A Non-Linear Least-Squares Approach to the Isothermal Perrin-Weber Plot in Terms of Rotational Correlation Times

Abstract

The study of the stationary fluorescence anisotropy, r¯, of chromo-phores attached to biopolymers, as originally developed by Weber (1953), can be used to detect rotational and segmental motions in these molecules. However, when several motions appear simultaneously it is often impossible to quantify each of them, because the value of r¯ at a given viscosity and temperature contains contributions from all the orientational processes active in these conditions (Weber, 1953). On the other hand, since the values of r¯ can be measured easily to a very high accuracy with present day instrumentation, it would be helpful to have methods to interpret those measurements on the frequent occasions where several reorientation processes are likely to occur. Here we present a semi-quantitative approach to the isothermal Perrin-Weber plots that could yield at least an order of magnitude estimation of the rotational correlation times present in a particular system.