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.
The structural stability and photoabsorption properties of Ni(II)-based metal-organic complexes with octahedral coordination having different planar ligand ring structures were investigated employing density functional theory (DFT) and its time-dependent extension (TD-DFT) considering the M06 exchange-correlation functional and the Def2-TZVP basis set. The results showed that the molecular composition of different planar cyclic ligand structures had significant influences on the structural stability and photoabsorption properties of metal-organic complexes. Only those planar ligands that contained aromatic rings met the basic criteria (thermal stability, structural reversibility, and appropriate excitation frequency domain) for light-induced excited spin state trapping, but their spin transition efficiencies were very different. While, in all three aromatic cases, the singlet electronic excitations induced charge distribution that could help in the singlet-to-triplet spin transition, and triplet excitations, which could assist in the backward (triplet-to-singlet) spin transition, was found only for one complex.
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