Unusual Salt and pH Induced Changes in Polyethylenimine Solutions

Area of Science:

• Polymer Chemistry
• Biomaterials Science
• Nanotechnology

Background:

• Linear poly(ethylene imine) (PEI) is a cationic polymer vital for DNA complexation in gene therapy.
• Its structure features amines for protonation and a hydrophobic backbone, influencing solution behavior.
• PEI exhibits multiple buffering mechanisms and shifts between aggregated and free states in solution.

Purpose of the Study:

• To investigate the interplay between aggregation and protonation in 2.5 kDa linear PEI.
• To elucidate the solution dynamics of PEI relevant to its application in gene delivery.

Main Methods:

• pH probing
• Vapor pressure osmometry
• Dynamic light scattering
• Ninhydrin assay

Main Results:

• At neutral pH, PEI chains associate, with NaCl initially decreasing then increasing association.
• Aggregates are uncollapsed and coexist with free chains.
• PEI buffering involves continuous or discontinuous charging between stalled states.
• The size of PEI-DNA complexes is independent of PEI's aggregated state.

Conclusions:

• Linear PEI displays intricate solution dynamics influenced by aggregation and protonation.
• These dynamics are crucial for its function in DNA delivery systems.
• Harnessing these properties can lead to improved environment-sensitive biomaterials and gene delivery strategies.