Search Results
Abstract
Selenite reacts with SeS3O 6 2− in acidic solutions forming selenanmonosulfandisulfonates with up to 6 Se-atoms in the chain. Se5S3O 6 2− and Se6S3O 6 2− have been detected for the first time. The decomposition causes precipitation of a sulfur/selenium-mixture. For the Se-precipitation giving reactions of SeO 3 2− with sulfite, S2O 3 2− , SeSO 3 2− , SeS2O 6 2− and SeS3O 6 2− a universal reaction scheme has been developed, prevailing of the following single steps: formation of monoselenandisulfonates, formation of build-up reagents, formation of higher selenopolythionates, decomposition of the selenopolythionates with the longest chains.
Abstract
Prior work had documented that99mTcCl
6
2–
could undergo ready ligand exchange reaction under non-aqueous condition. We now wish to report the ligand exchange reaction of bromine in99mTcBr
6
2–
in non-aqueous solvents using 8-hydroxyquinoline (oxine) as the displacing ligand. Analysis of the products obtained by paper chromatography, HPLC and electrophoresis suggest that a 1
2 Tcoxine complex appears to be the most stable of the complexes formed, probably99mTc(oxine)2 Br2. However, displacement of bromine by polar solvents (both protic and aprotic) can also occur, both on99mTcBr
6
2–
and in the above complex as a consequence of solvolytic reactions. Other Tc-oxine complexes can also be formed upon ligand exchange, but they appear to be stable only under aprotic, non solvolytic conditions. These studies again document that hexahalotechnetate complexes exhibit ligand exchange reactions under non-aqueous conditions, that they allow the ready synthesis of novel technetium complexes, but that because of their high reactivity the effect of competing reactions must be considered.
Abstract
The structural relaxation of Ge38S62 glass has been studied by length dilatometry and calorimetry. The Tool-Narayanaswamy-Moynihan model was applied on obtained data of structural relaxation and parameters of this model were determined: Δh*= 4832 kJ mol-1, ln(A/s)= -811, β= 0.70.1 and x=0.60.1. Both dilatometric and calorimetric relaxation data were compared on the basis of the fictive relaxation rate. It was found that the relaxation rates are very similar and well correspond to the prediction of phenomenological model.
Abstract
The enthalpies of formation of PbCl4, PbCl5 − and PbCl6 2−, originating from quantum mechanics, have enabled the thermodynamic behaviour of these ions with respect to Cl-detachment to be assessed. The stability of salts containing PbCl5 − and PbCl6 2− as a function of the dimensions of these anions and complementary cations was studied using an approach combining the Kapustinskii-Yatsimirskii equation with basic thermochemical relationships. It was found that hexachloroplumbates of monovalent metal cations will not dissociate into metal chlorides and PbCl4, provided the complementary cations are suitably large in size. Hexachloroplumbates of divalent metal cations have not yet been synthesised since no known metal cations attain the requisite large size. Such salts will not dissociate if the divalent metal cations are able to complex suitably large electron-donating ligands. The pentachloroplumbates of both monovalent and divalent metal cations are unstable, since no known metal cations have appropriately large ionic radii. The approach adopted appears to be useful for the examination of the thermal behaviour, stability and reactivity of chloroplumbates.
Abstract
Potassium zinc hexacyanoferate/II/ K2Zn3[Fe/CN/6]2 was prepared and used for the investigation of the uptake of ammonium ion NH 4 + . The obtained equilibrium data indicate higher selectivity of ammonium ion relative to potassium ion and much lower relative to cesium ion.
The kinetics of thermal dehydration of [Ni2Al(OH)6]2SO4.nH2O has been studied through the analysis of isothermal weight loss data. The results obtained seem to indicate that the process is governed by a diffusion mechanism up to anα value which is dependent on the temperature. An explanation is provided for this behaviour on the basis of the structural properties of the compound and the nature of the water loss.
Abstract
Stability constants (log b101) of Th4+, UO2 2+, NpO2 + and Am3+ with [NaP5W30O110]14- were determined by solvent extraction (m = 0.1M NaCl) and found to be 6.18±0.07, 3.80±0.06, 2.98±0.04, and 5.85±0.05, respectively. The order of stability constants: Th4+>Am3+>UO2 2+>NpO2 + is due to electrostatic repulsion between the actinyl oxygens and oxygens on the polyoxometalate surface. The order of stability constants for metal complexes with [P2W18O62]6- is Th4+>UO2 2+>Eu3+>NpO2 + because the steric repulsion between actinyl oxygens and oxygens on polyoxometalate are less important. Enthalpies of complexation were measured by calorimetric titration of Th4+, UO2 2+, Nd3+ with [NaP5W30O110]14- and [P2W18O62]6-. The results indicate that the conformation and charge distribution of the microscopic surface structures are important factors in the formation of pseudocolloids.
a-Galactosidase activity from Thermomyces lanuginosus strain of CBS 395.62/b was investigated in cultivation media with various compositions. Among the seven nitrogen sources only three L-asparagine, yeast extract and ammonium acetate supported the a-galactosidase synthesis. Ammonium acetate proved to be the best candidate as nitrogen source. When glucose or galactose was used as main carbon source, very low level, constitutive a-galactosidase activity was observed. In presence of raffinose, considerable a-galactosidase activity was detected. Raffinose can be replaced by sucrose in the cultivation medium, because the productivity reached by it was superior to that of raffinose. a-Galactosidase activity was improved by the optimisation of the concentrations of sucrose and ammonium acetate in the medium. Applying medium composition with 3% (w/v) sucrose and 0.6% (w/v) ammonium acetate led to at least 5 times higher activity which was observed in the reference medium containing 1.5% (w/v) raffinose and 0.45% (w/v) L-asparagine.
