Determination of p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> values of clinically important perfluorochemicals in nonaqueous media

Perfluorochemicals (PFCs) are clinically and biotechnologically important species. In this work, the potentiometric titration method in nonaqueous media is proposed for the determination of acidity constant values of six different perfluorinated compounds. The saturated and nonsaturated perfluoroacids, perfluorocarnosine, and perfluoroalkyl-β-alanine were potentiometrically titrated in acetonitrile, N,N-dimethylformamide, acetone, ethanol, methanol, and pyridine with tetrabutylammonium hydroxide. The half-neutralization potentials and acidity constants of PFCs have been calculated from the titration curves by using the computerized derivative method. Except for R_F-Carnosine, all of the potentiometric titration curves of the PFCs exhibited one stoichiometric and well-defined endpoints in all of the solvents employed. The reproducibility and sensitivity of the method were evaluated. The text was submitted by the authors in English.     

Synthesis of new <Emphasis Type="Italic">N</Emphasis>-aminoglycosides based on halo-substituted <Emphasis Type="Italic">p</Emphasis>-phenylenediamines and <Emphasis Type="Italic">p</Emphasis>-aminophenols

Condensation of the monosaccharides D-glucose and D-galactose with synthesized halo-substituted p-phenylenediamines and 4-amino-2,6-dibromophenol was studied. It was found that glycosylation occurred only at the 4-amino group that was sterically unhindered by the halogen atom. The position of the aglycon in the glycoside was established by PMR spectroscopy.     

Mechanism of OH radical-induced oxidation of <Emphasis Type="Italic">p</Emphasis>-cresol to <Emphasis Type="Italic">p</Emphasis>-methylphenoxyl radical

The OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical was studied in aqueous solution in a wide pH range by means of pulse radiolysis combined with optical spectroscopy. OH-adduct cyclohexadienyl type radicals were identified as intermediates of the reaction. In the acidic pH range the first-order rate coefficient of phenoxyl radical formation was found linearly dependent on the H₃O⁺ concentration yielding a bimolecular rate coefficient of 1.8 × 10⁸ mol^–1 dm³ s^–1. In the alkaline range a linear dependence was found on the OH^– concentration with rate coefficient of 4.9 × 10¹⁰ mol^–1 dm³ s^–1. These findings were interpreted in terms of acid-base catalysis of the H₂O elimination from the OH-adduct. With the time resolution applied, 30 ns, the radical cation p-CH₃C₆H₄OH^+. was not observed as intermediate.     

Reaction sites of <Emphasis Type="Italic">N,N′</Emphasis>-substituted <Emphasis Type="Italic">p</Emphasis>-phenylenediamine antioxidants

The geometries of N,N′-diphenylbenzene-1,4-diamine (DPPD), N-phenyl-N′-(1-phenylethyl)benzene-1,4-diamine (SPPD), N-(4-methylpentan-2-yl)-N′-phenylbenzene-1,4-diamine (6PPD), N-propan-2-yl-N′-phenylbenzene-1,4-diamine (IPPD), N-(2-methoxybenzyl)-N′-phenylbenzene-1,4-diamine (MBPPD), and N-phenyl-N′-(2-phenylpropan-2-yl)benzene-1,4-diamine (CPPD) as well as of their dehydrogenation products were optimized by the semiempirical AM1 method. The results support the idea of stable N_B=C_X structures formation during the consecutive dehydrogenation of SPPD, 6PPD, IPPD, and MBPPD antioxidants. The biradicals formed during the second step of dehydrogenation of substituted phenylenediamines might be important for their antioxidant effectiveness. Dedicated to Professor Vladimír Kvasnička, DrSc., in honour of his 65th birthday     

Infrared spectra of Hoffmann-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">d</Emphasis></Subscript>-type benzene clathrates

Six new title compounds in the form of Cd(cyclobutylamine)₂M′(CN)₄ · 2G (M′ = Cd or Hg; G = benzene, 1,2-dichlorobenzene, or 1,3-dichlorobenzene) have been prepared in powder form. Their spectral data were found to be consistent with the structure of the Hofmann-T _d -type clathrates.     

Reductive Acylamination of Pyridine <Emphasis Type="Italic">N</Emphasis>-Oxide with Aminopyridines and Their <Emphasis Type="Italic">N</Emphasis>-<Emphasis Type="Italic">p</Emphasis>-Tolylsulfonyl Derivatives

Pyridine N-oxide reacts with 2- and 3-aminopyridines and their N-p-tolylsulfonyl derivatives in alkaline medium in the presence of p-toluenesulfonyl chloride to give N-p-tolylsulfonyl-2,2′- and 2,3′-dipyridylamines, respectively, as a result of reductive acylamination. In the reactions with 4-aminopyridine and 4-p-tolylsulfonyl-aminopyridine, their N-p-tolylsulfonyl- and N,N-bis(p-tolylsulfonyl) derivatives are formed, while reductive acylamination does not occur.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 128–130.Original Russian Text Copyright © 2005 by Solekhova, Kurbatov.     

Structural analysis of <Emphasis Type="Italic">w</Emphasis>/<Emphasis Type="Italic">o</Emphasis>/<Emphasis Type="Italic">w</Emphasis> multiple emulsions by means of DSC

Summary The properties of the inner and the external aqueous phases, were studied in w/o/w multiple emulsions with light microscopic image analysis and differential scanning calorimetry (DSC). The importance of multiple emulsions lies in the presence of these aqueous phases, making them available for sustained, controlled drug delivery systems. Differentiation of these two aqueous phases, studying the effect of manufacturing technology on droplet structure, quantitative determination of phase volumes and any changes occurring during storage are essential when planning w/o/w emulsions. The present study uses microscopic observations combined with DSC measurements in order to identify the formed structure, at developmental stage in case of different components, preparation methods, and stirring rates. These tools are beneficial during manufacturing as in process controls, or to ensure product quality.     

Catalytic hydrogenation of persubstituted <Emphasis Type="Italic">p</Emphasis>-nitrosophenols

Catalytic hydrogenation of dialkyl 2-hydroxy-4,6-dimethyl-5-nitrosobenzene-1,3-dicarboxylates over Pd/C gave the corresponding previously unknown dialkyl 5-amino-2-hydroxy-4,6-dimethylbenzene-1,3-dicarboxylates. The first-order rate constants for the hydrogenation process were found to be linearly related to steric constants of the alkyl groups.     

A Study on the Photochemical Transformations of <Emphasis Type="Italic">p</Emphasis>- and <Emphasis Type="Italic">m</Emphasis>-Nitrosonitrobenzenes

Photochemical oxidation of p- and m-nitrosonitrobenzenes to corresponding dinitrobenzenes was studied. The reaction was described by a scheme involving two successive steps, with the rates of photochemical decomposition of isomeric nitrosonitrobenzenes being much higher than those of dinitrobenzenes. Oligomeric azo and azoxy compounds and the products of hydroxylation of the reaction medium were found as final products of the reaction upon long-term irradiation with UV light.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 287–292.Original Russian Text Copyright © 2005 by Zelentsov, Logunov.     

Spectrophotometric determination of hemoglobin with <Emphasis Type="Italic">p</Emphasis>-acetylarsenazo

In a Britton-Robinson buffer medium at pH 2.87, hemoglobin can form a color compound with p-acetylarsenazo in the presence of emulgent OP. The maximum absorption locates at 370 nm. The apparent molar absorptivity ɛ_{370 nm} is 4.11 × 10⁵ L/(mol cm). Beer’s law is obeyed over the range of 20–60 mg/L for hemoglobin. After the addition of a suitable amount of emulgent OP, the sensitivity and stability of the system can be obviously enhanced. Ethanol can increase the sensitivity of the system. Sodium chloride can enhance the sensitivity of the color system by 30%. The method has been applied to the determination of total proteins in human serums with satisfactory results. The text was submitted by the authors in English.     

Unsteady mass transfer into a sphere under equilibrium condition <Emphasis Type="Italic">y</Emphasis> = <Emphasis Type="Italic">Ax</Emphasis> + <Emphasis Type="Italic">B</Emphasis>

We obtained an analytical solution of a problem of unsteady mass transfer under the equilibrium condition y = Ax + B to compare results with a problem solution in the case of equilibrium condition looking as y = Ax.     

Estimation of uncertainty in p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> values determined by potentiometric titration

A procedure is presented for estimation of uncertainty in measurement of the pK(a) of a weak acid by potentiometric titration. The procedure is based on the ISO GUM. The core of the procedure is a mathematical model that involves 40 input parameters. A novel approach is used for taking into account the purity of the acid, the impurities are not treated as inert compounds only, their possible acidic dissociation is also taken into account. Application to an example of practical pK(a) determination is presented. Altogether 67 different sources of uncertainty are identified and quantified within the example. The relative importance of different uncertainty sources is discussed. The most important source of uncertainty (with the experimental set-up of the example) is the uncertainty of pH measurement followed by the accuracy of the burette and the uncertainty of weighing. The procedure gives uncertainty separately for each point of the titration curve. The uncertainty depends on the amount of titrant added, being lowest in the central part of the titration curve. The possibilities of reducing the uncertainty and interpreting the drift of the pK(a) values obtained from the same curve are discussed.     

Solid solutions Ru<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ir<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> synthesized by thermolysis of coordination compounds

The double complex salts [Ir(NH₃)₅Cl][IrCl₆], [Ru(NH₃)₅Cl][IrCl₆], and [Ru(NH₃)₅Cl]₂[IrCl₆]Cl₂ have been synthesized and characterized. An X-ray diffraction study demonstrated that these salts are isostructural with [Rh(NH₃)₅Cl][OsCl₆] and [Ir(NH₃)₅Cl]₂[PtCl₆]Cl₂ synthesized earlier. Thermolysis of these salts in hydrogen and helium has been studied. X-ray powder diffraction analysis show that thermolysis yields stoichiometric solid solutions of metals as the final products. The unit cell parameters of these products correspond to equilibrium phases.