Photodegradation of a 1,3,4-thiadiazole-urea herbicide. Isolation,characterization, X-ray crystal structure and synthesis of photoproducts

The photodegradation of 1,3-dimethyl-1-(2-(3-fluorobenzylthio)-1,3,4-thiadiazol-5-yl)urea as a thin film and in solution is described. The two photoproducts from thin-film photolysis were characterized by spectral and synthetic methods. The X-ray crystal structure of one of the photoproducts is also reported. The rearrangements were shown to involve an S-to-N benzyl migration, followed by a sulfur-oxygen substitution.     

New [Mo(eta3-allyl)(CO)2L3]+ complexes with monodentate or tridentate nitrogen-donor ligands

Cationic complexes [Mo(eta(3)-allyl)(CO)2L3]+ (L3 = either nitrogen-donor tridentate ligand or three monodentate ligands) were prepared in high yield and under mild conditions using as precursors either the triflato complex [Mo(eta(3)-allyl)(OTf)(CO)2(NCMe)2] or the combination of the chloro complex [Mo(eta(3)-allyl)Cl(CO)2(NCMe)2] and the salt NaBAr'(4)(Ar'= 3,5-bis(trifluoromethyl)phenyl). The tridentate ligands employed were 2,2':6',2'-terpyridine (terpy) and cis,cis-1,3,5-cyclohexanetriamine (CHTA), whereas the monodentate ligands imidazole (im) and 3,5-dimethylpyrazole (dmpz) were chosen. In order to stabilize the labile intermediates, an excess of acetonitrile was used in most of the syntheses. However, the pyrazole complex was prepared through a nitrile-free route to avoid reactions at the coordinated nitrile. The solid state structures of [Mo(eta(3)-methallyl)(CO)2(terpy)]OTf (2), [Mo(eta(3)-methallyl)(CO)2(CHTA)]BAr'4 (3), [Mo(eta(3)-methallyl)(CO)2(NCMe)3]BAr'4 (4), [Mo(eta(3)-allyl)(CO)2(im)3]OTf (5) and [Mo(eta(3)-allyl)(CO)2(dmpz)3]BAr'4 (6) were determined by means of single-crystal X-ray diffraction.     

Simple and rapid micellar electrokinetic capillary chromatographic method for simultaneous determination of four antiepileptics in human serum

A very rapid and simple MEKC method was developed for the simultaneous determination of four antiepileptic drugs, ethosuximide (Etho), primidone (Pri), phenytoin (Pht) and carbamazepine (Cbz) in human serum. Sample analysis required only 100 microL of human serum which only needed to be centrifuged, decanted and combined with the running buffer [5.3 mM Na(2)HPO(4)/3.2 mM borax buffer (pH 9.5) containing 55 mM SDS and 3.5% (v/v) acetone]. The analysis was performed in only 10 min into fused-silica capillaries (57 cm total length with 50 microm i.d. and 50 cm to the detector) using the MEKC methodology with diode-array detection at 220 nm. The calibration graphs were established for ethoximide, primidone, phenytoin and carbamazepine between 0 and 20 mg/L. Recoveries were between 85 and 87%. The simplicity of the proposed methodology makes it suitable for routine clinical use, especially for epileptic patients on polytherapy.     

Multicommutation as an environmentally friendly analytical tool in the hydride generation atomic fluorescence determination of tellurium in milk

The aim of this study is to show the advantages of the emerging multicommutation methodology based on the use of solenoid valves for Te determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS). The delivery of a series of alternating sequential insertions of small volumes of samples and reagents gives rise to new hydrodynamic processes and exciting analytical potentials by controlling the time of flow through the on/off-switched solenoid valves. This drastically reduces the reagent consumption by a factor of 4 and the generation of effluents (590 mL h^–1 instead of 750 mL h^–1 generated by the continuous-mode measurement) and also provides an improvement in the laboratory productivity by an increase of the sample throughput (85 h^–1 compared to 20 h^–1 found in the continuous mode). So, multicommutation is an environmentally and economically sustainable alternative to the methodology based on continuous measurements. The multicommutation-based method developed was applied to tellurium determination in commercially available milk samples; a calibration range of 0.0–0.5 ng mL^–1 and a detection limit of 0.20 ng L^–1 with average relative standard deviation of 2.1% were found. Comparable results were obtained for a series of samples using both continuous and multicommutation HG-AFS modes.     

Spectrafluorimetric method for the rapid screening of toxic heavy metals in water samples

A fast and inexpensive sensitive screening test for recognising potential wastewater contamination by the presence of highly toxic heavy metals is described. The test is based on the reaction of the toxic heavy metals Hg(II), Cd(II), Pb(II) and Ag(I) with 6-mercaptopurine (6-MP) to produce highly fluorescent complexes.Optimum experimental conditions include a buffer of pH 7.2 (0.1 M citric acid/0.2 M Na₂HPO₄), a chelating reagent concentration of 6×10⁻⁴ M and the addition of 10⁻⁴ M of o-phenanthroline. The fluorescence emitted by the complexes was measured at 380 and 540 nm for excitation and emission wavelengths, respectively.Detection limits of 4, 3, 6 and 3 μg l⁻¹ were achieved for Hg, Cd, Pb and Ag. Relative standard deviation (R.S.D.) were between ±2 and ±6% of the fluorescence signals for five identical samples. Potential interference effects from other heavy metals (Zn, Mn, Co, Fe, Ni and Cu), which could affect the response of the proposed screening test was investigated. Results showed that none of these metals give rise to noticeable fluorescence signals under the above described experimental conditions.Finally, the capability of the proposed heavy metal screening test for the analysis of contaminated water samples is discussed.     

Electronic structure and properties of isoreticular metal-organic frameworks: the case of M-IRMOF1 (M = Zn, Cd, Be, Mg, and Ca)

We investigate the possibility of tailoring the electronic properties of isoreticular metal-organic materials by replacing the metal atom in the metal-organic cluster and by doping. The electronic structure of M-IRMOF1, where IRMOF1 stands for isoreticular metal-organic framework 1 and M = Be, Mg, Ca, Zn, and Cd, was examined using density-functional theory. The results show that these materials have similar band gaps (ca. 3.5 eV) and a conduction band that is split into two bands, the lower of which has a width that varies with metal substitution. This variation prompted us to investigate whether doping with Al or Li could be used to tailor the electronic properties of the Zn-IRMOF1 and Be-IRMOF1 materials. It is shown that replacing one metal atom with Al can effectively be used to create IRMOFs with different metallic properties. On the other hand, adding Li produces structural changes that render this approach less suitable.     

Human serum albumin-mediated stereodifferentiation in the triplet state behavior of (S)- and (R)-carprofen

A remarkable stereodifferentiation has been observed in the interaction between the excited triplet state of carprofen (CP) and human serum albumin (HSA). Time-resolved measurements using laser flash photolysis reveal the presence of two components with different lifetimes in triplet decay. This is explained by complexation of CP to the two possible HSA binding sites. The shorter-lived components are ascribed to the CP/HSA complexes in site I, where stereodifferentiation is more important (tauR/tauS ca. 4). This is correlated with formation of a dehalogenated photoproduct upon steady-state photolysis.     

A fluorimetric study of pindolol and its complexes with cyclodextrins

Spectrofluorimetric characteristics of pindolol have been investigated with the aim of using this technique for analytical determinations. Other monosubstituted indole derivatives, 4-methoxy and 5-methoxyindole, have been also studied for comparative purposes. Corrected excitation and emission wavelengths in different solvents are reported and the effect of solvent on the Stokes shifts of these compounds has been analysed using the Lippert equation. In addition, the Stokes shift of pindolol has been determined in dioxan-water solvent mixtures and the presence of specific solvent effects is discussed. The fluorescence of pindolol is pH dependent, the quantum yields determined in water are lower than those in other solvents. With respect to the sensitivity, it has been found that the detection limits in aqueous solutions are improved in the presence of beta and methyl-beta-cyclodextrin. Finally, a fluorimetric analysis of the interaction between pindolol and different cyclodextrins has been carried out in order to determine the apparent stability constants of the complexes and the thermodynamic parameters associated to complexation.     

Fluorimetric determination of aflatoxins by flow-injection analysis

Summary A fast and inexpensive fluorimetric method for the determination of total aflatoxins (B₁, B₂, G₁, and G₂) in food of use in screening numerous samples suspectedly containing these substances is proposed. The sensitivity of the method (determination range between 0.5 and 200.0 ng ml^–1) allows these analytes to be detected at concentrations well below legal limits; hence, separation-detection techniques such as HPLC need only be used with samples in which these compounds are found to occur. The method has been applied to maize, peanut and tapioca samples, obtaining average recoveries of 100.9 with deviations of ±5% with respect to 100% recovery.

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Fluorometrische Bestimmung von Aflatoxinen durch Fließinjektionsanalyse

     

Excess thermodynamic properties of the 2-propanol + dichloromethane system at 25°C

Densities, viscosities, enthalpies, vapor-liquid equilibria, and surface tensions were determined at 25°C for the 2-propanol+dichloromethane system. From the experimental results excess volumes, viscosities, enthalpies, Gibbs energies, and excess surface tensions were calculated. An attempt has been made to explain the observed deviations from ideal behavior on the basis of intermolecular interactions.