Anion hosts zwitterions

In supramolecular chemistry, molecular recognition has evolved over the last 35 years and now much effort is directed towards the complexation of anionic [28], zwitterionic [29], ion-pairs [30] and neutral guests for various purposes, including catalysis [31[. Host molecules can be constructed covalently, or they can themselves also be assembled in a supramolecular fashion. This strategy, called receptor site self-assembly, has been exploited in recent years. Especially, dynamic host formation in the presence of a substrate is highly interesting [32]. 

Worm K, Schmidtchen FP (1995) Molecular recognition of anions by zwitterionic host molecules in water. Angew Chem Int Ed 34 65-66... 

Suggest experimental techniques for assessing the affinity of a host for a particular anion in solution. Which of these techniques might be appropriate for (a) podand (4.40), (b) diboryl hosts such as hydride sponge (4.69) and (c) zwitterions such as (4.35). 

We saw in Section 4.6.1 the use of zwitterionic hosts for anions in which the counter-cation is non-speciflcally bound on the outside of the molecule. We now turn to zwitterionic guests where the guest has both cationic and anionic parts. We have already described in Section 5.1.1 the zwitterionic structure of amino acids and amino acid binding has been a major part of the interest in the construction of hosts for zwitterions. An excellent example is compound 4.30 (Section 4.5) which is... 

Di- and polytopic host-guest systems have provided a convenient starting point for the construction of larger assemblies and many systems of this type are now known. For example, in an early study Kimura et synthesised the catecholamine complex 17. The crown ether unit of this ditopic host was known to be an effective receptor for primary alkyl ammonium salts, whereas the partially protonated form of the hexamine ring had been documented to bind anionic substrates (such as car-boxy lates) or electron-donor substrates (such as catechols). Accordingly, this host forms stable 1 1 complexes with zwitterionic guests such as amino acids, pep-... 

Compound 8, which was synthesized by Schmidtchen (49). This receptor provides a fixed-binding site for anions that operates through a combination of electrostatic and hydrophobic forces (50). The absence of donor protons prevents any opportunity for hydrogen bonding, but the crystal structure of the iodide complex still indicated that the anion-binding site was in the center of the cavity (51). Zwitterionic hosts such as 9, have also been reported (52, 53). These net neutral hosts prevent the need for the substrate to compete against a... 

The chapter is organized around the chemical composition of macromolecules. This leads to four main sections focused on neutral, zwitterionic, anionic, and cationic polymers. Most laboratories study one class of polymers. A host of different experimental techniques have been used to study the interactions between polymers and lipid membranes over the years. Unfortunately, outside of the antimicrobial field, there is little... 

Anion-binding properties of [Cu2(L14)2], which are further explored via solid-state and solution chemistry to define the effects of the strength of anion binding in the helical metallomacrocyclic cavity, have shown that these zwitterionic dicopper hosts can bind anions with an approximate volume of 0.09 nm and smaller. The dicopper host [Cu2(L14)2] is capable of binding anions in... 

Hemicryptophanes are molecular containers, constructed on the cryptophane structure, but where one CTB unit is changed for another C3 symmetiy group. Compounds 60 [74], and 61 [75], (Fig. 21.20) are representative of this new class of host molecules. They have been designed to allow the endohedral functionaUzation of the inner molecular cavity. They were found to be efficient and selective receptors for cations, anions, ion pairs, zwitterions and carbohydrates. 

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