Detection of streptomycin and dihydrostreptomycin residues in milk,honey and meat samples using an optical biosensor

Immuno-biosensor inhibition assays for the detection of streptomycin and dihydrostreptomycin residues in whole cows' milk, honey, pig kidney and pig muscle are reported. The antibody showed high cross-reactivity with dihydrostreptomycin in various foodstuffs (buffer 103%, milk 96%, honey 84%, kidney extract 129% and muscle extract 98%). There was no significant cross-reaction with other aminoglycosides or commonly used antibiotics. A streptomycin derivative was used to prepare a stable, reusable sensor chip surface. The assay allowed the direct analysis of bovine whole milk (fat content approximately 3.5%). Honey samples required dilution with buffer, while kidney and muscle samples from pigs were homogenized in an aqueous extraction buffer and clarified by centrifugation. The limit of detection for each assay was determined from known streptomycin-free samples (n = 20; mean - (3 x standard deviation)) and the results were as follows: milk 30 microg kg(-1), honey 15 microg kg(-1), kidney 50 microg kg(-1) and muscle 70 microg kg(-1). Repeatability (or relative standard deviation) between runs were calculated (n = 3) at the respective Community maximum residue limits (MRL) and 0.5 x MRL with the exception of honey since no European MRL exists at present. Results were determined as 4.3% (200 microg kg(-1)) and 2.8% (100 microg kg(-1)) in milk, 13.3% (40 microg kg(-1)) and 9.5% (20 microg kg(-1)) in honey, 7.1% (1000 microg kg(-1)) and 7.6% (500 microg kg(-1)) in kidney and 7.1% (500 microg kg(-1)) and 11% (250 microg kg(-1)) in muscle.     

2,8'-disubstituted-1,1'-binaphthyls: a new pattern in chiral ligands

The title binaphthyls 19 and 26, which are the positional isomers of 2-methoxy-2'-(diphenylphosphino)-1,1'-binaphthyl (MOP, 19) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN, 26), have been synthesized by Suzuki coupling as the key step (10 + 15-->18), followed by functional group transformations, involving C-P and C-N bond formation (18-->19 and 18-->23). Racemic intermediate 22 was resolved by co-crystallization with N-benzylcinchonidinium chloride and the absolute configuration determined by X-ray crystallography. These novel binaphthyls are configurationally stable and, as such, potentially usable as chiral ligands in asymmetric reactions. Michael addition of the glycine-derived enolate 40 to methyl acrylate, carried out in the presence of (R)-(-)-27 as the chiral phase-transfer catalyst, afforded L-glutamic acid (S)-(+)-43 of 92% ee (after hydrolysis of the primary product).     

The effects of oligomerization on <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> Mcm4/6/7 function

Background  

Minichromosome maintenance proteins (Mcm) 2, 3, 4, 5, 6 and 7 are related by sequence and form a variety of complexes that unwind DNA, including Mcm4/6/7. A Mcm4/6/7 trimer forms one half of the Mcm2-7 hexameric ring and can be thought of as the catalytic core of Mcm2-7, the replicative helicase in eukaryotic cells. Oligomeric analysis of Mcm4/6/7 suggests that it forms a hexamer containing two Mcm4/6/7 trimers, however, under certain conditions trimeric Mcm4/6/7 has also been observed. The functional significance of the different Mcm4/6/7 oligomeric states has not been assessed. The results of such an assessment would have implications for studies of both Mcm4/6/7 and Mcm2-7.     

Gasanalytische Apparate und Methoden

Ohne Zusammenfassung     

Confinement of halide ions within homologous inverse coordination hosts; modification of halide-ion selectivity

The structures of a series of spherical host-guest complexes [{MeE(PPh)(3)Li(4)·3thf}(4)(μ(4)-X)](-) (E = Al, [1X](-); E = Ga, [2X](-); E = In, [3X](-)) reveal that changing the halide ions (X = Cl, Br, or I) within their central tetrahedral Li(4) sites has negligible effect on the structural parameters.     

Structural, solid-state NMR and theoretical studies of the inverse-coordination of lithium chloride using group 13 phosphide hosts

The reaction of MeAlCl2 with 'PhPLi2' in THF gives [{MeAl(PPh)3Li(4).3 THF}4(mu4-Cl)]-Li+ (1). The GaIII and InIII analogues, [{MeE(PPh)3Li(4).3 THF}4(mu4-Cl)]-Li+(THF)3 (E=Ga (2), In (3)), are obtained by the in situ reactions of MeECl2 with PhPLi2 in THF. For all of the complexes, the cage anions have an unusual cubic arrangement that is similar to a zeolite, and contain large voids (ca. 17 A). The location of the Li+ counterions in 1-3 and their coordination environment appears to subtly reflect variations in packing and lattice energy. Whereas in 1 highly mobile, loosely coordinated Li+ counterions are present, 2 and 3 contain less mobile THF-solvated counterions within the cavities. X-ray crystallographic and solid-state NMR studies are reported on 1-3, together with model DFT calculations on the selectivity of halide coordination.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.