Interaction of divalent cations Zn,Cd and Hg on surface of silica gelwith aminoethanethiol as evaluated by calorimetric titration

Calorimetric titration was applied to study the interaction of zinc, cadmium and mercury on surface of silica gel modified with 2-aminoethanethiol, using 3-chloropropyltrimetoxysilane as precursor silylating agent. The anchored Sil–SNH₂ surface gave 0.70 mmol g^–1 of molecules covalently bonded per gram of silica. This surface displayed a chelating moiety containing sulfur and nitrogen basic centers, which are potentially capable of extracting cations from aqueous solutions, such as MCl₂ (M=Zn, Cd, Hg). This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. The data were adjusted to modified Langmuir equation. The sequence of the maximum retention capacity was Hg>Cd>Zn. The processes of cation interactions showed exothermic enthalpies. The calculated ΔG values are in agreement with the spontaneity of the proposed reactions and conformed to the values found by using Langmuir model applied to these systems. The endothermic entropic values, as expected, indicated that the reactions are favorable.     

Iron(III) complexes with benzoxazole derivatives

Summary Iron(III) complexes of the general formula Fe(L)_nX₃·mH₂O, where L=benzoxazole(benzox), 2-methylbenzoxazole(2-Mebenzox), 2, 5-dimethylbenzoxazole(2, 5-diMebenzox); n=2, 3, 4, 6; X=Cl, Br, NO₃ or ClO₄; m=0, 1, 2, 5, have been prepared and studied by chemical analysis, magnetic moments, i.r., electronic, Mössbauer spectra and molar conductivity values.The oxazoles are N_ring bonded and the complexes are hexacoordinate in the solid state with exception of the five-coordinate Fe(2, 5-diMebenzox)₂Br₃.     

Nuclear and related analytical methods applied to the determination of Cr, Ni, Cu, Zn, Cd and Pb in a red ferralitic soil and Sorghum samples

Several studies on the influence of heavy metals to the growth of vegetables have been carried out in Cuba by the Ministry of Agriculture in order to evaluate the effects resulting of the continuous application of fertilizers and other materials to the soils. The analysis of metal contents in soil and vegetable samples is often troublesome due to the low concentration levels to be determined. In the the present work EDXRF, AAS and ASV methods were applied and compared for the evaluation of Cr, Ni, Cu, Zn, Cd and Pb contents in red ferralitic soil and Sorghum samples. Several certified reference materials (CRM) (inorganic and organic matrixes) were analyzed in order to evaluate the performance of the analytical procedures and the bias and precision of the results. A study was performed with growing Sorghum in several series of pots where different quantities of metals were added to the soil substrate. The observed correlation between the metal contents in soil and plants as well as the influence of different additions of each metal on the plant growth is also presented.     

Astolides A and B,antifungal and cytotoxic naphthoquinone-derived polyol macrolactones from Streptomyces hygroscopicus

Two new natural compounds, astolides A,B, were isolated from Streptomyces hygroscopicus collected from the alkaline soil obtained from Saratov region, Russia. The structures were elucidated by interpretation of UV spectroscopic, MS, 1D and 2D NMR data. The relative configurations were determined by analysis of NOESY/ROESY spectra and coupling constants. The isolated compounds were evaluated for their inhibitory activity against bacteria, fungi and yeasts and showed pronounced antifungal activity. Both compounds are noticeably cytotoxic, being active against doxorubicin-resistant human leukemia cell line.