Organocobalt B12 models: axial ligand effects on the structural and coordination chemistry of cobaloximes

Bresciani–Pahor, Nevenka; Forcolin, Margherita; Marzillï, Luigi G.; Randaccio, Lucio; Summers, Michael F.; Toscano, Paul J.

doi:10.1016/0010-8545(85)80021-7

Cited by 359 publications

(230 citation statements)

References 199 publications

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“…37 Changing the alkyl group to ethyl lengthens the Co-C bond, to 1.99 Å, due to a combination of electronic and nonbonded ethyl-corrin interactions, while increasing the steric bulk further, to propyl, lengthens the Co-C bond to 2.03 Å. Interestingly, the Co-imidazole bond lengthens in the same order, to 2.26 and 2.32 Å, illustrating what has become known as the 'inverse trans influence'. [38][39][40][41][42][43] The computed frequencies fall in the same order, as expected. The Co-C stretching frequencies are in excellent agreement with reported values for MeCbl and EtCbl; no data are available for isopropyl derivatives.…”

Section: Alkyl Corrinssupporting

confidence: 82%

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B₁₂-Cofactors

et al. 2006

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Density functional theory (DFT)-based normal mode calculations have been carried out on models for B 12 -cofactors to assign reported isotope-edited resonance Raman spectra, which isolate vibrations of the organo-Co group. Interpretation is straightforward for alkyl-Co derivatives, which display prominent Co-C stretching vibrational bands. DFT correctly reproduces Co-C distances and frequencies for the methyl and ethyl derivatives. However, spectra are complex for adenosyl derivatives, due to mixing of Co-C stretching with a ribose deformation coordinate and to activation of modes involving Co-C-C bending and Co-adenosyl torsion. Despite this complexity, the computed spectra provide a satisfactory re-assignment of the experimental data. Reported trends in adenosyl-cobalamin spectra upon binding to the methylmalonyl CoA mutase enzyme, as well as on subsequent binding of substrates and inhibitors, provide support for an activation mechanism involving substrate-induced deformation of the adenosyl ligand.

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Section: Alkyl Corrinssupporting

confidence: 82%

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B₁₂-Cofactors

et al. 2006

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“…The rate constant of dissociation of the CoÐC bond in these reactions is about 10 10 times that of the free coenzyme, suggesting a weakening of the CoÐC bond by interaction with the enzyme in the presence of substrate (Halpern et al, 1984;Finke & Hay, 1984;Hay & Finke, 1986). It has been proposed that this weakening is a result of steric effects (Halpern et al, 1984;Bresciani-Pahor et al, 1985). However, comparison of the crystal structure of B 12r (Kra È utler et al, 1989) with that of the coenzyme (Lenhert & Hodgkin, 1961;Lenhert, 1968) reveals no major molecular distortion which would explain the observed CoÐC bond weakening.…”

Section: Introductionmentioning

confidence: 89%

Neutron Laue diffraction studies of coenzyme cob(II)alamin

Langan

Lehmann

Wilkinson

et al. 1999

Acta Crystallogr D Biol Cryst

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Using a recently designed neutron single-crystal diffractometer utilizing a narrow-band Laue concept (LADI), diffraction data were collected from a crystal of the coenzyme cob(II)alamin (B 12r ), crystallized from a mixture of D 2 O and perdeuterated acetone. The instrument was placed at the end of a cold neutron guide at the Institute Laue Langevin (ILL, Grenoble, France), and data collection with neutrons of 1.8± 8.0 A Ê wavelength to a crystallographic resolution of 1.43 A Ê was complete after about 36 h. This compares favourably with a previous experiment utilizing the same crystal specimen, where more than four weeks were required to collect monochromatic diffraction data to about 1 A Ê resolution. Using the Laue data, the structure was solved by molecular replacement with the known X-ray crystal structure. Difference density maps revealed the atomic positions (including deuterium atoms) of seven ordered solvent water molecules and two (partially disordered) acetone molecules. These density maps were compared with corresponding maps computed with monochromatic neutron-diffraction data collected to 1.0 A Ê resolution using the same crystal specimen, as well as to maps derived from high-resolution (0.90 A Ê ) synchrotron X-ray data. In spite of the better de®nition of atomic positions in the two high-resolution maps, the 1.43 A Ê LADI maps show considerable power for the determination of the location of hydrogen and deuterium positions.

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“…As a result, many triggering factors of Co-C bond breaking have been considered and various mechanistic mechanisms of the Co-C cleavage process have been proposed. Many researchers have considered axial ligand transinfl uence, steric effects, structural strain, protein infl uence, in addition to others [47][48][49][50][51][52][53][54][55][56][57][58] as determinant factors in the Co-C cleavage process. The hydrogen transfer from the substrate to 5-deoxysdenosyl ligand has also been considered as a triggering factor of the Co-C bond breaking [59][60][61][62][63][64][65][66][67].…”

Section: The Mechanisms Of Methylcobalamin and Adenosylcobalamin Actimentioning

confidence: 99%

The Nature of the Co-C Bond Cleavage Processes in Methylcob(II)Alamin and Adenosylcob(III)Alamin

Spataru¹,

Fernández²

2016

ChemJMold

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Abstract. Unfortunately, there are still signifi cant disagreements between experimental and theoretical data of rate constants, energy barriers for Co-C bond cleavage process and coordination numbers of vitamin B 12 coenzyme species in spite of the remarkable efforts done by research community. Therefore, no grounded mechanisms for Co-C vitamin B 12 coenzyme bond breaking process and subsequent reactions have been found up to now. The infl uence of the mixing orbitals e.g. Pseudo-Jahn-Teller and similar effects on the reactions paths of bond-cleavage mechanisms of vitamin B 12 co-factors must be taken into account by utilizing multi-reference methods, in particular multiconfi gurational self-consistent fi eld (MCSCF) method. Then, the change in total energy along the normal coordinate Q for the stretching mode including Co-C and Co-N bonds in vitamin B 12 cofactors is expected due to a "vibronic" coupling term, which couples an excited state and ground state by a second order derivative potential-energy operator. The strong state mixing effect is expected to lead to low energy barriers and to Co-C and Co-N axial bond cleavage events in agreement with experimental data. Afterward, the updated mechanisms of vitamin B 12 bio-processes can be determined.Keywords: vitamin B 12 , mechanism, bio-catalysis, Pseudo-Jahn-Teller effect, DFT, MCSCF. Received: December 2015/ Revised fi nal: February 2016/ Accepted: February 2016 IntroductionVitamin B 12 cofactor is one of eight B vitamins and is involved in mammalian cellular metabolism, infl uencing amino acid and DNA synthesis [1] and hematopoiesis. The best known human physiological function of vitamin B 12 is its role in promoting normal health in the brain and nervous system. Vitamin B 12 anemia can cause such neurologic dysfunction as weakness, fatigue, light-headedness, rapid heartbeat, rapid breathing, pale skin color, bruising, and bleeding (including bleeding gums). The more severe vitamin B 12 anemia dysfunctions are characterized by tingling or numbness of the fi ngers and toes, diffi culty walking, mood changes, depression, memory loss, disorientation and, in most severe cases, dementia [2]. Vitamin B 12 defi ciency has even been considered in playing a role in the development of Alzheimer's disease [3][4][5][6][7].The vitamin B 12 cofactor contains a cobalt atom surrounded by an equatorial corrin ring. Covalently linked to the central atom is a dimethylbenzimidazole that occupies one of the axial coordination positions. The opposite coordinate is available for several ligands in bio-medium or in solution; however, known biologically active structures containing adenosyl-or methyl have been considered most often (Figure 1).

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Organocobalt B12 models: axial ligand effects on the structural and coordination chemistry of cobaloximes

Cited by 359 publications

References 199 publications

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B₁₂-Cofactors

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B₁₂-Cofactors

Neutron Laue diffraction studies of coenzyme cob(II)alamin

The Nature of the Co-C Bond Cleavage Processes in Methylcob(II)Alamin and Adenosylcob(III)Alamin

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Organocobalt B12 models: axial ligand effects on the structural and coordination chemistry of cobaloximes

Cited by 359 publications

References 199 publications

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B12-Cofactors

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B12-Cofactors

Neutron Laue diffraction studies of coenzyme cob(II)alamin

The Nature of the Co-C Bond Cleavage Processes in Methylcob(II)Alamin and Adenosylcob(III)Alamin

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DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B₁₂-Cofactors

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B₁₂-Cofactors