Intermolecular interaction in systems with energy-rich phosphates. I. Stepwise protonation of PO4 3 minus, ADP and ATP salts, IR investigations.

IR spectra of aqueous solutions of P 043-, ADP3-, ATP4-, Mg ADPand (MgADP~ + P 043_) (in two cases hydrated layers) were plotted. The parameter for the investigation was the mole percent of protons relative to the anions. The other cations were sodium or potassium. The purpose of our work was to obtain a basis for understanding the results regarding the changes to the interactions in ATP systems on hydrolysis. The addition of protons to the different acceptors is discussed on the basis of the bands of the phosphate groups and of the base ring vibrations. The formation of easily polarizable hydrogen bonds could be demonstrated with the aid of an IR continuum. Such 0 H +-*,0 bonds between hydrogen phosphate ions as well as NH+>,-N bonds form in the systems investigated. Thus the conditions for forming such bonds and the resulting intermolecular interactions will become evident in this work.