Surface noncovalent attachment

Noncovalent interactions such as van der Waals, hydrogen bonding, n-n stacking and electrostatic interactions have been widely used to hybridize pristine nanocarbons via ex situ approaches. The major advantage of this route is that the nanocarbons do not require modification prior to hybridization and their structure remains undisturbed, an important factor in many electronic applications. The strength of hybridization is weaker compared to covalent interactions but the synthetic process is generally simpler. Noncovalent attachment of small molecules to nanocarbons is often used to change the surface chemistry for subsequent ex situ or in situ hybridization. 

For the majority of fibril systems, simple deposition results in layers of fibrils that are largely unordered. The thickness of the fibril layer can also vary. This section explores a variety of methods that can be used to induce fibrillar alignment on a surface or create surface patterns. It also details methods that can be used to induce covalent and noncovalent attachment of fibrils to the surface. 

Absorption. The noncovalent attachment of one substance to the surface of another. See Liquid-solid chromatography. 

Sorption. The noncovalent attachment of one substance to the surface of a packing. The term is generally used to indicate any or all types of attractive modes of LC that may be involved, for example, ion exchange, liquid-solid, and liquid-liquid partition. 

Fig. 4. Immobilization methods. (A) Attachment of biomolecules onto thiol-derivatized surfaces (see Subheading 3.2.1 for experimental details). (B) Attachment of biomolecules onto amine-derivatized surfaces (Subheading 3.2.2) using amine-amine linking (upper pathway, Subheading Amine-Amine (Homobifunctional Crosslinkers) ) and amine-thiol linking (lower pathway, Subheading Amine-Thiol Crosslinking (Heterobifunctional Crosslinkers) ). (C) Noncovalent attachment of gangliosides/globosides onto hydrophobic surfaces (Subheading 3.2.3),...

Figure 2.70 Immobilization of Cso on surfaces, (a) Covalent linking to gold or to indium-tin oxide and noncovalent attachment to gold modified with coronene ( RSC 2005) ...

Surface properties of proteins have also been altered by covalent attachment of hydrophobic groups. Of particular interest is a recent report by Haque [37]. Whey proteins and peptides were modified by noncovalently attaching lipids of controlled chain length by a proprietary procedure. These modifications have been reported to substantially enhance the functionality of these molecules at interfaces. Low-fat ice creams and whipped toppings that incorporate these molecules have been reported to have enhanced consumer acceptability. The regulatory fate and the application of these modified proteins and peptides remain uncertain. 

Enzyme noncovalent attachment to the matrix surface has the advantages of simphc-ity, lack of secondary and very toxic reagents. The absence of derivatization procedures... 

The high number and accessibility of surface groups of dendritic structures can be modified easily to provide multiple binding sites with which to anchor the catalyst to the macromolecular support. In 2001, Reek, Meijer and coworkers exploited the known pincer type hydrogenbonding motif to assemble 32 phosphine ligands around the surface of a polypropylene imine (PPI) dendrimer. Further modification of the surface by the addition of the palladium resulted in the formation of the active catalyst that was noncovalently attached to the dendrimer support (Scheme 25). 

To enhance the properties of carbon nanostructures, several strategies have been developed. For example, carbon surfaces are functionalized, modified, and customized to selectively detect molecules, chemicals, and biological compounds in liquid or gas phases. Noncovalent attachment can be utilized to preserve the structure of CNTs by adsorbing the material onto their surface. However, covalent attachment needs the surface of CNTs to have defect sites, often requiring the surface to be chemically activated to bind molecules to their surface. Alternatively, CNTs can be embedded or filled with material, as we will discuss later in this section. 

As mentioned earlier, one simple way to modify surfaces of CNTs is by utilizing noncovalent attachment. A simple method is to deposit the material onto CNTs through incubation or drying. For example, CNT-coated glassy carbon electrodes were incubated in a combination of proteins and surfactants to enhance interfacial electron transfer, whereas single-stranded DNA was deposited and left to dry on CNT-based FETs to detect vapors. ... 

Randomly dispersed CNT films can be used as electrochemical sensors. For instance, ferrocene was noncovalently attached to acid-treated SWCNT films to detect glutamate. The combination of SWCNTs and ferrocene provided enhanced surface area, direct electron transfer, and catalytic effect. Electrodes can also be coated with CNTs to enhance performance. Indeed, CNT-coated carbon nanoelectrodes significantly outperform the conventional carbon fiber electrodes of similar geometry. ... 

There are two main approaches for the surface modification of NTs. One is the covalent attachment of functional groups to the walls and/or rims of the NTs, and the other is the noncovalent attachment of molecules [31]. 

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