Aqueous coordination chemistry and photochemistry of uranyl(VI) oxalate revisited: a density functional theory study

Using density functional theory (DFT) calculations, we revisited a classical problem of uranyl(VI) oxalate photochemical decomposition. Photoreactivities of uranyl(VI) oxalate complexes are found to correlate largely with ligand-structural arrangements. Importantly, the intramolecular photochemical reaction is inhibited when oxalate is bound to uranium exclusively in chelate binding mode. Previously proposed mechanisms involving a UO(2)(C(2)O(4))(2)(2-) (1:2) complex as the main photoreactive species are thus unlikely to apply, because the two oxalic acids are bound to uranium in a chelating binding mode. Our DFT results suggest that the relevant photoreactive species are UO(2)(C(2)O(4))(3)(4-) (1:3) and (UO(2))(2)(C(2)O(4))(5)(6-) (2:5) complexes binding uranium in an unidentate fashion. These species go through decarboxylation upon excitation to the triplet state, which ensues the release of CO(2) and reduction of U(vi) to U(v). The calculations also suggest an alternative intermolecular pathway at low pH via an electron transfer between the excited state *UO(2)(2+) and hydrogen oxalate (HC(2)O(4)(-)) which eventually leads to the production of CO and OH(-) with no net reduction of U(VI). The calculated results are consistent with previous experimental findings that CO is only detected at low pH while U(IV) is detected only at high pH.     

Greatly attenuated experimental autoimmune encephalomyelitis in aquaporin-4 knockout mice

Background  

The involvement of astrocyte water channel aquaporin-4 (AQP4) in autoimmune diseases of the central nervous system has been suggested following the identification of AQP4 autoantibodies in neuromyelitis optica, an inflammatory demyelinating disease.     

Structure–Property Relationship of Thin Plasma Deposited Poly(allyl alcohol) Films

Poly(allyl alcohol) films with a thickness of about 150 nm were deposited by pulse plasma polymerization onto different substrates (inorganic and organic). The structure/property relationships of these samples were studied in dependence on the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time volume sensitive methods (FTIR and dielectric spectroscopy) are combined with surface analytics by employing XPS for that system. FTIR spectroscopy gives qualitatively the same dependence of the concentration of the OH groups on DC like XPS. The observed differences are discussed considering the different analytical depths of both the methods. The dielectric measurements show that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating. The results obtained by dielectric spectroscopy are discussed in detail with the data from FTIR and XPS measurements.     

Advanced binderless board-like green nanocomposites from undebarked cotton stalks and mechanism of self-bonding

Self-bonding of air-dried undebarked cotton stalks during hot pressing in a closely fitting mold was studied. Advanced board-like green nanocomposites from ground undebarked cotton stalks were introduced for the first time in the present work. The dry forming process was adopted. Moderate molding pressure and temperature were selected and applied in a tight die, thus saving water and energy and avoiding the use of any binders to achieve an environment-friendly green product. Green nanocomposites having densities in the range of 1.27–1.29 g/cm³ and 1.03–1.06 g/cm³ were prepared. Particle size and cell wall morphological structure were found to play a major role in self-bonding. Properties of composites prepared from the fine fraction of cotton stalks were superior to those prepared from the cotton stalk coarse fraction at the same conditions. This is attributed—among other things—to the dominance of pith (parenchymal cells) in the fine fraction. Such cells possess a high lumen-to-cell wall ratio, which renders them more deformable under pressure, leading to more intercellular or interparticle bonding. Advanced binderless green nanocomposites having bending strength as high as 637 kg/cm² and water absorption as low as 12.1 % were obtained from the ground undebarked cotton stalks. The results show clearly that the advanced green nanocomposite obtained by the dry forming process, without the addition of any binders, is superior to hardboard obtained from cotton stalks by the conventional wet web formation process. The mechanism of self-bonding is discussed.     

Spatial characterization of the transversal structure of rotationally symmetric pulsed beams

A simple analytical model is proposed to describe the transversal spatial structure of a tridimensional rotationally symmetric pulsed beam. The spatial behaviour of the pulse amplitude is shown to be linked to its (measurable) second- and higher-order intensity moments, namely, beam width, quality parameter and kurtosis. As an illustrative experimental example, this model has been applied to high-quality TEA CO2 laser pulses. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of Epinephrine and Insulin on Glucose Metabolism in Isolated Fat Cells

Since epinephrine and insulin are known to counteract each other in several metabolic respects, it was found of interest to evaluate the interaction of these hormones on glucose metabolism in isolated fat cells. Results indicate that in spite of reduced lipolysis, insulin potentiates the conversion of glucose to glyceride-glycerol. This means that a certain degree of esterification of fatty acids must take place. So the low rate of lipolysis is sufficient to provide fatty acids for this esterification.     

The electrochemical reduction of some fused ring systems

The electrochemical reduction of some fused ring systems containing four carbonyl moieties has been studied in alcoholic aqueous media. A mechanism has been proposed and clarified in which one carbonyl is reduced to a methylene group via an uptake of four electrons.     

Differences Between Consecutive Primes

Let p_n be the nth prime. Then this paper is concerned with provingthe following result on the distribution of consecutive primes. The exponent of x in this theorem improves on the work of Heath-Brownwho proved (1) with exponent . Under the Riemann hypothesisone can prove (1) with exponent .The proof of the theorem startswith the Heath-Brown–Linnik identity which leads to aformula giving the number of primes in an interval in termsof coefficients of certain Dirichlet series. I then estimatethe coefficients by using, among other things, the informationwhich can be gained from Montgomery's mean value theorem andHuxley's version of the Hal' asz lemma. Furthermore, by usingfamiliar sieve arguments I am able to discard some of the coefficientsallowing us to gain an improvement over the previous resultof Heath-Brown. 1991 Mathematics Subject Classification: 11N05.