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^1H NMR Studies of Tris(phenanthroline) Metal Complexes Bound to Oligonucleotides: Characterization of Binding Modest

Rehmann, Jill P. and Barton, Jacqueline K. (1990) ^1H NMR Studies of Tris(phenanthroline) Metal Complexes Bound to Oligonucleotides: Characterization of Binding Modest. Biochemistry, 29 (7). pp. 1701-1709. ISSN 0006-2960. https://resolver.caltech.edu/CaltechAUTHORS:20160516-112833530

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Abstract

The binding of Ru(phen)_3^(2+), Rh(phen)_3^(3+), and Co(phen)_3^(3+) to the oligonucleotides d(GTGCAC)_2 and 5'-pd(CGCGCG)_i has been examined by ^1H NMR spectroscopy as a function of temperature, concentration, and chirality of the metal complex. The duplex oligonucleotides act as chiral shift reagents for the metal complexes; phenanthroline protons associated with each enantiomer are resolved upon binding to the oligomer. The spectral titrations, consistent with photophysical studies, indicate that the complexes bind to the oligomer through two modes: one assigned as intercalation favoring the A-isomer, and the other assigned as the surface-bound interaction favoring the Λ-isomer. The ligand protons are perturbed in a manner that implies sensitivity of particular protons to binding mode; specifically, the H4,7 protons appear to be altered most for the Λ-enantiomer while the H5,6 protons are perturbed more for the Λ-enantiomer. The NMR chemical shift variations appear particularly sensitive to this surface-bound interaction, which, on the basis of a comparison of binding and photophysical parameters for Ru(phen)_3^(3+), appears more prominant in binding to oligonucleotides than that to polynucleotides. With respect to oligonucleotide proton shifts, the adenine H2 proton, positioned in the minor groove of the helix, shows the largest upfield shifts with metal binding, and more dramatically with Λ-isomers. The major groove thymine methyl protons (TMe) shift downfield to a lesser extent, and more so for Λ-isomers. The different binding modes also differ with respect to their dynamics of association; the longitudinal relaxation rates of Δ- and Λ-4,7 phenanthroline protons of Rh(phen)_3^(3+) are 0.88 and 1.14 s, respectively, in the presence of d(GTGCAC)_2. In contrast to studies with the substitutionally inert metal complexes, addition of racemic Co(phen)_3^(3+) to the oligonucleotide solution yields unequal populations of enantiomers, owing to the rapid racemization of the cobalt complex in the presence of oligomer and reequilibration to that form which favors binding. Duplex melting has also been monitored by ^1H NMR spectroscopy; the complexes increase the duplex melting temperature by ~5 ºC. In the case of Co(phen)_3^(3+), with increasing temperature, as the helix melts, a reequlibration of the enantiomers occurs, indicating that the chiral discrimination arises from enantioselective interactions with the helix rather than with the single-stranded oligonucleotides.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/bi00459a006DOIArticle
http://pubs.acs.org/doi/abs/10.1021/bi00459a006PublisherArticle
ORCID:
AuthorORCID
Barton, Jacqueline K.0000-0001-9883-1600
Alternate Title:Proton NMR studies of tris(phenanthroline) metal complexes bound to oligonucleotides: characterization of binding modes
Additional Information:© 1990 American Chemical Society. Received June 30, 1989; Revised Manuscript Received October 19, 1989. This work was supported by NIH Grant GM33309.
Funders:
Funding AgencyGrant Number
NIHGM33309
Issue or Number:7
Record Number:CaltechAUTHORS:20160516-112833530
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160516-112833530
Official Citation:Proton NMR studies of tris(phenanthroline) metal complexes bound to oligonucleotides: characterization of binding modes Jill P. Rehmann and Jacqueline K. Barton Biochemistry 1990 29 (7), 1701-1709 DOI: 10.1021/bi00459a006
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67129
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:16 May 2016 19:16
Last Modified:03 Oct 2019 10:03

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