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Characterization of pH-Dependent Poly(acrylic Acid) Complexation with Phospholipid Vesicles
Fujiwara1, Grubbs, Baldeschwieler
1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, 91125
Journal of Colloid and Interface Science
|January 1, 1997
Summary
Poly(acrylic acid) (PAA) binds to phospholipid vesicles, particularly below pH 4, altering their structure and increasing transition temperatures. This polymer-lipid interaction expands vesicle packing by changing headgroup conformation.
Area of Science:
- Biophysical Chemistry
- Polymer Science
- Materials Science
Background:
- Phospholipid vesicles are crucial in biological membranes and drug delivery.
- Poly(acrylic acid) (PAA) is a synthetic polymer with potential applications in biomaterials.
Purpose of the Study:
- To investigate the pH-dependent complexation between poly(acrylic acid) (PAA) and phospholipid (phosphatidylcholine) vesicles.
- To elucidate the structural and thermodynamic changes induced by PAA complexation in phospholipid vesicles and monolayers.
Main Methods:
- Fluorescence polarization to assess polymer mobility and binding.
- Differential scanning calorimetry (DSC) to determine phase transition thermodynamics (Tm, ΔH).
- Surface pressure measurements of phospholipid monolayers to evaluate polymer penetration.
Main Results:
- PAA complexation with vesicles is pH-dependent, pronounced below pH 4 due to carboxyl group protonation.
- Complexation strength is higher at low PAA concentrations and decreases with increasing concentration.
- PAA interaction increases vesicle phase transition temperature (Tm) and enthalpy (ΔH), reducing cooperativity.
- Polymer penetration into phospholipid monolayers increases as pH decreases, indicating pH-driven conformational changes.
Conclusions:
- PAA complexation significantly alters phospholipid vesicle structure and dynamics in a pH-dependent manner.
- The interaction leads to expansion of phospholipid packing within vesicles by modifying headgroup conformation.
- These findings offer insights into polymer-lipid interactions relevant for biomaterial design and understanding membrane behavior.