Metal Entity Research Articles

Effects of metal-ion binding on nucleobase pairing: stabilization, prevention and mismatch formation †

Depending on the site of metal binding to a nucleic acid constituent and the geometry of the metal entity, either a stabilization of a nucleobase ensemble, complementary or not (‘metal-modified’ base pair, triplet or quartet), or a prevention of nucleobase pairing may result.

The preparation and use of unbacked metal films as filters in the extreme ultraviolet.: W R Hunter, Physics of thin films, 7, 1973, 43–114.

The N2O decomposition (de-N2O) performance of Al2O3 supported, low content (0.25, 0.5 and 1.0 wt.%) noble metal (Pt, Pd, Ir) catalysts, is comparatively explored in the present study. The effect of metal content, operation temperature and feed composition on de-N2O performance is investigated. Characterization studies involving BET, XRD, TEM and H2-TPR were also carried out to reveal the impact of metal entity and content on the structural, morphological and redox characteristics of the catalysts. The catalytic results imply that the de-N2O performance is in general increased upon increasing metal loading, a fact being more intense over Ir-based catalysts. Under oxygen deficient conditions, N2O conversions as high as ∼100% and ∼80% are reached at 600 °C over Ir- and Pd-based catalysts, respectively, instead of only ∼30%, achieved over Pt-based catalysts. A moderate degradation in oxygen excess conditions is observed with Ir and Pd catalysts, while Pt-based catalysts are almost fully depressed. The superior de-N2O performance of Ir-, Pd-based catalysts can be mainly interpreted by taking into account the formation of metal oxide phases, not easily susceptible to oxygen poisoning. For Ir-based catalysts the active phase seems to be mainly the metal oxide phase (IrO2), as revealed by H2-TPR, XRD and TEM experiments. In the case of palladium catalysts two different metal phases, i.e. PdO and metallic Pd0 were detected. On the other hand, platinum catalysts presented only metallic Pt0 species, which are prone to poisoning by strongly adsorbed oxygen atoms.

The Extraction of Thallium(III) from Hydrochloric Acid Solutions with Ethyl Acetate

Abstract Ethyl acetate has been employed as a solvent for extracting thallium(III) from its hydrochloric acid solutions. The empirical formula of the extracted metal entity has been found to be HTCl4. Optimum conditions for the extraction of the metal have been determined, and the effect of various factors, e.g., metal concentration, salting-out agents, and the dilution of the solvent, have been investigated. It has been possible to separate thallium(III) from aluminum(III), gallium(III) and indium-(III) by performing a batch-by-batch extraction at a 1.0 n hydrochloric acid concentration. 1) The extracted species is an acid with an approximate formula of HTICl4, the distribution of the species between the two phases depends upon the concentration of the hydrochloric acid present in the system. 2) The extracted species is ionic and may associate in the organic phase to from ion pairs, ion triplets and higher clusters. This is evident from the fact that an increase in the metal concentration causes an increase in the distribution coefficient. 3) There is no primary solvation of thallium, which is tetrahedrally surrounded by chloride ions and which is apparently saturated. This is supported by the observation that the metal could not be extracted from its solution in perchloric acid. 4) The proton of the chlorothallic acid may be solvated (and possibly hydrated, too) in the organic phase, the solvation number being indefinite. 5) Ion pairing results in the formation of an extractable complex and a general mechanism of the type: H(S)++[TlS)2C14]−\ightleftharpoons[(HS+)(Tl(S2)C14)−] may be expected, where S is either H2O or ethyl acetate. The above equation may well represent qualitatively various reactions at different relative water and ethyl acetate activities. In general, the system is a simple ion-association extraction system and is quite similar to the extraction of iron(III) and gallium(III) chloride with oxygenated solvents.