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Journal of Spectroscopy
Volume 2016, Article ID 3137140, 9 pages
http://dx.doi.org/10.1155/2016/3137140
Research Article

The Influence of Molecular Structure Modifications on Vibrational Properties of Some Beta Blockers: A Combined Raman and DFT Study

1Department of Mathematics and Computer Science, “Iuliu Hatieganu” University of Medicine and Pharmacy, L. Pasteur 6, 400349 Cluj-Napoca, Romania
2Department of Pharmaceutical Physics-Biophysics, “Iuliu Hatieganu” University of Medicine and Pharmacy, L. Pasteur 6, 400349 Cluj-Napoca, Romania
3Faculty of Physics, “Babes-Bolyai” University, Kogalniceanu 1, 400084 Cluj-Napoca, Romania

Received 7 October 2015; Accepted 26 January 2016

Academic Editor: Stephen Cooke

Copyright © 2016 A. Farcaș et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We report results of a systematic Raman, SERS, and DFT study on four beta blocking molecules: Atenolol, Metoprolol, Propranolol, and, for the first time reported in the literature, Bisoprolol. The choice of these molecules was motivated by the structural similarities between Atenolol, Bisoprolol, and Metoprolol on one hand and by their differences relative to Propranolol. The density functional theory (DFT) approach, using the B3LYP method at the 6-311+G(d,p) level of theory, has been employed for geometry optimization and vibration bands assignments. The obtained results highlight the major role played by the central aromatic ring whose vibrations dominate the Raman spectra in all compounds. While the phenyl group vibrations dominate the Raman spectrum in the case of Atenolol, Bisoprolol, and Metoprolol, the spectrum of Propranolol presents high intensity vibrations of the naphthyl group. SERS performed on gold and silver colloids, at various pH conditions, revealed a higher sensitivity for Propranolol detection. The pH dependence of the spectrum indicates that the studied beta blockers attach themselves to the metal nanoparticles in a protonated form. The molecular adsorption geometry on metal nanoparticles surface has been evaluated by using the experimental SER spectra and the quantum chemical calculations.