Browsing by Author "Mulder, RJ"

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    Effect of acid dextrinisation on enzyme-resistant starch content in extruded maize starch
    (Elsevier, 2010-05) Htoon, AK; Uthayakumaran, S; Piyasiri, U; Appelqvist, IAM; Lopez-Rubio, A; Gilbert, EP; Mulder, RJ
    The enzyme-resistant starch (ERS) content in processed high amylose and regular maize starches has been studied, with and without acid dextrinisation. The physicochemical and structural characteristics of the starches were analysed using a variety of techniques. The increase in ERS in high amylose maize starch with dextrinisation was related to the formation of a critical molecular weight fraction (MW ~ 20,000) that could rearrange structurally. Further dextrinisation reduced the processed starch MW to below where it could still form ERS. Regular maize starch containing less than 30% amylose did not increase its resistance to amylase digestibility with acid dextrinisation, probably due to impairment of amylose rearrangement by the numerous branched amylopectin chains. The ERS, which is likely to form during the enzyme-digestion process, is a linear molecule with a maximum degree of polymerisation (DP) of 30, irrespective of the starch source, processing conditions applied or type and amount of acid used. © 2010, Elsevier Ltd.
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    Synthesis, structural characterization, and gas-phase unimolecular reactivity of the silver hydride nanocluster [Ag3((PPh2)2CH2)3(μ3-H)](BF4)2
    (ACS Publications, 2014-07-03) Zavras, A; Khairallah, GN; Connell, TU; White, JM; Edwards, AJ; Mulder, RJ; O'Hair, RAJ; Donnelly, PS
    A bis(diphenylphosphino)methane-ligated trinuclear silver hydride nanocluster, [Ag3((Ph2P)2CH2)3(μ3-H)](BF4)2, featuring three silver(I) ions coordinated to a μ3-hydride, and its deuteride analogue, [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2, have been isolated and structurally characterized using electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography, NMR and IR spectroscopy. The position of the deuteride in [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2 was determined by neutron diffraction. ESI-MS of [Ag3L3(μ3-H/D)](BF4)2 [L = ((Ph2P)2CH2)2] produces [Ag3L3(μ3-H/D)]2+ and [Ag3L3(μ3-H/D)(BF4)]+. A rich gas-phase ion chemistry of [Ag3L3(μ3-H/D)]2+ is observed under conditions of collision-induced dissociation (CID) and electron-capture dissociation (ECD). CID gives rise to the following complementary ion pairs: [Ag3L2]+ and [L+(H/D)]+; [Ag2(H/D)L2]+ and [AgL]+; [Ag2(H/D)L]+ and [AgL2]+. ECD gives rise to a number of dissociation channels including loss of the bis(phosphine) ligand, fragmentation of a coordinated bis(phosphine) ligand via C–P bond activation, and loss of a hydrogen (deuterium) atom with concomitant formation of [Ag3L3]+. Under CID conditions, [Ag3L3(μ3-H/D)(BF4)]+ fragments via ligand loss, the combined loss of a ligand and [H,B,F4], and cluster fragmentation to give [Ag2(BF4)L2]+ and [Ag2(L-H)L]+ [where (L-H) = (Ph2P)2CH–]. © 2014, American Chemical Society