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A solid‐state 23 Na NMR study of monovalent cation binding to double‐stranded DNA at low relative humidity
Author(s) -
Wong Alan,
Yan Zhimin,
Huang Yining,
Wu Gang
Publication year - 2008
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.2136
Subject(s) - chemistry , binding energy , titration , crystallography , dna , phosphate , resonance (particle physics) , relative humidity , ion , inorganic chemistry , organic chemistry , biochemistry , physics , particle physics , nuclear physics , thermodynamics
We report a solid‐state 23 Na NMR study of monovalent cation (Li + , Na + , K + , Rb + , Cs + and NH 4 + ) binding to double‐stranded calf thymus DNA (CT DNA) at low relative humidity, ca 0–10%. Results from 23 Na 31 P rotational echo double resonance (REDOR) NMR experiments firmly establish that, at low relative humidity, monovalent cations are directly bound to the phosphate group of CT DNA and are partially dehydrated. On the basis of solid‐state 23 Na NMR titration experiments, we obtain quantitative thermodynamic parameters concerning the cation‐binding affinity for the phosphate group of CT DNA. The free energy difference (Δ G ° ) between M + and Na + ions is as follows: Li + (−1.0 kcal mol −1 ), K + (7.2 kcal mol −1 ), NH 4 + (1.0 kcal mol −1 ), Rb + (4.5 kcal mol −1 ) and Cs + (1.5 kcal mol −1 ). These results suggest that, at low relative humidity, the binding affinity of monovalent cations for the phosphate group of CT DNA follows the order: Li + > Na + > NH 4 + > Cs + > Rb + > K + . This sequence is drastically different from that observed for CT DNA in solution. This discrepancy is attributed to the different modes of cation binding in dry and wet states of DNA. In the wet state of DNA, cations are fully hydrated. Our results suggest that the free energy balance between direct cation–phosphate contact and dehydration interactions is important. The reported experimental results on relative ion‐binding affinity for the DNA backbone may be used for testing theoretical treatment of cation‐phosphate interactions in DNA. Copyright © 2008 John Wiley & Sons, Ltd.