Importance of electronic relaxation for inter-coulombic decay in aqueous systems Page: 4 of 5
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which will lower the ground-state valence energies. Additional calculations show, for instance, that states
associated with core-excited nitrogen in protonated glycine, a simple amino acid, will not mix with water,
while those in the deprotonated anionic species permit mixing due to a smaller downward shift in energy.
Cytosine also exhibits significant mixing, implying that core-level ICD could be useful in radiooncology,
particularly when carbon and nitrogen atoms are excited at their corresponding K edges, rather than from
valence states, as discussed previously [4,5]. Sharp peaks in the PES of these systems would not be expected,
however, as the energetic overlap of the valence pDOS with the solvent spans a much broader energy range
than in hydroxide.Drugs containing heavy-metal targets capable of energy transfer
via ICD to cancerous DNA would be a valuable new tool in radiooncology
[4, 5, 17]. The state-mixing criterion established here would allow for
rational design of this type of therapeutic protocol: Core excitations in
heavy metals occur at characteristic wavelengths, such that irradiation of
cancerous tissue selectively bound to a heavy-metal complex with a tuned
x-ray source would help to localize the radiation dose [18-20] and energy
transfer, increasing the damage to cancerous tissue. There would also be a
reduction in the associated damage to healthy tissue owing to its
transparency to the greater portion of the secondary electrons emitted [21].
The specific nature of the impact of core excitations on valencestate
electronic structure indicates the potential for careful tailoring to individual
targets (such as DNA or other critical cell structures) by tuning the
structure of the heavymetal
complex. At the time of writing, we are actively pursuing this line of
investigation in simple models of biological solutions.
In conclusion, we have outlined a generally applicable,
computationally inexpensive approach to the prediction of core-excited
ICD in solutions. This approach is based on an explicit treatment of
electronic relaxation in the core-excited state, as approximated by the XCH
method, and on simple criteria of energetic and spatial orbital overlap.
This work was supported by the Director, Office of Basic Energy
Sciences, Office of Science, U.S. Department of Energy under Contract
No. DE-AC02-05CH11231 through the LBNL Chemical Sciences
Division and the Molecular Foundry, and by the National Science
Foundation. Computational resources were provided by NERSC, a DOE
Advanced Scientific Computing Research User Facility. We thank
Professor Mark Tuckerman for the solution snapshots and Dr. Keith
Lawler for helpful discussions.
This document was prepared as an account of work sponsored by
the United States Government. While this document is believed to contain
correct information, neither the United States Government nor any agency
thereof, nor The Regents of the University of California, nor any of their
employees, makes any warranty, express or implied, or assumes any legal
responsibility for the accuracy, completeness, or usefulness of any
information, apparatus, product, or process disclosed, or represents that its
use would not infringe privately owned rights. Reference herein to any
specific commercial product, process, or service by its trade name,
trademark, manufacturer, or otherwise, does not necessarily constitute or
imply its endorsement, recommendation, or favoring by the United States
Government or any agency thereof, or The Regents of the University of
California. The views and opinions of authors expressed herein do not
necessarily state or reflect those of the United States Government or any
agency thereof or The Regents of the University of California.446
A) l
o *
B)*
C)
FIG. 3 (color online). The 50% density
isosurfaces of a single p state of core-
excited (a) fluoride, (b) water, (c) three
coordinated hydroxide, and (d) four-
coordinated hydroxide. The green and
orange colors of the lobes (lighter and
darker shades of gray) indicate opposite
signs of the real-valued wave function. Note
the extensive delocalization over
neighboring water molecules donating
hydrogen bonds in panels (c) and (d). A
similar delocalization is not observed for
fluoride or water, as is supported by the
pDOS data in Fig. 2. The states are located
at- 14,-9,-6,and-6eV,respectively,as
referenced in Fig. 2.
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Schwartz, Craig P.; Fatehi, Shervin; Saykally, Richard J. & Prendergast, David. Importance of electronic relaxation for inter-coulombic decay in aqueous systems, article, October 1, 2010; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc841419/m1/4/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.