1
|
Zahid S, Anwar Z, Qadeer K, Ejaz MA, Wajidi M, Yasin H, Fatima K, Razzak M, Noreen A, Vaid FHM, Ahmad I. Ascorbic acid assisted photodegradation of methylcobalamin using corrective irrelevant absorption spectrophotometric assay: A kinetic study. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 323:124902. [PMID: 39126865 DOI: 10.1016/j.saa.2024.124902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Revised: 05/20/2024] [Accepted: 07/28/2024] [Indexed: 08/12/2024]
Abstract
Photodegradation of drug substances leads to the formation of known and unknown degradation products. These unknown degradation products interfere and give erroneous results because of absorption on analytical wavelengths. This interference could be eliminated using the correction of irrelevant absorbancies. This study is based on the application of linear and non-linear correction of irrelevant absorption for the determination of methylcobalamin (MC) and hydroxocobalamin in the photolytic degradation assisted by ascorbic acid (AH2). MC follows first-order degradation kinetics and the rate of degradation (kobs) ranges from 1.99-2.34 × 10-2, min-1 at pH 2.0-12.0. The second-order rate constants (k2) for the photochemical interaction of MC and AH2 are in the range of 17.9-60.3 × 10-2 M-1, min-1 (acidic region) and 10.3-24.6 × 10-2 M-1, min-1 (alkaline region). The k2-pH profile was found to be bell-shaped and the maximum rate of degradation in the presence of AH2 is at pH 5.0 (60.3 × 10-2 M-1, min-1) due to the protonation of MC. However, in alkaline pH, the rate of photodegradation decreases due to the ionization form of AH2 which is AH- species.
Collapse
Affiliation(s)
- Saima Zahid
- Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Super Highway, Gadap Road, Karachi, Pakistan
| | - Zubair Anwar
- Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Super Highway, Gadap Road, Karachi, Pakistan.
| | - Kiran Qadeer
- Institute of Pharmaceutical Sciences, Jinnah Sindh Medical University, Rafiqi H J Road, Karachi Cantonment, Karachi 75510, Pakistan
| | - Muhammad Ahsan Ejaz
- Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Super Highway, Gadap Road, Karachi, Pakistan
| | - Mehwish Wajidi
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Federal Urdu University of Arts Science and Technology, Karachi, Pakistan
| | - Hina Yasin
- Dow College of Pharmacy, Dow University of Health Sciences, Karachi, Pakistan
| | - Kaneez Fatima
- Institute of Pharmaceutical Sciences, Jinnah Sindh Medical University, Rafiqi H J Road, Karachi Cantonment, Karachi 75510, Pakistan
| | - Mariam Razzak
- Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Super Highway, Gadap Road, Karachi, Pakistan
| | - Aisha Noreen
- Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Super Highway, Gadap Road, Karachi, Pakistan
| | - Faiyaz Hussain Madni Vaid
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy and Pharmaceutical Sciences, University of Karachi, Pakistan
| | - Iqbal Ahmad
- Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Super Highway, Gadap Road, Karachi, Pakistan
| |
Collapse
|
2
|
Sension RJ, McClain TP, Michocki LB, Miller NA, Alonso-Mori R, Lima FA, Ardana-Lamas F, Biednov M, Chung T, Deb A, Jiang Y, Kaneshiro AK, Khakhulin D, Kubarych KJ, Lamb RM, Meadows JH, Otte F, Sofferman DL, Song S, Uemura Y, van Driel TB, Penner-Hahn JE. Structural Evolution of Photoexcited Methylcobalamin toward a CarH-like Metastable State: Evidence from Time-Resolved X-ray Absorption and X-ray Emission. J Phys Chem B 2024; 128:8131-8144. [PMID: 39150518 DOI: 10.1021/acs.jpcb.4c03729] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/17/2024]
Abstract
CarH is a protein photoreceptor that uses a form of B12, adenosylcobalamin (AdoCbl), to sense light via formation of a metastable excited state. Aside from AdoCbl bound to CarH, methylcobalamin (MeCbl) is the only other example─to date─of photoexcited cobalamins forming metastable excited states with lifetimes of nanoseconds or longer. The UV-visible spectra of the excited states of MeCbl and AdoCbl bound to CarH are similar. We have used transient Co K-edge X-ray absorption and X-ray emission spectroscopies in conjunction with transient absorption spectroscopy in the UV-visible region to characterize the excited states of MeCbl. These data show that the metastable excited state of MeCbl has a slightly expanded corrin ring and increased electron density on the cobalt, but only small changes in the axial bond lengths.
Collapse
Affiliation(s)
- Roseanne J Sension
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
- Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109-1040, United States
| | - Taylor P McClain
- Biophysics, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Lindsay B Michocki
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Nicholas A Miller
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Roberto Alonso-Mori
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Frederico Alves Lima
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Fernando Ardana-Lamas
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Mykola Biednov
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Taewon Chung
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Aniruddha Deb
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Yifeng Jiang
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - April K Kaneshiro
- Department of Biological Chemistry, 1150 W. Medical Center Dr., Ann Arbor, Michigan 48109-0600, United States
| | - Dmitry Khakhulin
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Kevin J Kubarych
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Ryan M Lamb
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Joseph H Meadows
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| | - Florian Otte
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Danielle L Sofferman
- Program in Applied Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109-1040, United States
| | - Sanghoon Song
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Yohei Uemura
- Femtosecond X-ray Experiments Group, European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Tim B van Driel
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - James E Penner-Hahn
- Department of Chemistry, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
- Biophysics, University of Michigan, 930 N University Ave. Ann Arbor, Michigan 48109-1055, United States
| |
Collapse
|
3
|
Marques HM. The inorganic chemistry of the cobalt corrinoids - an update. J Inorg Biochem 2023; 242:112154. [PMID: 36871417 DOI: 10.1016/j.jinorgbio.2023.112154] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Revised: 01/23/2023] [Accepted: 01/26/2023] [Indexed: 02/05/2023]
Abstract
The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B12, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B12-dependent enzymes is also given for the reader's convenience.
Collapse
Affiliation(s)
- Helder M Marques
- Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa.
| |
Collapse
|
4
|
Toda MJ, Lodowski P, Mamun AA, Kozlowski PM. Photoproduct formation in coenzyme B 12-dependent CarH via a singlet pathway. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2022; 232:112471. [PMID: 35644067 DOI: 10.1016/j.jphotobiol.2022.112471] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 03/26/2022] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
The CarH photoreceptor exploits of the light-sensing ability of coenzyme B12 ( adenosylcobalamin = AdoCbl) to perform its catalytic function, which includes large-scale structural changes to regulate transcription. In daylight, transcription is activated in CarH via the photo-cleavage of the Co-C5' bond of coenzyme B12. Subsequently, the photoproduct, 4',5'-anhydroadenosine (anhAdo) is formed inducing dissociation of the CarH tetramer from DNA. Several experimental studies have proposed that hydridocoblamin (HCbl) may be formed in process with anhAdo. The photolytic cleavage of the Co-C5' bond of AdoCbl was previously investigated using photochemical techniques and the involvement of both singlet and triplet excited states were explored. Herein, QM/MM calculations were employed to probe (1) the photolytic processes which may involve singlet excited states, (2) the mechanism of anhAdo formation, and (3) whether HCbl is a viable intermediate in CarH. Time-dependent density functional theory (TD-DFT) calculations indicate that the mechanism of photodissociation of the Ado ligand involves the ligand field (LF) portion of the lowest singlet excited state (S1) potential energy surface (PES). This is followed by deactivation to a point on the S0 PES where the Co-C5' bond remains broken. This species corresponds to a singlet diradical intermediate. From this point, the PES for anhAdo formation was explored, using the Co-C5' and Co-C4' bond distances as active coordinates, and a local minimum representing anhAdo and HCbl formation was found. The transition state (TS) for the formation of the Co-H bond of HCbl was located and its identity was confirmed by a single imaginary frequency of i1592 cm-1. Comparisons to experimental studies and the potential role of rotation around the N-glycosidic bond of the Ado ligand were discussed.
Collapse
Affiliation(s)
- Megan J Toda
- Department of Chemistry, University of Louisville, Louisville, KY 40292, United States
| | - Piotr Lodowski
- Institute of Chemistry, Faculty of Science and Technology, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Abdullah Al Mamun
- Department of Chemistry, University of Louisville, Louisville, KY 40292, United States
| | - Pawel M Kozlowski
- Department of Chemistry, University of Louisville, Louisville, KY 40292, United States.
| |
Collapse
|
5
|
Toda MJ, Lodowski P, Mamun AA, Kozlowski PM. Electronic and photolytic properties of hydridocobalamin. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2021; 224:112295. [PMID: 34548209 DOI: 10.1016/j.jphotobiol.2021.112295] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 07/06/2021] [Accepted: 08/17/2021] [Indexed: 06/13/2023]
Abstract
Hydridocobalamin (HCbl), is a known member of the B12 family of molecules (cobalamins, Cbls) yet unlike other well-studied Cbls, little is known of the electronic and photolytic properties of this species. Interest in HCbl has increased significantly in recent years when at least three experimentally proposed mechanisms implicate HCbl as an intermediary in the photoreaction of coenzyme B12-dependent photoreceptor CarH. Specifically, cleavage of the Co-C5' bond of coenzyme B12 could lead to a β-hydride or β‑hydrogen elimination reaction to form HCbl. HCbl is known to be a transient species where the oxidation state of the Co is variable; Co(I)-H+ ↔ Co(II)-H ↔ Co(III)-H-. Further, HCbl is a very unstable with a pKa of ~1. This complicates experimental studies and to the best of our knowledge there are no available crystal structures of HCbl - either for the isolated molecule or bound to an enzyme. In this study, the electronic structure, photolytic properties, and reactivity of HCbl were explored to determine the preferred oxidation state as well as its potential role in the formation of the photoproduct in CarH. Natural bond orbital (NBO) analysis was performed to determine the oxidation state of Co in isolated HCbl. Based on the NBO analysis of HCbl, Co clearly had excess negative charge, which is in stark contrast to other alkylCbls where the Co ion is marked by significant positive charge. In sum, NBO results indicate that the CoH bond is strongly polarized and almost ionic. It can be described as protonated Co(I). In addition, DFT was used to explore the bond dissociation energy of HCbl based on homolytic cleavage of the CoH bond. TD-DFT calculations were used to compare computed electronic transitions to the experimentally determined absorption spectrum. The photoreaction of CarH was explored using an isolated model system and a pathway for hydrogen transfer was found. Finally, quantum mechanics/molecular mechanics (QM/MM) calculations were employed to investigate the formation of HCbl in CarH.
Collapse
Affiliation(s)
- Megan J Toda
- Department of Chemistry, University of Louisville, Louisville, KY 40292, United States
| | - Piotr Lodowski
- Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Abdullah Al Mamun
- Department of Chemistry, University of Louisville, Louisville, KY 40292, United States
| | - Pawel M Kozlowski
- Department of Chemistry, University of Louisville, Louisville, KY 40292, United States.
| |
Collapse
|
6
|
Qadeer K, Arsalan A, Ahmad I, Fatima K, Anwar Z, Ahmed S, Khattak SUR, Mahmud S. Photochemical interaction of cyanocobalamin and hydroxocobalamin with cysteine. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2020.129441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
7
|
Weinstain R, Slanina T, Kand D, Klán P. Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials. Chem Rev 2020; 120:13135-13272. [PMID: 33125209 PMCID: PMC7833475 DOI: 10.1021/acs.chemrev.0c00663] [Citation(s) in RCA: 261] [Impact Index Per Article: 65.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Indexed: 02/08/2023]
Abstract
Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.
Collapse
Affiliation(s)
- Roy Weinstain
- School
of Plant Sciences and Food Security, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel
| | - Tomáš Slanina
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nám. 2, 166 10 Prague, Czech Republic
| | - Dnyaneshwar Kand
- School
of Plant Sciences and Food Security, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel
| | - Petr Klán
- Department
of Chemistry and RECETOX, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
| |
Collapse
|
8
|
Arsalan A, Ahmad I, Ali SA, Qadeer K, Mahmud S, Humayun F, Beg AE. The kinetics of photostabilization of cyanocobalamin in liposomal preparations. INT J CHEM KINET 2020. [DOI: 10.1002/kin.21343] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Adeel Arsalan
- Faculty of PharmacyZiauddin University Karachi Pakistan
- Baqai Institute of Pharmaceutical SciencesBaqai Medical University Karachi Pakistan
| | - Iqbal Ahmad
- Baqai Institute of Pharmaceutical SciencesBaqai Medical University Karachi Pakistan
| | - Syed Abid Ali
- H.E.J. Research Institute of ChemistryInternational Center for Chemical and Biological SciencesUniversity of Karachi Karachi Pakistan
| | - Kiran Qadeer
- Baqai Institute of Pharmaceutical SciencesBaqai Medical University Karachi Pakistan
| | - Shaukat Mahmud
- Baqai Institute of Pharmaceutical SciencesBaqai Medical University Karachi Pakistan
| | - Fozia Humayun
- H.E.J. Research Institute of ChemistryInternational Center for Chemical and Biological SciencesUniversity of Karachi Karachi Pakistan
| | | |
Collapse
|
9
|
Miller NA, Michocki LB, Konar A, Alonso-Mori R, Deb A, Glownia JM, Sofferman DL, Song S, Kozlowski PM, Kubarych KJ, Penner-Hahn JE, Sension RJ. Ultrafast XANES Monitors Femtosecond Sequential Structural Evolution in Photoexcited Coenzyme B 12. J Phys Chem B 2020; 124:199-209. [PMID: 31850761 DOI: 10.1021/acs.jpcb.9b09286] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Polarized X-ray absorption near-edge structure (XANES) at the Co K-edge and broadband UV-vis transient absorption are used to monitor the sequential evolution of the excited-state structure of coenzyme B12 (adenosylcobalamin) over the first picosecond following excitation. The initial state is characterized by sub-100 fs sequential changes around the central cobalt. These are polarized first in the y-direction orthogonal to the transition dipole and 50 fs later in the x-direction along the transition dipole. Expansion of the axial bonds follows on a ca. 200 fs time scale as the molecule moves out of the Franck-Condon active region of the potential energy surface. On the same 200 fs time scale there are electronic changes that result in the loss of stimulated emission and the appearance of a strong absorption at 340 nm. These measurements provide a cobalt-centered movie of the excited molecule as it evolves to the local excited-state minimum.
Collapse
Affiliation(s)
- Nicholas A Miller
- Department of Chemistry , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States
| | - Lindsay B Michocki
- Department of Chemistry , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States
| | - Arkaprabha Konar
- Department of Physics , University of Michigan , 450 Church Street , Ann Arbor , Michigan 48109-1040 , United States
| | - Roberto Alonso-Mori
- Linac Coherent Light Source , SLAC National Accelerator Laboratory , 2575 Sand Hill Road , Menlo Park , California 94025 , United States
| | - Aniruddha Deb
- Department of Chemistry , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States.,Department of Biophysics , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States
| | - James M Glownia
- Linac Coherent Light Source , SLAC National Accelerator Laboratory , 2575 Sand Hill Road , Menlo Park , California 94025 , United States
| | - Danielle L Sofferman
- Program in Applied Physics , University of Michigan , 450 Church Street , Ann Arbor , Michigan 48109-1040 , United States
| | - Sanghoon Song
- Linac Coherent Light Source , SLAC National Accelerator Laboratory , 2575 Sand Hill Road , Menlo Park , California 94025 , United States
| | - Pawel M Kozlowski
- Department of Chemistry , University of Louisville , 2320 South Brook Street , Louisville , Kentucky 40292 , United States
| | - Kevin J Kubarych
- Department of Chemistry , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States.,Department of Biophysics , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States
| | - James E Penner-Hahn
- Department of Chemistry , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States.,Department of Biophysics , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States
| | - Roseanne J Sension
- Department of Chemistry , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States.,Department of Physics , University of Michigan , 450 Church Street , Ann Arbor , Michigan 48109-1040 , United States.,Department of Biophysics , University of Michigan , 930 N. University Ave. , Ann Arbor , Michigan 48109-1055 , United States
| |
Collapse
|
10
|
Lukinović V, Woodward JR, Marrafa TC, Shanmugam M, Heyes DJ, Hardman SJO, Scrutton NS, Hay S, Fielding AJ, Jones AR. Photochemical Spin Dynamics of the Vitamin B 12 Derivative, Methylcobalamin. J Phys Chem B 2019; 123:4663-4672. [PMID: 31081330 DOI: 10.1021/acs.jpcb.9b01969] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Derivatives of vitamin B12 are six-coordinate cobalt corrinoids found in humans, other animals, and microorganisms. By acting as enzymatic cofactors and photoreceptor chromophores, they serve vital metabolic and photoprotective functions. Depending on the context, the chemical mechanisms of the biologically active derivatives of B12-methylcobalamin (MeCbl) and 5'-deoxyadenosylcobalamin (AdoCbl)-can be very different from one another. The extent to which this chemistry is tuned by the upper axial ligand, however, is not yet clear. Here, we have used a combination of time-resolved Fourier transform-electron paramagnetic resonance (FT-EPR), magnetic field effect experiments, and spin dynamic simulations to reveal that the upper axial ligand alone only results in relatively minor changes to the photochemical spin dynamics of B12. By studying the photolysis of MeCbl, we find that, similar to AdoCbl, the initial (or "geminate") radical pairs (RPs) are born predominantly in the singlet spin state and thus originate from singlet excited-state precursors. This is in contrast to the triplet RPs and precursors proposed previously. Unlike AdoCbl, the extent of geminate recombination is limited following MeCbl photolysis, resulting in significant distortions to the FT-EPR signal caused by polarization from spin-correlated methyl-methyl radical "f-pairs" formed following rapid diffusion. Despite the photophysical mechanism that precedes photolysis of MeCbl showing wavelength dependence, the subsequent spin dynamics appear to be largely independent of excitation wavelength, again similar to AdoCbl. Our data finally provide clarity to what in the literature to date has been a confused and contradictory picture. We conclude that, although the upper axial position of MeCbl and AdoCbl does impact their reactivity to some extent, the remarkable biochemical diversity of these fascinating molecules is most likely a result of tuning by their protein environment.
Collapse
Affiliation(s)
- Valentina Lukinović
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | - Jonathan R Woodward
- Graduate School of Arts and Sciences , The University of Tokyo , 3-8-1 Komaba , Meguro-ku, Tokyo 153-8902 , Japan
| | - Teresa C Marrafa
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | - Muralidharan Shanmugam
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | - Derren J Heyes
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | - Samantha J O Hardman
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | - Nigel S Scrutton
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | - Sam Hay
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| | | | - Alex R Jones
- Manchester Institute of Biotechnology , The University of Manchester , 131 Princess Street , Manchester M1 7DN , U.K
| |
Collapse
|
11
|
Toda MJ, Lodowski P, Mamun AA, Jaworska M, Kozlowski PM. Photolytic properties of the biologically active forms of vitamin B12. Coord Chem Rev 2019. [DOI: 10.1016/j.ccr.2018.12.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
12
|
Mamun AA, Toda MJ, Lodowski P, Kozlowski PM. Photolytic Cleavage of Co–C Bond in Coenzyme B12-Dependent Glutamate Mutase. J Phys Chem B 2019; 123:2585-2598. [DOI: 10.1021/acs.jpcb.8b07547] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Abdullah Al Mamun
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Megan J. Toda
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Pawel M. Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| |
Collapse
|
13
|
Ghosh AP, Mamun AA, Kozlowski PM. How does the mutation in the cap domain of methylcobalamin-dependent methionine synthase influence the photoactivation of the Co–C bond? Phys Chem Chem Phys 2019; 21:20628-20640. [DOI: 10.1039/c9cp01849b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The topology of the S1 PES is modulated by introducing a mutation at the F708 position. The mutation influences the photoactivation of the Co–C bond by decreasing the rate of geminate recombination and altering the rate of radical pair formation.
Collapse
|
14
|
Ghosh AP, Mamun AA, Lodowski P, Jaworska M, Kozlowski PM. Mechanism of the photo-induced activation of Co C bond in methylcobalamin-dependent methionine synthase. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2018; 189:306-317. [DOI: 10.1016/j.jphotobiol.2018.09.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Revised: 09/12/2018] [Accepted: 09/18/2018] [Indexed: 11/26/2022]
|
15
|
Vaid FH, Zahid S, Faiyaz A, Qadeer K, Gul W, Anwar Z, Ahmad I. Photolysis of methylcobalamin in aqueous solution: A kinetic study. J Photochem Photobiol A Chem 2018. [DOI: 10.1016/j.jphotochem.2018.05.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
16
|
Abstract
This Perspective provides the first detailed overview of the photoresponse of vitamin B12 and its derivatives, from the early, photophysical events to the burgeoning area of B12-dependent photobiology.
Collapse
Affiliation(s)
- Alex R. Jones
- School of Chemistry
- Photon Science Institute and Manchester Institute of Biotechnology
- The University of Manchester
- Manchester
- UK
| |
Collapse
|
17
|
Miller NA, Wiley TE, Spears KG, Ruetz M, Kieninger C, Kräutler B, Sension RJ. Toward the Design of Photoresponsive Conditional Antivitamins B12: A Transient Absorption Study of an Arylcobalamin and an Alkynylcobalamin. J Am Chem Soc 2016; 138:14250-14256. [DOI: 10.1021/jacs.6b05299] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Nicholas A. Miller
- Department
of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Theodore E. Wiley
- Department
of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Kenneth G. Spears
- Department
of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Markus Ruetz
- Institute of Organic Chemistry & Center for Molecular Biosciences, University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria
| | - Christoph Kieninger
- Institute of Organic Chemistry & Center for Molecular Biosciences, University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria
| | - Bernhard Kräutler
- Institute of Organic Chemistry & Center for Molecular Biosciences, University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria
| | - Roseanne J. Sension
- Department
of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| |
Collapse
|
18
|
Andruniów T, Lodowski P, Garabato BD, Jaworska M, Kozlowski PM. The role of spin-orbit coupling in the photolysis of methylcobalamin. J Chem Phys 2016; 144:124305. [DOI: 10.1063/1.4943184] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Affiliation(s)
- Tadeusz Andruniów
- Department of Chemistry, Advanced Materials Engineering and Modelling Group, Wroclaw University of Technology, 50-370 Wroclaw, Poland
| | - Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Brady D. Garabato
- Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40292, USA
| | - Maria Jaworska
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Pawel M. Kozlowski
- Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40292, USA
- Department of Food Sciences, Medical University of Gdansk, Al. Gen. J. Hallera 107, 80-416 Gdansk, Poland
| |
Collapse
|
19
|
Kozlowski PM, Garabato BD, Lodowski P, Jaworska M. Photolytic properties of cobalamins: a theoretical perspective. Dalton Trans 2016; 45:4457-70. [PMID: 26865262 DOI: 10.1039/c5dt04286k] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
This Perspective Article highlights recent theoretical developments, and summarizes the current understanding of the photolytic properties of cobalamins from a computational point of view. The primary focus is on two alkyl cobalamins, methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), as well as two non-alkyl cobalamins, cyanocobalamin (CNCbl) and hydroxocobalamin (HOCbl). Photolysis of alkyl cobalamins involves low-lying singlet excited states where photodissociation of the Co-C bond leads to formation of singlet-born alkyl/cob(ii)alamin radical pairs (RPs). Potential energy surfaces (PESs) associated with cobalamin low-lying excited states as functions of both axial bonds, provide the most reliable tool for initial analysis of their photochemical and photophysical properties. Due to the complexity, and size limitations associated with the cobalamins, the primary method for calculating ground state properties is density functional theory (DFT), while time-dependent DFT (TD-DFT) is used for electronically excited states. For alkyl cobalamins, energy pathways on the lowest singlet surface, connecting metal-to-ligand charge transfer (MLCT) and ligand field (LF) minima, can be associated with photo-homolysis of the Co-C bond observed experimentally. Additionally, energy pathways between minima and seams associated with crossing of S1/S0 surfaces, are the most efficient for internal conversion (IC) to the ground state. Depending on the specific cobalamin, such IC may involve simultaneous elongation of both axial bonds (CNCbl), or detachment of axial base followed by corrin ring distortion (MeCbl). The possibility of intersystem crossing, and the formation of triplet RPs is also discussed based on Landau-Zener theory.
Collapse
Affiliation(s)
- Pawel M Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
| | | | | | | |
Collapse
|
20
|
Rodgers ZL, Shell TA, Brugh AM, Nowotarski HL, Forbes MDE, Lawrence DS. Fluorophore Assisted Photolysis of Thiolato-Cob(III)alamins. Inorg Chem 2016; 55:1962-9. [PMID: 26848595 DOI: 10.1021/acs.inorgchem.5b02036] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Cobalamins are known to react with thiols to yield stable β-axial Co(III)-S bonded thiolato-cobalamin complexes. However, in stark contrast to the Co-C bond in alkylcobalamins, the photolability of the Co-S bond in thiolato-cobalamins remains undetermined. We have investigated the photolysis of N-acetylcysteinyl cob(III)alamin at several wavelengths within the ultraviolet and visible spectrum. To aid in photolysis, we show that attaching fluorophore "antennae" to the cobalamin scaffold can improve photolytic efficiency by up to an order of magnitude. Additionally, electron paramagnetic resonance confirms previous conjectures that the photolysis of thiolato-cobalamins at wavelengths as long as 546 nm produces thiyl radicals.
Collapse
Affiliation(s)
- Zachary L Rodgers
- Department of Chemistry, ‡Division of Chemical Biology and Medicinal Chemistry, and §Department of Pharmacology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| | - Thomas A Shell
- Department of Chemistry, ‡Division of Chemical Biology and Medicinal Chemistry, and §Department of Pharmacology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| | - Alexander M Brugh
- Department of Chemistry, ‡Division of Chemical Biology and Medicinal Chemistry, and §Department of Pharmacology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| | - Hannah L Nowotarski
- Department of Chemistry, ‡Division of Chemical Biology and Medicinal Chemistry, and §Department of Pharmacology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| | - Malcolm D E Forbes
- Department of Chemistry, ‡Division of Chemical Biology and Medicinal Chemistry, and §Department of Pharmacology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| | - David S Lawrence
- Department of Chemistry, ‡Division of Chemical Biology and Medicinal Chemistry, and §Department of Pharmacology, University of North Carolina , Chapel Hill, North Carolina 27599, United States
| |
Collapse
|
21
|
Lodowski P, Jaworska M, Garabato BD, Kozlowski PM. Mechanism of Co–C Bond Photolysis in Methylcobalamin: Influence of Axial Base. J Phys Chem A 2015; 119:3913-28. [DOI: 10.1021/jp5120674] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Piotr Lodowski
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Brady D. Garabato
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Pawel M. Kozlowski
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| |
Collapse
|
22
|
|
23
|
Rury AS, Wiley TE, Sension RJ. Energy cascades, excited state dynamics, and photochemistry in cob(III)alamins and ferric porphyrins. Acc Chem Res 2015; 48:860-7. [PMID: 25741574 DOI: 10.1021/ar5004016] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Porphyrins and the related chlorins and corrins contain a cyclic tetrapyrrole with the ability to coordinate an active metal center and to perform a variety of functions exploiting the oxidation state, reactivity, and axial ligation of the metal center. These compounds are used in optically activated applications ranging from light harvesting and energy conversion to medical therapeutics and photodynamic therapy to molecular electronics, spintronics, optoelectronic thin films, and optomagnetics. Cobalt containing corrin rings extend the range of applications through photolytic cleavage of a unique axial carbon-cobalt bond, permitting spatiotemporal control of drug delivery. The photochemistry and photophysics of cyclic tetrapyrroles are controlled by electronic relaxation dynamics including internal conversion and intersystem crossing. Typically the electronic excitation cascades through ring centered ππ* states, ligand to metal charge transfer (LMCT) states, metal to ligand charge transfer (MLCT) states, and metal centered states. Ultrafast transient absorption spectroscopy provides a powerful tool for the investigation of the electronic state dynamics in metal containing tetrapyrroles. The UV-visible spectrum is sensitive to the oxidation state, electronic configuration, spin state, and axial ligation of the central metal atom. Ultrashort broadband white light probes spanning the range from 270 to 800 nm, combined with tunable excitation pulses, permit the detailed unravelling of the time scales involved in the electronic energy cascade. State-of-the-art theoretical calculations provide additional insight required for precise assignment of the states. In this Account, we focus on recent ultrafast transient absorption studies of ferric porphyrins and corrin containing cob(III)alamins elucidating the electronic states responsible for ultrafast energy cascades, excited state dynamics, and the resulting photoreactivity or photostability of these compounds. Iron tetraphenyl porphyrin chloride (Fe((III))TPPCl) exhibits picosecond decay to a metal centered d → d* (4)T state. This state decays on a ca. 16 ps time scale in room temperature solution but persists for much longer in a cryogenic glass. The photoreactivity of the (4)T state may lead to novel future applications for these compounds. In contrast, the nonplanar cob(III)alamins contain two axial ligands to the central cobalt atom. The upper axial ligand can be an alkyl group as in the two biologically active coenzymes or a nonalkyl ligand such as -CN in cyanocobalamin (vitamin B12) or -OH in hydroxocobalamin. The electronic structure, energy cascade, and bond cleavage of these compounds is sensitive to the details of the axial ligand. Nonalkylcobalamins exhibit ultrafast internal conversion to a low-lying state of metal to ligand or ligand to metal charge transfer character. The compounds are generally photostable with ground state recovery complete on a time scale of 2-7 ps in room temperature aqueous solution. Alkylcobalamins exhibit ultrafast internal conversion to an S1 state of d/π → π* character. Most compounds undergo bond cleavage from this state with near unit quantum yield within ∼100 ps. Recent theoretical calculations provide a potential energy surface accounting for these observations. Conformation dependent mixing of the corrin π and cobalt d orbitals plays a significant role in the observed photochemistry and photophysics.
Collapse
Affiliation(s)
- Aaron S. Rury
- Department of Chemistry and
Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Theodore E. Wiley
- Department of Chemistry and
Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Roseanne J. Sension
- Department of Chemistry and
Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| |
Collapse
|
24
|
Lodowski P, Jaworska M, Andruniów T, Garabato BD, Kozlowski PM. Mechanism of Co–C Bond Photolysis in the Base-On Form of Methylcobalamin. J Phys Chem A 2014; 118:11718-34. [DOI: 10.1021/jp508513p] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Piotr Lodowski
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Tadeusz Andruniów
- Institute
of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland
| | - Brady D. Garabato
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Pawel M. Kozlowski
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| |
Collapse
|
25
|
Freitag L, González L. Theoretical spectroscopy and photodynamics of a ruthenium nitrosyl complex. Inorg Chem 2014; 53:6415-26. [PMID: 24745977 DOI: 10.1021/ic500283y] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Photoactive transition-metal nitrosyl complexes are particularly interesting as potential drugs that deliver nitric oxide (NO) upon UV-light irradiation to be used, e.g., in photodynamic therapy. It is well-recognized that quantum-chemical calculations can guide the rational design and synthesis of molecules with specific functions. In this contribution, it is shown how electronic structure calculations and dynamical simulations can provide a unique insight into the photodissociation mechanism of NO. Exemplarily, [Ru(PaPy3)(NO)](2+) is investigated in detail, as a prototype of a particularly promising class of photoactive metal nitrosyl complexes. The ability of time-dependent density functional theory (TD-DFT) to obtain reliable excited-state energies compared with more sophisticated multiconfigurational spin-corrected calculations is evaluated. Moreover, a TD-DFT-based trajectory surface-hopping molecular dynamics study is employed to reveal the details of the radiationless decay of the molecule via internal conversion and intersystem crossing. Calculations show that the ground state of [Ru(PaPy3)(NO)](2+) includes a significant admixture of the Ru(III)(NO)(0) electronic configuration, in contrast to the previously postulated Ru(II)(NO)(+) structure of similar metal nitrosyls. Moreover, the lowest singlet and triplet excited states populate the antibonding metal d → πNO* orbitals, favoring NO dissociation. Molecular dynamics show that intersystem crossing is ultrafast (<10 fs) and dissociation is initiated in less than 50 fs. The competing relaxation to the lowest S1 singlet state takes place in less than 100 fs and thus competes with NO dissociation, which mostly takes place in the higher-lying excited triplet states. All of these processes are accompanied by bending of the NO ligand, which is not confined to any particular state.
Collapse
Affiliation(s)
- Leon Freitag
- Institut für theoretische Chemie, Universität Wien , Währinger Straße 17, 1090 Vienna, Austria
| | | |
Collapse
|
26
|
Liu H, Kornobis K, Lodowski P, Jaworska M, Kozlowski PM. TD-DFT insight into photodissociation of the Co-C bond in coenzyme B12. Front Chem 2014; 1:41. [PMID: 24790969 PMCID: PMC3982521 DOI: 10.3389/fchem.2013.00041] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Accepted: 12/24/2013] [Indexed: 11/30/2022] Open
Abstract
Coenzyme B12 (AdoCbl) is one of the most biologically active forms of vitamin B12, and continues to be a topic of active research interest. The mechanism of Co-C bond cleavage in AdoCbl, and the corresponding enzymatic reactions are however, not well understood at the molecular level. In this work, time-dependent density functional theory (TD-DFT) has been applied to investigate the photodissociation of coenzyme B12. To reduce computational cost, while retaining the major spectroscopic features of AdoCbl, a truncated model based on ribosylcobalamin (RibCbl) was used to simulate Co-C photodissociation. Equilibrium geometries of RibCbl were obtained by optimization at the DFT/BP86/TZVP level of theory, and low-lying excited states were calculated by TD-DFT using the same functional and basis set. The calculated singlet states, and absorption spectra were simulated in both the gas phase, and water, using the polarizable continuum model (PCM). Both spectra were in reasonable agreement with experimental data, and potential energy curves based on vertical excitations were plotted to explore the nature of Co-C bond dissociation. It was found that a repulsive 3(σCo−C → σ*Co−C) triplet state became dissociative at large Co-C bond distance, similar to a previous observation for methylcobalamin (MeCbl). Furthermore, potential energy surfaces (PESs) obtained as a function of both Co-CRib and Co-NIm distances, identify the S1 state as a key intermediate generated during photoexcitation of RibCbl, attributed to a mixture of a metal-to-ligand charge transfer (MLCT) and a σ bonding-ligand charge transfer (SBLCT) states.
Collapse
Affiliation(s)
- Hui Liu
- Department of Chemistry, University of Louisville Louisville, KY, USA
| | - Karina Kornobis
- Department of Chemistry, University of Louisville Louisville, KY, USA
| | - Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia Katowice, Poland
| | - Maria Jaworska
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia Katowice, Poland
| | - Pawel M Kozlowski
- Department of Chemistry, University of Louisville Louisville, KY, USA
| |
Collapse
|
27
|
Photolytic cleavage of Co–C bond: A mechanistic study for the formation of solvent coordinated cobalt(II) complex. J Organomet Chem 2014. [DOI: 10.1016/j.jorganchem.2013.09.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
28
|
Bertini L, Bruschi M, Cosentino U, Greco C, Moro G, Zampella G, De Gioia L. Quantum mechanical methods for the investigation of metalloproteins and related bioinorganic compounds. Methods Mol Biol 2014; 1122:207-68. [PMID: 24639262 DOI: 10.1007/978-1-62703-794-5_14] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
It is well known that transition metal ions are often bound to proteins, conveying very specific functional properties. In fact, metalloproteins play crucial biological roles in the transport and activation of small molecules such as H2, O2, and N2, as well as in several other biochemical processes. However, even if the presence of transition metals in the active site of proteins allows a very rich biochemistry, the experimental disclosure of structure-activity relationships in metalloproteins is generally difficult exactly because of the presence of transition metals, which are intrinsically characterized by a very versatile and often elusive chemistry. For this reason, computational methods are becoming very popular tools in the characterization of metalloproteins. In particular, since computing power is becoming less and less expensive, due to the continuous technological development of CPUs, the computational tools suited to investigate metalloproteins are becoming more accessible and therefore more commonly used also in molecular biology and biochemistry laboratories. Here, we present the main procedures and computational methods based on quantum mechanics, which are commonly used to study the structural, electronic, and reactivity properties of metalloproteins and related bioinspired compounds, with a specific focus on the practical and technical aspects that must be generally tackled to properly study such biomolecular systems.
Collapse
Affiliation(s)
- Luca Bertini
- Department of Environmental Science, University of Milano-Bicocca, Milan, Italy
| | | | | | | | | | | | | |
Collapse
|
29
|
Can the local enzyme scaffold act as an H-donor for a Co(I)H bond formation? The curious case of methionine synthase-bound cob(I)alamin. J Inorg Biochem 2013; 126:26-34. [DOI: 10.1016/j.jinorgbio.2013.04.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2012] [Revised: 04/19/2013] [Accepted: 04/20/2013] [Indexed: 11/19/2022]
|
30
|
DFT Studies of Trans and Cis Influences in the Homolysis of the Co–C Bond in Models of the Alkylcobalamins. J Phys Chem A 2013; 117:3057-68. [DOI: 10.1021/jp311788t] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
31
|
Pan L, Bian W. Theoretical study on the photodegradation mechanism of nona-BDEs in methanol. Chemphyschem 2013; 14:1264-71. [PMID: 23426982 DOI: 10.1002/cphc.201200952] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Indexed: 11/07/2022]
Abstract
Polybrominated diphenyl ethers (PBDEs) have received special environmental concern due to their potential toxicity to humans and wildlife worldwide, however, it is difficult to reveal their dominant photochemical degradation pathways by experiment. We explored the reaction mechanisms of photochemical degradation-debromination of three nona-BDEs in methanol using theoretical calculations, in which time-dependent density functional theory (TDDFT) combined with the polarizable continuum (PCM) model is applied. The selectivity of debromination was studied, and the major octa-BDE products photochemically debrominated from nona-BDEs were identified. We find that the debromination reaction results from the electronic transitions from π to σ* orbitals when nona-BDEs are exposed to UV-light in the sunlight region, at which point the two low-lying excited states for each nona-BDE are πσ*(5Br) and πσ*(4Br), which correlate to the σ* orbitals located on the penta-Br and tetra-Br substituted phenyls, respectively. Our calculations indicate that each nona-BDE may degrade to form three kinds of octa-BDE products via the πσ*(5Br) state, whereas only one kind of octa-BDEs can be formed via the πσ*(4Br) state. Our calculations can interpret the recent experiments successfully.
Collapse
Affiliation(s)
- Lu Pan
- Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China
| | | |
Collapse
|
32
|
Kornobis K, Kumar N, Lodowski P, Jaworska M, Piecuch P, Lutz JJ, Wong BM, Kozlowski PM. Electronic structure of the S1state in methylcobalamin: Insight from CASSCF/MC-XQDPT2, EOM-CCSD, and TD-DFT calculations. J Comput Chem 2013; 34:987-1004. [DOI: 10.1002/jcc.23204] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Revised: 10/25/2012] [Accepted: 11/19/2012] [Indexed: 11/12/2022]
|
33
|
Pápai M, Vankó G, de Graaf C, Rozgonyi T. Theoretical Investigation of the Electronic Structure of Fe(II) Complexes at Spin-State Transitions. J Chem Theory Comput 2012; 9:509-519. [PMID: 25821416 PMCID: PMC4358629 DOI: 10.1021/ct300932n] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Indexed: 01/30/2023]
Abstract
![]()
The electronic structure relevant to low spin (LS)↔high
spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+ (1) (tz = 1H-tetrazole), [Fe(bipy)3]2+ (2) (bipy = 2,2′-bipyridine), and [Fe(terpy)2]2+ (3) (terpy = 2,2′:6′,2″-terpyridine)
complexes have been actively studied experimentally, and with their
respective mono-, bi-, and tridentate ligands, they constitute a comprehensive
set for theoretical case studies. The methods in this work include
density functional theory (DFT), time-dependent DFT (TD-DFT), and
multiconfigurational second order perturbation theory (CASPT2). We
determine the structural parameters as well as the energy splitting
of the LS–HS states (ΔEHL) applying the above methods and comparing their performance. We
also determine the potential energy curves representing the ground
and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The
results indicate that while DFT is well suited for the prediction
of structural parameters, an accurate multiconfigurational approach
is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement
is found between the TD-DFT and CASPT2 potential energy curves. Although
the TD-DFT results might differ in some respect (in our case, we found
a discrepancy at the triplet states), our results suggest that this
approach, with due care, is very promising as an alternative for the
very expensive CASPT2 method. Finally, the two-dimensional (2D) potential
energy surfaces above the plane spanned by the two relevant configuration
coordinates in [Fe(terpy)2]2+ were computed
at both the DFT and CASPT2 levels. These 2D surfaces indicate that
the singlet–triplet and triplet–quintet states are separated
along different coordinates, i.e., different vibration modes. Our
results confirm that in contrast to the case of complexes with mono-
and bidentate ligands, the singlet–quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration
coordinate.
Collapse
Affiliation(s)
- Mátyás Pápai
- Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary
| | - György Vankó
- Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary
| | - Coen de Graaf
- Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n, 43007 Tarragona, Spain ; Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010, Barcelona, Spain
| | - Tamás Rozgonyi
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1025 Budapest, Pusztaszeri út 59-67, Hungary
| |
Collapse
|
34
|
|
35
|
Navizet I, Perry CB, Govender PP, Marques HM. cis Influence in Models of Cobalt Corrins by DFT and TD-DFT Studies. J Phys Chem B 2012; 116:8836-45. [DOI: 10.1021/jp304007a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Isabelle Navizet
- Molecular Sciences
Institute, School of Chemistry, University of Witwatersrand, P.O. Wits, Johannesburg, 2050 South
Africa
| | - Christopher B. Perry
- Molecular Sciences
Institute, School of Chemistry, University of Witwatersrand, P.O. Wits, Johannesburg, 2050 South
Africa
| | - Penny P. Govender
- Molecular Sciences
Institute, School of Chemistry, University of Witwatersrand, P.O. Wits, Johannesburg, 2050 South
Africa
- Department
of Applied
Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein, Johannesburg, 2028 South Africa
| | - Helder M. Marques
- Molecular Sciences
Institute, School of Chemistry, University of Witwatersrand, P.O. Wits, Johannesburg, 2050 South
Africa
| |
Collapse
|
36
|
Eisenberg AS, Likhtina IV, Znamenskiy VS, Birke RL. Electronic Spectroscopy and Computational Studies of Glutathionylco(III)balamin. J Phys Chem A 2012; 116:6851-69. [DOI: 10.1021/jp301294x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Azaria S. Eisenberg
- Department of Chemistry, The City
College of New York,
and The Graduate School and University Center, The City University of New York, New York, New York 10031, United
States
| | - Iya V. Likhtina
- Department of Chemistry, The City
College of New York,
and The Graduate School and University Center, The City University of New York, New York, New York 10031, United
States
| | - Vasiliy S. Znamenskiy
- Department of Chemistry, The City
College of New York,
and The Graduate School and University Center, The City University of New York, New York, New York 10031, United
States
| | - Ronald L. Birke
- Department of Chemistry, The City
College of New York,
and The Graduate School and University Center, The City University of New York, New York, New York 10031, United
States
| |
Collapse
|
37
|
Kozlowski PM, Kumar M, Piecuch P, Li W, Bauman NP, Hansen JA, Lodowski P, Jaworska M. The Cobalt–Methyl Bond Dissociation in Methylcobalamin: New Benchmark Analysis Based on Density Functional Theory and Completely Renormalized Coupled-Cluster Calculations. J Chem Theory Comput 2012; 8:1870-94. [DOI: 10.1021/ct300170y] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Pawel M. Kozlowski
- Department of Chemistry, University
of Louisville,
2320 South Brook St., Louisville, Kentucky 40292, United States
| | - Manoj Kumar
- Department of Chemistry, University
of Louisville,
2320 South Brook St., Louisville, Kentucky 40292, United States
| | - Piotr Piecuch
- Department of Chemistry, Michigan State University,
578 S. Shaw Lane, East Lansing, Michigan 48824, United States
| | - Wei Li
- Department of Chemistry, Michigan State University,
578 S. Shaw Lane, East Lansing, Michigan 48824, United States
| | - Nicholas P. Bauman
- Department of Chemistry, Michigan State University,
578 S. Shaw Lane, East Lansing, Michigan 48824, United States
| | - Jared A. Hansen
- Department of Chemistry, Michigan State University,
578 S. Shaw Lane, East Lansing, Michigan 48824, United States
| | - Piotr Lodowski
- Institute
of Chemistry, University of Silesia, Szkolna
9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Institute
of Chemistry, University of Silesia, Szkolna
9, PL-40 006 Katowice, Poland
| |
Collapse
|
38
|
Zheng W, Wu S, Zhao S, Geng Y, Jin J, Su Z, Fu Q. Carbonyl Amine/Schiff Base Ligands in Manganese Complexes: Theoretical Study on the Mechanism, Capability of NO Release. Inorg Chem 2012; 51:3972-80. [DOI: 10.1021/ic2011953] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Weili Zheng
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| | - Shuixing Wu
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| | - Shanshan Zhao
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| | - Yun Geng
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| | - Junling Jin
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| | - Zhongmin Su
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| | - Qiang Fu
- Institute of Functional Material Chemistry, Faculty
of Chemistry, Northeast Normal University, Changchun 130024, Jilin, People’s Republic of China
| |
Collapse
|
39
|
Fry NL, Mascharak PK. Photolability of NO in designed metal nitrosyls with carboxamido-N donors: a theoretical attempt to unravel the mechanism. Dalton Trans 2012; 41:4726-35. [PMID: 22388493 DOI: 10.1039/c2dt12470j] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
During the past few years, photoactive metal nitrosyls (NO complexes of metals) have drawn attention as potential drugs for delivery of nitric oxide (NO) to biological targets under the control of light. Major success in this area has been achieved with designed metal nitrosyls derived from ligands that contain carboxamide group(s). A number of iron, manganese and ruthenium {MNO}(6) nitrosyls of such kind exhibit excellent NO photolability under low-power visible and near-IR light. The results of theoretical studies on these NO-donors have provided insight into (a) the electronic transitions that lead to photorelease of NO and (b) the structural features of the ligands that dictate the sensitivity of the nitrosyls to light of specific wavelengths. In addition, the results have afforded clear understanding of the electronic configurations of the various nitrosyls. This article highlights these results in a coherent manner. Good matches between the predicted and observed spectral features and NO photolability strongly suggest that theoretical studies should be an integral part of the smart design of such NO-donors in the future research.
Collapse
Affiliation(s)
- Nicole L Fry
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA
| | | |
Collapse
|
40
|
Merkle AC, Fry NL, Mascharak PK, Lehnert N. Mechanism of NO Photodissociation in Photolabile Manganese–NO Complexes with Pentadentate N5 Ligands. Inorg Chem 2011; 50:12192-203. [DOI: 10.1021/ic201967f] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Anna C. Merkle
- Department of Chemistry, University of Michigan, 930 North University Avenue,
Ann Arbor, Michigan 48109-1055, United States
| | - Nicole L. Fry
- Department of Chemistry and
Biochemistry, University of California,
Santa Cruz, California 95064, United States
| | - Pradip K. Mascharak
- Department of Chemistry and
Biochemistry, University of California,
Santa Cruz, California 95064, United States
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, 930 North University Avenue,
Ann Arbor, Michigan 48109-1055, United States
| |
Collapse
|
41
|
Lodowski P, Jaworska M, Kornobis K, Andruniów T, Kozlowski PM. Electronic and Structural Properties of Low-lying Excited States of Vitamin B12. J Phys Chem B 2011; 115:13304-19. [DOI: 10.1021/jp200911y] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Karina Kornobis
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Tadeusz Andruniów
- Institute of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland
| | - Pawel M. Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| |
Collapse
|
42
|
Solheim H, Kornobis K, Ruud K, Kozlowski PM. Electronically Excited States of Vitamin B12 and Methylcobalamin: Theoretical Analysis of Absorption, CD, and MCD Data. J Phys Chem B 2010; 115:737-48. [DOI: 10.1021/jp109793r] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Harald Solheim
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø, 9037 Tromsø, Norway, and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Karina Kornobis
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø, 9037 Tromsø, Norway, and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Kenneth Ruud
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø, 9037 Tromsø, Norway, and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Pawel M. Kozlowski
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø, 9037 Tromsø, Norway, and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| |
Collapse
|
43
|
Peng J, Tang KC, McLoughlin K, Yang Y, Forgach D, Sension RJ. Ultrafast Excited-State Dynamics and Photolysis in Base-Off B12 Coenzymes and Analogues: Absence of the trans-Nitrogenous Ligand Opens a Channel for Rapid Nonradiative Decay. J Phys Chem B 2010; 114:12398-405. [DOI: 10.1021/jp104641u] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Jian Peng
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055
| | - Kuo-Chun Tang
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055
| | - Kaitlin McLoughlin
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055
| | - Yang Yang
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055
| | - Danika Forgach
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055
| | - Roseanne J. Sension
- Department of Chemistry and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1055
| |
Collapse
|
44
|
Jones AR, Woodward JR, Scrutton NS. Continuous wave photolysis magnetic field effect investigations with free and protein-bound alkylcobalamins. J Am Chem Soc 2010; 131:17246-53. [PMID: 19899795 DOI: 10.1021/ja9059238] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The activation of the Co-C bond in adenosylcobalamin-dependent enzymes generates a singlet-born Co(II)-adenosyl radical pair. Two of the salient questions regarding this process are: (1) What is the origin of the considerable homolysis rate enhancement achieved by this class of enzyme? (2) Are the reaction dynamics of the resultant radical pair sensitive to the application of external magnetic fields? Here, we present continuous wave photolysis magnetic field effect (MFE) data that reveal the ethanolamine ammonia lyase (EAL) active site to be an ideal microreactor in which to observe enhanced magnetic field sensitivity in the adenosylcobalamin radical pair. The observed field dependence is in excellent agreement with that calculated from published hyperfine couplings for the constituent radicals, and the magnitude of the MFE (<18%) is almost identical to that observed in a solvent containing 67% glycerol. Similar augmentation is not observed, however, in the equivalent experiments with EAL-bound methylcobalamin, where all field sensitivity observed in the free cofactor is washed out completely. Parallels are drawn between the latter case and the loss of field sensitivity in the EAL holoenzyme upon substrate binding (Jones et al. J. Am. Chem. Soc. 2007, 129, 15718-15727). Both are attributed to the rapid removal of the alkyl radical immediately after homolysis, such that there is inadequate radical pair recombination for the observation of field effects. Taken together, these results support the notion that rapid radical quenching, through the coupling of homolysis and hydrogen abstraction steps, and subsequent radical pair stabilization make a contribution to the observed rate acceleration of Co-C bond homolysis in adenosylcobalamin-dependent enzymes.
Collapse
Affiliation(s)
- Alex R Jones
- Manchester Interdisciplinary Biocentre and Faculty of Life Sciences, University of Manchester M1 7DN, United Kingdom
| | | | | |
Collapse
|