Endo-receptor

Endohedral fullerenes, 12 230-231 chemistry of, 12 253 Endonucleases, artificial, 17 636 Endoperoxides, 18 442—443 Endopolygalacturonase, 11 598 Endo-receptors, convergent, 16 774 Endosseous dental implants, 8 344 Endothall (Aquathol Granular, Aquathol K), 13 315... 

Percec studied taper-shaped molecules like 67 and 68 (Scheme 35) and investigated their liquid crystalline properties upon complexation with NaOTf and KOTf [84, 85]. It was found that the neat materials exhibit only crystalline phases with 67 melting at 60 °C and 68 melting at 94 °C. The increased melting point in the latter system can be explained by the presence of an additional aromatic ring. Both 67 and 68 consist of an endo-receptor (the [15]crown-5 macrocycle) and an exo-receptor (the taper-shaped 3,4,5-tris(p-dodecyloxybenzoate)). 

The electric conductivity was also measured for complexes of taper-shaped mesogens with oligo(ethylene oxide) central groups. The DC conductivity is in a range of 10 9 to 10 6 S cm-1 and shows a step-like increase at the crystal-columnar phase transition [86]. It was also shown that taper-shaped molecules adjacent to different endo-receptors such as crown ethers or oligo(ethylene oxide) chains were miscible with a poly(methacrylate) matrix and formed isomorphic phases [87]. Applications as columnar reaction media for polymerizations were foreseen. Comprehensive summaries of Percec s taper-shaped molecules can be found in the literature [88, 89]. 

The first ferrocenyl dendrimers suitable for redox recognition contained amido groups attached to the ferrocenyl moiety [23,24], so that the H-bonding interaction with oxo-anions, known from Beer s work with endo-receptors [8-14], would be efficient. At this point, it is essential to point out that mononuclear amidoferrocenes that contain a linear substituent without any special topological requirement for anion recognition display no specific effect [23,24],... 

If the branch junctures or the coupling junctures are heteroatoms or contain designed moieties amenable to reaction or chelation, the dendrimer should exhibit endo-receptor characteristics [23c], Each of these bonding features has been observed experimentally (for examples, see Sect. 7). 

Figure 2 Schematic representations of formation of discrete molecular complexes by an endo receptor and a exo substrate (a), by an exo receptor and two exo substrate acting as stoppers (b) and of a linear molecular network by an exo receptor and a connector (c).

Ionic supramolecular self-assembly will be discussed in Chapter 6, but some supramolecular systems based upon ionic interactions will be discussed earlier, e.g. the organocyclosiloxanolates, which form sandwich compounds by intercalating transition metal ions between two macrocyclic rings (held together by ionic interactions) and acting as endo receptors which concurrently have crown-ether-type complexing properties (as exo receptors) (see Section 2.1.2). 

In this case, the supramolecular structure contains a central M4O unit, and the lanthanide cations do not behave as endo receptors and are not externally solvated by additional ligands. The encapsulation of the M4O fragment and its connectivity to cyclooctasiloxanolate ring is shown schematically in 13. 

An important development in this area was the synthesis of PPEs with endo receptors. Coupling of la to 2 (Chart 8.1), gives PPEs 3 with an Mn of up to 2.5 X 10. The polydispersity (PDI) for different samples of 3 ranged from 1.8 to 2.9, not unusual for this type of polycondensation reactions, An ideal... 

Applications of ferrocenes are numerous,in particular with the use of ferrocenyl phosphines, including chiral ones (see for insance the aminophosphine below), as ligands for catalysis. l,l -bis(diphenylphosphino)ferrocene (dppf, below) is the best known ferrocenyl-based ligand in the catalysis of most classic reactions, and its chemistry and uses are prolific. The redox property of ferrocene has been used to attach it to macrocycles (below), cryptands, calixarenes and other endo-receptors for sensing, a chemistry beautifully developed by Paul Beer at Oxford,... 

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