Free energy of membranes

Feis Helmholtz free energy of membrane phase... 

Being perturbed at the interface, the membrane profile u r) adjusts itself gradually to minimize the elastic energy. The corresponding free energy of membrane deformation can strongly affect both protein conformation and protein function. For the GA insertion considered below, these effects manifest themselves through the influence of membrane parameters (elastic constants, thickness of the bilayer) on the lifetime r of the ion channel,... 

Zhao, Q., Wang, S. Muller-Steinhagen, H. (2004). Tailored surface free energy of membrane diffusers to minimize microbial adhesion. Applied surface science, 230, 371-378. 

The electrostatic free energy of a macromolecule embedded in a membrane in the presence of a membrane potential V can be expressed as the sum of three separate terms involving the capacitance C of the system, the reaction field Orffr), and the membrane potential field p(r) [73],... 

For fluid membranes, in which neighbor relations are not maintained, the free energy of a membrane is often written in the form [27,30]... 

Fructose is present outside a cell at 1 /iM concentration. An active transport system in the plasma membrane transports fructose into this cell, using the free energy of ATP hydrolysis to drive fructose uptake. Assume that one fructose is transported per ATP hydrolyzed, that ATP is hydrolyzed on the intracellular surface of the membrane, and that the concentrations of ATP, ADP, and Pi are 3 mM, 1 mM, and 0.5 mM, respectively. T = 298 K. What is the highest intracellular concentration of fructose that this transport system can generate Hint Kefer to Chapter 3 to recall the effects of concentration on free energy of ATP hydrolysis.)... 

Because osmosis is a thermodynamic property, we can expect it to be related to the effect of the solute on the enthalpy and entropy of the solution solvent flows until the molar Gibbs free energy of the solvent is the same on each side of the membrane We have already seen several times that a solute lowers the molar Gibbs free energy of the solution below that of the pure solvent, and solvent therefore has a tendency to pass into the solution (Fig. 8.33). 

FIGURE 8.33 On the left of the semipermeable membrane is the pure solvent with its characteristic molar enthalpy, entropy, and Gibbs free energy. On the right is the solution. The molar Gibbs free energy of the solvent is lower in the solution (an entropy effect), and so there is a spontaneous tendency for the solvent to flow into the solution. 

Methods similar to those discussed in this chapter have been applied to determine free energies of activation in enzyme kinetics and quantum effects on proton transport. They hold promise to be coupled with QM/MM and ab initio simulations to compute accurate estimates of nulcear quantum effects on rate constants in TST and proton transport rates through membranes. 

Figure 25. The free energy of interaction between two DMPC membranes at various degrees of surface tension as indicated. We note that the indicated surface tension is the tension at large membrane-membrane spacing. The salt bulk volume fraction was cps — 0.002. Redrawn from [85] by permission of the American Chemical Society...

The partition coefficient KmK is directly related to the free energy of transfer between the aqueous and the membrane phase. The enthalpy and entropy contri-... 

Gibbs free energies of water sorption, AG "(/l), can be extracted from isopiestic vapor sorption isotherms this analysis shows that AG (T) < AG", where AG" = -44.7 kj moH is the Gibbs free energy for vapor sorption at a free water surface at ambient condihons. Water absorbed by the membrane is therefore more strongly bound than water at a free bulk water surface this affirms the hydrophilic nature of water sorption in PEMs. 

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