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Confocal Raman Microscopy of Hybrid-Supported Phospholipid Bilayers within Individual C18-Functionalized Chromatographic Particles

Journal Article · · Langmuir
 [1];  [2]
  1. University of Utah, Salt Lake City, UT (United States); University of Utah
  2. University of Utah, Salt Lake City, UT (United States)

Measuring lipid-membrane partitioning of small molecules is critical to predicting bioavailability and investigating molecule-membrane interactions. A stable model membrane for such studies has been developed through assembly of a phospholipid monolayer on n-alkane-modified surfaces. These hybrid-bilayers have recently been generated within n-alkyl-chain (C18) modified porous silica and used in chromatographic retention studies of small molecules. Despite their successful application, determining the structure of hybrid-bilayers within chromatographic silica is challenging, because they reside at buried interfaces within the porous structure. In this work, we employ confocal Raman microscopy to investigate the formation and temperature-dependent structure of hybrid-phospholipid bilayers in C18-modified, porous-silica chromato¬graphic particles. Porous silica provides sufficient surface area within a confocal probe volume centered in an individual particle to readily measure, with Raman microscopy, the formation of an ordered hybrid-bilayer of 1,2-dimyristoyl-sn-glycero-3-phospho¬choline (DMPC) with the surface C18 chains. The DMPC surface density was quantified from the relative Raman scattering intensities of C18 and phospholipid acyl chains and found to be ~40% of a DMPC vesicle membrane. By monitoring Raman spectra acquired versus temperature, the bilayer main phase transition was observed to be broadened and shifted to higher temperature compared to a DMPC vesicle, in agreement with differential scanning calorimetry (DSC) results. Raman scattering of deuterated phospholipid was resolved from protonated C18-chain scattering, showing that the lipid-acyl and C18 chains melt simultaneously in a single phase transition. The surface-density of lipid in the hybrid bilayer, the ordering of both C18 and lipid acyl chains upon bilayer formation, and decoupling of C18 methylene C–H vibrations by deuterated lipid acyl chains all suggest an interdigitated acyl-chain structure. Furthermore, the simultaneous melting of both layers is also consistent with an interdigitated structure, where immobility of surface-grafted C18-chains decreases the cooperativity and increases the melting temperature compared to a vesicle bilayer.

Research Organization:
University of Utah, Salt Lake City, UT (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
FG03-93ER14333
OSTI ID:
2480567
Journal Information:
Langmuir, Journal Name: Langmuir Journal Issue: 35 Vol. 32; ISSN 0743-7463
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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