Untersuchung von Kartoffeln, Gerste und Malz

Ohne Zusammenfassung     

Solvation of Ti(IV) in aqueous solution under ambient and supercritical conditions

We examine the structure of the hydrated Ti(IV) complex under both ambient and supercritical conditions using first-principles molecular dynamics. We find that an unanticipated fivefold coordination of Ti(IV) is favoured under ambient conditions, with rapid interconversions between square pyramidal and trigonal bipyramidal structures. At supercritical conditions the Ti coordination increases from five to six, adopting both octahedral and trigonal prismatic geometries. At 1000 K, the magnitude of the increase in the Ti to oxygen coordination number with increasing water density is similar to that of Li-O under comparable conditions. We present a detailed picture of the bonding in the hydrated Ti(IV) complex under both ambient and supercritical conditions.     

Resolving power in liquid chromatography: A trade‐off between efficiency and analysis time

This review describes chromatographic dispersion and different plate‐height models frequently used to assess the chromatographic performance of ultra‐high‐pressure liquid chromatography column technology. Furthermore, different performance indices, including the resolution, the separation impedance, and kinetic plots are discussed allowing to quantify and visualize the resolving power in liquid chromatography. The construction of kinetic plots is explained, and different visualization approaches are highlighted. Finally, key instrument and column‐technology developments to advance the kinetic performance limits are discussed and selected state‐of‐the‐art applications are highlighted.     

Anchoring BaII to Pd/HyWO3−x Nanowires Promotes a Photocatalytic Reverse Water–Gas Shift Reaction

Surface deposition of Ba^II on Pd/H_yWO_3−x nanowires was developed by using a solution-phase atomic layer deposition process. The procedure involves the generation of Brønsted surface OH sites by H₂ spillover on Pd/WO₃, which can then hydrolytically condense with Ba(OEt)₂ to produce surface Ba^II. At just 0.2 at % Ba, CO production by the light-assisted activity of the reverse water–gas shift (RWGS) reaction was observed to increase by about 300 %. In situ DRIFTS studies suggested enhanced CO₂ capturing capabilities of a Ba-decorated surface. This study further exemplifies the importance of surface chemistry in optimizing materials for catalysis.     

Potentiometrische p-Bestimmung

Ohne Zusammenfassung     

Mechanism of cis-dihydroxylation and epoxidation of alkenes by highly H(2)O(2) efficient dinuclear manganese catalysts

In the presence of carboxylic acids the complex [Mn(IV)2(micro-O)3(tmtacn)2]2+ (1, where tmtacn = N,N',N'-trimethyl-1,4,7-triazacyclononane) is shown to be highly efficient in catalyzing the oxidation of alkenes to the corresponding cis-diol and epoxide with H2O2 as terminal oxidant. The selectivity of the catalytic system with respect to (w.r.t.) either cis-dihydroxylation or epoxidation of alkenes is shown to be dependent on the carboxylic acid employed. High turnover numbers (t.o.n. > 2000) can be achieved especially w.r.t. cis-dihydroxylation for which the use of 2,6-dichlorobenzoic acid allows for the highest t.o.n. reported thus far for cis-dihydroxylation of alkenes catalyzed by a first-row transition metal and high efficiency w.r.t. the terminal oxidant (H2O2). The high activity and selectivity is due to the in situ formation of bis(micro-carboxylato)-bridged dinuclear manganese(III) complexes. Tuning of the activity of the catalyst by variation in the carboxylate ligands is dependent on both the electron-withdrawing nature of the ligand and on steric effects. By contrast, the cis-diol/epoxide selectivity is dominated by steric factors. The role of solvent, catalyst oxidation state, H2O, and carboxylic acid concentration and the nature of the carboxylic acid employed on both the activity and the selectivity of the catalysis are explored together with speciation analysis and isotope labeling studies. The results confirm that the complexes of the type [Mn2(micro-O)(micro-R-CO2)2(tmtacn)2]2+, which show remarkable redox and solvent-dependent coordination chemistry, are the resting state of the catalytic system and that they retain a dinuclear structure throughout the catalytic cycle. The mechanistic understanding obtained from these studies holds considerable implications for both homogeneous manganese oxidation catalysis and in understanding related biological systems such as dinuclear catalase and arginase enzymes.     

Bieruntersuchung

Ohne Zusammenfassung