MD and DFT Studies of O–H···N Bonded Hordenine Dimer, Aided by Experimental Vibrational Spectroscopy, NBO, AIM and NCI Calculations

The role of allelopathic and biochemical inhibitor hordenine in many applications may be determined by its potential tendency to the inter–molecular O–H···N bonding among other things. It is of interest to study multi-structural characterizations of the O–H···N bonding interaction to gain insights into the possible functional roles of the bonding, which may be correlated to the diverse application domains. In the present study, we have shown that the O–H···N bonded dimer computed from molecular dynamics (MD) simulation has short-range order and quasi-long range order consistent with the reported XRD results. We computed structural parameters from MD simulation in water yielding radius of gyration, minimum distance and root-mean-square-deviation and radial distribution function values that have been employed to understand the structural behaviour of the dimer. In addition, MD simulation also yielded O–H···O and C–H···N bonds as constituent links in dimer structures. We also combined molecular dynamics (MD) with DFT at B3LYP/6–311++G (d,p) level for computing the afore-mentioned stable structures and associated vibrational and electronic properties. Vibrational IR and Raman spectral features support the O–H···N bonded dimer structure. The orbitals overlap corresponding to the O–H···N bonding interaction has more contributions from s-orbitals of the O–H bond causing its elongation and stretching-mode red shift in the IR. The electron density and its Laplacian values have provided contour maps corresponding to the charge concentration and depletions around the O–H···N bond interaction.