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Structure and phase behavior of self-assembled DPPC-DNA-metal cation complexes
Michela Pisani1, Paolo Bruni, Giulio Caracciolo
1Dipartimento di Scienze dei Materiali e della Terra, Università Politecnica delle Marche, Via Brecce Bianche, I-60131 Ancona, Italy.
The Journal of Physical Chemistry. B
|June 30, 2006
Summary
Multilamellar liposomes of dipalmitoylphosphatidylcholine (DPPC) and DNA self-assemble into a ternary complex with metal cations. This complex exhibits altered thermotropic phase behavior compared to uncomplexed DPPC lipids.
Area of Science:
- Biophysics
- Materials Science
- Supramolecular Chemistry
Background:
- Liposomes composed of dipalmitoylphosphatidylcholine (DPPC) are widely studied for drug delivery.
- DNA condensation is crucial for gene therapy and nanotechnology.
- Metal cations play vital roles in biological systems and material self-assembly.
Purpose of the Study:
- To investigate the self-assembly of a ternary complex formed by DPPC liposomes, DNA, and bivalent metal cations.
- To characterize the structure and thermotropic phase behavior of the DPPC-DNA-Me2+ complex.
- To understand the role of metal cations in stabilizing DNA condensation within the lipid matrix.
Main Methods:
- Synchrotron X-ray diffraction was used to analyze the structural properties.
- Electron density profiles were calculated to deduce structural data.
- Thermotropic phase behavior was studied across a temperature range of 20-55°C.
Main Results:
- A ternary DPPC-DNA-Me2+ complex was successfully formed, exhibiting an ordered multilamellar structure.
- The complex coexists with uncomplexed DPPC, showing two distinct lamellar phases.
- The thermotropic behavior of DPPC within the complex is altered, with an increased transition temperature and loss of the ripple phase.
Conclusions:
- Bivalent metal cations facilitate and stabilize the condensation of DNA within DPPC liposomes.
- The ternary complex formation leads to modified lipid phase transitions compared to pure DPPC.
- This study provides insights into the supramolecular organization of lipid-DNA-cation systems.
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