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Dielectric relaxation of DNA solutions. IV. Effects of salts and dyes
Author(s) -
Sakamoto Masanori,
Hayakawa Reinosuke,
Wada Yasaku
Publication year - 1980
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.1980.360190508
Subject(s) - chemistry , intercalation (chemistry) , aqueous solution , dielectric , counterion , molecule , analytical chemistry (journal) , relaxation (psychology) , tetramethylammonium , dipole , inorganic chemistry , ion , organic chemistry , social psychology , psychology , physics , optoelectronics
The effects of salts (NaCl, LiCl, Me 4 NCl, AgNO 3 , MgCl 2 , CuCl 2 and MnCl 2 ) and dyes (acridine orange and methylene blue) on the low‐frequency dielectric relaxation (0.1 Hz–30 kHz) of dilute aqueous solutions of DNA were investigated with varying salt or dye concentrations. Both the dielectric relaxation time τ D and the rotational relaxation time τ estimated from the reduced viscosity decrease in quite parallel ways with increasing M / P ( M / P being the normality ratio of cation to phosphate residue), reflecting the contraction of DNA molecule due to electrostatic shielding and cation binding. The agreement between τ D and τ through the whole range of M / P supports our previous conclusion that the low‐frequency relaxation of DNA arises from rotation of the molecule. The dielectric increment Δε also decreases with increasing M / P on account of both the contraction of DNA and the decrease in effective degree of dissociation of DNA. Δε as a function of M / P is interpreted in terms of a quasi‐permanent dipole due to counterion fluctuation. These effects of cations are the strongest for divalent cations and rather weak for Na + , Li + , and Me 4 N + . Effects of dye on τ D and Δε are also well explained by the rotation of DNA molecule with a quasi‐permanent dipole due to counterion fluctuation on the basis of intercalation of dye at D / P < 0.2 ( D / P being the molarity ratio of dye to phosphate residue) and external binding at 0.2 < D / P < 1.0.