Mechanisms in membranes

Bitter, J. G. A. (1991) Transport Mechanisms in Membrane Separation Processes, Plenum Press, New York. 

Ryrie, I. J. The contribution of reconstituted proteinlipid vesicles to the elucidation of energy transduction mechanisms in membranes. In Light Transducing Membranes (Deamer, D.W., ed.). New York, San Francisco, London Academic Press 1978, pp. 201-213... 

In general, all elements of the mass transfer matrix depend on the process variables, and in particular on the vapor phase composition. The mass transfer mechanisms in membranes can be rather complicated. However, for the conceptual analysis of the considered membrane process, it is not advantageous to go into the details of mass transport. Therefore, in the following the effective binary mass transfer coefficients k,j are assumed to be constants. 

Belfort, G. Fluid mechanics in membrane filtration recent developments. J. Membr. Sci. 1989, 40, 123-147. 

It is understood that the economical success of any membrane process depends primarily on the quality of the membrane, specifically on flux, selectivity and service lifetime. Consideration of only the transport mechanisms in membranes, however, will in general, lead to an overestimation of the specific permeation rates in membrane processes. Formation of a concentration boundary layer in front of the membrane surface or within the porous support structure reduces the permeation rate and, in most cases, the product quality as well. For reverse osmosis. Figure 6.1 shows how a concentration boundary layer (concentration polarization) forms as a result of membrane selectivity. At steady state conditions, the retained components must be transported back into the bulk of the liquid. As laminar flow is present near the membrane surface, this backflow is of diffusive nature, i.e., is based on a concentration gradient. At steady state conditions, the concentration profile is calculated from a mass balance as... 

Kim, S. H. O. 2005. Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in membrane. Environmental Science and Technology 39 1764-1770. 

Gill, D. L., E. F. Grollman, and L. D. Kohn Calcium transport mechanism in membrane vesicles from guinea pig brain synaptosomes. J. Biol. Chem. 256, 184—192 (1981). 

The results deduced by spin trapping have suggested that both sulfonic add and acetic add groups can be attacked by HO radicals, and confirm two possible degradation mechanisms in membranes initiated at the backbone and at the side chain. 

Nonoxidizing Antimicrobials. Nonoxidizing antimicrobials usually control growths by one of two mechanisms. In one, microbes are inhibited or killed as a result of damage to the ceU membrane. In the other, microbial death results from damage to the biochemical machinery involved in energy production or energy utilization. 

Another mechanism in initiating the contraction is agonist-induced contraction. It results from the hydrolysis of membrane phosphatidylinositol and the formation of inositol triphosphate (IP3)- IP3 in turn triggers the release of intracellular calcium from the sarcoplasmic reticulum and the influx of more extracellular calcium. The third mechanism in triggering the smooth muscle contraction is the increase of calcium influx through the receptor-operated channels. The increased cytosolic calcium enhances the binding to the protein, calmodulin [73298-54-1]. 

Two other deposition mechanisms, in addition to the six listed, may be in operation under particular circumstances. Some dust particles may be collected on filters by sieving when the pore diameter is less than the particle diameter. Except in small membrane filters, the sieving mechanism is probably limited to surface-type filters, in which a layer of collected dust is itself the principal filter medium. 

The piezoelectric phenomena have been used to generate ultrasonic waves up to microwave frequencies using thin polyfvinylidene fluoride) transducers. In the audio range a new type of loudspeaker has been introduced using the transverse piezolectric effect on a mechanically biased membrane. This development has been of considerable interest to telephone engineers and scientists. 

The only feasible procedure at the moment is molecular dynamics computer simulation, which can be used since most systems are currently essentially controlled by classical dynamics even though the intermolecular potentials are often quantum mechanical in origin. There are indeed many intermolecular potentials available which are remarkably reliable for most liquids, and even for liquid mixtures, of scientific and technical importance. However potentials for the design of membranes and of the interaction of fluid molecules with membranes on the atomic scale are less well developed. 

A number of studies have recently been devoted to membrane applications [8, 100-102], Yoshikawa and co-workers developed an imprinting technique by casting membranes from a mixture of a Merrifield resin containing a grafted tetrapeptide and of linear co-polymers of acrylonitrile and styrene in the presence of amino acid derivatives as templates [103], The membranes were cast from a tetrahydrofuran (THF) solution and the template, usually N-protected d- or 1-tryptophan, removed by washing in more polar nonsolvents for the polymer (Fig. 6-17). Membrane applications using free amino acids revealed that only the imprinted membranes showed detectable permeation. Enantioselective electrodialysis with a maximum selectivity factor of ca. 7 could be reached, although this factor depended inversely on the flux rate [7]. Also, the transport mechanism in imprinted membranes is still poorly understood. 

Urry, D. W. On the Molecular Structure and Ion Transport Mechanism of the Gramicidin Transmembrane Channel. In Membranes and Transport, Vol. 2, (ed. Martonosi, A.), p. 285, Plenum Publishing Corporation, New York 1982... 

Adams, R.J., Pollard, T.D. (1989). Membrane bound myosin-I provides new mechanism in cell motility. Cell Mot. Cytoskel. 14, 178-182. 

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