Separation and Purification of EMFs

After solvent extraction, various species of fullerenes and EMFs enter into solution they must be separated further to obtain isomer-free samples. Liquid chromatography is certainly the most effective means to separate fullerenes into pure form. However, because of their low production yield and the large number of EMF isomers, as well as the similarities between them, HPLC is always relied upon to obtain pure isomers of EMFs. 

Currently, HPLC is the only general method that can yield isomer-free EMFs. Because it is expensive, extremely tedious, and time-consuming, alternative methods have been sought for effective separation of EMF isomers some successes have been achieved recently. 

Recently, a chemical reduction method was developed for the isolation of Gd-EMFs directly from raw soot [75]. Reduction of the raw soot with an Al-Ni alloy in toluene-THF gave rise to a solution of Gd Cg2 and Cd2 Cgo anions, whereas empty fullerenes remained in the soot. The anions of Gd Cg2 and Gd2 Cgo react with aqueous NaOH to form water-soluble Gd-metallofullerols, which are potential MRI contrast agents. It is particularly interesting that pure Gd2 Cgo was isolated directly from the raw soot merely by tuning the ratio of toluene to THE 

3 Host-Guest Complexation with Azacrown Ethers 

It is interesting that La Cg2 forms complexes with azacrown ethers that precipitate in toluene, but empty fullerenes do not and therefore remain in the solution [76]. These experimental facts spurred an attempt to use azacrown ethers to separate EMFs from empty fullerenes. When hexaazacyclooctadecane was added to a solution containing both empty fullerenes and La-EMFs, precipitates appeared immediately. Experimental data confirmed the separation of 

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