Biosensor assay of sulfadiazine and sulfamethazine residues in pork

Biosensor-based immunochemical screening assays for the detection of sulfadiazine (SDZ) and sulfamethazine (SMT) in muscle extract from pigs were developed. Samples were extracted with aqueous buffer and then centrifuged. This simple and straightforward preparation allowed up to 40 samples to be processed and analysed in 1 d. The limits of detection for the assays were found to be 5.6 ng g-1 for SDZ and 7.4 ng g-1 for SMT. These figures were well below the European and US legal limits for sulfonamides (100 ng g-1). The precision (RSD) between runs was < 8% and the recovery was between 91 and 98%. The validation proved the assays to be accurate and the analysis of routine field samples showed good correlation with an established TLC screening procedure. No false negative or positive results were obtained with blank and spiked samples. The influence of cross-reacting metabolites on immunoassays was demonstrated by testing incurred tissue samples, collected from sulfonamide treated pigs after only a short withdrawal period. The quantitative results obtained by biosensor analysis were a combination of parent sulfonamide plus N4-acetyl metabolite while the HPLC method used for confirmatory analysis detected only the parent sulfonamide. This gave rise to some false positive results and highlighted the need to use real samples in evaluating any assay thoroughly. False negative results were not obtained.     

Self-assembly,characterisation, and crystal structure of multinuclear metal complexes of the [2 x 3] and [3 x 3] grid-type

The self-assembly of new multimetallic complexes of grid-type architecture is described. The binding of a set of tris-terdentate ligands, 1 a-1 d, based on terpyridine-like subunits, with different octahedrally coordinated metal ions leads to the formation of species whose structure depends strongly on the ligand, the metal ion, the counterion, the solvent, and the reaction conditions. Under suitable conditions, the [3 x 3] grid was obtained from the reaction of ligand 1 a with zinc tetrafluoroborate and from ligand 1 b with mercury triflate. The other ligands led to the formation of mainly one compound of composition [M(6)L(5)](12+), which has the structure of an incomplete [2 x 3] grid. The crystal structure of such a [2 x 3] grid, [Co(6)(1 d)(5)](12+), has been determined. In this complex, the three central pyrimidine-pyridine-pyrimidine non-coordinating sites adopt transoid NCbond;CN conformations. The much less stable cisoid conformations, the "pinching" of the coordination sites in the complex, the weaker donor strength of the central binding site, and the steric demand of the substituents are all factors contributing to the reluctance to produce the [3 x 3] structure. A subtle interplay between the nature of the metal, the steric demand of the ligand, the reaction conditions, and the type of counterion determine the product of self-assembly. The results obtained show that by tuning the parameters, complexes containing six or nine octahedrally coordinated metal ions in a well-defined grid-type arrangement are accessible. Both types of arrays, [2 x 3] and [3 x 3 ], are of interest as self-assembled inorganic architectures of well-defined structure and nuclearity that may be suitable prototypes for selective information storage media.     

Test of the generalized standard addition method and linearization algorithms for the direct,simultaneous, multi-element analysis of solid samples by electrothermal atomic absorption spectrometry

The application of a multi-element electrothermal atomic absorption spectrometry (ETAAS) instrument with line sources and Zeeman-effect background correction to the direct, simultaneous determination of Ag, Cd, Cr and Pb in solid reference materials is described. Due to the occurrence of interference effects, the generalized standard addition method (GSAM) was required for calibration purposes. In order to extend the dynamic range for analytes present at high concentrations, linearization algorithms were tested. The combination of the GSAM and extension of the linear range, when necessary, generally yielded acceptable analytical results for the suite of elements studied, and may provide a useful approach to calibration in the direct analysis of solid samples by multi-element ETAAS. However, while linearization yielded good results for Ag and Cd in solid reference materials, it remains to be demonstrated that acceptable performance can be obtained for other elements in real samples.     

Biosynthesis of pebrolide

In pebrolide biosynthesised from MVA-[2.2-³H₂], 1, 1$\text{1}\text{3}$ and 2 tritium atoms respectively are retained at C-1, C-15 and C-7.     

Critical comparison of two standard digestion procedures for the determination of total mercury in natural water samples by cold vapour atomic absorption spectrometry

Two pretreatment procedures for total mercury determinations in natural water samples were compared. The first, the Swedish Standard method (DP1), involves digestion of water in the presence of concentrated nitric acid at 120°C and under pressure for 30 min. In the West German Standard method (DP2), small volumes of nitric and sulphuric acids, permanganate and peroxodisulphate are added to the sample, and digestion proceeded at 50°C in an ultrasonic bath. Mercury was determined after both digestion procedures using a modified cold vapour atomic absorption spectrometric method, in which mercury generated on addition of a reducing agent is collected and subsequently atomized in a platinum-lined graphite furnace. The efficacy of the two digestion procedures was tested using various standard organic mercury compounds and it was found that only DP2 provided quantitative recoveries. Purification of the reagents required by DP2 was achieved using a mercury-selective ion-exchange resin, Chelite S, resulting in blank levels below 1.5 ng Hg l^?1. Both methods were applied to the determination of total mercury in an unpolluted marsh water sample, giving 2.0 ng Hg l^?1 (DP1) and 2.7 ng Hg l^?1 (DP2). The West German Standard digestion procedure (DP2) is recommended for the determination of total mercury in natural water samples.     

Speciation of mercury in human whole blood by capillary gas chromatography with a microwave-induced plasma emission detector system following complexometric extraction and butylation.

Methyl- and inorganic mercury were extracted from human whole blood samples, as their diethyldithiocarbamate complexes, into toluene and butylated by using a Grignard reagent. The mercury species were then separated by gas chromatography (on a 12 m non-polar DB-1 capillary column) and detected by a microwave-induced plasma atomic emission spectrometric (GC-MPD) system. The accuracy and precision of the proposed method were established by the analysis of Seronorm lyophilized human whole blood standards for methyl- and inorganic mercury. No statistical difference (t-test) between the sum of these two species determined by the GC-MPD based method and the recommended total mercury concentrations in the Seronorm samples was observed. Results for the determination of methyl- and inorganic mercury in 60 controls and 90 previously occupationally exposed (to inorganic mercury) workers are presented to illustrate the practical utility of the proposed method. No significantly elevated inorganic mercury concentrations between the two groups were evident.     

Determination of polycyclic aromatic hydrocarbons by electron spin resonance spectrometry

The use of electron spin resonance spectrometry with a modern instrument is described for the determination of polynuclear aromatic hydrocarbons (PAHs) down to nanogram levels, after adsorption on calcined silica/alumina. A single PAH or the total number of moles of PAHs can be determined. Implication for liquid chromatography are discussed.     

SC-MEH-MO calculations on high Tc superconductors. 1: The YBa2Cu8O cluster in YBa2Cu3O7

SC-MEH-MO calculations have been carried out on select clusters of the YBa₂Cu₃O₇ lattice structure. The results of an earlier computation on small CuO clusters are presented for comparison with the finding obtained on a YBa₂Cu₈O₂₆⁺ extended cluster. In the latter, the antiferromagnetic coupling of singularly occupied Cu and O levels is analyzed.     

On the direct analysis of solid samples by graphite furnace atomic absorption spectrometry

Summary We have studied some limitations of the solid sampling, cup-in-tube technique by comparison with a constant temperature two-step atomiser and found consistently lower vapour-phase temperatures and greater interferences in the former. With the former, higher vapour-phase temperatures and improved analytical results for lead and cadmium were found using Pd(NO₃)₂+Mg(NO₃)₂ instead of NH₄H₂PO₄+Mg(NO₃)₂ as modifier. Investigations of methods to extend the useful calibration range revealed reduced vapour-phase temperatures in the presence of a convective gas flow during atomisation, and a greater potential for errors using non-resonance lines. With respect to the latter, the absorbance signal is much more sensitive to matrix induced changes in the temperature interval in which atoms are formed compared to resonance lines. Furthermore, at the lead 261.4 nm non-resonance line we observed overcompensation errors caused by cobalt when using a Zeeman-effect system, and undercorrection due to the AlCl(g) molecule with a continuum source background corrector.     

Hammett analysis of selective thyroid hormone receptor modulators reveals structural and electronic requirements for hormone antagonists

Selective thyroid hormone modulators that function as isoform-selective agonists or antagonists of the thyroid hormone receptors (TRs) might be therapeutically useful in diseases associated with aberrant hormone signaling. The most potent thyroid hormone antagonist reported to date is NH-3. To explore the significance of the 5'-p-nitroaryl moiety of NH-3 and understand what chemical features are important to confer antagonism, we sought to expand the structure-activity relationship data for the class of 5'-phenylethynyl GC-1 derivatives. Herein, we describe an improved synthetic route utilizing palladium-catalyzed chemistry for efficient access to a series of 5'-phenylethynyl compounds with varying size and electronic properties. We prepared and tested sixteen analogues for TR binding and transactivation activity. Substitution at the 5'-position decreased binding affinity, but retained TRbeta-selectivity. In transactivation assays, the analogues displayed a spectrum of agonist, antagonist, and mixed agonist/antagonist activity that correlated with electronic character in a Hammett analysis between sigma substituent value and TR modulation. Analogues NH-5, NH-7, NH-9, NH-11, and NH-23 displayed full antagonist activity with reduced potency compared to NH-3, indicating the nitro group is not required for antagonism. However, para-substitution with strong electron withdrawing properties on the 5'-aryl extension is important for antagonist activity, and antagonist potency-but not ligand receptor binding-was found to correlate linearly with the sigma values for the electron withdrawing substituents.