Structural study of poly(beta-benzyl-L-aspartate) monolayers at air-liquid interfaces

Area of Science:

• Biophysics
• Polymer Science
• Structural Biology

Background:

• Poly(beta-benzyl-L-aspartate) (PBLA) typically adopts a left-handed alpha-helical conformation in solid states and solutions.
• The helical stability of PBLA is sensitive to environmental factors, with potential for conformational inversion.
• Previous studies lacked direct conformational analysis of PBLA at interfaces.

Purpose of the Study:

• To determine the secondary structure of PBLA in the monolayer state at the air-water interface.
• To investigate the influence of environmental polarity on PBLA's helical conformation.
• To characterize the formation of alternative helical structures under specific conditions.

Main Methods:

• External reflectance Fourier transform infrared spectroscopy (FTIR) was employed to analyze PBLA conformation.
• Langmuir monolayers of PBLA were formed and compressed at the air-water interface.
• Varying the polarity of the aqueous subphase, including the addition of isopropanol, was used to perturb the system.

Main Results:

• PBLA forms right-handed alpha-helices immediately upon spreading at the air-water interface, irrespective of the solution conformation.
• The right-handed helical form is maintained during monolayer compression.
• Lowering subphase polarity reverses the helical screw sense, while isopropanol addition induces an omega-helix-like conformation.

Conclusions:

• The air-water interface promotes a right-handed alpha-helical conformation in PBLA, contrasting with its solution behavior.
• Environmental polarity is a critical factor in controlling the helical screw sense of PBLA.
• The study reveals the conformational plasticity of PBLA and the potential for omega-helix formation at interfaces.