Highly chemoselective calcium-catalyzed propargylic deoxygenation

A calcium-catalyzed direct reduction of propargylic alcohols and ethers has been accomplished by using triethylsilane as a nucleophilic hydride source. At room temperature a variety of secondary propargylic alcohols was deoxygenated to the corresponding hydrocarbons in excellent yields. Furthermore, for the first time, a catalytic deoxygenation of tertiary propargylic alcohols was generally applicable. The same protocol was suitable for an efficient reduction of secondary as well as tertiary propargylic methyl, benzyl and allyl ethers. Substrates containing an additional keto-, ester or secondary hydroxyl function were reduced with exceptional chemoselectivity at the propargylic position.     

Titanium-catalyzed vinylic and allylic cf bond activation-scope, limitations and mechanistic insight

The hydrodefluorination (HDF) of fluoroalkenes in the presence of a variety of titanium catalysts was studied with respect to scope, selectivity, and mechanism. Optimization revealed that the catalyst requires low steric bulk and high electron density; secondary silanes serve as the preferred hydride source. A broad range of substrates yield partially fluorinated alkenes, such as previously unknown (Z)-1,2-(difluorovinyl)ferrocene. Mechanistic studies indicate a titanium(III) hydride as the active species, which forms a titanium(III) fluoride by H/F exchange with the substrate. The HDF step can follow both an insertion/elimination and a σ-bond metathesis mechanism; the E/Z selectivity is controlled by the substrate. The catalysts' ineffieciency towards fluoroallenes was rationalized by studying their reactivity towards Group?6 hydride complexes.     

Salen‐Based Coordination Polymers of Manganese and the Rare‐Earth Elements: Synthesis and Catalytic Aerobic Epoxidation of Olefins

Treatment of N,N′‐bis(4carboxysalicylidene)ethylenediamine (H₄L), with MnCl₂ ? (H₂O)₄, and Ln(NO₃)₃ ? (H₂O)_m (Ln=Nd, Eu, Gd, Dy, Tb), in the presence of N,N‐dimethylformamide (DMF)/pyridine at elevated temperature resulted (after work up) in the formation of 1D coordination polymers {[Ln₂(MnLCl)₂(NO₃)₂(dmf)₅] ? 4 DMF}_n ( 1 – 5 ). In these coordination polymers the rare earth ions are connected through carboxylate groups from Mn–salen units in a 1D chain structure. Thus, the Mn–salen complex acts as a “metalloligand” with open coordination sites. All compounds were used as catalysts in the liquid‐phase epoxidation of trans‐stilbene with molecular oxygen, which resulted in the formation of stilbene oxide. Since the choice of the lanthanide had virtually no influence on the performance of the catalyst, only the manganese–gadolinium was studied in detail. The influence of solvent, catalyst concentration, reaction temperature, oxidant, and oxidant flow rate on conversion, yield, and selectivity was analyzed. A conversion of up to 70 %, the formation of 61 % stilbene oxide (88 % selectivity), and a TON of 84 were observed after 24 h. A hot filtration test confirmed that the reaction is mainly catalyzed through a heterogeneous pathway, although a minor contribution of homogeneous species could not be completely excluded. The catalyst could be reused without significant loss of activity.     

Multivalent interaction and selectivities in selectin binding of functionalized gold colloids decorated with carbohydrate mimetics

Colloidal gold particles with functionalized organic shells were applied as novel selectin binders. The ligand shell was terminated with different monocyclic carbohydrate mimetics as simplified analogs of the sLe(x) unit found in biological selectin ligands. The multivalent presentation of the sulfated selectin binding epitopes on the gold particles led to extremely high binding affinities towards L- and P-selectin and IC(50) values in the subnanomolar range. Depending on the ring size of the sulfated carbohydrate mimetic, its substitution pattern and its configuration, different selectivities for either L-selectin or P-selectin were obtained. These selectivities were not found for gold particles with simple acyclic sulfated alcohols, diols and triols in the ligand shell. In addition, the influence of the particle size and the thickness of the hydrophobic organic shell were systematically investigated.     

Long-Term Monokaryotic Cultures of Pleurotus ostreatus var. florida Produce High and Stable Laccase Activity Capable to Degrade ß-Carotene

An extracellular laccase (Lacc10) was discovered in submerged cultures of Pleurotus ostreatus var. florida bleaching ß-carotene effectively without the addition of a mediator (650 mU/L, pH 4). Heterologous expression in P. pastoris confirmed the activity and structural analyses revealed a carotenoid-binding domain, which formed the substrate-binding pocket and is reported here for the first time. In order to increase activity, 106 basidiospore-derived monokaryons and crosses of compatible progenies were generated. These showed high intraspecific variability in growth rate and enzyme formation. Seventy-two homokaryons exhibited a higher activity-to-growth-rate-relation than the parental dikaryon, and one isolate produced a very high activity (1800 mU/L), while most of the dikaryotic hybrids showed lower activity. The analysis of the laccase gene of the monokaryons revealed two sequences differing in three amino acids, but the primary sequences gave no clue for the diversity of activity. The enzyme production in submerged cultures of monokaryons was stable over seven sub-cultivation cycles.

     

On the Sensitiveness of Absorption Coefficient to Changes in Material Parameters

An essential property of porous absorbers is the resistance to the incident sound wave, resulting in a damping effect. Damping results from the friction between air molecules and absorber pore-walls. In practice, the known dependencies of the sound absorption coefficient are used in the design of absorbers. But not every material can be characterized by a one-parameter model. The reliability of prediction can be improved by using detailed material models. Hence, additional material parameters, especially the pore geometry are needed. Since in practice the effort for determining material parameters must be minimized, this paper discusses the sensitivity of prediction of absorbers' performance depending on the influence of material parameters that are input for the prediction model chosen. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Charged boson stars and black holes

We consider boson stars and black holes in scalar electrodynamics with a V-shaped scalar potential. The boson stars come in two types, having either ball-like or shell-like charge density. We analyze the properties of these solutions and determine their domains of existence. When mass and charge become equal, the space–times develop a throat. The shell-like solutions need not be globally regular, but may possess a horizon. The space–times then consist of a Schwarzschild-type black hole in the interior, surrounded by a shell of charged matter, and thus a Reissner–Nordström-type space–time in the exterior. These solutions violate black hole uniqueness. The mass of the black hole solutions is related to the mass of the regular shell-like solutions by a mass formula of the type first obtained within the isolated horizon framework.     

Enantioselective analysis of ketamine and its metabolites in equine plasma and urine by CE with multiple isomer sulfated beta-CD

CE with multiple isomer sulfated beta-CD as the chiral selector was assessed for the simultaneous analysis of the enantiomers of ketamine and metabolites in extracts of equine plasma and urine. Different lots of the commercial chiral selector provided significant changes in enantiomeric ketamine separability, a fact that can be related to the manufacturing variability. A mixture of two lots was found to provide high-resolution separations and interference-free detection of the enantiomers of ketamine, norketamine, dehydronorketamine, and an incompletely identified hydroxylated metabolite of norketamine in liquid/liquid extracts of the two body fluids. Ketamine, norketamine, and dehydronorketamine could be unambiguously identified via HPLC fractionation of urinary extracts and using LC-MS and LC-MS/MS with 1 mmu mass discrimination. The CE assay was used to characterize the stereoselectivity of the compounds' enantiomers in the samples of five ponies anesthetized with isoflurane in oxygen and treated with intravenous continuous infusion of racemic ketamine. The concentrations of the ketamine enantiomers in plasma are equal, whereas the urinary amount of R-ketamine is larger than that of S-ketamine. Plasma and urine contain higher S- than R-norketamine levels and the mean S-/R-enantiomer ratios of dehydronorketamine in plasma and urine are lower than unity and similar.