skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Photochemically Generated Thiyl Free Radicals Observed by X-ray Absorption Spectroscopy

Abstract

Sulfur-based thiyl radicals are known to be involved in a wide range of chemical and biological processes, but they are often highly reactive, which makes them difficult to observe directly. We report herein X-ray absorption spectra and analysis that support the direct observation of two different thiyl species generated photochemically by X-ray irradiation. The thiyl radical sulfur K-edge X-ray absorption spectra of both species are characterized by a uniquely low energy transition at about 2465 eV, which occurs at a lower energy than any previously observed feature at the sulfur K-edge and corresponds to a 1s → 3p transition to the singly occupied molecular orbital of the free radical. In conclusion, our results constitute the first observation of substantial levels of thiyl radicals generated by X-ray irradiation and detected by sulfur K-edge X-ray absorption spectroscopy.

Authors:
 [1]; ORCiD logo [2];  [3]; ORCiD logo [4];  [5];  [6]; ORCiD logo [7]; ORCiD logo [3]; ORCiD logo [3]
  1. Stanford Univ., Menlo Park, CA (United States)
  2. Univ. of Saskatchewan, Saskatoon, SK (Canada); Curtin Univ., Bentley, WA (Australia)
  3. Univ. of Saskatchewan, Saskatoon, SK (Canada)
  4. Stonybrook Apiary, Pittstown, NJ (United States)
  5. Chevron Energy Technology Co., Richmond, CA (United States)
  6. Tokyo Institute of Technology, Tokyo (Japan)
  7. Univ. at Albany, State Univ. of New York, Albany, NY (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1394076
Grant/Contract Number:
AC02-76SF00515; CHE-1265679; 04632-2014; 05810-2016; GM57375
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 33; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Sneeden, Eileen Y., Hackett, Mark J., Cotelesage, Julien J. H., Prince, Roger C., Barney, Monica, Goto, Kei, Block, Eric, Pickering, Ingrid J., and George, Graham N. Photochemically Generated Thiyl Free Radicals Observed by X-ray Absorption Spectroscopy. United States: N. p., 2017. Web. doi:10.1021/jacs.7b05116.
Sneeden, Eileen Y., Hackett, Mark J., Cotelesage, Julien J. H., Prince, Roger C., Barney, Monica, Goto, Kei, Block, Eric, Pickering, Ingrid J., & George, Graham N. Photochemically Generated Thiyl Free Radicals Observed by X-ray Absorption Spectroscopy. United States. doi:10.1021/jacs.7b05116.
Sneeden, Eileen Y., Hackett, Mark J., Cotelesage, Julien J. H., Prince, Roger C., Barney, Monica, Goto, Kei, Block, Eric, Pickering, Ingrid J., and George, Graham N. 2017. "Photochemically Generated Thiyl Free Radicals Observed by X-ray Absorption Spectroscopy". United States. doi:10.1021/jacs.7b05116.
@article{osti_1394076,
title = {Photochemically Generated Thiyl Free Radicals Observed by X-ray Absorption Spectroscopy},
author = {Sneeden, Eileen Y. and Hackett, Mark J. and Cotelesage, Julien J. H. and Prince, Roger C. and Barney, Monica and Goto, Kei and Block, Eric and Pickering, Ingrid J. and George, Graham N.},
abstractNote = {Sulfur-based thiyl radicals are known to be involved in a wide range of chemical and biological processes, but they are often highly reactive, which makes them difficult to observe directly. We report herein X-ray absorption spectra and analysis that support the direct observation of two different thiyl species generated photochemically by X-ray irradiation. The thiyl radical sulfur K-edge X-ray absorption spectra of both species are characterized by a uniquely low energy transition at about 2465 eV, which occurs at a lower energy than any previously observed feature at the sulfur K-edge and corresponds to a 1s → 3p transition to the singly occupied molecular orbital of the free radical. In conclusion, our results constitute the first observation of substantial levels of thiyl radicals generated by X-ray irradiation and detected by sulfur K-edge X-ray absorption spectroscopy.},
doi = {10.1021/jacs.7b05116},
journal = {Journal of the American Chemical Society},
number = 33,
volume = 139,
place = {United States},
year = 2017,
month = 7
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on July 27, 2018
Publisher's Version of Record

Save / Share:
  • ESR spectra of short-lived radicals made by photolysis at room temperature of acidic alcoholic solutions of imidazole, 1-methylimidazole, and 4(5)-methylimidazole containing acetone or hydrogen peroxide have been studied. The ESR spectra are attributed to ..pi..-radicals formed by the addition of photochemically produced ..cap alpha..-hydroxyalkyl radicals on the C-2 position of the imidazolium cations. The hyperfine coupling constants are compared with values obtained from Hueckel and INDO MO calculations.
  • A rare type of cis-trans isomerism arises from restricted rotation about a single C-C bond and has been seen here by level crossing resonance spectroscopy (LCR) in muonated free radicals. It is observed as a splitting of the proton's LCR when the C-atom adjacent to the unpaired electron density is an asymmetric sp{sup 2} hybrid. Free radicals which contain C's with sp{sup 3}, symmetric sp{sup 2}, or sp hybrid bonds do not show this geometric isomerism. The {alpha}-protons on these radicals show resolvable splitting less easily than the {beta}-protons. The radicals observed are those resulting from formal addition of muoniummore » to the C{double bond}C bonds of acrylates, and they occur regardless of whether the compounds are studied in dilute aqueous solution or as pure liquids.« less
  • Arrhenius rate expressions were determined for the abstraction of hydrogen atom from thiophenol and hexanethiol by the octanethiyl radical at 25-100 {degrees}C in nonane. Octanethiyl radicals were produced by steady-state photolysis of octyl thiobenzoate. Analysis of octyl disulfide and octanethiyl radical. For hexanethiol, log (k{sub abs}/K{sub t}{sup 1/2}) = (2.94 {plus_minus} 0.29) - (3.84 {plus_minus}0.41)/0, and for thiophenol, log (k{sub abs}/k{sub 5}{sup 1/2}) = (2.56 {plus_minus} 0.19) - (2.88 {plus_minus} 0.28)/0;0=2.3RT kcal/mol. Combining these expressions with the Smoluchowski expression for self-termination of octanethiyl in nonane, log (k{sub t}{sup 1/2}) = 5.96 - 1.335/0, which employs experimental diffusion coefficients of octanethiolmore » and a spin selection factor {sigma} = 1, yields, for thiophenol, log (k{sub abs}/M{sup {minus}1}s{sup {minus}1}) = (8.52 {plus_minus} 0.18) = (4.22 {plus_minus} 0.27)/0, and for hexanethiol, log (k{sub abs}/M{sup {minus}1} s{sup {minus}1}) = (8.90 {plus_minus} 0.29) = (5.18 {plus_minus} 0.41)/0 (errors are 2{sigma}). The rate of disappearance of octanethiyl/diphenylketyl radical pairs in SDS micelles, determined by nanosecond optical spectroscopy, was found to be unchanged in a 700-G magnetic field, providing evidence for rapid intersystem crossing of sulfur-centered radical pairs and support for the assignment of {sigma} = 1 above. Ab initio electronic structure calculations on the reaction HS{sup {lg_bullet}} + HSH {r_arrow} HSH + {sup {lg_bullet}}SH, performed at SCF and correlated levels, predict an activation barrier of {Delta}H{sub 298} {sup {double_dagger}}= 4.6 kcal/mol, in close agreement with the experimental barrier for the octanethiyl + hexanethiol reactions. 43 refs., 5 figs., 4 tabs.« less
  • Alkanethiyl radicals, typified by C{sub 2}H{sub 5}S{lg_bullet}, react rapidly in aqueous solution with C{sub 2}H{sub 5}ML(H{sub 2}O){sup 2}{sup +}, where ML = Co([14]aneN{sub 4}), k = 1.15 x 10{sup 8} L mol{sup -1} s{sup -1}, and Cr-([15]aneN{sub 4}), k = 5.9 x 10{sup 7} L mol{sup -1} s{sup -1}. The use of C{sub 2}D{sub 5}ML(H{sub 2}O){sup 2+} leads to k{sub h}/k{sub D} = 2.6 (Co) and 3.3 (Cr), consistent with {Beta}-hydrogen abstraction and formation of ethylene. The methylcobalt complex forms C{sub 2}H{sub 5}SCH{sub 3}, with k = 2.4 x 10{sub 7} L mol{sup -1} s{sup -1} and k{sub H}/k{sub D}more » {approx} 1. 12 refs.« less