Noncovalent derivatization

Noncovalent derivatization with metal complexes or nanoparticles is again based on van der Waals, electrostatic, H-bond and n-n stacking interactions. 

The technique of noncovalent derivatization employs the noncovalent intermolecular forces (hydrogen bonding, 7t-stacking, UpophUic-lipophilic interactions, and electrostatic interactions) to trap the molecular species in organized matrices. 

Further Noncovalent Derivatizations of Carbon Nanotubes By now there are numerous different approaches to derivatizing single- and multiwalled carbon nanotubes by way of noncovalent interactions. A multitude of further organic or inorganic substances can be bound to nanotubes besides those mentioned above. 

Cannon, A.S. Warner, J.C. Noncovalent derivatization green chemistry applications of crystal engineering. Crystal Growth and Design 2002, 2, 255. 

Fig. 3.20 (a) Schematic representation of noncovalent attachment (i.e., n-stacking) of benzyl alcohol molecules for subsequent coordination with Titanium resulting in the coating of the tube, (b) SEM image of pristine CNTs prior to derivatization. (c) SEM image of CNTs after derivatization with benzyl alcohol and subsequent coordination with Titanium resulting in the coating of the tubes. Adapted with permission from [102], 2008 Wiiey-VCH. 

Most ILMs are less acidic than the commonly used acidic matrices alone. This leads to the possibility to synthesize matrices with only weakly acidic or even neutral or basic pH values [48]. These matrices may be beneficial for the analysis of acid-labile compounds [40]. For example, these matrices were successfully used for the measurement of acid-labile compounds like sulphated oligosaccharides, which are a class of compounds with high biological relevance [49]. Using classical preparations, the detection of these challenging analytes was only possible after derivatization or in the form of noncovalent complexes formed with basic peptides. Upon use of the ILM,... 

An elegant alternative approach for noncovalent interaction relies on fluorous-lluorous interactions. A glycan array of monosaccharides and disaccharides bearing anomeric fluorous tags was noncovalently immobilized on fluorous-derivatized glass slides (19, 20). The attachment method is compatible with a wide range of functional groups and has been successfully used to probe carbohydrate-protein interactions. 

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),...

The reaction with pyrene is largely established as fundamental example for this kind of noncovalent functionalization for several reasons. Firstly, it allows for a wide scope of derivatization, secondly, it can be aligned in parallel with the tube s axis, and finally, the solubihty of pyrene compounds ensures an easy handling. In fact, larger aromatic systems already give rise to similar solubihty problems like fuUerenes or nanotubes themselves. 

Hitherto, many methods for the preparation of carbohydrate microarrays have been described, such as nitrocellulose coated slides for noncovalent immobilization of microbial polysaccharides [23], and self-assembled monolayers modified by Diels-Alder mediated coupling of cydopentadiene-derivatized oligosaccharides [24], just to name two. Unfortunately, the first method requires large polysaccharides or lipid modified sugars for the noncovalent interaction. The latter method requires the preparation of oligosaccharides bearing the sensitive cyclopentadiene moiety. 

Due to the nature of carbon materials, the presentation of representative methods for surface derivatization will follow an approach different from that described in the preceding section, which is based on the spatial target site where physical-chemical modification can take place (1) immobilization performed at edges and/or ends and defects of graphitic sheets, (2) immobilization onto the graphene sheets, and (3) exclusively for CNTs we present some examples of endohedral encapsulation of metal complexes. For the first two cases, covalent bonding and noncovalent interactions can occur directly between the transition metal complex and carbon supports or via spacers grafted to the carbon surface. 

Despite much interest in CNs, manipulation and processing of these materials has been limited by their lack of solubility in most common solvents. Many applications of CNs (mainly SWNTs) require chemical modification of the materials to make them soluble and more amenable to manipulation. Understanding the chemistry of SWNTs is critical for rational modification of their properties, and several different procedures for chemical derivatization of CNs have been described in the last four years. These methods have been developed in an effort to understand the chemical derivatization and to control the properties of these systems. There is substantial interest in studying the photophysical properties of single-walled carbon nanotube (SWNT) derivatives obtained by covalent [82] and noncovalent [83] functionalization, with the overall objective of obtaining materials with new properties [84]. Functionalization of SWNTs by covalent bonding can be achieved by two different approaches - the bonds can be formed either at the tube opening or on the lateral walls. 

Figure 9 Carbohydrate microplate arrays prepared by the noncovalent immobihzation of aliphatic alkyne-derivatized carbohydrates to microtiter plate surfaces. Carbohydrates can then be screened against a variety of biologically important substrates such as lectins and RNA.

Figure 10 Carbohydrate microplate arrays prepared by the noncovalent immobilization of azide-derivatized carbohydrates to microtiter plates via a 1,3-dipolar cycloaddition reaction between alkynes and azides. Carbohydrates displaying terminal azides can be captnred on microtiter plate surfaces through a terminal alkyne attached to a long, ahphatic tether and screened directly on the microtiter plate surface.

Protein expression encompasses an enormous dynamic range. Since rare proteins cannot be amplified by any type of PCR method, sensitive detection is critical to proteome projects. Fluorescence methods deliver streamlined detection protocols, superior detection sensitivity, broad linear dynamic range and excellent compatibility with modem microchemical identification methods such as mass spectrometry. Two general approaches to fluorescence detection of proteins are the covalent derivatization of proteins with fluorophores or noncovalent interaction of fluorophores through direct electrostatic interaction with proteins. One approach for quantifying fluorescence is to use a photomultiplier tube detector combined with a laser... 

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