A facile approach to hydrophilic oxidized fullerenes and their derivatives as cytotoxic agents and supports for nanobiocatalytic systems

A facile, environment-friendly, versatile and reproducible approach to the successful oxidation of fullerenes (oxC₆₀) and the formation of highly hydrophilic fullerene derivatives is introduced. This synthesis relies on the widely known Staudenmaier’s method for the oxidation of graphite, to produce both epoxy and hydroxy groups on the surface of fullerenes (C₆₀) and thereby improve the solubility of the fullerene in polar solvents (e.g. water). The presence of epoxy groups allows for further functionalization via nucleophilic substitution reactions to generate new fullerene derivatives, which can potentially lead to a wealth of applications in the areas of medicine, biology, and composite materials. In order to justify the potential of oxidized C₆₀ derivatives for bio-applications, we investigated their cytotoxicity in vitro as well as their utilization as support in biocatalysis applications, taking the immobilization of laccase for the decolorization of synthetic industrial dyes as a trial case.

Dependence of fullerene aggregation on lipid saturation due to a balance between entropy and enthalpy

It is well-known that fullerenes aggregate inside lipid membranes and that increasing the concentration may lead to (lethal) membrane rupture. It is not known, however, how aggregation and rupture depend on the lipid type, what physical mechanisms control this behavior and what experimental signatures detect such changes in membranes. In this paper, we attempt to answer these questions with molecular simulations, and we show that aggregation and membrane damage depend critically on the degree of saturation of the lipid acyl chains: unsaturated bonds, or "kinks", impose a subtle but crucial compartmentalization of the bilayer into core and surface regions leading to three distinct fullerene density maxima. In contrast, when the membrane has only fully saturated lipids, fullerenes prefer to be located close to the surface under the head groups until the concentration becomes too large and the fullerenes begin clustering. No clustering is observed in membranes with unsaturated lipids. The presence of "kinks" reverses the free energy balance; although the overall free energy profiles are similar, entropy is the dominant component in unsaturated bilayers whereas enthalpy controls the fully saturated ones. Fully saturated systems show two unique signatures: 1) membrane thickness behaves non-monotonously while the area per lipid increases monotonously. We propose this as a potential reason for the observations of low fullerene concentrations being effective against bacteria. 2) The fullerene-fullerene radial distribution function (RDF) shows splitting of the second peak indicating the emergence short-range order and the importance of the second-nearest neighbor interactions. Similar second peak splitting has been reported in metal glasses.

Effect of C60 on the phase transition behavior of a lipid bilayer under high pressure

Interactions between fullerenes and cells and effects on the main transition of lipid bilayers have attracted much attention in biophysics in recent years. By employing coarse-grained molecular dynamics simulations, we obtained the temperature-pressure phase diagrams of a dipalmitoylphosphatidylcholine bilayer, which exhibits a gel phase and a fluid phase, with variation of the C60 versus lipid ratios. The simulation results show that the critical area per lipid at the fluid-gel main phase transition boundary increases with the increasing ratios of C60. A critical area per lipid of 0.594 ± 0.002 nm2 is obtained when the ratio of C60 reaches 6.4% while that of the pure bilayer case is 0.572 ± 0.002 nm2. The main transition temperature, T m, remains almost unchanged with the addition of C60 below a ratio of 4.7%, while a 2 K decrease of T m is observed at a ratio of 6.4% under various pressures. Consequently, the presence of C60 in the bilayer, with the ratio of C60 less than 4.7%, will not influence the main transition behavior of the bilayer even under pressure as high as 1500 bar. The radial distribution function analyses suggest that the presence of C60 produces no impact on the radial distribution of the lipids in the bilayers. The lateral density profiles show that the incorporation of C60 with relatively high ratios stabilizes the thickness of the bilayer.