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Competitive substitution of hexammine cobalt(III) for Na + and K + ions in oriented DNA fibers
Author(s) -
Korolev Nikolay,
Lyubartsev Alexander P.,
Rupprecht Allan,
Nordenskiöld Lars
Publication year - 2001
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/1097-0282(200103)58:3<268::aid-bip1004>3.0.co;2-8
Subject(s) - chemistry , cobalt , substitution (logic) , ion , dna , crystallography , inorganic chemistry , biochemistry , organic chemistry , computer science , programming language
Competition of the trivalent cation, Co(NH 3 ) 3+ 6 , with K + and Na + ions in binding to DNA was studied by equilibrating oriented DNA fibers with ethanol/water solutions (65 and 52% v/v EtOH), containing different combinations and concentrations of KCl and NaCl and constant concentration (0.8 mM) of Co(NH 3 ) 6 Cl 3 . The degree of Co(NH 3 ) 3+ 6binding to DNA does not depend significantly on the ethanol concentration or on the kind of univalent cation (Na + or K + ). The ion exchange selectivity coefficient of monovalent–trivalent ion competition, D 1 c3 , increases with the concentration of Me + , C o + , and the monotonic dependence of log D 1 c3vs log C o +has an inflection between 100 and 300 m M that is caused by a structural transformation of DNA from A‐ to B‐form. The ion exchange experimental data are compared with results of grand canonical Monte Carlo (GCMC) simulations of systems of parallel and hexagonally ordered, discretely charged polyions with density and spatial distribution of the charged groups modeling B‐ and A‐forms of DNA. The GCMC method for discretely charged models of the DNA polyion produces a quantitative agreement with experimental data on trivalent–monovalent ion competition in dependence on DNA structural state and salt concentration. Based on this and previous studies it is concluded that the affinity of DNA for the cations decreases in the order Co(NH 3 ) 3+ 6≫ Ca 2+ > Mg 2+ ≫ Na + ≈ K + > Li + . DNA does not exhibit selectivity for Na + or K + in ethanol/water solutions either in the absence or in the presence of Co(NH 3 ) 3+ 6 , Ca 2+ , and Mg 2+ . © 2001 John Wiley & Sons, Inc. Biopolymers 58: 268–278, 2001