Electrostatics, Hydrogen Bonding, and Molecular Structure at Polycation and Peptide:Lipid Membrane Interfaces

Area of Science:

• Materials Science
• Biochemistry
• Surface Chemistry

Background:

• Polycation and peptide-modified surfaces offer novel biocidal material potential.
• Combating bacterial resistance necessitates understanding antimicrobial mechanisms.
• Quantifying surface-bound positive charges is crucial for optimizing biocidal compound design.

Purpose of the Study:

• To develop and apply a method for quantifying positive charges on surface-bound polycations and peptides.
• To gain mechanistic insight into polycation-membrane interactions.
• To correlate charge quantification with biocidal material performance.

Main Methods:

• Utilized second harmonic generation (SHG) spectroscopy.
• Employed quartz crystal microbalance with dissipation monitoring (QCM-D).
• Integrated atomistic simulations and supported lipid bilayers (SLBs) as a model system.

Main Results:

• At high surface coverage, large polycations showed significantly lower ionization percentages compared to smaller polycations and peptides.
• Evidence suggests a pKa shift and loop-like conformations in large polycations at high charge densities.
• Sum frequency generation (SFG) spectroscopy indicated water expulsion at high poly(allylamine hydrochloride) (PAH) density, suggesting contact-ion pair formation.

Conclusions:

• The developed approach provides essential quantification of surface charges for biocidal materials.
• Understanding polycation-membrane interactions, including charge density and conformation, is vital for designing effective antimicrobial surfaces.
• The findings on water expulsion offer insights into the initial steps of polycation-mediated cell lysis.