Carbohydrates in thermophile metabolism: Calculation of the standard molal thermodynamic properties of aqueous pentoses and hexoses at elevated temperatures and pressures

Experimental thermodynamic data for aqueous organic compounds can be combined with the revised Helgeson-Kirkham-Flowers (HKF) equations of state to generate parameters that can be used to estimate standard molal properties as functions of temperature and pressure. In this study, we regressed thermodynamic data for aqueous carbohydrates at temperatures up to 393 K reported in the literature to permit The calculation of the apparent standard molal Gibbs free energies and enthalpies of formation (DeltaG degrees and DeltaH degrees, respectively) and the standard molal entropies (S degrees (2)), heat capacities (C degrees (p,2)), and volumes (V degrees (2)) to 423 K and several hundred MPa of aqueous C-5 aldoses (ribose, arabinose, xylose, lyxose) and C-5 ketoses (ribulose, xylulose) as well as C-6 aldoses (glucose, mannose, galactose) and C-6 ketoses (fructose, sorbose). Values of AGO for these 11 aqueous carbohydrates are given as a function of temperature at the saturated water vapor pressure (P-SAT) and at 50 MPa. Values of DeltaG degrees for aqueous glucose are then combined with those of other aqueous organic and inorganic compounds to calculate values of the standard molal Gibbs free energies of 13 fermentation and respiration reactions (DeltaG degrees (r)) known or likely to be carried out by thermophilic microorganisms. Finally, values of the overall Gibbs free energies of these reactions (DeltaG(r)) are calculated at the temperature, pressure, and chemical. composition that obtain in the hydrothermal fluids of Vulcano Island, southern Italy, a site that is widely known for its tremendous diversity of organisms able to live at high temperatures. At likely activities of aqueous glucose, it is shown that thermophiles in the hot springs of Vulcano at 373 K and similar to0.1 MPa can gain between 400 and 3000 kJ per mole of glucose fermented or respired. Copyright (C) 2001 Elsevier Science Ltd.