The salt-induced destacking of purine in aqueous NaCl systems and its implications on life at elevated temperatures

Aqueous purine solutions in the absence and presence of NaCl have been studied by vapor-pressure osmometry and high-resolution proton-magnetic-resonance spectroscopy. The presence of NaCl causes a marked change in the temperature dependence of the molal osmotic coefficient and the chemical shift of the purine resonances when compared with the corresponding quantities in purine solutions containing no added salt. In the absence of salt, the destacking of the purine is gradual as the temperature is increased, whereas there is a sharp decrease in purine stacking at approximately 42 degrees C in the presence of NaCl. This salt-induced destacking of purine is consistent with the previously noted salt-induced bulk water destructuring at temperatures above approximately 42 degrees C. This effect has been deduced from considerations of species profiles in acid-water systems as a function of temperature (Leifer, L., and Inoue, K., manuscript in preparation). The implications of this phenomenon on biological systems at elevated temperatures will be discussed.