ANALYTICAL SPECTROSCOPY AND STRUCTURE OF BIOMOLECULES USING AN ABINITIO COMPUTATIONAL METHOD

An ab initio computational method has been applied to the study of biologically and pharmaceutically important phenethylamine and its derivatives (tyramine, dopamine, and tyrosine) in order to predict the structure of some of their stable conformers and consequently their spectroscopic properties. The structures were optimized at the HF/3-21G level and their stabilities were determined by performing vibrational frequency calculations on the optimized structures. In the case of phenethylamine and tyramine, three stable conformers were found, two of which have an ethylamine-folded structure and the other has an ethylamine-extended structure with the former two lying about 0.01 eV higher in energy than the latter. The stable conformers of phenethylamine found in the present study are compared with the results obtained by experiments and other theoretical methods. From the resulting structural calculations, IR and Raman vibrational frequencies of phenethylamine and tyramine were predicted which are particularly useful for the analyses of the experimental spectra when available. In particular, the capability lo visualize the vibrational motion responsible for a particular peak enhances its usefulness in the assignment of the features in the IR spectra. Ionization potentials, electron affinities, and the charge density distribution of phenethylamine and its derivatives were predicted, and their utility in the interpretation of the experimental spectroscopic data is demonstrated.