Interface aqueous-membrane

It is well known that the selective transport of ions through a mitochondrial inner membrane is attained when the oxygen supplied by the respiration oxidizes glycolysis products in mitochondria with the aid of such substances as flavin mononucleotide (FMN), fi-nicotinamide adenine dinucleotide (NADH), and quinone (Q) derivatives [1-3]. The energy that enables ion transport has been attributed to that supplied by electron transport through the membrane due to a redox reaction occurring at the aqueous-membrane interface accompanied by respiration [1-5],... 

In this chapter, a novel interpretation of the membrane transport process elucidated based on a voltammetric concept and method is presented, and the important role of charge transfer reactions at aqueous-membrane interfaces in the membrane transport is emphasized [10,17,18]. Then, three respiration mimetic charge (ion or electron) transfer reactions observed by the present authors at the interface between an aqueous solution and an organic solution in the absence of any enzymes or proteins are introduced, and selective ion transfer reactions coupled with the electron transfer reactions are discussed [19-23]. The reaction processes of the charge transfer reactions and the energetic relations... 

A. Voltammograms for Ion Transfers Through a Liquid Membrane and at Aqueous-Membrane interfaces... 

Interface on That at Another Aqueous-Membrane Interface Under an Applied Membrane Potential... 

The results given here suggest that even the ion transfer through a BLM is controlled mainly by the ion transfer reactions at two aqueous-membrane interfaces in analogy with... 

The voltammetry for ion transfer at an interface of two immiscible electrolyte solutions, VITIES, which is a powerful method for identifying the transferring ion and for determining the amount of ion transferred, must be helpful for the elucidation of the oscillation process [17 19]. The VITIES was also demonstrated to be useful for ion transport through a membrane, considering that the membrane transport of ions is composed of the ion transfers at two aqueous-membrane interfaces and the mass transfers and/or chemical reactions in three phases [2,20,21]. 

In this chapter, novel oscillations observed with liquid membrane systems by the present authors [22-25] will be introduced, and the mechanisms for the oscillation are clarified by using VITIES, taking into consideration ion transfer reactions and adsorptions at two aqueous-membrane interfaces. The mechanism of the spontaneous potential oscillation in a liquid membrane system proposed by Yoshikawa et al. is also discussed briefly. 

Adopting Eq. (16) as representative of the system, ion transfer reactions and adsorptions of respective ions participating in the oscillation were investigated individually at two aqueous-membrane interfaces in the system of Eq. (16) by use of VITIES, and as a result the mechanism of the oscillation was elucidated almost quantitatively. The mechanism can be summarized as follows [39]. 

The electrical oscillations at the aqueous-organic interface or at membranes in the absence of any substances relative to the channel or gate were introduced. These oscillations might give some fundamental information on the electrical excitability in living organisms. Since the ion transfer at the aqueous-organic or aqueous-membrane interface and the interfacial adsorption are deeply concerned in the oscillation, it has been stressed that the voltammetry for the ion transfer at an interface of two immiscible electrolyte solutions is... 

Considering only the lipid phase as the transport pathway for the peptide, as the solute enters and diffuses across the membrane it will encounter a number of different microenvironments. The first is the aqueous membrane interface (Fig. 23). In this region, the hydrated polar headgroups of the membrane phospholipids separate the aqueous phase from the apolar membrane interior. It has been shown that this region is capable of satisfying up to 70% of the hydrophobic effect... 

Two excellent examples of this membrane system have been developed, NS-lOO and PA-300 (5,15). The NS-lOO membrane was made by impregnating a polysulfone support with a 0.67 percent aqueous solution of polyethylenlmine, draining away excess reagent, then contacting the film with a 0.1 percent solution of toluenediisocyanate in hexane. An ultrathln polyurea barrier layer formed at the interface. This membrane was then heat-cured at 110°C. A later version of this membrane was developed (designated NS-101), which used isophthaloyl chloride in place of toluenedilsocyanate, producing a polyamide (16). With either type of membrane, salt rejections in simulated seawater tests at 1000 psi exceeded 99 percent. 

Electrochemical Processes at Aqueous/Organic Solution or Aqueous/Membrane Interfaces... 

Figure 13.1 represents schematically different types of HLM contactors. A liquid membrane solution flows (or circulates) between two membranes, which separate the LM phase (E) from the feed (F) and receiving (R) phases. A solute (or solutes) diffuses to the F/E interface and is extracted from feed phase by a carrier as a result of the thermodynamic conditions at the F/E interface. The solute-carrier complex diffuses to the E/R interface and is simultaneously stripped by the receiving phase due to the different thermodynamic conditions at the E/R interface. The membranes may be hydrophobic, immersed by LM, or hydrophilic (or ion exchange), immersed by feed and strip aqueous phases. 

Fig. 3. Diagrammatical representation of the effect of bile acid micelles (or vesicles) in overcoming diffusion barrier resistance. In the absence of bile acids, individual lipid molecules must diffuse across the barriers overlying the microvillus border of the intestinal epithelial cell (arrow 1). Hence, uptake of these molecules is largely diffusion limited. In the presence of bile acids (arrow 2) large amounts of these lipid molecules are delivered directly to the aqueous-membrane interface so that the rate of uptake is facilitated [11].

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