A Raman spectroscopic study of the interaction of divalent metal ions with adenine moiety of adenosine 5'-triphosphate.

Raman spectra of ATP at various pH values are affected by addition of equimolar solution of divalent metal ions such as Ca2+, Mg2+, Co2+, Cu2+, and Hg2+. The changes in frequency and intensity have been used to construct models describing the nature of metal-adenine and metal-triphosphate interactions under different conditions. The metal ions are found to co-ordinate the triphosphate group in the entire pH range studies (pH to 12). Calcium (II) and magnesium (II) interact strongly with the phosphate moiety at neutral pH, although a weak interaction with the ring occur at low pH values. Around neutrality, several Raman spectral changes are observed to implicate the interaction of cobalt (II) ion with the five-membered ring of the adenine. The changes in Raman frequency are too small to suggest a direct Co(II)-N7 binding. At least six different Cu(II)-ATP species are identified between pH 3 and 12. At pH approximately 7.0 Raman data are explained better by Cu(II) interacting with N7 simultaneously with the amino group of the adenine ring. However, a Cu(II) binding to N3 at pH 10 to 11 is indicated by the enhancement of the 760 and 1360 cm-1 vibrations. At neutral pH, mercury (II) ion shows a direct coordination at N1 while at low pH with N1 blocked by protonation, mercury (II) does not interact with the adenine moiety.