Continuous-Wave Terahertz Spectroscopy of Biotin: Vibrational Anharmonicity in the Far-Infrared
T M. Korter, David F. Plusquellic
Continuous-wave linear-absorption spectroscopy based on terahertz radiation generated by solid-state photomixers has been applied to the investigation of the dynamics of the B-complex vitamin, biotin. The terahertz spectrum of biotin has been obtained using a variable-temperature, cryogenic sampling system and displays a small number of discrete absorptions over the temperature range from 4.2 K to room temperature. Spectral predictions from the lowest energy ab initio conformations of biotin are in poor agreement with experiment, suggesting the need to include condensed-phase environmental interactions for qualitative predictions of the terahertz spectrum. Vibrational anharmonicity is used to model the line shapes that result from drastic changes in vibrational state populations of biotin over this temperature range. Anharmonicity factors (χeωe/ωe) at the levels of 1% to 2% are needed for most, but not all, of the observed resonances and illustrate their importance for refining model predictions.