Interfacial structures of 1-methyladenine, 3-methyladenine, 7-methyladenine, and 9-methyladenine on gold nanoparticles by Raman spectroscopy

Interfacial structures of 1-methyladenine (1 MA), 3-methyladenine (3 MA), 7-methyladenine (7 MA), and 9-methyladenine (9 MA) on gold nanoparticles (AuNPs) were investigated by means of surface-enhanced Raman scattering (SERS). Different positions of the methyl group in the purine ring of adenine were found to result in not only dissimilarity among Raman spectral features but also surface binding schemes. Density functional theory (DFT) calculations predicted that the amino-9H tautomeric form would be most stable among the conformers of 1 MA, 3 MA, 7 MA, and 9 MA including amino and imino tautomeric conformers. SERS spectral features were analyzed with appropriate vibrational assignments based on DPI calculations. After considering the enhancement factors, the Raman spectra of 1 MA, 3 MA, 7 MA, and 9 MA on AuNPs were dissimilar, suggesting the methyl group at the purine ring of methyladenine may be significantly affecting the binding on AuNPs. Our Raman study indicates the position of the methyl group in methyladenine may play a significant role in coordinating metal surfaces. (C) 2016 Published by Elsevier B.V.