Cooperative Hydration of Pyruvic Acid in Ice

 Abstract: 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 QH(T) = [PAH]/[PA] becomes temperature independent below ∼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 (ΔHH ∼ −22 kJ mol-1) be balanced by a multiple of the enthalpy of ice melting (ΔHM = 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 1δPAH and 1δPA methyl proton NMR resonances is nearly constant while, (3) line widths increase exponentially with decreasing temperature before diverging below ∼230 K, we infer that PA in ice remains cooperatively hydrated within interstitial microfluids until they vitrify. 

Abstract Image

Marcelo I. Guzmán, Lea Hildebrandt, Agustín J. Colussi, and Michael R. Hoffmann.Cooperative Hydration of Pyruvic Acid in Ice. Journal of the American Chemical Society 2006 128 (32), 10621-10624
DOI: 10.1021/ja062039v, https://doi.org/10.1021/ja062039v

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