Interaction of Biotin Tautomers with Magnesium Dication

In the present study, interactions of biotin tautomers and magnesium dication in their composites (in vacuum conditions) have been investigated within the constraints of density functional theory (DFT). Biotin may exhibit 1,3-proton tautomerism. All the composites presently considered have not only exothermic heat of formation values but also favorable Gibbs free energy of formation values. They are electronically stable. Various quantum chemical data have been collected and discussed including UV-VIS spectra. In all the cases, charge of the magnesium cation is less than the initial formal charge of +2 which means that some electron population has been transferred from biotin tautomers to the magnesium cation depending on the tautomeric structure or conformational form. The magnesium cation causes lowering of the frontier molecular orbitals in unequal extents and appears to be more effective on the LUMO energy level in some cases of the composites. Whereas in composite-B, it is more effective on the HOMO energy level. The calculated UV-VIS spectra occur in a large range of wavelengths such that some composites exhibit bathochromic shifts to above 600 nm.