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Title: Synchrotron X-radiolysis of l -cysteine at the sulfur K-edge: Sulfurous products, experimental surprises, and dioxygen as an oxidoreductant

Abstract

In-situ inventory of sulfurous products from the sulfur K-edge synchrotron X-radiolysis of L-cysteine, in solid-phase and anaerobic (pH 5) and air-saturated (pH 5, pH 7, and pH 9) solutions without and with 40% glycerol is reported. Sequential K-edge X-ray Absorption Spectroscopic (XAS) spectra were acquired. L-cysteine degraded systematically in the X-ray beam. Radiolytic products were inventoried by fits using the XAS spectra of sulfur model compounds. Solid L-cysteine declined to 92% fraction after a single K-edge XAS scan. After six scans 60 % remained, accompanied by 14 % cystine, 16 % thioether, 5.4 % of elemental sulfur, and smaller fractions of more highly oxidized products. In air-saturated pH 5 solution, 73 % of L-cysteine remained after ten scans, with 2 % cystine and 19 % elemental sulfur. Oxidation increased with 40% glycerol, yielding 67 %, 5 % and 23 % fractions, respectively, after ten-scans. Higher pH solutions exhibited less radiolytic chemistry. All the reactivity followed first-order kinetics. The anaerobic experiment displayed two reaction phases, with sharp changes in kinetics and radiolytic chemistry. Unexpectedly, the radiolytic oxidation of L-cysteine was increased in anaerobic solution. After ten-scans only 60% of the L-cysteine remained, along with 17 % cystine, 22 % elemental sulfur, and traces of more highly oxidized products. A new aerobic reaction cycle is hypothesized, wherein dissolved dioxygen captures radiolytic H• or e$$-\atop{aq}$$, enters HO 2•/O 2•-, reductively quenches cysteine thiyl radical, and cycles back to O 2. This cycle is suggested to suppress the radiolytic production of cystine in aerobic solution.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [2];  [1]
  1. Stanford Univ., CA (United States). Dept. of Chemistry; SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Institutes of Health (NIH)
OSTI Identifier:
1499007
Grant/Contract Number:  
AC02-76SF00515; P41GM103393
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 150; Journal Issue: 10; Related Information: ftp://ftp.aip.org/epaps/journ_chem_phys/E-JCPSA6-150-029909; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; synchrotron radiolysis; sulfur K-edge; cysteine; dioxygen cycle

Citation Formats

Frank, Patrick, Sarangi, Ritimukta, Hedman, Britt, and Hodgson, Keith O. Synchrotron X-radiolysis of l -cysteine at the sulfur K-edge: Sulfurous products, experimental surprises, and dioxygen as an oxidoreductant. United States: N. p., 2019. Web. doi:10.1063/1.5079419.
Frank, Patrick, Sarangi, Ritimukta, Hedman, Britt, & Hodgson, Keith O. Synchrotron X-radiolysis of l -cysteine at the sulfur K-edge: Sulfurous products, experimental surprises, and dioxygen as an oxidoreductant. United States. doi:10.1063/1.5079419.
Frank, Patrick, Sarangi, Ritimukta, Hedman, Britt, and Hodgson, Keith O. Mon . "Synchrotron X-radiolysis of l -cysteine at the sulfur K-edge: Sulfurous products, experimental surprises, and dioxygen as an oxidoreductant". United States. doi:10.1063/1.5079419.
@article{osti_1499007,
title = {Synchrotron X-radiolysis of l -cysteine at the sulfur K-edge: Sulfurous products, experimental surprises, and dioxygen as an oxidoreductant},
author = {Frank, Patrick and Sarangi, Ritimukta and Hedman, Britt and Hodgson, Keith O.},
abstractNote = {In-situ inventory of sulfurous products from the sulfur K-edge synchrotron X-radiolysis of L-cysteine, in solid-phase and anaerobic (pH 5) and air-saturated (pH 5, pH 7, and pH 9) solutions without and with 40% glycerol is reported. Sequential K-edge X-ray Absorption Spectroscopic (XAS) spectra were acquired. L-cysteine degraded systematically in the X-ray beam. Radiolytic products were inventoried by fits using the XAS spectra of sulfur model compounds. Solid L-cysteine declined to 92% fraction after a single K-edge XAS scan. After six scans 60 % remained, accompanied by 14 % cystine, 16 % thioether, 5.4 % of elemental sulfur, and smaller fractions of more highly oxidized products. In air-saturated pH 5 solution, 73 % of L-cysteine remained after ten scans, with 2 % cystine and 19 % elemental sulfur. Oxidation increased with 40% glycerol, yielding 67 %, 5 % and 23 % fractions, respectively, after ten-scans. Higher pH solutions exhibited less radiolytic chemistry. All the reactivity followed first-order kinetics. The anaerobic experiment displayed two reaction phases, with sharp changes in kinetics and radiolytic chemistry. Unexpectedly, the radiolytic oxidation of L-cysteine was increased in anaerobic solution. After ten-scans only 60% of the L-cysteine remained, along with 17 % cystine, 22 % elemental sulfur, and traces of more highly oxidized products. A new aerobic reaction cycle is hypothesized, wherein dissolved dioxygen captures radiolytic H• or e$-\atop{aq}$, enters HO2•/O2•-, reductively quenches cysteine thiyl radical, and cycles back to O2. This cycle is suggested to suppress the radiolytic production of cystine in aerobic solution.},
doi = {10.1063/1.5079419},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 10,
volume = 150,
place = {United States},
year = {2019},
month = {3}
}

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Works referenced in this record:

X-Ray Interactions: Photoabsorption, Scattering, Transmission, and Reflection at E = 50-30,000 eV, Z = 1-92
journal, July 1993

  • Henke, B. L.; Gullikson, E. M.; Davis, J. C.
  • Atomic Data and Nuclear Data Tables, Vol. 54, Issue 2, p. 181-342
  • DOI: 10.1006/adnd.1993.1013