Crystal structure of 1,2-bis-(phenylseleno)-1,2-dichlorethene

Vladimir State Pedagogical Institute. Institute for Elementorganic Compounds, Russian Academy of Sciences. Irkutsk Institute for Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 153–154, July–August, 1992.     

Triterpene glycosides from Kalopanax septemlobum. VII. Minor glycosides from stems of Kalopanax septemlobum var. maximowiczii and Kalopanax septemlobum var. typicum

Sixteen triterpene glycosides, three of which were new, hederagenin 28-O-β-D-glucuronopyranosyl ester and 28-O-β-D-gentiobiosyl ester and oleanolic acid 3-O-α-L-arabinopyranoside, were isolated from stem bark of Kalopanax septemlobum. The glycoside contents in stem bark of two varieties, maximowiczii and typicum, were compared. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 49–53, January–February, 2006.     

Measurement of adsorption heats of nitrogen on metal nitrides

Adsorption heats q and activation energies of the nitrogen exchange on several metal nitrides have been compared. For the systems capable of changing readily their composition upon varying conditions, the isotope exchange is suggested to be the most reliable method of the determination of q.

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Synthesis, structure, and X-band (9.5 GHz) EPR characterization of the new series of pH-sensitive spin probes: N,N-disubstituted 4-amino-2,2,5,5-tetramethyl-3-imidazoline 1-oxyls

[reaction: see text] An approach to the synthesis of new imidazoline nitroxides bearing an N',N'-disubstituted amidine group is reported. The approach is based on the alkylation of diamagnetic 4-R-amino-1,2,2,5,5-pentamethyl-3-imidazolines with bromoacetic acid ethyl ester; the products of alkylation are further oxidized to the corresponding nitroxides. The approach allows a variety of functional groups to be introduced into the nitroxide molecule structure. Alkylation with bromoacetic acid ethyl ester was found to proceed with high regioselectivity and afford the products of exo-alkylation. The regiochemical assignment is made on the basis of 13C NMR spectra and confirmed by X-ray diffraction study. All of the nitroxides synthesized here were shown to have pH-dependent EPR spectra with pKa ranging from 3.5 to 6.2. For nitroxides 13 bearing the carboxylic group remote to the nitroxide moiety, the changes in isotropic magnetic parameters of EPR spectra due to reversible deprotonation of the carboxylic group were found to be small. For these nitroxides, we demonstrate an alternative approach for pKa determination that is based on measuring the peak-to-peak line width of the EPR spectrum in the presence of the paramagnetic broadening agent potassium ferricyanide. The partition coefficients of nitroxides in octanol/H2O and octanol/phosphate buffer solution mixtures were measured to reveal a range of their lipophilicities.     

Ethylenediaminetetraacetato-monoperoxo complexes of vanadium(V)

Summary The monoperoxo complexes, M₂[VO(HEDTA)(O₂)]· 4H₂O, where M is K⁺ or NH ₄ ⁺ and H₄EDTA is ethylene-diaminetetraacetic acid, were prepared and characterized by Raman and i.r. spectra in the solid state and in aqueous solution. The single crystal X-ray study revealed a pentagonal bipyramidal anion structure with a tetradentate HEDTA(3—) ligand. The decomposition of complexes in aqueous solution to blue vanadium(IV) complexes as end products proceeds via a nonperoxo complex of vanadium.     

Reduction of Hg(II) salts in aqueous acidic solutions by SO2

Kinetic studies of the reduction of Hg(II) salts in aqueous acidic solutions by SO₂ in mild conditions have revealed that SO₂ quantitatively reduces Hg(II) to metal in the examined HClO₄ concentration range (2–8M^–1).

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Hg(II) . , HClO₄ (2–8 .^–1) SO₂ Hg(II) .

     

Convenient synthesis of 5′-methyl-2′-desoxyuridines

A convenient method has been developed for the synthesis of 5-methyl-2-desoxyuridines. Chlorination of 5-O-benzoyl-5-methyluridines with a mixture of Ph₃P and CCl₄ in DMF affords the 2-desoxy-2-chloro-derivatives, which are then reduced with tributyltin hydride. The crystalline 5-O-benzoyl-5-methyl-2-desoxyuridines were obtained in overall yields of 40–60%. In a similar way, 5-O-benzoyluridine has given 5-O-benzoyl-2-desoxyuridine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 246–248, February, 1989.     

Critical Points in a Crystal and Procrystal

The critical points in the model electron density distributions of LiF, NaF, NaCl, and MgO crystals, constructed from accurate X-ray diffraction data, are determined. For LiF and MgO they are compared with those obtained from a Hartree–Fock electron density calculation. Both experiment and theory show the same type of critical points on the bond lines. The topological features in areas between structural units, where the electron density is low and near-uniform, turn out to be model dependent and cannot be established well with the data available. Topological analysis of procrystals (hypothetical systems consisting of spherical atoms or ions placed on the same sites as atoms in real crystal) show that (3, –1) critical points, usually connected with bonding interaction, are observed on interatomic lines in these nonbonded systems as well.