Bulk membrane transport

Lee, S. S. Yoon, I. Park, K.-M. Jung, J. H. Lindoy, L. F. Nezhadali, A. Rounaghi, G. Competitive bulk membrane transport and solvent extraction of transition and post transition metal ions using mixed-donor acyclic ligands as ionophores. J. Chem. Soc.-Dalton Trans. 2002, 2180-2184. 

Competitive (seven-metal) solvent extraction experiments (water/chloroform) and related bulk membrane transport (water/chloroform/water) experiments have been performed in which each of the four tri-branched ligands as well as their single ring analogues were employed as the extractant/ionophore in the respective chloroform phases [37], In both sets of experiments the aqueous source phases contained an equimolar mixture of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) nitrates and were buffered at pH 4.9. For membrane transport the aqueous receiving phase was buffered at pH 3 under these conditions any transport will be driven by the back transfer of protons. Under the conditions employed, the results from the solvent extraction and the bulk membrane transport experiments clearly paralleled each other -for each ligand system high extraction/transport selectivity for Ag(I) was observed over the other six metal ions present in the respective source phases. 

A possible mechanism for the transport of the extracted species across the manbrane can be based on Fickian diffusion of its complex or ion pair with the carrier through the membrane liquid phase. Another mechanism that can be responsible for the bulk membrane transport of the extracted species is the so-called chained carrier mechanism proposed by Cussler et al. [36]. This mechanism applies to ion-exchange membranes with ionic sites covalently bound to... 

Barboiu [8] has synthesized and studied the bulk membrane transport with supramolecular polymeric systems resulted by the dynamic self-assembly of the hydrogen-bonded urea-crown ethers 10a, 10b and 10c (Fig. 10). 

Liquid-liquid extraction Bulk liquid membrane transport Liquid surfactant membrane transport... 

Bulk flow of water through membrane pores, resulting from osmotic differences across the membrane, transports drug molecules that fit through the membrane pores... 

The transport behavior of Li+ across membranes has been the focus of numerous studies, the bulk of which have concentrated upon the human erythrocyte for which the Li+ transport pathways have been elucidated and are summarized below. The movement of Li+ across cell membranes is mediated by transport systems which normally transport other ions, therefore the normal intracellular and subcellular electrolyte balance is likely to be disturbed by this extra cation. Additionally, Li+ has been shown to increase membrane phospholipid unsaturation in rat brain, leading to enhanced fluidity in the membrane, which could have repercussions for membrane-associated proteins and for membrane transport properties. 

For thick carrier membranes we may usually apply the assumption of a thermodynamic equilibrium at the phase boundaries as a good approximation (see above). On the other hand, it should be considered that a positive flux of cationic complexes within the membrane (as induced by an applied voltage E< 0) leads to a certain accumulation of free carriers at x = d, respectively to a depletion at x = 0 (see Fig. 1). For practical purposes the carriers are confined to the membrane phase in the case of ideal bulk membranes (in contrast, a supply of carriers from the outside solutions is stipulated for transport studies on bilayers45,51). 

Electroosmosis is the bulk fluid flow that occurs when a voltage gradient is imposed across a charged membrane. Transport by convection allows the delivery and extraction of neutral and zwitterionic compounds and plays a major role in the movement of large, poorly mobile cations. Electroosmosis is an electrokinetic phenomenon, which may be described by nonequilibrium thermodynamics [24] ... 

Figure 2. Bulk calcium transport by the osteoclast. Net acid transport is driven by the vacuolar-type H+-ATPase with a specialized large membrane subunit. Transport is balanced by chloride transport, probably involving both a chloride channel (CLIC-5) and a chloride bicarbonate antiporter (CLCN7). Supporting transport processes include chloride-bicarbonate exchange. Insertion of transporters is specific for subcellular locations and involves interaction of transporters with specific cytoskeletal components, including actin (See Colour Plate 29)...

Part II of this book represents the bulk of the material on the analysis and modeling of biochemical systems. Concepts covered include biochemical reaction kinetics and kinetics of enzyme-mediated reactions simulation and analysis of biochemical systems including non-equilibrium open systems, metabolic networks, and phosphorylation cascades transport processes including membrane transport and electrophysiological systems. Part III covers the specialized topics of spatially distributed transport modeling and blood-tissue solute exchange, constraint-based analysis of large-scale biochemical networks, protein-protein interactions, and stochastic systems. 

In the domain where the entity that is transported through a membrane is immiscible or not completely soluble in the contacting (exit) phase, such as the case of gas phase air or oxygen in water, the interfacial factor becomes overwhelmingly important over the transport characteristics of the bulk membrane phase, which is empty space. It is important to recognize that the surface of macroporous membrane consists of the solid phase and the gas phase (in the pore diameter exposed to the interface), and the interfacial aspect of the solid surface dominates the behavior of the gas phase that expands out of the pore. 

Similarly, impervious yttria-stabilized zirconia membranes doped with titania have been prepared by the electrochemical vapor deposition method [Hazbun, 1988]. Zirconium, yttrium and titanium chlorides in vapor form react with oxygen on the heated surface of a porous support tube in a reaction chamber at 1,100 to 1,300 C under controlled conditions. Membranes with a thickness of 2 to 60 pm have been made this way. The dopant, titania, is added to increase electron How of the resultant membrane and can be tailored to achieve the desired balance between ionic and electronic conductivity. Brinkman and Burggraaf [1995] also used electrochemical vapor deposition to grow thin, dense layers of zirconia/yttria/terbia membranes on porous ceramic supports. Depending on the deposition temperature, the growth of the membrane layer is limited by the bulk electrochemical transport or pore diffusion. 

Mishra D and Sharma U. Extraction and bulk liquid membrane transport of some main group metal ions facihtated by triethylene glycol monomethyl ether. Sep Purif Technol, 2002 27(1) 51-57. 

Jabbari A, Esmaeili M, and Shamsipur M. Selective transport of mercury as HgCl " through a bulk hquid membrane transport using K -dicyclohexyl-18-crown-6 as carrier. Sep Purif Technol, 2001 24(1-2) 139-145. 

The mechanism whereby drugs are absorbed from the GI tract is complex. Understanding the intestinal transport mechanism is crucial to the prediction of oral drug absorption. The physical model utilizes the basic principles of thermodynamics and mass transport. The physical model for the simultaneous passive and active membrane transport of drugs in the intestinal lumen is depicted in Fig. 7. The bulk aqueous solution with an aqueous boundary layer on the mucosal side is followed by a series of heterogeneous membranes consisting of parallel lipoidal and aqueous channel pathways for passive and active transport. Thereafter, a sink on the serosal side follows. 

The permeation of gases in membranes due to surface diffusion and capillary condensation has been discussed in Section 9.2.3.S. together with some illustrative data. The total flux of a single gas is usually calculated as the sum of the flux by surface diffusion and the flux through the gas phase. As shown the surface flux can contribute considerably to the total flux (increased by factor 2-3 of gas diffusional flux), especially with smaller and uniform pore sizes (compare Eqs. (9.9a) and (9.15). With decreasing pore size the flux through the bulk gas decreases while the surface diffusional flux increases. With very small pore diameter (< 2-3 nm) the effective diameter for bulk gas transport is less than the geometric pore diameter due to the thickness of the absorbed layer which... 

According to configuration definition, three groups of hquid membranes are usually considered (see Fig. 1.1) bulk (BLM), supported or immobilized (SLM or ILM), and emulsion (ELM) liquid membrane transport. Some authors add to these definitions polymeric inclusion membranes, gel membranes, dual module hollow-fiber membranes, but, to my opinion, the first two types are the modifications of the SLM and the third is the modification of BLM. It will be discussed in detail in the respective chapters. 

A mathematical model to be solved numerically has been developed and used to predict the separation effects caused by nonstationary conditions for a bulk liquid membrane transport. Numerical calculations compute such pertraction" characteristics as input and output membrane selectivity (ratio of respective fluxes), concentration profiles for cations bound by a carrier in a liquid membrane phase, and the overall separation factors all being dependent on time. The computations of fluxes and separation factors as dependent on time have revealed high separation efficiency of unsteady-state pertraction as compared with steady or near-steady-state process (with reactions near equilibrium). 

Berhe HG, Bourne SA, Bredenkamp MW, Esterhuysen C, Habtu MM, Koch KR, Luckay RC. High and selective Ag(I) bulk liquid membrane transport with N,N-diethyl-.Y-camphanyl thiourea and structure of the complex. Inorg Chem Commun 2006 9 99-102. 

Alpoguz HK. Bulk liquid membrane transport of Hg(II) by a crown ether derivative. J Macromol Sci A 2006 43 1265-1272. 

Habtu MM, Bourne SA, Koch KR, Luckay RC. Competitive bulk liquid membrane transport and solvent extraction of some transition and post-transition metal ions using acylthiourea ligands as ionophores. New J Chem (S Afr) 2006 30 1155-1162. 

Wirgau JI, Crumbhss AL. Carrier-facilitated bulk hquid membrane transport of iron (III) hydroxamate complexes utilizing a labile recognition agent and amine recognition in the second coordination sphere. Dalton Trans 2003 19 3680-3685. 

Interaction of small molecules and ions with lipid bilayers is of importance from the point of view of membrane transport and other processes such as aaion of drugs and anesthetics on membranes. This includes a number of antibiotics and fatty acids also. The effect of these perturbations on the lipid bilayer in terms of differences in the structure and dynamics of the lipids close to the perturbative group versus the bulk lipids is also interesting and may... 

Case 3 Reaction Occurring Within fluid Film. As a third example consider die silantion when species A disappears by homogeneous reaction in Ihe fluid film. Such a model has been used to predict die effect of chemical reaction on gas absorption rales (Chapter 6) or on canier-faciliimed transport in membranes (Chapter 19). For simplicity, assume die reection to be first order and irreversible and the solution to be dilute so that bulk flow transport is negligible and Ihe total molar concentration constant. The standy-state belsuce for A is obtained from simplification of Eq, (2.3-14) ... 

The output of the mass spectrometer, P u is proportional to the rate of entry of a specific gas species into the vacuum system (Equation 5). At membrane steady-state conditions, the output of the mass spectrometer is also proportional to partial pressures at the membrane-fluid interface, Pji A relationship between Pr. and the partial pressure in the bulk fluid, Pf. is needed. For P7i = Pf. a negligible rate of gas transport out of the fluid or a high degree of concentration uniformity within the fluid is required. The latter can be approached through vigorous convective mixing or by rapid fluid diffusing properties. Because of the sensitivity limitations of the mass spectrometer, the necessary membrane transport, is relatively fixed. 

The controlled-release micropump (Figure 2) is a recently invented device that uses the principles of membrane transport and controlled release of drugs to deliver insulin at variable rates (20,26). With a suitable supply of insulin connected to the pump, the concentration and/or pressure difference across the membrane results in diffusion or bulk transport through the membrane ). This process is the basal delivery and requires no external power source. Augmented delivery is achieved by repeated compression of the foam membrane by the coated mild-steel piston. The piston is the core of the solenoid, and compression is effected when current is applied to the solenoid coil. Interruption of the current causes the membrane to relax, drawing more drug into the membrane in preparation for the next compression cycle. 

---