Calculation of the thermodynamic properties of biomolecules at high temperatures and pressures is fundamental to understanding the energetics of metabolism in hydrothermal systems. Perhaps the most direct interaction between hyperthermophilic microbes and their aquatic and mineralogic habitat involves conversion of environmentally available redox potential into biochemically useful energy. Although chemical thermodynamics can be used to quantify this process, little is known about the thermodynamic properties of the biomolecules involved, especially at high temperatures. However, recent advances in theoretical biogeochemistry make it possible to calculate these proper-ties using the limited experimental data available in the literature, together with group additivity and correlation algorithms, reference model compounds and reactions, and the revised-HKF equations of state. This approach permits calculation of the standard molal thermodynamic properties and equations of state parameters for magnesiumcomplexed adenosine nucleotides, nicotinamide adenine dinucleotides (NADs), and nicotinamide adenine dinucleotide phosphates (NADPs) as a function of pressure and temperature. The thermodynamic properties and revised-HKF equations of state parameters generated in the present study can be used to carry out comprehensive mass transfer and Gibbs energy calculations to quantify the energetics of microbial energy production in hydrothermal systems. (c) 2006 Elsevier B.V. All rights reserved.