Tris(pyrazolyl)hydroboratozinc hydroxide complexes as functional models for carbonic anhydrase: on the nature of the bicarbonate intermediate

Looney, Adrian; Han, Runyu; McNeill, Kristopher; Parkin, Gerard

doi:10.1021/ja00064a033

Cited by 200 publications

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“…The significant upfield shift of the H-d resonances may be explained by a spin delocalization mechanism, as opposed to a Fermi contact shift mechanism. [42] Incorporation of OH À : synthesis of [(Py 2 S) 4 Fe [28] and self-assembly reactions [25-27, 43, 44] (3): The molecular structure of the cation in 3 is shown in Figure 4, and selected bond lengths and angles are given in Table 3. This molecule can be viewed as two Fe II À(m-OH)ÀFe II complexes joined together by a central iron(ii) ion (Fe1).…”

Section: Resultsmentioning

confidence: 99%

“…Traditional syntheses of (L) n M/OH complexes involve self-assembly [25][26][27][28] or substitution [29,30] reactions with excess OH À /H 2 O in protic solvents. Here we describe a new strategy involving aprotic conditions (THF) and a nearly stoichiometric amount of water to give the hydroxide-containing complexes [(Py 2 S) 4 Fe 5 (m-OH) 2 ](BF 4 ) 4 (3) and [(Py 2 S) 2 Fe 2 (m-OH)]BF 4 (4).…”

Section: Introductionmentioning

confidence: 99%

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Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

Krishnamurthy

Sarjeant

Goldberg

et al. 2005

Chemistry A European J

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The mixed N3S(thiolate) ligand 1-[bis[2-(pyridin-2-yl)ethyl]amino]-2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(II) complexes: [(Py2S)FeCl] (1), [(Py2S)FeBr] (2), [(Py2S)4Fe5II(mu-OH)2](BF4)4 (3), and [(Py2S)2Fe2II(mu-OH)]BF4 (4). The X-ray structures of 1 and 2 revealed monomeric iron(II)-alkylthiolate complexes with distorted trigonal-bipyramidal geometries. The paramagnetic 1H NMR spectra of 1 and 2 display resonances from delta = -25 ppm to +100 ppm, consistent with a high-spin iron(II) ion (S = 2). Spectral assignments were made on the basis of chemical shift information and T1 measurements and show the monomeric structures are intact in solution. To provide entry into hydroxide-containing complexes, a novel synthetic method was developed involving strict aprotic conditions and limiting amounts of H2O. Reaction of Py2SH with NaH and Fe(BF4)2.6 H2O under aprotic conditions led to the isolation of the pentanuclear, mu-OH complex 3, which has a novel dimer-of-dimers type structure connected by a central iron atom. Conductivity data on 3 show this structure is retained in CH2Cl2. Rational modification of the ligand-to-metal ratio allows control over the nuclearity of the product, yielding the dinuclear complex 4. The X-ray structure of 4 reveals an unprecedented face-sharing, biooctahedral complex with an [S2O] bridging arrangement. The magnetic properties of 3 and 4 in the range 1.9-300 K were successfully modeled. Dinuclear 4 is antiferromagnetically coupled [J = -18.8(2) cm(-1)]. Pentanuclear 3 exhibits ferrimagnetic behavior, with a high-spin ground state of S(T) = 6, and was best modeled with three different exchange parameters [J = -15.3(2), J' = -24.7(3), and J'' = -5.36(7) cm(-1)]. DFT calculations provided good support for the interpretation of the magnetic properties.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

Krishnamurthy

Sarjeant

Goldberg

et al. 2005

Chemistry A European J

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“…The reactant is a terminal hydroxide species affording a unidentate bicarbonate (η 1 -OCO 2 H) product. Far more common is the reaction of bridged M II 2 ðμ-OHÞ 1;2 precursors to afford binuclear or occasional trinuclear products bridged by carbonate utilizing two or three oxygen atoms (4)(5)(6)(7)(8)(9). A second feature is the apparently fast reaction rate, given that CO 2 comprises only 0.039 vol % of the atmosphere.…”

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confidence: 99%

Kinetics and mechanistic analysis of an extremely rapid carbon dioxide fixation reaction

Huang

Makhlynets

Tan

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

121

101

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Carbon dioxide may react with free or metal-bound hydroxide to afford products containing bicarbonate or carbonate, often captured as ligands bridging two or three metal sites. We report the kinetics and probable mechanism of an extremely rapid fixation reaction mediated by a planar nickel complex ½Ni II ðNNNÞðOHÞ 1− containing a tridentate 2,6-pyridinedicarboxamidate pincer ligand and a terminal hydroxide ligand. The minimal generalized reaction is M-OH þ CO 2 → M-OCO 2 H; with variant M, previous rate constants are ≲10 3 M −1 s −1 in aqueous solution. For the present bimolecular reaction, the (extrapolated) rate constant is 9.5 × 10 5 M −1 s −1 in N, N′-dimethylformamide at 298 K, a value within the range of k cat ∕K M ≈10 5 -10 8 M −1 s −1 for carbonic anhydrase, the most efficient catalyst of CO 2 fixation reactions. The enthalpy profile of the fixation reaction was calculated by density functional theory. The initial event is the formation of a weak precursor complex between the Ni-OH group and CO 2 , followed by insertion of a CO 2 oxygen atom into the Ni-OH bond to generate a four center Niðη 2 -OCO 2 HÞ transition state similar to that at the zinc site in carbonic anhydrase. Thereafter, the Ni-OH bond detaches to afford the Niðη 1 -OCO 2 HÞ fragment, after which the molecule passes through a second, lower energy transition state as the bicarbonate ligand rearranges to a conformation very similar to that in the crystalline product. Theoretical values of metric parameters and activation enthalpy are in good agreement with experimental values [ΔH ‡ ¼ 3.2ð5Þ kcal∕mol].nickel hydroxide | carbon dioxide-bicarbonate conversion | reaction mechanism R ecent research in this laboratory has been directed toward the attainment of synthetic analogues of the NiFe 3 S 4 active site of the enzyme carbon monoxide dehydrogenase (1, 2), which catalyzes the interconversion reactionIn the course of this work, we have prepared binuclear Ni II ∕Fe II bridged species with the intention of simulating the Ni…Fe component of the enzyme site that is the locus of substrate binding, activation, and product release (3). The nickel site in the binuclear species has been prepared separately in the form of the planar hydroxide complex ½NiðpyN 2 Me2 ÞðOHÞ 1− containing a N,N′-2,6-dimethylphenyl-2,6-pyridinedicarboxamidate dianion. Whereas bridging hydroxide ligation is common, terminal binding is not and in general is stabilized in divalent metal complexes by hydrogen bonding or by steric shielding, as is the case here. As reported recently (3), exposure of a solution of ½NiðpyN 2 Me2 ÞðOHÞ 1− to the atmosphere results in an instantaneous color change from red to red-orange. This results in the fixation of CO 2 as the bicarbonate complex ½NiðpyN 2 Me2 ÞðHCO 3 Þ 1− accompanied by the spectral changes in Fig. 1. Several features of the CO 2 fixation reaction 1 are noteworthy. The reactant is a terminal hydroxide species affording a unidentate bicarbonate (η 1 -OCO 2 H) product. Far more common is the reaction of bridged M II 2 ðμ-OHÞ 1;2 pr...

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“…The [HB(pz R,R' ) 3 ]Zn(OH) complexes (R = tBu, Ph, Cum, R' = H, Me, tBu) (Fig. 10a) (Alsfasser et al, 1991;Looney et al, 1993;, including [HB(pz R ) 3 ] -incorporating hydrogen bonding accepting ester substituents, react as functional models according to the carbonic anhydrase mechanism (Looney et al, 1993;Hammes et al, 2002;Bergquist et al, 2003;Lipton et al, 2003;Lipton & Ellis, 2007) and form bicarbonate from CO 2 . Hydrogensulfido, thiolato, phenolato and alcoholato [HB(pz R ) 3 ] -complexes are accessed by substitution reactions with H 2 S, thiols, phenols or alcohols Bergquist et al, 2000;Brand et al, 2001).…”

Section: Zinc Biomimetic Systemsmentioning

confidence: 99%

Biomimetic Applications of Metal Systems Supported by Scorpionates

Pellei¹,

Santini²

2011

Biomimetic Based Applications

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Tris(pyrazolyl)hydroboratozinc hydroxide complexes as functional models for carbonic anhydrase: on the nature of the bicarbonate intermediate

Cited by 200 publications

References 0 publications

Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

Kinetics and mechanistic analysis of an extremely rapid carbon dioxide fixation reaction

Biomimetic Applications of Metal Systems Supported by Scorpionates

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