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

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.