Nido-6-metalladecaborane chemistry: Molecular structure and fluxionality of [6,6,6,6-(CO)2(PPh3)2-nido-6-WB9H13]

The molecular and crystal structure of the nido-6-tungstadecaborane [6,6,6,6-(CO)₂(PPh₃)₂-nido-6-WB₉H₁₃] (1) has been determined showing that the tungsten atom is incorporated into the 6-position of a nido 10-vertex (WB₉) cage. The tungsten atom has a seven-coordinate capped trigonal prismatic environment and is bonded to two hydrogen and three boron atoms of the {B₉H₁₃} cage, in addition to two CO groups and two PPh₃ ligands. Variable-temperature (−90°C to +50°C) ³¹P{¹H} NMR spectroscopy of 1 reveals that the exo-polyhedral ligands about the tungsten atom are fluxional with respect to PPh₃ site exchange with an activation energy (ΔG‡), at the coalescence temperature (−73°C), of <38 kJ mol⁻¹.     

Radiative transfer for a cylindrical beam scattered isotropically

Radiation intensities in an isotropically scattering slab irradiated by a cylindrical beam have been obtained by numerical solution of the radiative transport equation in two dimensions. In contrast to the usual one-dimensional solutions, solutions to the two-dimensional case provide a basis for the use of a narrow diagnostic beam to examine optically-thick media. It is shown that measurements of the intensity of radiation scattered from a narrow beam in an optically-thick slab, as well as of the transmitted beam, can be used to deduce the albedo and the optical thickness.     

Electrochemical detection of aniline: an electrochemically initiated reaction pathway

The electrochemically initiated reaction of aromatic amines with catechol has been examined as a facile route to the electrochemical determination of the former. The effects of the different structural isomers of sulfanilic acid on the analytical system has been studied and appraised. The report illustrates how by varying oxidation times of the catechol species or by increasing the number of repetitive voltammetric scans from one to four the analytical parameters (linear range and limit of detection) can be improved. The results provide a linear detection range of 2-40 muM for aniline with a corresponding limit of detection of 1.4 muM. The efficacy of the approach has been shown by a 99.5% (RSD=5.5%, N=5) recovery of 2.47 muM spiked aniline in river water.     

Some new mitragyna-type indoles and oxindoles; The influence of stereochemistry on mass spectra

The indole alkaloids corynantheidine and paynantheine have been epimerized to two new compounds and corynantheidine and mitragynine have been transformed to the corresponding oxindoles. The stereochemistry of the new compounds is deduced from physical data. Mass spectral fragmentation of the mitragyna indole and oxindole alkaloids is discussed with reference to their stereochemistry.     

Identification and quantitative analysis of phendimetrazine and some of its metabolites in biological fluids

In urine, after oral doses of phendimetrazine to man, were found unchanged drug, the N-demethylated metabolite, phenmetrazine, and the N-oxide of phendimetrazine, but not N-hydroxyphenmetrazine; the metabolites were identified using t.l.c. and g.l.c. The stability of the drug and its metabolites in biological fluids and in ether was studied. A gas chromatographic procedure for the quantitative determination of unchanged drug, its N-oxide and phenmetrazine in urine, plasma and saliva was developed, the N-oxide being reduced before analysis.

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Identifizierung und quantitative Analyse von Phendimetrazin und einigen Metaboliten in biologischen Flüssigkeiten

Zusammenfassung Nach oralen Dosen von Phendimetrazin an Menschen wurde im Harn unverändertes Phendimetrazin, der N-demethylierte Metabolit, Phenmetrazin und das N-Oxid von Phendimetrazin, nicht jedoch N-Hydroxyphenmetrazin gefunden; die Metaboliten wurden mittels TLC und GLC identifiziert. Die Stabilität von Phendimetrazin und dessen Metaboliten wurde in biologischen Flüssigkeiten und in Ether untersucht. Es wurde eine gaschromatographische Methode für die quantitative Bestimmung von Phendimetrazin, seinem N-Oxid und Phenmetrazin in Harn, Plasma und Speichel entwickelt, wobei das N-Oxid vor der Analyse reduziert wurde.

     

Assessment of the distribution of pesticides on soil particle fractions in simulated irrigation run-off using centrifugal SPLITT fractionation and ELISA

This study was designed to measure the distribution of pesticides within the mobile phase of simulated irrigation run-off water, using centrifugal split-flow thin-channel (SPLITT) fractionation, a novel technique providing a gentle separation of natural sediment and suspended particles. Particular attention is paid to the extraction of pesticide residues for enzyme-linked immunosorbent assay (ELISA) analysis; ELISA was used because of the limited sample size.Centrifugal SPLITT fractionation combined laminar flow hydrodynamics and centrifugal sedimentation to obtain a continuous binary separation of suspended particles. The non-destructive technique allowed an accurate separation of particles into fractions with divisions at 0.5, 2 and 10 μm, with those above 25 μm being performed by wet sieving. ELISA was used to analyse the concentration of endosulfan and diuron for each fraction generated by the SPLITT technique.This data can be used to determine the role that particulate fines and colloidal fractions play in the transport of bound organic pollutants within the environment and to examine prospects for remediation on farms.     

Synthetic 6-aryl-2-hydroxy-6-ketohexa-2,4-dienoic acid substrates for C-C hydrolase BphD: investigation of a general base catalytic mechanism

A chemical synthesis of the 2-hydroxy-6-ketohexa-2,4-dienoic acid intermediates on bacterial meta-cleavage pathways has been established, using a Heck coupling strategy. Coupling of ethyl 3-bromo-2-acetoxyacrylate with 1-aryl vinyl ketals or 1-aryl allylic alcohols proceeded in 70-90% yield. Heck coupling with an alkyl vinyl ketal was also successful, allowing the synthesis of an alkyl-substituted ring fission intermediate. The synthetic ring fission intermediates were used to investigate the enzymatic reaction catalysed by C-C hydrolase BphD from Pseudomonas LB400. A reduced substrate analogue 2,6-dihydroxy-6-phenylhexa-2,4-dienoic acid was processed enzymatically to benzaldehyde by C-C hydrolase BphD, consistent with a catalytic mechanism involving general base-catalysed attack of water to give a gem-diol intermediate, and not consistent with a nucleophilic mechanism. A series of para-substituted 2-hydroxy-6-keto-6-phenylhexa-2,4-dienoic acid substrates were assayed against BphD, and the derived Hammett plot (rho=-0.71) is consistent with a departing carbanion in the transition state for C-C cleavage.     

Effect of saline groundwater on the aggregation and settling of suspended particles in a turbid Australian river

Laboratory studies have modelled the interaction of Darling River water and a saline groundwater intrusion. Kinetic measurements have shown that the rate determining step in water column clarification is the aggregation of small colloidal particles which then settle rapidly after reaching a critical diameter. Divalent cations (Ca²⁺ and Mg²⁺) are extremely effective in enhancing the rate of clarification by increasing the colloid stability factor. Three different phases have been observed in the cation-mediated removal of iron from solution: (i) rapid coagulation induced by the initial velocity shear resulting from solution mixing; (ii) a slower second-order iron removal, consistent with conventional aggregation kinetics; and (iii) a decrease in rate after 90% iron removal which is attributed to a lower iron content in the ultrafine colloid fraction. Specific interactions between the divalent cations and the organic coatings on the particles are proposed in order to explain the much higher rate of coagulation than expected on electrostatic grounds when compared with the monovalent Na⁺ and K⁺.

Water column clarification occurred more rapidly in these model laboratory studies than was observed in the Darling River weir pool. Iron removal rates in the river tend to be inhibited by hydrological effects. Turbulence inducing processes are required to mix the dense saline groundwater with the overlying water column and thus may ultimately limit the rate of turbidity reduction.     

Voltammetric investigation of hair dye constituents: application to the quantification of p-phenylenediamine.

The application of electrochemical techniques to the determination of common hair dye constituents was investigated. Cyclic voltammetry was used to probe the electrode response to p-phenylenediamine (PPD), 4-chlororesorcinol and m-aminophenol with square wave voltammetry used to effect quantitative measurements. The nature of the electrode response was characterised and issues of surface fouling resulting from the deposition of electrogenerated reaction products were addressed. A procedure designed to allow the facile determination of PPD in hair care products is presented.