Confocal Raman Microscopy Investigation of Self-Assembly of Hybrid Phospholipid Bilayers within Individual Porous Silica Chromatographic Particles

Abstract

Hybrid-supported phospholipid bilayers are a model structure utilized for measurement of molecular interactions that typically occur at cell membranes. These membrane models are prepared by adsorption of a lipid monolayer onto a stable n-alkyl chain layer that is covalently bound to a support surface. Hybrid bilayers have been adapted to chromatographic retention measurements of lipophilicity through the assembly of a phospholipid monolayer onto n-alkane-modified silica surfaces in reversed-phase chromatographic particles. Recent Raman microscopy studies of these particles have shown that the acyl chains of the phospholipid interact with the C18-alkyl chains immobilized on the silica surface, where both lipid and C18 alkyl chains become ordered because of chain interdigitation. Confocal Raman microscopy has also been used to investigate the association of small molecules with hybrid-lipid bilayers in C18 chromatographic silica particles; the partitioning of model solutes compares favorably to that in lipid vesicle membranes with similar changes in acyl-chain structure (disordering) with solute partitioning. The present study seeks information about how these membrane-mimetic bilayers assemble onto the C18-derivatized silica surfaces of reversed-phase chromatographic silica particles. Confocal Raman microscopy is capable of interrogating the time-dependent internal composition and structure within individual silica particles. The Raman scattering data can be resolved into component Raman spectra and corresponding composition vectors that describe the time-dependent changes in intensity of the component spectra. This analysis provides insight into how the structures of both the lipid and C18 alkyl chains of hybrid lipid bilayers evolve during deposition and organization on the internal surfaces of reversed-phase chromatographic silica particles.

Confocal Raman Microscopy Investigation of Phospholipid Monolayers Deposited on Nitrile-Modified Surfaces in Porous Silica Particles

“…These hybrid-supported lipid bilayers are formed through the interaction of the acyl chains of the phospholipid monolayer with a hydrophobic support surface. They can be self-assembled on alkane-thiol monolayers on planar gold or silver substrates, − on n -alkyl silane-functionalized glass, and on porous reversed-phase chromatographic silica surfaces. − These C 18 alkyl chain-derivatized porous particles, dynamically modified with lipid monolayers, have been shown to be useful for chromatographic separations based on lipophilicity. They exhibit solute retention for both small molecules and proteins that track the partitioning of these solutes into phospholipid vesicle bilayers. − The high surface areas of these particles have allowed Raman spectroscopy investigations of both the lipid bilayer structure and its interactions with membrane-active molecules. − …”

Raman Scattering Reveals Ion-Dependent G-Quadruplex Formation in the 15-mer Thrombin-Binding Aptamer upon Association with α-Thrombin

“…SMCR is a multivariate statistical method that resolves correlated changes in a series of spectra across a variation in composition by eigenvector decomposition of the variance–covariance matrix of the data (Supporting Information). − The pure-component spectra and corresponding composition vectors that describe the data are determined from linear combinations of the eigenvectors, subject to non-negativity constraints on the spectral intensities and component amplitudes (Supporting Information).…”