Comparison of two spectrophotometric assays for blood urea nitrogen: Influence of apomorphine

An animal model for apomorphine-induced azotemia is being sought. This investigation requires numerous blood urea nitrogen (BUN) determinations in the presence of apomorphine (APO). Aqueous solutions of APO undergo spontaneous oxidation in air producing a blue-green chromagen. The urease-Berthelot and Fearon spectrophotometric assays for the determination of BUN rely on the production of colored chromagens. The purpose of this investigation, therefore, was to determine (1) if the presence of APO in plasma samples interferes with the measurement of BUN and (2) what is the method of choice for measuring BUN. The results indicate that (1) APO does not interfere with BUN determinations by either method and (2) the urease-Berthelot procedure has the greater accuracy and is the method of choice for routine determinations of BUN.     

Graph—theoretical approach to the calculation of physico-chemical properties of polymers

A topological extrapolation method for the calculation of various properties (melting points, refractive indices, specific rotation, etc.) of infinite linear polymers is developed. The rapid convergence of the oligomer extrapolation series results in very good agreement between calculated and experimental values. Comparison between the proposed method and other empirical or semi-empirical methods (the group addition method and the Pade-approximation) is also presented.     

Electrochemical oxidation of 9-methylxanthine

The electrochemical oxidation of 9-methylxanthine proceeds via four voltammetric oxidation peaks at the pyrolytic graphite electrode. The first voltammetric oxidation peak (peak I_a) is a 1e reaction giving a radical which dimerizes to 8,8′-bi-9-methyl-9H-purine-2,6-(1H, 3H)-dione. Peak II_a is a further 2e electrooxidation of the peak I_a dimer to another yellow dimer 8,8′-bi-9-methyl-9H-purine-2,6-(1H)-dione-3,5-(3H)-diiminylidene. This dimer is not very stable and it hydrolyzes to 1-methyl allantoin. Peak III_a is an adsorption pre-peak to peak IV_a which corresponds, overall, to a direct 4e?4H⁺ electrooxidation of 9-methylxanthine to an unstable diimine of 9-methyluric acid. Hydrolysis of this diimine leads to a variety of ultimate products.     

Semiautomatic indirect titration of alkaline-earth ions with catalytic endpoint indication

A semiautomatic spectrophotometric method of endpoint indication for indirect catalytic titrations of microamounts of alkaline-earth ions is described. The manganese(II)-catalyzed autoxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone is used as indicator reaction. Calcium and magnesium (10–150 μg), strontium (20–250 μg), and barium (20–450 μg) can be determined by adding a known excess of EDTA to the sample solution and back-titrating the unconsumed inhibitor agent with standard manganese(II) solution. This catalytic method was applied to determine the total concentration in calcium and magnesium (total hardness) in natural waters and milk. The method is fast, accurate (1–3%), precise (0.2–0.8%, relative standard deviation), and specially useful for the determination of microamounts where metallochromic indicator are ineffective (for concentrations ranges below 10^?4M).     

Electrochemical and peroxidase-catalyzed redox chemistry of 9-Methyl uric acid

The electrochemical and peroxidase/H₂O₂ oxidation of 9-methyl uric acid has been studied over a wide pH range. Electrochemical, spectral, kinetic and analytical results support the view that the electrochemical and enzymic oxidations proceed by virtually identical mechanisms.     

Molecular structures of (SiCl3)2CH2 and (SiCl3)2CCl2 as studied by electron diffraction

An electron diffraction analysis of the molecular structures of 1,1,1,3,3,3-hexachloro-1,3-disilapropane and octachloro-1,3-disilapropane has been carried out. Deviations from the staggered conformation are indicated. The data may be approximated by models with C₂ symmetry and a small tilt of the SiCl₃ groups. The main bond lengths (r_g) and bond angles obtained for (SiCl₃)₂ CH₂ are: SiCl, 202.7(4); SiC, 186.6(6); CH, 109.8(24) pm, ClSiCl, 107.9(1); SiCSi, 118.3(7)°; and for (SiCl₃)₂CCl₂: SiCl, 202.0(4); SiC, 190.2(9); CCl, 179.6(9) pm; ClSiCl, 109.5(1); SiCSi, 120.6(9); ClCCl, 110.9(16); SiCCl, 106.3(3)°.     

Enhanced Raman spectra from species formed by the coadsorption of halide ions and water molecules on silver electrodes

The enhanced Raman spectra of water molecules and chloride ions coadsorbed at an electrochemically roughened silver electrode are reported. The spectra are discussed in terms of specifically adsorbed chloride ions.     

Cationic degradation of poly(2-methyl-2-ethylthiirane)

Treatment of 2-methyl-2-ethylthiirane (MET) with the cationic initiator triethyloxonium tetrafluoroborate (TEFB) gives a fast and quantitative polymerization followed by a slow degradation of the polymer to a mixture of low molecular weight polymer, 2,5-dimethyl-2,5-diethyl-1,4-dithiane (cyclic dimer of MET), 3,6-dimethyl-3,6-diethyl-1,2,5-trithiepane and 2-methyl-2-butene. When high molecular weight poly-MET, obtained by anionic polymerization of MET with carbazyl potassium, is treated with a trace amount of TEFB, the polymer also degrades to the same low molecular weight compounds. In both cases both the cyclic degradation products were present as nearly equimolar mixtures of the cis- and trans-isomers. In the 1,4-dithianes mixture, a small amount of a third isomer was also detected. A mechanism for the degradation and the possible relation between polymer microstructure and the isomer distribution of the cyclic compounds are discussed.     

New semiconducting oxide photoanodes for water splitting in a photoelectrochemical cell Electrochemistry of n-type NiTiO3

The electrochemical behaviour of NiTiO₃ has been studied. The interest in this mixed-metal oxide lays in its possible use for solar-energy conversion. Anodic oxidation of NiTi0₃ was very irreversible. The electrode became aged, probably due to formation of a porous film of an irreducible higher oxide. The stirring-independent Cottrell behaviour of the anodic oxidation of NiTiO₃ should be due to current limitation by diffusion of a reaction product away from the NiTi0₃ surface through this irreducible higher oxide, which should be of a porous nature. The diffusion-limiting species could not be OH^?, as the Cottrell slopes only increased by about five times for a pH increase from 3 to 14. Five and two processes were involved in the anodic oxidation of NiTiO₃ at pH 14 and 3 respectively, as determined by chronopotentiometry. The same number of processes appeared upon inversion of the current.     

Reassessment of the electronic absorption spectra of Cr(η6-C6H6)2, Cr(CO)6 and Cr(η6-C6H6)(CO)3

The UV absorption bands between approximately 330 and 200 nm have been assigned to Rydberg transitions for the d⁶ complexes Cr(η⁶-C₆H₆)₂, Cr(CO)₆ and Cr(η⁶-C₆H₆)(CO)₃     

The stability and thermodynamic functions of 4-amino-1,6-dihydro-1-methyl-2-methylthio-5-nitroso-6-oxo-pyrimidine complexes with Zn(II), Cd(II) and Hg(II)

The stability constants of the complexes formed by 4-amino-1,6-dihydro-1-methyl-2-methylthio-5-nitroso-6-oxo-pyrimidine with Zn(II), Cd(II) and Hg(II) ions, in aqueous media at different ionic strengths and temperatures, have been calculated by Bjerrum's method.From the data obtained, the thermodynamic functions of complexation processes are reported.     

Solvent extraction and spectrophotometric determination of titanium(IV) with 3-phenyl-3-methyl-2-mercaptopropenoic acid

The distribution equilibria of 3-phenyl-3-methyl-2-mercaptopropenoic acid (PhMMP) and the titanium(IV)-PhMMP complex have been studied. An extraction-photometric method for the determination of microamounts of titanium has been developed. We have investigated the influence of pH, the reagent, and the presence of electrolytes and masking agents in the aqueous phase on the equilibrium. From the slope analysis of the distribution curves the composition of the extracted species has been found to be Ti(OH)₂(HR)₂. The complex is extracted quantitatively. Beer's Law is followed over the range 0.09–3.74 μg ml^?1 of titanium(IV), the molar absorptivity is 1.65 × 10⁴ liters mol^?1 cm^?1, and the Sandell sensitivity is 2.8 ng cm^?2 at 439 nm. This method has been applied to the determination of titanium in a bauxite.     

Harmonic force field for monomeric gallium trifluoride with application of the keating bendings

A normal coordinate analysis for GaF₃ is presented for the first time. Several force field approximations were investigated. The new type of so-called Keating coordinates were applied in addition to the familiar valence and central coordinates. A Coriolis constant was estimated from the theory of its mass dependence. The unobserved ω₁(A_1′) frequency was calculated. A final (‘exact’) force field was determined with the aid of a reported Δω₃ isotopic frequency shift. Finally the mean amplitudes of vibration and Bastiansen-Morino shrinkage effect at temperatures up to 1000°C were computed.     

Infrared study of trapped carbon dioxide in thermally treated apatites

The formation of molecular CO₂ in synthetic apatites (prepared in aqueous systems), dental enamel, dentine, and various apatitic rock phosphates after heating in the range 120–900°C has been investigated by infrared spectroscopy. The CO₂ band at 2340 cm^?1 was observed in the synthetic samples, enamel, and some of the rock phosphates, but not in dentine or bone. It is suggested that the absence of this band in dentine and bone is caused by the small crystal size of their apatites. The CO₂ band at 667 cm^?1 was never observed. The polarized infrared spectrum of heated dental enamel showed that the linear CO₂ molecules were either randomly oriented or oriented so that the length of the molecules made an angle of about 56° with the c axis. It is suggested that, if the latter is correct, the CO₂ originates from a CO^2?₃ ion which occupied the sloping face of the phosphate ion site.     

Sampling and analysing mixtures of sulphate, sulphite, thiosulphate and polythionate

Interpreting the redox chemistry of sulphur in aqueous systems requires the analysis of mixtures of various sulphoxy anions. Previous methods have been too involved to permit high sample throughout if good quality control is to be maintained. Methods based on ion chromatography have been developed for the direct determination of SO(2-)(4), SO(2-)(3), S(2)O(2-)(3), and SCN(-). The determination of thiocyanate permits the indirect determination of polythionates by treatment with cyanide. Formate, acetate, F(-), Cl(-), CO(2-)(3), and PO(3-)(4), do not interfere, but NO(-)(2) and NO(-)(3) interfere with determination of SO(2-)(3),. The sample preservation treatment includes addition of formaldehyde, cation-exchange and cold storage, to retard oxidation of S(2)O(2-)(3), and SO(2-)(3), and inhibits the rearrangement of SO(2-)(3),/S(2)O(2-)(3),/S(n)O(2-)(6), mixtures caused by bimolecular nucleophilic displacement (S(N)2) reactions. Treated samples may be stored for up to 6 weeks with only minor loss of thiosulphate.     

A fluorimetric kinetic method for the determination of tonin activity in rat submaxillary glands

A method for the kinetic determination of tonin activity in rat submaxillary gland extracts is described. The method is based on the fluorogenic reaction of o-phthalaldehyde with the dipeptide histidyl-leucine generated in the enzymatic hydrolysis of angiotensin I. The reaction is monitored by fluorescence at 440 nm. At pH 7.5, the method allows the determination of 2–15 nmol/ml histidyl-leucine with relative standard deviation of 6%.