Identification of cholesterol in different media by using the FT-IR, FT-Raman and UV–visible spectra combined with DFT calculations.

[Display omitted] • Complete vibrational assignments of 216 vibration modes of cholesterol in gas phase and ethanol solution are reported. • AIM calculations predicted intra-molecular interactions between CH 3 /CH 3 , CH 3 /CH 2 and CH 2 /CH 2 groups. • NBO studies predicted that the OH group and the four fused rings play important roles in the stability of cholesterol. • Electronic spectra at different ethanol concentrations suggest that positions of maxima increase with the solution concentration. • Frontier orbitals predicted low reactivity of cholesterol in ethanol probably due to its high ω value in this medium. In this investigation, the experimental FT-IR and FT-Raman spectra of cholesterol in the solid phase and in ethanol solution have been combined with the B3LYP/6–311++G** calculations and the scaled quantum mechanical force field (SQMFF) methodology, normal internal coordinates and transferable scaling factors to obtain the complete vibrational assignments of 216 vibration modes expected. Hence, complete vibrational assignments for that steroid of greatest biological importance are reported for first time in gas phase and ethanol solution together with its scaled force constants. Changes in the positions of some bands and in force constants values are observed in the different media due to the predicted intra-molecular interactions between CH 3 /CH 3 , CH 3 /CH 2 and CH 2 /CH 2 groups by atoms in molecules (AIM) calculations. The 1H- and 13C NMR chemical shifts of normal and deuterated cholesterol in aqueous solution confirm that the H atom of OH group is involved in the formation of H bonds in solution. Studies of experimental electronic spectra of cholesterol in different concentrations of ethanol revealed that the positions of peaks maxima increase conform increase the solution concentration. The natural bond orbital (NBO) analyses reveal that the polar OH group and the four fused rings play important roles in the stability and properties of cholesterol than the large hydrophobic moiety. Frontier orbitals predicted low reactivity of cholesterol in ethanol probably due to its high ω value in this medium. [ABSTRACT FROM AUTHOR]