Phase Behavior and Molecular Packing of Octadecyl Phenols and their Methyl Ethers at the Air/Water Interface

Abstract

Noncovalent molecular interactions, such as hydrogen bonding and van der Waals forces, play an important role in self-assembling to supramolecular structures. To study these forces, we chose monolayers at the air/water interface to limit the possible arrangements of the interacting molecules. Furthermore, monolayers provide useful tools to understand and study interactions between molecules in a controlled and fundamental way. The phase behavior and molecular packing of the phenols 1-(4-hydroxyphenyl)-octadecane (5a), 1-(3,4-dihydroxyphenyl)-octadecane (6), and 1-(2,3,4-trihydroxyphenyl)-octadecane (3) and their methyl ethers in monolayers at the air/water interface have been examined by π/A isotherms, Brewster angle microscopy (BAM), grazing incidence X-ray diffraction (GIXD) measurements, and density functional theory (DFT) calculations. The phenols are synthesized by Friedel-Crafts acylation of methoxybenzenes, hydrogenation of the resulting aryl ketones, and cleavage of the aryl methyl ethers. In the π/A isotherms and in BAM, the phenols show patches of the solid condensed phase at large molecular areas and the monolayers collapse at high pressures. Furthermore, the dimensions of the unit cell obtained by GIXD measurements are compatible with an arrangement of the phenyl rings that allows one aryl ring to interact with four adjacent phenyl rings in an edge-to-face arrangement, which leads to a significant binding energy. The experimental data are in good agreement with DFT calculations of 2D crystalline benzene and p-cresol arrangements. The enhanced monolayer stability of phenol 5a can be explained by hydrogen bonds of the hydroxyl group with water and van der Waals forces between the alkyl chains and aryl-aryl interactions.

Strong Headgroup Interactions Drive Highly Directional Growth and Unusual Phase Co-Existence in Self-Assembled Phenolic Films

“…Such an organization was proposed based on simulations for ether-linked, monoand di-hydroxy phenolic surfactants but not observed by GIXD. 10 Organization of the headgroup leads to the possibility that the centered rectangular herringbone arrangement arises because of a molecular lattice with a nonequivalent headgroup orientation. If the alkyl chains were also to be in the herringbone arrangement, a corresponding strong [1,2] r peak should be observed at the same Q xy = 1.86 Å −1 , but such a peak would need to be out-of-plane because of the tilting of the chain.…”

“…8 Our group has previously reported the monolayer properties of a phenol lipid, dipalmitoylgalloylglycerol, and found evidence of a highly cohesive and rigid film attributed to an extensive hydrogen bond network between the phenol headgroups which comprise multiple hydroxyl groups. 9 Peikert et al 10 studied phenolic surfactant films with variation in the hydroxyl position. Using grazing incidence X-ray diffraction (GIXD) and computational methods, they determined possible arrangements of the headgroups where the aromatic ring can interact with four adjacent rings, maximizing the πstacking interactions, hinting that despite the weakness of the π-stacking relative to hydrogen bonding, this can still significantly influence the organization of the monolayer.…”

Homology Modelling, In Silico Prediction And Characterization Of Cytochrome c oxidase In Cyprinus carpio And Tubifex tubifex And Molecular Docking Studies Between The Modelled Protein And Three Commonly Used Surfactants Sodium Dodecyl Sulphate, Cetylpyridinium Chloride And Sodium Laureth Sulphate

“…Referencing to literature, several standard values of distance cutoffs to consider the formation of hydrophobic interactions have been found and the optimum range is in between 3.3 – 3.8 Å (Janiak 2000). While other researchers have suggested a relatively higher ranges (Burley and Petsko 1985, Peikert et al 2014, Piovesan et al 2016). The interactions and active site residues responsible for bindings between surfactants and target protein Cytochrome c oxidase subunit 2 of Cyprinus carpio and Cytochrome c oxidase subunit 1 of Tubifex tubifex are presented in Fig 8 and 9 respectively.…”

“…It is The copyright holder for this preprint this version posted July 10, 2021. ; https://doi.org/10.1101/2021.07.09.451643 doi: bioRxiv preprint the formation of hydrophobic interactions have been found and the optimum range is in between 3.3 -3.8 Å (Janiak 2000). While other researchers have suggested a relatively higher ranges (Burley and Petsko 1985, Peikert et al 2014, Piovesan et al 2016 . CC-BY-ND 4.0 International license made available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.…”

Extension of “Interfacial Adsorption Denaturation” Behavior Interpretation Based on Gibbs Monolayer Formation by Biomolecules

“…The stage where the surface pressure gradually rises corresponds to the liquid expansion phase 23 , and interactions between the molecules are still weak. Subsequently, by means of two-dimensional phase transition, or alternatively a liquid condensation phase 24 , the solid condensed phase is achieved 25 . The state in which the molecules are as densely packed as in the condensed phase indicates deactivation of the activity 26 , which is not preferable for the functional utilization of biomolecular groups.…”