Transfer through membranes

Carrier proteins are highly selective, transporting solutes with specific chemical structures. As they are normally involved in the transport of many naturally occurring compounds they will often transport drugs with structures related to these natural products. This type of structural relationship can be use in the approach to the design of new drugs. 

Facilated diffusion also involves the use of a carrier protein. It differs from active transport in that it occurs from a high to a low concentration and so does not require energy to be supplied by the cell. However, falicilated diffusion appears to play a minor role in the transport of drugs through membranes. 

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In general, movement is an intrinsic property of living creatures. It occurs at different structural levels, including ion transfer through membranes, separation of replicated chromosomes, beating of cilia and flagella or, the most common, contraction of muscles. These contractions enable... 

It is interesting to compare the thermal-treatment effect on the secondary structure of two proteins, namely, bacteriorhodopsin (BR) and photosynthetic reaction centers from Rhodopseudomonas viridis (RC). The investigation was done for three types of samples for each object-solution, LB film, and self-assembled film. Both proteins are membrane ones and are objects of numerous studies, for they play a key role in photosynthesis, providing a light-induced charge transfer through membranes—electrons in the case of RC and protons in the case of BR. 

Williams, R. J. P. (1981). Physico-chemical aspects of inorganic element transfer through membranes, Phil. Trans. R. Soc. Lond. B., 294, 57-74. 

In the purple bacterium Halobactium halobium, light driven proton transfer through membranes is executed by bacteriorhodopsin [41a]. This protein consisting of seven helical fragments criss-crosses the membrane seven times,... 

Besides the work with Carr and Schmidt, I had a very pleasant interaction with Ed Cussler over some problems in mass transfer through membranes with barriers [238], through anisotropic membranes [232], and by facilitated diffusion [247]. A severely mathematical problem of diffusion through a slot could be solved by a Schwartz-Christoffel transformation,41 and provided an asymptotic formula that proved useful in the barrier problem [223]. Cussler was delightful to work with because he refused to accept any mathematical solution that could not be unpacked and shown to be physically sensible (cf. [244]). Next to Bosanquet, he is the most intuitive problem solver with whom I have worked. Chapter 19 [232] is reprinted here. 

Bienvenue et al. [96] used the expression similar to Eq. (40) to describe quantitatively the dependence of the photocurrent through the planar BLM upon the applied photo voltage AU in the System 40 of Table 1. Photocurrent was caused by the the transfer through membrane of ZnTPP+ radical cations. Note that in this case the potential difference affecting the motion of ZnTPP+ cation is equal to only 60% of the external voltage apparently due to the location of ZnTPP+ sufficiently deep below the surface of the membrane. 

Zaika Yu.V. (1996) The solvability of the equations for a model of gas transfer through membranes with dynamic boundary conditions, Computer Mathematics and Math. Physics 36(12), 1731-1741. 

The heat transfer through membrane material takes place by conduction and the latent heat transferred by vapor flow through the membrane, which is small and could be neglected. The equation for heat transfer through the membrane can be written as... 

Membrane processes for separation of chemical species from a mixture are gaining in importance and are emerging as a viable altemative to conventional separation processes. The interest in the mass transfer through membranes can be attributed to membrane processes being technically simple and having low energy consumption. 

The main parameters influencing mass transference through membranes in flow analysis have been discussed in specialised texts that generally deal with both gas diffusion and dialysis [254—257],... 

IT processes are generally classed as simple (unassisted) or facilitated (assisted), borrowing terminology from the literature on charge transfer through membranes [79]. Unassisted IT is generally denoted... 

The diffusion of solutes through a porous polymer membrane under the temperature gradient is named thermal diffusion or Soret effect. Few studies deal with this phenomenon. Its importance in the transfer through membranes is often neglected compared to the other coupled mechanisms of transfer. 

The membrane model is able to describe the mass transfer through membranes and takes into account the specific effects of different membrane materials. Simulation studies with the non-equilibrium model for distillation and the semi-empirical membrane model illustrate the influence of the mass flow of the side stream and the heating energy on the required membrane area. Both parameters have a major effect on the membrane area. Rigorous models for both unit operations are necessary to perform detailed process studies of the integrated process, because all physical effects have to be taken into account especially for membrane separation. 

At a fixed ratio of methane and air flows, the inerease of methane concentration in the fuel mixture from 1 to 5 vol.% insignificantly affects the degree of its conversion, while increasing syngas selectivity (Fig. 124). Hence, in this ease, the increase of the rate of CH4 activation on the layer of catalyst supported on membrane helps to consume the oxygen transferred through membrane forming mainly selective oxidation products. 

Mass transfer through membranes involves the concepts of permeation and diffusion. Permeation involves transferring components from an upstream fluid phase to a downstream fluid phase. If a porous membrane is used, mass transfer takes place in the pores, by convection. In the case of dense membranes, the components being transferred are sorbed on the surface of the membrane (usually in equilibrium with the adjacent fluid phase) and diffuse all along the membrane thickness until reaching the other surface, as described above. Permeation is based on the driving force difference between the upstream and downstream fluid phases, while diffusion is based on the driving force difference between the two surfaces but within the membrane phase. ... 

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