Structural changes of nucleic acid base in aqueous solution as observed in X-ray absorption near edge structure (XANES)

X-ray absorption near edge structure (XANES) spectra for adenine-containing nucleotides, adenosine 5′-monophosphate (AMP) and adenosine 5′-triphosphate (ATP) in aqueous solutions at the nitrogen K-edge region were measured. The two intense peaks in XANES spectra are assigned to transitions of 1s electrons to the π∗ orbitals of different types of N atoms with particular bonding characteristics. The difference between their spectra is ascribed to protonation of a particular N atom. Similarity observed in XANES spectra of guanosine 5′-monophosphate (GMP) and ATP is also interpreted as similar bonding characters of the N atoms in the nucleobase moiety.