Sers And Dft Study Of 5f-Pb-22

In this work, a joint experimental and theoretical study on the synthetic cannabinoid, 5F-PB-22 (1-(5-fluoropentyl)-8-quinolinyl ester-1H-indole-3-carboxylic acid) is reported. The molecular vibrations of 5F-PB-22 were investigated by Raman and surface-enhanced Raman spectroscopy (SERS) spectroscopies. In parallel, quantum chemical calculations based on density functional theory (DFT) with the hybrid B3LYP exchange-correlation functional coupled with the standard 3-21G basis set were used to determine the geometrical and vibrational characteristics of 5F-PB-22 and to predict the adsorption geometry of the molecule on the silver colloidal surface. The SERS spectrum of 5F-PB-22 was recorded using a 532-nm laser line and a hydroxylamine phosphate reduced silver colloid as the SERS substrate. SERS and Raman spectral bands have been assigned by comparison with the DFT calculated spectrum. A self-aggregation spectrum was obtained, but in order to obtain a spectrum with NaCl as the aggregating agent, a two-step procedure was developed. It was found that 10-mM NaCl can be used as a trigger for aggregation before adding 5F-PB-22 followed by the addition of 20- to 100-mM NaCl to complete aggregation. Using this procedure, 5F-PB-22 was easily detected at 2.12x10(-8)M. Based on a predicted molecular adsorption geometry from the calculated molecular electrostatic potential and the SERS spectrum, it is proposed that the quinoline moiety of the molecule lies in a preponderant parallel orientation to the silver surface with the plane of the indole ring being perpendicular to the surface. The molecular orientation is affected by the surface coverage by 5F-PB-22 and the presence of Cl-.