Demetallation of α,β,γ,δ-tetrakis(p-sulfophenyl) porphiniron(III) in mineral acid–alcohol–water media

Demetallation rates of α,β,γ,δ-tetrakis(p-sulfophenyl)porphiniron(III) in hydrochloric acid–ethanol–water, perchloric acid–ethanol–water, and sulfuric acid–alcohol–water media were determined. For a given acidity value H₀ the order of the rates for the three acids was HCl > H₂SO₄ > HClO₄. This is also the order for complex formation between acid anion and iron(III). Consequently ligands as well as protons are involved in the breaking of bonds between the metal and the porphyrin leading to the formation of the activated complex. The log k values for HCl and HClO₄ media were not linearly related to the Hammett acidity function as they were for sulfuric acid–ethanol–water media. The average ΔH? and ΔS?values for the HCl media were 18.4 ± 1.4 kcal/mol and ? 19 ± 3 cal K mol, respectively, in very close agreement with those for H₂SO₄ media despite the difference in H ₀ dependence. For H₂SO₄–alcohol–water media the order of the rates was butanol > propanol > ethanol with little difference between isomeric alcohols.     

Hydrolysis of acetylcholinesterase inhibitors--organophosphorus acid anhydrolase enzyme immobilization on photoluminescent porous silicon platforms

We report on the immobilization of an OPAA enzyme on luminescent porous silicon devices, and on the utilization of this new platform to hydrolyze p-nitrophenyl-soman.     

The determination of glycerol : General introduction: volumetric determination as the copper complex

A method for the determination of glycerol by means of the copper-glycerol complex is described; the complex is filtered free of excess copper(II) hydroxide and the copper is determined iodimetrically. Earlier difficulties due to adsorption of the complex are overcome by the use of glass-fibre filter discs. The method gives accurate results in the range 40-4% glycerol in the solution (400 to 40 mg glycerol in the aliquot taken).     

The structure of some methyl and benzyl malonate derivatives of pyrimidine

Reaction of 2,4,6-trichloropyrimidine with sodium dibenzylmalonate in p-dioxane gave 4,6-dichloro-2-(dibenzylmalonyl)pyrimidine, while reaction of 2,4,6-trichloropyrimidine with sodium dimethylmalonate yielded both 4,6-dichloro-2-(dimethylmalonyl)pyrimidine and 2,2-bis-(4,6-dichloropyrimidin-2-yl)dimethylmalonate. Structural studies using nmr, ir and uv spectroscopy indicate that for the former two compounds in basic solvent, an equilibrium exists between the keto forms and resonance-stabilized enolate ions.     

Aquation of chloropentaamminecobalt(III) Perchlorate in chloride-ion containing water–nonaqueous solvent mixtures

The equilibrium quotients for the formation of Co(NH₃)₅Cl²⁺ from Co(NH₃)₅OH₂³⁺ and Cl^? were 3.74±0.25 M^?1 and 6.07±0.54 M^?1 at 45.0°C in 10:1 mole ratio water: dimethyl sulfoxide and in 25 w/w % aqueous ethanol, respectively, and those forthe formation of the ion pair Co(NH₃)₅OH₂³⁺ . Cl^? were 1.21±0.20 M^?1 and 1.58±0.17 M^?1, respectively, in the same solvents. The aquation and anation rateconstants were determined at 45.0°C for these two solvents over the range of chloride-ion concentrations 0.0 ≤ [Cl^?] ≤ 0.9 M. The aquation rate constant was essentially independent of chloride-ion concentration in each solvent over this range. The inverse of the pseudo-first-order anation rate constant was linearly dependent on the inverse of the chloride-ion concentration in each solvent. The least squares relationships between (1/k_an) and (1/[Cl^?]) gave intercepts and ratios of intercept to slope which were analyzed interms of I_d and D mechanisms. It was concluded that the data were not satisfied by a D mechanism, but that they were consistent with an I_d mechanism.     

Calculation of some N and C nuclear shielding parameters for some ureas and thioureas

Molecular orbital calculations using CNDO/S parameters are employed to determine bond-orders, charge-densities and the shielding of the ¹⁵N and ¹³C nuclei of a series of ureas and thioureas. For the sterically uncrowded molecules a linear relationship is noticed between the ¹⁵N chemical shifts and C---N bond-orders. When steric crowding occurs this simple relationship is no longer applicable.     

Deconvolution of the light- and heavy-hole free exciton fine structure in AlxGa1−xAs---GaAs multi quantum wells using photoluminescence excitation spectroscopy

Sharp-line structure associated with both the light-hole free exciton (LHFE) and heavy-hole free exciton (HHFE) transitions has been observed in multi-quantum-well (MQW) structures of four well sizes in photoluminescence (PL) and reflection spectra. These spectra have been deconvulated using photoluminescence excitation spectroscopy (PLE). The LHFE and HHFE sharp-line structure is associated with interface structure composed of growth islands at the interface between the barriers and the wells. Estimates of the average interface island sizes for the four different MQW structures are made based on theoretical modelling. A correlation is established between particular LHFE fine structure components and specific HHFE fine structure components. A model is developed to account for the LHFE and HHFE fine structure based on a non-random distribution of the interface structure. The physical location of the excitons is demonstrated to be in regions of the wells with essentially identical interfacial microstructure. Evidence for diffusion of excitons from effectively narrow well regions to wider well regions is presented.