Reactions of superoxide anion radical with antioxidants and their use in voltammetry

Kinetic parameters were calculated for the electrochemical reduction of oxygen at a glassy-carbon electrode with the generation of superoxide radical anions in a 0.05 M solution of (C₂H₅)₄NI in dimethylformamide in the presence of fat-soluble antioxidants, retinol and -tocopherol. A procedure based on the protonation of the radical anion with antioxidant molecules is proposed for the voltammetric determination of antioxidants to determine milligram amounts of retinol and -tocopherol in model solutions (RSD = 1–2%). The calibration graphs for retinol and -tocopherol are linear in the concentration ranges 9.7 × 10^–5–2.3 × 10^–3 and 6.2 × 10^–4–3.1 × 10^–3 M, respectively. The detection limits for retinol and -tocopherol are 4.8 × 10^–5 and 4.1 × 10 ^–4 M, respectively. The procedure was applied to the determination of the active component (retinol and -tocopherol) in pharmaceuticals.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 56–59.Original Russian Text Copyright © 2005 by Ziyatdinova, Gilmetdinova, Budnikov.     

Reformatsky Reaction with N-Substituted 6-Bromo-2-oxochromene-3-carboxamides

Reformatsky reactions of ethyl -bromopropionate, methyl -bromobutyrate, and methyl -bromo-isobutyrate with N-substituted 6-bromo-2-oxochromene-3-carboxamides in the system diethyl ether–benzene– HMPA give N-benzyl-6-bromo-4-(1-alkoxycarbonylalkyl)-2-oxochroman-3-carboxamides, while in the system diethyl ether–benzene–HMPA–THF, 3-R¹-1-R²-1-R³-9-bromo-2,3,4,4a,5,10b-hexahydro-1H-chromeno[3,4-c]-pyridine-2,4,5-triones are obtained.     

Thermodynamics of Binding of α:-Cyclodextrin to Straight-Chain Alkyl Derivatives in Aqueous Solution

Apparent standard Gibbs energy, enthalpy, entropy, and heatcapacity data of the interactions of -cyclodextrin (CD) to some n-carboxylatesH(CH₂)_nCOO^- (n = 4–6), are determined by isothermal titration microcalorimetryat different temperatures in phosphate buffer, pH 9.0, assuming a 1 : 1 model indilute solution. Modelling of contributions of the thermodynamic properties of the solutionindicates that CD undergoes conformational change upon binding to homologousseries of n-carboxylates, n-alcohols, ,-alkane dicarboxylates and ,-alkane diols.     

Molar cotton-mouton constants and anisotropy of magnetic susceptibility of benzyl chlorides and benzyl bromides

Conclusions Due to thearom^–gsC-Hal* interaction, the magnetic susceptibility ellipsoids of -haloalkylbenzenes, with the exception of ,'-p-xylylidene bromide, undergo rearrangement of the semimajor axes with a decrease in the diamagnetic component in direction 1, 4 and along the axis of symmetry of the electrons in the ring.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No No. 7, pp. 1552–1557, July, 1986.     

Influence of chelating agents in eluent on the separation factor of lithium isotopes

The influence of chelating agents on the separation factor, , of lithium isotopes separation was studied by ion exchange elution chromatography. Eluents contained the chelating agent having different number of coordination sites. The chelating agents used in eluent were Na-glycine (Na–Gly), 2Na-iminodiacetic acid (2Na-IDA), 3Na-nitrilotriacetic acid (3Na-NTA), and 4Na-ethylenediaminetetraacetic acid (4Na-EDTA). The ion exchanger was Dowex 50W-X8, sulfonic acid type, sodium form. As a result,⁶Li was enriched in resin phase, and⁷Li was in solution phase. The separation factor, , was gradually increased with increasing number of coordination site (=1.0022–1.0038) at the same distribution coefficient and with increasing distribution coefficients (=1.0017–1.0026) at the same concentration of chelating agents.     

Zur Kenntnis der gemeinsamen Einwirkung von elementarem Selen und gasförmigem Ammoniak bzw. Ethylenimin auf Ketone

Elemental sulfur reacts with ketones and gaseous ammonia at room temperature yielding thiazoline-3 in excellent yields. Under the same conditions elemental selenium does not react at all. Attempts using the known techniques which have been applied in improving the reactivity of slowly reacting ketones in thiazoline-3-synthesis have been unsuccessful (Exp. No. 1–17). The reaction of -halogenketones with sodiumhydrogenselenide to synthesize -hydroselenoketones gives only the original ketones and selenium in almost quantitative yields (No. 18–23). The same is observed with -haloketones and sodium ore magnesium-diselenides (No. 24–45). The explanation of these unexpected results is the strong reducing power of the hydrogenselenide (No. 46–52). Even -bromoketones with activated bromine (i.g. by phenyl groups) were reduced by sodiumhydrogensulfide giving red undefinite oils. However, -chloroketones give -mercaptoketones in excellent yields (No. 53–61). Hydrogenselenide reduces -mercaptoketones to sulfur and ketones in the presence of triethylamine (No. 62–67). Also the transformation of -selenocyanketones to ,-diketodisenides by alkali or the oxidative hydrolysis of selenium-BUNTE salts does not work and gives elementary selenium only. Studies about the concomitant reaction of elementary selenium and ethylenimine on ketones were continued (No. 68–82).

     

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)][Cu(NO3)4]· H2O

The thermal decomposition process of the complex [Cu(NBOCTB)][Cu(NO₃)₄] H₂O has been studied by TG and DTG technique, and possible intermediates of the thermal decomposition have also been conjectured from the TG and DTG curves. The results suggest that the decomposition of the complex involves five steps: The non-isothermal kinetics of steps 1, 2 and 3 have been studied by means of the Achar and Coats-Redfern method based on TG and DTG curves. Step 1 is a Coring and Growth mechanism (n= 1), its kinetic equation may be expressed as: d/dt=Ae^–E/RT(1–). Steps 2 and 3 are both two order chemical reaction mechanisms, their kinetic equations can be expressed as: d/dt=Ae^–E/RT(1–)².This project was supported by the National Natural Science Youth Fundation of China.     

Improvement for α-energy resolution in determination of low level plutonium by liquid scintillation counting

An improvement of -energy resolution for determining low level plutonium has been investigated using combined solvent extraction-low level liquid scintillation counter. In the present work, -energy resolution of 270–290 keV for liquid scintillation spectra of²³⁶Pu and²³⁹Pu is attained. Thus the simultaneous determination of low level plutonium with -liquid scintillation spectrometry may be practized.     

/α, xn/ reactions on159Tb

Target foil stacks of terbium were bombarded with -particles of incident energies 55 MeV. Excitation functions for the /,xn/ x=2–5 reactions were determined. On the basis of the cross sections, the thick target yields of^/163–x/Ho /x=2.5/ have been evaluated. Activation and stacked-foil techniques were applied.     

Triterpene glycosides ofHedera taurica I. Structure of tauroside E from the leaves ofHedera taurica

The structure of taurorisde E — the predominating triterpene glycoside from the leaves of Crimean ivy,Hedera taurica Carr. has been established by¹H and¹³C NMR spectroscopy using nuclear Overhauser effects. It is 3-O-[O--L-rhamnopyranosyl-(12)--L-arabinopyranosyl]hederagenin.M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedenenii, No. 3, pp. 363–366, May–June, 1987.     

Withasteroids ofPhysalis VI.1H and13C NMR spectra of withasteroids ixocarpalactone A and ixocarpanolide

The¹H and¹³C NMR spectra of two withasteroids isolated fromPhysalis ixocarpa Brot. have been studied in detail. Their spectral characteristics are discussed. A comparison of the results obtained has led to the identification of a withasteroid with the composition C₂₈H₄₀O₈, mp 291–292°C (from methanol) as ixocarpalactone A, in spite of some difference in its physical constants. The other compound, with mp 252–253°C (from methanol), had the composition C₂₈H₄₀O₆, [] _D ²⁰ +27±4°, is new and has been called ixocarpanolide. The structure of 5,20R-dihydroxy-1-oxo-6, 7-epoxy-22R-witha-2-enolide has been proposed for it.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 326–332, May–June, 1986.     

Infrarotspektroskopische Charakterisierung von Carbons?uren durch ihre Trimethylsilylester

Zusammenfassung 91 Carbonsäuren wurden mit Dialkoxytrimethylsiloxy-N-trimethylsilylphosphoriminen (besonders Diäthoxytrimethylsiloxy-N-trimethylsilylphosphorimin, DASPI) oder mit Trimethylsilylmethyl acetamid, TMSMA, silyliert. Die C=O-Frequenzen der entsprechenden Trimethylsilylester können zur Ermittlung des Substitutionstyps am-C-Atom der Carbonsäuren dienen.-Aminosäuren bilden eine Ausnahme. Diese Säuren wurden wegen ungenügender Silylierung mit DASPI nur mit TMSMA silyliert. Folgende Frequenzbereiche der Silylesterbande wurden gefunden: aliphatisch, aliphatisch-verzweigt 1713 bis 1733 (1722±4) cm^–1;-heterosubstituiert, einschließlich-Acylamino- 1721–1754 (1737±11) cm^–1, in den meisten Fällen von einer zweiten, längerwelligen Bande begleitet im Abstand von 10–25 cm^–1:-unge-sättigt 1687–1736 (1701±13) cm^–1; aromatisch 1673–1721 (1705+10) cm^–1;-Amino- 1702–1731 (1719±7) cm^–1. (In Klammern: Mittelwerte mit Standardabweichung.)

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Infrared-spectroscopic characterisation of carboxylic acids by their trimethylsilyl esters

91 Carboxylic acids were silylated by dialkyltrimethylsilyl-N-trimethylsilyl phosphorimidates (mainly diethyltrimethylsilyl-N-trimethylsilyl phosphorimidate, DESPI) or trimethylsilylmethyl acetamide, TMSMA, and the C=O frequencies of the corresponding trimethylsilyl esters were investigated. Exceptions were -amino acids. Due to uncomplete silylation by DESPI these were silylated by TMSMA, but investigations in the region lower than 1690 cm^–1 could not be made because of the strong absorption by the amide I band of TMSMA.The following frequency regions of the silyl ester band were found: aliphatic, aliphatic-branched 1713–1733 (1722±4) cm^–1;-heterosubstituted, including-acylamino- 1721–1754 (1737±11) cm^–1 and, in most cases a second, lower frequency band at a distance of 10–25 cm^–1 originating from conformational isomers:-unsa-turated 1687–1736 (1701±13) cm^–1; aromatic 1673–1721 (1705±10) cm^–1;-amino-1702–1731 (1719±7) cm^–1. (In brackets: mean value ± standard deviation.)

     

Spectrophotometric determination of papaverine hydrochloride by reaction with phloxin

A new withasteroid — vamonolide — has been isolated from the epigeal part ofPhysalis angulata L. (Solanaceae). On the basis of spectral characteristics, its structure has been established as 5,14-dihydroxyl-l-oxo-6,7-epoxy-20R,22R-with-2-enolide.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 856–858, November–December, 1987.     

Chemical transformations and evaluation of the basicities of 4,5-dihydropyrrolo[1,2,3-e,f][1,5]benzodiazepin-6(7h)-ones

The alkaline hydrolysis, amidation, and methylation of 4,5-dihydropyrrolo[1,2,3-e,f][1,5]benzodiazepin-6(7H)-one derivatives under various conditions were investigated. The ionization constants (pK) for 1,2-dimethyl-4,5-dihydro[1,2,3-e,f][1,5]benzodiazepin-6(7H)-one were calculated by the Hammett indicator method, and two values, viz., pK ¹ = –2.37 and pK ² = 5.53, which were ascribed to protonation of the diazepine ring and the indole ring of the molecule, respectively, were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 983–986, July, 1981.     

R?ntgenspektrometrische Goldbestimmung in sulfidischen Erzen nach chemischer Anreicherung

Zusammenfassung Es wird eine Goldbestimmung an sulfidischen Erzen für den Bereich von 0,05–5 ppm bei 20 g Einwaage beschrieben. Das Gold wird durch Salpetersäurebehandlung von den übrigen Metallen getrennt, mit Salzsäure/ Salpetersäure gelöst und mit Selen als innerem Standard und Tellur als Spurenfänger mittels Zinn(II)-chlorid gefällt. Der Niederschlag wird auf ein Membranfilter aufgezogen. Die Goldbestimmung erfolgt über den Impulsratenquotienten der Gold L- und Selen K-Linien. Die störende Molybdän K-Strahlung und die Comptonstreuung werden durch ein Zirkoniumblech auf dem Röhrenfenster unterdrückt. Der Variationskoeffizient beträgt 20% für 0,2–5 ppm und 53,6% für 0,05 ppm.

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Summary A method is described for the determination of gold in sulphide ores within the concentration range of 0.05–5 ppm with sample weights of 20 g. Gold is separated from the other metals by treatment with nitric acid, dissolved by hydrochloric acid, containing some nitric acid, and is finally precipitated by stannous chloride applying selenium as internal standard and tellurium as collecting agent. The precipitate is mounted on a diaphragm filter and the determination of gold is carried out by X-ray analysis suppressing the disturbing Mo _K radiation and compton scattering by a zirconium sheet-metal on the X-ray tube. The pulse rate quotient of the lines Au _L /Se _K is a function of the concentration of gold. The variation coefficient is 20% for 0.2–5 ppm and 53.6% for 0.05 ppm.

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Herrn Prof. Dr.-Ing. habil. J. Hesemann zum 65. Geburtstag gewidmet.     

Ferrocene-containing polyelectrolyte multilayer film-covered electrodes: electrocatalytic determination of ascorbic acid and use of inner blocking layers to improve the upper detection limit of the electrodes

A multilayer film composed of ferrocene(Fc)-appended poly(allylamine hydrochloride) (Fc-PAH) and poly(potassium vinylsulfate) (PVS) has been prepared on the surface of a gold(Au) electrode by using a layer-by-layer self-assembly technique. Fc-containing polyelectrolyte multilayer (PEM) film-modified electrodes can electrochemically catalyze the oxidation of ascorbic acid successfully. For a 2 (Fc-PAH/PVS) bilayer-covered electrode the catalytic current increased linearly with increasing concentration of ascorbic acid over the concentration range 6 mol L^–1–3 mmol L^–1. To extend the dynamic range for ascorbic acid, the surface of the Au electrode was first covered with a (PAH/PVS)₂ film on which an additional (Fc-PAH/PVS)₅ film was coated. This strategy successfully extended the dynamic range of the electrode up to 25 mmol L^–1 ascorbic acid, because the (PAH/PVS)₂ layer blocked access of ascorbic acid to the electrode surface. The upper detection limit of the (PAH/PVS)₂ (Fc-PAH/PVS)₅ film-modified electrode is much higher than those of Fc-based ascorbic acid sensors reported so far. Electron transfer is diffusion-controlled within the (PAH/PVS)₂(Fc-PAH/PVS)₅ film.     

Kalorimetrische und Infrarotspektroskopische Untersuchung von mechanisch hervorgerufenen Konformationsumwandlungen bei Poly-[L-alanin]

Zusammenfassung Es wurden die Wärmestrom- und Kraft-Dehnungskurven von Poly[L-alanin]-Fasern und -Folien bei uniaxialer Verstreckung in einem Verstreckungskalorimeter gemessen. Aus der zum Verstrecken benötigten Arbeit A und der zugehörigen Wärmetönung, ergab sich die Änderung der inneren Energie U der Proben. Es zeigte sich, daß im allgemeinen bis etwa 1 % Dehnung, wobei weitgehend reversibles energieelastisches Verhalten vorherrscht, U um 0,25-0,3 J/g (60–70 mcal/g) zunimmt. Bei weiterer Dehnung steigt U erheblich stärker an (bis 1,5 J/g bei 2% Dehnung), jedoch ist U stark abhängig von der Vorbehandlung z. B. durch Vorverstreckung oder vom Gehalt an niedermolekularen, als Weichmacher wirkenden Substanzen.Da die irreversiblen Änderungen in der Probe hier besonders interessieren, vor allem im Hinblick auf Konformationsumwandlungen wie z. B. , wurde stufenweise verstreckt und nach jedem Dehnzyklus (Dehnen + Entlastung) die Summe der Energieänderung gegen den maximalen Dehnungsgrad aufgetragen. Oberhalb 1 % Dehnung ist diese Energieänderung > 0 und geht mit einer bleibenden Dehnung einher, abhängig von Probenart und Vorgeschichte. Es wurde daher die Änderung von U nach einem Dehnzyklus ( U _D + U _E ) auf diese bleibende Dehnung bezogen.Für die Ermittlung der mit einer Konformationsänderung verbundenen Änderung der inneren Energie ist es erforderlich,die Anteile der verschiedenen Konformationen zu ermitteln. Hierzu wurden die IR-Spektren verwendet. Für die Bestimmung des -Helix-Anteils dienten die Absorptionsbanden bei 1270 bzw. 370 cm^–1, für die der -Faltblattstruktur die Doppel-Banden bei 1220 () und 1240 () cm^–1 und die bei 440 cm^–1, die aus den Banden bei 445 cm^–1 () und 432 cm^–1 () besteht. Dabei wurden als Normierungsbanden die weitgehend konformationsunabhängigen Banden bei 1380 cm^–1 sowie die bei 1050 cm^–1 verwendet.Es zeigte sich, daß nach dem Verstrecken -helicaler Poly-[L-alanin]-Proben um 5% eine bleibende Dehnung von um 2% auftritt, wobei der -Helix-Gehalt um 4% abnimmt. Bei Orientierung in Verstreckrichtung bedeutet dies auf Grund des Längenverhältnisses eines Aminosäurerestes in der -Helix zu der in einer gestreckten Anordnung von 1,5:3,5 = 1:2,3, daß der Anteil an ß-Struktur um 1,5 % zugenommen hat. Man kann demnach davon ausgehen, daß die restlichen 2,5 % -Helices in eine nichtperiodische Konformation übergegangen sind. Aus den dehnungskalorimetrischen Messungen ergab sich aufgrund der Zunahme von U um 2,1 J/g bei 1% irreversibler Dehnung eine Energieänderung von 19 kJ/mol (4,6 kcal/mol). Geht man davon aus, daß -Helix und ß-Faltblattstruktur dieselbe innere Energie haben, so entspricht das einer Energiedifferenz von 16 kJ/mol (3,8 kcal/mol) zwischen den o. a. periodischen Konformationen und der nichtperiodischen, was mit dem vonBirshtein undSkvortsov theoretisch ermittelten Wert von 3,5 kcal/mol gut übereinstimmt (30).

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Summary The heat-flux and stress-strain-curves of poly-[L-alanine]-fibers and films were measured using a stretching-calorimeter. The change in the internal energy U was determined from the mechanical workA necessary for stretching and the heat Q. Up to 1% stretching reversible energyelastic behaviour is predominant and U increases at about 0,25-0,3 J/g (60–70 mcal/g). At higher degrees of stretching U increases considerably more (e. g. up to 1,5 J/g at 2% stretch), however, U depends strongly on the pretreatment of the sample like prestretching or the content of low molecular weight substances acting as a plastifier.In respect to conformation changes of the poly-[L-alanine] e. g. , irreversible changes of the sample during stretching were of special interest. Therefore the samples were stretched stepwise and the sum of the energy changes after each stretching cycle (i. e. after loading and deloading) was plotted against the maximum degree of stretching. Above 1 % this energy change is > 0 and is accompagnied by an irreversible change in length, depending on pretreatment and the kind of sample. According to this, the change of U after one stretching cycle ( U _D + U _E ) was divided by this irreversible change in length.For determining the change in internal energy U due to a conformation change it is essential to determine the content of the different conformation types like , and random. IR-spectroscopy seems to be the most suited method at present for this purpose. For the determination of the -helix content we used the absorption bands at 1270 cm^–1 resp. 370 cm^–1 and for the ß-pleated sheet-structure the double-bands at 1220 cm^–1 () and 1240 cm^–1 () and that at 440 cm^–1, consisting of the bands at 445 cm^–1 () and 432 cm^–1 (). As reference bands which are independent on conformation to a high degree we used those at 1380 cm^–l and 1050 cm^–1.After stretching of almost pure a-helical poly-[L-alanine] at about 5% an irreversible stretch of 2% occurs and the -helix content decreases at about 4%. This means that, if molecules are oriented in stretching direction, the content of ß-structure has increased by 1,5% because the relation in length of one amino-acid residue in the a-helix and in the ß-structure is 1,5 : 3,6 = 1 : 2,4. Therefore it seems that 2,5% -helix content have changed into a non-periodic (random)-conformation. From the increase in U of 2,1 J/g at 1% irreversible stretch a change of 19 kJ/mole (4,6 kcal/mol) occurs. Assuming that the internal energy of -helix and ß-pleated-sheet-structure is the same, this is equivalent to a difference in H between these periodic structures and the non-periodic one of 16 kJ/mole (3,8 kcal/mole) which is in a reasonable agreement with that of 3,5 kcal/mole calculated byBirshtein andSkvortsov from theoretical considerations (30).

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Herrn Prof. Dr.G. Rehage zum 60. Geburtstag gewidmet.

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Mit 9 Abbildungen und 2 Tabellen     

ESR study of NiIII complexes with nitrosonaphthols and dithio acids

Mixed-ligand Ni^III complexes with -nitroso--naphthol, -nitroso--naphthol,o-ethylxanthate, andN,N-diethyldithiocarbamate as ligands have been studied by ESR in liquid and frozen solutions. The degrees of symmetry distortion for the first coordination sphere of these complexes have been determined. It is shown that the transition from planar square Ni^IIL₂ complexes to more stable octahedral Ni^IIIL₂L and Ni^IIILL₂ complexes occursvia the radical addition mechanism. A method for trapping short-lived radicals is suggested on the basis of the complex formation scheme.Translted fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1513–1515, August, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-5050)     

Synthesis and characterization of α-[P2W15O62M3]12- (M = Ti or Zr) heteropolyanions

Summary The trisubstituted Dawson anions -XaHb[P₂W₁₅O₆₂M₃]· nH₂O (X = K or Me₄N; a + b = 12; M = Ti or Zr) have been prepared from the lacunary precursor Na₁₂[-P₂ W₁₅O₅₆]·24H₂O and characterized by elemental analysis, i.r., u.v. and ¹⁸³W-n.m.r. spectroscopy, and by an electrochemical method. The ¹⁸³W-n.m.r. spectrum of -[P₂W₁₅Ti₃O₆₂]^12– exhibits three lines of 122 intensity at –148.32, –182.91 and –212.95 p.p.m., as expected for the C _3v structure of the trisubstituted -Dawson anion.Author to whom all correspondence should be directed.