Surface-Enhanced Raman Scattering of the Complexes of Silver with Adenine and dAMP

The behaviour of adenine and 2’-deoxyadenosine-5’-monophosphate (dAMP) at positive surface potentials of a silver working electrode was investigated using surface-enhanced Raman scattering (SERS). The use of positive potentials in the presence of adenine or dAMP leads to a rapid accumulation of an intense spectrum. It is proposed that complexes of adenine (dAMP) with silver generate the observed spectra. Adenine and dAMP can be distinguished spectroscopically due to various different complexes that can be formed for adenine and not for dAMP. The SERS spectra of the silver-adenine complexes show broad, unresolved bands between 1200 and 1500 cm-I, while the spectra of complexes of silver with dAMP show clearly resolved bands. The formation of Ag+-adenine complexes gives rise to a decrease in pH and must therefore be associated with deprotonation of the adenine ring system. The SERS spectra of adenine can be obtained in solutions with a pH of 3.0, 7.5 and 11.0 whereas the SERS spectra of dAMP can only be obtained at a pH of 7.5 and 11.0. The time dependence of the SERS spectra of dAMP suggests that at least two different complexes of silver with dAMP are involved. The observed spectra are completely different from the ‘classical’ SERS spectrum of adenine and dAMP. This spectrum is characterized by an intense band at 729 cm-’ (at -700 mV YS. SCE). At open loop potential, however, the spectra of the Ag-dAMP complex change slowly to the ‘classical’ SERS spectrum of dAMP.