A study of the d.c. susceptibility of granular superconductors by means of Josephson-junction array models

Il Nuovo Cimento D - The field-cooled d.c. susceptibility of granular superconductors is studied by means of simple Josephson-junction array models. It is shown that a paramagnetic behaviour after...     

Isolated Mn12 single-molecule magnets grafted on gold surfaces via electrostatic interactions

Electrostatic interactions drive the adsorption of polycationic single-molecule magnets onto anionic monolayers self-assembled on gold surfaces. Well-isolated magnetic clusters have been deposited and characterized using scanning tunneling microscopy and X-ray photoemission spectroscopy.     

A crystallographic study of (2-acetylpyridine-κN 4-phenylthyosemicarbazonate-κ2N1,S) methyl-trans-dichlorotin(IV)

The preparation and characterization of [Sn(C₁₄H₁₃N₄S)(CH₃)Cl₂], an organotin(IV) complex containing 2-acetylpyridine(4)-phenylthiosemicarbazone, is described. The molecular structure was studied by single crystal X-ray diffraction, and IR and Mössbauer spectroscopies. The title compound crystallizes in the centric triclinic space group, P , as discrete neutral complexes, with the Sn(IV) ion in a distorted octahedral coordination geometry, with the thiosemicarbazone derivative in a meridional configuration and the chlorides in trans positions.     

Quantitative determination and separation of analogues of aminoglycoside antibiotics by high-performance liquid chromatography

Commercial bulk products and pharmaceutical drug formulations of aminoglycoside antibiotics obtained by fermentation (kanamycin, gentamicin, sisomicin and tobramycin) or by synthesis (amikacin) were analysed with high-performance liquid chromatography on a C8 reversed-phase column. The method is based on a pre-column derivatization of the aminoglycosides with a 2,4,6-trinitrobenzenesulphonic acid reagent and UV detection (350 nm). The quantitative determination was carried out vs. an external standard; both peak heights and areas were used. A gentamicin mixture was separated into five or four components, depending on the column used. Amikacin was separated from its possible regioisomers and kanamycin A was easily separated from its minor components B and C.     

Activation of carbon dioxide by bicyclic amidines

Activation of the carbon dioxide molecule was achieved using bicyclic amidines (DBU, PMDBD, and DBN). The solution reaction of CO(2) with amidines yielded the corresponding zwitterionic complexes through the formation of a N-CO(2) bond. (13)C NMR data confirmed the carbamic nature of the carbamic zwitterions, DBU-CO(2) and PMDBD-CO(2). However, when these adducts were crystallized, the X-ray analyses of the single crystals were in agreement with bisamidinium bicarbonate salt structures, indicating that structural changes occurred in the crystallization process. The elemental and thermogravimetric analysis data for the carbamic zwitterions, DBU-CO(2) and PMDBD-CO(2), initially obtained by the direct reaction of amidines with CO(2), suggest that these molecules are probably associated with one molecule of water by hydrogen-bond formation (amidinium(+)-COO(-)...H(2)O). A correlation was observed between the thermal stability and the transcarboxylating activity for the amidine-CO(2) complexes. Theoretical calculations of hardness were performed at the B3LYP/cc-pVTZ level of theory and showed concordance with the experimental reactivity of DBU and PMDBD toward CO(2).