Structural researches on the chelating behaviour of the biguanide ligand. The crystal structures of Co(C2H6N5)3 · 2H2O and Cu(C2H7N5)2CO3·4H20

Summary Crystals of the title compounds are both monoclinic, with unit cell dimensions:a = 9.293(5),b = 10.122(5),c = 16.737(7) Å. = 103.44(3)°,Z = 4, space groupP2₁/c for the cobalt derivative;a = 13.1ß5(7),b = 17.546(ß),c = 6.871(3) Å, = 107.01(4)°Z = 4, space groupP2₁/n for the copper derivative. The structures were solved from diffractometer data by the heavy-atom technique for the first compound and by direct methods for the second compound. Refinement by block diagonal least-squares gaveR = 5.9% for 3511 independent reflections andR = 8.8% for 2885 independent reflections for the cobalt and copper compound respectively. In both compounds the biguanide moiety behaves as a bidentate chelating ligand in a symmetrical tautomeric form, but it is deprotonated in the octahedral cobalt compound and neutral in the square planar copper compound.     

Synthesis,characterization and a thermogravimetric study of copper,cobalt and tin mono- and bis-adducts with ethyleneurea,ethylenethiourea and propyleneurea

This paper describes the synthesis, characterization and a thermogravimetric (t.g.) study of 11 adducts of general formula MCl₂·nL (M = Cu, Co and Sn; n = 1 and 2 for Sn, and 2 for Cu and Co; L = ethyleneurea eu, ethylenethiourea etu, and propyleneurea pu). The i.r. results shows that the eu and pu adducts are coordinated through oxygen, whereas for etu nitrogen is the coordination site. The (C=O) or (C=S) trend is: Cu > Co > Sn. The t.g. curves show that the adducts release ligand molecules in a single mass loss step. As regards considering adducts with the same stoichiometry, the observed thermal stability trend is: etu > pu > eu.     

Symmetries and asymmetries in classical and relativistic electrodynamics

By a comparison between Maxwell's electrodynamics classically interpreted (MT) and relativistic electrodynamics (RED), this paper discusses whether the asymmetries in MT mentioned by A. Einstein in his 1905 relativity paper are only of a conceptual nature or rather involve specific empirical claims. It is shown that in fact MT predicts strongly asymmetric behaviour for very simple interactions, and an analysis is made of the extent of the symmetry achieved by means of relativistic postulates. A low velocity experiment is suggested which could provide another test of the accuracy of RED with respect to MT.     

Chiral HPLC Separation of Rosiglitazone and its Main Metabolites and Studies on Their Racemization

Rosiglitazone (RSG) is marketed as a racemic mixture although the antidiabetic activity is essentially related to the (S)-enantiomer. The chiral center has an adjacent carbonyl group; therefore, the (R)-enantiomer could be transformed to the (S)-enantiomer or vice versa by keto-enolic tautomerism. The literature indicates that this racemization is slow enough to allow the evaluation of the properties of the isolated enantiomers. However, there is no information about the enantioselective kinetic disposition and metabolism of RSG. Additionally, there are no studies on the racemization of its metabolites. Considering these facts, a chiral HPLC method was developed and used for the first time to study the racemization of RSG and its main metabolites. Different conditions, including those used to evaluate the in vitro enantioselective metabolism, were employed. The simultaneous chiral separation of RSG and metabolites was achieved on a Chiralcel OJ-H column by employing methanol/ethanol (90:10, v/v) as mobile phase. The racemization studies showed that the half-life of RSG decreased more than 30 times when the temperature increased from 4 to 37 °C. It was also observed that the half-life of RSG changed from approximately 20 h at pH 3.5 to approximately 2 h at pH 7.4. The same profile was observed for its metabolites. Organic solvents and UV light did not present influence on the racemization process. In addition, a Complete Factorial Design was conducted to evaluate the influence of some parameters that can be changed during an in vitro metabolism study. The results obtained showed that the racemization occurs under in vitro metabolism conditions.

     

Transfer behaviors of 90Sr and 137Cs from soil to grass to cow milk under natural conditions in Central Italy and their exposure risk

Journal of Radioanalytical and Nuclear Chemistry - Based on the newly-developed techniques, the transfer behaviors of 90Sr and 137Cs under natural conditions were studied. The concentrations of...     

Rapid and easy quantification of elemental sulphur in aqueous samples from biological reactors: the turbidimetric method revisited

Recent developments in wastewater treatment have led to a renewed interest to obtain elemental sulphur (S°) as a by-product from bioreactors. However, practical studies are limited by the gap of adequate analytical techniques for its determination. This paper provides a statistical study and matrix effect evaluation of an adapted spectrophotometric method for routine S° analyses in aqueous samples, based on a methodology previously described by Hart (1961). Four complex matrices were tested: domestic sewage and effluent samples from three different bioreactors. Tested performance criteria included linearity, matrix effect, limit of detection and quantification and S° recovery. Results were linear (R² = 0.99994) in the studied range (5 to 100 mg S° L^?1) and no matrix effect was observed. The accuracy was based on recovery values that varied from 100% to 106%. The colloidal S° separation and extraction protocol was also considered suitable for aqueous samples, reaching more than 99.0% of S° recovery.