Effect of the Protons Arising in Aqueous Hydrolysing ATP Solutions, IR Investigations

Abstract

IR spectra of 0.3 ᴍ aqueous solutions of Mg_0.5K_3-nHM_n ATP were plotted. The dependence of the spectra on the hydrolysis was investigated for three different K/H ratios of the nonhydrolysed system. Changes to bands provide information as to the protons added to the phosphate groups and base residues as a function of the initial protonation and degree of hydrolysis. More and more proton addition to the -PO₃^-- groups is observed as the initial protonation increases and as the degree of hydrolysis rises. The same applies as far as the addition of protons to the base residues is concerned to the systems with a higher initial protonation. At low degrees of hydrolysis the PO₄^3- ions which occur do not bind the two hydrolysis protons completely. 150% protonated PO₄^3- ions first form which cross-like via OH⁺···O hydrogen bonds, which only become more strongly protonated in the systems with a higher initial protonation at large degrees of hydrolysis. The OH⁺···O bonds between the 150% protonated hydrogen phosphate ions as well as the NH⁺···N hydrogen bonds between the base residues cause an IR continuum and are thus easily polarizable. An extremely large change to the hydrate structure within narrow hydrolysis ranges is indicated by changes to the bands of the water molecules. The biological relevance of these findings is briefly discussed in the conclusions.