Abstract
The reaction of deprotonation of the guanosyl cation radical formed in the photoinduced reaction of guanosine monophospate (GMP) with triplet 2,2′-dipyridyl-d8 is studied in aqueous solution by time-resolved chemically induced dynamic nuclear polarization (TR-CIDNP). In the course of the cyclic photoreaction, spin-polarized products are generated. Their polarization patterns that reflect the properties at the radical stage are analyzed using high-resolution nuclear magnetic resonance. The identification of transient radicals contributing to the polarization kinetics is based on its sensitivity to the degenerate electron exchange reaction of transient radicals with the parent diamagnetic molecules. Degenerate electron exchange is allowed only for the cation radical and manifests itself in the fast decay of the CIDNP signal in time with the rate of decay proportional to the concentration of parent GMP molecules. Because the formation of the neutral transient radical stops the exchange, the deprotonation changes the CIDNP kinetics from a decaying to a growing one. The rate constant of deprotonation, k d, was obtained from modeling of CIDNP kinetics data with taking into consideration the difference of the CIDNP enhancement factors for neutral and cation guanosyl radicals. The value obtained at pH* 5 for k d = 1 × 106 s−1 is consistent with the proton dissociation constant of the radical (pK a = 3.9). The linear dependence of the deprotonation rate on the buffer concentration is revealed for phosphate, formate, and acetate. Deprotonation is catalyzed by the buffer to a degree that depends on the difference in pK a value of the buffer and the guanosyl cation radical in full accordance with Eigen’s model.
Similar content being viewed by others
References
S. Steenken, S.V. Jovanovic, J. Am. Chem. Soc. 119, 617 (1997)
K. Kobayashi, S. Tagawa, J. Am. Chem. Soc. 125, 10213 (2003)
T. Douki, D. Angelov, J. Cadet, J. Am. Chem. Soc. 123, 11360 (2001)
C.J. Burrows, J.G. Muller, Chem. Rev. 98, 1109 (1998)
J.R. Milligan, J.A. Aguilera, O. Hoang, A. Ly, N.Q. Tran, J.F. Ward, J. Am. Chem. Soc. 126, 1682 (2004)
A. Ly, N.Q. Tran, J.F. Ward, J.R. Milligan, Biochemistry 43, 9098 (2004)
A. Ly, S.L. Bandong, N.Q. Tran, K.J. Sullivan, J.R. Milligan, J. Phys. Chem. B 109, 13368 (2005)
J.R. Milligan, N.Q. Tran, A. Ly, J.F. Ward, Biochemistry 43, 5102 (2004)
A. Ly, N.Q. Tran, K. Silliavan, S.L. Bandong, J.F. Ward, J.R. Milligan, Org. Biomol. Chem. 3, 917 (2005)
J.R. Milligan, J.A. Aguilera, A. Ly, O. Hoang, N.Q. Tran, J.F. Ward, Nucleic Acid Res. 31, 6258 (2003)
R.L. Willson, P. Wardman, K.D. Asmus, Nature 252, 323 (1974)
O.B. Morozova, A.S. Kiryutin, R.Z. Sagdeev, A.V. Yurkovskaya, J. Phys. Chem. B 111, 7439 (2007)
O.B. Morozova, A.S. Kiryutin, A.V. Yurkovskaya, J. Phys. Chem. B 112, 2747 (2008)
S. Steenken, Chem. Rev. 89, 503 (1989)
A. Adhikary, A. Kumar, D. Becker, M.D. Sevilla, J. Phys. Chem. B 110, 24171 (2006)
R. Kaptein, K. Dijkstra, K. Nicolay, Nature 274, 293 (1978)
P.J. Hore, R.W. Broadhurst, Prog. Nucl. Magn. Reson. Spectrosc. 25, 345 (1993)
K.H. Mok, P.J. Hore, Methods (San Diego, CA, United States) 34, 75 (2004)
S. Stob, R.M. Scheek, R. Kaptein, Photochem. Photobiol. 49, 717 (1989)
A.V. Yurkovskaya, O.A. Snytnikova, O.B. Morozova, Y.P. Tsentalovich, R.Z. Sagdeev, Phys. Chem. Chem. Phys. 5, 3653 (2003)
M. Eigen, Angew. Chem. Int. Edit. 3, 1 (1964)
A. Krezel, W. Bal, J. Inorg. Biochem. 98, 161 (2004)
Yu.P. Tsentalovich, O.B. Morozova, A.V. Yurkovskaya, P.J. Hore, J. Phys. Chem. A 103, 5362 (1999)
Yu.P. Tsentalovich, O.B. Morozova, A.V. Yurkovskaya, P.J. Hore, R.Z. Sagdeev, J. Phys. Chem. A 104, 6912 (2000)
R. Kaptein, J. Chem. Soc., Chem. Commun. 732 (1971)
S. Stob, R. Kaptein, Photochem. Photobiol. 49, 565 (1989)
G.L. Closs, E.V. Sitzmann, J. Am. Chem. Soc. 103, 3217 (1981)
J. Burri, H. Fischer, Chem. Phys. 161, 429 (1992)
O.B. Morozova, A.V. Yurkovskaya, Y.P. Tsentalovich, M.D.E. Forbes, P.J. Hore, R.Z. Sagdeev, Mol. Phys. 100, 1187 (2002)
J.-K. Vollenweider, H. Fischer, Chem. Phys. 124, 333 (1988)
J.-K. Vollenweider, H. Fischer, J. Hennig, R. Leuschner, Chem. Phys. 97, 217 (1985)
F.J. Adrian, J. Chem. Phys. 53, 3374 (1970)
S. Grosse, A.V. Yurkovskaya, J. Lopez, H.-M. Vieth, J. Phys. Chem. A 105, 6311 (2001)
Acknowledgments
Financial support by the Russian Foundation for Basic Research (projects No. 09-03-91006-FWF, 09-03-00837-a, and 11-03-00296-a), the program of the President of Russia for support of leading scientific schools (NSh-7643.2010.3), the Program of the Division of Chemistry and Material Science of the Russian Academy of Sciences (RAS, project 5.1.1), and the Siberian branch of RAS (projects No. 28) is gratefully acknowledged.
Author information
Authors and Affiliations
Corresponding author
Additional information
Dedicated to Professor Renad Sagdeev on the occasion of his 70th birthday.
Rights and permissions
About this article
Cite this article
Morozova, O.B., Saprygina, N.N., Fedorova, O.S. et al. Deprotonation of Transient Guanosyl Cation Radical Catalyzed by Buffer in Aqueous Solution: TR-CIDNP Study. Appl Magn Reson 41, 239–250 (2011). https://doi.org/10.1007/s00723-011-0252-2
Received:
Revised:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00723-011-0252-2