The Hydrogenobyric Acid Structure Reveals the Corrin Ligand as an Entatic State Module Empowering B<sub>12</sub> Cofactors for Catalysis

Kieninger, Christoph; Deery, Evelyne; Lawrence, Andrew D.; Podewitz, Maren; Wurst, Klaus; Nemoto‐Smith, Emi; Widner, Florian J.; Baker, Joseph A.; Jockusch, Steffen; Kreutz, Christoph; Liedl, Klaus R.; Gruber, Karl; Warren, Martin J.; Kräutler, Bernhard

doi:10.1002/anie.201904713

Cited by 32 publications

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References 42 publications

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“…A separate estimate of the quantum yield can be obtained from recent fluorescence lifetime measurements and quantum yield determinations for the natural cobalt-free corrin Hby 36 and its zinc complex Znby, 35 with fluorescence lifetimes τ fl of 3.3 and <0.4 ns, respectively. If the intrinsic radiative lifetimes of HOPryCbl, F 2 PhEtyCbl, and CNCbl are similar to Hby (τ r = τ fl /φ fl = 3.3 ns/0.18 = 18 ns) 36 and Znby (τ r = τ fl /φ fl = 0.4 ns/0.025 = 16 ns), 35 the lifetime for stimulated emission of 200 fs in HOPryCbl and F 2 PhEtyCbl corresponds to a slightly higher quantum yield of 1.2 × 10 –5 . These yields of 10 –6 –10 –5 are small but expected to provide a measurable signal.…”

Section: Resultsmentioning

confidence: 99%

“…The visible absorption spectrum is dominated by the ππ* transitions of the corrin ring and is similar for typical cobalamins, zinc-substituted analogues, 35 and metal-free Hby. 36 The presence of a Co atom opens a rapid channel for depopulation of the “bright” state. This precipitates the changes in the axial bonding that are observed in time-resolved XANES measurements.…”

Section: Discussionmentioning

confidence: 99%

“…This hypothesis is further supported by comparison of spectra of the metal free hydrogenobyric acid (Hby) and zinc-substituted zincobyric acid (Znby). 35 , 36 …”

Section: Introductionmentioning

confidence: 99%

“…Fluorescence from the ππ* state of the corrin ring has been reported for metal-free corrins. 36 − 38 The fluorescence spectra of metal-free corrins 36 , 38 and Zn corrins 35 exhibit varied vibrational structure, providing the strongest evidence to date for a vibrational assignment of the αβ-band absorption of “typical” cobalamins. 34 , 39 The data on the metal free corrins are complicated, however, as their strong emission in the visible features considerable temperature dependence.…”

Section: Introductionmentioning

confidence: 99%

“…34 , 39 The data on the metal free corrins are complicated, however, as their strong emission in the visible features considerable temperature dependence. 36 , 38 The zinc corrins also exhibit strong fluorescence spectra with a clear vibrational progression, 35 although the rapid decrease in intensity at longer wavelengths suggests that the entire width of the αβ-band in the absorption spectrum cannot be attributed to a vibrational progression in a single electronic state (see below).…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Excited State Dynamics and Fluorescence from Vitamin B₁₂ and Organometallic [Co]–C≡C–R Cobalamins

et al. 2020

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Cobalamins are cobalt-centered cyclic tetrapyrrole ring-based molecules that provide cofactors for exceptional biological processes and possess unique and synthetically tunable photochemistry. Typical cobalamins are characterized by a visible absorption spectrum consisting of peaks labeled α, β, and sh. The physical basis of these peaks as having electronic origin or as a vibronic progression is ambiguous despite much investigation. Here, for the first time, cobalamin fluorescence is identified in several derivatives. The fluorescence lifetime is ca. 100–200 fs with quantum yields on the order of 10 –6 –10 –5 because of rapid population of “dark” excited states. The results are compared with the fluorescent analogue with zinc replacing the cobalt in the corrin ring. Analysis of the breadth of the emission spectrum provides evidence that a vibrational progression in a single excited electronic state makes the dominant contribution to the visible absorption band.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…This hypothesis is further supported by comparison of spectra of the metal free hydrogenobyric acid (Hby) and zinc-substituted zincobyric acid (Znby). 35 , 36 …”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultrafast Excited State Dynamics and Fluorescence from Vitamin B₁₂ and Organometallic [Co]–C≡C–R Cobalamins

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Zinc Substitution of Cobalt in Vitamin B₁₂: Zincobyric acid and Zincobalamin as Luminescent Structural B₁₂‐Mimics

et al. 2019

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Replacing the central cobalt ion of vitamin B 12 by other metals has been al ong-held aspiration within the B 12field. Herein, we describe the synthesis from hydrogenobyric acid of zincobyric acid (Znby)a nd zincobalamin (Znbl), the Zn-analogues of the natural cobalt-corrins cobyric acid and vitamin B 12 ,r espectively.T he solution structures of Znby and Znbl were studied by NMR-spectroscopy. Single crystals of Znby were produced, providing the first X-ray crystallographic structure of az inc corrin. The structures of Znby and of computationally generated Znbl were found to resemble the corresponding Co II -corrins,m aking such Zn-corrins potentially useful for investigations of B 12 -dependent processes.The singlet excited state of Znby had as hort life-time,l imited by rapid intersystem crossing to the triplet state. Znby allowed the unprecedented observation of ac orrin triplet (E T = 190 kJ mol À1 )and was found to be an excellent photo-sensitizerThe biological use of cobalt as the specific transition metal center in natural B 12 -cofactors and the interaction between cobalt and the corrin ligand raise intriguing questions concerning the origins of its natural selection.[1] Engineered B 12 -biosynthesis [2] has opened up ap reparative route to hydrogenobyric acid (Hby), [3] the metal-free corrin ligand of vitamin B 12 ,p roviding an excellent opportunity for the synthesis of transition-metal analogues of the natural cobaltcorrinoids. [4] Zn II -analogues of natural corrinoids have hardly been explored [4b] but are attractive,asZn-and low-spin Co IIcenters exhibit similar structural properties in small complexes and in metalloproteins. [5] Fischli and Eschenmoser reported the synthesis and characterization of the first Zn-corrin (ZnCor), when exploring the synthesis and chemistry of corrins in model studies towards the total synthesis of vitamin B 12 . [4a, 6] Indeed, in the Eschenmoser [7] and Woodward labs [8] a5 ,15-nor-zincobyrinate was an intermediate of the B 12 -synthesis.U V/Visspectroscopically characterized samples of zincobalamin (Znbl)a nd zincobyric acid (Znby), the Zn-analogues of vitamin B 12 (CNCbl)and cobyric acid (Cby)(Scheme 1), were first reported by Koppenhagen and Pfiffner. [9] Herein, we delineate an effective synthesis of Znby and of Znbl,s tarting from crystalline Hby, [3] describe the pertinent spectroscopic and structural properties of these luminescent Scheme 1. Formulae of metal-free, cobalt-and zinc-corrinoids. Left: General formula of the cobalamins vitamin B 12 (R = CN, CNCbl), coenzyme B 12 (R = 5'-deoxyadenosyl, AdoCbl), cob(II)alamin (R = e À , Cbl II )C enter:F ormulae of hydrogenobyric acid (Hby), Co II -cobyric acid (Cby II )and zincobyrate (Znby), where the axial solvent ligands for both the Zn II and Co II have been omitted. Right:formula of zincobalamin (Znbl)i nits "base-on"f orm.

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Replacement of the Cobalt Center of Vitamin B₁₂ by Nickel: Nibalamin and Nibyric Acid Prepared from Metal‐Free B₁₂ Ligands Hydrogenobalamin and Hydrogenobyric Acid

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The (formal) replacement of Co in cobalamin (Cbl) by Ni II generates nibalamin (Nibl), an ew transition-metal analogue of vitamin B 12 .Described here is Nibl,synthesized by incorporation of aN i II ion into the metal-free B 12 ligand hydrogenobalamin (Hbl), itself prepared from hydrogenobyric acid (Hby). The related Ni II corrin nibyricacid (Niby)was similarly synthesized from Hby,t he metal-free cobyric acid ligand. The solution structures of Hbl,a nd Niby and Nibl, were characterized by spectroscopic studies. Hbl features two inner protons bound at N2 and N4 of the corrin ligand, as discovered in Hby.X-rayanalysis of Niby shows the structural adaptation of the corrin ligand to Ni II ions and the coordination behavior of Ni II .T he diamagnetic Niby and Nibl,a nd corresponding isoelectronic Co I corrins,w ere deduced to be isostructural. Nibl is as tructural mimic of four-coordinate base-off Cbls,a sv erified by its ability to act as as trong inhibitor of bacterial adenosyltransferase.

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The Hydrogenobyric Acid Structure Reveals the Corrin Ligand as an Entatic State Module Empowering B₁₂ Cofactors for Catalysis

Cited by 32 publications

References 42 publications

Ultrafast Excited State Dynamics and Fluorescence from Vitamin B₁₂ and Organometallic [Co]–C≡C–R Cobalamins

Ultrafast Excited State Dynamics and Fluorescence from Vitamin B₁₂ and Organometallic [Co]–C≡C–R Cobalamins

Zinc Substitution of Cobalt in Vitamin B₁₂: Zincobyric acid and Zincobalamin as Luminescent Structural B₁₂‐Mimics

Replacement of the Cobalt Center of Vitamin B₁₂ by Nickel: Nibalamin and Nibyric Acid Prepared from Metal‐Free B₁₂ Ligands Hydrogenobalamin and Hydrogenobyric Acid

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The Hydrogenobyric Acid Structure Reveals the Corrin Ligand as an Entatic State Module Empowering B12 Cofactors for Catalysis

Cited by 32 publications

References 42 publications

Ultrafast Excited State Dynamics and Fluorescence from Vitamin B12 and Organometallic [Co]–C≡C–R Cobalamins

Ultrafast Excited State Dynamics and Fluorescence from Vitamin B12 and Organometallic [Co]–C≡C–R Cobalamins

Zinc Substitution of Cobalt in Vitamin B12: Zincobyric acid and Zincobalamin as Luminescent Structural B12‐Mimics

Replacement of the Cobalt Center of Vitamin B12 by Nickel: Nibalamin and Nibyric Acid Prepared from Metal‐Free B12 Ligands Hydrogenobalamin and Hydrogenobyric Acid

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The Hydrogenobyric Acid Structure Reveals the Corrin Ligand as an Entatic State Module Empowering B₁₂ Cofactors for Catalysis

Ultrafast Excited State Dynamics and Fluorescence from Vitamin B₁₂ and Organometallic [Co]–C≡C–R Cobalamins

Ultrafast Excited State Dynamics and Fluorescence from Vitamin B₁₂ and Organometallic [Co]–C≡C–R Cobalamins

Zinc Substitution of Cobalt in Vitamin B₁₂: Zincobyric acid and Zincobalamin as Luminescent Structural B₁₂‐Mimics

Replacement of the Cobalt Center of Vitamin B₁₂ by Nickel: Nibalamin and Nibyric Acid Prepared from Metal‐Free B₁₂ Ligands Hydrogenobalamin and Hydrogenobyric Acid