Electro-Optics of Unilamellar Vesicles

Abstract

Electric field-induced transient birefringence and light scattering are reported for aqueous suspensions of synthetic unilamellar bilayer vesicles, prepared from the lipid dioleoylphosphatidylcholine (DOPC). The multiexponential birefringence relaxations observed on the microsecond and millisecond timescales are interpreted in terms of elongation and reorientation of induced dipolar vesicles, their linear chain formation, and electrofusion (and possibly electroporation) of the vesicles. Above certain threshold values of vesicle concentration, field-induced light scattering occurs concomitant with the birefringence. The corresponding transient signals corroborate the linear chain formation and subsequent fusion of the induced dipolar vesicles.

Dynamics of Electroporation of Synthetic Liposomes Studied Using a Pore-Mediated Reaction, Ag+ + Br- → AgBr

“…The underlying electromechanical deformation of vesicles and the rotational relaxation of the dipoles typically occur on the microsecond time scale. 10,11 Not surprisingly, the nature and dynamics of the overall polarization and deformation processes are similar to those observed in other spheroid organized assemblies such as reverse micelles and water-in-oil microemulsions. 12 Although it is generally known that the experimental parameters must be within certain limits for electroporation to occur * Author to whom correspondence should be addressed.…”

“…The resulting structural anisotropy of the solution is manifested in a transient birefringence which can be monitored. The underlying electromechanical deformation of vesicles and the rotational relaxation of the dipoles typically occur on the microsecond time scale. , Not surprisingly, the nature and dynamics of the overall polarization and deformation processes are similar to those observed in other spheroid organized assemblies such as reverse micelles and water-in-oil microemulsions …”

Electroporation of Unilamellar Vesicles Studied by Using a Pore-Mediated Electron-Transfer Reaction

“…Prior to perturbation by the high-voltage (2 kV) square pulse, the vesicles undergo thermal shape fluctuations, with a time average spherical shape. Upon application of the electric field E at time t ) 0, its primary effects are the polarization (electronic and Maxwell-Wagner interfacial polarizations) and elongation of the bilayer shells to prolate ellipsoids in the direction of E. The structural anisotropy of the system resulting from the elongation and alignment of the induced dipolar vesicles parallel to E is exhibited in a rising transient birefringence observed 9,10,20,21 (Figure 4). These processes are analogous to those observed in other spheroid organized assemblies such as reverse micelles and water-in-oil microemulsions.…”

“…In previous studies of the effects of electric field on organized assemblies, our laboratory focused on the dynamics of field-induced phase separation in water-in-oil microemulsions, and structural changes in reverse micelles − and synthetic vesicles. , In recent papers, we have reported the preparation of quantum dots via the electroporation of vesicles and studied the timing of pore opening relative to structural changes of the bilayer shell

1 Schematic representation of the DOPC liposome system studied, with [Fe(II), inside] = 2 × 10 -3 M and [Ir(IV), outside] = 5.6 × 10 -5 M. The amount of compartmentalized Fe(II) present corresponds to a global Fe(II) concentration of 3 × 10 -5 M.

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“…In previous studies of the effects of electric field on organized assemblies, our laboratory focused on the dynamics of field-induced phase separation in water-in-oil microemulsions, 5 and structural changes in reverse micelles 6-8 and synthetic vesicles. 9,10 In recent papers, we have reported the preparation of quantum dots via the electroporation of vesicles 11 and studied the timing of pore opening relative to structural changes of the bilayer shell. 12 In the present paper, the dynamics of electroporation of unilamellar bilayer vesicles, prepared from the phospholipid dioleoylphosphatidylcholine (DOPC), is investigated by the use of a pore-mediated indicator reaction By entrapping Fe(II) in the interior compartment of the vesicle and placing Ir(IV) in the bulk medium (Figure 1), we can use the spectral changes associated with the electron-transfer Fe(II) + Ir(IV) f Fe(III) + Ir(III) to signal the opening of pores in the separating bilayer.…”