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| 3. |
- Carlsson, Håkan, et al.
(författare)
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Hydrolytically active tetranuclear nickel complexes with structural resemblance to the active site of urease
- 2002
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 41:20, s. 4981-4983
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of the new asymmetric ligand 2-(N-isopropyl-N-((1-methylimidazolyl)methyl)aminomethyl)-6-(N-carboxylm ethyl-N-((1-methylimidazolyl)methyl) aminomethyl)-4-methylphenol (ICIMP) with nickel perchlorate and diphenylacetic acid leads to the formation of tetranuclear nickel complexes, whose crystal structures reveal that they consist of dimers of dimers in which each Ni-2 unit has a coordination environment that is similar to the active site of urease. One complex has been shown to coordinate urea and catalyze the hydrolysis of an organophosphate monoester.
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| 4. |
- Carlsson, Håkan, et al.
(författare)
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Nickel Complexes of Carboxylate-Containing Polydentate Ligands as Models for the Active Site of Urease
- 2004
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 43:26, s. 8252-8262
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Tidskriftsartikel (refereegranskat)abstract
- Two new carboxylate-containing polydentate ligands have been synthesized, the symmetric ligand 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-aminomethyl)-4-methylphenol (ICIMP). The ligands have been used to prepare model complexes for the active site of the dinuclear nickel enzyme urease, viz. [Ni2(BCIMP)Ac2]- (6), [Ni2(BCIMP)(Ph2Ac)2]- (7), [Ni2(ICIMP)(Ph2Ac)2] (14), [Ni4(ICIMP)2(Ph2Ac)2][ClO4]2 (15), [Ni4(ICIMP)2(Ph2Ac)2(DMF)2][ClO4]2 (16), and [Ni4(ICIMP)2(Ph2Ac)2(urea)(H2O)][ClO4]2 (17), where the latter complex contains urea coordinated in a unidentate fashion through the carbonyl oxygen. The N2O-N2O2 donor set of ICIMP provides a good framework for the preparation of urease models, but in some cases tetranuclear nickel complexes are formed due to coordination of the carboxylate moiety of one dinickel-ICIMP unit to one or both of the nickels of a second Ni2 unit. Reactivity and kinetics studies of 7 and 15 show that these model complexes catalyze hydrolysis of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) at basic pH. In this assay, complexes based on the asymmetric ligand ICIMP exhibit a significantly faster rate of hydrolysis than the corresponding BCIMP complexes. Magnetic measurements indicate that there are weak antiferromagnetic interactions between the nickel ions in complex 16.
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| 5. |
- Carlsson, Håkan, et al.
(författare)
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Structural and Functional Models of the Active Site of Zinc Phosphotriesterase
- 2004
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 43:18, s. 5681-5687
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Tidskriftsartikel (refereegranskat)abstract
- In an attempt to prepare structural and functional models for the active site of the hydrolytic enzyme zinc phosphotriesterase, five new zinc complexes of the ligands 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-methylimidazolyl)methyl)aminomethyl)-6-(N-carboxylmethyl-N-((1-methylimidazolyl)methyl)aminomethyl)-4-methylphenol (ICIMP) have been synthesized, viz. Na[Zn2(BCIMP)Ac2] (1), [Zn2(BCIMP)(Ph2Ac)] (2), [Zn2(ICIMP)Ac2] (3), [Zn4(ICIMP)2(Me3Ac)2][ClO4]2 (4), and [Zn4(ICIMP)2(Ph2Ac)2][ClO4]2 (5). The X-ray structure of complex 5 has been determined and reveals that the complex is a dimer of dimers in the solid state, which in solution dissociates to potent structural models. Studies using NMR show that only one carboxylate coligand bridges the dizinc units in the case of diphenyl acetate and pivalate, while the steric bulk of acetate is sufficiently small to permit the coordination of two acetates/dizinc unit. Functional studies involving the hydrolysis/transesterification of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) show that the complex with ICIMP (compound 5) has a significantly higher rate of catalysis than the BCIMP complex (compound 2). This is attributed to the vacant/labile coordination site that is available in the ICIMP complex but not the BCIMP complex.
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| 6. |
- Carlsson, Håkan, et al.
(författare)
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Synthesis and reactivity studies of model complexes for dinuclear active sites in metalloenzymes
- 2001
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Konferensbidrag (refereegranskat)abstract
- Several new polydentate and potentially dinucleating ligands have been synthesized in order to model the coordination environments of a number of structurally related dinuclear active sites in metalloenzymes, including methane monooxygenase, the ribonucleotide reductase R2 protein, urease, arginase, red kidney bean purple acid phosphatase and zinc phosphotriesterase.~ Ligands 1 and 2 have proven to be versatilebuilding blocks for the preparation ofhomodinuclear Fe2, Mn2 and Ni2 complexes which funcion as adequate structural models for hydrolytic enzymes. Stepwise syntheses of heterodinuclear Fe-Zn complexes have been achieved using ligand 2. Reactivity studies indicate that some of these model complexes exhibit biomimetic activity. The catalytic mechanisms of some hydrolytic enzymes, e.g. urease and kidney bean purple acid phosphatase, have been probed using a combination of synthetic and computational modelling approaches.
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| 8. |
- Deeming, Antony J, et al.
(författare)
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Oxidative addition of silanes R3SiH to the unsaturated cluster [Os3(µ-H){µ3-Ph2PCH2PPh(C6H4)}(CO)8]: Evidence for reversible silane formation in the dynamic behaviour of [Os3(µ-H)(SiR3)(CO)9(µ-dppm)]
- 2004
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Ingår i: Dalton Transactions. - 1477-9234. ; 2004:21, s. 3709-3714
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Tidskriftsartikel (refereegranskat)abstract
- Oxidative addition of the silanes R3SiH (R3= Ph3, Et3, EtMe2) to the unsaturated cluster [Os3(µ-H){µ3-Ph2PCH2PPh(C6H4)}(CO)8] leads to the saturated clusters [Os3(µ-H)(SiR3)(CO)9(µ-dppm)](SiR3= SiPh31, SiEt32 and SiEtMe23) and the unsaturated clusters [Os3(µ-H)2(SiR3){µ3-Ph2PCH2PPh(C6H4)}(CO)7](SiR3= SiPh34, SiEt35 and SiEtMe26). Structures are based on spectroscopic evidence and a XRD structure of [Os3(µ-H)(SiPh3)(CO)9(µ-dppm)]1 in which all non-CO ligands are coordinated equatorially and the hydride and the silyl groups are mutually cis. From variable-temperature 1H NMR spectra of the SiEt3 compound 2, exchange of the P nuclei is clearly apparent. Simultaneous migrations of the SiEt3 group and of the hydride from one Os–Os edge to another generate a time-averaged mirror plane in the molecule. VT 1H NMR spectra of the somewhat less bulky compound [Os3(µ-H)(SiMe2Et)(CO)9(µ-dppm)]3 have been analysed. Two isomers 3a and 3b are observed with the hydride ligand located on different Os–Os edges. Synchronous migration of the hydride and SiMe2Et groups is faster than the observed interconversion of isomers which occurs by hydride migration alone. The synchronous motion of H and SiR3only occurs when these ligands are mutually cis as in the major isomer 3a and we propose that this process requires the formation of a transient silane complex of the type [Os3(2-HSiR3)(CO)9(µ-dppm)]. Turnstile rotation within an Os(CO)3(2-HSiR3) group leads to the observed exchange within the major isomer 3a without exchange with the minor isomer. This process is not observed for the minor isomer 3b because the hydride and the silyl group are mutually trans. Protonation to give [Os3(µ-H)2(SiR3)(CO)9(µ-dppm)]+ totally suppresses the dynamic behaviour because there are no edge vacancies.
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| 9. |
- Grachova, E V, et al.
(författare)
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The structure and dynamic behaviour of disubstituted derivatives of Rh6(CO)16 containing heterobidentate bridging phosphine ligands
- 2003
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; :12, s. 2468-2473
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Tidskriftsartikel (refereegranskat)abstract
- The solution structures and dynamic behaviour of [Rh6(CO)14(µ-PX)][PX = diphenyl(2-pyridyl)phosphine, (PN); diphenyl(2-thienyl)phosphine, (PS); diphenyl(vinyl)phosphine, (PV)] have been studied by multinuclear NMR and the X-ray structure of [Rh6(CO)14(µ,3-PV)] is reported. In solution, the above clusters undergo a variety of localised CO-exchanges and the mechanisms of these are discussed. The PV ligand in [Rh6(CO)14(µ,3-PV)] is hemilabile and exhibits facile exchange/reorientation of the vinyl group.
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