On the Origin of C₆₀ Fullerene Solubility in Aqueous Solution

Abstract

In this work, we report that the surface hydroxylation of C 60 molecules is the most likely mechanism for pristine C 60 fullerenes/C 60 fullerene aggregate stabilization in water, being independent of the method of C 60 fullerene aqueous solution preparation. ■ INTRODUCTIONNanocarbon materials are used in a wide variety of biomedical applications, including biosensorics, targeted drug delivery, chemotherapy, cellular imaging, and diagnostics. 1 For example, the pristine C 60 fullerenes as a unique class of carbon allotropes are able to penetrate the cell membrane, 2,3 to exhibit antioxidant properties, 4,5 and, being nontoxic (at least at low concentration), 6 to exert specific health effects (e.g., antibacterial, 7 antitumor, 8 and drug carrier 9 ).Biomedical applications require a dispersal of C 60 fullerene in a solvent, with aqueous dispersions being preferred because of biocompatibility, safety, or environmental concerns. Although pristine C 60 fullerenes have extremely low water solubility, they can form stable colloid solutions containing individual C 60 fullerenes as well as C 60 fullerene aggregates (clusters) in water when subjected to extended mixing, sonication, or solvent exchange 10−16 (to be further referred to as a C 60 fullerene aqueous colloid solution (C 60 FAS)). However, the origin of stabilization of such particles in water still remains poorly investigated.At least two approaches have been suggested in order to explain the stability of fullerene particles in water solutions. One of them 17 postulates the formation of a water shell around C 60 molecules stabilized simultaneously by the H-bonding network between the water molecules and charge transfer from water to the C 60 fullerene. Another one 18 suggests that the sonication process induces the covalent attachment of water hydroxyls to C 60 fullerene carbons, resulting in the formation of alcohol moieties that enable C 60 fullerene dissolution. The problem here is that the properties of C 60 FAS (including biological properties) as well as the mechanism of water solubility may depend on the method of preparation of C 60 fullerene aqueous solution. 13,16,17 Indeed, these two approaches differ by the underlying method of C 60 FAS preparation although the sonication step is presented in both methods. The question therefore arises as to whether the mechanism of solubility of C 60 fullerene in water depends on the method of C 60 FAS preparation. This question has been investigated in this article. ■ EXPERIMENTAL SECTIONSample Preparation. For the preparation of C 60 FAS, we used a saturated solution of pure C 60 fullerene (purity >99.99%) in toluene with a C 60 molecule concentration corresponding to maximum solubility near 2.9 mg/mL and the same amount of distilled water in an open beaker. The two phases that formed were treated in an ultrasonic bath. The procedure was continued until the toluene had completely evaporated and the water phase became yellow. Filtration of the aqueous solution allowed us to separate the product from un...

Towards better understanding of C60organosols

“…The numerous and sometimes conflicting results of experimental 5,14,[16][17][18][19][20][21][22][23][24][25][43][44][45][46][47][48][49] and theoretical [73][74][75][76][77][78][79] investigations demand such a comparison. Indeed, the theoretical calculations often predict strong interaction between C 60 and water (as a recent example, the work by Choi et al 77 may be proposed), which may be considered as a type of expressed hydration, whereas the coagulation data indicate the hydrophobic nature of the fullerene hydrosols.…”

“…[1][2][3][4][5][6][7] Therefore, it is important to better understand their behavior in a solution. One of the specific features of fullerenes is their ability to form aggregates.…”

“…[8][9][10][11][12][13][14] While in low-polar aromatic solvents, fullerenes are well solvated and relatively well dissolved, 14,15 in water they generate hydrosols and suspensions. 5,11,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] In highly polar organic solvents, the molecular solubility of fullerenes is negligible, 14,15 but they readily form colloidal solutions. [9][10][11][12][13][14][31][32][33][34][35] The state of fullerenes, either molecular or colloidal, in the so-called 'good' or 'strong' solvents, such as CS 2 , toluene, and benzene, is still a matter of discussion.…”

Fullerene Clustering in C70/N-Methyl-2-Pyrrolidone/Toluene Liquid System

“…Зразки (об'ємом 500 мкл) були за-литi у кварцевi кювети (Hellma Analytics) з товщи-ною 1 мм, якi знаходились при температурi 20 ∘ С. За фоновi зразки були використанi розчинники та їх сумiшi без фулерену, так званi, буфернi зразки. Для калiбрування iнтенсивностi розсiяння нейтро-нiв був використаний стандартний ванадiєвий зра-зок [30,31]. Обробка отриманих даних здiйснюва-лась програмою SAS у режимi згладжування [32].…”

Adsorption of polyhydroxy fullerene on polyethylenimine-modified montmorillonite

“…In contrast, much less work about the pollution control of PHF has been reported up to now. On the other hand, Prylutskyy et al (2014) indicated that the origin of fullerene solubility in water was probably based on the surface hydroxylation of fullerene molecules; therefore, nC 60 could be considered as fullerene aggregates with a certain amount of hydroxyls on the outer surfaces. Furthermore, when exposed to the environment, fullerenes and nC 60 could be transformed into PHF by many factors (e.g., long-term mixing, ultraviolet radiation, and interaction with microbes and oxidants) Qu et al, 2010;Chae et al, 2014).…”