Fullerene water solutions

One of the examples of inclusion complexes formed by intermolecular forces is the C60/PVP complex for the first time described by Yamakoshi et al. (1994). The non-covalent intermolecular nature of forces that stabilizes this complex confirms the fact that fullerene can be quantitatively extracted from its water solution by toluene. 

Sushko ML, Klenin SI, Dumpis MA et al. (1999) Light scattering in water solutions of fullerene-containing polymers Part 2. Effect of the molecular weight of the carrier molecule. Tech Phys Lett. 25 778-779. 

In water solutions, the scandium ion has a triple positive charge. Studies show, however, that the simple Sc1+ ion seldom exists. Rather, the form is highly polymerized and hydrolyzed—with hydroxy-bonded structures, In forming compounds, scandium parallels aluminum, yttnum. gallium, indium, and tellurium. Several carbides of scandium have been reported, the most stable carbide being ScC, including scandium clusters in fullerene cages. 

A technology, which has allowed producing of fullerene molecular-colloidal water solutions (FWS), has made new step for the biological applications of fullerenes. Such technology is now available [4], and CeoFWS produced by means of it is highly stable (8-24 months and longer) and finely dispersed without any stabilizers. The fact that this colloid consists of individual molecules of Ceo and the water only has been proved earlier by means of different experimental methods. 

Pulse radiolysis of 2-propanol has also been used to investigate elementary redox and radical reactions of fullerenes in solution [18]. For example, reduction of Ceo to C6o by Cs (k > 10 dm mol" s ) and (CH3)2 COH [k = (5 2) x 10 dm mor s ] was observed, and Ceo " was found to be stable for hours in the absence of oxygen. Ceo is insoluble in water, but its reduction in this solvent by (CH3)2 C0H was achieved by imbedding the fullerene in y-cyclodextrin to form a soluble guest-host complex in a 9 1 (vol %) water 2-propanol mixture. In this case, the reaction rate was two times slower than that in neat 2-propanol. Information was also obtained [18] on the addition of CH3 to Ceo in 2-propanol by the follow-... 

In a review on the relationship of fullerenes with biological sciences, fullerenes and their derivatives were reported by Jensen et al. [126] to influence biological processes in vivo. However, the mechanism was not yet fully understood as interactions of fullerenes at the biomolecular level had not been sufficiently studied. This was due, in turn, to the low solubihty of fullerenes in water, a drawback which has led to some work on the production of stable water solutions of fullerenes. Indeed, the low solubility in water of fullerenes and the... 

Due to its distinctly hydrophobic character, C,5o is also practically insoluble in water. The concentration of a saturated solution is a homeopathic 3 x 10 molT. This value increases upon addition of amines as they may form donor-acceptor complexes with the fullerene. Colloidal solutions with particles measuring 0.22 pm and a concentration of 7 x 10" moll" have been obtained by the aid of ultrasound. Also did the application of complexing host molecules Uke y-cydodextrines lead to a higher solubihty. Surfactants serve to the same purpose. Strictly speaking, however, there are no real solutions in this case, but the fidlerene molecules are located inside of miceUes. 

Sundahl M, Andersson T, Nilsson K, Wennerstrom O and Westman G 1993 Clusters of Cgg-fullerene in a water solution containing y-cyclodextrin a photophysical study Synth. Met. 55 3252-7... 

The elution of [60]- and [70]fullerenes was measured in water-methanol as a function of temperature on a poly(octadecylsiloxane) phase.67 The retention was shown to be dependent on the surface tension of the stationary phase through a simple geometrical model in which the solute formed a cavity in the stationary phase. In affinity chromatography, it was demonstrated that low ligand density may be a requirement for specificity of binding.68... 

In recent years, a great diversity of structurally well-defined functionalized fullerenes has been designed and synthesized for that purpose. Some of them exhibit pronounced solubility in water (vide infra). But even for compounds being virtually insoluble in water, stable aqueous phases can be obtained in plenty of cases by diluting stock solutions of the compounds in polar organic solvents with various amounts of water. Notably, dimethyl sulfoxide (DMSO) and tetrahydro-furan (THF) have turned out to be excellent surfactants for preparing stable aqueous fullerene solutions (Angelini et al., 2005 Cassell et al., 1999 Da Ros et al., 1996 Gun kin et al., 2006 Illescas et al., 2003). Also cosolvents such as dimethylforma-mide (DMF) and methanol can be used to promote water solubility. After subsequent dilution of a saturated solution of C60 in benzene with THF, acetone and finally water, actually stable aqueous suspensions of pristine fullerene can be obtained (Scrivens et al., 1994). 

Unfortunately, these nonionic but polar fullerene adducts exhibit virtually no water solubility over the whole pH range, indicating that even four polyethylene units are not sufficient to provide tme water solubility. However, as mentioned before for other fulleienes, by diluting DMSO solutions with various amounts of water stable aqueous phases containing dispersed fullerenes can be obtained. 

A comparable addition pattern with as many as five attached groups allowing further functionalization is represented in pentaaryl-fullerenes like 25-27 (Troshina et al., 2007 Zhong et al., 2006). Whereas the free acids are virtually insoluble in pure water, the use of basic water in the case of 25 (Zhong et al., 2006) and conversion of the polyacids 26 and 27 to the corresponding potassium salts leads to stable aqueous solutions with high fullerene concentrations. 

Water colloid solutions of fullerenes C60 (10 4 M) were prepared as described in Scharff et al. (2004). Fullerene-aminopropylaerosyl (fullerene C60-composite-l) was synthesized (Golub et al., 2003) by the introduction of aminopropyl chains oriented ad extra by amine groups (0.9 mM/g), to the surface layer of sihcon dioxide nanoparticles that were bound to fullerene C60 (0.12 mM/g) (Fig. 6.1). Fullerene-anthracenaliminopropylaerosyl (fullerene C60-composite-2) was composed also from anthraccnaliminc (0.2mM/g) that was introduced via azomethine condensation of aldehyde group of anthracenal with surface amino group. 

The method of preparation of this complex is simple enough and consists of mixing of fullerene solution in toluene with solution of PVP in chloroform with the following evaporation of organic solvents and dissolution of the residue in water. It was shown that the complex formation caused the bathochromic and hypochromic shifts of the fullerene absorption bands in UV-VIS spectra (Yamakoshi et al., 1994). 

Avdeev MV, Khokhryakov AA, Tropin TV, Andrievsky GV, Klochkov VK, Derevyanchenko LI, Rosta L, Garamus VM, Priezzhev VB, Korobov MV, Aksenov VL (2004) Structural features of molecular-colloidal solutions of C-60 fullerenes in water by small-angle neutron scattering. Langmuir 20 4363 4368. 

It had been reported that fullerene Cgo forms a water-soluble complex with y-cyclodextrin by heating with an excess amount of y-cyclodextrin in water [10] or in a mixture of refluxing water and toluene for a long time, such as 30 h [ 11]. The isolated complex is considered to have the Cgo structure bicapped with y-cyclodextrin in a molar ratio of 1 2 [11], and the complex dissolved in water to give a solution of C o with a concentration of nearly 10 mol L 410,11 ]. Fullerene Qo was also solubilized in water by complexation with a sulfocalix[8] arene, i.e., calix-[8]aryloxy-49,50,51,52,53,54,55,56-octakis(propane-3-sulfonate). The concentration of this complex in water is estimated as 5x10 mol L [12]. Complex formation between fullerene and various calixarenes has also been reported [8]. 

The complexation of fullerenes and y-cyclodextrin was found to take place more efficiently by the use of a HSVM. Thus, when Cgo was vigorously shaken with 4 molar equivalents of y-cyclodextrin for only 10 min by HSVM and the resulting mixture dissolved in 4 mL of water, a magenta-colored solution of Cgo was obtained by filtration with a membrane filter (Scheme 1) [16]. The concentration of Cgo was 1.4x10 mol L which is the highest value for Cgo dissolved in water. When this aqueous solution was let stand for 2 weeks, the Cgo-y-cy-clodextrin 1 2 complex was obtained as purple crystals. 

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