Experimental Study of Reaction Kinetics by Light Scattering. II. Helix–Coil Transition of the Copolymer Deoxyadenylate–Deoxythymidylate (dAT)

Abstract

The average rate of configuration transition of the (dAT) copolymer has been determined by the study of the spectrum of light scattering. For the alkaline transition of (dAT) at 18.7°C, $p\mathrm{H}\text{\hspace{0.17em}=\hspace{0.17em}11.0}$ , and ionic strength of $\text{0.1M}$ Na⁺, we find a rate ${\tau }_R^{\text{−1}}{\text{\hspace{0.17em}=\hspace{0.17em}2.33\hspace{0.17em}±\hspace{0.17em}0.21\hspace{0.17em}×\hspace{0.17em}10}}^3{\sec }^{\text{−1}}$ . This compares favorably with previous measurements obtained by the temperature‐jump technique. Simultaneously, we have measured the linear diffusion coefficient within the transition region to be ${\text{D\hspace{0.17em}=\hspace{0.17em}2.91\hspace{0.17em}±\hspace{0.17em}0.14\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−8}}{\mathrm{cm}}^2/\sec$ . There is a 6%–10% variation of the diffusion rates between the samples at the low‐pH (10.4) helical conformation and at the high‐pH(11.6) random coil conformation.