Spectroscopic study of the isomerization of Z- to E-pyridine-2-formyl thiosemicarbazone

Abstract Pyridine-2-formyl thiosemicarbazone (PATS2) was synthesized in the E (anti) and Z (syn) configurations. Raman spectra were obtained in the solid state, and in DMSO and aqueous solutions. The SER spectra of PATS2 adsorbed on a silver electrode in DMSO and in aqueous solutions showing striking differences. The comparison of Raman data revealed that PATS2 is present on the silver electrode surface in the same configuration as the predominant isomer of the corresponding parent solutions. The prevalence of the E (anti) isomer in DMSO solutions was confirmed by Raman and 1 H NMR spectroscopies, and by means of the latter technique, the anti configuration is also proved to be predominant in aqueous solutions of different pHs, even starting with Z -PATS2 solutions. A strong interaction of E -PATS2 with water molecules by hydrogen bonding accounts for marked differences in Raman spectra of this isomer in DMSO and water solutions, and for the corresponding E -PATS2 species adsorbed on the silver electrode surface.