Dick Bedeaux

Is the Ca2+-ATPase from sarcoplasmic reticulum also a heat pump?

We calculate, using the first law of thermodynamics, the membrane heat fluxes during active transport of Ca2+ in the Ca2+-ATPase in leaky and intact vesicles, during ATP hydrolysis or synthesis conditions. The results show that the vesicle interior may cool down during hydrolysis and Ca2+-uptake, and heat up during ATP synthesis and Ca2+-efflux. The heat flux varies with the SERCA isoform. Electroneutral processes and rapid equilibration of water were assumed. The results are consistent with the second law of thermodynamics for the overall processes. The expression for the heat flux and experimental data, show that important contributions come from the enthalpy of hydrolysis for the medium in question, and from proton transport between the vesicle interior and exterior. The analysis give quantitative support to earlier proposals that certain, but not all, Ca2+-ATPases, not only act as Ca2+-pumps, but also as heat pumps. It can thus help explain why SERCA 1 type enzymes dominate in tissues where thermal regulation is important, while SERCA 2 type enzymes, with their lower activity and better ability to use the energy from the reaction to pump ions, dominate in tissues where this is not an issue.

Coefficients for Active Transport and Thermogenesis of Ca2+-ATPase Isoforms

Coefficients for active transport of ions and heat in vesicles with Ca(2+)-ATPase from sarcoplasmic reticulum are defined in terms of a newly proposed thermodynamic theory and calculated using experiments reported in the literature. The coefficients characterize in a quantitative manner different performances of the enzyme isoforms. Four enzyme isoforms are examined, namely from white and red muscle tissue, from blood platelets, and from brown adipose mitochondria. The results indicate that the isoforms have a somewhat specialized function. White muscle tissue and brown adipose tissue have the same active transport coefficient ratio, but the activity level of the enzyme in white muscle is higher than in brown adipose tissue. The thermogenesis ratio is high in both white muscle and brown adipose tissue, in agreement with a specific role in nonshivering thermogenesis. Other isoforms do not have this ability to generate heat. A calcium-dependence of the coefficients is found, which can be understood as being in accordance with the role of this ion as a messenger in muscle contraction as well as in thermogenesis. The investigation points to new experiments related to structure as well as to function of the isoforms.

Jumps in electric potential and in temperature at the electrode surfaces of the solid oxide fuel cell

The electric potential profile and the temperature profile across a formation cell have been derived for the first time, using irreversible thermodynamics for bulk and surface systems. The method was demonstrated with the solid oxide fuel cell. The expression for the cell potential reduces to the classical formula when we assume equilibrium for polarized oxygen atoms across the electrolyte. Using data from the literature, we show for some likely assumptions, how the cell potential is generated at the anode, and how the energy is dissipated throughout the cell. The thermal gradient amounts to 5 × 108 Km−1 when the current density is 104 Am−2 and the thermal resistance of the surface scales like the electrical resistance.

Local Properties of a Formation Cell as Described by Nonequilibrium Thermodynamics

Abstract The current description of a formation cell using nonequilibrium thermodynamics gives an overall picture. It does not consider the behaviour of the temperature, chemical potential and electric potential locally. Thus it is unclear where temperature and potential change in the cell. Are these quantities discontinuous at the electrode surfaces, and if yes: how this should be described. Using methods developed in our earlier work we present such a local description. A differential equation is derived and solved for the transference coefficient of the salt in the electrolyte between the electrodes. Boundary conditions are essential for this purpose.

Chapter 12:Electrochemical Energy Conversion

We show how non-equilibrium thermodynamics can be used to describe energy conversion in electrochemical cells. The entropy production is actively used to find the electric potential profile under reversible conditions and to define the overpotential. Two variable sets are useful, and we give the transformations between these. We next prescribe procedures for calculations of profiles of temperature, concentrations and electric potential across a cell. Applications to saline power plants and thermoelectric generators are briefly discussed.

Chapter 1:Basis and Scope

This book is a collection of chapters which report on recent developments in the field of non-equilibrium thermodynamics. It is meant for readers that would like to know what the field can add to their understanding of transport phenomena, or what it means for experimental design. Classical non-equilibrium thermodynamics was established in 1931 and developed during the subsequent thirty years for transport in homogeneous phases. This chapter gives a short presentation of the basic assumptions, along with advice on how to derive the entropy production and find the flux–force relations for transport of heat, mass and charge. In the end of the chapter, we put the subsequent chapters of the book into perspective. The book presents recent results for homogeneous systems, for mesoscopic systems and for heterogeneous systems.

Chapter 4:Local Equilibrium in Non-equilibrium Thermodynamics

The hypothesis of local equilibrium is central in non-equilibrium thermodynamics. We define and review support for this hypothesis for three-, two- and one-dimensional, macroscopic thermodynamic systems. The hypothesis can also be supported in mesoscopic systems. It does not apply to density-gradient theories as these introduce nonlocal variables, but is found to apply if we define surface excess variables according to Gibbs. The hypothesis can therefore be actively used to predict surface properties.

Chapter 8:Non-equilibrium Thermodynamics for Evaporation and Condensation

Non-equilibrium thermodynamics gives dynamic boundary conditions for transport of heat and mass into and through surfaces far from reversible conditions. Conversions between thermal, mechanical and chemical energy are described through force–flux relations. Among the transfer coefficients, the coupling coefficient is large at interfaces, unlike in the homogeneous phase. The magnitude and sign of the coupling coefficient are determined by the enthalpy of the phase transformation. This has a bearing on the modelling of phase transitions, as simple laws of transport become insufficient, even wrong. The coefficients for evaporation and condensation are given and compared to results from kinetic theory. Transfer coefficients from experiments, molecular dynamics simulations and from the use of the van der Waals square gradient theory, are reviewed. The need for more work along these lines is pointed out. A short discussion is also given about contact lines.

Chapter 14:Applied Non-Equilibrium Thermodynamics

Non-equilibrium thermodynamics describes all kinds of transport processes. This chapter must focus on a few, namely transport of heat and mass in homogeneous and heterogeneous systems, in the absence or presence of chemical reactions. This introduction gives a brief history of the field, a list of g...