The interaction of n-nonyl-β-d-glucopyranoside and sodium dodecyl sulfate with DMPC and DMPG monolayers studied by infrared reflection absorption spectroscopy

The interaction of the surfactants n-nonyl-β-D-glucopyranoside and sodium dodecyl sulfate with lipid monolayers of 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-d54-sn-3-[phospho-rac(1-glycerol)] at the air–water interface was studied by infrared reflection absorption spectroscopy. Isotopically labeled lipids were used in order to obtain separate information about the quantity and structural changes of both, the lipid and the surfactant component during the interaction. Knowing the extinction coefficients of the pure components, the number of lipid and surfactant molecules in the mixed monolayer can be calculated directly from the absorbance of the antisymmetric CD2 and CH2 stretching vibrational bands, respectively. This allows the calculation of the partition coefficient for the surfactant incorporated into the lipid monolayer. The influence of electrostatic interactions on the partition coefficient was investigated by use of the negatively charged lipid 1,2-dimyristoyl-d54-sn-3-[phospho-rac(1-glycerol)] and the surfactant sodium dodecyl sulfate. Finally, the effect of a 0.1 M NaCl subphase on the partitioning is described.