Functionalization noncovalent

In the last few years, the noncovalent treatment of CNTs has been widely used in the preparation of both aqueous and organic solutions to obtain a high weight 

Methodology Part of the CNT which reacts Functionality added General procedure and considerations Applications in electrochemistry 

Oxidation Cap ends and defects. Under certain circumstances, the sidewalls -CO OH, -OH, =0 groups 1) Liquid-phase hot concentrated HNO3 or HN03/H2S0 piranha solution. Ultrasound treatment 2) Gas-phase UV irradiation in O3, Oj plasma, and HNO3 vapor Dispersion of oxidized CNTs in a wide variety of solvents, for electrode modification [53] 

Oxidation, esterification/ amidation Carboxylated groups -OH, -NHj groups 1) Activation via formation of acyl-chloride reaction with SOClj usually in DMF, high temperatures 2) Activation via aqueous solution of EDC/DCC and NHS or HOBt, mild conditions Electrochemical biosensing Immobilization of proteins, DNA, and antibodies [54, 55] 

Oxidation and thiolation Cycloadditions Carboxylated groups -SH groups 1) Reduction with NaBH, activation with SOQ2, and thiolation with Na2S/NaOH 2) Activation with SOCIj and thiolation withH2N-R-SH Self-assembly of thiolated CNTs [56, 57] Functionalization of CNTs with MNps [58] 

The insolubility of pristine graphene in most solvents makes its solution very difficult, which eventually restricts the practical application of graphene in many fields. As mentioned previously, many 

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Zheng W, Li QE, Su L, Yan YM, Zhang J, Mao LQ. 2006. Direct electrochemistry of multicopper oxidases at carhon nanotubes noncovalently functionalized with cellulose derivatives. Electroanalysis 18 587-594. 

Alpatova, A.L. et al. (2010) Single-walled carbon nanotubes dispersed in aqueous media via noncovalent functionalization effect of dispersant on the stability, cytotoxicity, and epigenetic toxicity of nanotube suspensions. Water Research, 44 (2), 505-520. 

Scheme 27. Noncovalent functionalization of SWNTs by using an amphiphilic glycopolymer, ending with a lipid tail for mucin mimicry.249...

The preparation of biocompatible SWNTs, noncovalently functionalized with bioactive glycodendrimers, has been reported (Scheme 29).253 A bifunctional dendritic scaffold 284 was built using the 2,2-bis(hydroxymethyl)propanoic acid as a building block 281, which was linked to an azidopyrene tail (280) capable of binding the surface... 

The alternative noncovalent functionalization does not rely on chemical bonds but on weaker Coulomb, van der Waals or n-n interactions to connect CNTs to surface-active molecules such as surfactants, aromatics, biomolecules (e.g. DNA), polyelectrolytes and polymers. In most cases, this approach is used to improve the dispersion properties of CNTs [116], for example via charge repulsion between micelles of sodium dodecylsulfate [65] adsorbed on the CNT surface or a large solvation shell formed by neutral molecule (e.g. polyvinylpyrrolidone) [117] around the CNTs. 

One good example of noncovalent functionalization for subsequent hybridization is the use of benzyl alcohol (BA) [118]. n-n interactions between the aromatic ring of BA and the CNT sidewalls result in a good dispersibility in ethanol. Furthermore, BA offers a well-ordered and well-distributed functionalization [119] of hydroxyl groups on the sidewalls of the CNTs that can be used to hybridize the material with a large number of metal oxides using conventional chemical methods [60]. 

The vast majority of functionalization methods of carbon nanotubes belong to two broad categories (a) covalent and (b) noncovalent functionalization of the external CNT surface. The former is achieved by covalent attachment of functional groups to the C-C double bond of the n-conjugated framework. The latter is based on the adsorption through van der Waals type bonds of various functional entities. 

It is possible to divide the noncovalent functionalization according to the type of molecules used, thus four categories are found (1) surfactants, (2) polymers, (3) bio-... 

Encapsulation of different entities inside the CNT channel stands alone as an alternative noncovalent functionalization approach. Many studies on the filling of carbon nanotubes with ions or molecules focus on how the presence of these fillers affects the physical properties of the tubes. From a different point of view, confinement of materials inside the cylindrical structure could be regarded as a way to protect such materials from the external environment, with the tubes acting as a nanoreactor or a nanotransporter. It is fascinating to envision specific reactions between molecules occurring inside the aromatic cylindrical framework, tailored by CNT characteristic parameters such as diameter, affinity towards specific molecules, etc. 

In order to overcome this drawback, there are two main approaches for the surface modification of carbon nanostructures that reoccur in the literature. The first one is covalent functionalization, mainly by chemical bonding of functional groups and the second one is noncovalent functionalization, mainly by physical interactions with other molecules or particles. Both strategies have been used to provide different physical and chemical properties to the carbon nanostructures. Those that will be presented here are only a few examples of the modifications that can be achieved in carbon nanostructure surfaces and composite fabrication. 

Summarizing, noncovalent functionalization methods can be used to prepare materials with specific biological properties because they are quick, efficient and clean. In order to increase biocompatibility of carbon nanostructures, these materials now need to be integrated into living systems and to be potentially used as tissue regeneration scaffolds, prostheses or drug deliverers. 

H. Dai, Noncovalent functionalization of carbon nanotubes for highly specific electronic biosensors, Proceeding of the National Academic of Science of the United States of America, vol. 48, pp. 4984-4989, 2003. 

Yang, W., et al., Carbon nanotubes decorated with PtnNanocubes by a noncovalent functionalization method and their role in oxygen reduction. Advanced Materials, 2008. 20(13) p. 2579-2587. 

It often becomes necessary to prepare dispersions of graphene in organic or aqueous media [73-74]. For this purpose, different approaches have been successfully employed for few-layer graphene. The two main approaches for obtaining this type of graphene are covalent functionalization or by means of noncovalent interactions. There has been some recent effort to carry out covalent and noncovalent functionalization of graphene with aromatic molecules, which help to exfoliate and stabilize the individual graphene sheets and to modify their electronic properties [75 84]. 

Noncovalent functionalization of graphene is important, as it does not affect the electronic structure and planarity of this 2D material. Stable aqueous dispersions of polymer-coated graphitic nanoplatelets can be prepared through an exfoliation and... 

Noncovalent functionalization of graphene nanoplatelets with single-stranded DNA (ssDNA) has increased the solubility of graphene to as high as 2.5 mg/1 in water... 

Preparation of photoelectrodes by using noncovalently functionalized graphene... 

Scheme 4.18 Self-sorting noncovalent functionalization of a universal polymer backbone.

Nair KP, Pollino JM, Week M. Noncovalently functionalized block copolymers possessing both hydrogen bonding and metal coordination centers. Maciomolecules 2006 39 931-940. 

In this chapter we will focus on side chain functionalized supramolecular polymers as well as main chain noncovalent functionalized polymers, which are the two main areas of supramolecular polymers. We will initially discuss the design principles and methodology of side chain functionalization, in particular, multifunctionalization. In the later part of the chapter, we will discuss in detail two important applications of side chain functionalized supramolecular polymers. The first application involves the use of noncovalent interactions to yield highly functionalized materials, whereas the second application involves the reversible noncovalent cross-linking of polymers to yield responsive materials. 

APPLICATIONS OF NONCOVALENTLY FUNCTIONALIZED SIDE CHAIN COPOLYMERS... 

Having discussed self-assembly strategies toward noncovalently functionalized side chain supramolecular polymers as well as studies toward the orthogonahty of using multiple noncovalent interactions in the same system, this section presents some of the potential applications of these systems as reported in the literature. The apphcations based on these systems can be broadly classified into two areas 1) self-assembled functional materials and 2) functionalized reversible network formation. 

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