Distribution of Fullerene Nanomaterials between Water and Model Biological Membranes

Biological membranes are one of the important interfaces between cells and pollutants. Many polar and hydrophobic chemicals can accumulate within these membranes. For this reason, artificial biological membranes are appealing surrogates to complex organisms for assessing the bioaccumulation potential of engineered nanomaterials (ENMs). To our knowledge, this work presents the first quantitative study on the distribution of fullerene ENMs between lipid bilayers, used as model biological membranes, and water. We evaluated the lipid bilayer–water association coefficients (K lipw) of aqueous fullerene aggregates (nC60) and fullerol (C60(ONa) x (OH) y , x + y = 24). Kinetic studies indicated that fullerol reached apparent equilibrium more rapidly than nC60 (2 h versus >9 h). Nonlinear isotherms can describe the distribution behavior of nC60 and fullerol. The lipid bilayer–water distributions of both nC60 and fullerol were pH-dependent with the accumulation in lipid bilayers increasing systematically as the pH decreased from 8.6 (natural water pH) to 3 (the low end of physiologically relevant pH). This pH dependency varies with the zeta potentials of the ENMs and leads to patterns similar to those previously observed for the lipid bilayer–water distribution behavior of ionizable organic pollutants. The K lipw value for nC60 was larger than that of fullerol at a given pH, indicating a greater propensity for nC60 to interact with lipid bilayers. For example, at pH 7.4 and an aqueous concentration of 10 mg/L, K lipw was 3.5 times greater for nC60 (log K lipw = 2.99) relative to fullerol (log K lipw = 2.45). Comparisons with existing aquatic organism bioaccumulation studies suggested that the lipid bilayer–water distribution is a potential method for assessing the bioaccumulation potentials of ENMs.