DYNAMIC STRUCTURE FACTOR OF SEMIFLEXIBLE MACROMOLECULES IN DILUTE-SOLUTION

The dynamic structure factor for molecular chains with variable stiffn ess in a dilute solution is investigated. In the limit of small scatte ring vectors q only the overall translational motion of the macromolec ules contributes to the dynamic structure factor. The translational di ffusion coefficient D exhibits a chain length dependence D similar to 1/root L for flexible chains and D similar to lnL/L+const/L for rodlik e chains. For flexible chains there is an intermediate scattering vect or regime in which the decay rate or spectral linewidth of the dynamic structure factor is proportional to q(3) indicating that stretching m odes are dominant. Such an intermediate scattering vector regime canno t be observed for semiflexible or rodlike chains. At large scattering vectors q/2p>1.5, where 1/2p is the persistence length of the macromol ecules, the chain stiffness becomes important for any kind of molecule s, i.e., even for very flexible ones. The dynamic structure factor and the decay rate are compared with experimental results of quasielastic neutron and light scattering experiments on different natural and syn thetic macromolecules. These experimental results are in good agreemen t with the theoretical predictions. Furthermore, we determine the pers istence length of F-actin from a dynamic light scattering experiment. (C) 1996 American Institute of Physics.