Biomembrane surfaces

Otherwise it has been shown that the accumulation of electrolytes by many cells runs at the expense of cellular energy and is in no sense an equilibrium condition 113) and that the use of equilibrium thermodynamic equations (e.g., the Nemst-equation) is not allowed in systems with appreciable leaks which indicate a kinetic steady-state 114). In addition, a superposition of partial current-voltage curves was used to explain the excitability of biological membranes112 . In interdisciplinary research the adaptation of a successful theory developed in a neighboring discipline may be beneficial, thus an attempt will be made here, to use the mixed potential model for ion-selective membranes also in the context of biomembrane surfaces. 

For the biomembrane surfaces the situation zei i0 >> kT often occurs. In this limit, eq 12 is simplified and has the form... 

Experimental Results. The DLVO theory, which is based on a continuum description of matter, explains the nature of the forces acting between membrane surfaces that are separated by distances beyond 10 molecular solvent diameters. When the interface distance is below 10 solvent diameters the continuum picture breaks down and the molecular nature of the matter should be taken into account. Indeed the experiment shows that for these distances the forces acting between the molecularly smooth surfaces (e.g., mica) have an oscillatory character (8). The oscillations of the force are correlated to the size of the solvent, and obviously reflect the molecular nature of the solvent. In the case of the rough surfaces, or more specifically biomembrane surfaces, the solvation force displays a mono tonic behavior. It is the nature of this solvation force (if the solvent is water, then the force is called hydration force) that still remains a puzzle. The hydration (solvation) forces have been measured by using the surface force apparatus (9) and by the osmotic stress method (10, II). Forces between phosphatidylcholine (PC) bilayers have been measured using both methods and good agreement was found. 

A biomembrane surface-biological fluid interface may be regarded as a solid-liquid interface exhibiting electrical behavior similar to that at an electrode-electrolyte solution interface (Pilla, 1974). Similarities between electrode interfaces and biomembranes in contact with aqueous solutions have recently been noted (Berry et al., 1985 Bowden et al., 1985). 

As has been mentioned before, most biomembrane surfaces are exposed to aqueous phases where the polar groups of membrane molecules are situated. 

Another similarity between the interfaces of electrodes and biomembranes in contact with aqueous solutions is the existence of an ordered water layer at their respective surfaces. Considerable attention has been given to understanding the structure of water at biomembrane surfaces. Studies of... 

Hayward JA, Chapman D. Biomembrane surfaces as models for polymer design — the potential for hemocompatibility. Biomaterials 1984 5(3) 135—42. 

Stable Biomembrane Surfaces formed by Phospholipid Polymers. 

In the last decade, many efforts have been devoted to the study of the influence of chiral molecules on the enzymatic processes at the membrane surfaces. V -Acyl-L-and D-amino acid derivatives have been employed as model substances for simulating biomembranes and interfacial processes at biomembrane surfaces [32]. It has been found that chiral monolayers of V -acylamino acid methyl esters on a pure water surface showed that hydrogen bond formation via NH, COOH, and p-hydroxyphenyl groups (i.e., tyrosine side chains) lead to a pronounced chiral discrimination [33,34]. Homochiral (d-d or L-L interactions) and heterochiral (d-l interaction) discrimination can be observed depending on the area per molecule ( min)> which depends on the conformation of the amino acid residue and on the alkyl chain length. 

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