Fullerenes are entirely insoluble in water, but suitable functionalization makes the molecules soluble. Studies on water-soluble fullerene derivatives led to the discovery of the interaction of organofullerenes with DNA, proteins, and living cells, which was first reported in the summer of 1993. Subsequent studies have revealed interesting biological activity aspects of organofullerenes owing to their photochemistry, radical quenching, and hydrophobicity to form one- to three-dimensional supramolecular complexes. In these areas of research, synthetic organic chemistry has played an important role in the creation of tailor-made molecules.

Functionalized fullerenes in water. The first 10 years of their chemistry, biology, and nanoscience

Challenges and breakthroughs in recent research on self-assembly

To characterize fullerenes (C60 and C70) as photosensitizers in biological systems, the generation of active oxygen species, through energy transfer (singlet oxygen 1O2) and electron transfer (reduced active oxygen radicals such as superoxide anion radical O2-• and hydroxyl radical •OH), was studied by a combination of methods, including biochemical (DNA-cleavage assay in the presence of various scavengers of active oxygen species), physicochemical (EPR radical trapping and near-infrared spectrometry), and chemical methods (nitro blue tetrazolium (NBT) method). Whereas 1O2 was generated effectively by photoexcited C60 in nonpolar solvents such as benzene and benzonitrile, we found that O2-• and •OH were produced instead of 1O2 in polar solvents such as water, especially in the presence of a physiological concentration of reductants including NADH. The above results, together with those of a DNA cleavage assay in the presence of various scavengers of specific active oxygen species, indicate that the active...

Active Oxygen Species Generated from Photoexcited Fullerene (C60) as Potential Medicines: O2-• versus 1O2

The production of significant quantities of engineered nanomaterials will inevitably result in the introduction of these materials to the environment. Mobility in a well-defined porous medium was evaluated for eight particulate products of nanochemistry to assess their potential for migration in porous media such as groundwater aquifers and water treatment plant filters. Contrary to the assertion that nanomaterials present monolithic environmental risks, here we show that these nanomaterials exhibit widely differing transport behaviors. Fullerene-based nanomaterials that had been functionalized to facilitate dispersal in water displayed the highest mobilities, with a calculated potential to migrate approximately 10 m in unfractured sand aquifers. Colloidal aggregates of C60, which have been the focus of recent toxicity studies, were among the least mobile of the nanomaterials evaluated.

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Laboratory Assessment of the Mobility of Nanomaterials in Porous Media

Surfactants and membrane lipids readily assemble into complex structures1 such as micelles, liposomes or hollow vesicles owing to their amphiphilic character—the fact that part of their structure is attracted to polar environments while another part is attracted to non-polar environments. The self-assembly of complex structures also occurs in polyoxometallate chemistry, as exemplified by the molybdenum blue solutions known for centuries. But while the presence of nanometre-sized metal oxide aggregates in these solutions has long been recognized, unravelling the composition and formation process of these aggregates proved difficult. Recent work has indicated that discrete, wheel-shaped mixed-valence polyoxomolybdate clusters of the type {Mo154} (refs 2–4) assemble into well-defined nanometre-sized aggregates, including spherical structures5. Here we report light-scattering data and transmission electron microscopy images of hollow spherical structures with an average, almost monodisperse radius of about 45 nm and composed of approximately 1,165 {Mo154} wheel-shaped clusters. The clusters appear to lie flat and homogeneously distributed on the vesicle surface. Unlike conventional lipid vesicles, the structures we observe are not stabilized by hydrophobic interactions. Instead, we believe the polyoxomolybdate-based vesicles form owing to a subtle interplay between short-range van der Waals attraction and long-range electrostatic repulsion, with important further stabilization arising from hydrogen bonding involving water molecules encapsulated between the wheel-shaped clusters and in the vesicles’ interior.

Self-assembly in aqueous solution of wheel-shaped Mo154 oxide clusters into vesicles.

The low solubility of fullerenes in aqueous solution limits their applications in biology. By appropriate substitution, the fullerenes can be transformed into stabilized anions that are water soluble and can form large aggregated structures. A laser light scattering study of the association behavior of the potassium salt of pentaphenyl fullerene (Ph5C60K) in water revealed that the hydrocarbon anions Ph5C60- associate into bilayers, forming stable spherical vesicles with an average hydrodynamic radius and a radius of gyration of about 17 nanometers at a very low critical aggregation concentration of less than 10(-7) moles per liter. The average aggregation number of associated particles in these large spherical vesicles is about 1.2 x 10(4).

https://science.sciencemag.org/content/sci/291/5510/1944.full.pdf

Spherical bilayer vesicles of fullerene-based surfactants in water: a laser light scattering study

A new class of hydrocarbon anions, pentaaryl- and pentamethylfullerene anions R5C60− (R = Ph, 4-BuC6H4, 4-PhC6H4, Me) was found to be stable and soluble in water. Atomic force microscopic observation and dynamic light scattering measurements indicated that the potassium salt Ph5C60K in water forms spherical aggregates with an averaged radius of about 17 nm.

Pentaorgano[60]fullerene R5C60−. A Water Soluble Hydrocarbon Anion

Single-step synthesis of pentaaryl-monohydro[60]fullerenes through fivefold addition of organocopper reagent to C60

Pentaorgano[60]fullerene R5C60-. A Water Soluble Hydrocarbon Anion.

Stereoselective Complexation of Amino Acid Carboxylates in Aqueous Solutions: Automated, Parallel Synthesis of a Guanidiniocarbonylpyrrole Receptor Library

Ulrich E. Hackler

Papers

Spherical bilayer vesicles of fullerene-based surfactants in water: a laser light scattering study

Pentaorgano[60]fullerene R5C60−. A Water Soluble Hydrocarbon Anion

Single-step synthesis of pentaaryl-monohydro[60]fullerenes through fivefold addition of organocopper reagent to C60

Pentaorgano[60]fullerene R5C60-. A Water Soluble Hydrocarbon Anion.

Stereoselective Complexation of Amino Acid Carboxylates in Aqueous Solutions: Automated, Parallel Synthesis of a Guanidiniocarbonylpyrrole Receptor Library