Membrane dependence

Membrane asymmetries in the transverse direction (from one side of the membrane to the other) can be anticipated when one considers that many properties of a membrane depend upon its two-sided nature. Properties that are a consequence of membrane sidedness include membrane transport, which is driven in one direction only, the effects of hormones at the outsides of cells, and the immunological reactions that occur between cells (necessarily involving only the outside surfaces of the cells). One would surmise that the proteins involved in these and other interactions must be arranged asymmetrically in the membrane. 

For a charged species, the situation is slightly more complicated. In this case, the movement of a molecule across a membrane depends on its electrochemical potential. This is given by... 

FIGURE 10.1 Passive diffusion of an uncharged species across a membrane depends only on the concentrations (Q and Cg) on the two sides of the membrane. 

FIGURE 10.2 The passive diffusion of a charged species across a membrane depends upon the concentration and also on the charge of the particle, Z, and the electrical potential difference across the membrane, Ai/<. 

With regard to the enantioselective transport through the membrane, one advantage of liquid membrane separation is the fact that the diffusion coefficient of a solute in a liquid is orders of magnitude higher as compared to the diffusion coefficient in a solid. The flux through the membrane depends linearly on the diffusion coefficient and concentration of the solute, and inversely on the thickness of the membrane [7]. 

Palozza, P. et al., Dual role of beta-carotene in combination with cigarette smoke aqueous extract on the formation of mutagenic lipid peroxidation products in lung membranes dependence on pOj, Carcinogenesis, 2006. 

Kalafatis M., Swords N. A., Rand M. D Mann K. G. Membrane-dependent reactions in blood coagulation Role of Vitamin K-dependent enzyme complexes. Biochim Biophys Acta 1994 1227,113-29. 

Fig. 6.1 Distribution of cations and anions in pores of a cation-exchanger membrane depends on pore radius which decreases in the sequence A- B— C. In case C the membrane becomes permselective. (According to K. Sollner)... 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Ajoene has antitumor activity, inhibits cholesterol biosynthesis, modulates membrane-dependent functions of immune cells, inhibits protein prenylation83 and is an anti-leukaemia agent for acute myeloid leukaemia.85 In antithrombotic assays, the Z isomer is more active than the E isomer.84... 

Krishna, A. G., Menon, S. T., Terry, T. J., and Sakmar, T. P. (2002) Evidence that helix 8 of rhodopsin acts as a membrane-dependent conformational switch. Biochemistry 41, 8298-8309. 

The equilibrium constant for this reaction depends on the stability constants of the ionophore-M+ complexes and on the distribution of ions in aqueous test solution and organic membrane phases. For a membrane of fixed composition exposed to a test solution of a given pH, the optical absorption of the membrane depends on the ratio of the protonated and deprotonated indicator which is controlled by the activity of M+ in the test solution (H,tq, is fixed by buffer). By using a to represent the fraction of total indicator (Ct) in the deprotonated form ([C]), a can be related to the absorbance values at a given wavelength as... 

The rejection of dissolved ions at reverse osmosis membranes depends on valence. Typically, a membrane which rejects 93 per cent of Na+ or Cl- will reject 98 per cent of Ca2+ or SO42- when rejections are measured on solutions of a single salt. With mixtures of salts in solution, the rejection of a single ion is influenced by its... 

The movement of solute across a semipermeable membrane depends upon the chemical concentration gradient and the electrical gradient. Movement occurs down the concentration gradient until a significant opposing electrical potential has developed. This prevents further movement of ions and the Gibbs-Donnan equilibrium is reached. This is electrochemical equilibrium and the potential difference across the cell is the equilibrium potential. It can be calculated using the Nemst equation. 

Combining Eq. (4.9) with the lumped-model Eq. (3.24), one gets an expression for the temperature on the membrane depending on the source drain-current ... 

The effective conductivity of the membrane depends on its random heterogeneous morphology—namely, the size distribution and connectivity of fhe proton-bearing aqueous pafhways. On fhe basis of the cluster network model, a random network model of microporous PEMs was developed in Eikerling ef al. If included effecfs of varying connectivity of the pore network and of swelling of pores upon water uptake. The model was applied to exploring the dependence of membrane conductivity on water content and... 

The separation efficiency (e.g. permselectivity and permeability) of inorganic membranes depends, to a large extent, on the microstructural features of the membrane/support composites such as pore size and its distribution, pore shape, porosity and tortuosity. The microstructures (as a result of the various preparation methods and the processing conditions discussed in Chapter 2) and the membrane/support geometry will be described in some detail, particularly for commercial inorganic membranes. Other material-related membrane properties will be taken into consideration for specific separation applications. For example, the issues of chemical resistance and surface interaction of the membrane material and the physical nature of the module packing materials in relation to the membranes will be addressed. 

Nicotine is distilled from bnming tobacco and carried proximally on tar droplets (also called particnlate matter), which are inhaled. Absorption of nicotine across biological membranes depends on pH. Nicotine is a weak base with a p fa of 8.0. In its ionized state, snch as in acidic environments, nicotine does not rapidly cross membranes. The pH of smoke from fine-cured tobaccos, found in most cigarettes. 

The development of a successful zeolite/polymer mixed-matrix membrane with properties superior to the corresponding polymer membrane depends upon good performance match and good compatibility between zeolite and polymer materials, as well as small enough zeolite particle size for membrane manufacturing on a large scale. 

In the physical model, there are two separate structures for the membrane depending on whether the water at the boundary is vapor or liquid these are termed the vapor- or liquid-equilibrated membrane, respectively. The main difference between the two is that, in the vapor-equilibrated membrane, panel c, the channels are collapsed, while, in the liquid-equilibrated case, panel d, they are expanded and filled with water. These two structures form the basis for the two types of macroscopic models of the membrane. 

Finally, the result of a theoretical treatment of a similar system with almost complete association in the membrane will be given without calculations [66,67]. The diffusion potential in the membrane depends not only on electrodiffusion of J, and A but also on diffusion of associates JA and KA. The resultant formula for the membrane potential is... 

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