Membrane systems, surface properties

BIOELECTROCHEMISTRY. Application of the principles and techniques of electrochemistry to biological and medical problems. It includes such surface and interfacial phenomena as the electrical properties of membrane systems and processes, ion adsorption, enzymatic clotting, transmembrane pH and electrical gradients, protein phosphorylation, cells, and tissues. 

Some details of the microstructures and physical, chemical and surface properties of inorganic membranes (particularly the porous ones) have been described in Cluster 4. In this chapter, those properties related to membrane performance during and between applications and general features of commercial membrane elements, modules and systems will be discussed along with application characteristics and design and operating considerations. 

Biomimetic membrane-enclosed compartments have numerous advantages when it comes to model biological systems. However, at shorter length scales, surface properties become increasingly important. In applications where the length scales are of the order of micrometers to submicrometers, the chemistry can be completely dominated by surface interactions [31]. This fact and... 

Up until 1977, the non-covalent polymeric assemblies found in biological membranes rarely attracted any interest in supramolecular organic chemistry. Pure phospholipids and glycolipids were only synthesized for biophysical chemists who required pure preparations of uniform vesicles, in order to investigate phase transitions, membrane stability and leakiness, and some other physical properties. Only very few attempts were made to deviate from natural membrane lipids and to develop defined artificial membrane systems. In 1977, T. Kunitake published a paper on A Totally Synthetic Bilayer Membrane in which didodecyl dimethylammonium bromide was shown to form stable vesicles. This opened the way to simple and modifiable membrane structures. Since then, organic chemists have prepared numerous monolayer and bilayer membrane structures with hitherto unknown properties and coupled them with redox-active dyes, porous domains and chiral surfaces. Recently, fluid bilayers found in spherical vesicles have also been complemented by crystalline mono-... 

The use of supports in asymmetric, supported membranes introduces a number of complications in the interpretation of permeation and separation data as well as in the optimalisation of membrane systems. If the flow resistance of the support is not negligible, there is a pressure drop across the support. This implies that the pressure and so the occupancy at the interface of separation layer and support is different from the (directly accessible) pressure at the support surface, usually the permeate side. Consequently, the driving force for permeation through the separation layer is different from the total driving force across the membrane system. In cases where one wants to calculate or compare transport properties of the separation layer material, it is necessary to correct for this effect (for illustration see below). 

Cells are not mere bags of dilute solutions. Aside from the organelles, the cells possess a cytoskeleton, MTL, and various membrane systems, which provide a vast surface area. It is then almost inescapable that these surfaces interact with the neighboring water in a way that alters the physical properties of water and affects water molecules over some considerable distance. A conservative estimate of the distance is 30 A, though estimates of up to 300-500 A have been made. If one accepts as reasonable the 30 A estimate, then 20-40% of the water in the aqueous cytoplasm would be directly influenced by membrane surfaces. 

The experimental methods based on electrokinetic phenomena (and especially electrophoresis) have found very widespread application for routine characterization of electrical surface properties of solid particles, liquid droplets, porous media, synthetic membranes, etc. A systematic presentation of the main results obtained on different types of systems is given in chapters 6 to 8 of Reference 716, and in chapters 8 to 33 of Reference 718. A glance at the books " and review articles " " " in the field, however, shows that the properties of air-water and oil-water interfaces are either not considered at all or only briefly mentioned. This fact is surprising, as a number of studies " " (the first performed more than 70 years ago) have convincingly demonstrated a substantial negative potential at bare (without any surfactant) air-water and oil-water interfaces. This spontaneous charging cannot be explained in a trivial way — it requires the specific preferential adsorption of some kind of ion, because from a purely electrostatic viewpoint the approach of an ion to the... 

Surface Properties of Membrane Systems Influence of Chemistries on Surface Viscosity... 

In general the labeled compound is an analog of a compound found naturally in the membrane system, and thus it is assumed that the motional behavior of the labeled species is very similar to that of its analog. It is surprising, therefore, that the surface properties of the spin labeled compounds have not been studied as extensively as those of the unlabeled... 

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