Novel polymer-bound chiral selenium electrophiles

[reaction: see text]. Polymer-bound chiral electrophilic selenium reagents have been developed and applied to stereoselective selenenylation reactions of various alkenes. Different cleavage protocols allow further functionalization of the addition products leading to improvements in selenium-based solid-phase chemistry.     

Coprecipitation/accumulation/distribution of manganese and iron, and electrochemical characteristics of Mn in calcareous seawater

A study of managanese and iron associated with particulate matter in seawaters derived from the English Channel (and North Sea). Sequential extraction procedures have been used to identify geochemical processes that govern Mn and Fe coprecipitation/accumulation/distribution in different particulate phases (carbonate; Fe-Mn(hydr)oxides; organic matter and residual phase). The oxidation states of Mn and Fe, some mechanisms of bonding and the magnetic characteristics of particles have been investigated by Mössbauer spectroscopy, electron spin resonance(ESR) spectroscopy, and mass susceptibility balance. The effect of pH and redox potential on stability of different dissolved and particulate Mn species was also examined. In the these calcareous seawaters, manganese (II) is predominantly bound to the carbonate phase (calcite) in the form of Mn_xCa_1-xCO₃. However the persistent occurrence of Mn in oxidation states > 2 in these particles has suggested the existence of manganese(III) in the polymeric FeOOH structures as an intermediate entity during Mn(II) oxidation in the sea. The activity coefficient of the entity MnOOH in FeOOH has been evaluated and p-pH diagrams of Mn have been proposed under marine conditions.     

Flavonoids of the peel of the fruit ofCitrus unshiu

Institute of Biochemistry, Academy of Sciences of the Georgian Republic, Tbilisi, and Samara Medical Institute, Russia. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 821–822, November–December, 1994.     

Use of cyclotron-produced isotopes for analytical investigation: Determination of vanadium in gallium

The extraction of the V(V)-BPHA complex into chloroform and benzene was investigated using⁴⁸V tracer produced from the⁴⁵V reaction using the Variable Energy Cyclotron, Calcutta. A neutron activation analysis procedure for the estimation of vanadium in gallium metal samples based on the extraction of V(V)-BPHA complex into benzene is given.     

Structure of phenolic stabilizers for polymers VIII. Crystal structure of 2,2′-methylenebis(4-methyl-6-ter-butylphenol) monoacrylate

L. Ya. Karpov Scientific-Research Physicochemical Institute. Scientific-Research Institute of Rubber and Latex Goods. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 5, pp. 162–164, September–October, 1991.     

Topological incremental scheme for calculating13C NMR chemical shifts in polysubstituted benzenes with substituents of one kind

A new topological approach to predicting the¹³C NMR chemical shifts of polysubstituted benzenes has been proposed (in the example case of compounds with substituents of one kind of the type C₆H_6–nX_n). The collective interactions of several substituents X [X=CH₃, C₂H₅, iso-C₃H₇, CF₃, COOH, f, Cl, Br, Si(CH₃)₃] have been expressed in the framework of a regression treatment in terms of two-particle increments. The chemical shift of each carbon atom has been represented in the form of an equation containing 17 parameters. The calculation scheme can be transformed and expanded for use even in the calculation of the spectra of compounds not previously studied. The calculated shifts for some previously investigated compounds and some compounds not previously investigated have been presented. The error in reproducing chemical shifts is equal to 0.2–0.3 ppm (and may be as high as 0.8 ppm for only a few measurements).V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 62–71, March–April, 1991.     

Thermal decomposition of ulexite

The thermal decomposition of ulexite, NaCa[B₅O₆(OH)₆] · 5H₂O, monocrystals was investigated by thermal, X-ray, IR and optical microscopy methods at normal and elevated temperatures.It was found that the thermal decomposition has an intraframework character and proceeds in a few separate stages: 1) release of part of the molecular water coordinating the Ca and Na cations; this leads to a rearrangement of the ulexite structure; 2) release of the remaining molecular water and some part the OH groups, which causes breakdown of the ulexite structure, with the simultaneous crystallization of CaO · B₂O₃ and 2CaO·B₂O₃; 3) the slow release of the remaining OH groups up to 600°C, which causes decomposition of the borate rings and the crystallization of NaB₃O₅ and NaCaBO₃.

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Zusammenfassung Mittels thermischer, röntgenographischer, IR- und optisch mikroskopischer Verfahren wurde bei Normal- und bei hohen Temperaturen die thermische Zersetzung von Ulexiteinkristallen NaCa[BsO₆(OH)₆]·5H₂O untersucht.Die Untersuchungen zeigten, daß die thermische Zersetzung von Ulexit einen Innergittercharakter trägt und in einigen separaten Schritten verläuft: 1) Freisetzung desjenigen molekularen Wassers, welches Ca und Na Kationen koordiniert; hierdurch geschieht eine Wiederherstellung der Ulexit-struktur, 2) Freisetzung des verbleibenden Kristallwassers und einem Teil der OH-Gruppen, wodurch eine Zersetzung der Ulexit-struktur unter gleichzeitiger Kristallisation von CaO · B₂O₃ und 2CaO · B₂O₃ erfolgt, 3) langsame Freisetzung der verbleibenden OH-Gruppen bis 600°C, was eine Spaltung der Boratringe und die Kristallisation von NaB₃O₅ und NaCaBO₃ zur Folge hat.

     

Direct determination of cadmium at parts-per-billion level in waters by derivative atomic absorption spectrometry using atom trapping technique

A method has been described for the direct determinations of trace cadmium using derivative atom trapping flame atomic absorption spectrometry with an improved water-cooled stainless steel trapping equipment. The characteristic concentration (gave a derivative absorbance of 0.0044) and detection limit (3sigma) of cadmium were 0.028 and 0.02 ng ml(-1) when collecting for a 1 min, respectively, which were 992 and 145-fold better than those of the conventional flame atomic absorption spectrometry. The detection limit and sensitivity of the proposed method for a 2 min collection time were 1 and 2 orders of magnitude higher than those of conventional flame atomic absorption spectrometry. The present method was applied to the determinations of cadmium in water samples with a recovery range of 91 approximately 111% and a relative standard deviation of 4.7 approximately 5.6%.     

Intraframework thermal reactions of solids

Temperature-activated reactions of decomposition, the synthesis of new compounds, and reduction and oxidation, termed here intraframework reactions, take place within the structural framework of solids. They are distinguished in that they occur within the bulk volume of the substance, in the area of the influence of crystal fields. The atoms and ions participating in these reactions are displaced by diffusion, which is usually directional diffusion. The regularities governing some of these reactions are presented in the paper.

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Zusammenfassung Im Strukturgefüge von Feststoffen treten sogenannte Intratexturreaktionen auf: durch Wärme hervorgerufene Zersetzungsreaktionen, Sýnthese neuer Verbindungen, Reduktion und Oxidation. Diese sind dadurch gekennzeichnet, daß sie im gesamten Volumen der Substanz, in einem vom Kraftfeld des Kristalles beeinflußten Raum ablaufen. Der Austausch der an den Reaktionen teilnehmenden Atome und Ionen wird durch eine stets gerichtete Diffusion verursacht. Es werden Gesätzmäßigkeiten beschrieben, denen einige dieser Reaktionen unterliegen.

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IR spectroscopic study of substituent effects in N,N-dimethylhydrazides of aromatic acids

Conclusions An IR spectroscopic study showed that the C=0 values in the spectra of N,N-dimethylhydrazides of aromatic acids, RCONHN(Me)₂, correlate linearly with a regression equation obtained for the unsubstituted hydrazides of aromatic acids, RCONHNH₂. This dependence differs significantly from that for N-methyl-N-aroylhydrazines, in which ,-conjugation in the RC(O)N group is more pronounced.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2353–2355, October, 1987.