Tautomers of 2-aminothiazole molecules in aqueous solutions explored by Raman, SERS and DFT methods

2-Aminothiazole, as a typical heterocyclic amine, may exist amino-imino tautomeric equilibrium in nature. In present report, the optimized structural parameters and vibrational wavenumbers of amino and imino tautomers of the molecule have been predicted by density functional theoretical (DFT) calculation. Comparing the experimental and the calculated Raman spectra, it indicates that the amino tautomer would be the main configuration in the 2-aminothiazole saturated solution. In the concentration-dependent SERS spectra of 2-aminothiazole adsorbed on gold nanoparticles, it is found that the tautomeric equilibrium shifts toward to the amino tautomer when the concentrations is decreased. While the amino tautomer is end-on the surface through the nitrogen atom of thiazole ring at the higher concentrations, the molecule becomes to stand on the metal surface by interacting simultaneously with two nitrogen atoms of the molecule in the diluted solution.