Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.     

Investigation of ion-pair precipitates of selected alkoxylates and complex salts of specific metal cations by liquid secondary ion mass spectrometry

Liquid secondary ion (LSI) mass spectra of ion-pair precipitates obtained for Triton X-100 with strontium, lead, cadmium and mercury tetraphenylborates and for selected butoxylene-ethoxylene monoalkyl ethers with barium tetraiodobismuthate(III) are discussed. On the basis of LSI mass spectra, recorded in both positive and negative modes, the formulae of the ion-pair precipitates were determined. On the basis of B/E mass spectra, the fragmentation routes of [M - H + Ba](+) ions for butoxylene-ethoxylene monoalkyl ether complexes of barium and [M - H + Cd](+) ions for the Triton X-100 complex of cadmium are proposed.     

Effects of Sludge Concentrations and Different Sponge Configurations on the Performance of a Sponge-Submerged Membrane Bioreactor

The performance of a novel sponge-submerged membrane bioreactor (SSMBR) was evaluated to treat primary treated sewage effluent at three different activated sludge concentrations. Polyurethane sponge cubes with size of 1?×?1?×?1?cm were used as attached growth media in the bioreactor. The results indicated the successful removal of organic carbon and phosphorous with the efficiency higher than 98% at all conditions. Acclimatised sponge MBR showed about 5% better ammonia nitrogen removal at 5 and 10?g/L sludge concentration as compared to the new sponge system. The respiration test revealed that the specific oxygen uptake rate was around 1.0?C3.5?mgO₂/gVSS.h and likely more stable at 10?g/L sludge concentration. The sludge volume index of less than 100?mL/g during the operation indicated the good settling property of the sludge. The low mixed liquor suspended solid increase indicated that SSMBR could control the sludge production. This SSMBR was also successful in reducing membrane fouling with significant lower transmembrane pressure (e.g. only 0.5?kPa/day) compared to the conventional MBR system. Further study will be conducted to optimise other operating conditions.     

Investigations of dehydroepiandrosterone. Part I: crystal structure of sublimed DHEA

The crystal structure of an orthorhombic polymorph of the title compound, crystallized by sublimation, has been determined. Dehydroepiandrosterone, C₁₉H₂₈O₂, space groupP2₁2₁2₁ witha=6.6408(4)b=11.4423(11)c=22.085(2)Å,V=1678.2(4)ų,Z=4. The structure was refined toR=0.051 for 2645 observed reflections. The conformation of the molecule is similar to that found in other polymorphs and solvates, with a chair A ring, an 8, 9 half-chair B ring, a chair C ring, and a 14 envelope D ring. Molecules are linked in chains by OH...O hydrogen bonds involving the carbonyl oxygen atom. The O...O distance is 2.855(3) Å, and the angle about H is 171(2)^o.     

X-ray structure of 2,6-dimethoxy-7-methylpurine

The title compound (C₈H₁₀N₄O₂) is monoclinic, with a = 7.740(2), b = 17.044(7), c = 6.992(3) Å, = 100.60(1)°, and space group P2₁/c. Two O-methyl groups are coplanar with the pyrimidine ring. Whereas, the O(6)-methyl group is directed away from the imidazole ring toward the N(1) atom, the O(2)-methyl is pointed away from the N(1) atom toward the N(3) atom. Two intermolecular hydrogen bonds H(8)···N(1) and H(711)···O(2) of 2.48(2) and 2.58(3) Å make a linear arrangement of the molecules. The conformation of the O-methyl groups explains some results of thermal rearrangement of 2,6-dialkoxy-7-methylpurines and differences in alkylations of 2,4-dialkoxypyrimidines and 2,6-dialkoxy-7-methylpurines.     

Crystal and molecular structures of 1-isoquinolyl(phenyl)methyl benzoate and 1-isoquinolylisopropyl benzoate

Both of the title compounds crystallize in the monoclinic system: C₂₃H₁₇NO₂ (Ib),P2₁/c,a = 8.970(1),b = 22.629(5),c = 9.101(1) Å, = 106.08(1) °,Z = 4,D _x = 1.27 Mg m^–3; C₁₉H₁₇NO₂ (Ic),P2₁/a,a = 15.225(2),b = 6.429(1),c = 17.190(1) Å, = 112.99(1) °,Z = 4,D _x = 1.25 Mg m^–3. The structures were solved and refined by standard methods, both toR 0.04. In compound Ib, a weak intramolecular interaction is observed between the nitrogen atom from the isoquinoline ring and the carbon atom from the carbonyl group, with the N(2) . C(18)distance being 2.98 Å. In compound Ic, the PhCO₂ -fragment is twisted in the opposite direction to that in compound Ib, without hydrogen bonding. The pK _a and IR data were considered in the light of the results of the X-ray investigation.     

Crystal and molecular structure of 3-methoxy-6-nor-6,7-secooestra-1,3,5(10),9(11), 14-penten-17-one-8β-ethyl carboxylate

C₂₀H₂₂O₄,M _r =326.39, triclinic,P¯1,a=10.365(2),b=11.383(2),c=8.461(1) Å, =103.60(1),=104.44(1), =105.23(1)°,Z=2, (CuK)=1.54178 Å;R=0.0633 for 1940 reflections. The results of the X-ray analysis have shown that the ethyl carboxylate substituent is oriented. The geometry of the main skeleton of the molecule has not revealed any significant differences in the present compound and in the case of the epimeric molecule.     

Tb3+ luminescence enhancement of YAG:Tb3+ nanocrystals embedded in silica xerogel

The luminescence behavior of composite materials consisting of nanocrystals of Y_3?xAl₅O₁₂:Tb (YAG:Tb³⁺) embedded into silica xerogel has been studied. Blue and green luminescence of the materials is due to a cross-relaxation effect in Tb³⁺ ions doped into a YAG lattice. The materials with YAG:Tb³⁺ nanocrystals immobilized in silica exhibit enhancement of Tb³⁺ luminescence in comparison with the macrocrystalline YAG:Tb³⁺ powder. The Tb³⁺ luminescence intensity of a composite material dried at room temperature can be improved when higher aliphatic alcohols are applied in a one-pot procedure during a sol–gel synthesis. On the other hand, the Tb³⁺ luminescence is quenched in the presence of Ag nanoparticles in the material. The composite material (YAG:Tb³⁺ in silica) exhibits thermal stability at higher temperatures and achieves the highest emission intensity after having been annealed at 700 °C.