Transport of small solutes and ions across membrane interfaces

TRANSPORT OF SMALL SOLUTES AND IONS ACROSS MEMBRANE INTERFACES 

Regulating the distribution and transport of small molecular species across cell walls and providing a permeability barrier to ions are among the most essential membrane functions. Although many nutrients, waste products and ions needed for the proper functioning of a cell are transported through its walls via 

The dynamic process of permeation is not the only issue of interest in studies the on interactions of small solutes with membranes. Some molecules, such as ligands, some drugs and anesthetics, act in the membrane environment by affecting membrane receptors either inside the membrane or at the water-membrane interface. For these molecules, the relevant quantity is their equilibrium distribution across the membrane. At low solute concentration, this distribution can be determined by calculating the change in the excess chemical potential, (c), 

Although the number of computer simulations on small molecules in membranes performed so far has been rather limited, a consistent picture has begun to emerge from these simulations. In particular, we have markedly improved our understanding of such key issues as the relationship between the distribution of a solute and its chemical and electronic structure, the mechanism of permeation and its dependence on both the size of the solute and the type of the membrane, the nature of solute-induced changes in the structure of the membrane and their influence on permeation. This section is devoted to reviewing this recent progress. 

It is often convenient to consider the process of dissolving a solute as consisting of two hypothetical steps. First, a cavity that is sufficiently large to accommodate the solute is formed in the solvent. Creating such a cavity requires 

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