Kiyohiro Fukudome

Adsorption of deoxyribonucleic acid and poly(cytidylic acid)•Poly(inosinic acid) onto the poly(styrene) latex

Abstract Adsorption of native and heat-denatured calf thymus DNA (Mw = 2.5 × 105 and 4.5 × 106) and poly(cytidylic acid) · poly(inosinic acid) ((C)n · (I)n, Mw = 1.5 × 105, and 7.7 × 105) duplex onto the negatively charged poly(styrene) latex was examined at 4°C with emphasis on the effect of the molecular chain length, the species of added salts (NaCl, CaCl2, and MgCl2), and their ionic strengths ((1–10) × 10−3). The amount of adsorbed nucleic acids was determined photometrically from teh difference in the concentrations before and after mixing with the latex (average diameter, 471 nm; surface charge density, −3.52 μC/cm2). For native DNA, the higher the molecular weights and ionic strengths were, the more was adsorbed, the effect of the added ions being Mg2+ > Ca2+ ⩾ Na+. For denaturated DNA, the adsorption behavior was qualitatively the same but the adsorbed amount was less. These trends were reversed for (C)n · (l)n, but the effect of added ions remained the same as that for DNA. The divalent cations play a role of a binder between two types of negative charges on nucleic acids and on latex.

Brownian dynamics of weakly bendable macromolecules: Effects of bending fluctuations on electric dichroism

The expression of the steady‐state value of electric dichroism (ED), over the entire electric field strength, for semistiff linear polymers with an electric polarizability along the chain has been derived by a normal mode approximation on the basis of the Brownian dynamics. Only a flexibility parameter, L/P defined as the contour length L to the persistence length P, is introduced into the expression without any assumption of the configuration. Our ED theory predicts that, with the increase in an L/P value, the steady state value is decreased over a low‐to‐medium field strength range but remains to be unchanged at infinitely high fields. The expression of the ED relaxation after the removal of an electric field is also derived, when the field strength is low. The off‐field relaxation decays multiexponentially not only due to rotational diffusion but also due to bending diffusion. The contribution of the bending to the decay amplitude is increased with increasing L/P. The flexibility strongly affects the t...