A Caltech Library Service

Os(phen)_2dppz^(2+) in Photoinduced DNA-Mediated Electron Transfer Reactions

Holmlin, R. Erik and Stemp, Eric D. A. and Barton, Jacqueline K. (1996) Os(phen)_2dppz^(2+) in Photoinduced DNA-Mediated Electron Transfer Reactions. Journal of the American Chemical Society, 118 (22). pp. 5236-5244. ISSN 0002-7863. doi:10.1021/ja953941y.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


The photoinduced electron transfer chemistry between Os(phen)_2dppz^(2+) and Rh(phi)_2bpy^(3+) bound to DNA has been characterized. Os(phen)_2dppz^(2+) serves as an isostructural analogue for Ru(phen)_2dppz^(2+) with a red-shifted emission spectrum, access to a 3+ oxidation state which is stabilized by ∼500 mV relative to the ruthenium complex, and excited-state lifetimes below 10 ns in the presence of DNA. Emission from Δ-Os(phen)_2dppz^(2+) bound to calf thymus DNA is efficiently quenched by Δ-Rh(phi)_2bpy^(3+), and a lower limit for the quenching constant is set at 7 × 10^9 s^(-1). The quenching profile over a range of quencher concentrations is found to be remarkably similar to that of the ruthenium analogue, despite an increase of ∼200 mV in ΔG for the photoinduced, forward electron transfer reaction. Such an observation may indicate the importance of the HOMO energy in the donor excited state, which is similar for both donors. Owing to the lack of spectral overlap between Os(phen)_2dppz^(2+) emission and Rh(phi)_2bpy^(3+) absorption, energy transfer does not contribute to the observed quenching, and therefore, on the basis of the similarity in quenching profiles for the osmium and ruthenium donors, we can also rule out energy transfer in the photoinduced quenching of intercalated Ru(phen)_2dppz^(2+) by Rh(phi)_2bpy^(3+). Moreover, diffusional processes are found not to contribute to quenching, since the faster intrinsic excited state of the osmium complex compared to ruthenium does not lead to a reduction in quenching efficiency. Transient absorption measurements on the microsecond time scale furthermore reveal a transient signal for this electron transfer process, and this transient intermediate has been assigned to the oxidized donor (Os(III)) on the basis of full spectral characterization and comparison to chemical oxidation of Os(II).

Item Type:Article
Related URLs:
URLURL TypeDescription
Stemp, Eric D. A.0000-0003-2098-4214
Barton, Jacqueline K.0000-0001-9883-1600
Additional Information:© 1996 American Chemical Society. Received November 27, 1995. Publication Date (Web): June 5, 1996. We are grateful to the NIH (GM49216 to J.K.B.) for financial support of this work. We also thank the NSF for a predoctoral fellowship to R.E.H. and the American Cancer Society for a postdoctoral fellowship to E.D.A.S. We would also like to thank Dr. J. Winkler and C. N. Kenyon of BILRC for expert technical support and helpful discussions.
Funding AgencyGrant Number
American Cancer SocietyUNSPECIFIED
Issue or Number:22
Record Number:CaltechAUTHORS:20171107-133435500
Persistent URL:
Official Citation:Os(phen)2dppz2+ in Photoinduced DNA-Mediated Electron Transfer Reactions. R. Erik Holmlin, Eric D. A. Stemp, and Jacqueline K. Barton. Journal of the American Chemical Society 1996 118 (22), 5236-5244. DOI: 10.1021/ja953941y
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83036
Deposited By: Tony Diaz
Deposited On:07 Nov 2017 21:47
Last Modified:15 Nov 2021 19:54

Repository Staff Only: item control page