The free radical distribution in emulsion polymerization using oil-soluble initiators

A new approach is presented to calculate both the distribution of particles with iradicals and the average number of radicals per particle in emulsion polymerizations carried out using oil-soluble initiators. The convergence and accuracy of the approach were examined. It was found that, in agreement with previously published experimental results, the present approach predicts a kinetic behavior similar to that found for water-soluble initiators. This effect is primarily due to the desorption of initiator radicals from the polymer particles rather than the contribution of the fraction of oil-soluble initiator dissolved in the aqueous phase.     

Simultaneous spectrophotometric determination of cadmium, copper and zinc

A method for the simultaneous spectrophotometric determination of cadmium, copper and zinc based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene)thiocarbonohydrazide is proposed. The absorption curves of these complexes overlap severely in the scanning range 380–480 nm. The analyte concentrations are calculated by a least squares fit of the pure spectra to the mixture spectra. A linear determination range of 0.1–1.7 μg/ml for cadmium, 0.1–1.3 μg/ml for copper and 0.2–1.2 μg/ml for zinc were obtained. The effect of interference was studied. The method has been applied to the determination of these metal ions in various type of materials.     

Synthesis of 1,2-di-(4-pyridyl)ethylenediamine and related compounds

Hydrolysis of N,N'-diacyl-1,2-di(4-pyridyl)ethylenediamines 1 in aqueous sulfuric acid gave the corresponding imidazolines 3. 1,2-Di-(4-pyridyl)ethylenediamine 2 was prepared in 61 % yield by treating N,N'-di-t-butyl-oxycarbonyl-1,2-di(4-pyridyl)ethylenediamine 4 with trifluoroacetic acid or in 94% yield by the hydrolysis under basic conditions of N,N'-diphthaloylglycyl-1,2-di(4-pyridy)ethylenediamine 13.     

Photooxygenation of 9-methyl-1,2,3,4-tetrahydrocarbazole: A kinetic study

The reaction of the singlet oxygen with 9-methyl-1,2,3,4-tetrahydrocarbazole has been undertaken to give a benzazonine derivative in good yield. Rose-bengal supported on an anionic resin was used as heterogeneous photosensitizing agent. Kinetic evaluation has been made for the additon of singlet oxygen to the indole ring at room temperature.

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9--1,2,3,4- . , , . .

     

Adsorptive stripping voltammetry of bovine serum albumin

The behaviour of bovine serum albumin in cyclic voltammetry and differential-pulse adsorptive stripping voltammetry is described. Under the optimized conditions, with an accumulation potential of +0.15 V (vs. Ag/AgCl) and accumulation times of 50 s or 120 s, linear calibration graphs were obtained for 1.0–4.0×10^?8 M BSA and 0.2–1.5×10^?8 M BSA, respectively.     

Routine Analysis of Catecholamines and Metabolites in Urine by a Liquid Chromatographic Column Switching System

Abstract

A reversed-phase liquid chromatographic technique including a column switching system has been adapted for the routine measurement of catecholamines and their metabolites (14 compounds) in urine. From 1 ml of urine all the compounds and the internal standards were obtained according to combined extraction procedures involving organic solvent, anionic and weakly cationic resins. Finally four extracts (catecholamines, methoxamines, acidic and neutral derivatives) had to be chromatographed throughout a wholly automated apparatus. For each run, the column switching system determined the analytical columns to be used to obtain the separation of the compounds from interferences due to other co-extracted endogenous substances, while the analysis times remained between 20 and 40 min. Such a system allowed the rapid clean-up of columns (in direct- and back-flush mode) carried out between two consecutive injections. By coupling on-line fluorimetric and electro-chemical detections the specificity of the technique could be checked, since the ratio of the responses of both detectors was an index of the purity of the peaks. Finally the advanced automation of the equipment allowed weekly the evaluation of catecholamines and the whole range of their known metabolites in 36 urine samples.     

Sub‐millisecond transient vertical chevron formation during the electroclinic effect in the smectic A∗ phase

X‐ray diffraction studies are carried out in order to probe the smectic layer structure in liquid crystal devices filled with FLC mixture SCE8 and AFLC mixture CS4001, at a temperature just above the SmA?–SmC? phase transtion. The data gathered are time‐resolved in synchronization with a bipolar voltage pulse applied across the device. The layers are observed to move dynamically and reversibly with voltage application and removal, giving evidence for temporary vertical chevron formation due to the electroclinic effect on a timescale consistent with this phenomenon.     

Understanding the Deactivation Pathways of Iridium(III) Pyridine-Carboxiamide Catalysts for Formic Acid Dehydrogenation

The degradation pathways of highly active [Cp*Ir(κ²-N,N-R-pica)Cl] catalysts (pica=picolinamidate; 1 R=H, 2 R=Me) for formic acid (FA) dehydrogenation were investigated by NMR spectroscopy and DFT calculations. Under acidic conditions (1 equiv. of HNO₃), 2 undergoes partial protonation of the amide moiety, inducing rapid κ²-N,N to κ²-N,O ligand isomerization. Consistently, DFT modeling on the simpler complex 1 showed that the κ²-N,N key intermediate of FA dehydrogenation ( I_NH ), bearing a N-protonated pica, can easily transform into the κ²-N,O analogue ( I_NH2 ; ΔG^≠≈11 kcal mol⁻¹, ΔG ≈−5 kcal mol⁻¹). Intramolecular hydrogen liberation from I_NH2 is predicted to be rather prohibitive (ΔG^≠≈26 kcal mol⁻¹, ΔG≈23 kcal mol⁻¹), indicating that FA dehydrogenation should involve mostly κ²-N,N intermediates, at least at relatively high pH. Under FA dehydrogenation conditions, 2 was progressively consumed, and the vast majority of the Ir centers (58 %) were eventually found in the form of Cp*-complexes with a pyridine-amine ligand. This likely derived from hydrogenation of the pyridine-carboxiamide via a hemiaminal intermediate, which could also be detected. Clear evidence for ligand hydrogenation being the main degradation pathway also for 1 was obtained, as further confirmed by spectroscopic and catalytic tests on the independently synthesized degradation product 1 c . DFT calculations confirmed that this side reaction is kinetically and thermodynamically accessible.     

Pd‐PEPPSI‐IHeptCl: A General‐Purpose,Highly Reactive Catalyst for the Selective Coupling of Secondary Alkyl Organozincs

Dichloro[1,3‐bis(2,6‐di‐4‐heptylphenyl)imidazol‐2‐ylidene](3‐chloropyridyl)palladium(II) (Pd‐PEPPSI‐IHept^Cl), a new, very bulky yet flexible Pd–N‐heterocyclic carbene (NHC) complex has been evaluated in the cross‐coupling of secondary alkylzinc reactants with a wide variety of oxidative addition partners in high yields and excellent selectivity. The desired, direct reductive elimination branched products were obtained with no sign of migratory insertion across electron‐rich and electron‐poor aromatics and all forms of heteroaromatics (five and six membered). Impressively, there is no impact of substituents at the site of reductive elimination (i.e., ortho or even di‐ortho), which has not yet been demonstrated by another catalyst system to date.