2D Chiral Structures in Quinoline Mixed Langmuir Monolayers

Abstract

Chirality at interfaces is a relevant topic in nanoscience, as well as a key point for prebiotic chemistry. Mixed Langmuir monolayers, composed of the anionic phospholipid dimyristoyl phosphatidic acid (DMPA) and the cationic amphiphilic quinoline derivative 2-methyl-1-octadecylquinoline (MQ) have been built at the air−water interface. Both DMPA and MQ molecules are miscible, thus the equimolar mixture yields homogeneous monolayers completely. Chiral domains have been formed by this monolayer and observed in situ by Brewster angle microscopy (BAM). These chiral domains display a large array of shapes and sizes. The chirality of the monolayers has been confirmed by circular dichroism spectroscopy. The ordered aggregation of the quinoline group into large chiral supramolecular structures is proposed as the molecular origin of the observed chirality. Theoretical simulations using molecular mechanics confirm the strong trend of the quinoline group to form chiral aggregates. The great diversity in the size and shape of the chiral domains has been found to be strongly influenced by the competition between two nuclei growth mechanisms. An experimental procedure allowing a minimized growth through one of these mechanism is proposed, achieving a homogeneous distribution of ring-shaped domains. An overshoot in the π−A isotherms of this mixed monolayer appears at an intermediate surface pressure. This overshoot is interpreted as being due to the large difference between the surface pressure which starts the nuclei formation, π crit , and the superficial pressure in which the nuclei can grow, π e . The rather small π e value compared to π crit observed for this system must be attributed to the molecular interactions involved in the mixed monolayer, which facilitate the incorporation of molecules in preformed nuclei.

Stereochemistry and Twisted Crystals

“…This phenomenon was associated with the fact that the amphiphiles must form polar structures at the interface, with the hydrophilic groups in contact with the water, centrosymmetric structures are greatly unfavored. [108,109] The occurrence of chiral morphologies in two-component domains [110] suggests the breadth of asymmetric objects that can be created at interfaces.…”

Diacetylene Mixed Langmuir Monolayers for Interfacial Polymerization

“…All these intermolecular interactions contribute to the miscibility of the DA and OTCC molecules at the air/water interface. The overshoot in the π– A isotherms of the DA:OTCC mixed monolayer indicates the complete miscibility of the components . Pure DA Langmuir monolayer collapses at area values below 0.25 nm 2 /molecule (Figure , black line, for π = 40 mN/m, A = 0.1 nm 2 /molecule), forming a trilayer .…”

“…The overshoot in the π−A isotherms of the DA:OTCC mixed monolayer indicates the complete miscibility of the components. 40 Pure DA Langmuir monolayer collapses at area values below 0.25 nm 2 /molecule (Figure 1, black line, for π = 40 mN/m, A = 0.1 nm 2 /molecule), forming a trilayer. 41 For the pure OTCC Langmuir monolayer (Figure 1, blue line), the takeoff of the isotherm occurs at ca.…”

Exploring the Impact of Tail Polarity on the Phase Behavior of Single Component and Mixed Lipid Monolayers Using a MARTINI Coarse-Grained Force Field

“…Mixed monolayer films of surfactants are invaluable systems for probing numerous important physical and chemical phenomena, ranging from phase-separation and intermolecular interactions, to dynamics of surface processes. − The spatial distribution and organization of surfactants in mixed films is a key area of interest, in part because mixed monolayers (and bilayers) are excellent, albeit highly simplified model systems for biological membranes and interfaces, such as the gas exchange interface in lungs and the tear film in eyes, which exhibit complex spatial distributions of surface-active species. − A significant effort has been made to understand and control factors that regulate intermolecular interactions between surfactants in complex mixed films, though many of these factors are still poorly understood. The development of a simple, minimal model for predicting the spatial distribution of surfactants based on the chemical identity of film constituents and the composition of mixed monolayer systems is an important but challenging research goal, and efforts to develop such models are ongoing.…”