Synthesis of tetravalent metal antimonates: Characteristics and use in treatment of radioactive waste solutions

Eight di-n-butyltin(IV) complexes with glycolic, 2-hydroxy-propionic, succinic and malic acids, have been prepared by two different procedures. The compounds were characterised by elemental analysis, FTIR, Raman and¹¹⁹Sn Mössbauer spectroscopy. The IR and Raman data indicated the presence of bidentate and/or monodentate carboxylate groups, non linear C?Sn?C bonds, and Sn?O bonds within the complexes. The results of Mössbauer spectroscopic measurements, based on point-charge model calculations, have shown the occurrence of trigonal bipyramidal environment in the central tin(IV) atom, besides the octahedral and tetrahedral structure.     

Synthesis and biological activity of some new 3-and 6-substituted coumarin amino acid derivatives. Part I

The synthesis of 6-nitrocouarrain-3-CO-amino acids and their corresponding methyl esters (II-XVII) and some dipeptide methyl esters (XVIII-XXVI) are described. 6-(N-Tosyl- or N-phthalylaminoacyl)aminocoumarin-3-carboxylic acid methyl esters (XXXIV-XL) and 3-(N-phthalyl- or N-tosylaminoacytyaminocoumarins (XLV-LVI) have been prepared via the carbodiimide and acid chloride methods. Hydrazinolysis of 3- or 6-(N-phthalylaminoacyl)aminocoumarin derivatives in tetraline gave the corresponding 3- and 6-(aminoacyl)aminocoumarins and the carboxylic acid hydrazides (XLI-LVIII), respectively. 3-(N-Tosyl-L-Val-L-Leu-)aminocoumarin (LIX) was synthesized via the azide method. Twenty four of various substituted 3- and 6-aminoacylcoumarin derivatives were found to possess specific antimicrobial activities towards different microorganisms.     

Electrochemical and thermodynamic studies of the ion-pair formation of chloropentamminecobalt(III) ion in ethyl alcohol-water media containing different dicarboxylate ligands

The ion-pair dissociation constants, K(D), of the ion-pair formed between chloropentamminecobalt(III) ion (CpX(2+)) and a variety of dicarboxylate ligands, have been determined from EMF measurements of a cell composed of glass and calomel electrodes. Measurements were made in water and in aqueous binary mixtures of ethyl alcohol, over a wide range of solvent composition (0-60 wt% ethyl alcohol), at six different temperatures (ranging from 30 to 55 degrees C at intervals of 5 degrees C). The thermodynamic parameters of association DeltaG(ass)(0), DeltaH(ass)(0) and DeltaS(ass)(0) have been calculated and discussed. DeltaH(ass)(0)-DeltaS(ass)(0), DeltaS(ass)(0)-DeltaS(1(or 2))(0), DeltaG(ass)(0)-G(1(or 2))(0) and DeltaH(ass)(0)-DeltaH(1(or 2))(0) correlations among different solvent media and different dicarboxylate ligands were examined (where 1 and 2 denote the first and the second dissociation reactions of the studied dicarboxylic acids). The pK(D) value has been correlated with the dielectric constant of the medium according to Born's equation.     

Radical cyclization of sugar-derived beta-(alkynyloxy)acrylates: synthesis of novel fused ethers

[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran.     

Solvent effects on the dissociation reactions of tartaric, maleic and phthalic acids; comparative study and analysis of thermodynamic functions

The first and second dissociation constants of tartaric, maleic and phthalic acids have been determined using EMF method in water-ethanol mixed solvents, over a wide range of solvent composition (0-60 wt% ethanol) at six different temperatures (ranging from 30 to 55 degrees C at intervals of 5 degrees C). The thermodynamic parameters (DeltaG degrees , DeltaH degrees and DeltaS degrees ) for the first and the second ionization reactions were calculated from the well known equations. The results have been discussed in terms of the solute-solvent interactions and were compared with those of malic, malonic and succinic acids in the same mixed solvents.     

Structure and swelling-release behaviour of poly(vinyl pyrrolidone) (PVP) and acrylic acid (AAc) copolymer hydrogels prepared by gamma irradiation

Copolymer network hydrogels were prepared by gamma irradiation of aqueous solutions of poly(vinyl pyrrolidone) (PVP) and acrylic acid monomer (AAc). The composition of the final hydrogels compared to the composition of the initial preparation solutions of hydrogels was determined. The chemical structure and nature of bonding was characterized by IR spectroscopy analysis, while the thermal durability of the prepared hydrogels was assessed by thermogravimetric analysis (TGA). The kinetic swelling in water and the pH-sensitivity of PVP/AAc copolymer hydrogels was studied. The drug release properties of PVP/AAc hydrogels taking methyl orange indicator as a drug model was investigated. The IR spectra indicate the formation of copolymer networks, whereas the TGA study showed that the PVP/AAc hydrogels possess higher thermal stability than pure PAAc and lower than PVP hydrogels. The kinetic swelling in water showed that all the hydrogels reached equilibrium after 24 h and that the degree of swelling increases with increasing the ratio of AAc in the initial feeding solutions. It was found that the degree of swelling of PVP/AAc hydrogels increases greatly within the pH range 4-7 depending on composition.     

Influence of atomic hydrogen annealing on the optical properties of vacuum-deposited a-Si:H films

The influence of atomic hydrogen annealing on the optical parameters of a-Si:H films was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200-3000 nm. In this annealing, the deposition of a thin layer and treatment with atomic hydrogen were repeated alternately, where the thickness of the thin cyclic layer, d_cyc, and the treatment time of each cycle, t_ca, were kept fixed for each sample. A series of different samples with average thickness of 0.5 μm and different d_cyc and t_ca were prepared. It was found that the refractive index, n, and the optical energy gap, E_g, increase as the treatment time, t_ca, increases from 0 to 60 s, while at t_ca=120 s both n and E_g decrease. Also, both the refractive index and the optical energy gap decrease with increasing the relative diffusion length of hydrogen, √t_ca/d_cyc from 0.39 to 0.77. The widening of E_g is due to the structural relaxation resulting from impingement of atomic hydrogen on the growing surface. Thus, a good-quality a-Si:H with Urbach parameter 65 mev and optical energy gap of 1.78 eV was successfully prepared.