Noncovalent modification

Covalent modification yields a very stable and effective derivatization. However, some drawbacks can emerge when pursuing applications, especially with SWNTs. 

A high density of reactive sites or covalently functionalized points can lead to a loss of the CNT conjugation network with the consequent degradation of the CNT mechanical and electronic properties. 

The large aromatic and hydrophobic character of CNTs make them ideal surfaces for noncovalent interaction vfith molecules via Van der Waals, 7t-stacking or hydro-phobic forces [39, 44]. 

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Sandanaraj BS, Vutukuri DR, Simard JM, Klaikherd A, Hong R, Rotello VM, Thayumanavan S. Noncovalent modification of chymotrypsin surface using an amphiphilic polymer scaffold implications in modulating protein function. J Am Chem Soc 2005 127 10693-10698. 

N-Myristoylation is achieved by the covalent attachment of the 14-carbon saturated myristic acid (C14 0) to the N-terminal glycine residue of various proteins with formation of an irreversible amide bond (Table l). 10 This process is cotranslational and is catalyzed by a monomeric enzyme called jV-myri s toy 11ransferase. 24 Several proteins of diverse families, including tyrosine kinases of the Src family, the alanine-rich C kinase substrate (MARKS), the HIV Nef phosphoprotein, and the a-subunit of heterotrimeric G protein, carry a myr-istoylated N-terminal glycine residue which in some cases is in close proximity to a site that can be S-acylated with a fatty acid. Functional studies of these proteins have shown an important structural role for the myristoyl chain not only in terms of enhanced membrane affinity of the proteins, but also of stabilization of their three-dimensional structure in the cytosolic form. Once exposed, the myristoyl chain promotes membrane association of the protein. 5 The myristoyl moiety however, is not sufficiently hydrophobic to anchor the protein to the membrane permanently, 25,26 and in vivo this interaction is further modulated by a variety of switches that operate through covalent or noncovalent modifications of the protein. 4,5,27 In MARKS, for example, multiple phosphorylation of a positively charged domain moves the protein back to the cytosolic compartment due to the mutated electrostatic properties of the protein, a so-called myristoyl-electrostatic switch. 28 ... 

The planar purple dye thionine (Fig. 1.11) was found to show strong noncovalent interactions with the sidewalls of individual CNTs. The noncovalent modification with thionine enriched the surface of the tubes with NH2 groups, opening... 

Fig. 2 A three-step model of p53 activation by stress signals. Activation of p53 requires covalent and noncovalent modifications in distinct domains of the protein. The first step involves phosphorylation in the N terminus, dissociation of complexes with mdm-2, and binding of histone-acetyl-transferases of the CBP/p300 family. The second step consists of coordinated modifications of the C terminus, including acetylation, changes in phosphorylation, and binding of specific proteins such as 14-3-3cr. The third step concerns the central portion of the protein and involves reduction of cysteines that play an important role in the conformation of the DNA-binding domain. For explanations and references, see text.

Metzger, J. M., and M. V. Westfall. 2004. Covalent and noncovalent modification of thin filament action. The essential role of troponins in cardiac muscle regulation. Circulation Research 94 146-158. 

Tran PD, Le Goff A, Heidkamp J, Jousselme B, Guillet N, Palacin S, Dau H, Fontecave M, Artero V (2011) Noncovalent modification of carbon nanotubes with pyrene-functionalized nickel complexes carbon monoxide tolerant catalysts for hydrogen evolution and uptake. Angew Chem Int Ed 50(6) 1371-1374. doi 10.1002/anie.201005427... 

A related selectivity-enhancing noncovalent modification of Candida rugosa lipase, which does not require tedious protein chromatography and which is therefore applicable to large-scale reactions is based on the treatment of crude CRL with 50% aqueous wo-propanol, which led (after simple centrifugation and dialysis) to a modified lipase preparation, which was not only more active, but also showed considerably enhanced enantioselectivity [424],... 

As illustrated in Figure 6.71, noncovalent modifications consist of either wrapping the CNT with polymers or biological macromolecules, " or placement... 

Khan, M.A.K., Kerman, K., Petryel, M., et al, 2008. Noncovalent modification of carbon nanotubes with ferrocene-amino acid conjugates for electrochemical sensing of chemical warfare agent mimics. Anal. Chem. 80, 2574-2582. 

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