Analysis of Chemical and Physical Relaxation Processes of Polyelectrolytes by Electric Field Pulse Methods: A Comparison of Critical Comments with Facts

摘要

According to some statements in the literature, it is very hard or virtually impossible to get meaningful relaxation data for macromolecular systems by methods involving electric field pulses (electric field jump and Joule temperature jump), mainly because of perturbations resulting from field induced orientation effects. These statements have been presented until recently, in spite of the fact that the magic angle technique for suppression of such effects has been described in the literature quite some time ago. Apparently there is not sufficient knowledge on the existence/validity/practicability of this technique. More than 20 years experience with magic angle detection is summarized, including a recent detailed comparison of magic angle fluorescence T-jump data with corresponding stopped flow data for the case of ethidium intercalation into DNA double helices. The results demonstrate that chemical relaxation induced by application of electric field pulses to macromolecular solutions can be measured without perturbations, provided that appropriate procedures are used. Moreover, techniques using electric field pulses proved to be the only practicable approach to analysis of many macromolecular reactions. It is not always necessary to suppress orientation effects; on the contrary, orientation effects can be very useful to follow reactions which cannot be detected by other procedures. A special case is demonstrated where reaction and orientation effects appear as a convolution product.