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  • 1. Acharya, Shravan S.
    et al.
    Easton, Christopher D.
    McCoy, Thomas M.
    Spiccia, Leone
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry. School of Chemistry, Monash University, Clayton, Australia.
    Winther-Jensen, Bjorn
    Diverse composites of metal-complexes and PEDOT facilitated by metal-free vapour phase polymerization2017In: Reactive & functional polymers, ISSN 1381-5148, E-ISSN 1873-166X, Vol. 116, p. 101-106Article in journal (Refereed)
    Abstract [en]

    Abstract Oxidative polymerization for the manufacture of conducting polymers such as poly(3,4-ethylenedioxy-thiophene) has traditionally employed iron(III) salts. Demonstrated in this study is vapour phase polymerization of 3,4-ethylenedio- xythiophene using a metal-free oxidant, ammonium persulfate, leading to films with an estimated conductivity of 75 S/cm. Additionally, a route for embedding active transition metal complexes into these poly(3,4-ethylenedioxythiophene)/-poly(styrene-4-sulfonate) (PEDOT/PSS) films via vapour assisted complexation is outlined. Here, the vapour pressure of solid ligands around their melting temperatures was exploited to ensure complexation to metal ions added into the oxidant mixture prior to polymerization of PEDOT. Four composite systems are discussed, viz. PEDOT/PSS embedded with tris(8-hydroxyquinolinato)cobalt(III), tris(2,2-bipyridine)cobalt(II), tris(1,10- phenanthroline)cobalt(II) and tris(8-hyd-roxyquinolinato)aluminium(III). Using these composites, electrochemical reduction of nitrite to ammonia with a faradaic efficiency of 61% was reported.

  • 2. Acharya, Shravan
    et al.
    Winther-Jensen, Bjorn
    Spiccia, Leone
    Ohlin, André C.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rates of water exchange in 2,2'-bipyridine and 1,10-phenanthroline complexes of CoII and MnII2017In: Australian journal of chemistry (Print), ISSN 0004-9425, E-ISSN 1445-0038, Vol. 70, no 6, p. 751-754Article in journal (Refereed)
    Abstract [en]

    The rates and activation parameters of water exchange at pH 3.0 have been determined using variable temperature 17O NMR spectroscopy for four CoII complexes and one MnII complex: [Co(bpy)(H2O)4]2+, [Co(bpy)2 (H2O)2]2+, [Co(phen)-(H2O)4]2+, [Co(phen)2 (H2O)2]2+, and [Mn(bpy)(H2O)4]2+ (bpy = 2,2′-bipyridyl and phen = 1,10-phenanthroline). Substitution of aquo ligands with 1,10-phenanthroline or 2,2′-bipyridyl leads to an increase in the rate of exchange in the manganese complexes, from k298 (1.8 ± 0.1) × 107 s-1 for [Mn(H2O)6]2+ to (7.2 ± 0.3) × 107 s-1 for [Mn(phen)2 (H2O)2]2+, whereas the trends are more complex for the cobalt complexes. We have used the new data in conjunction with literature data for similar complexes to analyse the effect of M–OH2 distance and degree of substitution.

  • 3. Andrew, Rhiann E.
    et al.
    Ferdani, Dominic W.
    Ohlin, C. Andre
    Chaplin, Adrian B.
    Coordination Induced Atropisomerism in an NHC-Based Rhodium Macrocycle2015In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 34, no 5, p. 913-917Article in journal (Refereed)
    Abstract [en]

    Reversible interaction with carbon monoxide results in the onset of dynamic atropisomerism at 298 K in an otherwise static NHC-based rhodium pincer complex, [Rh(C boolean AND N boolean AND C-(CH2)(12))(CO)][BArF4] (1, ArF = 3,5-C6H3(CF3)(2)). The mechanism of this process has been comprehensively interrogated by a combination of variable-temperature NMR spectroscopy, IR spectroscopy, and computational modeling. In addition, a structural analogue of a high-energy symmetrical intermediate species-invoked in the process but not directly observed spectroscopically-has been prepared and characterized in solution and the solid-state.

  • 4. Aureliano, M.
    et al.
    Ohlin, C. Andre
    Decavanadate in vitro and in vivo effects: facts and opinions2014In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 137, p. 123-130Article in journal (Refereed)
    Abstract [en]

    This review covers recent advances in the understanding of the in vitro and in vivo effects of decavanadate, (V10O28)(6-), particularly in mitochondria. In vivo toxicological studies involving vanadium rarely account for the fact that under physiological conditions some vanadium may be present in the form of the decavanadate ion, which may behave differently from ortho- and metavanadates. It has for example been demonstrated that vanadium levels in heart or liver mitochondria are increased upon decavanadate exposure. Additionally, in vitro studies have shown that mitochondrial depolarization (IC50, 40 nM) and oxygen consumption (IC50, 99 nM) are strongly affected by decavanadate, which causes reduction of cytochrome b (complex III). We review these recent findings which together suggest that the observed cellular targets, metabolic pathway and toxicological effects differ according to the species of vanadium present. Finally, the toxicological effects of decavanadate depend on several factors such as the mode of administration, exposure time and type of tissue. (C) 2014 Elsevier Inc. All rights reserved.

  • 5. Aureliano, Manuel
    et al.
    Fraqueza, Gil
    Ohlin, C. Andre
    Ion pumps as biological targets for decavanadate2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 33, p. 11770-11777Article in journal (Refereed)
    Abstract [en]

    The putative applications of poly-, oligo-and mono-oxometalates in biochemistry, biology, pharmacology and medicine are rapidly attracting interest. In particular, these compounds may act as potent ion pump inhibitors and have the potential to play a role in the treatment of e. g. ulcers, cancer and ischemic heart disease. However, the mechanism of action is not completely understood in most cases, and even remains largely unknown in other cases. In the present review we discuss the most recent insights into the interaction between mono-and polyoxometalate ions with ion pumps, with particular focus on the interaction of decavanadate with Ca2+-ATPase. We also compare the proposed mode of action with those of established ion pump inhibitors which are currently in therapeutic use. Of the 18 classes of compounds which are known to act as ion pump inhibitors, the complete mechanism of inhibition is only known for a handful. It has, however, been established that most ion pump inhibitors bind mainly to the E2 ion pump conformation within the membrane domain from the extracellular side and block the cation release. Polyoxometalates such as decavanadate, in contrast, interact with Ca2+-ATPase near the nucleotide binding site domain or at a pocket involving several cytoplasmic domains, and therefore need to cross through the membrane bilayer. In contrast to monomeric vanadate, which only binds to the E2 conformation, decavanadate binds to all protein conformations, i.e. E1, E1P, E2 and E2P. Moreover, the specific interaction of decavanadate with sarcoplasmic reticulum Ca2+-ATPase has been shown to be non-competitive with respect to ATP and induces protein cysteine oxidation with concomitant vanadium reduction which might explain the high inhibitory capacity of V-10 (IC50 = 15 mu M) which is quite similar to the majority of the established therapeutic drugs.

  • 6. Aureliano, Manuel
    et al.
    Ohlin, C. André
    Vieira, Michele O.
    Marques, M. Paula M.
    Casey, William H.
    Batista de Carvalho, Luis A. E.
    Characterization of decavanadate and decaniobate solutions by Raman spectroscopy2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 17, p. 7391-7399Article in journal (Refereed)
    Abstract [en]

    The decaniobate ion, (Nb-10 = [Nb10O28](6-)) being isoelectronic and isostructural with the decavanadate ion (V-10 = [V10O28](6-)), but chemically and electrochemically more inert, has been useful in advancing the understanding of V-10 toxicology and pharmacological activities. In the present study, the solution chemistry of Nb-10 and V-10 between pH 4 and 12 is studied by Raman spectroscopy. The Raman spectra of V-10 show that this vanadate species dominates up to pH 6.45 whereas it remains detectable until pH 8.59, which is an important range for biochemistry. Similarly, Nb-10 is present between pH 5.49 and 9.90 and this species remains detectable in solution up to pH 10.80. V-10 dissociates at most pH values into smaller tetrahedral vanadate oligomers such as V-1 and V-2, whereas Nb-10 dissociates into Nb-6 under mildly (10 > pH > 7.6) or highly alkaline conditions. Solutions of V-10 and Nb-10 are both kinetically stable under basic pH conditions for at least two weeks and at moderate temperature. The Raman method provides a means of establishing speciation in the difficult niobate system and these findings have important consequences for toxicology activities and pharmacological applications of vanadate and niobate polyoxometalates.

  • 7. Colla, Christopher A.
    et al.
    Casey, William H.
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Computational prediction of Mg-isotope fractionation between aqueous [Mg(OH2)6]2+ and brucite2018In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 227, p. 64-74Article in journal (Refereed)
    Abstract [en]

    The fractionation factor in the magnesium-isotope fractionation between aqueous solutions of magnesium and brucite changes sign with increasing temperature, as uncovered by recent experiments. To understand this behavior, the Reduced Partition Function Ratios and isotopic fractionation factors (Δ26/24Mgbrucite-Mg(aq)) are calculated using molecular models of aqueous [Mg(OH2)6]2+ and the mineral brucite at increasing levels of density functional theory. The calculations were carried out on the [Mg(OH2)6]2+·12H2O cluster, along with different Pauling-bond-strength-conserving models of the mineral lattice of brucite. Three conclusions were reached: (i) all levels of theory overestimate 〈Mg‒O〉 bond distances in the aqua ion complex relative to Tutton’s salts; (ii) the calculations predict that brucite at 298.15 K is always enriched in the heavy isotope, in contrast with experimental observations; (iii) the temperature dependencies of Wimpenny et al. (2014) and Li et al. (2014) could only be achieved by fixing the 〈Mg‒O〉 bond distances in the [Mg(OH2)6]2+·12H2O cluster to values close to those observed in crystals that trap the hydrated ion.

  • 8. Dyson, P J
    et al.
    Laurenczy, G
    Ohlin, C A
    Vallance, J
    Welton, T
    Determination of hydrogen concentration in ionic liquids and the effect (or lack of) on rates of hydrogenation2003In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 19, p. 2418-2419Article in journal (Refereed)
    Abstract [en]

    The solubility of hydrogen and the corresponding Henry coefficients for 11 ionic liquids have been determined in situ at 100 atm H(2) pressure and are much lower than expected; attempts to correlate the solubility of hydrogen in the ionic liquids with the rate of reaction for the hydrogenation of benzene to cyclohexane in these solvents have been made.

  • 9. Fraqueza, G.
    et al.
    Carvalho, L.
    Marques, P.
    Ohlin, C. Andre
    Casey, W.
    Aureliano, M.
    Functional and structural interactions of Nb, V, Mo and W oxometalates with the sarcoplasmic reticulum Ca2(+) -ATPase reveal new insights into inhibition processes: a combination of NMR, Raman, AA and EPR spectroscopie with kinetic studies2012In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 279, no 1, SIArticle in journal (Refereed)
  • 10. Fraqueza, Gil
    et al.
    Batista de Carvalho, Luis A. E.
    Marques, M. Paula M.
    Maia, Luisa
    Ohlin, C. Andre
    Casey, William H.
    Aureliano, Manuel
    Decavanadate, decaniobate, tungstate and molybdate interactions with sarcoplasmic reticulum Ca2+-ATPase: quercetin prevents cysteine oxidation by vanadate but does not reverse ATPase inhibition2012In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, no 41, p. 12749-12758Article in journal (Refereed)
    Abstract [en]

    Recently we demonstrated that the decavanadate (V-10) ion is a stronger Ca2+-ATPase inhibitor than other oxometalates, such as the isoelectronic and isostructural decaniobate ion, and the tungstate and molybdate monomer ions, and that it binds to this protein with a 1 : 1 stoichiometry. The V-10 interaction is not affected by any of the protein conformations that occur during the process of calcium translocation (i.e. E1, E1P, E2 and E2P) (Fraqueza et al., J. Inorg. Biochem., 2012). In the present study, we further explore this subject, and we can now show that the decaniobate ion, [Nb-10 = Nb10O28](6-), is a useful tool in deducing the interaction and the non-competitive Ca2+-ATPase inhibition by the decavanadate ion [V-10 = V10O28](6-). Moreover, decavanadate and vanadate induce protein cysteine oxidation whereas no effects were detected for the decaniobate, tungstate or molybdate ions. The presence of the antioxidant quercetin prevents cysteine oxidation, but not ATPase inhibition, by vanadate or decavanadate. Definitive V(IV) EPR spectra were observed for decavanadate in the presence of sarcoplasmic reticulum Ca2+-ATPase, indicating a vanadate reduction at some stage of the protein interaction. Raman spectroscopy clearly shows that the protein conformation changes that are induced by V-10, Nb-10 and vanadate are different from the ones induced by molybdate and tungstate monomer ions. Here, Mo and W cause changes similar to those by phosphate, yielding changes similar to the E1P protein conformation. The putative reduction of vanadium(V) to vanadium(IV) and the non-competitive binding of the V-10 and Nb-10 decametalates may explain the differences in the Raman spectra compared to those seen in the presence of molybdate or tungstate. Putting it all together, we suggest that the ability of V-10 to inhibit the Ca2+-ATPase may be at least in part due to the process of vanadate reduction and associated protein cysteine oxidation. These results contribute to the understanding and application of these families of mono-and polyoxometalates as effective modulators of many biological processes, particularly those associated with calcium homeostasis.

  • 11. Fraqueza, Gil
    et al.
    Ohlin, C. Andre
    Casey, William H.
    Aureliano, Manuel
    Sarcoplasmic reticulum calcium ATPase interactions with decaniobate, decavanadate, vanadate, tungstate and molybdate2012In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 107, no 1, p. 82-89Article in journal (Refereed)
    Abstract [en]

    Over the last few decades there has been increasing interest in oxometalate and polyoxometalate applications to medicine and pharmacology. This interest arose, at least in part, due to the properties of these classes of compounds as anti-cancer, anti-diabetic agents, and also for treatment of neurodegenerative diseases, among others. However, our understanding of the mechanism of action would be improved if biological models could be used to clarify potential toxicological effects in main cellular processes. Sarcoplasmic reticulum (SR) vesicles, containing a large amount of Ca(2+)-ATPase, an enzyme that accumulates calcium by active transport using ATP, have been suggested as a useful model to study the effects of oxometalates on calcium homeostasis. In the present article, it is shown that decavanadate, decaniobate, vanadate, tungstate and molybdate, all inhibited SR Ca(2+)-ATPase, with the following IC(50) values: 15, 35, 50, 400 mu M and 45 mM, respectively. Decaniobate (Nb(10)), is the strongest P-type enzyme inhibitor, after decavanadate (V(10)). Atomic-absorption spectroscopy (AAS) analysis, indicates that decavanadate binds to the protein with a 1:1 decavanadate:Ca(2+)-ATPase stoichiometry. Furthermore, V10 binds with similar extension to all the protein conformations, which occur during calcium translocation by active transport, namely El, El P, E2 and E2P, as analysed by MS. In contrast, it was confirmed that the binding of monomeric vanadate (H(2)VO(4)(2-):V(1)) to the calcium pump is favoured only for the E2 and E2P conformations of the ATPase, whereas no significant amount of vanadate is bound to the E1 and E1P conformations. Scatchard plot analysis, confirmed a 1:1 ratio for decavanadate-Ca(2+)-ATPase, with a dissociation constant, k(d) of 1 mu M(-1). The interaction of decavanadate V(10)O(28)(6-) (V(10)) with Ca(2+)-ATPase is prevented by the isostructural and isoelectronic decaniobate Nb(10)O(28)(6-) (Nb(10)), whereas no significant effects were detected with ATP or with heparin, a known competitive ATP binding molecule, suggesting that V(10) binds non-competitively, with respect to ATP, to the protein. Finally, it was shown that decaniobate inhibits SR Ca(2+)-ATPase activity in a non competitive type of inhibition, with respect to ATP. Taken together, these data demonstrate that decameric niobate and vanadate species are stronger inhibitors of the SR calcium ATPase than simple monomeric vanadate, tungstate and molybdate oxometalates, thus affecting calcium homeostasis, cell signalling and cell bioenergetics, as well many other cellular processes. The ability of these oxometalates to act either as phosphate analogues, as a transition-state analogue in enzyme-catalysed phosphoryl group transfer processes and as potentially nucleotide-dependent enzymes modulators or inhibitors, suggests that different oxometalates may reveal different mechanistic preferences in these classes of enzymes. (C) 2011 Elsevier Inc. All rights reserved.

  • 12. Gumerova, Nadiia I.
    et al.
    Caldera Fraile, Tania
    Roller, Alexander
    Giester, Gerald
    Pascual-Borràs, Magda
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rompel, Annette
    Direct Single- and Double-Side Triol-Functionalization of the Mixed Type Anderson Polyoxotungstate [Cr(OH)3W6O21]6–2019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, p. 106-113Article in journal (Refereed)
    Abstract [en]

    Since the first successful triol-functionalization of the Anderson polyoxometalates, the six protons of their central octahedron X(OH)6 (X—heteroatom, p- or d-element) have been considered as a prerequisite for their functionalization with tripodal alcohols, and therefore, the functionalization of Anderson structures from the unprotonated sides have never been reported. Here, we describe the triol-functionalization of [Cr(OH)3W6O21]6– leading to the single-side grafted anions [Cr(OCH2)3CRW6O21]6– (CrW6-tris-R, R = −C2H5, −NH2, −CH2OH) and the unprecedented double-side functionalized anion [Cr((OCH2)3CC2H5)2W6O18]3– (CrW6-(tris-C2H5)2), despite the lack of protons in the parent anion in the solid state. CrW6-(tris-C2H5)2 demonstrates the first example of double-side functionalized Anderson POT with the partially one-side protonated corresponding parent anion. The new heteropolytungstates were characterized by single-crystal X-ray diffraction, elemental analysis, Fourier-transform infrared spectroscopy, thermal gravimetric analysis, cyclic voltammetry, and electrospray ionization mass spectrometry. Density functional theory calculations were performed to investigate and compare the stability among the different isomers of the parent anion [Cr(OH)3W6O21]6–.

  • 13. Harley, Steven J.
    et al.
    Ohlin, C. Andre
    Casey, William H.
    Geochemical kinetics via the Swift-Connick equations and solution NMR2011In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, no 13, p. 3711-3725Article in journal (Refereed)
    Abstract [en]

    Signal analysis in Nuclear Magnetic Resonance spectroscopy is among the most powerful methods to quantify reaction rates in aqueous solutions. To this end, the Swift-Connick approximations to the Bloch-McConnell equations have been used extensively to estimate rate parameters for elementary reactions. The method is primarily used for O-17 NMR in aqueous solutions, but the list of geochemically relevant nuclei that can be used is long, and includes Si-29, Al-27, F-19, C-13 and many others of particular interest to geochemists. Here we review the derivation of both the Swift-Connick and Bloch-McConnell equations and emphasize assumptions and quirks. For example, the equations were derived for CW-NMR, but are used with modern pulse FT-NMR and can be applied to systems that have exchange rates that are shorter than the lifetime of a typical pulse. The method requires a dilute solution where the minor reacting species contributes a negligible amount of total magnetization. We evaluate the sensitivity of results to this dilute-solution requirement and also highlight the need for chemically well-defined systems if reliable data are to be obtained. The limitations in using longitudinal relaxation to estimate reaction rate parameters are discussed. Finally, we provide examples of the application of the method, including ligand exchanges from aqua ions and hydrolysis complexes, that emphasize its flexibility. Once the basic requirements of the Swift-Connick method are met, it allows geochemists to establish rates of elementary reactions. Reactions at this scale lend themselves well to methods of computational simulation and could provide key tests of accuracy. (C) 2011 Elsevier Ltd. All rights reserved.

  • 14. Harley, Steven J.
    et al.
    Ohlin, C. Andre
    Johnson, Rene L.
    Panasci, Adele F.
    Casey, William H.
    The Pressure Dependence of Oxygen Isotope Exchange Rates Between Solution and Apical Oxygen Atoms on the [UO2(OH)(4)](2-) Ion2011In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 19, p. 4467-4469Article in journal (Refereed)
  • 15. Hawley, Andrew L.
    et al.
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry. School of Chemistry, Melbourne, Australia).
    Fohlmeister, Lea
    Stasch, Andreas
    Heavier Group 13 Metal(I) Heterocycles Stabilized by Sterically Demanding Diiminophosphinates: a Structurally Characterized Monomer–Dimer Pair For Gallium2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 2, p. 447-455Article in journal (Refereed)
    Abstract [en]

    We have synthesized and characterized the monomeric diiminophosphinate-stabilized Group 13 metal(I) complexes [DipLE:], DipL=Ph2P(NDip)2, Dip=2,6-iPr2C6H3; E=Ga (1), In (2) and Tl (3). In addition, we structurally characterized the dimeric complex [(DipLGa)2], 12. Similar synthetic attempts using MesL=Ph2P(NMes)2, Mes=2,4,6-Me3C6H2 afforded product mixtures from which the mixed oxidation state species [(MesL)3Ga4I3] 4 was isolated. [DipLGa:] 1 is converted with dry air to the gallium(III) oxide species [(DipLGaO)2] 5. Density Functional Theory studies on [DipLE:] and [(DipLE)2], E=Al−Tl, shed light on the bonding in these compounds and show that the newly formed E−E bonding interactions can be described as weak single σ-bond with no significant π-bonding contribution for E=Al, Ga. A large contribution to the dimer binding enthalpies results from London dispersion forces.

  • 16. Johnson, Rene L.
    et al.
    Harley, Stephen J.
    Ohlin, C. Andre
    Panasci, Adele F.
    Casey, William H.
    Multinuclear NMR Study of the Pressure Dependence for Carbonate Exchange in the UO2(CO3)34-(aq) Ion2011In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, no 16, p. 2903-2906Article in journal (Refereed)
  • 17. Johnson, Rene L.
    et al.
    Ohlin, C. Andre
    Pellegrini, Kristi
    Burns, Peter C.
    Casey, William H.
    Dynamics of a Nanometer-Sized Uranyl Cluster in Solution2013In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 29, p. 7464-7467Article in journal (Refereed)
  • 18. Johnson, Rene L.
    et al.
    Villa, Eric M.
    Ohlin, C. Andre
    Rustad, James R.
    Casey, William H.
    O-17 NMR and Computational Study of a Tetrasiliconiobate Ion, [H2+xSi4Nb16O56]((14-x)-)2011In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 34, p. 9359-9367Article in journal (Refereed)
    Abstract [en]

    Rates of oxygen-isotope exchange were measured in the tetrasiliconiobate ion [H2+xSi4Nb16O56]((14-x)-) to better understand how large oxide ions interact with water. The molecule has 19 nonequivalent oxygen sites and is sufficiently complex to evaluate hypotheses derived from our previous work on smaller clusters. We want to examine the extent to which individual oxygen atoms react independently with particular attention given to the order of protonation of the various oxygen sites as the pH decreases from 13 to 6. As in our previous work, we find that the set of oxygen sites reacts at rates that vary over approximately 104 across the molecule at 6 < pH < 13 but with similar pH dependencies. There is NMR evidence of an intra-or intermolecular reaction at pH similar to 7, where new peaks began to slowly form without losing the O-17 isotopic tag, and at pH <= 6 these new peaks formed rapidly. The oxygen atoms bonded to silicon atoms began to isotopically exchange at pH 9 and below. The 17O NMR peak positions also vary considerably with pH for some, but not all, nonequivalent oxygen sites. This variation could be only partly accounted by electronic calculations, which indicate that oxygen atoms should shift similarly upon protonation. Instead, we see that some sites change enormously with pH, whereas other, similarly coordinated oxygen atoms are less affected, suggesting that either some protons are exchanging so rapidly that the oxygen sites are seeing an averaged charge, or that counterions are modulating the effect of the coordinated protons.

  • 19. Knighton, Richard C.
    et al.
    Emerson-King, Jack
    Rourke, Jonathan P.
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Chaplin, Adrian B.
    Solution, Solid-State, and Computational Analysis of Agostic Interactions in a Coherent Set of Low-Coordinate Rhodium(III) and Iridium(III) Complexes2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 19, p. 4927-4938Article in journal (Refereed)
    Abstract [en]

    A homologous family of low‐coordinate complexes of the formulation trans‐[M(2,2′‐biphenyl)(PR3)2][BArF4] (M=Rh, Ir; R=Ph, Cy, iPr, iBu) has been prepared and extensively structurally characterised. Enabled through a comprehensive set of solution phase (VT 1H and 31P NMR spectroscopy) and solid‐state (single crystal X‐ray diffraction) data, and analysis in silico (DFT‐based NBO and QTAIM analysis), the structural features of the constituent agostic interactions have been systematically interrogated. The combined data substantiates the adoption of stronger agostic interactions for the IrIII compared to RhIII complexes and, with respect to the phosphine ligands, in the order PiBu3>PCy3>PiPr3>PPh3. In addition to these structure–property relationships, the effect of crystal packing on the agostic interactions was investigated in the tricyclohexylphosphine complexes. Compression of the associated cations, through inclusion of a more bulky solvent molecule (1,2‐difluorobenzene vs. CH2Cl2) in the lattice or collection of data at very low temperature (25 vs. 150 K), lead to small but statistically significant shortening of the M−H−C distances.

  • 20. Li, Xin
    et al.
    Lu, Xue Min
    Lu, Qing Hua
    Ohlin, C. André
    Re-writable multi-domain liquid crystal alignment layers through laser-induced micropatterning2006In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 45, no 20-23, p. L591-L594Article in journal (Refereed)
    Abstract [en]

    We report a method for the preparation of multi-domain liquid crystal (LC) alignment layers on polyimide surfaces with laser-induced periodic surface structures. Atomic force microscopy confirmed that the laser-induced microstructures could be easily erased and re-constructed by repeated laser exposure. The microstructures demonstrated excellent abilities to align LCs in a multi-domain way. The intricate micropatterning of LCs with high resolution was obtained. The opto-electric properties of the LC cells were also determined. In addition, the method is available to a wide range of polymeric substrates, including flexible ones such as poly(ethylene terephthalate).

  • 21. Liu, Yu Ping
    et al.
    Guo, Si-Xuan
    Ding, Liang
    Ohlin, C. Andre
    Bond, Alan M.
    Zhang, Jie
    Lindqvist Polyoxoniobate Ion-Assisted Electrodeposition of Cobalt and Nickel Water Oxidation Catalysts2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 30, p. 16632-16644Article in journal (Refereed)
    Abstract [en]

    A method has been developed for the efficient electrodeposition of cobalt and nickel nanostructures with the assistance of the Lindqvist ion [Nb6O19](8). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry, and a range of electrochemical techniques have been used to characterize the morphology, composition, catalytic water oxidation activity and stability of the films in alkaline solution. SEM images show that films consisting of nanoparticles with diameters of ca. 30 to 40 nm are formed after 40-50 potential cycles of deposition. Nb and Co/Ni are detected in the films by EDX. ICP-MS results show an elemental ratio of 1:1 for Co:Nb and 1:3 for Ni:Nb, respectively. Raman spectra reveal the presence of both [Nb6O19](8) and Co(OH)(2)/Ni(OH)(2). The films exhibit excellent stability and efficiency for electrocatalytic water oxidation in alkaline solution. Turnover frequencies of 12.9 and 13.2 s(-1) were determined by rotating ring disk electrode voltammetry at an overpotential of 480 mV for Co and Ni films, respectively. Fourier transformed large amplitude alternating current (FTAC) voltammetry reveals an additional underlying oxidation process for Co under catalytic turnover conditions, which indicates that a Co-IV species is involved in the efficient catalytic water oxidation reactions. FTAC voltammetric data also suggest that the Ni films undergoes a clear phase transformation upon aging in aqueous 1 M NaOH and the electrogenerated higher oxidation state Ni from beta-NiOOH is the more active form of the catalyst.

  • 22. McAlpin, J. Gregory
    et al.
    Stich, Troy A.
    Ohlin, C. Andre
    Surendranath, Yogesh
    Nocera, Daniel G.
    Casey, William H.
    Britt, R. David
    Electronic Structure Description of a [Co(III)(3)Co(IV)O-4] Cluster: A Model for the Paramagnetic Intermediate in Cobalt-Catalyzed Water Oxidation2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 39, p. 15444-15452Article in journal (Refereed)
    Abstract [en]

    Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co4O4(C5H5N)(4)(CH3CO2)(4)](+) (1(+)), a cobalt tetramer with total electron spin S = 1/2 and formal cobalt oxidation states III, III, III, and IV. The cuboidal arrangement of its cobalt and oxygen atoms is similar to that of proposed structures for the molecular cobaltate clusters of the cobalt-phosphate (Co-Pi) water-oxidizing catalyst. The Davies electron-nuclear double resonance (ENDOR) spectrum is well-modeled using a single class of hyperfine-coupled Co-59 nuclei with a modestly strong interaction (principal elements of the hyperfine tensor are equal to [-20(+/- 2), 77(+/- 1), -5(+/- 15)] MHz). Mims H-1 ENDOR spectra of 1(+) with selectively deuterated pyridine ligands confirm that the amount of unpaired spin on the cobalt-bonding partner is significantly reduced from unity. Multifrequency N-14 ESEEM spectra (acquired at 9.5 and 34.0 GHz) indicate that four nearly equivalent nitrogen nuclei are coupled to the electron spin. Cumulatively, our EPR spectroscopic findings indicate that the unpaired spin is delocalized almost equally across the eight core atoms, a finding corroborated by results from DFT calculations. Each octahedrally coordinated cobalt ion is forced into a low-spin electron configuration by the anionic oxo and carboxylato ligands, and a fractional electron hole is localized on each metal center in a Co 3d(xz,yz)-based molecular orbital for this essentially [Co4+3.125O4] system. Comparing the EPR spectrum of 1(+) with that of the catalyst film allows us to draw conclusions about the electronic structure of this water-oxidation catalyst.

  • 23. Ng, Chun Hin
    et al.
    Ohlin, C. Andre
    Qiu, Siyao
    Sun, Chenghua
    Winther-Jensen, Björn
    Mechanistic studies of the photo-electrochemical hydrogen evolution reaction on poly(2,2'-bithiophene)2016In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 6, no 9, p. 3253-3262Article in journal (Refereed)
    Abstract [en]

    The realisation of poly(2,2’-bithiophene) (PBTh) as an effective photo-electrocatalyst for the hydrogen evolution reaction is a novel discovery [Ng et al., Int. J. Hydrogen Energy, 2014, 39, 18230]; however, the underlying mechanism of this catalysis remains unknown. In this article, studies using electrochemical, photo-electrochemical, Raman spectroscopy and computational modelling are undertaken to shed some light on the mechanistic process. From these studies, a compelling reaction scheme is proposed involving the protonation of the PBTh chain via the sulphur atom and subsequent intersystem crossing to a long-lived triplet state for the reaction to form H-2. This suggested mechanism is tentative but cohesively integrates all experimental and computational findings. Importantly, these insights into the PBTh system form an important mechanistic milestone study and will help inspire new developments and applications for polythiophenes and conducting polymers.

  • 24. Ng, Chun Hin
    et al.
    Ohlin, C. Andre
    Winther-Jensen, Bjorn
    Characterisation of a series of triarylmethane dyes as light harvesters for photo-electrochemical systems2015In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 115, p. 96-101Article in journal (Refereed)
    Abstract [en]

    A series of commercially available dyes were characterised by electrochemical, spectroscopic and computational methods. Several dyes, including Fuchsin Basic and Malachite Green were found to have properties that make them potential candidates for use in photo-electrochemical systems. The risks of combining different characterisation methods are also highlighted, namely the combination of thermodynamic reactions (electrochemical redox reactions), electronic transitions (optical spectroscopy) and the use of computational techniques to describe them.

  • 25. Ng, Chun Hin
    et al.
    Winther-Jensen, Orawan
    Kolodziejczyk, Bartlomiej
    Ohlin, C. Andre
    Winther-Jensen, Bjorn
    Photo-electrocatalytic H-2 evolution on poly(2,2 ‘-bithiophene) at neutral pH2014In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, no 32, p. 18230-18234Article in journal (Refereed)
    Abstract [en]

    Vapour phase polymerised (VPP) polybithiophene (PBTh) on glassy carbon is revealed to be an efficient photo-electrocatalytic electrode for the hydrogen evolution reaction (HER). An onset potential of -0.03 V vs SCE for the HER is observed on illumination using visible light in 0.1 mol L-1 phosphate buffer at pH 6.9, 600 mV lower in energy than E-o. Hydrogen evolution is confirmed using gas chromatography with a calculated faradaic efficiency of 34% when holding at a potential of -0.5 V. Importantly, this process occurs without platinum and under neutral aqueous conditions thus revealing a significant but overlooked application for PBTh: a potential low-cost cathode material for the splitting of water. 

  • 26. Ng, Chun Hin
    et al.
    Winther-Jensen, Orawan
    Ohlin, C. Andre
    Winther-Jensen, Bjorn
    Exploration and optimisation of poly(2,2 ‘-bithiophene) as a stable photo-electrocatalyst for hydrogen production2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 21, p. 11358-11366Article in journal (Refereed)
    Abstract [en]

    An organic photo-electrochemical catalyst for the hydrogen evolution reaction (HER) based on the conducting polymer, poly(2,2 ‘-bithiophene) (PBTh), is further explored. Long-term stability testing shows the successful operation of the catalyst over a period of 12 days at neutral pH with corresponding turnover numbers exceeding 6 x 10(4). Experimental parameters such as substrate type, electrolyte, pH and thickness of the film are explored and their subsequent effects on catalytic behaviour and performance discussed. Significant findings include the four-fold increase in performance by the reduction of thickness to better facilitate charge transfer and the successful photo-catalysis of the HER at pH 11, with an onset that is 0.14 V below E-0. Faradaic efficiency was also determined with a maximum recorded efficiency of 80% despite known losses such as crossover reactions and H-2 escape from within the system.

  • 27. Ohlin, C. Andre
    Reaction Dynamics and Solution Chemistry of Polyoxometalates by Electrospray Ionization Mass Spectrometry2012In: Chemistry - An Asian Journal, ISSN 1861-4728, E-ISSN 1861-471X, Vol. 7, no 2, p. 262-270Article in journal (Refereed)
    Abstract [en]

    Mass spectrometry both complements other analytical techniques and allows for types of analyses and experiments not possible with common analytical methods, such as NMR, IR, and UV/Vis spectroscopy. Electrospray constitutes one of the mildest forms of ionization, making it the preferred method for the analysis of large fragile or reactive ions. There is particular promise for mass spectrometry in aiding the characterization of polyoxometalates and their solutions, but caution must be taken in designing the experiments in order to yield reliable data and to avoid the temptation of over-interpreting the relevance of gas-phase data to solution chemistry.

  • 28. Ohlin, C. Andre
    et al.
    Brimblecombe, Robin
    Spiccia, Leone
    Casey, William H.
    Oxygen isotopic exchange in an (MnMn3IV)-Mn-III-oxo cubane2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 27, p. 5278-5280Article in journal (Refereed)
    Abstract [en]

    The rate and activation parameters for oxygen exchange of the mu(3)-oxo bridges in a manganese tetranuclear cluster with (H2O)-O-18 have been measured by ESI-MS; the observed Delta S double dagger of -146 +/- 22 J K-1 mol(-1) is consistent with the expected associative mechanism of substitution.

  • 29. Ohlin, C. Andre
    et al.
    Harley, Stephen J.
    McAlpin, J. Gregory
    Hocking, Rosalie K.
    Mercado, Brandon Q.
    Johnson, Rene L.
    Villa, Eric M.
    Fidler, Mary Kate
    Olmstead, Marilyn M.
    Spiccia, Leone
    Britt, R. David
    Casey, William H.
    Rates of Water Exchange for Two Cobalt(II) Heteropolyoxotungstate Compounds in Aqueous Solution2011In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 16, p. 4408-4417Article in journal (Refereed)
    Abstract [en]

    Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to Co-II atoms in two polyoxotungstate sandwich molecules using the O-17-NMR-based Swift-Connick method. The compounds were the [Co-4(H2O)(2)(B-alpha-PW9O34)(2)](10-) and the larger alpha beta beta alpha-[Co-4(H2O)(2)(P2W15O56)(2)](16-) ions, each with two water molecules bound trans to one another in a Co-II sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal Xray crystallography, and potentiometry. For [Co-4(H2O)(2)(B-alpha-PW9O34)(2)](10-) at pH 5.4, we estimate: k(298) = 1.5(5) +/- 0.3 x 10(6) s(-1), Delta H-not equal = 39.8 +/- 0.4 kJ mol(-1), Delta S-not equal = + 7.1 +/- 1.2 J mol(-1)K(-1) and Delta V-not equal = 5.6 +/- 1.6 cm(3)mol(-1). For the Wells-Dawson sandwich cluster (alpha beta beta alpha-[Co-4(H2O)(2)(P2W15O56)(2)](16-)) at pH 5.54, we find: k(298) = 1.6(2) +/- 0.3 x 10(6)s(-1), Delta H-not equal = 27.6 +/- 0.4 kJ mol(-1) Delta S-not equal = -33 +/- 1.3 J mol(-1)K(-1) and Delta V-not equal = 2.2 +/- 1.4 cm(3)mol(-1) at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR spectroscopy as S=3/2 Co-II species (such as the [Co(H2O)(6)](2+) monomer ion) and by the significant reduction of the Co-Co vector in the XAS spectra.

  • 30. Ohlin, C. Andre
    et al.
    Rustad, James R.
    Casey, William H.
    The energetics of isomerisation in Keggin-series aluminate cations2014In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 43, no 39, p. 14533-14536Article in journal (Refereed)
    Abstract [en]

    Electronic-structure calculations show that the e-isomer of the polyoxoaluminate ion in the Keggin structure [AlO4-(Al(OH)(2)-(H2O))(12)](7+) is the thermodynamically favoured one. Direct interconversion between the epsilon- and delta-isomers via cap rotation has a prohibitively high energy barrier in vacuo, suggesting that isomerisation in solution either proceeds via a dissolution-precipitation pathway, or that solvation and/or coordination to counterions reduces the barrier significantly. The implications for the formation of the [Al2O8Al28(OH)(56)(H2O)26](18+) ion are discussed.

  • 31. Ohlin, C. Andre
    et al.
    Villa, Eric M.
    Casey, William H.
    One-pot synthesis of the decaniobate salt [N(CH3)(4)](6)[Nb10O28] center dot 6H(2)O from hydrous niobium oxide2009In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 362, no 4, p. 1391-1392Article in journal (Refereed)
    Abstract [en]

    A robust and easily reproducible one-pot synthetic method for the preparation of [N(CH3)(4)](6)[Nb10O28] center dot 6H(2)O is introduced.

  • 32. Ohlin, C. Andre
    et al.
    Villa, Eric M.
    Fettinger, James C.
    Casey, William H.
    A new titanoniobate ion-completing the series [Nb10O28](6-), [TiNb9O28](7-) and [Ti2Nb8O28](8-)2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 15, p. 2677-2678Article in journal (Refereed)
    Abstract [en]

    A new water-soluble polyoxometalate, [TiNb9O28](7-), completes an isostructural and homologous decametalate series from the decaniobate to the dititano-octaniobate ion.

  • 33. Ohlin, C. Andre
    et al.
    Villa, Eric M.
    Fettinger, James C.
    Casey, William H.
    Distinctly Different Reactivities of Two Similar Polyoxoniobates with Hydrogen Peroxide2008In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 47, no 43, p. 8251-8254Article in journal (Refereed)
  • 34. Ohlin, C. Andre
    et al.
    Villa, Eric M.
    Fettinger, James C.
    Casey, William H.
    The first peroxotitanoniobate cluster - [N(CH3)(4)](10)[Ti12Nb6O38(O-2(I))(6)]2010In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 363, no 15, p. 4405-4407Article in journal (Refereed)
    Abstract [en]

    The synthesis and structure of the first discrete peroxotitanoniobate cluster, [N(CH3)(4)](10)[Ti12Nb6O38(O-2(I))(6)], is described. (C) 2010 Elsevier B.V. All rights reserved.

  • 35. Ohlin, C. Andre
    et al.
    Villa, Eric M.
    Rustad, James R.
    Casey, William H.
    Dissolution of insulating oxide materials at the molecular scale2010In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 9, no 1, p. 11-19Article, review/survey (Refereed)
    Abstract [en]

    Our understanding of mineral and glass dissolution has advanced from simple thermodynamic treatments to models that emphasize adsorbate structures. This evolution was driven by the idea that the best understanding is built at the molecular level. Now, it is clear that the molecular questions cannot be answered uniquely with dissolution experiments. At the surface it is unclear which functional groups are present, how they are arranged, and how they interact with each other and with solutes as the key bonds are activated. An alternative approach has developed whereby reactions are studied with nanometre-sized aqueous oxide ions that serve as models for the more complicated oxide interface. For these ions, establishing the structure is not a research problem in itself, and bond ruptures and dissociations can be followed with much confidence. We review the field from bulk-dissolution kinetics to the new isotope-exchange experiments in large oxide ions.

  • 36. Ohlin, C. André
    et al.
    Beni, Zoltan
    Laurenczy, Gábor
    Ruiz, Nuria
    Masdeu-Bulto, Anna M.
    Heterogeneous dehalogenation of arylhalides in the presence of ionic liquids2007In: Applied organometallic chemistry, ISSN 0268-2605, E-ISSN 1099-0739, Vol. 21, no 3, p. 156-160Article in journal (Refereed)
    Abstract [en]

    Dehydrohalogenation of haloaromatics in ionic liquids derived from ethylmethylimidazolium or similar salts has been performed using Pd-C, Pd(OAc)(2) and other catalysts using formate salts as a hydrogen source. In the ionic liquid [emim][BF4], chlorobenzene was dehalogenated by up to 40%, bromobenzene up to 25% and iodobenzene up to 41% in 2 h. Reactions in the absence of the ionic liquid were also performed.

  • 37.
    Ohlin, C. André
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Casey, William H.
    17O NMR as a Tool in Discrete Metal Oxide Cluster Chemistry2018In: Annual Reports on NMR Spectroscopy / [ed] Webb, Graham A., Elsevier, 2018, p. 187-248Chapter in book (Refereed)
    Abstract [en]

    This chapter covers recent developments in 17O NMR spectroscopy as applied to discrete metal oxide clusters, particularly in the context of their use as models in geochemistry and catalysis. Dynamic 17O NMR methods based on the McConnell–Bloch equations are explored in depth, and recent advances are reviewed. High-pressure NMR methods are also discussed and reviewed, as are recent developments in the use of density functional theory in the computation of 17O NMR shifts in polyoxometalates. The emphasis of the chapter is on the new developments that promise to reinvigorate 17O NMR as a central tool in the study of aqueous chemical kinetics, with the most urgent challenges being understanding the rates of isotopic substitution into bridging oxygens in clusters.

  • 38. Ohlin, C. André
    et al.
    Dyson, Paul J.
    Laurenczy, Gábor
    Carbon monoxide solubility in ionic liquids: determination, prediction and relevance to hydroformylation2004In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 9, p. 1070-1071Article in journal (Refereed)
    Abstract [en]

    The solubility of carbon monoxide in 37 ionic liquids and in some organic solvents has been determined using high-pressure (13)C NMR spectroscopy; a method for predicting the CO solubility is demonstrated, and it was shown that the rate of the hydroformylation of 5-hexen-2-one does not correlate with the CO solubility, as expected from the determined relative solubility of CO compared to H(2).

  • 39. Ohlin, C André
    et al.
    Laurenczy, G
    Carbon dioxide reduction in biphasic aqueous-ionic liquid systems by pressurized hydrogen2003In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 23, no 3, p. 239-242Article in journal (Refereed)
    Abstract [en]

    This work reports the hydrogenation of carbon dioxide/inorganic carbonate salts to formic acid/formate in two phase systems comprising an ionic phase, in which the catalyst is immobilized, and an aqueous phase in which the carbonates and formate are confined, is reported. The reactions were followed in situ by multinuclear NMR. Pressurized H-2 gas was used for the reduction.

  • 40.
    Ohlin, C. André
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pascual-Borràs, Magda
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Protonation and water exchange kinetics in sandwich polyoxometalates2018In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 38, p. 13602-13607Article in journal (Refereed)
    Abstract [en]

    Density functional theory is used to explore the locus and consequences of protonation in [Zn4(HO)2(PW9O34)2]10−. The results are used to explain recent observations regarding the contrasting pH effects on the water-ligand exchange in [Mn4(H2O)2(P2W15O56)2]16− and [Co4(H2O)2(P2W15O56)2]16−, and the general effect of protonation on solvent exchange in metal oxides is discussed.

  • 41. Ohlin, C. André
    et al.
    Villa, Eric M.
    Fettinger, James C.
    Casey, William H.
    The [Ti(12)Nb(6)O(44)](10-) ion: A new type of polyoxometalate structure2008In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 47, no 30, p. 5634-5636Article in journal (Refereed)
  • 42. Panasci, Adele F.
    et al.
    McAlpin, J. Gregory
    Ohlin, C. Andre
    Christensen, Shauna
    Fettinger, James C.
    Britt, R. David
    Rustad, James R.
    Casey, William H.
    Cooperation between bound waters and hydroxyls in controlling isotope-exchange rates2012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 78, p. 18-27Article in journal (Refereed)
    Abstract [en]

    Mineral oxides differ from aqueous ions in that the bound water molecules are usually attached to different metal centers, or vicinal, and thus separated from one another. In contrast, for most monomeric ions used to establish kinetic reactivity trends, such as octahedral aquo ions (e.g., Al(H(2)O)(6)(3+)), the bound waters are closely packed, or geminal. Because of this structural difference, the existing literature about ligand substitution in monomer ions may be a poor guide to the reactions of geochemical interest. To understand how coordination of the reactive functional groups might affect the rates of simple water-exchange reactions, we synthesized two structurally similar Rh(III) complexes, [Rh(phen)(2)(H(2)O)(2)](3+) [1] and [Rh(phen)(2)(H(2)O)Cl](2+) [2] where (phen) = 1,10-phenanthroline. Complex [1] has two adjacent, geminal, bound waters in the inner-coordination sphere and [2] has a single bound water adjacent to a bound chloride ion. We employed Rh(III) as a trivalent metal rather than a more geochemically relevant metal like Fe(III) or Al(III) to slow the rate of reaction, which makes possible measurement of the rates of isotopic substitution by simple mass spectrometry. We prepared isotopically pure versions of the molecules, dissolved them into isotopically dissimilar water, and measured the rates of exchange from the extents of (18)O and (16)O exchange at the bound waters. The pH dependency of rates differ enormously between the two complexes. Pseudo-first-order rate coefficients at 298 K for water exchanges from the fully protonated molecules are close: k(0)(298) = 5 x 10(-8) (+/- 0.5 x 10(-8)) s(-1) for [1] and k(0)(298) = 2.5 x 10(-9)(+/- 1 x 10(-9)) for [2]. Enthalpy and entropy activation parameters (Delta H(double dagger) and Delta S(double dagger)) were measured to be 119(+/- 3) kJ mol(-1), and 14(+/- 1) J mol(-1) K(-1), respectively for [1]. The corresponding parameters for the mono-aquo complex, [2], are 132(+/- 3) kJ mol(-1) and 41.5(+/- 2) J mol(-1) K(-1). Rates increase by many orders of magnitude upon deprotonation of one of the bound waters in complex [1] because of the close proximity of a transferable proton that can convert the bound hydroxyl to a bound water. This interconversion allows the oxygen to exchange as a bound water, rather than as a bound hydroxyl, which is slow at near-neutral pH conditions. (C) 2011 Elsevier Ltd. All rights reserved.

  • 43. Panasci, Adele F.
    et al.
    Ohlin, C. Andre
    Harley, Stephen J.
    Casey, William H.
    Rates of Water Exchange on the [Fe-4(OH)(2)(hpdta)(2)(H2O)(4)](0) Molecule and Its Implications for Geochemistry2012In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 12, p. 6731-6738Article in journal (Refereed)
    Abstract [en]

    The ammonium salt of [Fe4O(OH)(hpdta)(2)(H2O)(4)](-) is soluble and makes a monospecific solution of [Fe-4(OH)(2)(hpdta)(2)(H2O)(4)](0)(aq) in acidic solutions (hpdta = 2-hydroxypropane-1,3-diamino-N,N,N’,W-tetraacetate). This tetramer is a diprotic acid with pK(a1) estimated at 5.7 +/- 0.2 and pK(a2) = 8.8(5) +/- 0.2. In the pH region below pK(a1), the molecule is stable in solution and O-17 NMR line widths can be interpreted using the Swift-Connick equations to acquire rates of ligand substitution at the four isolated bound water sites. Averaging five measurements at pH < 5, where contribution from the less-reactive conjugate base are minimal, we estimate: k(ex)(298) = 8.1 (+/- 2.6) X 10(5) s(-1), Delta H-double dagger = 46 (+/- 4.6) kJ mol(-1), Delta S-double dagger = 22 (+/- 18) J mol(-1) K-1, and Delta V-double dagger = +1.85 (+/- 0.2) cm(3) mol(-1) for waters bound to the fully protonated, neutral molecule. Regressing the experimental rate coefficients versus 1/[H+] to account for the small pH variation in rate yields a similar value of k(ex)(298) = 8.3 (+/- 0.8) X 10(5) s(-1). These rates are similar to 10(4) times faster than those of the [Fe(OH2)(6)](3+) ion (k(ex)(298) = 1.6 X 10(2) s(-1)) but are about an order of magnitude slower than other studied aminocarboxylate complexes, although these complexes have seven-coordinated Fe(III), not six as in the [Fe-4(OH)(2)(hpdta)(2)(H2O)(4)](0)(aq) molecule. As pH approaches pK(a1), the rates decrease and a compensatory relation is evident between the experimental Delta H-double dagger and Delta S-double dagger values. Such variation cannot be caused by enthalpy from the deprotonation reaction and is not well understood. A correlation between < Fe-III-OH2 > bond lengths and the logarithm of k(ex)(298) is geochemically important because it could be used to estimate rate coefficients for geochemical materials for which only DFT calculations are possible. This molecule is the only neutral, oxo-bridged Fe(III) multimer for which rate data are available.

  • 44. Pautler, Brent G.
    et al.
    Colla, Christopher A.
    Johnson, Rene L.
    Klavins, Peter
    Harley, Stephen J.
    Ohlin, C. Andre
    Sverjensky, Dimitri A.
    Walton, Jeffrey H.
    Casey, William H.
    A High-Pressure NMR Probe for Aqueous Geochemistry2014In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 53, no 37, p. 9788-9791Article in journal (Refereed)
    Abstract [en]

    A non-magnetic piston-cylinder pressure cell is presented for solution-state NMR spectroscopy at geochemical pressures. The probe has been calibrated up to 20kbar using insitu ruby fluorescence and allows for the measurement of pressure dependencies of a wide variety of NMR-active nuclei with as little as 10L of sample in a microcoil. Initial (BNMR)-B-11 spectroscopy of the H3BO3-catechol equilibria reveals a large pressure-driven exchange rate and a negative pressure-dependent activation volume, reflecting increased solvation and electrostriction upon boron-catecholate formation. The inexpensive probe design doubles the current pressure range available for solution NMR spectroscopy and is particularly important to advance the field of aqueous geochemistry.

  • 45. Perera, Ishanie Rangeeka
    et al.
    Daeneke, Torben
    Makuta, Satoshi
    Yu, Ze
    Tachibana, Yasuhiro
    Mishra, Amaresh
    Baeuerle, Peter
    Ohlin, C. André
    Bach, Udo
    Spiccia, Leone
    Application of the Tris(acetylacetonato)iron(III)/(II) Redox Couple in p-Type Dye-Sensitized Solar Cells2015In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 54, no 12, p. 3758-3762Article in journal (Refereed)
    Abstract [en]

    An electrolyte based on the tris(acetylacetonato)iron( III)/(II) redox couple ([Fe(acac)(3)](0/1)) was developed for p-type dye-sensitized solar cells (DSSCs). Introduction of a NiO blocking layer on the working electrode and the use of chenodeoxycholic acid in the electrolyte enhanced device performance by improving the photocurrent. Devices containing [Fe(acac)(3)](0/1-) and a perylene-thiophene-triphenylamine sensitizer (PMI-6T-TPA) have the highest reported short-circuit current (J(SC)=7.65 mA cm(-2)), and energy conversion efficiency (2.51%) for p-type DSSCs coupled with a fill factor of 0.51 and an open-circuit voltage V-OC=645 mV. Measurement of the kinetics of dye regeneration by the redox mediator revealed that the process is diffusion limited as the dye-regeneration rate constant (1.7 x 10(8) M-1 S-1) is very close to the maximum theoretical rate constant of 3.3 x 10(8) M-1 S-1. Consequently, a very high dye-regeneration yield (>99%) could be calculated for these devices.

  • 46. Perera, Ishanie Rangeeka
    et al.
    Gupta, Akhil
    Xiang, Wanchun
    Daeneke, Torben
    Bach, Udo
    Evans, Richard A.
    Ohlin, C. Andre
    Spiccia, Leone
    Introducing manganese complexes as redox mediators for dye-sensitized solar cells2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 24, p. 12021-12028Article in journal (Refereed)
    Abstract [en]

    The abundance and low toxicity of manganese have led us to explore the application of manganese complexes as redox mediators for dye sensitized solar cells (DSCs), a promising solar energy conversion technology which mimics some of the key processes in photosynthesis during its operation. In this paper, we report the development of a DSC electrolyte based on the tris(acetylacetonato) manganese(III)/(IV), [Mn(acac)(3)](0/1+), redox couple. PEDOT-coated FTO glass was used as a counter electrode instead of the conventionally used platinum. The influence of a number of device parameters on the DSC performance was studied, including the concentration of the reduced and oxidized mediator species, the concentration of specific additives (4-tert-butylpyridine, lithium tetrafluoroborate, and chenodeoxycholic acid) and the thickness of the TiO2 working electrode. These studies were carried out with a new donor-pi-acceptor sensitizer K4. Maximum energy conversion efficiencies of 3.8% at simulated one Sun irradiation (AM 1.5 G; 1000 W m(-2)) with an open circuit voltage (V-OC) of 765 mV, a short-circuit current (J(SC)) of 7.8 mA cm(-2) and a fill factor (FF) of 0.72 were obtained. Application of the commercially available MK2 and N719 sensitizers resulted in an energy conversion efficiency of 4.4% with a V-OC of 733 mV and a J(SC) of 8.6 mA cm(-2) for MK2 and a V-OC of 771 mV and a J(SC) of 7.9 mA cm(-2) for N719. Both dyes exhibit higher incident photon to current conversion efficiencies (IPCEs) than K4.

  • 47. Phillips, Brian L.
    et al.
    Ohlin, C. Andre
    School of Chemistry, Monash University, Clayton, Australia.
    Vaughn, John
    Woerner, William
    Smart, Scott
    Subramanyam, Ravi
    Pan, Long
    Solid-State 27Al NMR Spectroscopy of the γ-Al13 Keggin Containing Al Coordinated by a Terminal Hydroxyl Ligand2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 23, p. 12270-12280Article in journal (Refereed)
    Abstract [en]

    We report solid-state 27Al NMR spectroscopic results for the sulfate salt of the γ-Al13 Keggin cluster, γ-[AlO4Al12(OH)25(OH2)11][SO4]3·[H2O]14, that provide a spectroscopic signature for partial hydrolysis of this Keggin-type cluster. In 27Al multiple-quantum magic-angle spinning NMR spectra, all 13 Al positions of the cluster are at least partially resolved and assigned with the aid of density functional theory (DFT) calculations of the 27Al electric field gradients. The isotropic chemical shift of the single tetrahedral site, 75.7 ppm, is nearly identical to that reported for solutions from which the cluster crystallizes. Reflecting broadly similar coordination environments, the octahedral Al show mostly small variations in isotropic chemical shift (+7 to +11 ppm) and quadrupolar coupling constant (CQ; 6–7.5 MHz), except for one resonance that exhibits a much smaller CQ and another site with a larger value. DFT calculations show that deprotonation of a terminal water ligand, to form an η-OH group, causes a large reduction in the 27Al CQ, allowing assignment of a distinct, narrow peak for octahedral Al to this hydroxyl-terminated site. This result suggests a relationship between octahedral 27Al NMR line width and hydrolysis for solids prepared from Keggin-type clusters.

  • 48. Pilgrim, C. D.
    et al.
    Callahan, J. R.
    Colla, C. A.
    Ohlin, André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mason, H. E.
    Casey, W. H.
    27Al MQMAS of the δ-Al13-Keggin†2017In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 7, p. 2249-2254Article in journal (Refereed)
    Abstract [en]

    One-dimensional 27Al, 23Na Magic-Angle-Spinning (MAS) NMR and 27Al Multiple-Quantum Magic-Angle-Spinning NMR (MQMAS) measurements are reported for the [small delta]-isomer of the Al13 Keggin structure at high spinning speed and 14.1 T field. Values for the CQ and [small eta] parameters are on the same scale as those seen in other isomers of the Al13 structure. Density functional theory (DFT) calculations are performed for comparison to the experimental fits using the B3PW91/6-31+G* and PBE0/6-31+G* levels of theory, with the Polarizable Continuum Model (PCM).

  • 49. Sharma, Rupali
    et al.
    Zhang, Jie
    Ohlin, C. Andre
    pH-Dependent solution dynamics of a manganese(II)polyoxometalate, [Mn-4(H2O)(2)(P2W15O56)(2)](16-), and [Mn(H2O)(6)](2+)2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 44, p. 19068-19071Article in journal (Refereed)
    Abstract [en]

    The aqueous reaction dynamics of the manganese(II)-functionalised Wells-Dawson polyoxometalate [Mn-4(H2O)(2)(P2W15O56)(2)](16-) has been determined as a function of pH using variable temperature O-17 NMR, and compared with that of the well-studied monomeric manganese(II) hexa-aqua ion, [Mn(H2O)(6)](2+). While the rate of aquo-ligand exchange on the hexa-aqua ion remains independent of pH in the range 3.2-6.0, the rate of water exchange of the polyoxometalate ion varies by a factor of fifteen, from 1.98 x 10(7) s(-1) at pH 3.2 to 1.3 x 10(6) s(-1) at pH 6.0. This decrease in the rate of exchange correlates with the deprotonation of the polyoxometalate framework.

  • 50. Sharma, Rupali
    et al.
    Zhang, Jie
    Ohlin, C. André
    Predicting O-17 NMR chemical shifts of polyoxometalates using density functional theory2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 11, p. 8235-8241Article in journal (Refereed)
    Abstract [en]

    We have investigated the computation of O-17 NMR chemical shifts of a wide range of polyoxometalates using density functional theory. The effects of basis sets and exchange-correlation functionals are explored, and whereas pure DFT functionals generally predict the chemical shifts of terminal oxygen sites quite well, hybrid functionals are required for the prediction of accurate chemical shifts in conjunction with linear regression. By using PBE0/def2-tzvp//PBE0/cc-pvtz(H-Ar), lanl2dz(K-) we have computed the chemical shifts of 37 polyoxometalates, corresponding to 209 O-17 NMR signals. We also show that at this level of theory the protonation-induced pH dependence of the chemical shift of the triprotic hexaniobate Lindqvist anion, [HxNb6O19]((8-x)), can be reproduced, which suggests that hypotheses regarding loci of protonation can be confidently tested.

12 1 - 50 of 71
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