Electrochromic and structural characteristics of mesoporous WO<Subscript>3</Subscript> films prepared by a sol-gel method

The preparation of electrochromic films of mesoporous tungsten trioxide from tungstic acid and tungstic hexaethoxide precursors with the addition of an organic stabiliser via a sol-gel method is reported. These films have been structurally characterised and both the film morphology and crystalline composition of the films were found to be significantly dependent on the temperature at which the films were annealed and upon the choice of precursor. Films annealed at lower temperatures consisted of amorphous and hexagonal tungsten trioxide, whereas films annealed above 500 °C comprised solely of monoclinic WO₃. The electrochromic activity of the films was found to be equally dependent on method of preparation, and both the composition and the structure of the WO₃ films were shown to clearly influence the colouration efficiency of the films.Dedicated to Zbigniew Galus on the occasion of his 70^th birthday.     

Cosorption of Zn(II) and 2-, 3-, or 4-aminopyridine by montmorillonite

Data from acid-base titrations at 25 degrees C of Zn(NO(3))(2) and 2-, 3-, or 4-aminopyridine in 10 mM KNO(3) as background electrolyte suggested that soluble complexes ZnL(2+) and Zn(OH)L(+) form, where L represents aminopyridine. Zinc-hydroxyaminopyridine complexes have not been reported previously. The cosorption of Zn(II) with each of the aminopyridines to K-saturated Wyoming (SWy-K) and Texas (STx-K), and Ca-enriched Texas (STx-Ca) montmorillonites was measured at 25 degrees C, with 10 mM KNO(3) or 3.3 mM Ca(NO(3))(2) as background electrolyte. Comparison with previous data for sorption of Zn(II) and the aminopyridines separately and surface complexation modeling of the cosorption data showed that under acid conditions competition between Zn(2+) and aminopyridinium ions for the permanent negatively charged sites of montmorillonite results in suppression of the uptake of each sorbate by the other, but only when a large excess of the competing sorbate is present. Under alkaline conditions the sorption of Zn(II) was not affected by the presence of even a large excess of aminopyridine, but the sorption of 4-aminopyridine in particular was slightly enhanced when a large excess of Zn(II) was present. The enhancement was attributed to the formation of metal-bridged ternary surface complexes at the variable-charge sites on the edges of the montmorillonite crystals.     

Raising the conductivity of crystalline polymer electrolytes by aliovalent doping

Polymer electrolytes, salts dissolved in solid polymers, hold the key to realizing all solid-state devices such as rechargeable lithium batteries, electrochromic displays, or SMART windows. For 25 years conductivity was believed to be confined to amorphous polymer electrolytes, all crystalline polymer electrolytes were thought to be insulators. However, recent results have demonstrated conductivity in crystalline polymer electrolytes, although the levels at room temperature are too low for application. Here we show, for the first time, that it is possible to raise significantly the level of ionic conductivity by aliovalent doping. The conductivity may be raised by 1.5 orders of magnitude if the SbF6- ion in the crystalline conductor poly(ethylene oxide)6:LiSbF6 is replaced by less than 5 mol % SiF6(2-), thus introducing additional, mobile, Li+ ions into the structure to maintain electroneutrality.     

Prediction of Complexation Properties of Crown Ethers Using Computational Neural Networks

A computational neural network method was used for the prediction of stability constants of simple crown ether complexes. The essence of the method lies in the ability of a computer neural network to recognize the structure-property relationships in these host-guest systems. Testing of the computational method has demonstrated that stability constants of alkali metal cation (Na+, K+, Cs+)-crown ether complexes in methanol at 25 °C can be predicted with an average error of ±0.3 log K units based on the chemical structure of the crown ethers alone. The computer model was then used for the preliminary analysis of trends in the stabilities of the above complexes.     

Conformationally gated electron transfer in iso-1-cytochrome c: engineering the rate of a conformational switch

An engineered form of iso-1-cytochrome c with lysine 73 mutated to histidine is shown to increase by nearly 500-fold the rate of a conformational gate that modulates the rate of electron transfer into this protein. This result demonstrates the potential of protein engineering to provide electron transfer gates with tailored properties. The pH dependence of the rate of the conformational electron transfer gate correlates well with the pH dependence of the conformational change from a His 73-ligated heme to a Met 80-ligated heme, determined independently by pH jump methods, allowing unambiguous assignment of the conformational electron transfer gating step. The rate of the electron transfer gate is also modulated by a cis to trans proline isomerization, indicating that both amino acid sequence and the nature of the heme ligand provide avenues for rational design of electron transfer gates which open at different rates.     

Studies of organotin(IV)-orthoquinone systems

The primary process in the reaction of hexaphenylditin with various substituted orthoquinones (Q) is shown to involve attack by the quinone at a phenyl ligand. The intermediate thus formed decomposes to yield Ph₃Sn(SQ^·), where S(Q^·−) is the corresponding semiquinonate. Rearrangement of these species in solution gives rise to biradicals, while intramolecular electron transfer may lead to the formation and precipitation of Ph₂Sn(CAT), where CAT²⁻ is the corresponding substituted catecholate. The identification of these processes depends in part on electron paramagnetic resonance spectroscopy. The reaction of Ph₃SnCl or Ph₂SnCl₂ with Na(TBSQ^·) (TBSQ^·−=3,5-di-tert-butyl-orthobenzosemiquinonate) results in the formation of Ph₂Sn(TBSQ^·), which can undergo redistribution and intramolecular electron transfer, so that the solution chemistry of these latter systems is similar to that of the products of the Sn₂Ph₆+Q reaction.     

Solar Radiation Is Shown to Select for Pigmented Bacteria in the Ambient Outdoor Atmosphere

Abstract— The percentage of pigmented to total bacteria in the outdoor atmospheric population was studied in the field and in controlled laboratory experiments to evaluate the effects of solar radiation (SR) on bacterial survival. The field experiments showed that the percentage of pigmented bacteria positively correlated with SR activity during clear summer days. The percentage was lowest during darkness before dawn and around midnight ( ca 33%) and as the SR increased during the day, gradually increased to a maximum of ca 50–60% at noontime to early afternoon and decreased thereafter. In the laboratory the ambient outdoor atmospheric bacteria impacted on culture plates were exposed to simulated SR and a germicidal light. With increased exposure, more nonpig-mented bacteria were killed and the percentage of pigmented bacteria gradually increased. These observations suggest an inverse relationship between the atmospheric bacterial survival and the percentage of pigmented bacteria contained therein, thus supporting the notion that pigmentation might provide protection for outdoor atmospheric bacteria from sunlight damage. As a consequence, viable pigmented bacteria (and other UV-resistant forms) in the atmosphere could be enriched under areas of stratospheric ozone depletion.     

Multiply doped nanostructured silicate sol-gel thin films: spatial segregation of dopants, energy transfer, and distance measurements

Physical and chemical strategies that place designed molecules in spatially separated regions of surfactant-templated mesostructured silicate thin films are used to prepare films containing rhodamine 6G (R6G), lanthanide complexes, and both simultaneously. Fluorescence and photoexcitation spectra of R6G in amorphous and structured thin films show that it is located inside the surfactant micelles of structured thin films. A silylated ligand that binds lanthanides condenses to form part of the silica framework and causes the lanthanide to localize in the silica. Luminescence and photoexcitation spectra show that energy transfer from the metal complex to R6G occurs in the films. R6G quenches Tb emission in a concentration-dependent manner. Energy transfer efficiency is calculated using the Tb luminescence lifetime, and this quantity is used to calculate the distance between Tb and R6G with the aid of Forster theory.     

Proton-mediated electron configuration change in high-spin iron(II) porphyrinates

The synthesis, molecular structure, and electronic structure characterization of two five-coordinate high-spin imidazolate-ligated iron(II) porphyrinates are reported. Their electronic structure, as deduced from M?ssbauer spectra obtained in strong magnetic fields, is distinctly different from that of the analogous imidazole-ligated species. The resulting electronic structure models are consistent with all observed differing features in the two classes.