Phospholipid-Assisted Formation and Dispersion of Aqueous Nano-C60
Yanjing Chen and Geoffrey D. Bothun. Chemical Engineering, University of Rhode Island, 205 Crawford Hall, Kingston, RI 02881
In this study we evaluate the use of dipalmitoylphosphatidylcholine (DPPC) as a biomolecular dispersing agent to aid in the formation aqueous C60 fullerene nanoparticles. Fullerenes are candidates for widespread application in, for example, the fields of cosmetics, drug delivery and energy conversion. However, the instability and potential toxicity of C60 in aqueous solution, both of which have been related to the synthesis route and surface chemistry, are clear limitations. Based on the reserves phase evaporation method, we are developing a new technique to prepare nano-C60 with the aid of DPPC vesicle assemblies. The preference of C60 to partition into the vesicle bilayer or form nano-C60, the size distribution of the nano-C60, and the effect of C60 incorporation within the lipid bilayers were examined as a function of the DPPC/C60 ratio and presence of magnesium perchlorate. Mg(ClO4)2 has been shown to prevent C60 aggregation. Cryogenic transmission electron microscopy (cryo-TEM) has revealed nano-C60 particle sizes ranging from approximately 20 to 80 nm at a DPPC/C60 molar ratio of 100:1. However, not all C60 present formed nano-C60. C60 incorporated within the bilayer decreased the gel to liquid-crystalline phase transition temperature and increased membrane fluidity in the gel and liquid-crystalline phases as determined by differential scanning calorimetry (DSC) and fluorescent anisotropy, respectively. These results suggest that C60 molecules within DPPC bilayers distorted the acyl carbon chains. Attempts to back-extract DPPC from the samples indicated that DPPC was adsorbed to the nano-C60 surface and provided stability. In addition to developing a new technique for nano-C60 formation, our results show that C60 disrupts model biological membranes, which may relate to its reported toxicity.