Enantioselective interaction of carbamoylated quinine and (S)-3,5-dinitrobenzoyl alanine: theoretical and experimental circular dichroism study.

The interaction between tert-butylcarbamoylquinine selector and (S)-3,5-dinitrobenzoyl alanine selectand was studied experimentally and theoretically by chiroptical methods. Using a combination of experimental and calculated circular dichroism spectra, we present the first work dealing with the interaction of two dissimilar chiral molecules interacting by diverse types of interactions: ion pairing, hydrogen bonding and π-π stacking. Conformational analysis of the free selector, free selectand and the complex of selector with selectand was carried out and the obtained conformers were optimized at the BHandH/6-31+G** and B97d/6-31+G** levels. Consequently, vibrational (VCD) and electronic (ECD) circular dichroism spectra were calculated at the BHandH/6-31+G** and B97d/6-31+G** levels for the VCD and HF/6-31++G** and CAM-B3LYP/6-31++G** levels for the ECD. Spectral patterns of the free selectand and selector together with the complexation-induced spectral changes were compared with experimental data. Despite many simplifications within the theoretical model, the calculated ECD and VCD spectra are in good agreement with experimental data, which proves that the density functional theory (DFT) methods are able to model complicated systems interacting via multiple interactions of different natures.