| 1. |
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| 2. |
- Abu-Youssef, Morsy A.M., et al.
(författare)
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Synthesis, a case of isostructural packing, and antimicrobial activity of silver(I)quinoxaline nitrate, silver(I)(2,5-dimethylpyrazine) nitrate and two related silver aminopyridine compounds
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 2006:21, s. 2542-2550
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and low temperature crystal structures of [Ag(quinoxaline)]n(NO3)n, 1, [Ag(2,5-dimethylpyrazine)(NO3)]n, 2 and [Ag4(3-aminopyridine)4(NO3)4]n 3 are presented. The quinoxaline compound forms a 1D coordination polymer with the characteristic linear 2-coordination figure of silver(I), the NAgN angle being 164.2(1)°, and only weak silvernitrate interactions. In addition there is an interaction giving pairs of parallel chains as the main structural theme. The 2,5-dimethylpyrazine compound has approximately trigonal-planar coordination, also binding one nitrate at the relatively short AgO distances 2.444(3)Å and 2.484(3)Å, respectively, for the two crystallographically different silver atoms. This also results in a 1D coordination polymer that, despite the large differences in the Ag(I) coordination environment, is isostructural with 1. [Ag4(3-aminopyridine)4(NO3)4]n 3 forms a 2D coordination polymer by bridging nitrate ions. The antimicrobial activity of 13, and also of [Ag3(2-aminopyridine)4](NO3)3, 4 was screened for 13 different pathogens and substantial activity was shown for 1 against Escherichia coli and Pseudomonas aeruginosa (MIC 4 µg cm3) and somewhat lower activity was registered against Sarcina lutea and Salmonella typhi for 1, Bordetella bronchiseptica for 2, Salmonella typhi and Pseudomonas aeruginosa for 3, and Escherichia coli and Shigella sonnie for 3 (MIC 8 µg cm3). Only low activity was shown against the yeast Candida albicans for 1, 2 and 4 whereas no activity against this pathogen was registered for 3.
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| 3. |
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| 4. |
- Andersson, Ingegärd, et al.
(författare)
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Speciation in the aqueous H+/H2VO4–/H2O2/phosphate system
- 2005
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Ingår i: DALTON TRANSACTIONS. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 22, s. 3658-66
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Tidskriftsartikel (refereegranskat)abstract
- The speciation in the aqueous H+/H2VO4- /phosphate (dihydrogen phosphate, P) and H+/H2VO4/H2O2/P systems has been determined in the physiological medium of 0.150 M Na(Cl) at 25 degrees C. A combination of multinuclear NMR integral and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and treated simultaneously by the computer program LAKE. The pK(a)-values for phosphoric acid have been determined by potentiometric and P-31 NMR chemical shift data, and have been found to be 1.85 +/- 0.02, 6.69 +/- 0.02 and 11.58 +/- 0.07. The errors given are 3 sigma. Altogether nine vanadate phosphate species have been found in the ternary H+/H2VO4-/P- system in the PH region 1-11, with the following compositions: VP, VP2 and V14P. Equilibrium is very slow in acidic solutions, requiring more than 3 months for the formation of V14P species. On the other hand, less than 15 min are needed for equilibration at neutral and alkaline pH. In the H+/H2VO4-/H2O2/P- system, four new species have been found in addition to all binary and ternary complexes. They are of VXP and VX2P compositions, where X denotes the peroxo ligand. V-51 and P-31 NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Biological and medical relevance of the species is also discussed and physiological conditions are modelled.
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| 5. |
- Arunachalampillai, Athimoolam, et al.
(författare)
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Synthesis and characterisation of PCsp3P phosphine and phosphinite iridium complexes. Cyclometallation and dehydrogenation of a cyclohexyl ring.
- 2009
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :40, s. 8626-8630
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Tidskriftsartikel (refereegranskat)abstract
- A cyclohexyl based pincer phosphine ligand undergoes cyclometalation with an iridium cyclooctadiene precursor to give a highly thermally stable iridium(III) complex where a C(sp3)-H bond has been oxidatively added. This iridium(III) hydride complex is reduced with potassium to give a terminal iridium(I) dinitrogen complex with no tendency to dimerization. The corresponding cyclohexyl phosphinite ligand undergoes reversible dehydrogenation to give the aromatic cyclometalated iridium(III) hydride complex together with 3 equivalents of dihydrogen.
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| 6. |
- Berggren, Gustav, et al.
(författare)
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Two tetranuclear Mn-complexes as biomimetic models of the oxygen evolving complex in Photosystem II - A synthesis, characterisation and reactivity study
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45, s. 10044-10054
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the preparation of two metallamacrocyclic tetranuclear manganese(II) complexes, [L1(4)Mn(4)](ClO4)(4) and [L2(4)Mn(4)](ClO4)(4) where L1 and L2 are the anions of the heptadentate ligands 2-((2-(bis(pyridin-2-ylmethyl) amino) ethyl)(methyl) amino) acetic acid and 2-(benzyl(2-(bis(pyridin-2-ylmethyl) amino) ethyl) amino) acetic acid), respectively. The complexes have been fully characterized by ESI-MS, elemental analysis, single-crystal X-ray diffraction, magnetic susceptibility, and EPR spectroscopy. Electrochemical reactions as well as reactions with different chemical redox reagents have been performed and a reversible two electron oxidation per manganese ion has been identified. The reaction of [L1(4)Mn(4)](ClO4)(4) with oxone or cerium(IV) results in the evolution of oxygen which makes this system interesting for future studies in the search for a functional mimic of the oxygen evolving complex in Photosystem II.
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| 7. |
- Bromfield, Karen M., 1976, et al.
(författare)
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Synthetic applications of cationic iron and cobalt carbonyl complexes
- 2009
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; :26, s. 5051-5061
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Tidskriftsartikel (refereegranskat)abstract
- Metal carbonyl stabilized cationic species react with a wide range of nucleophiles under mild conditions, and have thus found many synthetic applications. In this Perspective, we describe the utility of iron carbonyl dienyl cations in solution and solid phase parallel synthesis, and in the development of a new synthetic route towards oseltamivir phosphate (Tamiflu). We also discuss the solid phase version of the Nicholas reaction, employing cobalt carbonyl stabilized propargylic cations, and giving access to substituted alkynes.
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| 8. |
- Damian, Emiliana, et al.
(författare)
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Theoretical and experimental sulfur K-edge X-ray absorption spectroscopic (XANES) study of cysteine, cystine, methionine and methionine sulfoxide
- 2009
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; 18, s. 3542-3558
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Tidskriftsartikel (refereegranskat)abstract
- The experimental sulfur K-edge x-ray absorption near edge structure (XANES) spectra of the amino acids cysteine, homocysteine, penicillamine, methionine, the oxidation products methionine sulfoxide and the disulfide cystine, have been analyzed by transition potential DFT calculations. The absolute energies and intensities of the main pre-edge sulfur 1s electron transitions have been computed to determine the character of the receiving low energy unoccupied molecular orbitals (MO), and to investigate the influence of external interactions, especially by introducing water molecules hydrogen bonded to the ionic species present in different pH ranges. When the thiol group deprotonates for the three amino acids cysteine, homocysteine and penicillamine the energy of the main transition, to an MO with antibonding σ*(S-H) character, reduces by ~1.1 eV and the receiving MO obtains σ*(S-C) character. The energy shifts due to hydrogen bonding were in most cases found to be relatively small, although the transition intensities could vary significantly due to the changes induced in the molecular charge distribution, thereby affecting the shapes of the spectral features. For the cysteine and penicillamine zwitterions deconvolution of the experimental spectra allowed the microscopic acid dissociation constants to be extracted separately for the thiol and the protonated amine groups, pKaT = 8.5 ± 0.1 and 8.2 ± 0.1, and pKaN = 8.9 ± 0.1 and 8.8 ± 0.1, respectively, in both cases with the thiol group the more acidic. Coordination of cysteine to nickel(II) or mercury(II) introduced a new low energy transition involving metal ion orbitals in the receiving LUMO. The small experimentally observed energy differences between the similar main absorption features of the cysteine and methionine zwitterions, 0.2-0.3 eV in comparable surrounding, as well as a minor difference in their intensity ratio, are reflected in the calculated transitions. The S K-edge XANES spectrum of the disulfide cystine displays a characteristic double peak with the lower energy transition (2469.9 eV) into the antibonding σ*(S-S) MO. The second peak, at 2471.5 eV in aqueous solution, contains several transitions into MO:s with σ*(S-C) character involving also charge transfer to the water molecules hydrating the protonated amine groups (NH3+) of cystine. The experimental energy difference between the two peaks increases by 0.2 eV for solid cystine, while no such increase occurs for the –S-S- bond between the cysteine residues in the oxidized disulfide of glutathione, where the amine groups are engaged in peptide bonds. This study shows that externally induced changes in the intramolecular bonding, e.g. by coordination, conformation geometry or hydrogen bonding, can significantly influence the S K-edge spectra, and emphasizes the importance of a similar chemical surrounding of the model compounds for standard spectra of sulfur functional groups, used to deconvolute composite experimental spectra.
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| 9. |
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| 10. |
- Ekström, Jesper, et al.
(författare)
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Bio-inspired, side-on attachment of a ruthenium photosensitizer to an iron hydrogenase active site model
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :38, s. 4599-4606
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Tidskriftsartikel (refereegranskat)abstract
- The first ruthenium - diiron complex [(mu- pdt) Fe-2(CO)(5){PPh2(C(6)H(4)CCbpy)} Ru(bpy)(2)](2+) 1 (pdt = propyldithiolate, bpy = 2,2'-bipyridine) is described in which the photoactive ruthenium trisbipyridyl unit is linked to a model of the iron hydrogenase active site by a ligand directly attached to one of the iron centers. Electrochemical and photophysical studies show that the light-induced MLCT excited state of the title complex is localized towards the potential diiron acceptor unit. However, the relatively mild potential required for the reduction of the acetylenic bipyridine together with the easily oxidized diiron portion leads to a reductive quenching of the excited state, instead. This process results in a transiently oxidized diiron unit which may explain the surprisingly high light sensitivity of complex 1.
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| 11. |
- Fermvik, Anna, 1978, et al.
(författare)
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Radiolysis of solvents containing C5-BTBP: identification of degradation products and their dependence on absorbed dose and dose rate
- 2009
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; 32, s. 6421-6430
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Tidskriftsartikel (refereegranskat)abstract
- Solvents intended for the separation of trivalent actinides from trivalent lanthanides in spent nuclear fuel have been irradiated with gamma-radiation. The solvents initially contained 0.005 M C5-BTBP dissolved in either hexanol or cyclohexanone and they were exposed to doses up to 20 kGy. Identification of degradation products was done using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). Structures were suggested for a number of degradation products and the relative intensity of the peaks in the MS spectra was estimated. It was clear that the content of the original molecule, C5-BTBP, decreased with dose, while the content of the various degradation products increased. It was also shown that both the choice of diluent and the dose rate (Gy/h) affect the amount of degradation products formed. A degradation scheme was proposed for the radiolytic degradation of C5-BTBP.
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| 12. |
- González Baró, Ana, et al.
(författare)
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Speciation in the aqueous peroxovanadate-maltol and (peroxo)vanadate-uridine systems
- 2008
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 8, s. 1095-102
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Tidskriftsartikel (refereegranskat)abstract
- The speciation in the aqueous H+/H2VO4-/H2O2/maltol (Ma), H+/H2VO4-/uridine (Ur) and H+/H2VO4-/H2O2/Ur systems was determined in the physiological medium of 0.150 M Na(Cl) at 25 °C. A combination of quantitative 51V NMR (Bruker AMX500) and potentiometric data (glass electrode) was collected and treated simultaneously by the computer program LAKE. In the quaternary maltol system, the two species VXMa2- and VX2Ma2- (where X denotes the peroxo ligand) were found in the pH region 5-10, in addition to all binary and ternary complexes. Their formation was fast. In the ternary uridine (H+/H2VO4-/Ur) subsystem, altogether three vanadate-uridine (V-Ur) species were found in the pH region 4-10, with compositions VUr2-, V2Ur22- and V2Ur23-. Equilibrium was fast except in weakly acidic solutions when slowly decomposing decavanadates formed. In the quaternary H+/H2VO4-/H2O2/Ur system, five additional species were found at pH > 7. They were of VXUr and VX2Ur compositions. Their formation was fast. Formation constants, compositions and 51V NMR chemical shifts are given for all the species found in the systems, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Biological and medical relevance of the species (in the treatment of diabetes) are also discussed, with pseudo-physiological conditions modelled.
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| 13. |
- Gorlov, Mikhail, et al.
(författare)
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Ionic liquid electrolytes for dye-sensitized solar cells
- 2008
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :20, s. 2655-2666
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Tidskriftsartikel (refereegranskat)abstract
- The potential of room-temperature molten salts (ionic liquids) as solvents for electrolytes for dye-sensitized solar cells has been investigated during the last decade. The non-volatility, good solvent properties and high electrochemical stability of ionic liquids make them attractive solvents in contrast to volatile organic solvents. Despite this, the relatively high viscosity of ionic liquids leads to mass-transport limitations. Here we review recent developments in the application of different ionic liquids as solvents or components of liquid and quasi-solid electrolytes for dye-sensitized solar cells.
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| 14. |
- Gutkina, EA, et al.
(författare)
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Tetranuclear iron(III) complexes of an octadentate pyridine-carboxylate ligand and their catalytic activity in alkane oxidation by hydrogen peroxide
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; :3, s. 492-501
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of the octadentate ligand 2,6-bis{3-[N,N-di(2-pyridylmethyl)amino]propoxy}benzoic acid (LH) with Fe(ClO4)(3) leads to the formation of the tetranuclear complexes [Fe-4(mu-O)(2)(LH)(2)(ClCH2 CO2)(4)](ClO4)(4) (1), [{Fe-2(mu-O)L(R-CO2)}(2)](ClO4)(4) (2 R = C6H5-, 3 R = CH3-, 4, R = ClCH2-). The crystal structures of complexes 1 and 2 reveal that they consist of two Fe-2(III)(mu-O)(mu-RCO2)(2) cores that are linked via the two LH/L ligands to give a "dimer of dimers" structure. Complex I assumes a helical shape, with protonated carboxylic acid moieties of the two ligands forming a hydrogen-bonded pair at the center of the cation. In complexes 2, 3 and 4, central carboxylates of the two ligands bridge the iron ions in each of the two Fe, O units, with an interdimer iron-iron separation of approximately 10 angstrom and an intradimer separation of approximately 3.1 angstrom. The second carboxylate bridge within the Fe2O units is defined by exogenous benzoate (2), acetate (3) or chloroacetate (4) ligands. The aqua complex [{Fe-2(mu-O)L(H2O)(2)}(2)](ClO4)(6) (5) is proposed to have a similar structure, but with the exogenous bridging carboxylates replaced by two terminal water ligands. These complexes exhibit electronic and Mossbauer spectral features that are similar to those of (mu-oxo)diiron(iii) proteins as well as other related (mu-oxo)bis(mu-carboxylato)diiron(III) complexes. This similarity shows that these properties are not significantly affected by the nature of the bridging exogenous carboxylate, and that the octadentate framework ligand is essential in stabilizing the "dimer of dimers" structure. This structural feature remains in highly diluted solution (10(-5) M) as evidenced by electrospray ionization mass-spectroscopy (ES MS). Cyclic voltammetric studies of complexes 2 and 5 showed two irreversible two-electron reductions, indicating that the two Fe2O units of the tetranuclear complexes behave as distinct redox entities. Complexes 2, 3 and, especially, the aqua complex 5 are active alkane oxidation catalysts. Catalytic reactions carried out with alkane substrate molecules and hydrogen peroxide predominantly gave alcohols. High stereospecificity in the oxidation of cis- 1,2-dimethylcyclohexane supports the metal-based molecular mechanism of O-insertion into C-H bonds postulated for non-heme iron enzymes such as methane monooxygenase.
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| 15. |
- Hashimoto, Masato, et al.
(författare)
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A 31P-NMR study of the H+-MoO42--(HP)O32--HPO42--(C6H5P)O32--(CH3P)O32- system at low Motot/Ptot ratio - Formation of mixed-hetero X2M5-type polyanions
- 2009
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Ingår i: Dalton Transactions. - : The Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; :17, s. 3321-3327
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Tidskriftsartikel (refereegranskat)abstract
- Formation of X2M5-type heteropolyanions in the aqueous mixed-hetero H+-MoO42--(HP)O32--HPO42--(C6H5P)O32--(CH3P)O32- system has been studied by 31P-NMR at [Mo]tot/[Pall]tot = 1.5 at 298(1) K in 0.600 M Na(Cl) ionic medium. The -log[H+] range 1.4-6.2 has been covered. The pKa values of methylphosphonate were determined from 31P-NMR chemical shift data in the range of 0 < -log[H+] < 13.2 as H(CH3P)O3- 7.30 and H2(CH3P)O3 2.05. All four-component H+-MoO42--P1-P2 subsystems (P1 and P2 are two of the four phosphorus-containing components), except H+-MoO42--(HP)O32--HPO42-, which has been studied previously, were examined instead of the full six-component system in order to simplify the evaluation of the NMR spectra. The concentrations were adjusted to [Mo]tot = 60 mM and [P1]tot = [P2]tot = 20 mM in the measurements. All conceivable P2M5 and (P1)(P2)M5 heteropolyanions were identified. The following novel X2M5-type polyanions were found and their formation constants are given in logarithmic values with 3 in parentheses: (CH3P)2Mo5O214- 69.68(7), (HP)(C6H5P)Mo5O214- 67.09(4), (C6H5P)PMo5O225- 63.23(5), H(C6H5P)PMo5O224- 68.11(4), (HP)(CH3P)Mo5O214- 67.85(4), (CH3P)PMo5O225- 64.14(7), H(CH3P)PMo5O224- 68.89(4) and (C6H5P)(CH3P)Mo5O214- 69.18(4). The equilibrium conditions are illustrated in distribution diagrams. Phosphite proved to bind more weakly in X2M5-type polyoxometallates than phosphate or phosphonates, which are almost equally favoured in complexation.
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| 16. |
- Hashimoto, Masato, et al.
(författare)
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An equilibrium analysis of the aqueous H+- MoO4(2-)-(HP)O3(2-) and H+-MoO4(2-)-(HP)O3(2-)-HPO4(2-) systems
- 2007
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). ; , s. 124-32
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Tidskriftsartikel (refereegranskat)abstract
- The speciation in the phosphitomolybdate system, H+–MoO42––(HP)O32–, has been determined from combined potentiometric and 31P NMR measurements in 0.600 M Na(Cl) medium at 298(1) K. Potentiometric titration data were collected in the ranges 2.5 < –log[H+] < 6.2, 40.0 [Mo]tot 240.0 mM, 10.0 [P]tot 40.0 mM and 1 [Mo]tot/[P]tot 10. 31P NMR data were collected in the same ranges with the exception that –log[H+] was decreased to 0.8. The pKa values of phosphite were determined by means of potentiometric (1.5 < –log[H+] < 8.6) and 31P NMR chemical shift data (0.0 < –log[H+] < 12.0). The following log (3) values were deduced: H(HP)O3–, 6.09(2); H2(HP)O3, 7.23(4) (pKa = 1.14). In the phosphitomolybdate system, the following complexes were found along with their formation constants ((HP) denotes phosphite): Mo5(HP)24–, 65.31(4); Mo6(HP)25–, 71.94(5); Mo5(HP)4–, 51.25(8); Mo5(HP)3–, 54.9(3); Mo6(HP)2–, 68.99(9); Mo7(HP)5–, 71.25(3); Mo7(HP)4–, 74.2(2). Because hydrolysis and oxidation of phosphite to phosphate were observed by NMR, with a mixed-hetero species of low [Mo]tot/[P]tot ratio being detected, the four-component H+–MoO42––(HP)O32––HPO42– system was also studied in the same way over the range 0.8 < –log[H+] < 6.2 and [Mo]tot/[P]tot fixed at 1.5. The following mixed heteropolyanion species have been found (P denotes the phosphate group): Mo5(HP)P5–, 62.27(6); Mo5(HP)P4–, 66.76(4). The equilibrium speciation in the two systems are illustrated by distribution diagrams. In addition, the aqueous structures are proposed for all the species formed in the systems.
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| 17. |
- Hellström, Stefan, 1978, et al.
(författare)
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Structure-property relationships of small bandgap conjugated polymers for solar cells
- 2009
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Ingår i: DALTON TRANSACTIONS. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45, s. 10032-10039
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polymers as electron donors in solar cells based on donor/acceptor combinations are of great interest, partly due to the possibility of converting solar light with a low materials budget. Six small bandgap polymers with optical bandgap ranging from 1.0-1.9 eV are presented in this paper. All polymers utilize an electron donor-acceptor-donor (DAD) segment in the polymer backbone, creating a partial charge-transfer, to decrease the bandgap. The design, synthesis and the optical characteristics as well as the solar cell characteristics of the polymers are discussed. The positions of the energy levels of the conjugated polymer relative to the electron acceptor are of significant importance and determine not only the driving force for exciton dissociation but also the maximum open-circuit voltage. This work also focuses on investigating the redox behavior of the described conjugated polymers and electron acceptors using square wave voltammetry. Comparing the electrochemical data gives important information of the structure-property relationships of the polymers.
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| 18. |
- Hull, Stephen, et al.
(författare)
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Neutron total scattering study of the delta and beta phases of Bi2O3
- 2009
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; :40, s. 8737-8745
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Tidskriftsartikel (refereegranskat)abstract
- The highly disordered structure of the delta phase of Bi2O3, which possesses the highest known oxide-ion conductivity, has been studied using neutron powder diffraction. A detailed analysis of data collected at 1033(3) K using Rietveld refinement indicates that the time-averaged structure of delta-Bi2O3 can be described using the accepted model of a disordered, anion-deficient fluorite structure in space group Fm (3) over barm. However, reverse Monte Carlo modelling of the total (Bragg plus diffuse) scattering demonstrates that the local anion environment around the Bi3+ resembles the distorted square pyramidal arrangement found within the stable a and metastable beta phases at ambient temperature, which is characteristic of the cation's 6s(2) lone-pair configuration. Similarities between the structures of the highly disordered delta phase and the ambient temperature metastable beta phase are used to support this assignment and assess the validity of previous structural models based on short-range ordering of vacancies within the cubic lattice of delta-Bi2O3.
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| 19. |
- Ionescu, Adriana, et al.
(författare)
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Regioselectivity in aqueous palladium catalysed hydroxycarbonylation of styrene: a catalytic and mechanistic study
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :32, s. 3934-3940
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Tidskriftsartikel (refereegranskat)abstract
- Regioselectivity control was studied in palladium catalysed hydroxycarbonylation of styrene in neat water with water-soluble phosphines, mostly trisulfonated triphenylphosphine, TPPTS, but also N-bis(N', N'-diethyl-2-aminoethyl)-4-aminomethylphenyl-diphenylphosphine, N3P. The factor giving the highest changes in regioselectivity in the TPPTS system, under similar reaction conditions, is the temperature. In the N3P case, only a minor variation in the n/i ratio as a function of temperature is observed. In situ normal- and high-pressure NMR experiments were performed to obtain further information about the catalytic cycle and the reaction intermediates. Two palladium hydride intermediates, a palladium eta(3)-benzylic complex and both the branched and linear palladium acyl complexes were identified in the HP NMR experiments. The hydroxycarbonylation in water using styrene as a substrate operates using a hydride mechanism for pathways leading to both linear and branched product. Insertion of styrene in the palladium - hydride bond gives an eta(3)-benzyl compound. A high CO pressure gives a kinetic preference for the iso-acyl in the next step. In the TPPTS system, at moderate temperatures, the hydrolysis of the iso-acyl is faster than its conversion to the thermodynamically more stable n-acyl. A low n/i therefore requires high pressures and reasonably low temperatures. The N3P ligand always favours the linear product since isomerisation of the iso-acyl to the n-acyl in this system is fast under all conditions investigated.
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| 20. |
- Jarenmark, Martin, et al.
(författare)
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Symmetrical and unsymmetrical dizinc complexes as models for the active sites of hydrolytic enzymes.
- 2008
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; :8, s. 993-996
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Tidskriftsartikel (refereegranskat)abstract
- Dinuclear carboxylate-bridged zinc complexes of one symmetric and one asymmetric phenolate-based ligand catalyse the transesterification of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) at different rates, with an unsymmetrical complex being more active than a symmetric one.
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| 21. |
- Jiang, Shi, et al.
(författare)
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Fe-S complexes containing five-membered heterocycles : novel models for the active site of hydrogenases with unusual low reduction potential
- 2007
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :8, s. 896-902
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Tidskriftsartikel (refereegranskat)abstract
- Three biomimetic 2Fe2S complexes [{(mu-SCH2)(2)NCH2(2-C4H3O)}](Fe-2(CO)(6)) (6a), [{(mu-SCH2)(2) NCH2(2-C4H3S)}](Fe-2(CO)(6)) (6b) and [{(mu-SCH2)(2)NCH2(5-Br-2-C4H2S)}Fe-2(CO)(6)] (6c) were prepared as models for the active site of Fe-only hydrogenase by the convergent process from [(mu-S-2)Fe-2(CO)(6)] and N,N-bis(hydromethyl)-2-furan and thiophene. The structures of these complexes were identified spectroscopically and crystallographically. The electrochemical behavior of the complexes 6a and 6c was unique as they showed catalytic proton reduction with a low reduction potential at -1.13 and -1.09 V vs Fc/Fc(+), respectively, in the presence of HClO4.
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| 22. |
- Johansson, Adam Johannes, 1976-, et al.
(författare)
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Observed enhancement of the reactivity of a biomimetic diiron complex by the addition of water - mechanistic insights from theoretical modeling
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 34, s. 6741-6750
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Tidskriftsartikel (refereegranskat)abstract
- The biomimetic diiron complex [FeIIIFeIV(m-O)2(5-Me3-TPA)2](ClO4)3 (TPA = tris(2- pyridylmethyl)amine) has been found to be capable of oxidizing 9,10-dihydroanthracene in a solution of acetonitrile. Addition of water up to 1 M makes the reaction 200 times faster, suggesting that the water molecule in some way activates the catalyst for more efficient substrate oxidation. It is proposed that the enhanced reactivity results from the coordination of a water molecule to the iron(III) half of the complex, converting the bis-m-oxo structure of the diiron complex to a ring-opened form where one of the bridging oxo groups is transformed into a terminal oxo group on iron(IV). The suggested mechanism is supported by DFT (B3LYP) calculations and transition state theory. Two different computational models of the diiron complex are used to model the hydroxylation of cyclohexane to cyclohexanol. Model 1 has a bis-m-oxo diiron core (diamond core) while model 2 represents the “open core” analogue with one bridging m-oxo group, a terminal oxo ligand on iron(IV), and a water molecule coordinated to iron(III). The computational results clearly suggest that the terminal oxo group is more reactive than the bridging oxo group. The free energy of activation is 7.0 kcal mol-1 lower for the rate limiting step when the oxidant has a terminal oxo group than when both oxo groups are bridging the irons.
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| 23. |
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| 24. |
- Johansson, Roger, et al.
(författare)
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Insertion of CO2 into a palladium allyl bond and a Pd(II) catalysed carboxylation of allyl stannanes
- 2007
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; :4, s. 488-492
-
Tidskriftsartikel (refereegranskat)abstract
- The complex 2,6-bis[(di-t-butylphosphino)methyl]phenyl allyl palladium ((PCPPd)-Pd-tBu-allyl, 3) reacts with CO2 in a very fast insertion reaction to give the corresponding butenoate complex. The reaction is thought to occur via a cyclic six-membered transition state (7), where the gamma-carbon of the allyl group is linked up with the CO2-carbon. A group of related PCP complexes were investigated as catalysts for the carboxylation of tributyl(allyl) stannane. A catalytic cycle is proposed for this reaction where the rate determining step is the transmetallation between tin and palladium. The carboxylation reaction is faster using less sterically crowded catalysts whereas the electron richness of the palladium complexes seems less important for reactivity. Thus, there was no apparent difference in reactivity between 2,6-bis[(di-phenylphosphino)methyl]phenyl palladium triflouroacetate (13) and resorcinolbis(diphenyl)phosphinite palladium triflouroacetate (10). Both of these complexes give high turnovers for the carboxylation of tributyl(allyl) stannane (80% in 16 h using a ca. 5% catalyst loading and 4 atm CO2 pressure). On the other hand complex 3 was inactive in the catalytic carboxylation reaction.
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| 25. |
- Kurz, Philipp, et al.
(författare)
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Oxygen evolving reactions catalysed by synthetic manganese complexes : A systematic screening
- 2007
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :38, s. 4258-4261
-
Tidskriftsartikel (refereegranskat)abstract
- A set of six multinuclear manganese complexes was screened for the ability to catalyse reactions yielding O(2) under coherent experimental conditions; we identify a much larger number of manganese compounds than previously known that catalyse oxygen formation.
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| 26. |
- Legagneux, Nicolas, et al.
(författare)
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Characterization of silica-supported dodecatungstic heteropolyacids as a function of their dehydroxylation temperature.
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :12, s. 2235-40
-
Tidskriftsartikel (refereegranskat)abstract
- Dodecatungsto-silicic H(4)SiW(12)O(40) and -phosphoric acids H(3)PW(12)O(40) were deposited on silica by a classical impregnation technique. The resulting materials were studied by in situ Raman and infrared spectroscopy, XPS and by solid-state (1)H MAS NMR as a function of their dehydroxylation temperature. The data show that in the case of H(3)PW(12)O(40) three silanol groups are protonated while in the case of H(4)SiW(12)O(40) at least one acidic proton remains. Upon heating this proton reacts leading to a disordered structure and a broadening of the W-O Raman bands.
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| 27. |
- Lele, Duan, et al.
(författare)
-
Carbene-pyridine chelating 2Fe2S hydrogenase model complexes as highly active catalysts for the electrochemical reduction of protons from weak acid (HOAc)
- 2007
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :13, s. 1277-1283
-
Tidskriftsartikel (refereegranskat)abstract
- Two asymmetrically disubstituted diiron complexes (mu-pdt)[Fe(CO)(3)][Fe(CO)(eta(2)-L)] (L = 1-methyl-3-(2-pyridyl)imidazol-2-ylidene (NHCMePy), 2; 1,3-bis(2-picolyl) imidazol-2-ylidene (NHCdiPic), 4) and a mono-substituted diiron complex (mu-pdt)[Fe(CO)(3)][Fe(CO)(2)(NHCdiPic)] (3) were prepared as biomimetic models of the Fe-only hydrogenase active site. X-Ray studies show that the NHCMePy and NHCdiPic ligands in 2 and 4 each coordinate to the single iron atom as NHC-Py chelating ligands in two basal positions and the NHCdiPic ligand of complex 3 lies in an apical position as a monodentate ligand. The large ranges of the highest and the lowest nu(CO) frequencies of 2 and 4 reflect that the relatively uneven electron density on the two iron atoms of the 2Fe2S model complexes 2 and 4 is as that observed for mono-substituted diiron complexes of good donor ligands. The cyclic voltammograms and the electrochemical proton reduction by 2 and 3 were studied in the presence of HOAc to evaluate the effect of asymmetrical substitution of strong donor ligands on the redox properties of the iron atoms and on the electrocatalytic activity for proton reduction.
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| 28. |
- Li, F., et al.
(författare)
-
Mono- and binuclear complexes of iron(II) and iron(III) with an N4O ligand : synthesis, structures and catalytic properties in alkane oxidation
- 2006
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :20, s. 2427-2434
-
Tidskriftsartikel (refereegranskat)abstract
- Three mononuclear iron complexes and one binuclear iron complex, [Fe(tpoen)Cl]center dot 0.5(Fe2OCl6) (1), [Fe(tpoen)Cl]PF6 (2), Fe(tpoen)Cl-3 (3) and [{Fe(tpoen)}(2)(mu-O)](ClO4)(4) (4) (tpoen = N-(2-pyridylmethoxyethyl)-N,N-bis(2-pyridylmethyl)amine), were synthesized as functional models of non-heme iron oxygenases. Crystallographic studies revealed that the Fe(II) center of 1 is in a pseudooctahedral environment with a pentadentate N4O ligand and a chloride ion trans to the oxygen atom. The Fe(III) center of 3 is ligated by three nitrogen atoms of tpoen and three chloride ions in a facial configuration. Each Fe(III) center of 4 is coordinated with four nitrogen atoms and an oxygen atom of tpoen with the Fe-O-Fe angle of 172.0(3) angstrom. Complexes 2, 3 and 4 catalysed the oxidation of cyclohexane with H2O2 in the total TNs of 24 - 36 with A/K ratios of 1.9-2.4. Under the same conditions they also catalysed both the oxidation of ethylbenzene to benzylic alcohol and acetobenzene with good activity (30-47 TN) and low selectivity (A/K 0.7), and the oxidation of adamantane with moderate activity (15-18 TN) and low regioselectivity (3 degrees/2 degrees 3.0-3.2). With mCPBA as oxidant the catalytic activities of 2, 3 and 4 increased 1.8 to 2.3-fold for the oxidation of cyclohexane and ethylbenzene and 6.3 to 7.5-fold for the oxidation of adamantane. Drastic enhancement of the regioselectivity was observed in the oxidation of adamantane (3 degrees/2 degrees 18.5-30.3).
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| 29. |
- Li, Ping, et al.
(författare)
-
Structures, protonation, and electrochemical properties of diiron dithiolate complexes containing pyridyl-phosphine ligands
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :11, s. 1919-1926
-
Tidskriftsartikel (refereegranskat)abstract
- Diiron complexes containing pyridyl-phosphine ligands, that is, (mu-pdt)[Fe-2(CO)(5)L] (pdt = S(CH2)(3)S, L = Ph2PCH2Py, 3a; Ph2PPy, 3b) and (mu-pdt)[Fe(CO)(2)(PMe3)][Fe(CO)(2)L] (L = Ph2PCH2Py, 4a; Ph2PPy, 4b) were prepared as model complexes of the [FeFe]-hydrogenase active site. Protonation of 3a and 3b by HOTf afforded the pyridyl-nitrogen protonated products [3aH(N)][OTf] and [3bH(N)][OTf], respectively. The molecular structures of 3a, 3b, 4a, 4b, as well as [3aH(N)][OTf] and [3bH(N)][OTf] were confirmed by X-ray diffraction studies, which show that the Ph2PCH2Py ligand occupies the basal position both in 3a and its protonated species [3aH(N)][OTf], while the Ph2PPy ligand prefers the apical position in 3b and [3bH(N)][OTf]. The double protonation process of complex 4b was monitored by in situ IR, H-1 and P-31 NMR spectroscopy at low temperature. The spectroscopic evidence indicates that the protonation of 4b occurs first at the Fe-Fe bond and then at the pyridyl-nitrogen atom. Cyclic voltammograms reveal that protonation of 3a and 3b results in a considerable decrease in the overpotential for electrocatalytic proton reduction in the presence of HOTf, while the efficiency is not influenced by protonation. The electrocatalytic efficiency of 4a for proton reduction in the presence of HOAc in CH3CN-H2O (50:1, v/v) is 5 times higher than that in pure CH3CN.
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| 30. |
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| 31. |
- Lomoth, Reiner, et al.
(författare)
-
Introducing a dark reaction to photochemistry : photocatalytic hydrogen from [FeFe] hydrogenase active site model complexes
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :45, s. 9952-9959
-
Tidskriftsartikel (refereegranskat)abstract
- The light-driven splitting of water into its constituting elements gives access to a valuable fuel from an abundant substrate, using sunlight as the only energy source. Synthetic diiron complexes as functional models of the [FeFe] hydrogenase H(2)ase enzyme active site have moved into the centre of focus as potentially viable catalysts for the reductive side of this process, i.e. the reduction of protons to molecular hydrogen. The active site of the enzyme, as well as its mimics in an artificial system, are required to accumulate two electrons from single electron transfer events and to combine them with two protons to form hydrogen. Whereas in biology this reaction is not coupled to photosynthesis and thus proceeds in the dark, additional aspects need to be considered when designing a functional artificial system for the light-driven reduction of protons. Suitable photosensitizers have to be chosen that not only provide sufficient driving force for the reduction of the synthetic diiron catalyst, but also allow for selective excitation to minimize photodegradation. Electron transfer efficiencies have to be optimized for all steps and the sequential nature of the catalyst reduction requires a sufficient stability of potentially labile intermediates of the catalytic cycle. In this perspective, systems for the light-driven conversion of protons to molecular hydrogen are discussed where the catalyst is based on model complexes of the [FeFe] H(2)ase active site. Covalently linked dyads, supramolecular assemblies and multi-component systems will be examined with an emphasis on mechanistic electron transfer schemes, the properties of the individual components, their scope and their potential limitations.
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| 32. |
- Macak, Peter, et al.
(författare)
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A theoretical study of the fluoride exchange between UO2F+(aq) and UO22+(aq)
- 2006
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :30, s. 3638-3646
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental data on the thermodynamics and reaction mechanism of the inner-sphere. uoride exchange reaction (UO22+)-O-17 + UO2F+ reversible arrow (UO2F+)-O-17 + UO22+ have been compared with different intimate reaction mechanisms using quantum chemical methods. Two models have been tested that start from the outer sphere complexes, (H2O)[UAO2F(OH2)(4)(+)] center dot center dot center dot [UBO2(OH2)(5)(2+)] and [UAO2F(OH2)(4)(+)] center dot center dot center dot [UBO2(OH2)(5)(2+)]; the geometry and energies of the intermediates and transition states along possible reaction pathways have been calculated using different ab initio methods, SCF, B3LYP and MP2. Both the experimental data and the theoretical results suggest that the. uoride exchange takes place via the formation and breaking of a U - F - U bridge that is the rate determining step. The calculated activation enthalpy Delta H-not equal = 30.9 kJ mol(-1) is virtually identical to the experimental value 31 kJ mol(-1); however this agreement may be a coincidence as we do not expect a larger accuracy than 10 kJ mol(-1) with the methods used. The calculations show that the. uoride bridge is formed as an insertion of UAO2F(OH2)(4)(+) into UBO2(OH2)(5)(2+) followed by a subsequent transfer of water from the first to the second coordination sphere of U-B.
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| 33. |
- Moberg, Viktor, et al.
(författare)
-
Chiral and achiral phosphine derivatives of alkylidyne tricobalt carbonyl clusters as catalyst precursors for (asymmetric) inter- and intramolecular Pauson-Khand reactions.
- 2008
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :18, s. 2442-2453
-
Tidskriftsartikel (refereegranskat)abstract
- Phosphine derivatives of alkylidyne tricobalt carbonyl clusters have been tested as catalysts/catalyst precursors in intermolecular and (asymmetric) intramolecular Pauson-Khand reactions. A number of new phosphine derivatives of the tricobalt alkylidyne clusters [Co(3)(mu(3)-CR)(CO)(9)] (R = H, CO(2)Et) were prepared and characterised. The clusters [Co(3)(mu(3)-CR)(CO)(9-x)(PR'(3))(x)] (PR'(3) = achiral or chiral monodentate phosphine, x = 1-3) and [Co(3)(mu(3)-CR)(CO)(7)(P-P)] (P-P = chiral diphosphine; 1,1'- and 1,2-structural isomers) were assayed as catalysts for intermolecular and (asymmetric) intramolecular Pauson-Khand reactions. The phosphine-substituted tricobalt clusters proved to be viable catalysts/catalyst precursors that gave moderate to very good product yields (up to approximately 90%), but the enantiomeric excesses were too low for the clusters to be of practical use in the asymmetric reactions.
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| 34. |
- Moberg, Viktor, et al.
(författare)
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Synthesis, characterization and reactivity of tetranuclear ruthenium hydrido clusters containing chiral phosphine ligands
- 2006
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234. ; :1, s. 279-288
-
Tidskriftsartikel (refereegranskat)abstract
- The chiral clusters [H4Ru4(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H4Ru4(CO)(10)(L - L)] (L - L = DUPHOS, DIPAMP), 1,2-[H4Ru4(CO)(10)(DIOP)] and [{H4Ru4(CO)(10)(DIOP)}(2)] have been synthesized by derivatizing the parent carbonyl cluster [H4Ru4(CO)(12)] with the appropriate mono- or didentate chiral phosphine ligand. The phosphine-substituted clusters were found to be able to catalyze the ( asymmetric) hydrogenation of tiglic acid albeit with relatively low selectivity (enantiomeric excesses varying from 0 to 23%). It was found that the stability of the chiral ruthenium hydride clusters and the product distribution obtained in the catalytic reactions are dependent on the nature of the chiral phosphine. The crystal structures of [H4Ru4(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H4Ru4(CO)(10)(L-L)] (L - L = DUPHOS, O-DUPHOS ( partially oxygenated ligand), DIPAMP), 1,2-[H4Ru4(CO)(10)(DIOP)] and [{H4Ru4(CO)(10)(DIOP)}(2)] are presented.
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| 35. |
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| 36. |
- Nilsson, Jessica, et al.
(författare)
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Bis- and tris(pyridyl)amine-oxidovanadium complexes: characteristics and insulin-mimetic potential.
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :38, s. 7902-7911
-
Tidskriftsartikel (refereegranskat)abstract
- Two novel vanadium complexes, [V(IV)O(bp-O)(HSO4)] (1) and [V(IV)O(bp-OH)Cl2] x CH3OH (2 x CH3OH), where bp-OH is 2-{[bis(pyrid-2-yl)methyl]amine}methylphenol, were prepared and structurally characterised. EPR spectra of methanol solutions of 2 suggest exchange of Cl- for CH3OH and partial conversion to [VO(bp-OH)(CH3OH)3]2+. Speciation studies on the VO2+-bpOH system in a water/dmso mixture (4:1 v/v) revealed [VO(bp-O)(H2O)n]+ as the dominating species in the pH range 2-7. The insulin-mimetic properties of 1 and 2, [V(IV)O(SO4)tpa] (3), [V(IV)O(pic-trpMe)2] (5) and the new mixed-ligand complexes [V(V)O(pic-trpH)tpa]Cl2 (4Cl2) and [V(V)O(pic-OEt)tpa]Cl2 (6Cl2), tpa = tris(pyrid-2-yl)methylamine, picH-trpH = 2-carboxypyridine-5-(L-tryptophan)carboxamide (picH-trpMe is the respective tryptophanmethyl ester), pic-OEt = 5-carboethoxypyridine-2-carboxylic acid, were evaluated with rat adipocytes, employing two lipolysis assays (release of glycerol and free fatty acids (FFA)), respectively and a lipogenesis assay (incorporation of glucose into lipids). The IC50 values for the inhibition of lipolysis in the FFA assay vary between 0.41 (+/-0.03) (5) and 21.2 (+/-0.6) mM (2), as compared to 0.81 (+/-0.2) mM for VOSO4.
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| 37. |
- Nilsson, K.B., et al.
(författare)
-
Structure of solvated mercury(ii) halides in liquid ammonia, triethyl phosphite and tri-n-butylphosphine solution
- 2008
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :17, s. 2303-2313
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Tidskriftsartikel (refereegranskat)abstract
- Liquid ammonia, trialkyl phosphites, and especially trialkylphosphines, are very powerful electron-pair donor solvents with soft bonding character. The solvent molecules act as strongly coordinating ligands towards mercury(ii), interacting strongly enough to displace halide ligands. In liquid ammonia mercury(ii) chloride solutions separate into two liquid phases, the upper contains tetraamminemercury(ii) complexes, [Hg(NH3)4] 2+, and chloride ions in low concentration, while the lower is a dense highly concentrated solution of [Hg(NH3)4] 2+ entities, ca. 1.4 mol dm-3, probably ion-paired by hydrogen bonds to the chloride ions. Mercury(ii) bromide also dissociates to ionic complexes in liquid ammonia and forms a homogeneous solution for which 199Hg NMR indicates weak bromide association with mercury(ii). When dissolving mercury(ii) iodide in liquid ammonia and triethyl phosphite solvated molecular complexes form in the solutions. The Raman ?(I-Hg-I) symmetric stretching frequency is 132 cm-1 for the pseudo-tetrahedral [HgI 2(NH3)2] complex formed in liquid ammonia, corresponding to DS = 56 on the donor strength scale. For the Hg(ClO4)2/NH4I system in liquid ammonia a 199Hg NMR study showed [HgI4]2- to be the dominating mercury(ii) complex for mole ratios n(I-): n(Hg 2+) 6. A large angle X-ray scattering (LAXS) study of mercury(ii) iodide in triethyl phosphite solution showed a [HgI2(P(OC 4H9)3)2] complex with the Hg-I and Hg-P bond distances 2.750(3) and 2.457(4) Å, respectively, in near tetrahedral configuration. Trialkylphosphines generally form very strong bonds to mercury(ii), dissociating all mercury(ii) halides. Mercury(ii) chloride and bromide form solid solvated mercury(ii) halide salts when treated with tri-n-butylphosphine, because of the low permittivity of the solvent. A LAXS study of a melt of mercury(ii) iodide in tri-n-butylphosphine at 330 K resulted in the Hg-I and Hg-P distances 2.851(3) and 2.468(4) Å, respectively. The absence of a distinct I-I distance indicates flexible coordination geometry with weak and non-directional mercury(ii) iodide association within the tri-n-butylphosphine solvated complex. This journal is © The Royal Society of Chemistry.
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| 38. |
- Nyhlén, Jonas, et al.
(författare)
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On the possibility of catalytic reduction of carbonyl moieties with tris(pentafluorophenyl)borane and H2: a computational study
- 2009
-
Ingår i: Dalton Transactions. - : The Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; :29, s. 5780-5786
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Tidskriftsartikel (refereegranskat)abstract
- The study thoroughly examines the Gibbs free energy surfaces of a new mechanism for redn. of ketones/aldehydes by tris(pentafluorophenyl)borane (1) and H2. Key elements of the proposed mechanism are the proton and the hydride transfer steps similar to Stephan's catalytic redn. of imines by 1. The proton is transferred to the ketone/aldehyde in the process of H2 cleavage by the carbonyl-borane couple and the hydride is transferred in a nucleophilic attack on the carbonyl carbon by the hydridoborate in the ionic pair, [HOCRR']+[HB(C6F5)3]-. The in solvent Gibbs free energy barriers of H2 splitting by adducts of B(C6F5)3 with acetone, acetophenone and benzaldehyde are predicted to be in the range of 24.5 ± 2.5 kcal mol-1, which corresponds to potential energy barriers in the range of 17.0 ± 2.0 kcal mol-1. Significantly lower barrier of H2 activation is predicted in cases of bulky ketones such as 2,2,4,4-tetramethylpentan-3-one. With respect to the hydridoborate intermediate, the nucleophilic attack on the activated carbon is predicted to have a relatively low barrier for the sterically unhindered substrates, while this barrier is considerably higher for the sterically encumbered substrates. Since the formation of the hydridoborate intermediates is found to be endothermic, the transition state of the nucleophilic attack is the highest point of the computed energy profile for all tested substrates. Overall, according to in solvent d. function calcns. the proposed redn. of "compact" ketones/aldehydes by 1 and H2 is allowed both thermodynamically and kinetically at elevated temp., but it is expected to be slower and more substrate specific than the corresponding redn. of imines. [on SciFinder(R)]
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| 39. |
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| 40. |
- Ohlin, C. Andre, et al.
(författare)
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Oxygen isotopic exchange in an (MnMn3IV)-Mn-III-oxo cubane
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :27, s. 5278-5280
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 41. |
- Oliveira, Paulo, et al.
(författare)
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Transcriptional regulation of the cyanobacterial bidirectional Hox-hydrogenase
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :45, s. 9990-9996
-
Tidskriftsartikel (refereegranskat)abstract
- The overall processes of transcription and its regulation have advanced significantly in the last years, making our understanding of prokaryotic biology more complex and detailed. In fact, a systematic study of different aspects of transcriptional regulation opens up outstanding opportunities to improve and develop the perception of complex reaction mechanisms, genetic processes and cell functions. In close connection to the cyanobacterial bidirectional hydrogenase, the main hydrogen-evolving enzyme in non-nitrogen fixing strains, two novel transcription factors have received increasing attention over the past five years: a LexA-related protein and the AbrB-like family members. Recent work on these regulators has produced new insights and advances towards the understanding ( and possible interconnection) of several regulatory networks in cyanobacteria, namely nitrogen metabolism, redox response, toxin production, CO2 concentrating mechanisms and hydrogen metabolism. The fact that a LexA-related protein and AbrB-like family members have been co-purified in independent laboratories studying different sets of cyanobacterial genes suggests a possible common and/or complementary function of these regulators. In this review, we summarize the knowledge gained thus far regarding the transcriptional regulation of the cyanobacterial bidirectional hydrogenase, with special focus on the above mentioned transcription factors. Moreover, we discuss several additional points that warrants further investigation to increase our knowledge in this fast evolving research field.
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| 42. |
- Olsson, Daniel, et al.
(författare)
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A catalytic and mechanistic investigation of a PCP pincer palladium complex in the Stille reaction
- 2005
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; 2005:11, s. 1924-1929
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Tidskriftsartikel (refereegranskat)abstract
- In an improved procedure, the complex {2,6-bis[(diphenylphosphino)methyl]benzene}chloropalladium(II) (1) was synthesised as its THF adduct and the structure was determined by X-ray crystallography. The catalytic properties of the derivative {2,6-bis[(diphenylphosphino)methyl]benzene} (trifluoroacetato)palladium(II) (2) was investigated in the Stille reaction. Complex 2 proves to be an excellent catalyst for the C-C cross-coupling between trimethyl phenyl stannane and aryl bromides using a very low catalyst loading (0.1-0.0001%), giving high turnover numbers (TONs) up to 6.9 x 10(5). A kinetic investigation of the catalytic reaction suggests a heterogeneous colloidal palladium catalyst formed from the PCP Pd(II) pre-catalyst.
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| 43. |
- Olsson, Daniel, et al.
(författare)
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Synthesis and characterisation of PCsp3P phosphine and phosphinite platinum (II) complexes. Cyclometallation and simple coordination
- 2007
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; , s. 5427-5433
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Tidskriftsartikel (refereegranskat)abstract
- New and improved preparative routes to the previously known PCP ligands cis-1,3-bis(di-isopropylphosphinito)cyclohexane and cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane are reported. They react with 1 equivalent of dichloro(1,5-cyclooctadiene)platinum(II) [(COD)PtCl2] to give the cis coordinated complex cis-[PtCl2{cis-1,3-bis(di-isopropylphosphinito)}cyclohexane] and the Csp3-H activated complex trans-[PtCl{cis-1,3-bis(di-tert-butylphosphino)}cyclohexane]. The new PCP ligand cis-1,3-bis(di-tert-butylphosphinito)cyclohexane was synthesised and reacts with [(COD)PtCl2] giving the di-nuclear trans-[PtCl2{cis-1,3-bis(di-tert-butylphosphinito)cyclohexane}]2, which is highly insoluble. All metal complexes were characterised with X-ray crystallography. DFT calculations indicate that the inability of the phosphinite ligands to cyclometallate is due to a kinetic barrier, possibly involving an axial–equatorial conformational change necessary for the C–H activation process.
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| 44. |
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| 45. |
- Pal, S., et al.
(författare)
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Calculations of interfacial interactions in pyrene-Ipa rod sensitized nanostructured TiO2
- 2009
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; 45, s. 10021-10031
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Tidskriftsartikel (refereegranskat)abstract
- Pyrene chromophores carrying different rigid rod spacer groups (ethynylene, ethynylene-phenylene-ethynylene, and ethynylene-bicyclo[2.2.2]octylene-ethynylene) and bound to TiO2 nanostructured materials via an isophthalic acid (Ipa) anchor group have been investigated using quantum chemical calculations in order to elucidate structural and electronic properties of dye-sensitized semiconductor structures capable of long-range photoinduced interfacial electron transfer. The calculations are used to study firstly the effect of the anchor and spacer groups on the electronic properties of the pyrene-dyes, secondly the binding of isophthalic acid to nanostructured TiO2, and thirdly the interfacial electronic interactions for dye-sensitized nanostructured TiO2 relevant to dye-sensitized solar cell applications. Together, these calculations provide theoretical insights into the effect of incorporating rigid rod anchor-cum-spacer group motifs in sensitizers for e.g. solar cell applications. In particular, the calculations help to rationalize the strong influence of the rods on the photophysical properties of the sensitizers in terms of electronic interactions between the individual chromophore, spacer, and anchor segments, as well as to provide information about interfacial electronic interactions of interest for the capabilities of the rods to act as efficient mediators of photoinduced interfacial charge separation.
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| 46. |
- Palladino, Giuseppe, et al.
(författare)
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Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)-ethylenediamine-N,N '-diacetic acid-fluoride system : a potentiometric, NMR and X-ray crystallographic study
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :43, s. 5176-5183
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Tidskriftsartikel (refereegranskat)abstract
- The structure, thermodynamics and kinetics of the binary and ternary uranium(VI)-ethylenediamine- N,N'-diacetate (in the following denoted EDDA) fluoride systems have been studied using potentiometry, H-1, F-19 NMR spectroscopy and X-ray diffraction. The UO22+ - EDDA system could be studied up to - log[H3O+] = 3.4 where the formation of two binary complexes UO2(EDDA)(aq) and UO2(H(3)EDDA)(3+) were identified, with equilibrium constants log beta(UO(2)EDDA) = 11.63 +/- 0.02 and log beta(UO(2)H(3)EDDA(3+)) = 1.77 +/- 0.04, respectively. In the ternary system the complexes UO2(EDDA) F-, UO2(EDDA)(OH)(-) and (UO2)(2)(mu-OH)(2)(HEDDA)(2)F-2(aq) were identified; the latter through F-19 NMR. H-1 NMR spectra indicate that the EDDA ligand is chelate bonded in UO2(EDDA)(aq), UO2(EDDA) F- and UO2(EDDA)(OH)(-) while only one carboxylate group is coordinated in UO2(H(3)EDDA)(3+). The rate and mechanism of the fluoride exchange between UO2(EDDA) F- and free fluoride was studied by F-19 NMR spectroscopy. Three reactions contribute to the exchange; (i) site exchange between UO2(EDDA) F- and free fluoride without any net chemical exchange, (ii) replacement of the coordinated fluoride with OH- and (iii) the self dissociation of the coordinated fluoride forming UO2(EDDA)(aq); these reactions seem to follow associative mechanisms. H-1 NMR spectra show that the exchange between the free and chelate bonded EDDA is slow and consists of several steps, protonation/deprotonation and chelate ring opening/ring closure, the mechanism cannot be elucidated from the available data. The structure (UO2)(2)(EDDA)(2)(mu-H(2)EDDA) was determined by single crystal X-ray diffraction and contains two UO2( EDDA) units with tetracoordinated EDDA linked by H(2)EDDA in the zwitterion form, coordinated through a single carboxylate oxygen from each end to the two uranium atoms. The geometry of the complexes indicates that there is no geometric constraint for an associative ligand substitution mechanism.
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| 47. |
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| 48. |
- Papsai, Pal, et al.
(författare)
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Platination of full length tRNA(Ala) and truncated versions of the acceptor stem and anticodon loop.
- 2008
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :38, s. 5225-5234
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear DNA is a well characterized target for many low molecular metal-based drugs, with cisplatin and related antineoplastic compounds as typical examples. Much less is known concerning to what extent targeting of RNA may influence the activity spectrum of these types of drugs. In a preliminary communication by us (Papsai et al., Dalton Trans., 2006, 3515) we were able to show that the folded, three-dimensionally well defined structure of tRNA(Ala) readily interacts with cisplatin. In the present study we have further analyzed the binding preferences within the preferentially targeted stem region (sMh(Ala)) by modulation of the sequence around the G-U wobble base-pair and the net charge of the 3' and 5' ends. Our data show that the adduct profile is strongly influenced by the presence of the 5' end phosphate group. Further, the adduct formation reaction can be prevented by replacement of the G-U wobble base-pair with the fully complementary G-C pair. To further investigate the influence from local sequence on the platination process, a model of the anticodon region (acMh(Ala)) was also investigated. In the absence of consecutive guanine-residues in the stem- and anticodon regions, preferential platination was found to take place at the terminal AG-site in the stem region. However, after introduction of a GG-pair in the anticodon loop, platination was observed also here. At 37 degrees C, pH 6.3 and C(Pt) = 0.10 mM the rate of platination was determined to be ca. 1 x 10(-4) s(-1), with the most rapid reaction observed for interaction with the anticodon model carrying two adjacent guanines in the single-stranded loop. Together, these data show that platination of RNA is highly sequence- and structure-dependent.
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| 49. |
- Parajo, Y., et al.
(författare)
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Effect of bridging ligand structure on the thermal stability and DNA binding properties of iron(II) triple helicates
- 2009
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :25, s. 4868-4874
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Tidskriftsartikel (refereegranskat)abstract
- Triple helical di-iron complexes, readily prepared through interaction of iron(II) ions with imine-based ligands, are cylinder-shaped tetracations comparable in size and shape to common protein DNA recognition units. They have a strong tendency to coil DNA, and have recently been found to induce formation of three-way junctions in palindromic oligonucleotides. To introduce potential H bond acceptor units onto the surface of triple-helicates, new iron(II) complexes have been synthesized in which the central linking unit in the bridging ligand is S or O, instead of CH2. The DNA binding properties of these new metallo-helicates were studied using UV-vis spectroscopy and circular and linear dichroism. Results show that the three iron triple helicates bind the DNA in a similar way but that the stability of the triple helicate unit is decreased with the O linked bridging ligand.
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| 50. |
- Persson, Ingmar
(författare)
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The hydrated platinum(II) ion in aqueous solution—a combined theoretical and EXAFS spectroscopic study
- 2009
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 2009, s. 1512-1515
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Tidskriftsartikel (refereegranskat)abstract
- The hydrated platinum(II) ion, previously characterized as square-planar in aqueous solution, has been shown by quantum mechanical charge field molecular dynamic (QMCF MD) simulations and EXAFS experiments to be hexa-coordinated with two additional ligands in elongated axial positions
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