Direct conversion of N-methoxy-N-methylamides (Weinreb amides) to ketones via a nonclassical Wittig reaction

[reaction: see text] N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product.     

Novel deoxygenation reaction of epoxides by indium

[reaction: see text] A novel, mild, ecofriendly protocol for the deoxygenation of epoxides to alkenes using indium metal and indium(I) chloride or ammonium chloride in alcohol has been developed. It was necessary for the presence of good radical-stabilizing groups adjacent to the oxirane ring for the deoxygenation reaction to occur. It is proposed that this reaction occurs through an SET process with indium as an electron donor.     

A New Route to Crystalline Salts of the Hydrolytic Dimer of Chromium(III)

Crystalline salts of the hydrolytic dimer of Cr(III), [Cr₂(μ-OH)₂(H₂O)₈]X₄·n H₂O (X = p-toluenesulfonate (tos) or mesitylene-2-sulfonate (dmtos)) have been prepared in good yields via a simple two-step procedure: H⁺ oxidation of Cr metal to give Cr²⁺ (T ≈? 70°) followed by O₂ oxidation, of Cr²⁺ to give the dimer (T ≈? 25°). The mechanism of conversion of Cr²⁺ into the dimer is discussed.     

CdS nanoclusters stabilized by thiolate ligands: A mini-review

One of the most exciting frontiers in materials chemistry in recent years is the optoelectronics of quantum-confined semiconductor nanoclusters. These nanoclusters are 10–200 A in diameter, and in this size regime exhibit extra-ordinarily interesting quantum mechanical effects. Cadmium sulfide is a popular semiconductor for these studies, and reviewed here is the synthesis and charac-terization of such CdS nanoclusters, with emphasis on how chemical control of the surface by thiolates influences product formation and properties. Also described are the syntheses and structures of true molecular clusters of CdS capped with thiolate ligands.     

The determination of aluminium in seawater and freshwater by cathodic stripping voltammetry

Dissolved aluminium in seawater and freshwater is determined by cathodic stripping voltammetry (c.s.v.) preceded by adsorptive collection of complex ions with 1,2-dihydroxyanthraquinone-3-sulphonic acid (DASA) on the hanging mercury drop electrode. Complexation of aluminium by DASA is rapid and no waiting period or heating of the sample is required. Optimal conditions are a DASA concentration of 10^?5 M, a solution pH of 7.1–7.3 and an adsorption potential of ?0.9 V; the c.s.v. scan is done in the differential-pulse mode. The limit of detection is 1 nM aluminium for an adsorption time of 45 s. The total time needed, including 50min deaeration and a standard addition, is 10–15 min per sample. No serious interferences were found; u.v. irradiation is recommended for samples containing high levels of organic materials.     

Synthesis of alpha-glucuronic acid and amide derivatives in the presence of a participating 2-acyl protecting group

[reaction: see text] Participating acyl groups located at C-2 in glucosyl and related donors generally promote formation of 1,2-trans-glycosides. Reactions of some glucuronic acid donors with TMSN(3)/SnCl(4) or ROH/SnCl(4) gave only the 1,2-cis-glycoside. The stereoselectivity is consistent with participation of the C-6 group. The methodology was used for the synthesis of a Kdn2en mimetic with the alpha-configuration.     

Rapid PCR in a continuous flow device

Continuous flow polymerase chain reaction (CFPCR) devices are compact reactors suitable for microfabrication and the rapid amplification of target DNAs. For a given reactor design, the amplification time can be reduced simply by increasing the flow velocity through the isothermal zones of the device; for flow velocities near the design value, the PCR cocktail reaches thermal equilibrium at each zone quickly, so that near ideal temperature profiles can be obtained. However, at high flow velocities there are penalties of an increased pressure drop and a reduced residence time in each temperature zone for the DNA/reagent mixture, that potentially affect amplification efficiency. This study was carried out to evaluate the thermal and biochemical effects of high flow velocities in a spiral, 20 cycle CFPCR device. Finite element analysis (FEA) was used to determine the steady-state temperature distribution along the micro-channel and the temperature of the DNA/reagent mixture in each temperature zone as a function of linear velocity. The critical transition was between the denaturation (95 degrees C) and renaturation (55 degrees C-68 degrees C) zones; above 6 mm s(-1) the fluid in a passively-cooled channel could not be reduced to the desired temperature and the duration of the temperature transition between zones increased with increased velocity. The amplification performance of the CFPCR as a function of linear velocity was assessed using 500 and 997 base pair (bp) fragments from lambda-DNA. Amplifications at velocities ranging from 1 mm s(-1) to 20 mm s(-1) were investigated. The 500 bp fragment could be observed in a total reaction time of 1.7 min (5.2 s cycle(-1)) and the 997 bp fragment could be detected in 3.2 min (9.7 s cycle(-1)). The longer amplification time required for detection of the 997 bp fragment was due to the device being operated at its enzyme kinetic limit (i.e., Taq polymerase deoxynucleotide incorporation rate).     

Determination of malachite green and leucomalachite green in a variety of aquacultured products by liquid chromatography with tandem mass spectrometry detection

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for determining the residues of malachite green (MG) and leucomalachite green (LMG) in a number of aquatic species. MG and its metabolite were extracted from homogenized tissues with a perchloric acid-acetonitrile solution; the extract was centrifuged; and an aliquot was taken, concentrated, and passed through a chemically bonded octadecyl C18 solid-phase extraction column. The compounds of interest were eluted with acetonitrile, and the eluate was evaporated to dryness. The residue was dissolved in acetonitrile and diluted with water in preparation for analysis by LC/MS/MS. MG and its metabolite were determined by reversed-phase LC using a Luna C18 column with an ammonium hydroxide-formic acid buffer in acetonitrile gradient and MS/MS detection using multiple reaction monitoring. Calibration curves were linear for all analyses between 5 and 500 pg injected for both analytes, with recoveries ranging from 81% for LMG to 98% for MG in salmon spiked at the 1 ng/g level. Detection limits of 0.1 ng/g for both MG and LMG were easily obtainable using the recommended method. The operational errors, interferences, and recoveries for spiked samples compared favorably with those obtained by established methodology. The recommended method is simple, rapid, and specific for monitoring residues of MG and LMG in a number of aquatic species.     

Quality control of a detector for the calculations of radiopharmacokinetic parameters of 99mTc-glucarate in rats

Good manufacturing practices specify that a well-type scintillation NaI(Tl) crystal detector has to be validated in order to detect radioactivity from any radiopharmaceutical used to obtain radiopharmacokinetic parameters. A 5 cm well-type NaI(Tl) scintillation detector was coupled to a multi-channel analyzer centered at the 140 keV ^99mTc peak with a 20% window. The area represents counts per minute (cpm). All the net cpm were decay corrected. The activity source was ^99mTc-glucarate developed as an imaging agent for acute myocardial infarction. Wistar rats were injected in a tail vein with 0.1 ml (3.7 MBq) of ^99mTc-glucarate solution and 13 blood samples were taken. The cpm were the input data for the WINNONLN program which calculates radiopharmacokinetic parameters. The detector's efficiency for ^99mTc was 15.03% and the sensitivity 1.12 kBq/ml in plasma. The response was linear between 0.31-14.3 kBq/ml of ^99mTc-glucarate. The maximum assay variation coefficient was 2.79 and recovery of ^99mTc-glucarate in plasma was 99.8%±0.2%. LOD was 0.31 kBq and LOQ = 1.12 kBq in plasma samples. ^99mTc-glucarate follows a two-compartment model of distribution with Vd of 21.74 ml±2.71 ml; a Vdss of 74.36 ml±12.67 ml; t _{1/2 a}0.74 h±0.19 h; t _{1/2 b} 18.98 h±4.36 h; AUC = 32.75 mCi/min^.ml ± 3.73 mCi/min^.ml; MRT = 24.35 h±5.51 h and total clearance 3.05 ml/h±0.35 ml/h. The well-type detector fulfills the quality system requirements and the radiopharmacokinetic parameters for ^99mTc-glucarate in rats are reliable. This revised version was published online in July 2006 with corrections to the Cover Date.