, and Wheeler and co-workers have undertaken very detailed studies of structures and properties of plasto-, ubi-, and menaquinone models, employing tools similar those utilized in the present work.…”