Cooperative hydration of pyruvic acid in ice

摘要

About 3.5 +/- 0.3 water molecules are still involved in the exothermic hydration of 2-oxopropanoic acid (PA) into its monohydrate (2,2-dihydroxypropanoic acid, PAH) in ice at 230 K. This is borne out by thermodynamic analysis of the fact that Q(H)(T)) [PAH]/[PA] becomes temperature independent below similar to 250 K (in chemically and thermally equilibrated frozen 0.1 <= [PA]/M <= 4.6 solutions in D2O), which requires that the enthalpy of PA hydration (Delta H-H similar to -22 kJ mol(-1)) be balanced by a multiple of the enthalpy of ice melting (Delta H-M) 6.3 kJ mol(-1)). Considering that: ( 1) thermograms of frozen PA solutions display a single endotherm, at the onset of ice melting, ( 2) the sum of the integral intensities of the (1)delta(PAH) and (1)delta(PA) methyl proton NMR resonances is nearly constant while, ( 3) line widths increase exponentially with decreasing temperature before diverging below similar to 230 K, we infer that PA in ice remains cooperatively hydrated within interstitial microfluids until they vitrify.