Assignment of acetyl groups to O-2 and/or O-3 of pectic oligogalacturonides using negative electrospray ionization ion trap mass spectrometry

Partially acetylated and methylated oligogalacturonides produced by enzymatic hydrolysis of sugar beet pectin were analysed by negative electrospray ionization ion trap mass spectrometry (ESI-ITMS). The (18)O labelling of the oligomer reducing end allowed the precise assignment of the fragments resulting from glycosidic bond and cross-ring cleavages. The collisional-induced dissociation of the C(i) and Z(j) fragment ions through sequential MS(n) experiments always displayed (0, 2)A-type cross-ring cleavage ions which were related to C(2)H(4)O(2) losses. These (0, 2)A ions appeared to be highly diagnostic ions allowing the precise location of the acetyl groups to the O-2 and/or O-3 of the acetylated galacturonic acid residues.     

The localized electrons detector as an ab initio representation of molecular structures

The local single particle momentum is proposed as a localized‐electrons detector (LED) that provides a direct three‐dimensional representation of bonding interactions in molecules. It is given exclusively in terms of the electron density and its gradient. We show that the graphical representation of bonding interactions given by LED is consistent with the local curvatures of the electron density as given by the eigenvalues of the Hessian matrix, according to a local symmetry classification of the critical points here introduced. LED consistently complements the topological analysis of the electron density given by the quantum theory of atoms in molecules, by providing a graphical representation of the symmetry of the bonding interactions in molecular systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2418–2425, 2010     

Application of solid-phase microextraction combined with gas chromatography-mass spectrometry to the determination of butylated hydroxytoluene in bottled drinking water

Butylated hydroxytoluene (BHT) is an antioxidant utilized as additive in foods and packaging plastic. Its presence in drinking water is possible if it is used as an antioxidant in the packaging plastic because it may migrate into the package's contents. A method for the determination of BHT in water by means of solid-phase microextraction and gas chromatography-mass spectrometry has been developed and evaluated with respect to the time of fiber exposure, limits of detection and quantitation, linearity and precision. Finally, the method was applied to evaluate the presence of this substance in samples of mineral and mineralized bottled drinking water, and it appeared to be present in seven out of a total of fifteen commercial brands.     

Optimization of azeotropic protein separations in gradient and isocratic ion-exchange simulated moving bed chromatography

The separation of dilute binary mixtures of proteins by salt aided ion-exchange simulated moving bed (SMB) chromatography is optimized with respect to throughput, desorbent consumption and salt consumption. The optimal flow-rate ratios are analytically determined via an adopted "triangle theory". Azeotropic phenomena are included in this procedure. The salt concentrations in the feed and recycled liquid are subsequently determined by numerical optimization. The azeotropic separation of bovine serum albumin and a yeast protein is used to illustrate the procedure. Gradient operation of the SMB is generally preferred over isocratic operation. A feed of azeotropic salt concentration can only be separated in a gradient SMB. Desorbent and salt consumption are always lower in gradient than in isocratic SMB chromatography.     

Facile formation of molybdenum(VI) monooxo aryloxides MoO(OAr)4-nCln from molybdenum dioxo dichloride

Molybdenum monooxo compoundsMoO(OAr)4-nCln (n=0-2, Ar=2,6-Me2C6H3 or 2,6-i-Pr2C6H3) have been synthesized starting from the dioxo precursor MoO2Cl2. The complexes are characterized spectroscopically and by X-ray diffraction. The formation mechanism likely involves phenol precoordination followed by addition across the Mo=O bond.     

Zn3(C6H14N2)3[B6P12O39(OH)12] · (C6H14N2)[HPO4]: A Chiral Borophosphate – Triethylenediammonium Hydrogenphosphate Composite

A novel borophosphate, Zn₃(C₆H₁₄N₂)₃[B₆P₁₂O₃₉(OH)₁₂] · (C₆H₁₄N₂)[HPO₄] has been synthesised under mild hydrothermal conditions at T = 165 °C. The chiral crystal structure was determined by single crystal X‐ray diffraction data (trigonal, R3 (no. 146), Z = 3, a = 2089.55(4) pm, c = 1237.03(4) pm, V = 4677.5(2) · 10⁶ pm³, R₁ = 0.066, wR₂ = 0.164 for 5100 observed reflections). The title compound can be considered as an ordered composite of the two different and neutral structures which fit into each other: An open framework of composition Zn₃(C₆H₁₄N₂)₃[B₆P₁₂O₃₉(OH)₁₂] and columns of composition (C₆H₁₄N₂)[HPO₄]. The framework structure is formed by mixed octahedral‐tetrahedral secondary building units, in a three‐dimensional arrangement reflecting a hierarchical derivative of the NbO structure type. The underlying NbO topology is illustrated with the help of Periodic Nodal Surfaces. The composite nature of the compound is resolved in the spatial segregation of two frameworks with a separating surface.     

Nitrogen inversion in cyclic amines and the bicyclic effect

The hitherto unsolved problem of the origin of the unusually high nitrogen inversion-rotation (NIR) barriers in 7-azabicyclo[2.2.1]heptanes (the bicyclic effect) was examined using the natural bond orbital (NBO) approach. Reinvestigating the NIR barrier for tropane by DNMR, we found that NIR barriers increase smoothly on going from nitrogen-bridged bicyclic systems of a larger ring size to the smaller ring homologous systems. The experimental NIR barriers are reproduced with good accuracy using the MP2/6-31G level of theory. The NBO analysis for these and other azabicycles led to the conclusion that the height of these barriers is mostly determined by the energy of the sigma-orbitals of the C(alpha)(-)C(beta) bonds as well as the nitrogen lone pair. Thus, the bicyclic effect is actually an extreme case of a common C(alpha-)N-C(alpha) tripyramid geometry-NIR barrier dependence for N-bridged bicyclic amines. By establishing the rate-determining role of the C(alpha-)N-C(alpha) tripyramid fragment for NIR, we have derived the first sufficiently accurate quantitative correlations amine geometry-NIR barrier for monocyclic as well as bicyclic N-H and N-Me amines (i.e., for an amine set which also includes the bicyclic effect systems).     

Insertion reactions of [M(SR)3(PMe2Ph)2] with CS2 (M = Ru, Os; R = C6F4H-4, C6F5). X-ray structures of [Ru(S2CSC6F4H-4)2(PMe2Ph)2], trans-thiolates [M(SR)2(S2CSR)(PMe2Ph)2] (M = Ru; R = C6F5 and M = Os; R = C6F4H-4), and trans-thiolate-phosphine [Os(SC6F5)2(S2CSC6F5)(PMe2Ph)2

Reactions of [M(SR)(3)(PMe(2)Ph)(2)] (M = Ru, Os; R = C(6)F(4)H-4, C(6)F(5)) with CS(2) in acetone afford [Ru(S(2)CSR)(2)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 1; C(6)F(5), 3) and trans-thiolates [Ru(SR)(2)(S(2)CSR)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 2; C(6)F(5), 4) or the isomers trans-thiolates [Os(SR)(2)(S(2)CSR)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 5; C(6)F(5), 7) and trans-thiolate-phosphine [Os(SR)(2)(S(2)CSR)(PMe(2)Ph)(2)] (R = C(6)F(4)H-4, 6; C(6)F(5), 8) through processes involving CS(2) insertion into M-SR bonds. The ruthenium(III) complexes [Ru(SR)(3)(PMe(2)Ph)(2)] react with CS(2) to give the diamagnetic thiolate-thioxanthato ruthenium(II) and the paramagnetic ruthenium(III) complexes while osmium(III) complexes [Os(SR)(3)(PMe(2)Ph)(2)] react to give the paramagnetic thiolate-thioxanthato osmium(III) isomers. The single-crystal X-ray diffraction studies of 1, 4, 5, and 8 show distorted octahedral structures. (31)P [(1)H] and (19)F NMR studies show that the solution structures of 1 and 3 are consistent with the solid-state structure of 1.