Cation-anion Binding Research Articles

N-Doped Photocatalytic Titania Thin Films on Active Polymer Substrates

Active polymer substrates have found their way in the semiconductor industry as a base layer for flexible electronics, as well as in sensor and actuator applications. The optimum performance of these systems may be affected by dirt adsorbed on its surface, which can also originate mechanisms for the degradation of the polymer. Titanium dioxide (titania) semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron sputtering on one of the most applied and investigated electroactive polymer: poly(vinilidene fluoride), PVDF. In order to increase the photocatalytic efficiency of the titania coatings, a reduction of the semiconductor band-gap has been attempted by using a nitrogen doping. Rutherford Backscattering Spectroscopy was used in order to assess the composition of the titania thin films, whereas Heavy Ion Elastic Recoil Detection Analysis provided the evaluation of the doping level of nitrogen. X-ray Photoelectron Spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The photocatalytic performance of the titania films have been characterized by decomposing an organic dye illuminated with combined UV/visible light.

Enhancement in the photocatalytic nature of nitrogen-doped PVD-grown titanium dioxide thin films

Nitrogen-doped titanium dioxide semiconductor photocatalytic thin films have been deposited by unbalanced reactive magnetron physical vapor deposition on glass substrates for self-cleaning applications. In order to increase the photocatalytic efficiency of the titania coatings, it is important to enhance the catalysts absorption of light from the solar spectra. Bearing this fact in mind, a reduction in the titania semiconductor band-gap has been attempted by using nitrogen doping from a coreactive gas mixture of N2:O2 during the titanium sputtering process. Rutherford backscattering spectroscopy was used in order to assess the composition of the titania thin films, whereas heavy-ion elastic recoil detection analysis granted the evaluation of the doping level of nitrogen. X-ray photoelectron spectroscopy provided valuable information about the cation-anion binding within the semiconductor lattice. The as-deposited thin films were mostly amorphous, however, after a thermal annealing in vacuum at 500 °C the crystalline polymorph anatase and rutile phases have been developed, yielding an enhancement in the crystallinity. Spectroscopic ellipsometry experiments enabled the determination the refractive index of the thin films as a function of the wavelength, while from the optical transmittance it was possible to estimate the semiconductor indirect band-gap of these coatings, which has been proven to decrease as the N-doping increases. The photocatalytic performance of the titania films has been characterized by the degradation rate of an organic reactive dye under UV/visible irradiation. It has been found that for a certain critical limit of 1.19 at. % of nitrogen doping in the titania anatase crystalline lattice enhances the photocatalytic behavior of the thin films and it is in accordance with the observed semiconductor band-gap narrowing to 3.18 eV. By doping the titania lattice with nitrogen, the photocatalytic activity is enhanced under both UV and visible light.

Relation between Heat of Vaporization, Ion Transport, Molar Volume, and Cation−Anion Binding Energy for Ionic Liquids

A number of correlations between heat of vaporization (H(vap)), cation-anion binding energy (E(+/-)), molar volume (V(m)), self-diffusion coefficient (D), and ionic conductivity for 29 ionic liquids have been investigated using molecular dynamics (MD) simulations that employed accurate and validated many-body polarizable force fields. A significant correlation between D and H(vap) has been found, while the best correlation was found for -log(DV(m)) vs H(vap) + 0.28E(+/-). A combination of enthalpy of vaporization and a fraction of the cation-anion binding energy was suggested as a measure of the effective cohesive energy for ionic liquids. A deviation of some ILs from the reported master curve is explained based upon ion packing and proposed diffusion pathways. No general correlations were found between the ion diffusion coefficient and molecular volume or the diffusion coefficient and cation/anion binding energy.

Calix[4]pyrrole: An Old yet New Ion‐Pair Receptor

Ditopic cation–anion binding is revealed by solid-state studies of the anion-recognition behavior of the calix[4]pyrrole unit. Anion binding causes an electron-rich conelike cavity to be formed that can then bind large polarizable cations. Furthermore, complexation of calix[4]pyrrole with cesium carbonate results in dimerization, in which a single anion bridges two calix[4]pyrroles (see the crystal structure of the Cs2CO3 complex).

Anion effects in selective bifunctional metal salt extractants based on aza-thioether macrocycles: co-operative cation–anion binding?

The binding of AgX salts (X = NO3−, BF4− and ClO4−) to [15]aneS2ON2–(CH2CONHCONH–tBu)2 (L1) has been assessed by 1H NMR spectroscopy. 1H NMR titration studies of AgX with L1 and related ligands are interpreted in terms of a range of metal–salt binding interactions. Anion binding occurs via a switching mechanism whereby co-ordination of a metal cation to L1 breaks internal hydrogen-bonding to allow anions to bind to the inner urea hydrogen site on the attached pendant arm. No anion binding occurs in the absence of a bound metal ion. Crystal structures of two complexes L·AgNO3 confirm this feature [for N–H⋯ONO2, N⋯O = 2.866(5)–2.940(5) A in L1·AgNO3], but also show chelate binding of the amide O-donor of the acylurea pendant arm to AgI in the solid state. Two-phase metal extraction studies with AgX salts and L1 confirm that the anion plays an important role, although it is likely that solubility of the resulting metal complexes in the organic phase is the predominant factor. A range of related amide substituted macrocycles has also been prepared and anion binding interactions appear strongest with those ligands containing the highest number of amide/urea units. At high anion concentrations, and in the presence of AgI, all of the ligands participate in anion–ligand interactions.

Ion-exchange reactions of proteins during DNA binding.

The equilibrium association constant observed for many DNA/protein interactions in vitro (K(obs)) is strongly dependent on the salt concentration of the reaction buffer ([MX]). This dependence is often used to estimate the number of ionic contacts between protein and DNA by assuming that displacement of cations from the DNA is the predominant form of the involvement of ions in the binding reaction. With this assumption, the graph of log K(obs) versus log [MX] is predicted to have a constant slope proportional to the number of ions displaced from the DNA upon protein binding [Record, M. T., Lohman, T. M. & deHaseth, P. L. (1976) J. Mol. Biol. 107, 145-158]. Experimental data often deviate from linearity, however, at lower salt concentrations. Such deviations can be due to differential cation binding, anion binding or changes in macromolecular hydration, or differential screening effects of the electrolyte on protein and/or DNA charges. Here the theoretical effects on K(obs) of a simple form of ion-protein interaction are examined. A model for binding interactions is used that includes a mass balance of ions bound to both protein and DNA as the protein is transferred from the salt concentration of bulk solvent to the typically higher cation and lower anion concentrations characteristic of the volume adjacent to the DNA. We show that models in which the cation and anion stoichiometries of a protein change as it associates with DNA are consistent with the curvature of plots of log K(obs) versus log [MX]. Such mechanisms could reduce the sensitivity of gene-regulatory interactions to changes in environmental salt concentration.

Dependence of ion pairing and solvation on solution temperature: Evidence from DMSO solution and matrix-solvation spectra

Infrared and Raman Spectra for alkali-metal nitrate solutions in dimethylsulfoxide (DMSO) have been measured as a function of concentration (0.5 to 2.0 M) and temperature (298 to 400 K) to determine the influence of temperature on structural changes that favor the incorporation of the nitrate anion into the solvation shell of the M+ cations. It is apparent from the spectra observed at elevated temperatures that this contact pairing of the ions in liquid DMSO occurs endothermically. It is also shown, by invoking the known spectra of the solvates (DMSO)3⋅LiNO3 and (DMSO)4⋅LiNO3 that are available from low temperature matrix-solvation measurements, that partial desolvation of the contact-ion-pair solvates occurs endothermically over this temperature range. These observations are interpreted as evidence that the energetics for the structural changes that lead to anion incorporation into the cation inner coordination sphere are dominated by the endothermic partial desolvation of the ions (in particular the cation). The DMSO solvates of the contact ion pair dominate the Raman spectra at 400 K for all of the alkali metal nitrates provided the concentration exceeds 1.0 M. In the case of LiNO3, polarization Raman data indicate that the cation-anion binding for (DMSO)3⋅LiNO3 is bidentate while that for (DMSO)4⋅LiNO3 is monodentate. This switch in cation–anion binding has been anticipated from considerations of steric repulsive forces in the inner coordination shell of the Li+ cation but has proved difficult to document.

Effect of Heating on the Functional Properties of Ovotransferrin

The effect of heating on the functional properties of ovotransferrin greatly varied with both the pH and ionic strength of the solution. When small amounts of inorganic salts (μ<0.1) were present in the ovotransferrin solution of which the pH was between 6.0 and 8.5, both the solubility and foaminess greatly decreased upon heating at a temperature above 60°C for 5 min. However, when the amounts of inorganic salts were larger μ≥0.3), no decrease in either property was observed. These phenomena were assumed to be caused by either cation binding (at a low concentration of salts) or anion binding (at a high concentration of salts) of ovotransferrin. Among the anions tested, both phosphate and citrate which are assumed to have a rather high affinity for ovotransferrin did not cause any heat-induced defect at any of the salt concentrations tested.

Effect of heating on the functional properties of ovotransferrin.

The effect of heating on the functional properties of ovotransferrin greatly varied with both the pH and ionic strength of the solution. When small amounts of inorganic salts (μ<0.1) were present in the ovotransferrin solution of which the pH was between 6.0 and 8.5, both the solubility and foaminess greatly decreased upon heating at a temperature above 60°C for 5 min. However, when the amounts of inorganic salts were larger μ≥0.3), no decrease in either property was observed. These phenomena were assumed to be caused by either cation binding (at a low concentration of salts) or anion binding (at a high concentration of salts) of ovotransferrin. Among the anions tested, both phosphate and citrate which are assumed to have a rather high affinity for ovotransferrin did not cause any heat-induced defect at any of the salt concentrations tested.

Magnetic susceptibility of alkali n -butyrates and isovalerates near their melting points

Various physical properties of alkali carboxylates can be used to study precursor effects immediately below or above their melting points. The present paper describes unusual pre-transition behaviour observed in the magnetic susceptibility of molten n -butyrates and isovalerates. This takes the form of a transitory enhancement of diamagnetic susceptibility, by nearly 10% in some cases, when the isotropic melt is cooled through the clearing point and into the mesophase region while a magnetic field (up to 1 T(10 4 G)) is applied. No corresponding changes are observed on taking the salt through the same temperature range but in the inverse direction. Again, no corresponding change is observed with an alkali carboxylate which shows no mesophase melting transition. Present findings can be accounted for on the assumption of cluster formation in the molten salts as these approach their upper melting points, which is also indicated by other evidence. The (transient) enhancement of molecular diamagnetism in this region of temperature may also indicate transient perturbations in the actual cation-anion binding near the transition temperature.