This work deals with the theoretical study on the molecular structure of two well-known neurotransmitter receptors tyramine hydrochloride and dopamine hydrochloride. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities, and Raman scattering activities were calculated by the density functional B3LYP method employing 6-311G(d,p) as the basis set and the vibrational studies were interpreted in terms of the potential energy distribution (P.E.D.). The internal coordinates were optimized repeatedly to maximize the P.E.D. contributions. A detailed interpretation of the infrared and Raman spectra of tyramine and dopamine hydrochloride is reported in the present work. The similarities and differences between the vibrational spectra of the two molecules studied have been highlighted. The scaled theoretical wave numbers are in perfect agreement with the experimental values. The thermodynamic calculations related to the title compounds were also performed at B3LYP/6-311G(d,p) level of theory. The FT-Raman and FT-IR spectra of tyramine and dopamine hydrochloride have been taken from literature.

A complete normal coordinate analysis was performed for andrographolide in terms of the calculation by using Wilson's G-F matrix method and Urey Bradley force field. Normal coordinate analysis has been carried out to understand the dynamical behaviour of the bioactive labdane diterpenoid of the medicinally useful terrestrial plant Andrographis paniculata. The structural elucidation of a novel, biologically active natural product followed by its total synthesis lays the groundwork for investigations into its biological mechanism of action including putative cellular receptor isolation.

This work deals with a theoretical study of the molecular structure of colchicine. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated by the ab initio Hartree-Fock method and the Density Functional B3LYP method employing 6-31G(d) as the basis set, and the vibrational studies were interpreted in terms of the potential energy distribution (P.E.D.). The internal coordinates were optimized repeatedly to maximize the P.E.D. contributions. A detailed interpretation of the infrared and Raman spectra of colchicine is reported. The scaled theoretical wave numbers are in perfect agreement with the experimental values. The FT-IR spectra of colchicine was recorded in solid phase, and the FT-Raman spectra of colchicine have been taken from the literature.

A complete normal coordinate analysis was performed for five-coordinate non-rigid triarylantimony diester SbPh3(O2CR)2, known to be a bioactive molecule, using Wilson G-F matrix method and Urey Bradley force field. The study of vibrational dynamics was performed using the concept of group frequencies and band intensities.

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