Quantitative Reactivity Model for the Hydration of Carbon Dioxide by Biomimetic Zinc Complexes

Bräuer, Michael; Lustres, J. Luis Perez; Weston, Jennie; Anders, Ernst

doi:10.1021/ic0010510

Cited by 86 publications

(105 citation statements)

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“…reaction in the gas phase at a measurable rate requires the initial formation of a reasonably well-bound complex ( + ions in the gas phase bearing a real Coulomb charge, the nucleophilicity of the hydroxy group decreases with lower values of n. Model studies show that the nucleophilicity of the hydroxy group depends on the energy of the lone pair (LP) orbital of the oxygen atom (E 0 LP ). [2] This energy increases with n, whereas the ZnÀO bond order (BO ZnÀO ) decreases (Table 2). For small values of n, the ZnÀO bond is predominantly covalent, whereas increasing n stabilizes multiply-charged metal-containing fragments [20][21][22] such as [L n Zn] 2+ and favors formation of a "free" and therefore more nucleophilic hydroxide ion.…”

Section: Znoh]mentioning

confidence: 99%

“…15 AE 5 kJ mol À1 above the energy of the isolated reactants [(im) 2 ZnOH] + + CO 2 ; it is assumed that the internal energy of the reactant ion corresponds to the temperature of the ion source (100 8C). [13,14] Thus, much like in the enzymatic system, the gas-phase mimic [(im) 2 [15][16][17] degenerate 16 O/ 18 O exchange in the gas phase must involve an intramolecular hydrogen rearrangement as well (Scheme 2, the oxygen atom of the initial hydroxy group is in bold); the alternative Lindskog mechanism [18] cannot account for 16 O/ 18 O exchange in the gas phase. To assess the role of hydrogen migration, the associated kinetic isotope effect (KIE) is determined in a double-labeling experiment.…”

Section: Znoh]mentioning

confidence: 99%

“…To this end, a dilute solution of ZnCl 2 in an approximately 1:1 mixture of D 2 O and CH 3 OH with a trace of pyridine is subjected to ESI. Figure 1 a shows the region of the [(py) 2 …”

Section: Znoh]mentioning

confidence: 99%

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…”

mentioning

confidence: 99%

“…In contrast, no significant 16 + . However, the reaction occurs with only about 1 % of the gaskinetic collision rate, which indicates that the degenerate oxygen-atom exchange between [(im) 2 …”

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confidence: 99%

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A Gas‐Phase Reaction as a Functional Model for the Activation of Carbon Dioxide by Carbonic Anhydrase

et al. 2003

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Dedicated to Professor Wolfgang Steglich on the occasion of his 70th birthday.Carbonic anhydrase is a zinc-centered enzyme, with a molecular weight of around 30 kDa, which efficiently catalyzes the conversion of carbon dioxide into soluble bicarbonate (HCO 3 À ), thereby greatly facilitating the transport of CO 2 in biological systems.[1] The function of carbonic anhydrase is outlined in Scheme 1: [2] [3] The protein environment of the active center, obtained through evolution, provides an ideal arrangement of three histidine residues which serve as ligands L and to enables acceleration of the rate-limiting steps by proton relays. [3][4][5] Herein, we report an investigation of the intrinsic requirements for CO 2 activation according to Scheme 1 in the idealized gas phase. This approach raises two immediate questions: 1) can the nucleophilic attack formally required for bond activation of CO 2 be achieved at all by a gaseous cation bearing a real Coulomb charge? 2) If so, what is the optimal number of ligands (n) for activation of CO 2 by [L n ZnOH] + ions in the gas phase?Electrospray ionization (ESI) [6] allows a variety of ligated metal ions to be generated directly from solution. The experiments described herein were performed with a VG BIO-Q instrument consisting of an ESI source combined with a tandem mass spectrometer of QHQ configuration (Q = quadrupole and H = hexapole). [7] When dilute solutions of ZnX 2 (X = F-I, NO 3 ) in methanol/water containing a trace of either imidazole (im) or pyridine (py) as the nitrogen ligands L are subjected to ESI, [L n Zn] 2+ and [L n ZnX] + species form as the main zinc-containing cations.[+ ratio depends on the coordination ability of the counterion X À : the weaker-coordinating X À is, the more the Equilibrium (1) is shifted to the left. With more weakly coordinatingcounterions (X = Cl, Br, and NO 3 ), solvolysis of the dication (Equilibrium (2)) can compete with anion rebound to afford the desired [L n ZnOH] + species.In ESI, the degree of ligation can be controlled by the cone voltage, a parameter reflecting the degree of collisioninduced dissociation (CID) of the initially formed ions during their transfer to the high-vacuum manifold of the mass spectrometer.[ + . We note that the isotope patterns [10] observed are fully consistent with the formulae [L n ZnOH]+ and that CID of the mass-selected ions is as expected: exclusive loss of L is detected for n = 3, for n = 1 and 2 competing eliminations of L and H 2 O are detected, where the loss of water involves transfer of one hydrogen atom from the ligand to the hydroxy group.To mimic the activation of CO 2 by carbonic anhydrase in a gas-phase experiment, a further indicator is required because the heterolytic cleavage [

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Section: Znoh]mentioning

confidence: 99%

Section: Znoh]mentioning

confidence: 99%

“…To this end, a dilute solution of ZnCl 2 in an approximately 1:1 mixture of D 2 O and CH 3 OH with a trace of pyridine is subjected to ESI. Figure 1 a shows the region of the [(py) 2 …”

Section: Znoh]mentioning

confidence: 99%

“…

…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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A Gas‐Phase Reaction as a Functional Model for the Activation of Carbon Dioxide by Carbonic Anhydrase

et al. 2003

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New Insights into the Mechanistic Details of the Carbonic Anhydrase Cycle as Derived from the Model System [(NH3)3Zn(OH)]+/CO2: How does the H2O/HCO3− Replacement Step Occur?

Mauksch¹,

Bräuer

Weston

et al. 2001

ChemBioChem

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The full reaction path for the conversion of carbon dioxide to hydrogencarbonate has been computed at the B3LYP/6-311+G** level, employing a [(NH(3))(3)Zn(OH)](+) model catalyst to mimic the active center of the enzyme. We paid special attention to the question of how the catalytic cycle might be closed by retrieval of the catalyst. The nucleophilic attack of the catalyst on CO(2) has a barrier of 5.7 kcal mol(-1) with inclusion of thermodynamic corrections and solvent effects and is probably the rate-determining step. This barrier corresponds well with prior experiments. The intermediate result is a Lindskog-type structure that prefers to stabilize itself via a rotation-like transition state to give a Lipscomb-type product, which is a monodentate hydrogencarbonate complex. By addition of a water molecule, a pentacoordinated adduct with pseudo-trigonal-bipyramidal geometry is formed. The water molecule occupies an equatorial position, whereas the hydrogencarbonate ion is axial. In this complex, proton transfer from the Zn-bound water molecule to the hydrogencarbonate ion is extremely facile (barrier 0.8 kcal mol(-1)), and yields the trans,trans-conformer of carbonic acid rather than hydrogencarbonate as the leaving group. The carbonic acid molecule is bound by a short O...H-O hydrogen bond to the catalyst [(NH(3))(3)Zn(OH)](+), in which the OH group is already replaced by that of an entering water molecule. After deprotonation of the carbonic acid through a proton relay to histidine 64, modeled here by ammonia, hydrogencarbonate might undergo an ion pair return to the catalyst prior to its final dissociation from the complex into the surrounding medium.

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Eine Gasphasenreaktion als funktionales Modell der Aktivierung von Kohlendioxid durch die Carboanhydrase

et al. 2003

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Quantitative Reactivity Model for the Hydration of Carbon Dioxide by Biomimetic Zinc Complexes

Cited by 86 publications

References 67 publications

A Gas‐Phase Reaction as a Functional Model for the Activation of Carbon Dioxide by Carbonic Anhydrase

A Gas‐Phase Reaction as a Functional Model for the Activation of Carbon Dioxide by Carbonic Anhydrase

New Insights into the Mechanistic Details of the Carbonic Anhydrase Cycle as Derived from the Model System [(NH3)3Zn(OH)]+/CO2: How does the H2O/HCO3− Replacement Step Occur?

Eine Gasphasenreaktion als funktionales Modell der Aktivierung von Kohlendioxid durch die Carboanhydrase

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