# Surface Symphony: Orchestrating DPPC/DOPC Monolayer Behavior

## TL;DR

This study explores how temperature, ions, and lipid mixtures affect the structure and behavior of DPPC/DOPC monolayers.

## Contribution

The study reveals how environmental factors and lipid composition influence monolayer properties through experimental observations.

## Key findings

- Temperature affects DPPC monolayer phase behavior, with coexistence at 15°C and 20°C but not at 25°C.
- Divalent ions (CaCl2) lead to more compact DPPC packing compared to monovalent ions (KCl).
- Adding DOPC to DPPC at 20°C increases fluidity and disrupts domain formation.

## Abstract

This study investigates the impact of environmental factors and lipid composition on the structural and morphological properties of DPPC/DOPC (1,2‐Dipalmitoyl‐sn‐glycero‐3‐phosphocholine/1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine) monolayers. Temperature plays a significant role in DPPC monolayer behavior; at 15°C and 20°C, DPPC exhibits liquid expanded–liquid condensed coexistence, while at 25°C, this coexistence region disappears. Divalent ions (CaCl2) enhance more compact and uniform DPPC packing compared to monovalent ions (KCl), reducing mean area per molecule. The incorporation of DOPC into DPPC at 20°C increases the monolayer fluidity, disrupting the DPPC domain formation. For all systems, increasing surface pressure improves surface coverage and transforms micro domains into compact and continuous films at higher pressures. These findings highlight the critical roles of ionic interactions, temperature, and lipid composition in modulating lipid monolayer properties.

Langmuir trough and atomic force microscopy reveals the physical nature of DPPC and DOPC mixed monolayers.