Purine N-oxides—XLI : The 3-acyloxypurine 8-substitution reaction: On the mechanism of the reaction

The 3-acyloxypurine 8-substitution reaction involves elimination of the 3-acyloxy group and nucleophilic substitution at C-8 to yield 8-substituted xanthines or guanines. In aqueous solutions the reaction of 3-acetoxyxanthine proceeds slowly below pH 2, but is greatly accelerated with an increase of the pH from 3 to 7. It is proposed that the slow reaction involves heterolytic cleavage of the 3-acetoxy moiety from 3-acetoxyxanthine to yield a nitrenium ion at N-3 followed by intermolecular nucleophilic substitution of the incipient carbonium ion at the allylic C-8 position, also the most probable mechanism in polar aprotic solvents. The beginning of the fast reaction coincides with the beginning of ionization of the imidazole hydrogen of 3-acetoxyxanthine. It is proposed that this ionization induces a similar but more rapid departure of the 3-acetoxy group from the anion of 3-acetoxyxanthine to produce dehydroxanthine. The latter, upon protonation, yields the same reactive carbonium ion at C-8 that is formed in the slow reaction. Some reduction of 3-acetoxyxanthine to xanthine accompanies the fast reaction. That reduction has the characteristics of a free-radical mediated reaction. It is proposed that reduction results from a homolytic cleavage of the NO bond in the 3-acetoxyxanthine anion to produce a radical-anion, which abstracts hydrogen from water to yield xanthine. These reaction mechanisms and possible alternatives are evaluated.     

Micelle studies using a metal ion/murexide indicator system

Summary Complex formation between divalent metal ions and the hydrophilic murexide anion in the presence of anionic micelles has been employed to study aspects of micelle formation, the binding of divalent metal ions to micelles, and the kinetics of metal-complex formation in the presence of micelles.

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Zusammenfassung Die Komplexbildung zweiwertiger Metallionen mit dem hydrophilen Indikator Murexid wurde in Gegenwart anionischer Mizellen untersucht. Die Indikatorreaktion wurde benutzt, um Aussagen über Mizellbildung, Bindung zweiwertiger Metallionen an Mizellen und die Kinetik der Metallkomplexbildung bei Anwesenheit von Mizellen zu erhalten.

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With 8 figures and 1 table

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Dedicated to Prof.G. Rehage on the occasion of his 60th birthday.     

Synthesis of lepidine and its derivatives from aromatic amines and quaternary salts of Mannich bases

A quaternary salt of 4-(diethylamino)butan-2-one, methyldiethyl-3-ketobutylammonium methyl sulfate, is used as an alkylating agent to synthesize lepidine and 1-phenyllepidine salts. The method gives good yields, under mild conditions, of lepidine and 1-phenyllepidine perchlorate. An intermediate product is isolated, and a reaction mechanism suggested.     

Studies in qualitative inorganic analysis. V

Summary The interference of borate ion in the group separation of inorganic cations has been examined. Contrary to statements often made in text books, alkaline earth borates do not precipitate in Group III because they are soluble in the ammonium chloride present; Group IV metals [Zn, Co], which form more insoluble borates co-precipitate extensively in Group III when borate is present. It is essential, therefore, to remove most of the borate before precipitating Group III metals. A convenient-method for this removal is described.

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Zusammenfassung Die störende Wirkung von Boration bei der Gruppentrennung anorganischer Kationen wurde untersucht. Im Gegensatz zu Feststellungen vieler Lehrbücher fallen Erdalkaliborate nicht in der 3. Gruppe aus, da sie in Ammoniumchlorid löslich sind. Metalle der 4. Gruppe (Zn, Co), die schwerer lösliche Borate bilden, fallen bei Gegenwart von Borat weitgehend in der 3. Gruppe aus. Es ist daher wichtig, Borat vor der Fällung der 3. Gruppe größtenteils zu entfernen. Eine dazu geeignete Methode wird beschrieben.

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Résumé L'effet perturbateur de l'ion borate dans la séparation par groupes des cations minéraux a été étudié. Contrairement à ce qu'on peut lire souvent dans les livres d'analyse les borates alcalino-terreux ne précipitent pas dans le groupe III car ils sont solubles dans le chlorure d'ammonium qui est présent; les métaux du groupe IV (Zn, Co), qui donnent lieu à formation de borates plus insolubles, coprécipitent abondamment avec le groupe III en présence de borate. En conséquence, il est nécessaire d'éliminer la plus grande partie du borate avant de précipiter les métaux du groupe III. Les auteurs décrivent une méthode commode permettant de procéder à cette élimination.

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Part IV: Mikrochim. Acta [Wien] 1957, 137.     

Application of neutron activation analysis for mercury species determination in scalp hair samples from Malaysia, Libya and Jordan

The sorption of Ba²⁺ ion on natural kaolinite and chlorite-illite clays was investigated at different initial concentrations and temperatures using the radiotracer method. The sorption data were well described by Freundlich and Dubinin-Radushkevich isotherms. Ba²⁺ sorption on both clays showed an exothermic behavior with ΔH° (kJ/mol) values being -7 and -5 for sorption on kaolinite and chlorite illite mixed clay, respectively. The ΔG° values indicate that the sorption was spontaneous with sorption energies corresponding to ion-exchange type sorption. X-ray diffraction studies showed that no significant change in the matrix of the clays occurred upon Ba²⁺ sorption. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of glycol in aircraft ground deicing/anti-icing fluids using flow injection with refractive index detection

A simple method for determining glycol in deicing/anti-icing fluids has been developed. The method uses a single line FIA system with detection based on Schlieren optics. The concentration range was 0-5% glycol and the limit of detection was 0.05%. Samples were preferably pumped at a flow rate of 0.7 ml/min and 100 mul of distilled water was injected (reverse FIA). Detection was accomplished with an 18 mul spectrophotometric flow cell at a wavelength of 410 nm. The conduit connecting the injector and the detector was 10 cm long and had an inner diameter of 0.5 mm. The traditional FIA approach can also be applied, i.e. injection of samples into a carrier of water, but the linear working range is narrower in comparison to the reverse FIA method. Standard addition and near infrared spectroscopy confirmed the validity of the developed method.     

Inelastic scattering of unpolarized neutrons on dimer clusters

On the basis of a microscopic calculation of the inelastic neutron scattering spectra for scattering by exchange dimer clusters, we have determined the conditions for applicability of the semiphenomenological approach to determination of the scattering cross sections based on the spin model. The scattering cross sections obtained in the spin model are distinguished from the exact values by the fact that modified form factors of the SS transitions are used in the exact calculation instead of the magnetic form factors of the individual atoms. In the case of weak overlap of the one-electron wave functions for different centers, the exact scattering cross sections coincide with the cross sections calculated on the basis of the spin model.We have investigated the inelastic neutron spectrum for scattering by a dimer d²–d¹ of mixed valency. Tunneling transfer of the extra electron leads to splitting of the exchange line corresponding to the transition with S=1 in the system with localized electrons and the appearance of new lines. The spectrum consists of a series of forbidden transitions (with conservation of parity and S=1) and allowed transitions (with a change in parity and S=0, 1). The results obtained allow us to determine the parameters of Heisenberg and double exchange in mixed-valency dimers using the inelastic neutron scattering spectra.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 392–398, July–August, 1988.     

Track membrane with immobilized colloid silver particles

A method for modification of track membranes by immobilization of polymer complexes of colloid silver nanoparticles on the surface of microfiltration membranes was developed. The antimicrobial properties of track membranes modified with silver nanoparticles were tested on E. coli, Ps. aeruginosa, St. aureus, and B. cereus.     

Instrumental neutron activation analysis of tree rings for dendrochemical studies

Instrumental neutron activation analysis (INAA) was employed to determine zinc, cadmium and potassium concentrations in the growth rings of ponderosa pine (Pinus ponderosa Dougl.) trees growing along the shores of Lake Roosevelt in Washington State, U.S.A. where mineral processing activities have resulted in high burdens of zinc and cadmium in the lake sediments. The tree growing along the contaminated waterway display elevated concentrations of zinc in its growth rings relative to a tree growing along an uncontaminated tributary of Lake Roosevelt. Cadmium concentrations in the growth rings from both sites are similar from 1988 to 1993. Water quality data indicate an increased concentration of cadmium in the lake from 1984 to 1988. The increased concentrations of cadmium in the lake water were reflected in apparent increases in concentrations of cadmium in individual rings of the tree sampled at the contaminated site. This suggests that translocation of cadmium in the sapwood of heartwood-forming species does not occur in the short term, and thus may not be a limiting factor in using trees as environmental monitors for cadmium. In addition, five-year tree ring segments were analyzed and subsequently reanalyzed as individual single-year ring segments. The analytical data obtained for the pooled individual rings are essentially the same as for the five-year segments, demonstrating the utility of NAA for dendrochemical studies.     

Acoustically levitated droplets — a new tool for micro and trace analysis

First experiences with the technique of acoustical levitation of droplets in the field of analytical and atmospheric chemistry are reported. Acoustical levitation enables the contactless handling of solid and liquid microsamples. This avoids adsorption of analyte at and desorption of contaminants from container walls especially for liquid samples. Common experiments of sample preparation procedures were conducted in levitated drops like liquid/liquid extractions, solvent exchange, and analyte enrichment by evaporation of the solvent. A first approach was made to use acoustical levitation for the simulation of atmospheric chemistry situations. Received: 10 October 1996 / Revised: 25 October 1996 / Accepted: 25 October 1996