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

Subramanian, Ganesh; Zhang, Xiaoyi; Kodis, Gerdenis; Kong, Qingyu; Liu, Cunming; Chizmeshya, Andrew; Weierstall, Uwe; Spence, John

doi:10.1021/acs.jpclett.8b00083

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

Abstract

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:

^[1];

^[2]; Kodis, Gerdenis ^[1];

^[2]; Liu, Cunming ^[2]; Chizmeshya, Andrew ^[1]; Weierstall, Uwe ^[1]; Spence, John ^[1]

Arizona State Univ., Tempe, AZ (United States)
Argonne National Lab. (ANL), Argonne, IL (United States)

Publication Date:: 2018-03-06

Research Org.:: Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; National Science Foundation (NSF)

OSTI Identifier:: 1437278

Grant/Contract Number:: AC02-06CH11357

Resource 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

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Co-C; Xanes; coordination; fine structure; photolysis

Citation Formats


                    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., 2018. 
Web.  doi:10.1021/acs.jpclett.8b00083.

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                    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.  https://doi.org/10.1021/acs.jpclett.8b00083

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                    Subramanian, Ganesh, Zhang, Xiaoyi, Kodis, Gerdenis, Kong, Qingyu, Liu, Cunming, Chizmeshya, Andrew, Weierstall, Uwe, and Spence, John. Tue .  
"Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy".  United States.  https://doi.org/10.1021/acs.jpclett.8b00083.  https://www.osti.gov/servlets/purl/1437278.

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@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}

}

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Figures / Tables:

Figure 1: (a) Pre-laser exposure (solid black) and post-laser exposure (dotted black) steady-state XANES experimental spectrum of MeCbl. (b) Reference steady-state XANES experimental spectra of MeCbl (solid black) and OHCbl (dotted black). Labels for fine-structure features, (A) Pre-edge peak, (B) edge-kink, (C) rising absorption edge, (D) Shoulder peak, (E) Mainmore »

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