Nitriles at Silica Interfaces Resemble Supported Lipid Bilayers

Area of Science:

• Surface Chemistry
• Physical Chemistry
• Materials Science

Background:

• Nitriles are versatile solvents used in bulk reactions and interfacial processes like separations and catalysis.
• Traditionally, nitriles are not considered amphiphiles due to insufficient hydrophilicity of the cyano group.
• Emerging research suggests nitriles exhibit unique interfacial organization at silica surfaces.

Purpose of the Study:

• To investigate the unexpected self-organization of nitriles at silica interfaces.
• To understand how this organization influences the interfacial behavior and dynamics of nitrile solvents.
• To explore the implications for chemical processes utilizing nitrile solvents.

Main Methods:

• Optical Kerr Effect (OKE) spectroscopy to study orientational dynamics of confined acetonitrile.
• Molecular dynamics simulations to visualize molecular organization and dynamics at silica interfaces.
• Vibrational Sum-Frequency Generation (VSFG) experiments to probe interfacial structures.

Main Results:

• Nitriles form lipid-bilayer-like (LBL) structures at silica surfaces, with ordered layers of molecules.
• Alkyl chain length and branching (e.g., ethyl vs. t-butyl) significantly affect LBL organization.
• Surface-induced organization persists in mixtures, even with high water or methanol content.

Conclusions:

• Liquid nitriles display complex, surface-dictated organizational and dynamic behaviors not seen in bulk.
• This interfacial organization is crucial for understanding and optimizing applications in separations and catalysis.
• The findings necessitate a re-evaluation of nitrile solvent behavior at interfaces with various materials.