Quantitative analyses of PEGylated phospholipids adsorbed on single walled carbon nanohorns by high resolution magic angle spinning 1H NMR

Adsorption of polyethylene glycol conjugated phospholipids with various PEG chain length (DSPE-PEG5000, 2000, 750) onto single-walled carbon nanohorns (SWCNH), a type of graphene nano-tubule, in aqueous solution was investigated by means of high-resolution magic angle spinning (HRMAS) 1H NMR. Peak integral ratio of PEG chains and alkyl chains of DSPE-PEGs in the NMR spectra linearly decreased to zero with the increase of SWCNH quantity, indicating that the adsorption of DSPE-PEGs on SWCNH was virtually irreversible. The area of SWCNH surface allocated to the individual DSPE-PEG5000, 2000, 750 molecule were estimated to be 7.06, 5.18, and 4.45 nm2, respectively. Coverages of the alkyl chains on the surface area of SWCNH were about 28%, 39% for DSPE-PEG5000, 2000 and 46% for DSPE-PEG750, suggesting single layer adsorption. We presumed that the electrostatic repulsion may prevent DSPE-PEGs from multiple layer and keep away neighbouring DSPE-PEGs on the surface. According to the molecular areas of the DSPE-PEGs, PEG5000 and 2000 chains were considered to be in brush-regimes, while PEG750 was considered to be in mushroom regime on the SWCNH surface.