Carbonato complexes of cobalt(III)

Mac-Coll, Carlos R. Piriz

doi:10.1016/s0010-8545(00)80085-5

“…Internal hydrogen bonding between nonbound carbonate oxygens and coordinated water as well as steric hindrance favor, the trans coordination of carbonates, as is observed for [Co(CO 3 ) 2 (H 2 O) 4 ] 2and [Co(NH 3 ) 4 CO 3 H 2 O] complexes. 38,45 Species with two carbonates may already show elongation of the Cu-O bond at the axial position. Distinction between species with one or two coordinated carbonates based on the ESE modulation depth 46 is difficult because there is no proper reference system available and the sample contains a mixture of species.…”

Section: Discussionmentioning

confidence: 99%

Complexation of Copper(II) with Carbonate Ligands in Aqueous Solution: A CW and Pulse EPR Study

Schosseler

¹

,

Wehrli

²

,

Schweiger

³

1997

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The pH dependent complexation between copper and (13)C-labeled carbonate ligands in aqueous solution is investigated by optical spectroscopy and continuous wave and pulse EPR. The small (13)C hyperfine coupling observed in the pulse EPR spectra at low temperature and pH 5.5 is assigned to weak, monodentate coordination of carbonates to the Cu(2+) ion. The (13)C hyperfine couplings found at pH 6.5 and 8 are of the same magnitude as twice the nuclear Larmor frequency (matching range) and are assigned to bidentate coordination of carbonate. The larger coupling for the bidentate complexes is explained by a higher covalency of the pi bonding in the four-membered ring. The elongation of the axial bonds to the water ligands caused by coordination of carbonate ligands in the equatorial plane of the copper complex leads to smaller proton couplings. The observation of both mono- and bidentate coordination at pH 6.5 and 8 by pulse EPR at low temperature is in contradiction to the calculated concentrations of copper-carbonate complexes at room temperature. Although equilibrium shifts during the freezing of the samples cannot be excluded, the basic mechanisms of mono- and bidentate complexation observed in frozen solution should also apply in aqueous solution at ambient temperature.

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“…The p K a values of H 2 CO 3 are at approx. 6.5 and 10.5, and p K a values of HCO 3 − coordinated to metal ions of 5 to 6 have been reported [28,44–48] . While we do not accurately know the p K a value of the bridging bicarbonate of our dicopper(II) complexes in INT3,4, it likely is in the region of 6 to 8.…”

Section: Resultsmentioning

confidence: 76%

A Dicopper(II)‐Based Carbonic Anhydrase Model—Quantum‐Chemical Evaluation of the Mechanistic Pathway

Velmurugan,

Baur,

Comba

2024

Angewandte Chemie

0

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The cyanobacterium Prochloron didemni, an obligate symbiont of different species of colonial ascidians, occurring in the Pacific and Indian Oceans, produces a variety of cyclic peptides. These patellamide‐type macrocycles lead to relatively stable dicopper(II) complexes that are extremely efficient carbonic anhydrase mimics, the most active model systems known so far. Importantly, it recently was shown that copper(II) is coordinated to patellamide derivatives in Prochloron cells. An interesting question therefore is, whether the biological function of patellamide‐type macrocycles is related to the catalytic activity in CO2 hydration or its reverse. Here, we present a computational study to evaluate the energetics of the catalytic cycle in search of a possible answer to these questions and compare the computed energy barriers with the experimental kinetic data. It emerges that release of the bridging carbonate is a critical step and that the catalysis product inhibits catalysis at pH values above approx. 7. Therefore, carbonate transport rather than CO2 hydrolysis is proposed as the biological function of copper(II)‐patellamide complexes in the Prochloron‐Ascidian symbiosis.

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“…6.5 and 10.5, and pK a values of HCO 3 À coordinated to metal ions of 5 to 6 have been reported. [28,[44][45][46][47][48] While we do not accurately know the pK a value of the bridging bicarbonate of our dicopper-(II) complexes in INT3,4, it likely is in the region of 6 to 8. For the release of CO 3 2À /HCO 3 À (sequence starting with INT3), one expects typical saturation kinetics with (1 + K a [H + ]) in the denominator and, in the pH range of the experimental studies (6 < pH < 9) [21][22] the pseudo first order rates are linearly dependent on [H + ] (rate = kK a [H + ], where k relates to the energy barrier involving TS4,5).…”

Section: Angewandte Chemiementioning

confidence: 88%

A Dicopper(II)‐Based Carbonic Anhydrase Model—Quantum‐Chemical Evaluation of the Mechanistic Pathway

Velmurugan,

Baur,

Comba

2024

Angew Chem Int Ed

0

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The cyanobacterium Prochloron didemni, an obligate symbiont of different species of colonial ascidians, occurring in the Pacific and Indian Oceans, produces a variety of cyclic peptides. These patellamide‐type macrocycles lead to relatively stable dicopper(II) complexes that are extremely efficient carbonic anhydrase mimics, the most active model systems known so far. Importantly, it recently was shown that copper(II) is coordinated to patellamide derivatives in Prochloron cells. An interesting question therefore is, whether the biological function of patellamide‐type macrocycles is related to the catalytic activity in CO2 hydration or its reverse. Here, we present a computational study to evaluate the energetics of the catalytic cycle in search of a possible answer to these questions and compare the computed energy barriers with the experimental kinetic data. It emerges that release of the bridging carbonate is a critical step and that the catalysis product inhibits catalysis at pH values above approx. 7. Therefore, carbonate transport rather than CO2 hydrolysis is proposed as the biological function of copper(II)‐patellamide complexes in the Prochloron‐Ascidian symbiosis.

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Carbonato complexes of cobalt(III)

Cited by 17 publications

References 118 publications

Complexation of Copper(II) with Carbonate Ligands in Aqueous Solution: A CW and Pulse EPR Study

Complexation of Copper(II) with Carbonate Ligands in Aqueous Solution: A CW and Pulse EPR Study

A Dicopper(II)‐Based Carbonic Anhydrase Model—Quantum‐Chemical Evaluation of the Mechanistic Pathway

A Dicopper(II)‐Based Carbonic Anhydrase Model—Quantum‐Chemical Evaluation of the Mechanistic Pathway

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