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A study of the quadrupolar NMR splittings of 7 Li + , 23 Na + , and 133 Cs + counterions in macroscopically oriented DNA fibers
Author(s) -
Schultz Johan,
Nordenskiöld Lars,
Rupprecht Allan
Publication year - 1992
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/bip.360321206
Subject(s) - counterion , chemistry , ion , counterion condensation , crystallography , analytical chemistry (journal) , organic chemistry , chromatography
The hydration and temperature dependencies of the 23 Na + , and 133 Cs + , and 7 Li + quadrupolar splitting have been determined in hydrated, macroscopically oriented DNA fibers. At low water contents the quadrupolar splitting is found to decrease as the water content increases, regardless of counterion, while at high water contents the hydration dependence is reversed. The 23 Na + and 133 Cs + quadrupolar splittings decrease as the temperature increases, while the 7 Li + splitting shows the opposite behavior. At high water contents the 23 Na + and 133 Cs + splittings decrease, and then, after passing zero splitting, increase as the temperature increases. The interpretation of the temperature dependence is discussed in terms of a two‐site model (free and bound ions) and a three‐site model (free ions and specifically or nonspecifically bound ions). It is suggested that a three‐site model is more consistent with the data for the present system. At high water contents, the temperature dependence of the 7 Li + splitting vanishes, indicating counterion condensation. The behavior of the 7 Li + splitting is confirmed by measurements on DNA fibers in equilibrium with a C 2 H 5 OD‐D 2 O‐LiCl solution. The salt dependence in this system is weak. The counterion quadrupolar splitting is seen to be very sensitive to structural transitions in double‐helical DNA. © 1992 John Wiley & Sons, Inc.