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.     

pH dependence of hydrochloric acid diffusion through gastric mucus: correlation with diffusion through a water layer using a membrane-mounted glass pH electrode

Solute diffusion coefficients (D) can indicate a dependence upon actual solute concentrations. Here a single compartment has been utilized, in which effective HCl diffusion to a membrane-mounted glass pH electrode can be measured across the pH spectrum. The study has investigated HCl diffusion through both mucus and water layers as a function of HCl concentration. The observed dynamic responses of a liquid-film and mucus-coated electrodes over a range of HCl concentrations suggest that the speed at which equilibrium is attained is pH dependent; equilibrium was reached rapidly under more acidic and alkaline conditions. Estimated values of DHCl also indicate a strong pH dependence for both liquid film and mucus. In both instances, a greater than 10-fold reduction in DHCl at pH 7.5 as compared with that at pH 3.5 has been demonstrated. Furthermore, estimated values of DHCl are approximately 4-fold smaller through the mucus gel, as compared with a water layer. The findings indicate that the most powerful influence on diffusional resistance is pH itself, whereby a marked drop in H+ diffusion is likely to occur towards neutral pH irrespective of the composition of the gel barrier. Possible implications of the findings are discussed in relation to mucosal protection from acid.     

Spectroscopic and theoretical evidence for the cooperativity between red-shift hydrogen bond and blue-shift hydrogen bond in DMSO aqueous solutions

The cooperativity between red-shifted hydrogen bond and blue-shifting hydrogen bond in dimethyl sulfoxide aqueous solutions was studied by methods of quantum chemical calculations and infrared spectroscopy. The water molecule plays a different role in two types of hydrogen bonds: proton-donor in red-shifted hydrogen bond and proton-acceptor in blue-shifting hydrogen bond. The cooperativity is not prominent if the ring structure is formed through the OHcdots, three dots, centeredOS H-bond and CHcdots, three dots, centeredO(w) H-bond. However, if the methyl groups in the above ring structure participate in second CHcdots, three dots, centeredO(w) H-bond, the cooperativity is increased. The second CHcdots, three dots, centeredO(w) H-bond enhances OHcdots, three dots, centeredOS H-bond and weakens the first CHcdots, three dots, centeredO(w) H-bond.     

Spectroscopic evidence for a persistent benzenium cation in zeolite H-beta

Experimental evidence of protonation of an aromatic ring by a zeolite is hereby presented for the first time. The changes in vibrational properties and electronic transitions of the highest polymethylbenzene homologue, that is, hexamethylbenzene, were investigated after introducing the compound directly into a H-beta zeolite. Protonation of the aromatic ring, and thus the loss of symmetry, activated a vibrational ring mode at 1600 cm(-)(1). Furthermore, an electronic transition around 26 000 cm(-)(1), which was totally absent for the neutral species, was an obvious consequence of protonation. A parallel study of hexamethylbenzene adsorbed on a beta zeolite virtually free from protons did not show those distinctive spectral features. On the basis of the gas-phase proton affinity of hexamethylbenzene, a complete proton transfer from the zeolite framework to the molecule is, according to conventional considerations, not expected. The hexamethylbenzenium ion is stable in the zeolite cavities at least up to 200 degrees C. The remarkable persistence of this carbenium ion may be attributed to spatial constraints imposed by the tight fit of the cation inside the zeolite channels. Hexamethylbenzene is a relevant reaction intermediate in the methanol-to-hydrocarbons reaction and also plays a central role as a coke precursor in zeolite-catalyzed reactions that involve polymethylbenzenes.     

Spectroscopic evidence for the formation of goldfingers

Gold(I) has long been used in the treatment of rheumatoid arthritis, but the therapeutically relevant biological targets of gold(I) are not well understood. Here, we report the results of a spectroscopic investigation into the formation of goldfingers. By exploiting a thiolate to gold charge-transfer band in the UV, we observed that gold(I) interacts with zinc finger peptides with a stoichiometry of one gold ion for each two cysteine residues, forming 1:1, 1.5:1, and 2:1 adducts with zinc finger peptides containing CCHH, CCHC, and CCCC donor sets, respectively. In addition, circular dichroism experiments provided evidence that goldfingers are more ordered than the corresponding metal-free peptides but do not exhibit the canonical zinc finger structure.     

Chemical assembly of a titanium oxide layer on microporous silica

Russian Journal of General Chemistry - The chemical assembly of a titanium oxide coating on a regular microporous silica surface by the atomic layer deposition method was considered. The change in...     

Spectroscopic evidence for a delocalized excited state in the magnus salts

The polarized single-crystal spectra of the Magnus salts [Pt(NH₃)₄][PtCl₄], [Pd(NH₃)₄] [PtCl₄], [Pt(NH₃)₄] [PdCl₄], and [Pd(NH₃)₄][PdCl₄] have been obtained in the quartz ultraviolet and visible regions. These results provide strong evidence for a delocalized excited state being associated with the intense ultraviolet transition found in the spectra of the Magnus salts. One thus has available an important new criterion for the evaluation of the theoretical treatments of these systems.     

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.     

Spectroscopic probes of the quasi-liquid layer on ice

Raman spectra of the water OH-stretch region were acquired at air-ice and air-water interfaces at a glancing angle, which allowed observation of surface characteristics. The shapes of the OH-stretch bands indicate that the environment at the air-ice interface is different from that at the air-water interface and from that seen in bulk water. Water spectra measured at the surface of dodecane under low relative humidity indicate that this method is sensitive to fewer than 50 monolayers of water. Changes in the local environment of the surfacial water molecules may be induced by the presence of different solute species, giving rise to changes in the shape of the band. Dissolved sodium chloride disrupts hydrogen bonding in liquid water and has the same effect at the air-ice interface. However, when either HCl or HNO(3) is adsorbed from the gas phase onto an ice surface, the opposite effect is seen: Their presence appears to increase the extent of hydrogen bonding at the ice surface. At the same time, shifts in the laser-induced fluorescence spectra of acridine, a fluorescent pH-probe present at the air-ice interface, indicate that dissociation of acids occurs there. These observations suggest that the formation of hydronium ions at the air-ice interface enhances the hydrogen bonding of surfacial water molecules.     

Diffusion of acid and alkaline salt solutions through the Nernst diffusion layer

The behavior of diffusion layer under the conditions of salt transfer with excess of acid or alkali, involving the hydrogen and hydroxyl ions, is studied. The transfer is affected by the applying of current. The method of investigation was mathematical simulation based on the solving of boundary problems by using the Nernst-Planck equation with regard to the corresponding conditions of the transfer.     

Membranes with a plasma deposited titanium isopropoxide layer

Porous polypropylene membranes were coated with plasma polymerized titanium isopropoxide in a 75 kHz plasma reactor. It was noted that the presence of air in the plasma chamber increased the amount of deposited polymer. Selection of the process parameters enabled obtaining membranes with up to 300 εg cm^?2 of polymerized titanium isopropoxide. Deposition of the titanium oxide layer resulted in the reduction of permeate flux but it significantly improved the membrane photocleaning ability. The recovery index reached the level of 95 % for membranes with the highest amount of the titanium oxide deposit.     

Effective thickness of the diffusion layer during hydrogen ion reduction in aqueous hydrochloric acid solutions

The process of mass transport during hydrogen ion reduction in aqueous hydrochloric acid solutions is examined both with and without excess supporting electrolyte. The study of this process is based on a numerical solution to a system of equations of material balance and the movement of particles in solution under the influence of forces for diffusion, migration, and convection. The homogeneous chemical reaction of water dissociation is also taken into account. The results of calculations show that a diffusion layer forms near the electrode during the passage of current in these solutions and that the effective thickness of this layer is the same at any instant for all particles participating in mass transport in solution in spite of differences in their diffusion coefficients. The value of the diffusion coefficient measured in these multicomponent solutions by the methods of chronopotentiometry and rotating disk electrode should differ little from that of hydrogen ions in spite of the fact that other particles with different diffusion coefficients participate in the mass transport.     

Spectroscopic and DFT evidence for a nonclassical radical cation derived from 7-benzhydrylidenenorbornene

Nanosecond time-resolved UV/vis absorption spectroscopy on laser flash photolysis was conducted for photoinduced electron-transfer reactions of 7-benzhydrylidenenorbornene (1) and 7-benzhydrylidenenorbornane (5). The differences in the observed absorption bands and the structures of 1⁺ and 5⁺ were evaluated successfully using calculations based on (time dependent) density functional theory, confirming the nonclassical nature of 1⁺.     

The reduction of the central manganese ion in MnCl tetraphenylporphyrinate upon hydrogen diffusion through a palladium membrane

Conclusions Manganese(III) in its tetraphenylporphyrinate complex may be reduced to manganese(II) using hydrogen passed through a palladium alloy membrane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 688–689, March, 1985.     

Spectroscopic evidence for gas-phase formation of successive beta-turns in a three-residue peptide chain

We report the first gas-phase spectroscopic study of a three-residue model of a peptide chain, Ac-Phe-Gly-Gly-NH2 (Ac = acetyl), using the IR/UV double resonance technique. The existence of at least five different conformers under supersonic expansion conditions is established, most of them exhibiting rather strong intramolecular H-bonds. One of the most populated conformers, however, exhibits a different H-bonding network characterized by two weak H-bonds. Comparison of the amide A and I/II experimental data with density functional theory calculations carried out on a series of selected conformations enables us to assign this conformer to two successive beta-turns along the peptide chain, the two H-bonds being of C10 type, i.e., each of them closing a 10-atom ring in the molecule. The corresponding form is found to be more stable than the 310 helix secondary structure (not observed), presumably because of specific effects due to the glycine residues.     

Spectroscopic and structural evidence for the hydrogen bond nature of CC---H…C=C contacts in ethynyl steroids

Structural and IR-spectroscopic evidence is given that directed contacts from terminal alkynes to C=C double bonds possess the essential characteristics of weak hydrogen bonds. The contacts are directed at the center of the π-bond rather than at one of the individual C-atoms. The contact distances from H to the center of the C=C bond are typically 2.8 Å, with the shortest distances being 2.5 Å. The interaction is of pronounced long-range nature and can be detected in the infrared spectrum even with a long H…π distance of almost 3.0 Å. The sample used is mainly composed of ethynyl steroids belonging to the progestine family.