The interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy

The first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air-liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050-1450 cm −1 , 2750-3180 cm −1 , and 3200-3825 cm −1 , it was concluded that in the presence of Ca 2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O-H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure. Chondroitin sulfate interacts with the headgroups of a lipid monolayer at the air-liquid interface and shows a chiral secondary structure.