Palladium catalysed aryl amination reactions in supercritical carbon dioxide

Palladium catalysed C-N bond formation in supercritical carbon dioxide has been accomplished. Carbamic acid formation is avoided in part through the use of an N-silylamine as the coupling partner. Employing a catalyst system of Pd2dba3(1 mol%) and 2-dicyclohexylphosphino-2',4',6'-triisopropyl-1,1'-biphenyl (X-Phos)(2 mol%) enabled the catalytic amination of aryl bromides and chlorides with N-silylanilines to be realised in excellent yield. Extension of the methodology to the N-arylation of N-silyldiarylamines, N-silylazoles and N-silylsulfonamides is reported.     

Luminescent rhenium(I) diimine indole conjugates--photophysical, electrochemical and protein-binding properties

Two novel luminescent rhenium(I) diimine indole complexes have been designed and their properties studied; these conjugates can be recognised by indole-binding proteins including bovine serum albumin, lysozyme and tryptophanase.     

Poly(ethylene glycol)-supported nitroxyls: branched catalysts for the selective oxidation of alcohols

Nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) are highly selective oxidation catalysts for the conversion of primary alcohols into the corresponding aldehydes. In this study, direct tethering of TEMPO units onto linear poly(ethylene glycol) (PEG) has afforded macromolecular catalysts that exhibit solubility in both aqueous and organic solvents. Recovery of the dissolved polymer-supported catalyst has been carried out by precipitation with a suitable solvent such as diethyl ether. The high catalyst activities and selectivities associated traditionally with nitroxyl-mediated oxidations of alcohols are retained by the series of "linker-less" linear PEG-TEMPO catalysts in which the TEMPO moiety is coupled directly to the PEG support. Although the selectivity remains unaltered, upon recycling of the linker-less polymer-supported catalysts, extended reaction times are required to maintain high yields of the desired carbonyl compounds. Alternatively, attachment of two nitroxyl radicals onto each functionalized PEG chain terminus via a 5-hydroxyisophthalic acid linker affords branched polymer-supported catalysts. In stark contrast to the linker-less catalysts, these branched nitroxyls exhibit catalytic activities up to five times greater than 4-methoxy-TEMPO alone under similar conditions. In addition, minimal decrease in catalytic activity is observed upon recycling of these branched macromolecular catalysts via solvent-induced precipitation. The high catalytic activities and preservation of activity upon recycling of these branched systems is attributed to enhanced regeneration of the nitroxyl species as a result of intramolecular syn-proportionation.     

Mechanism of alkyl halide photolysis by a pulsed CO2 tea laser

A CO₂ TEA laser has been used to photolyze dilute samples of various alkyl halides in helium. The mechanism of the high intensity infrared photolysis of these molecules involves the decomposition of molecules into molecular or radical fragments. The reaction pathway is always dissociation into the lowest thermal dissociation channel(s) of the molecule photolyzed. Products from the initial process are also photo-dissociated by the laser pulse and their decomposition pathways are similarly governed. The molecules being photolyzed are not thermally equilibrated with the bath or with each other and the molecular-specific nature of the laser excitation is demonstrated.     

DETERMINING THE OPTIMAL DOSE OF PHOTOFRIN® IN MINISWINE ATHEROSCLEROTIC PLAQUE

The purpose of this study was to determine the lowest dose of Photofrin (P) that would produce a 3:1 or greater ratio between atherosclerotic (AS) and control arterial walls. Aortoiliac AS was created in 24 Yucatan miniswine by a combination of balloon endothelial injury and 2% cholesterol and 15% lard diet for 7 weeks. Arteriography was then performed to demonstrate AS lesions. Following this, swine were given intravenously P in one of the following single dosages: 2.5, 1.0 or 0.5 mg/kg. Twenty-four hours later, swine were sacrificed and aortoiliac and control carotid artery segments removed and photographed with ultraviolet light to differentiate fluorescent from nonfluorescent areas. Arterial specimens were submitted for histologic analysis and chemical extraction for determination of fluorescence using a spectrofluorometer. Tissue concentration (ng/g tissue) of P from AS vessels were: Group I, 130.4 ± 82.7; Group II, 10.0 ± 1.2; and Group HI, 9.1 ± 0.6, respectively (P < 0.05). Ratios of P concentration in AS:control vessels were: Group I, 8.1 ± 13.7; Group II, 1.1 ± 0.2; and Group III, 0.9 ± 0.1, respectively (P < 0.05). These results demonstrated that a P dose of 2.5 mg/kg provided at least a 3:1 ratio between AS:control artery wall.     

Application of free-radical chromogens to determination of nitrite and nitrate ions by EPR spectrometry

Various azines and substituted phenylene diamines are oxidized by the nitrite ion to give stable radicals in an autocatalytic reaction. This finding has now been developed into highly sensitive methods for nitrite determination by EPR spectrometry. Thus, when the reagent is phenothiazine, the detection limit for nitrite is 0.012 ppm, the relative standard deviation at 0.05 ppm is 1.9%, and the analytical range is 0-1.5 ppm. With N,N,N',N'-tetramethyl-p-phenylenediamine as the reagent, the corresponding values are 0.025 ppm, 2.6%, and 0-1.3 ppm. Nitrate can be determined after prior reduction to nitrite. A mixture of nitrite and nitrate ions can also be quantitatively analysed. The EPR methods were applied to the determination of the nitrite and nitrate contents of prepacked cooked ham and of soft-spreading cheese. The results agreed well with those obtained by ISO and AOAC standard methods for these samples. ca*|Author for correspondence.     

Synthesis of Lower Valent Molybdenum Oxides by an Ambient Temperature Reduction of Aqueous K(2)MoO(4) by KBH(4)

Reduction of aqueous K(2)MoO(4) with aqueous KBH(4) at ambient temperatures has been investigated systematically to obtain lower valent molybdenum oxides. Several lower valent oxides such as MoO(2), Mo(4)O(11), K(0.26)MoO(3) (red bronze), K(0.30)MoO(3) (blue bronze), and K(0.85)Mo(6)O(17) are formed during the reduction process; however, only MoO(2) has been obtained as single-phase product. The nature of the product formed is strongly influenced by the reducing power of KBH(4). The reducing power increases with decreasing pH or increasing concentration and volume of KBH(4). The as-prepared samples are amorphous as revealed by X-ray diffraction and transmission electron microscopy. They crystallize sharply at around 350-500 degrees C as revealed by differential scanning calorimetry. Since the products formed are amorphous in nature, they may become particularly attractive for battery electrodes and catalysis.