Stability constants of some bivalent first row transition metal chelates of dicarboxylic acids containing ether linkages

The stability constants of the Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+) and Zn(2+) complexes with four acids of the type HOOCCH(2)O(CH(2)CH(2)O)(n) CH(2)COOH (n = 0-3) are reported. For n = 0 the constants are in the Irving-Williams order, but not for n = 1-3.     

Assessment of drinking water radioactivity content by liquid scintillation counting: set up of high sensitivity and emergency procedures

In our institute, different procedures have been developed to measure the radioactivity content of drinking water both in normal and in emergency situations, such as those arising from accidental and terrorist events. A single radiometric technique, namely low level liquid scintillation counting (LSC), has been used. In emergency situations a gross activity screening is carried out without any sample treatment by a single and quick liquid scintillation counting. Alpha and beta activities can be measured in more than one hundred samples per day with sensitivities of a few Bq/L. Higher sensitivity gross alpha and beta, uranium and radium measurements can be performed on water samples after specific sample treatments. The sequential method proposed is designed in such a way that the same water sample can be used in all the stages, with slight modifications. This sequential procedure was applied in a survey of the Lombardia district. At first tap waters of the 13 largest towns were examined, then a more detailed monitoring was carried out in the surroundings of Milano and Lodi towns. The high sensitivity method for the determination of uranium isotopes was used to check the presence of depleted uranium in Lake Garda. Reduced equipment requirements and relative readiness of radiochemical procedures make LSC an attractive technique which can also be applied by laboratories lacking specific radiochemistry facilities and experience.     

Gas chromatography/negative-ion chemical ionisation mass spectrometry for the quantitative analysis of morphine in human plasma using pentafluorobenzyl carbonate derivatives

A sensitive and specific method for the quantitative determination of morphine in human plasma is presented. Morphine was extracted from plasma by solid phase extraction on C18 and converted to its pentafluorobenzyl carbonate trimethylsilyl derivative. The derivatives were analysed without further purification. Using gas chromatography/negative ion chemical ionisation mass spectrometry, a useful diagnostic fragment ion at m/z 356 is obtained at high relative abundance. Deuterated morphine was used as internal standard. Calibration graphs were linear within the range 1.25 to 320 nmol/L. Intra-day precision was 3.82% (15 nmol/L), 2.85% (75 nmol/L) and 4.13% (225 nmol/L), inter-day variability was found to be 1.77% (15 nmol/L), 4.95% (75 nmol/L) and 9.88% (225 nmol/L). Inter-day accuracy showed deviations of 2.18% (15 nmol/L), -0.72% (75 nmol/L) and -0.13% (225 nmol/L). The method is rugged and robust and has been applied to the batch analysis of morphine during pharmacokinetic profiling of the drug.     

Anion-exchange behaviour of various metals on DEAE-cellulose in mixed acetic acid-nitric acid media

A number of nitrato complexes of metals have been found to be adsorbed on DEAE-cellulose from mixed acetic acid-nitric acid media, although none can be adsorbed from aqueous nitric acid solutions. The distribution coefficients of Sc, Mo, La, Sm, W, Re, Bi, Th and U are given as functions of acetic acid and nitric acid concentrations (sometimes in the presence of hydrogen peroxide to prevent hydrolytic precipitation). For 25 other metals column adsorption behaviour is described for a 90% acetic acid-10% 7.6M nitric acid mixture. Favourable differences in the distribution coefficients allow useful separations such as FeMoW and USmMoBiTh, to be achieved.     

Dynamics of charge transfer states on metal surfaces: the competition between reactivity and quenching

The dynamics of excited states of adsorbates on surfaces caused by charge transfer is studied. Both negative and positive charge transfer processes are possible. In particular we are interested in positive charge transfer from a metal surface to molecular or atomic oxygen adsorbed on the surface. Once the negatively charged oxygen on the surface loses an electron it becomes chemically activated. The ability of this species to react depends on the quenching time or back transfer. The analysis of these processes is based on a set of diabatic potential energy surfaces each representing a different charged oxygen species. The dynamics is followed by solving the multichannel time-dependent Schr?dinger equation or Liouville von Neumann equation. Due to the nonadiabatic character of these reactions large isotope effects are predicted.     

Cathodic and anodic stripping voltammetry: simultaneous determination of As-Se and Cu-Pb-Cd-Zn in the case of very high concentration ratios

Arsenic(III), selenium(IV), copper(II), lead(II), cadmium(II) and zinc(II) are determined in environmental matrices. The voltammetric measurements were carried out using a conventional three-electrode cell and the ammonia-ammonium chloride buffer pH 9.3 as supporting electrolyte. The analytical procedure was verified by the analysis of the standard reference materials Estuarine Sediment BCR-CRM 277 and River Sediment BCR-CRM 320. The precision, expressed as relative standard deviation (s(r)), and the accuracy, expressed as relative error, were, in all cases, less than 5%; the detection limits, for each element and in the experimental conditions employed, were around 10(-9) M. The standard addition technique significantly improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios.     

Emulsifying and foaming properties of amaranth seed protein isolates

The emulsifying and foaming properties of amaranth seed protein isolates prepared by wet extraction methods, such as isoelectric precipitation and dialysis, were investigated. The various isolates differ from each other in many ways. The isolate prepared by isoelectric precipitation mainly contains the globulin but not the albumin fraction and a considerable amount of polysaccharides, while the other isolate prepared by the dialysis method contains all the globulin and albumin fractions. The protein-polysaccharide complexes enhance emulsion stability due to steric repulsion effects. Measurements of the emulsion stability show that the studied protein isolates act as effective stabilizing agents. Foam expansion is dominated by the surface activity and availability of protein in the solution, while foam stability is determined by the properties of the interfacial layer. The results show that amaranth protein isolates act as an effective foaming agent. Both foaming properties intensified from the presence of protein-polysaccharide complexes.     

(6-4)-photolyase activity requires a charge shift reaction

A model compound containing a thymine oxetane moiety linked to a flavin chromophore was investigated regarding (6-4)-photolyase activity. The need for a charge shift reaction was demonstrated by a detailed pH-dependent kinetic analysis.     

Novel polymer-bound chiral selenium electrophiles

[reaction: see text]. Polymer-bound chiral electrophilic selenium reagents have been developed and applied to stereoselective selenenylation reactions of various alkenes. Different cleavage protocols allow further functionalization of the addition products leading to improvements in selenium-based solid-phase chemistry.     

Photoinduced Electron Transfer Reactions of alpha-Cyclopropyl- and alpha-Epoxy Ketones. Tandem Fragmentation-Cyclization to Bi-, Tri-, and Spirocyclic Ketones

Reductive photoinduced electron transfer (PET) reactions have been performed with various bicyclic alpha-cyclopropyl-substituted ketones and tertiary amines. The reaction resulted in a regioselective cleavage of one cyclopropyl bond under formation of an exocyclic radical with an endocyclic enolate unit. In the case of bicyclic ketones with an unsaturated side chain, various bicyclic, spirocyclic, and tricyclic products are accessible via radical cyclization, depending on the position of the alkenyl substituent. In addition to triethylamine, N-silylated amines have also been used as electron donors, leading to a variety of compounds, among them are silylated fragmentation products, indicating that a proton is transferred from not only the amine radical cation but also the cationic silyl group. The intramolecular Paternó-Büchi reaction has also been studied for cyclopropane derivatives of the jasmone type leading to tetracyclic oxetanes. Finally, alpha-epoxy-substituted ketones have been investigated under PET conditions, yielding ring-opened products.