Tether-directed functionalization methods

Prior to the development of tether-directed functionalization methods, Krautler and co-workers developed a very elegant topochemically controlled, solid-state group-transfer synthesis [12,13] to obtain the trans-1 bisanthracene adduct 9 (Figure 2). 

Prior to the development of tether-directed functionalization methods, regioisomerically pure higher adducts of C50 usually were obtained by additions of transition metal complexes [31-33] or radical halogenations [34, 35]. These reactions either occur under thermodynamic control or lead to the precipitation of the least soluble derivative. Iso-merically pure higher adducts of C o sometimes are also readily isolated out of more complex product mixtures [36]. Tether-directed remote functionalization of CgQ allows the construction of fullerene derivatives with addition patterns that are difficult to obtain by thermodynamically or kinetically controlled reactions with free untethered reagents. Since the description of the first such reaction in 1994 [7], which is the subject of Section 7.3.1, an increasing variety of such regioselective functionalization protocols have... 

To help avoid this problem a method has been developed4 to determine directly the position of tethers bearing functional groups within a mesoporous matrix. The solution is composed of four parts ... 

Hawker et al. 2001 Hawker and Wooley 2005). Recent developments in living radical polymerization allow the preparation of structurally well-defined block copolymers with low polydispersity. These polymerization methods include atom transfer free radical polymerization (Coessens et al. 2001), nitroxide-mediated polymerization (Hawker et al. 2001), and reversible addition fragmentation chain transfer polymerization (Chiefari et al. 1998). In addition to their ease of use, these approaches are generally more tolerant of various functionalities than anionic polymerization. However, direct polymerization of functional monomers is still problematic because of changes in the polymerization parameters upon monomer modification. As an alternative, functionalities can be incorporated into well-defined polymer backbones after polymerization by coupling a side chain modifier with tethered reactive sites (Shenhar et al. 2004 Carroll et al. 2005 Malkoch et al. 2005). The modification step requires a clean (i.e., free from side products) and quantitative reaction so that each site has the desired chemical structures. Otherwise it affords poor reproducibility of performance between different batches. 

We have presented the first method for directly imaging the position of functional tethers grafted onto the surface of a mesoporous material and, at the same time, validated a simple method by which one may direct the location of grafted functionality within mesoporous solids. This has been made possible by a strong partnership between supramolecular organometallic and solid state chemistry. The results presented now provide a foundation for the future examination of mesopore confinement effects on catalysis. 

Aside from intercalators, a number of other tethered electroactive moieties can provide added functionality to nucleic acids. These moieties are often based on ferrocene chemistry [180-182] but others derived from quinones [176,183,184] have also emerged. Additionally, derivatives with altered linker and ancillary groups are used to make the functionalized nucleic acids electro chemically distinguishable [185-188], and thus compatible with identification methodologies that rely upon detection of sequence variants. Whilst some efforts have been directed at solid phase synthetic routes for probe production, others have focussed on construction of electroactive nucleotides ( electrotides ) compatible with enzymatic methods of incorporation into nucleic acids (Fig. 4). 

Several interesting new concepts for the design of CdSe nanocrystal based polymer solar cells have been introduced recently. Snaith et al. have infiltrated CdSe nanocrystals into polymer brushes and demonstrated EQEs of up to 50% [256]. In this case the poly(triphenylamine acrylate) (PTPAA) chains were directly grown from the substrate by a surface-initiated polymerization on tethered initiator sites (Fig. 58). The authors pronounced the wide applicability of this method for the design of nanocrystal-polymer functional blends [256]. 

The chemical methods involve chemical linking of functional groups present over QCNs surface with the complementary groups over polymeric backbone. There are three ways by which QCNs can chemically tether the CP viz. ligand exchange, direct grafting ( onto and from approach), and in-situ growth of QCNs [156,157]. 

A second method for the formation of nanostructured surfiice-functionalized ionosilicas consists in the cocondensation reaction involving ionic precursor displaying surfactant-like behavior (Scheme 16.8) [108]. Template-directed syntheses of long chain-substituted silylated imidazolium or ammoniiun precursors in the presence of cationic surfactant such as CTAB or cetylpyridinium chloride yield highly structured ionosilica materials with surface-tethered ionic groups. 

---