Cation effects on phosphatidic acid monolayers at various pH conditions

Area of Science:

• * Biophysical Chemistry
• * Surface Science
• * Environmental Chemistry

Background:

• * Dipalmitoylphosphatidic acid (DPPA) is a key lipid in biological membranes and interfaces.
• * Understanding DPPA monolayer behavior is crucial for various applications, including environmental science.

Purpose of the Study:

• * To investigate the impact of pH and various cations on the phase behavior, stability, and surface morphology of DPPA monolayers.
• * To elucidate the relationship between cation complexation, pH, and the protonation state of DPPA.

Main Methods:

• * Investigation of DPPA monolayers at the air-water interface.
• * Controlled variation of pH and presence of different cations (Na+, K+, Mg2+, Ca2+).
• * Analysis of monolayer phase behavior, packing density, stability, and surface morphology.

Main Results:

• * At pH<10, neutral DPPA species dominate, leading to highest packing density.
• * Cations expand and stabilize DPPA monolayers, with order of effect at pH 5.6: Na+>K+∼Mg2+>Ca2+.
• * Cation binding affinity (Ca2+>Mg2+>Na+>K+) correlates with the law of matching water affinities and influences 3D lipid structure nucleation.

Conclusions:

• * pH and cation complexation are primary drivers of DPPA monolayer surface behavior.
• * The findings provide insights into complex systems like marine aerosols, where organic films are affected by aqueous phase conditions.
• * Understanding these interactions is vital for predicting the behavior of organic films in environmental interfaces.