pH responsiveness of block copolymer vesicles with a polypeptide corona

Area of Science:

• Polymer Science
• Materials Science
• Biophysical Chemistry

Background:

• Amphiphilic block copolymers self-assemble into various nanostructures in solution.
• Poly(L-lysine) is a polypeptide with pH-dependent conformational changes (coil to helix).
• Understanding self-assembly is crucial for designing novel nanomaterials.

Purpose of the Study:

• To investigate the aggregation behavior of polybutadiene-block-poly(L-lysine) in saline solution.
• To determine the influence of polypeptide secondary structure on aggregate morphology and size.
• To correlate structural changes with colloid stabilization mechanisms.

Main Methods:

• Combined static and dynamic light scattering (SLS/DLS) analyses were employed.
• Experiments were conducted in saline solution across different pH values (7.0 and 10.3).
• Hydrodynamic radius and interchain distances were measured.

Main Results:

• Vesicle formation was observed at both pH 7.0 (100% coil) and pH 10.3 (80% alpha-helical).
• At pH 10.3, aggregates exhibited reduced size (364 nm to 215 nm hydrodynamic radius).
• Increased polypeptide helical content led to denser packing at the core-corona interface (interchain distance reduced from 3.2 nm to 2.4 nm).

Conclusions:

• The secondary structure of the poly(L-lysine) segment influences the size and packing density of polybutadiene-block-poly(L-lysine) aggregates.
• Observed changes in aggregate structure can be adequately explained by fundamental colloid stabilization theories.
• Secondary structure effects do not require explicit consideration to understand the observed aggregation behavior.