ELECTROOPTIC ANALYSIS OF MACROMOLECULE DIPOLE-MOMENTS USING ASYMMETRIC REVERSING ELECTRIC PULSES

The use of symmetric reversing electric field pulses in electrooptic s tudies of rigid macromolecules in order to determine the ratio between the permanent and the induced dipole moments is well established. App lication of this method to studies of small macromolecules requires a field reversal time of only a few nanoseconds. No high current pulse g enerator capable of producing symmetric kV pulses with such a short re versal time is available for studies of small macromolecules in physio logical salt solutions, but it has long been known how to make such re versing pulses that are asymmetric. In order to take advantage of the opportunity offered by the latter fact, we here present a theoretical analysis in the thermal domain of the electrooptic properties of solut ions containing rigid macromolecules with axial symmetry when exposed to asymmetric reversing electric field pulses. The analytical expressi ons needed for quantitative determination of the ratio between the per manent and the induced electric dipole moments of rigid macromolecules using electrooptic data obtained employing reversing electric pulses with given asymmetry are presented. The feasibility of this new approa ch is demonstrated by including experimental electric birefringence da ta for a 12 kDa protein (segment 14 of alpha-spectrin from Drosophila brains) in near physiological salt solutions obtained using a coaxial cable pulser producing 2 mu s long pulses with a reversal time of abou t 15 ns. (C) 1998 Elsevier Science B.V. All rights reserved.