The covalent methods previously discussed for fullerene modification using cycloaddition reactions also can be applied to carbon nanotubes. This strategy results in chemically link- ing molecules to the graphene rings on the outer surface of the cylinder, resulting in stable conjugates that can be designed to include hydrophilic groups for water solubilization. Georgakilas et al. (2002) describe the use of a 1,3-dipolar cycloaddition process to carbon nan- otubes with azomethine ylides, generated by condensation of an amino acid derivative and an aldehyde. The reaction occurs in organic solvent at high temperature over a time period of sev- eral days.
Typically, SWNTs are suspended in DMF using sonication and the aldehyde and glycine derivatives are added to the mixture with stirring. The ð-amine derivative of glycine can include hydrophilic spacers to make the resultant nanotube water-soluble as well as include protected functional groups to couple affinity ligands after deprotection (Kurz et al., 1998). The aldehyde also can include R groups that add water solubility or functionality to the nanotube. A combi- nation of a glycine derivative with an aldehyde derivative can result in both hydrophilicity and a functional group to conjugate ligands (Figure 15.16). Felekis and Tagmatarchis (2005) used this cycloaddition process to prepare SWNT deriva- tives possessing photoactive components, such as the addition of ferrocene groups. They used a short PEG-type spacer on the glycine to impart water solubility at the same time.
Singh et al. (2006) also used cycloaddition to prepare carbon nanotubes containing indium labeled diethylenetriamine pentaacetic acid (DTPA) derivatives (Figure 15.17). In the initial modification, a SWNT was derivatized to contain a primary amine at the end of a short PEG spacer. The resultant water-soluble nanotube then was reacted with DTPA to create a metal chelating group at the end of the chain. Subsequent loading of the chelate with 111In created a radionuclide–SWNT complex for in vivo biodistribution studies.
The covalent methods previously discussed for fullerene modification using cycloaddition reactions also can be applied to carbon nanotubes. This strategy results in chemically link- ing molecules to the graphene rings on the outer surface of the cylinder, resulting in stable conjugates that can be designed to include hydrophilic groups for water solubilization. Georgakilas et al. (2002) describe the use of a 1,3-dipolar cycloaddition process to carbon nan- otubes with azomethine ylides, generated by condensation of an amino acid derivative and an aldehyde. The reaction occurs in organic solvent at high temperature over a time period of sev- eral days.Typically, SWNTs are suspended in DMF using sonication and the aldehyde and glycine derivatives are added to the mixture with stirring. The ð-amine derivative of glycine can include hydrophilic spacers to make the resultant nanotube water-soluble as well as include protected functional groups to couple affinity ligands after deprotection (Kurz et al., 1998). The aldehyde also can include R groups that add water solubility or functionality to the nanotube. A combi- nation of a glycine derivative with an aldehyde derivative can result in both hydrophilicity and a functional group to conjugate ligands (Figure 15.16). Felekis and Tagmatarchis (2005) used this cycloaddition process to prepare SWNT deriva- tives possessing photoactive components, such as the addition of ferrocene groups. They used a short PEG-type spacer on the glycine to impart water solubility at the same time.Singh et al. (2006) also used cycloaddition to prepare carbon nanotubes containing indium labeled diethylenetriamine pentaacetic acid (DTPA) derivatives (Figure 15.17). In the initial modification, a SWNT was derivatized to contain a primary amine at the end of a short PEG spacer. The resultant water-soluble nanotube then was reacted with DTPA to create a metal chelating group at the end of the chain. Subsequent loading of the chelate with 111In created a radionuclide–SWNT complex for in vivo biodistribution studies.
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