A novel and simple procedure for the enantiospecific synthesis of bridgehead norbornane thioethers and thiocyanates

An easy three-step route for the enantiospecific synthesis of novel 1-norbornyl thioethers and thiocyanates from readily available natural fenchone and camphor is described. The key step of the synthetic route is the nucleophilic substitution over the sulfenyl sulfur atom of the intermediate thiotriflates by the corresponding C-nucleophiles.     

Metal ion-binding properties of (1H-benzimidazol-2-yl-methyl)phosphonate (Bimp2-) in aqueous solution. Isomeric equilibria, extent of chelation, and a new quantification method for the chelate effect

The acidity constants of the 2-fold protonated (1H-benzimidazol-2-yl-methyl)phosphonate, H2(Bimp)(+/-), are given, and the stability constants of the M(H;Bimp)+ and M(Bimp) complexes with the metal ions M2+ = Mg2+, Ca2+, Ba2+, Mn2+, Co2+, Cu2+, Zn2+, or Cd2+ have been determined by potentiometric pH titrations in aqueous solution at I = 0.1 M (NaNO3) and 25 degrees C. Application of previously determined straight-line plots of log KM(M(Bi-R)) versus pKH(H(Bi-R)) for benzimidazole-type ligands, Bi-R, where R represents a residue which does not affect metal ion binding, proves that the primary binding site in the M(H;Bimp)+ complexes is (mostly) N3 and that the proton is located at the phosphonate group; outersphere interactions seem to be important, and the degree of chelate formation is above 60% for all metal ion complexes studied, except for Zn(H;Bimp)+. A similar evaluation based on log KM(M(R-PO3)) versus pKH(H(R-PO3)) straight-line plots for simple phosph(on)ate ligands, R-, where R represents a residue which cannot participate in the coordination process, reveals that the primary binding site in the M(Bimp) complexes is (mostly) the phosphonate group with all metal ions studied. In this case, the formation degree of the chelates varies more widely in dependence on the kind of metal ion involved, i.e., from 17 +/- 11% to nearly 100% for Ba(Bimp) and Cu(Bimp), respectively. For all the M(H;Bimp)+ and M(Bimp) systems, the intramolecular equilibria between the isomeric complexes are evaluated in a quantitative manner. The fact that for Bimp2- the metal ion affinity of the two binding sites, N3 and PO3(2-), can be calculated independently, i.e., the corresponding micro stability constants become known, allows us to present for the first time a method for the quantification of the chelate effect solely based on comparisons of stability constants which carry the same dimensions. This effect is often ill defined in textbooks because equilibrium constants of different dimensions are compared, which is avoided in the present case. For the M(Bimp) complexes, it is shown that the chelate effect is close to zero for Ba(Bimp) whereas for Cu(Bimp) it amounts to about four log units. This method is also applicable to other chelating systems. Finally, considering that benzimidazole as well as phosphonate derivatives are employed as therapeutic agents, the potential biological properties of Bimp, especially regarding nucleic acid polymerases, are briefly discussed.     

Polyphosphate content and fine structure of acidocalcisomes of Plasmodium falciparum.

Although acidocalcisomes have been well characterized morphologically in other apicomplexan parasites, no such characterization has been done in Plasmodium spp. Here, we report that Plasmodium falciparum merozoites possess electron-dense organelles rich in phosphorus and calcium, as detected by X-ray microanalysis of intact cells, which are similar to the acidocalcisomes of other apicomplexans, but of more irregular form. In agreement with these results malaria parasites possess large amounts of short- and long-chain polyphosphate (polyP), which are associated with acidocalcisomes in other organisms. PolyP levels were highest in the trophozoite stage of the parasite. Treatment of isolated trophozoites with chloroquine resulted in a significant hydrolysis of polyP. Taken together, these results provide evidence that acidocalcisomes from Plasmodium falciparum do not differ significantly from acidocalcisomes of other apicomplexan parasites.     

Silica Sol-Gel Coatings on Metals Produced by EPD

The objective of this work has been to combine the sol-gel method and the electrophoretic deposition (EPD) process to prepare thick coatings onto metallic substrates. Two different routes were used for preparing the sol-gel silica suspensions. On one hand, silica particulate sols were obtained by basic catalysis of alkoxides and alkylalkoxides. On the other, silica suspensions were prepared by adding a commercial colloidal silica sol to an organic-inorganic acid catalysed silica sol. The properties of the suspension and the physical parameters associated to EPD (current density, potential, electric field and deposition time) were studied. Crack-free deposits up to 20 m were obtained after drying and crack-free glass-like coatings of 12 m after sintering at 500°C for 30 minutes. The electrochemical behaviour of these coatings was evaluated by potentiodynamic methods, showing an excellent behaviour against corrosion.     

Trace determination of alpha- and beta-endosulfan and three metabolites in human serum by gas chromatography electron capture detection and gas chromatography tandem mass spectrometry

Endosufan, alpha and beta, and three conversion products, sulphate, ether and lactone, were simultaneously determined in human serum by means of an analytical procedure which combines extraction with organic solvents, clean-up with H(2)SO(4) and by liquid column chromatography, and detection by gas chromatography (GC) using electron capture detection (ECD) and tandem mass spectrometry (MS/MS). The procedure was validated and the values of some merit figures, such as linear range, detection and quantitation limits, accuracy, precision and recovery, obtained with the GC/ECD and the GC/MS/MS methods, were compared. The lower limits of detection in GC/ECD and GC/MS/MS were 0.03 and 0.05 microg I(-1), respectively. The recovery of the pesticides at the 20 microg I(-1) concentration level was 60-65%, with the exception of endosufan alpha. Recovery studies at higher levels (100 and 200 microg I(-1)) were independent of pesticide concentration in serum samples. The application of the proposed analytical methodology to the determination of endosulfans and their metabolites in real samples was tested by analyzing serum samples from a population living in agricultural areas of Almeria (Spain). The results show the advantage of MS/MS over the ECD detector in the analysis of serum samples where matrix interferences can be confused with target pesticides.     

Spectrophotometric determination of zirconium with alizarin red S in the presence of polyvinylpyrrolidone

The absorbance of the microcolloidal zirconium/alizarin red S/polyvinylpyrrolidone complex is measured at 525 nm in acetate buffered medium at pH 4.75. The molar absorptivity is 3.8 × 10⁴ l mol^?1 cm^?1, which is much greater than that of the classical method. Sulphate and fluoride do not interfere.