113 research outputs found
Molecular simulation analysis of structural variations in lipoplexes
We use a coarse-grained molecular model to study the self-assembly process of
complexes of cationic and neutral lipids with DNA molecules ("lipoplexes") - a
promising nonviral carrier of DNA for gene therapy. We identify the resulting
structures through direct visualization of the molecular arrangements and
through calculations of the corresponding scattering plots. The latter approach
provides a means for comparison with published data from X-ray scattering
experiments. Consistent with experimental results, we find that upon increasing
the stiffness of the lipid material, the system tends to form lamellar
structures. Two characteristic distances can be extracted from the scattering
plots of lamellar complexes - the lamellar (interlayer) spacing and the
DNA-spacing within each layer. We find a remarkable agreement between the
computed values of these two quantities and the experimental data [J. O.
R\"{a}dler, I. Koltover, T. Salditt and C. R. Safinya, Science Vol. 275, 810
(1997)] over the entire range of mole fractions of charged lipids (CLs) studied
experimentally. A visual inspection of the simulated systems reveals that, for
very high fractions of CLs, disordered structures consisting of DNA molecules
bound to small membrane fragments are spontaneously formed. The diffraction
plots of these non-lamellar disordered complexes appear very similar to that of
the lamellar structure, which makes the interpretation of the X-ray data
ambiguous. The loss of lamellar order may be the origin of the observed
increase in the efficiency of lipoplexes as gene delivery vectors at high
charge densities.Comment: Accepted for publication in "Soft Matter
Hyperradiance from Soliton Oscillators Synchronized by Capacitive or Inducitve Coupling
The output power from coupled Josephson oscillators is investigated when the junctions are operated in their single fluxon mode. We demonstrate that both inductive and capacitive coupling mechanisms can give rise to hyperradiance when the power is coupled out through a boundary resistor. Analytical expressions are derived from adiabatic perturbation theory and excellent agreement is found between the analytical expression and numerical simulations
- …