The influence of the solvent on the molecular structures and the ESR (EPR) spectra of the three title semiquinones is investigated by theoretical calculations, using density functional theory (DFT) and polarizable continuum models (PCM). The reordering of the relative magnitudes of the isotropic hyperfine constants observed when passing from an aprotic to a protic solvent is well reproduced by integral equation formulation PCM (IEFPCM) calculations, provided discreet solute-solvent hydrogen-bonding interactions in the protic solvent is considered explicitly. A mixed discreet-continuum procedure with a simplified super-molecular model leads to excellent prediction of all proton hyperfine constants measured in methanol solution, including methine as well as alkyl protons. The relation between alkyl proton hyperfine constants and conformation of the A rings in the semiquinones of 7-deoxyaklavinone and aclacinomycin T is discussed.
- Solvent sensitivities
- Hydrogen bonding
- Electron spin resonance (ESR, EPR)
- Isotropic hyperfine coupling constants
- Polarizable continuum model (PCM)
- Mixed discreet-continuum solvation model