Neutron reflection from a dimyristoylphosphatidylcholine monolayer adsorbed on a hydrophobised silicon support

Neutron specular reflection has been used to study the structure of a monol ayer of dimyristoylphosphatidylcholine (DMPC) deposited using the Langmuir- Blodgett technique onto a silicon oxide substrate. A self-assembled monolay er of octadecyltrichlorosilane with a deuterated alkyl chain (d-OTS) had be en previously bonded onto this silicon oxide substrate which rendered it hy drophobic, In the system under study, the alkyl chains of the phospholipid were found to penetrate extensively into the d-OTS layer with the mixed cha in region (d-OTS and DMPC) having a total thickness of 30.5 Angstrom. This mixed region was divided into two halves for analysis; the 'lower half (nea rest to the substrate surface) was found to comprise anchored d-OTS chains mixed with the lipid chains in the volume ratio approx. 0.60:0.35. The corr esponding volume ratio in the 'upper half of this region was determined to be approx. 0.50:0.40. The thicknesses of these regions were found to be 17. 9 Angstrom (incorporating approx. 6% solvent) and 12.6 Angstrom (incorporat ing approx. 9% solvent) for the lower and upper halves respectively. The DM PC head groups were found to be confined to the most external layer (furthe st away from the silicon substrate). This layer was found to have a thickne ss of 9.4 Angstrom and included a small fraction of the lipid alkyl chains with approx. 47% solvent. (C) 2001 Elsevier Science B.V. All rights reserve d.