Perturbation of the adenine ring ultraviolet absorption spectrum is used to detect its inner sphere coordination by metal ions. Perturbations in adenine nucleotides are compared with those derived from complexes of aqueous metal ions and protonated tripolyphosphate complexed metal ions, HOPSO&-. HOPSOJVia-'forms an I I times stronger complex with adenosine than aqueous Ni", and also shows greater selectivity for complexation at N7 over Nl. It is estimated that for Ni(H) intramolecular macrochelate formation between the phosphate residues and an inner sphere coordinated adenine base occurs in ATP, ADP3, and AMPZ-with mole percentages 3W0, 65%, and 80%, respectively. Thus increasing the number and hence denticity of phosphate residues reduces the ability of the nucleic base portion of a nucleotide to enter into inner sphere coordination in a monomeric complex. For other complexes with ATP'-, mol percentages of macrochelate are about 10% for Mn" and zero for Mg': It is suggested that small percentages of an intramolecular outer sphere adenine complexed species may occur with Ni(II)