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Title: Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy

Cobalt-carbon bond cleavage is crucial to most natural and synthetic applications of the cobalamin class of compounds, and here we present the first direct electronic and geometric structural characteristics of intermediates formed following photoexcitation of methylcobalamin (MeCbl) using time-resolved X-ray absorption spectroscopy (XAS). We catch transients corresponding to two intermediates, in the hundreds of picoseconds and a few microseconds. Highlights of the picosecond intermediate, which is reduced in comparison to the ground state, are elongation of the upper axial Co-C bond and relaxation of the corrin ring. This is not so with the recombining photocleaved products captured at a few microseconds, where the Co-C bond almost (yet not entirely) reverts to its ground state configuration and a substantially elongated lower axial Co-N Im bond is observed. In conclusion, the reduced cobalt site here confirms formation of methyl radical as the photoproduct.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [2] ;  [2] ;  [1] ;  [1] ;  [1]
  1. Arizona State Univ., Tempe, AZ (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry Letters
Additional Journal Information:
Journal Volume: 9; Journal Issue: 7; Journal ID: ISSN 1948-7185
Publisher:
American Chemical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Co-C; Xanes; coordination; fine structure; photolysis
OSTI Identifier:
1437278

Subramanian, Ganesh, Zhang, Xiaoyi, Kodis, Gerdenis, Kong, Qingyu, Liu, Cunming, Chizmeshya, Andrew, Weierstall, Uwe, and Spence, John. Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy. United States: N. p., Web. doi:10.1021/acs.jpclett.8b00083.
Subramanian, Ganesh, Zhang, Xiaoyi, Kodis, Gerdenis, Kong, Qingyu, Liu, Cunming, Chizmeshya, Andrew, Weierstall, Uwe, & Spence, John. Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy. United States. doi:10.1021/acs.jpclett.8b00083.
Subramanian, Ganesh, Zhang, Xiaoyi, Kodis, Gerdenis, Kong, Qingyu, Liu, Cunming, Chizmeshya, Andrew, Weierstall, Uwe, and Spence, John. 2018. "Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy". United States. doi:10.1021/acs.jpclett.8b00083.
@article{osti_1437278,
title = {Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy},
author = {Subramanian, Ganesh and Zhang, Xiaoyi and Kodis, Gerdenis and Kong, Qingyu and Liu, Cunming and Chizmeshya, Andrew and Weierstall, Uwe and Spence, John},
abstractNote = {Cobalt-carbon bond cleavage is crucial to most natural and synthetic applications of the cobalamin class of compounds, and here we present the first direct electronic and geometric structural characteristics of intermediates formed following photoexcitation of methylcobalamin (MeCbl) using time-resolved X-ray absorption spectroscopy (XAS). We catch transients corresponding to two intermediates, in the hundreds of picoseconds and a few microseconds. Highlights of the picosecond intermediate, which is reduced in comparison to the ground state, are elongation of the upper axial Co-C bond and relaxation of the corrin ring. This is not so with the recombining photocleaved products captured at a few microseconds, where the Co-C bond almost (yet not entirely) reverts to its ground state configuration and a substantially elongated lower axial Co-NIm bond is observed. In conclusion, the reduced cobalt site here confirms formation of methyl radical as the photoproduct.},
doi = {10.1021/acs.jpclett.8b00083},
journal = {Journal of Physical Chemistry Letters},
number = 7,
volume = 9,
place = {United States},
year = {2018},
month = {3}
}