Computer Simulation of Cation-Exchange Membrane Structure: An Elementary Act of Hydrated Ion Transport

A fragment of the structure of a sulfo cation exchanger, which is the basis of most cation-exchange membranes, is calculated by an ab initio method. An analysis of interatomic bonds in the structure shows that, to detach a mobile ion from a fixed ion, it is necessary to break the hydrogen bond between hydration water molecules of the counterion in addition to overcoming the electrostatic attraction. As the hydrogen bond cleavage work for simple hydrated ions is ten times the electrostatic attraction energy, an elementary act of ion transport in a cation-exchange membrane is considered mostly as the hydrogen bond transfer reaction.     

Amyloid fiber formation and membrane disruption are separate processes localized in two distinct regions of IAPP, the type-2-diabetes-related peptide

Aggregation of Islet Amyloid Polypeptide (IAPP) has been implicated in the development of type II diabetes. Because IAPP is a highly amyloidogenic peptide, it has been suggested that the formation of IAPP amyloid fibers causes disruption of the cellular membrane and is responsible for the death of beta-cells during type II diabetes. Previous studies have shown that the N-terminal 1-19 region, rather than the amyloidogenic 20-29 region, is primarily responsible for the interaction of the IAPP peptide with membranes. Liposome leakage experiments presented in this study confirm that the pathological membrane disrupting activity of the full-length hIAPP is also shared by hIAPP 1-19. The hIAPP 1-19 fragment at a low concentration of peptide induces membrane disruption to a near identical extent as the full-length peptide. At higher peptide concentrations, the hIAPP 1-19 fragment induces a greater extent of membrane disruption than the full-length peptide. Similar to the full-length peptide, hIAPP 1-19 exhibits a random coil conformation in solution and adopts an alpha-helical conformation upon binding to lipid membranes. However, unlike the full-length peptide, the hIAPP 1-19 fragment did not form amyloid fibers when incubated with POPG vesicles. These results indicate that membrane disruption can occur independently from amyloid formation in IAPP, and the sequences responsible for amyloid formation and membrane disruption are located in different regions of the peptide.     

Optical and photochemical properties of N-benzalaminophenylpyridinium perchlorates

The electronic spectra of a number of benzylidene derivatives of N-aminoarylpyridinium perchlorates are associated with absorption localized on the individual pyridinium and azomethine fragments and with intramolecular charge transfer (ICT) from the azomethine fragment to the pyridinium ring. The luminescence is associated with the latter process. The photochromism is due to proton transfer in the excited state of the azomethine fragment, which competes with ICT, and is also due to structural factors.     

Solvent extraction through a double-pass parallel-plate membrane channel with recycle

The reflux indeed has much influence on the heat and mass transfer, which in turn plays a significant role on the design, calculation, and operation of the equipment. The effects of recycle on membrane extraction through a double-pass parallel-plate channel have been studied both theoretically and experimentally. Theoretical analysis of mass transfer in multipass membrane extractors was analogous to heat transfer in multipass heat exchangers. Experiments were carried out with the use of a membrane sheet made of microporous polypropylene coated with polytetrafluoroethylene as a permeable barrier to extract acetic acid from aqueous solution by methyl isobutyl ketone. Theoretical predictions are in qualitative agreement with the experimental results. Contrast a single-pass parallel-plate membrane channel without recycle, considerable improvement in mass transfer is obtainable if membrane extraction is operated in a double-pass device of same size with recycle which provides the increase of fluid velocity and pre-extraction (or pre-mixing) effect. It is found that recycle can enhance mass transfer, especially for operations with higher inlet volume rate or shorter conduit length.     

Exploration on regulating factors for proton transfer along hydrogen-bonded water chains.

Proton transfer along a single-file hydrogen-bonded water chain is elucidated with a special emphasis on the investigation of chain length, side water, and solvent effects, as well as the temperature and pressure dependences. The number of water molecules in the chain varies from one to nine. The proton can be transported to the acceptor fragment through the single-file hydrogen-bonded water wire which contains at most five water molecules. If the number of water molecule is more than five, the proton is trapped by the chain in the hydroxyl-centered H(7)O(3) (+) state. The farthest water molecule involved in the formation of H(7)O(3) (+) is the fifth one away from the donor fragment. These phenomena reappear in the molecular dynamics simulations. The energy of the system is reduced along with the proton conduction. The proton transfer mechanism can be altered by excess proton. The augmentation of the solvent dielectric constant weakens the stability of the system, but favors the proton transfer. NMR spin-spin coupling constants can be used as a criterion in judging whether the proton is transferred or not. The enhancement of temperature increases the thermal motion of the molecule, augments the internal energy of the system, and favors the proton transfer. The lengthening of the water wire increases the entropy of the system, concomitantly, the temperature dependence of the Gibbs free energy increases. The most favorable condition for the proton transfer along the H-bonded water wire is the four-water contained chain with side water attached near to the acceptor fragment in polar solvent under higher temperature.     

Asymmetric transmembrane transfer caused by a difference in adsorption characteristics at interfaces

A surface adsorption mechanism is proposed for the effect of asymmetric diffusion permeability of a modified membrane. A model is developed to describe diffusion transfer through the modified membrane with regard to the finiteness of the rate of adsorption on external membrane surfaces. Expressions are derived for diffusion fluxes as functions of transfer direction, and asymmetry coefficient is calculated for the diffusion permeability of the membrane. It is shown that the difference in the kinetic properties of the external surfaces of the membrane, which results from the modification of one of the surfaces, may induce the effect of asymmetric diffusion permeability.     

Zinc Transfer Kinetics of Metallothioneins and Their Fragments with Apo‐carbonic Anhydrase

The zinc transfer reactions from Zn₇‐MT‐I, Zn₇‐MT‐II, Zn₄‐α fragment (MT‐I) and Zn₄,‐α fragment (MT‐II) to apo‐carbonic anhydrase have been studied. In each reaction, no more than one zinc ion per molecule is involved in metal transfer. Zn₇‐MT‐I and Zn₇‐MT‐II donate zinc to apo‐carbonic anhydrase and de novo constitute it at a comparable efficiency, while Zn₇‐MT‐II exhibits a little faster rate. Surprisingly, Zinc is released from Zn₄‐α fragment (MT‐II) with a much faster rate than from Zn₄‐α fragment (MT‐I), whose rate is close to that of Zn₇‐MT‐I. The reason for the difference is still unknown. Introducing complex compounds into this system may give rise to an effect on the reaction. The transfer from Zn₇‐MT‐II in the presence of reduced glutathione shows little difference compare to the control, suggesting that the reduced glutathione is not involved in zinc transfer process. However, glutathione disulfide does accelerate this zinc transfer reaction remarkably, indicating that the oxidative factors contribute to zinc release from metallothioneins.     

Diffusive transport across unconfined hollow fiber membranes

The mass transfer characteristics of gas permeable, hollow fiber membranes in a liquid jet mixed reactor are studied. A membrane module, operated in the sealed-end mode, was pressurized with oxygen at the base of the fibers and centered within a submerged jet discharge. Unlike conventional membrane module designs, this configuration did not have the hollow fibers enclosed within a tubular shell. The membranes were unconfined and free to move within the generated flow field. This design is especially well suited for use in waters containing high solid concentrations. The membranes have a greater degree of freedom for movement and are therefore less likely to become fouled due to solids being lodged within the fiber bundle. Mass transfer rates were measured over a practical range of physical and process parameters. A mass transfer correlation for the unconfined configuration is presented and the transfer performance of this configuration is compared with conventional membrane contactor designs.     

Imaging the activity of nitrate reductase by means of a scanning electrochemical microscope

Scanning electrochemical microscopy (SECM) was used to characterize immobilized nitrate reductase (NaR) from Pseudonomonas stutzeri (E.C. 1.7.99.4). Nitrate reductase with membrane fragment was embedded in a polyurethane hydrogel in a capillary and solubilized NaR without membrane fragment was covalently coupled to a diaminoethyl-cellulose-carbamitate film on glass. After systematic studies of possible mediators, SECM feedback imaging of both forms of immobilized NaR was accomplished with methylviologen as redox mediator.     

Three layer membrane model for characterizing ultrafiltration membranes

To characterize ultrafiltration membranes, it is important to understand their intrinsic, macromolecular-rejection properties. Defining these properties in terms of a membrane's permselectivity parameters requires an understanding of the mass transfer of the solute at the membrane interface. The solute concentration is difficult to measure experimentally, and has been previously estimated using various forms of a mass transfer coefficient. In this paper, we present an analytical, steady-state model for predicting ultrafiltration solute concentrations at the membrane interface from experimentally measured parameters and known solute physical properties - without the use of a mass transfer correlation. We then extend the model by looking at mass transfer through the membrane itself, in order to predict membrane permselectivity parameters.     

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid liquid interfaces (ITIES).     

Membrane-based Enthalpy Exchanger: material considerations and clarification of moisture resistance

The fundamental dimensionless groups for coupled heat and moisture transfer in a cross flow air-to-air enthalpy exchanger with hydrophilic membrane cores are derived and validated with experimental data. The thermal and moisture transfer mechanisms in membranes are studied. The finite difference numerical solutions of the model are used to study heat and moisture transfer in enthalpy exchangers. The variations of sensible, latent, and enthalpy effectiveness with various operating parameters are calculated for different types of material. Studies show that the sensible effectiveness is mainly determined by number of transfer units (NTU) of the exchanger, while the latent effectiveness is influenced by both the material and the operating conditions. Unlike thermal diffusive resistance, the moisture diffusive resistance in membrane is not a constant. It is co-determined by the slopes of sorption curves and the operating conditions. To account for these influences, a new dimensionless factor named the coefficient of moisture diffusive resistance (CMDR) is defined. With this coefficient, the performance of an enthalpy exchanger can be more easily predicted and clearly understood. By comparing the performances with different membrane materials, it is revealed that the membrane material with a linear sorption curve performs better than other materials under common conditions.     

Phototransfer of an electron in frozen solutions of cyanine dyes

The irradiation of frozen vitreous solutions of cyanine dyes in the absorption band of the quinoline fragment of the dye molecule leads to the two-quantum phototransfer of an electron from the pigment to the acceptor. The intermediate stages of the charge separation involve the transfer of electronic excitation energy from the quinoline fragment to the dye molecule as a whole. The transfer to the acceptor from a molecule of the dye in the monomeric state is more than 12 times as effective as the transfer of an electron from the dye in an associated state (reckoned for a single molecule in the aggregate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1734–1737, August, 1990.     

Hydrogen diffusion transfer through an asymmetric three-layer vanadium membrane

Hydrogen diffusion transfer through a three-layer membrane has been studied within the framework of the lattice model under the Bragg?Williams approximation. A set of equations describing hydrogen transfer through a vanadium membrane coated with thin palladium layers has been derived taking into account the interactions of hydrogen atoms in the membrane layers. The obtained equations have been solved using the Mathcad-14 software package. It has been shown that the interaction between hydrogen atoms has a significant influence on hydrogen permeability at near-atmospheric pressures. It has been found that the permeability of the vanadium membrane is markedly higher than that of a palladium one at the same thickness. The effect of asymmetric vanadium membrane embrittlement has been shown to depend on the location of palladium layers with different thicknesses. The embrittlement of the vanadium membrane begins at higher pressures, when a thicker palladium layer is located at the inlet. It has been revealed that, for asymmetric membranes, the value of the diffusion flux of hydrogen atoms may depend on the transfer direction. At the same membrane thickness, the permeability of the asymmetric membrane is actually equal to that of a symmetrical membrane, provided that a thicker palladium layer is located at the inlet. At the opposite orientation, of the permeability of the asymmetric membrane is lower than that of the symmetric one.     

Mathematical simulation of atomic hydrogen diffusion transfer through a bimetallic membrane

Mathematical simulation of atomic hydrogen diffusion transfer through a bimetallic membrane is performed under the approximation of an ideal lattice gas. Analytical expressions are derived for diffusion fluxes at different membrane orientations. The intensity of diffusion transfer of hydrogen atoms through a bimetallic membrane depends on the direction of transfer, provided that they have different solubilities in metal layers. It is shown that the effect of diffusion asymmetry must be taken into account when developing and using bimetallic membranes.     

Important parameters in semi-dry electrophoretic transfer.

The efficiency of semi-dry electrophoretic transfer after sodium dodecyl sulfate (SDS)-electrophoresis using PhastGel media was investigated in a model system using three isotope labelled proteins. To give a full picture of the blotting process the amount of protein present in the gel, membranes, and filter papers was determined after different transfer times. The influence of the transfer buffer, commonly used additives such as methanol and SDS, and several different immobilizing matrices was investigated. Soybean trypsin inhibitor, bovine serum albumin, and ferritin were used as model proteins to study the effect of size on transfer efficiency. Basically, all three stages of the blotting process decide the result; the elution of protein from the gel, the immobilization of protein to the membrane, and the loss of material from the membrane during transfer. A theoretical explanation for the observed poor binding to a second membrane is discussed. Our results show that the buffer composition has little influence on the efficiency of transfer from the gel, but can be significant to the binding capacity of the membrane. In all experiments performed, there was never one moment during the transfer when all protein was eluted from the gel and simultaneously still bound to the membrane. The highest recovery in the membrane was obtained at different time intervals for different proteins. This indicates that quantitative transfer procedures cannot be generalized. However, obtaining an optimal method for reliable quantification of a specific protein or group of proteins is possible. For general protein staining of nitrocellulose and polyvinylidene difluoride membranes, a highly sensitive silver staining method requiring only 15 min has been used.     

Mathematical simulation of atomic hydrogen diffusion transfer through a multilayer metal membrane at finite pressures

Diffusion transfer of atomic hydrogen through multilayer metal membranes has been studied within the lattice model of an ideal gas, with the transfer being described by a set of nonlinear algebraic equations. It has been shown that, for multilayer membranes composed of less than four layers, an analytical expression describing a diffusion flux can be derived. Atomic hydrogen transfer through a membrane consisting of a vanadium layer, the surfaces of which are coated with palladium films, has been analyzed in detail. It has been found that the value of the flux may depend on the transfer direction. The effect of diffusion asymmetry arises at finite pressures of hydrogen on the outer membrane surfaces, when its dissolution in metals is described by nonlinear sorption isotherms. The degree of the diffusion asymmetry increases with a rise in hydrogen pressure and depends on the arrangement of the layers composing a membrane.     

二(2,4,4-三甲基戊基)膦酸在中空纤维膜器中萃取镱、铒及传质研究

中空纤维膜萃取技术是将液液萃取过程与膜过程相结合的新型分离技术．二（２,４,４三甲基戊基）膦酸（ＨＢＴＭＰＰ,ＨＬ）萃取稀土及其它高价金属离子时所需水相酸度低,反萃容易,加之空间位阻等因素,很可能成为优于２乙基己基膦酸单２乙基己基酯（ＨＥＨ／...     

Double proton transfer behavior and one-electron oxidation effect in double H-bonded glycinamide-formic acid complex

The behavior of double proton transfer occurring in a representative glycinamide-formic acid complex has been investigated at the B3LYP/6-311 + + G( * *) level of theory. Thermodynamic and, especially, kinetic parameters, such as tautomeric energy, equilibrium constant, and barrier heights have been discussed, respectively. The relevant quantities involved in the double proton transfer process, such as geometrical changes, interaction energies, and intrinsic reaction coordinate calculations have also been studied. Computational results show that the participation of a formic acid molecule favors the proceeding of the proton transfer for glycinamide compared with that without mediate-assisted case. The double proton transfer process proceeds with a concerted mechanism rather than a stepwise one since no ion-pair complexes have been located during the proton transfer process. The calculated barrier heights are 11.48 and 0.85 kcal/mol for the forward and reverse directions, respectively. However, both of them have been reduced by 2.95 and 2.61 kcal/mol to 8.53 and -1.76 kcal/mol if further inclusion of zero-point vibrational energy corrections, where the negative barrier height implies that the reverse reaction should proceed with barrierless spontaneously, analogous to that occurring between glycinamide and formamide. Furthermore, solvent effects on the thermodynamic and kinetic processes have also been predicted qualitatively employing the isodensity surface polarized continuum model within the framework of the self-consistent reaction field theory. Additionally, the oxidation process for the double H-bonded glycinamide-formic acid complex has also been investigated. Contrary to that neutral form possessing a pair of two parallel intermolecular H bonds, only a single H bond with a comparable strength has been found in its ionized form. The vertical and adiabatic ionization potentials for the neutral complex have been determined to be about 9.40 and 8.69 eV, respectively, where ionization is mainly localized on the glycinamide fragment. Like that ionized glycinamide-formamide complex, the proton transfer in the ionized complex is characterized by a single-well potential, implying that the proton initially attached to amide N4 in the glycinamide fragment cannot be transferred to carbonyl O13 in the formic acid fragment at the geometry of the optimized complex.