Transferable specific scaling factors for interpretation of infrared spectra of biomolecules from density functional theory.

A set of transferable local scaling factors is established for assignment of infrared spectra of molecular systems of biological interest experimentally recorded under gas-phase conditions. Each scaling factor is specific for an experimentally observable vibrational mode chosen among those bringing significant structural information. Those factors are provided for harmonic calculations at the DFT B3LYP and DFT B3PW91 levels respectively with 7 and 2 different basis sets. The used training set of neutral molecules comprises nucleobases, aminoacids, peptides, sugars, and neurotransmitters. The proposed specific scaling factors usable for unambiguous conformer assignments lead to typical prediction errors ca. 10 cm -1 for free and moderately hydrogen-bonded group frequencies with red-shifts up to 200 cm -1 .