The Structure of Model Membranes Studied by Vibrational Sum Frequency Spectroscopy
The structure and order of insoluble Langmuir monolayers consisting of 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC or 18:0 PC) and the surrounding water molecules have been investigated by vibrational sum frequency spectroscopy (VSFS). At surface pressures of 1, 15, and 57 mN/m corresponding to molecular areas of 53, 50, and 43 Å2, respectively, the DSPC molecules formed a well ordered film. Both the VSF signal from the methyl stretching vibrations of the lipid and the surrounding water increased with enhanced surface pressure, as a result of the higher surface density and increased order of the system. Water molecules hydrating the polar parts of the headgroup and in close contact to the hydrocarbon groups of the lipid were observed in all three polarization combinations of the laser beams, and distinguished by their different vibrational frequencies.
KeywordsVibrational sum frequency spectroscopy SFG DSPC Langmuir film membrane
The authors thank Dr. Eric Tyrode (KTH) for valuable discussions. This project was supported by the Swedish Centre for Biomimetic Fiber Engineering (Biomime), the Swedish foundation for strategic research (SSF), and the Swedish research council (VR). Rutland is a fellow of VR and Johnson holds an Ingvar Carlsson (SSF) grant.
- 1.Berg JM, Tymoczko JL, Stryer L (2002) Biochemistry 5th ed., W.H. Freeman & Co, New YorkGoogle Scholar