Dielectric relaxation of collagen in aqueous solutions

The complex dielectric constant of collagen in aqueous solutions (polymer concentration, C_p = 0.02–0.2%) was measured at 10°C in the frequency range from 3 Hz to 30 kHz. The loss peak for C_p = 0.02% is located at 90 Hz and the dielectric relaxation time τ_D is estimated to be 1.8 ± 0.3 msec. The τ_D agrees well with the rotational relaxation time estimated from the reduced viscosity, and the relaxation is ascribed to the end-over-end rotation of the molecule. The C_p dependence of τ_D and the dielectric increment Δε are interpreted in terms of the aggregation of molecules. The dipole moment of a molecule, obtained from Δε at C_p = 0.02% and pH 6.5, is (5.2 ± 0.2) × 10⁴D, which is explained by the asymmetrical distribution of the ionized side chains of the molecule.     

Dielectric relaxation of DNA solutions. IV. Effects of salts and dyes

The effects of salts (NaCl, LiCl, Me₄NCl, AgNO₃, MgCl₂, CuCl₂ and MnCl₂) 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 Me₄N⁺. 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.     

Dielectric relaxation of DNA solutions. II

Real and imaganiry parts of complex dielectric constant of dilute solutions of DNA in 10^?3M NaCl with molecular weight ranging from 0.4 × 10⁶ to 4 × 10⁶ were measured at frequencies from 0.2 Hz to 30 kHz. Dielectric increments Δε were obtained from Cole-Cole plots and relaxation times τ_D from the loss maximum frequency. The τ_D of all samples agrees well with twice of the maximum viscoelastic relexation time in the Zimm theory, indicating that the low-frequency dielectric relaxiation should be ascribed to be the rotation of DNA. The rms dipole moment, which was obtained from Δε, agree well with that calculated from the counterion fluctuation theory. The dielectric increment was found to be greatly depressed in MgCl₂, which is resonably interpreted in terms of a strong binding of Mg⁺⁺ ions with DNA.