Angewandte Chemie International Edition
10.1002/anie.201916493
COMMUNICATION
1
.525 Å. This effect could not be attributed to different electron
Separated Biomolecular Ions, Lecture Notes in Chemistry, vol. 83,
pp. 93–116. Springer, Heidelberg (2013)
[13] J. E. P. Syka, J. J. Coon, M. J. Schroeder, J. Shabanowitz, D. F.
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[14] S. A. Shaffer, F. Tureček, J. Am. Chem. Soc. 1994, 116, 8647-
8653.
distributions in the TS which were nearly identical for the syn and
anti-facial TS. However, syn-TS2d showed a larger displacement
of the departing H atom from the ring plane than did anti-TS2d,
allowing a more efficient atomic orbital overlap in the adenine ring
HOMO as it was developing in the course of dissociation.
The calculated TS energies were used for transition-state
theory (TST) calculations of unimolecular rate constants for the H-
atom loss to be compared with the experimental value of k = 0.56
[15] D. E. Goeringer, S. A. McLuckey, J. Chem. Phys. 1996, 104,
2214-2221.
[16] S. Gronert, J. Am. Soc. Mass Spectrom. 1998, 9, 845-848.
(17] E. R. Lovejoy, R. R.; Wilson, J. Phys. Chem. A 1998, 102,
2309-2315.
-
1
s . The TST rate constants calculated for the syn and anti N-3‒H
-4
-1
dissociations were too low (<10
s at 360 K) to be compatible
with the experimental value. The rate constants for the syn- and
[18] W. A. Donald, G. N. Khairallah, R. A. J. O'Hair, R. J. Am.
Soc. Mass Spectrom. 2013, 24, 811-815.
[19] A. Dang, Y. Liu, F. Tureček, J. Phys. Chem. A 2019, 123,
3272-3284.
anti-N-1‒H dissociations, which had low calculated TS energies
‡
(
‒
Table 1), were affected by negative activation entropies, S =
-
1
-1
16.4 and ‒29.7 J mol K , respectively, at 360 K. These rate
constants are shown in Figure S19a. The rate constant calculated
for the syn-TS2d energy (95 kJ mol , Table 1) matched the
[20] J. Reynisson, S. Steenken, Phys. Chem. Chem. Phys. 2005, 7,
659-665.
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1
experimental value for an effective ion temperature of 351 K
[21] S. D. Wetmore, R. J. Boyd, L. A. Eriksson, J. Phys. Chem. B
1998, 102, 10602-10614.
-
1
(Figure S19b). Considering the estimated 3 kJ mol accuracy of
the calculated TS energy, the range of ion effective temperatures
giving matching TST rate constants can be expanded to 340-362 K.
This fits within or is close to previous estimates of the effective
[
15-18]
temperature of ions stored in radiofrequency ion traps
. Thus,
Keywords: charge-tagged adenosine radicals; UV-vis action
spectroscopy; vibronic spectra; H-loss kinetics; transition states
+
●
the calculated dissociation kinetics of the N-7‒H adduct 2d was
compatible with the experimental result.
In summary, a new method for the generation of charge-
tagged nucleoside radicals has been developed that was combined
with photodissociation action spectroscopy of well-defined
transient molecular species in the gas phase. As illustrated with
adenine riboside, the charge-tagged radicals are electronically
equivalent to natural nucleoside radicals, and derivatization of the
+●
2
' and 3'-OH groups in (1+H) by a non-polar group has a
negligible effect on the electronic properties of the radicals. Thus,
the method has the potential of being applied to the other
nucleosides relevant to electron transfer in DNA and RNA to
provide electronic structure of reactive intermediates pertinent to
the early stages of ionization damage.
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