ROTATIONAL DIFFUSION AND INTERNAL MOTIONS OF CIRCULAR DNA .1. POLARIZED PHOTON CORRELATION SPECTROSCOPY

摘要

Dilute solutions of DNA plasmid pUC18 (2687 base pairs) have been studied by polarized photon correlation spectroscopy. The autocorrelation functions of the scattered light have been measured and fitted to a sum of exponentials. When a two exponential fit of the autocorrelation functions is performed, the slower relaxation rate corresponds to the expected translational diffusion coefficient of the plasmid while the faster one shows a linear behavior below K-2 similar or equal to 5x10(14) m(-2), being superlinear at larger K-2 values. The translational diffusion coefficient at T=25 degrees is D-t=5141+/-0.25x10(-12) m(2)/s while the extrapolation of the fast relaxation rate to K-2=0 yields the tumbling rotational coefficient R(perpendicular to)=1.5+/-0.2 kHz. Monte Carlo simulations of the plasmid conformation have been performed with different sets of dynamical parameters (bending and torsional rigidities, Debye length), and the hydrodynamic coefficients have been computed according to known algorithms. The translational diffusion coefficient determined experimentally shows good agreement with the results of Monte Carlo simulations, while the simulated rotational tumbling coefficient is slightly larger than that found experimentally. (C) 1996 American Institute of Physics. [References: 65]