Three-coordinate bis(phosphinimino)methanide derivatives of ‘open shell’ [M(II)] (M = Mn, Fe, Co) transition metals

An alternative two-step synthesis of the previously reported bis(diphenylphosphinimino)methane [CH₂(Ph₂P = NC₆H₃ⁱPr₂-2,6)₂] involving bromine oxidation of dppm and metathesis with 2,6-diisopropylaniline is described. [CH₂(Ph₂PNC₆H₃ⁱPr₂-2,6)₂] is readily deprotonated by the transition metal silylamides [M{N(SiMe₃)₂}₂] (M = Mn, Fe and Co) to provide a series of exclusively three-coordinate derivatives [{CH(Ph₂PNC₆H₃ⁱPr₂-2,6)₂M{N(SiMe₃)₂}] which have been characterised by elemental analysis, magnetic measurements and, in the case of the Fe derivative, X-ray structural analysis. Reactivity studies have shown that even such sterically demanding bis(phosphinimino)methanide ligands are prone to protonolysis and reductive [P(V) to P(III)] degradation which limits their utility as stable platforms for further M(II) derivitisation.     

Use of novel immobilized β-galactosidase reactor to hydrolyze the lactose constituent of skim milk

A novel chemical reactor, consisting of β-galactosidase fromAspergillus oryzae immobilized on a ribbed membrane made from polyvinyl-chloride and silica, was used to hydrolyze the lactose constituent of skim milk. Multiresponse nonlinear regression methods were employed to determine the kinetic parameters of rate expressions based on a proposed enzymatic mechanism that includes the formation of oligosaccharides. HPLC methods were employed to monitor the concentrations of all species present in the effluent stream. For the experimental conditions used in this research, a rate expression that includes the inhibition effect of α-galactose is sufficient to model the reaction network.     

Decomposition of a-type sandwiches. Synthesis and characterization of new polyoxometalates incorporating multiple d-electron-centered units

The controlled decomposition of the sandwich-type polyoxometalates K(12)[(M(OH(2))(2))(3)(A-alpha-PW(9)O(34))(2)] (where M = Mn(II) or Co(II)) in 0.5 M NaCl yields a new family of transition metal substituted POMs of the general formula [((MOH(2))M(2)PW(9)O(34))(2)(PW(6)O(26))](17)(-) (where M = Mn(II) (1Mn) or Co(II) (1Co)). The structure of 1Mn, determined by single-crystal X-ray diffraction (a = 17.4682(10) A, b = 22.3071(12) A, c = 35.1195(18) A, beta = 95.898(1) degrees, monoclinic, P2(1)/c, Z = 4, R(1) = 6.19%, based on 50264 independent reflections), consists of two B-alpha-(Mn(II)OH(2))Mn(II)(2)PW(9)O(34)(3)(-) units joined by a B-type hexavacant PW(6)O(26)(11)(-) fragment to form a C-shaped polyoxometalate. A low resolution X-ray structure of the Co(II) analogue, 1Co, was also obtained. The UV-visible spectrum of 1Co shows the characteristic charge-transfer bands of polyoxometalates as well as a new Co-centered peak (560 nm, epsilon = 416 M(-)(1) cm(-)(1)) which appears at a higher wavelength relative to that exhibited by the parent A-type sandwich, K(12)[(Co(OH(2))(2))(3)(A-alpha-PW(9)O(34))(2)]. The methyltricaprylammonium salt of 1Mn is an effective catalyst for the H(2)O(2)-based epoxidation of cis-cyclooctene, cyclohexene, and 1-hexene.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of lipids: ionization and prompt fragmentation patterns

Ionization and prompt fragmentation patterns of triacylglycerols, phospholipids (PLs) and galactolipids were investigated using matrix-assisted laser desorption/ionization (MALDI). Positive ions of non-nitrogen-containing lipids appeared only in the sodiated form, while nitrogen-containing lipids were detected as both sodiated and protonated adducts. Lipids containing acidic hydroxyls were detected as multiple sodium adducts or deprotonated ions in the positive and negative modes, respectively, with the exception of phosphatidylcholines. The positive MALDI spectra of triacylglycerols contained prompt fragments equivalent to the loss of RCOO(-) from the neutral molecules. Prompt fragment ions [PL-polar head](+) were observed in the positive MALDI spectra of all phospholipids except phosphatidylcholines. The phosphatidylcholines produced only a minor positive fragment corresponding to the head group itself (m/z 184). Galactolipids did not undergo prompt fragmentation. Post-source decay (PSD) was used to examine the source of prompt fragments. PSD fragment patterns indicated that the lipid prompt fragment ions did not originate from the observed molecular ions (sodiated or protonated), and suggested that the prompt fragmentation followed the formation of highly unstable, probably protonated, precursor ions. Pathways leading to the formation of prompt fragment ions are proposed.     

Investigation of the early stages in soraphen A biosynthesis

The unusual benzoate starter unit in soraphen A derives from phenylalanine via cinnamate in a beta-oxidative (plant-like) pathway; 3-phenyl-3-hydroxypropanoate incorporates directly into soraphen by loading onto module 2 of the PKS and indirectly from the beta-oxidative pathway to generate benzoyl CoA.     

Thermodynamics of lonization of aqueous lodic acid,an “almost-strong” electrolyte

We have made calorimetric measurements of enthalpies of dilution of aqueous iodic acid and have used these results for evaluation of the standard enthalpy of ionization of HIO₃(aq.). We have also made calorimetric measurements of enthalpies of addition of perchloric acid solution to aqueous solutions of KIO₃, KNO₃, NaIO₃, and NaNO₃ and have used these results to obtain further values for the standard enthalpy of ionization of HIO₃(aq.). On the basis of all these results, we have selected H^o=–660±125 cal-mole^–1 as the best available standard enthalpy of ionization of HIO₃(aq.) at 298.15°K, compared to the previously accepted –2400 cal-mole^–1. Using the best available K=0.157 for ionization, we also obtain G^o=1097 cal-mole^–1 and S^o=–5.9 cal-^oK^–1-mole^–1 for ionization of HIO₃(aq) at 298.15°K.On study leave from Department of Inorganic and Analytical Chemistry, LaTrobe University, Bundoora, Victoria, 3083, Australia, to University of Lethbridge.On study leave from Department of Chemistry, University of Wollongong, Wollongong, N.S.W. 2500, Australia, to University of Lethbridge.     

Halogenated compound response in an oxygen doped ion mobility detector for capillary gas chromatography

An ion mobility detector that has been specifically developed for interfacing with capillary gas chromatography is investigated in the negative ion mode. Like the electron capture detector, to which this instrument is closely related, the ion mobility detector shows an enhanced response to low molecular weight halogenated compounds when a small quantity of oxygen is doped into the make-up gas flow. Under O₂ doping conditions, the device can operate in a reactant ion monitoring mode responding universally to compounds capable of capturing thermal electrons and in a tunable selective product ion mode providing increased selectivity over that achieved by the ECD. At an oxygen concentration of 0.5%, minimum detectable amounts as low as 600 femtograms have been realized for carbon tetrachloride. Selectivity of chloro- versus bromo- compounds is demonstrated using a mixture of p-dichlorobenzene and p-dibromobenzene.     

Preparation of mono- and diacylglycerols by enzymatic esterification of glycerol with conjugated linoleic acid in hexane

Esterification of glycerol with conjugated linoleic acid (CLA) was carried out in hexane. Lipase from Rhizomucor miehei provided a high degree of esterification (80%) in 8 h at 50°C when used at 15% (w/w) in a system containing a 1∶2 molar ratio of glycerol to free fatty acids. Esterification levels >80% were obtained in 8 h at 40°C with 15% (w/w) lipase from Candida antarctica at the same molar ratio of reactants. The extent of esterification of CLA was >90% after 4h of reaction at 50°C with a 5% (w/w) loading of either R. miehei or C. antarctica lipase, together with a 1∶1 molar ratio of substrates. Both enzymes incorporated the original CLA as acylglycerol residues in primarily 1,3-diacylglycerol and 1-monoacylglycerol. The CLA-rich acylglycerols can be employed as emulsifiers or as substitutes for natural fats and oils.     

Electron capture ion mobility spectrometry for the selective detection of chlorinated and brominated species after capillary gas chromatography

This paper reports the first investigation of electron capture ion mobility spectrometry as a detection method for capillary gas chromatography. In previous work with negative ion mobility detection after gas chromatography, the principal reactant ion species were O₂^? or hydrated O₂^? due to the presence of oxygen in the drift gas. These molecular reactant ions have a mobility similar to chloride and bromide ions, which are the principal product ions formed by most halogenated organics via dissociative ion-molecule reactions. Oxygenated reactant ions thus interfere with the selective detection of chloride and bromide product ions. A recently described ion mobility detector design efficiently eliminated ambient impurities, including oxygen, from infiltrating the ionization region of the detector; consequently, in the negative mode of operation, the ionization species with N₂ drift gas were thermalized electrons. Thermalized electrons have a high mobility and their drift time occupies a region of the ion mobility spectrum not occupied by chloride, bromide, or other product ions. The result was improved selectivity for halogenated organics which ionize by dissociative electron capture. This was demonstrated by the selective detection of 4,4′-dibromobiphenyl from the components of a polychlorinated biphenyl mixture (Aroclor 1248).     

Facile aerial oxidation of a porphyrin. Part 18 . N-alkylation of the oxidised product derived from Meso-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)porphyrin

In basic solutions, the oxidised porphyrin 2 readily undergoes macrocyclic N-alkylation, with up to four bulky alkyl groups, including decyl and substituted benzyl moieties, being accomodated: an argument is presented to show that N-di-alkylation occurs on opposite nitrogen atoms, on the same side of the macrocycle.