Vibrational characterization of α-aminophosphinic acid derivatives of pyridine: DFT, Raman and SERS spectroscopy studies ✠

This paper shows Fourier-transform Raman (FT⬜RS) and surface-enhanced Raman spectroscopy (SERS) studies of three α-aminophosphinic acid derivatives of pyridine: [(butylamino)(pyridin-2-yl)methyl]phenylphosphinic acid (α-PyNH), [(butylamino)(pyridin-3-yl)methyl]phenylphosphinic acid (β-PyNH), and [(benzylamino)(pyridin-4-yl)methyl]phenylphosphinic acid (γ-PyNH) immobilized onto colloidal sol nanoparticles and electrochemically roughened surface of silver. The molecular geometries and vibrational wavenumbers were calculated based on density functional theory (DFT) at the B3LYP 6-311G(df,p) level of theory. Based on the comparison of the FT⬜RS experimental and theoretical vibrational bands with the SERS results the orientation of the α-aminophosphinic acid derivatives of pyridine onto two silver substrates was proposed. The changes in the adsorption process under the influence of the position of substituent in regard to the ring N atom (in α-, β-, and γ-positions, respectively) and modification of the substituent (replacement of the butyl chain by the phenyl ring of high affinity to silver (γ-PyNH)) were also discussed.