Covalent approach

Balbo Block MA, Kaiser C, Khan A, Hecht S (2005) Discrete Organic Nanotnbes Based on a Combination of Covalent and Non-Covalent Approaches. 245 89-150 Balczewski P, see MikoloajczykM (2003) 223 161-214 Ballauff M (2001) Structure of Dendrimers in DUnte Solntion. 212 177-194... 

It has been emphasized that in the construdion of complex molecular and supramolecular architectures the use of non-covalent bonding can be more efficient and more economic than the conventional covalent approach.1351 We outline here, how the interplay of a hydrogen bonding and alkyl chain... 

Fig. 1. Concept of molecular imprinting - the non-covalent approach. 1. Self-assembly of template with functional monomers. 2. Polymerization in the presence of a cross-linker. 3. Extraction of the template from the imprinted polymer network. 4. Selective recognition of the template molecule...

Two different techniques have been developed for MIP production, namely the covalent and the non-covalent approaches. The covalent way is based on the chemical derivatization of the template with molecules containing polymerizable groups using reversible covalent bonds. Different chemical reactions can be ap-... 

Various covalent and non-covalent approaches for the incorporation of fullerene building blocks into liquid crystalline mesomorphic materials have been developed [35]. Lyotropic mesophases (buckysomes) were obtained upon dissolving globular amphiphilic fullerene dendrimers in water [145]. 

The successful use of - interactions to anchor an electron-donating extTTF to the surface of SWNT was recently demonstrated (Scheme 9.23).73 Interaction between the concave hydrocarbon skeleton of exTTF and the convex surface of SWNT adds further strength and stability to the SWNT/pyrene-exTTF nanohybrid. Because of the close proximity of the exTTF to the electron acceptor SWNT, a very rapid intrahybrid electron transfer affords a photogenerated radical ion pair, whose lifetime is only a few nanoseconds. The present method for the preparation of SWNT/ exTTF nanohybrids nicely complements the covalent approach and bears a strong... 

Sellergren B (2001) The non-covalent approach to molecular imprinting. In Sellergren B (ed) Molecularly imprinted polymers. Man made mimics of antibodies and their applications in analytical chemistry. Elsevier, Amsterdam... 

In 1994 Shea et al. reported the preparation of gel-like imprinted polymers with enantioselective esterolytic activity toward the Boc-D-phenyl-alanine p-nitrophenol ester (28) [19]. The polymers were prepared using a covalent approach, rather than metal complexes or non-covalent interactions, by attaching the catalytic phenol-imidazole unit to the TSA phosphonate via ester linkage (29). The imprinted polymer, containing the catalytic unit (30), showed little selectivity toward the D-enantiomer used for the imprinting. 

The use of polymerisable imidazole as functional monomer has been largely used for the preparation of hydrolytic imprinted polymers from other groups as well. Ohkubo et al. [38], for instance, described the preparation of imprinted polymers with esterolytic activity towards /V-dodecanoyl leucine-p-nitrophenyl ester (57) using a system similar to the Shea one but based on a stoichiometric non-covalent approach. The imprinting was carried out with a phosphonate TSA and the activity of the resulting imprinted polymer was twice the non-imprinted. 

In addition to metal centres and covalent approaches, anions such as Cl may also be used as templating auxiliary linkages.80 Paul Beer and co-workers from the University of Oxford, UK, recognised that ion pairing in non-polar solvents such as acetone allowed the coordination of a neutral hydrogen bond donor such as 10.110 to the pyridinium salt 10.109, with a binding constant... 

Covalent Approach Nolte and coworkers also reported on the synthesis and characterization of well-defined biohybrids through covalent coupling of a polymer directly to the enzyme.272 In order to achieve the covalent coupling in a predefined position, a disulfide... 

A similar, but covalent, approach was employed by Raymo and Cejas, who functionalized the surface of commercially available silica nanoparticles (20 nm diameter) with 2,7-diazapyrenium dications and used them for the detection of dopamine in... 

While technically simpler than the covalent approach, the self-assembly approach creates more heterogeneous sites and also requires templates with specific functional groups.8 Since sol-gel chemistry is aqueous based, H-bonding interactions are significantly weaker compared to the conventional organic polymerization methods. Often, hydrophobic effects and ionic interactions are utilized. A number of other examples of the noncovalent approach to imprinting in sol-gel-derived materials are provided in recent reviews.5 17 In the sections below, the focus will be on some of the newer aspects of small molecule imprinting in silica that involve the use of chiral templates... 

Whether dendritic catalysis can compete successfully in commercial applications with other strategies that allow recycling of the catalyst remains to be seen. Dendrimer supports are still relatively expensive, but for applications that do not require the well-defined structure of the dendrimer support, hy-perbranched polymers can offer a cheaper alternative. A recent novel strategy in this research area that might provide the added value required to make the step towards commercial applications involves the noncovalent functionalization of dendritic support with catalysts (Fig. 1). This offers several advantages above the traditional covalent approaches. In this chapter we will review the progress in the area of supramolecular dendritic catalysis. 

More sophisticated methods have been developed for the assembly of very complex two dimensional molecules (i.e., palytoxin, Mwt. 2680 or vitamin B12) or three dimensional architecture (i.e., cryptates/carcerands) involving a convergent covalent approach. The resulting assemblies of covalently linked atoms are precise... 

The syntheses of the Q1T4-H2TPPS chiral hetero-aggregate samples for EDXD analysis need particular care, and were carried out by following a purely non-covalent approach [48],... 

There are two ways by which a chiral auxiliary can be attached to a molecule of interest in order to insure that it crystallizes in a chiral space group—covalently and ionically. The covalent approach requires little explanation, typical examples being ester or amide formation between the achiral carboxylic-acid-containing photoreactant and an optically pure alcohol or amine. The ionic attachment is similarly straightforward, consisting of salt formation between the carboxylic-acid-containing reactant and an optically pure amine. In this case, the resulting chiral ammonium ion is referred to as an ionic chiral auxiliary. 

The very efficient non-covalent approach to nanotubes by molecular self-assembly of cyclic peptides is limited by the kinetic instability of the resulting constructs. An elegant solution to... 

Fig. 1.8. The covalent approach to molecular imprinting in organic polymers, as introduced by the group of Wulff, exemplified by the o-glyceraldehyde MIP reported in 1972 [1],...

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