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Vesicles and membranes (475-481)
COLL
475: Electric birefringence, light scattering, and
electroporation of synthetic liposomes
Zoltan A Schelly, Niloofar Asgharian, N. Mariano Correa, Hongguang
Zhang, Viktor Peikov, and Hongxia Zeng, Center for Colloidal and
Interfacial Dynamics, University of Texas at Arlington, Department of
Chemistry and Biochemistry, Arlington, TX 76019-0065, schelly@uta.edu
Abstract
The dynamics of transient electric birefringence, electric light
scattering and electroporation of unilamellar bilayer vesicles are
reported. Monodisperse liposomes with mean hydrodynamic diameter <Dh>
ranging from 95 nm to 190 nm were prepared from the zwitterionic
phospholipid dioleoylphospahatidylcholine (DOPC) through multiple
extrusion. Effects of the experimental parameters (strength and length of
the applied rectangular or reversing electric field E pulse,
temperature, lipid concentration, vesicle size, and ionic strength) on the
amplitudes Ai and relaxation times ti
of the observed multiexponential relaxations were investigated. Mechanisms
of polarization, sources and stages of the induced structural anisotropy
of the solution, and the requisite conditions for membrane electroporation
were elucidated. The utility of electroporation of synthetic liposomes for
the preparation of ultra-small (~5 Ĺ) quantum dots is also discussed.
References
COLL
476: Electrodiffusion of genetic oligoelectrolytes
through electroporated planar lipid membranes
Eberhard Neumann, and Nadejda I. Hristova-Betow, Department of
Physical and Biophysical Chemistry, Faculty of Chemistry, University of
Bielefeld, P.O.Box 100 131, D-33501, Bielefeld, Germany, Fax: 49 521 106
2981, eberhard.neumann@uni-bielefeld.de
Abstract
Gene DNA and the various genetic oligonucleotides are anionic
polyelectrolytes which are functionally involved in life processes
occurring near intracellular membranes. The contact between cell membrane
and biopolyelectrolytes can be qualified as surface-inserted adsorption of
DNA or oligonucleotides. Adsorbed DNA, single-stranded and double-stranded
oligonucleotides cause channel-like ionic current events. Throughout, the
conductances are strongly non-linearly dependent on the applied membrane
voltage, suggesting membrane electroporation facilitated by the adsorbed
linear polyelectrolytes. Interestingly, the experimental polarization
volume is dependent on the length, suggesting length-wise electromigration
of the oligonucleotides across the electroporated bilayer. The initiation
of the single current events requires that the electric potential of the
cis side of the membrane where the DNA is added, is negative and that of
the trans side is positive. In summary, the data indicate that
oligoelectrolytes and DNA, above a certain threshold voltage of 120 mV,
are electrophoretically drawn through the locally electroporated lipid
bilayer.
COLL
477: Selective electroporation of a vesicle
population in high-frequency electric fields
Ephrem Tekle, and Boon P. Chock, Laboratory of Biochemistry, NHLBI,
NIH, 50 south drive, room 2127, Bethesda, MD 20892-0342, Fax:
301-496-0599, ephrem@helix.nih.gov
Abstract
The principal effect of external electric fields on the integrity of
spherical cell or vesicle membranes is studied at low (MHz) and high (GHz)
field frequencies. The magnitude of the external field-induced critical
transmembrane potential, responsible for membrane permeabilization, can be
significantly attenuated when the period of the oscillating field (GHz) is
shorter than the charging time of the membrane dielectric (~ms).
These frequency dependences allow the selective permeabilization of
smaller vesicles (or cells) in the presence of larger vesicles at GHz
field frequencies, and permeabilization of larger vesicles in the presence
of smaller ones at MHz frequencies. Additional selective permeabilization
is further possible in vesicle populations of similar size distributions,
provided the charging time constant of the membrane capacitance can be
adjusted through the resistivities of the internal and external media.
These various possibilities are discussed using homogeneous set of vesicle
preparations as test samples.
COLL
478: Kinetics of optical membrane probes for lipid
vesicle elongation and electroporation in high electric fields
Sergej A. Kakorin, Thomas Liese, and Eberhard Neumann, Department
of Physical and Biophysical Chemistry, Faculty of Chemistry, University of
Bielefeld, P. O. Box 100 131, D-33501 Bielefeld, Germany, Fax: 49 521 106
2981, sergej.kakorin@uni-bielefeld.de
Abstract
The kinetics of membrane probes ß-DPH pPC, TMA-DPH, DPH, PATMAN,
Zeaxanthin and DiIC16(3) in electroelongated unilamellar lipid vesicles,
prepared from 20% (weight) commercial Lecithin (20 % phophatidylcholine,
10 % phosphatidic acid, 30 % phophatidylethanolamine, 20 %
phophatidylinositol and 20 % other lipids), vesicle diameter after
extrusion D=50, 100, 180 and 360 nm, have been studied by the absorbance
of polarized light at its wavelength in vacuum. Vesicle elongation has
been caused by rectangular field pulses of high strengths and pulse
duration t=10 µs. Analysis of the electric absorbance dichroism has
revealed that the positional changes of the optical transition moments of
the membrane probes inserted in the different parts of the membrane all
reflect membrane thinning, smoothing of membrane undulations, sliding of
the monolayers against each other, tilting of lipid molecules relative to
the membrane normal, and membrane electroporation.
COLL
479: Modeling of the electric field-induced
birefringence of vesicles
Viktor T. Peikov, NeoPharm, Inc, 1850 Lakeside Drive, Waukegan, IL
60085, Fax: 847-887-9281, vpeykov@neophrm.com, and Zoltan A Schelly,
Center for Colloidal and Interfacial Dynamics, University of Texas at
Arlington
Abstract
Electric birefringence of lipid vesicles, elongated in the direction of
the applied field E, is modeled for low degree of
deformation to prolate ellipsoid of the original spherical shells.
Existing theory for water-in-oil microemulsion is adapted, and the
intrinsic birefringence of the lipid membrane and the form birefringence
of the aqueous inner core of the vesicle are taken into account.
Deformation under both constant surface area and constant volume
conditions are considered, but thinning of the bilayer at the polar caps
and rotational/orientational effects are neglected. The extent of
elongation of large unilamellar DOPC vesicles is calculated, and the axial
ratio of the deformed vesicle is found to be in the range 1.02-1.08. The
equations derived are also suitable for calculation of the bending
elasticity modulus k of the
bilayer from experimental values of the Kerr constant K, provided
the electrical and optical properties of the vesicle membrane are known.
Free
reprints of the full article (J. Phys. Chem. B 2004, 108, 9357-9363) can be downloaded from the web at
http://pubs.acs.org/cgi-bin/download.pl?jp0369488/L2jT
COLL
480: Interpretation of electric and optical
signals associated with the function of transmembrane ion pumps
András Dér, Institute of Biophysics, Biological Research Centre
of the Hungarian Academy of Sciences, Temesvári krt. 62, Szeged H-6701,
Hungary, Fax: 36-62-433 133, derandra@nucleus.szbk.u-szeged.hu
Abstract
Ion pumps are often investigated experimentally by photoelectric
measurements in model systems. In addition to the most widely used systems
based on model membranes, a fundamentally different class is represented
by the so-called suspension methods. In this technique the electric signal
is measured on a bulk suspension of oriented ion pumps in the form of a
displacement current. Orientation, as a prerequisite for measuring
electric signals, is achieved by the application of electric field, and it
is subsequently fixed by a gel. On such a sample, electric and optical
experiments can be performed simultaneously. Using the information from
both types of measurements, and utilizing the three-dimensional nature of
the system, it is possible to follow the intramolecular charge motions in
all three spatial directions. The derivable dipole moment changes
associated with conformational transitions allow the verification of
molecular dynamic models.
COLL
481: Geometry of purple membranes in aqueous
medium
Alexandar M. Zhivkov, Institute of Physical Chemistry, Bulgarian
Academy of Sciences, Acad. G. Bontchev str., bl. 11, 1113 Sofia, Bulgaria,
zhivkov@ipc.bas.bg
Abstract
In previous works, it was shown that purple membranes (PM) are bent in
aqueous environment. In the present work the geometry of the undisturbed
PM was determined by two approaches: In the first, the membrane curvature
was obtained by comparison of the measured radius of gyration Rg
to calculated ones. For this purpose theoretical expressions for Rg
of cylindrically and spherically bent elliptical disks are derived, and
experimental values of Rg and the membrane area were
determined by small angle light scattering and electric light scattering,
respectively. In the second approach, the value of pH-induced changes of
the intensity of light scattered at 90° are compared to those
theoretically calculated for cylindrically or spherically bent elliptical
disks. The values of the curvature calculated in these two approaches are
in very good agreement. Comparison of light scattering intensity at two
different wavelengths shows that PM are cylindrically bent in aqueous
media.
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