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Competitive binding exchange between alkali metal ions (K + , Rb + , and Cs + ) and Na + ions bound to the dimeric quadruplex [d(G 4 T 4 G 4 )] 2 : a 23 Na and 1 H NMR study
Author(s) -
Cesare Marincola Flaminia,
Virno Ada,
Randazzo Antonio,
Mocci Francesca,
Saba Giuseppe,
Lai Adolfo
Publication year - 2009
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2509
Subject(s) - chemistry , alkali metal , ion , titration , metal ions in aqueous solution , ion exchange , crystallography , inorganic chemistry , aqueous solution , nuclear magnetic resonance spectroscopy , qualitative inorganic analysis , phosphate , stereochemistry , organic chemistry
A comparative study of the competitive cation exchange between the alkali metal ions K + , Rb + , and Cs + and the Na + ions bound to the dimeric quadruplex [d(G 4 T 4 G 4 )] 2 was performed in aqueous solution by a combined use of the 23 Na and 1 H NMR spectroscopy. The titration data confirm the different binding affinities of these ions for the G‐quadruplex and, in particular, major differences in the behavior of Cs + as compared to the other ions were found. Accordingly, Cs + competes with Na + only for the binding sites at the quadruplex surface (primarily phosphate groups), while K + and Rb + are also able to replace sodium ions located inside the quadruplex. Furthermore, the 1 H NMR results relative to the CsCl titration evidence a close approach of Cs + ions to the phosphate groups in the narrow groove of [d(G 4 T 4 G 4 )] 2 . Based on a three‐site exchange model, the 23 Na NMR relaxation data lead to an estimate of the relative binding affinity of Cs + versus Na + for the quadruplex surface of 0.5 at 298 K. Comparing this value to those reported in the literature for the surface of the G‐quadruplex formed by 5′‐guanosinemonophosphate and for the surface of double‐helical DNA suggests that topology factors may have an important influence on the cation affinity for the phosphate groups on DNA. Copyright © 2009 John Wiley & Sons, Ltd.