Composites membranes

It has been found that the influence of the membrane composition on the ISE selectivity is mainly governed by substitution degree of the nitrogen atom, but virtually does not depend upon the length of hydrocarbon substituents. The key factor in the selectivity of DBP-plasticized membranes with both kinds of ion-exchangers and of the o-NPOE-TNOBS-membrane is the ionic... 

The results obtained indicate that the ion-exchanger nature, generally not taken into account when developing ISEs for alkylammonium cations, actually influences strongly the selectivity of such ISEs and should be paid attention to when choosing optimal membrane composition. These data will be useful for finding ways to control the ISEs selectivity by rational choice of the membrane composition. 

Amphotericin B, is a polyene antibiotic, used in the therapy of systemic fungal infections. Its mode of action exploits differences in membrane composition between the pathogen and the human host. Ergosterol, the predominant sterol of fungi, plants, and some protozoan parasites, interacts with Amphotericin B, resulting in an increased ion permeability of the membrane. Humans contain cholesterol, which has a low affinity for amphotericin B. 

Jiang J, Kucernak A. 2005. Sohd pol3nner electrolyte membrane composite microelectrode investigations of fuel cell reactions. B Voltammetric study of methanol oxidation at the nanostructured platinum microelectrode Nafion membrane interface. J Electroanal Chem 576 223-236. 

Major determinants of membrane fluidity may be grouped within two categories [53] (1) intrinsic determinants, i.e., those quantifying the membrane composition and phase behavior, and (2) extrinsic determinants, i.e., environmental factors (Table 1). In general, any manipulation that induces an increase in the molal volume of the lipids, e.g., increase in temperature or increase in the fraction of unsaturated acyl chains, will lead to an increase in membrane fluidity. In addition, several intrinsic and extrinsic factors presented in Table 1 determine the temperature at which the lipid molecules undergo a transition from the gel state to liquid crystalline state, a transition associated with a large increase in bilayer fluidity. 

Improved ISEs. In 1980, Ammann et al.154 reported on clinical and biological applications of liquid membrane electrodes based on an ion-selective component and a suitable plasticizer in a PVC matrix for the determination of Na +, K, Ca2, Cl and H + in blood serum or whole blood and Na+ and K4 in urine. They gave extensive information on membrane compositions and selectivity... 

Good accuracy and precision were obtained in connection to 100 pL blood samples. A wide range of amperometric enzyme electrodes, differing in the electrode design or material, membrane composition, or immobilization approach have since been described. 

B.D. Pendley, R.E. Gyurcsanyi, R.P. Buck, and E. Lindner, A chronoamperometric method to estimate changes in die membrane composition of ion-selective membranes. Anal. Chem. 73, 4599—4606... 

Selectivity is one of the most important characteristics of an electrode, as it often determines whether a reliable measurement in the sample is possible or not. In practice, most pH sensitive membranes will also respond slightly to some interfering ions. As can be seen in Eq. (5), the potential of such a membrane is governed mainly by the activity of the hydrogen ion and also by the concentration of other interfering ions. To improve selectivity, advanced membrane compositions or protection membranes with size-exclusion or ion-exchange properties are often utilized. 

General Membrane Function Membrane Composition Phospholipid Bilayer Membrane Structure Posttranslational Modification Membrane Fluidity Diffusion in Membranes... 

The impact of hemodialysis on drug therapy depends on drug characteristics (e.g., molecular weight, protein binding, and Vp), dialysis prescription (e.g., dialysis membrane composition, filter surface area, blood and dialysate flow rates, and reuse of the dialysis filter), and clinical indication for dialysis. 

Most recently, a highly unusual membrane composition was reported from anaerobic ammonium-oxidising (anammox) bacteria. In these bacteria, nitrite is reduced, nitrogen gas generated, and carbon dioxide is converted into organic carbon, as the consequence of ammonia reduction. This central energygenerating process can be described as ... 

Recent results indicate that not only topogenic signals and membrane composition contribute to the proper topology of a membrane protein. The antimicrobial peptide nisin, produced by Lactococcus lactis, kills Gram-positive bacteria via pore formation, thus leading to the permeabilisation of the membrane. Nisin depends on the cell-wall precursor Lipid II, which functions as a docking molecule to support a perpendicular stable transmembrane orientation [43]. 

For carrier-based ISEs, the selectivity is determined by the composition of the membrane. Eq. (18a.l8) describes the relationship between the ion selectivity and the membrane composition of cation-selective membranes by using charge balance and mass balance considerations [69]. 

Conversely, the fundamentals for the UDL he on the coextraction of counterions into the membrane therefore, the membrane is no longer permselective (Donnan failure) [9]. Ideally, when the ionophores are saturated by ions, the ion-ionophore complex functions as an ion-exchanger and the membrane shows an anion Nernstian response. The UDL can be estimated from the membrane composition, formation constant and coextraction coefficients obtained from the so-called sandwich membrane method [73]. 

A very high separation factor has been obtained in phenol dehydration by using pervaporation process and PVA/PAA as membranes. The membrane composition and the process characteristics are presented in table 1. 

Table 1. Characteristics of the separation process by pervaporation function of the membrane composition and structure, composition of feed mixture and temperature [18]...

Membrane composition PVA/PAA Composition of liquid mixture Permeation rate / / (g m"2 h"1) T/ C Separation factor... 

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