Host-guest chemistry construction

The shape-persistent, structurally well-defined nature of PAMs and PDMs make them attractive models for binding guest molecules within their cavities. In 1995, Hoger and Enkelmann reported the construction of the first meta/para-PAM/PDM hybrid designed to possess hydrophobic and hydrophilic substituents for subsequent use in host guest chemistry [71]. Macrocyclic amphiphile 116 was assembled via the straightforward manner depicted in Scheme 26. 

The main aim in host-guest chemistry is to construct molecular receptors by a self-assembly process so that such receptors could, to some extent, gain molecular recognition capability. The goal of such molecular recognition capability is to either mimic or block a biological effect caused by molecular interactions [157]. 

Indeed, we anticipate that the Platonic and Archimedean solids may be used for the construction of hosts which conform to those solids not yet realized and additional members of each family, where supramolecular synthesis, via self-assembly, will play a major role in their design, ushering in an era of spherical host-guest chemistry. 

The stoichiometric selective oxidation of the benzyhc alcohol function in (di)hydroxy-substituted benzylalcohols (Eq. 14) has been demonstrated by Nolte et al., using host-guest chemistry to steer the regiospecificity in the reaction [167-170]. The host-receptor used to construct dicopper complex 21 is based on the building block diphenylglycoluril, which was functionahzed... 

We saw in Figure 1.2c that supramolecular chemistry is not just about solid state or solution host-guest chemistry but increasingly emphasises self-assembly and the construction of multi-nanometre scale devices and ultimately materials based on nanometre-scale components (a nanometre is 10 9 of a metre). Strict supramolecular self-assembly (Chapter 10) involves the spontaneous formation of a multi-component aggregate under thermodynamically controlled conditions based on information encoded within the individual building blocks (referred to as tectons ) themselves. The aggregate might comprise only one kind of molecule (as in the multiple copies of the same protein that comprise... 

The design aspect of host-guest chemistry mandates the knowledge-based construction of novel compounds possessing desired properties. The concept of structure seems indispensable in this enterprise, although the term is ill-defined and the International Union of Pure and Applied Chemistry (IUPAC),for instance, consciously avoids the close specification. As a corollary, many fields in science have developed their own interpretation of structure, which sometimes clash with each other and lead to misunderstandings when issues at the common interface of subdisciplines are in need of rationalization. 

The construction of macrocyles containing TTF units has received considerable attention since such molecules may act as a host in host-guest chemistry. Planar derivatives containing the TTF-crown ether 971 and TTF-crown thiaether 972 have been investigated for potential use as electroactive cation sensors <2000CSR153>. 

Another example of how PET can be modulated by complexation involves the use of bulky carboxylates as molecular curtains . Intramolecular PET occurs in the Zn complex of the poly amine (166) between the dimethylaniline donors and the anthracene acceptor, however when triphenylacetic acid is added a strong enhancement of fluorescence occurs. This effect is ascribed to complexation of the triphenylacetate at the Zn cation in such a way as to block PET between the other two units in the complex. The host-guest chemistry afforded by calixarenes has also been adapted to the construction of efficient ET systems. 

Construction of supramolecular structures using specific intermolecular interactions is one of the most important procedures for the construction of nano-scale architectures by bottom-up procedures. Recently, with the advent of host-guest chemistry and chemistry of molecular recognition, supramolecular science has made its appearance. 

This stabilization was carried to extremes in work that ultimately led to the 1987 Nobel Prize in Chemistry for Charles J. Pedersen (1904—1989) of du Pont, Donald J. Cram (1919-2001) of UCLA, and Jean-Marie Lehn (b. 1939) of Universite Louis Pasteur in Strasbourg for opening the field of host-guest chemistry. Pedersen discovered that certain cyclic polyethers (the hosts) had a remarkable affinity for metal cations (the guests). Molecules were constructed whose molecular shapes created different-sized cavities into which different metal ions fit well. Because of their vaguely crown-shaped structures, these molecules came to be called crown ethers. Rgure 6.60 shows two of them. 

The intramolecular photochemical synthesis of phanes can be apphed to the construction of covalent templates. Moreover, the cyclobutane ring(s) formed by the cycloaddition reaction can act as a stereochemical control forcing the phane conformation to one side similar to a caUper system. Other work has been directed towards the synthesis of receptors and ionophores apphcable to host-guest chemistry. ... 

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