Theoretical study on the hydrogen bond interaction of 1:1 supermolecular complexes of protonated adrenaline with formate anion and its derivatives

Abstract

The hydrogen bond (H-bond) interaction of 1:1 supermolecular complexes of protonated adrenaline (PAd⁺) with formate anion and its derivatives (denoted as RCOO⁻, RH, CH₃, CH₂F, CH₂Cl, and CH₂Br) has been investigated by performing density functional theory calculations at the B3LYP/6-31G+(d) level. We obtained the most stable three conformations for each complex, which are denoted as PAd⁺–RCOO⁻(I), PAd⁺–RCOO⁻(II), PAd⁺–RCOO⁻(III), respectively, and calculated the interaction energy between PAd⁺ and RCOO⁻. In all PAd⁺–RCOO⁻ complexes, PAd⁺–CH₃COO⁻ is found to be the most favorable energetically. There exists low-barrier hydrogen bond (LBHB) in PAd⁺–HCOO⁻(III), PAd⁺–CH₂FCOO⁻(III), PAd⁺–CH₂ClCOO⁻(III), and PAd⁺–CH₂Br⁻(III) complexes. The solvent effects on the geometry and energy of the complexes are also considered by using the polarizable continuum model (PCM) model in aqueous solvent. It is found that PAd⁺–R⁻ complexes in solution are significantly less stable than those in the gas-phase. The theoretical results for the present model systems will be useful for experimental researchers working in this field.