Characterization of aggregates of surface modified fullerenes byasymmetrical flow field-flow fractionation with multi-angle light scattering detection

“Fullerenes are carbon nanoparticles with widespread biomedical, commercial and industrial applications.Attributes such as their tendency to aggregate and aggregate size and shape impact their ability to betransported into and through the environment and living tissues. Knowledge of these properties is there-fore valuable for their human and environmental risk assessment as well as to control their synthesis andmanufacture. In this work, asymmetrical flow-field flow fractionation (AF4) coupled to multi-angle lightscattering (MALS) was used for the first time to study the size distribution of surface modified fullereneswith both polyhydroxyl and carboxyl functional groups in aqueous solutions having different pH (6.5–11)and ionic strength values (0–200 mM) of environmental relevance. Fractionation key parameters suchas flow rates, flow programming, and membrane material were optimized for the selected fullerenes.The aggregation of the compounds studied appeared to be indifferent to changes in solution pH, but wasaffected by changes in the ionic strength. Polyhydroxy-fullerenes were found to be present mostly as4 nm aggregates in water without added salt, but showed more aggregation at high ionic strength, withan up to 10-fold increase in their mean hydrodynamic radii (200 mM), due to a decrease in the elec-trostatic repulsion between the nanoparticles. Carboxy-fullerenes showed a much stronger aggregationdegree in water (50–100 nm). Their average size and recoveries decreased with the increase in the saltconcentration. This behavior can be due to enhanced adsorption of the large particles to the membraneat high ionic strength, because of their higher hydrophobicity and much larger particle sizes comparedto polyhydroxy-fullerenes. The method performance was evaluated by calculating the run-to-run preci-sion of the retention time (hydrodynamic radii), and the obtained RSD values were lower than 1%. MALSmeasurements showed aggregate sizes that were in good agreement with the AF4 data. A comparisonof the scattering radii from the MALS with the hydrodynamic radii obtained from the retention times inAF4 indicated that the aggregate shapes are far from spherical. TEM images of the fullerenes in the drystate also showed branched and irregular clusters.”

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(Citaat: Astefanei, A., Kok, W.Th., et al. Charaterization of aggregates of surface modified fullerenes by asymmetrical flow field-flow fractionation with multi-angle light scattering detection – Journal of Chromatography A 1408(2015)197-206)