Coronands

Podates AcycHc analogues of crown ethers /coronands and cryptands (podands, eg, (11) (30) are also capable of forming inclusion compounds (podates) with cations and uncharged organic molecules, the latter being endowed with a hydrogen bond fiinctionahty. Podates normally are less stable than coronates and cryptates but have favorable kinetics. 

Coronand Any medium sized or macrocyclic system having only one ring and containing any heteroatom(s). 

Podand Open-chained (acyclic) analogs of either coronands or cryptands. 

Crown ether This term would refer specifically to coronands (see above) containing only oxygen heteroatoms in the ring. 

Complexes Tlie term cryptate is now accepted to mean the complex formed between a cryptand and a substrate. Tlie corresponding complex with a coronand would be a coronate, a term suggested some years ago by the same authors . Presumably, a complex between a podand and some substrate would be a podate . 

The problem of molecular recognition has attracted biologically oriented chemists since Emil Fischer s lock-and-key theory l0). Within the last two decades, many model compounds have been developed micelle-forming detergents11, modified cyclodextrins 12), many kinds of crown-type compounds13) including podands, coronands, cryptands, and spherands. Very extensive studies using these compounds have, however, not been made from a point of view of whether or not shape similarity affects the discrimination. 

The following structures will show that macrocyclic rings between metal ions or BR2 units and acyloxy or acylamino groups have some relationship with rigid coronands [Ic]. 

An unusual A-chelate is the anion R MI PR2 S, which has no carbon atoms amongst the four-membered chelate ring atoms, and forms a tetrahedral bis Co11 spirocyclic complex.512 Higher denticity ligands also feature in the literature. A dipyrazoyl-dithioether ((119), bddh) forms a simple octahedral cw-a-Co(bddh)(NCS)2 complex.513 The ketal coronand (120) forms a... 

Marquis D, Desvergne JP, Bouas-Laurent H (1995) Photoresponsive supramolecular systems synthesis and photophysical and photochemical study of bis-(9,10-anthracenediyl) coronands AAOnOn. J Org Chem 60 7984-7996... 

Examples of PET sensors containing various kinds of crowns are given in Figure 10.11. PET-1 is the first and simplest coronand PET sensor. Its fluorescence quantum yield increases from 0.003 to 0.14 upon binding of K+ in methanol. 

Fig. 10.27. Oxyquinoline-based chelators, podands and coronands (M-l and M-2 K. Soroka et al. (1987) Anal. Chem. 59, 629. Bardez E. et al. (1997) J. Phys. Chem. B 101, 7786. M-3 and M-4 Hiratani K. (1987) Chem.

Figure 2.1. Schematic illustration of various structures of fluoroionophores. (a) Chelators and podands (b) coronands (c) cryptands (d) other structures.

This paper is not a review covering the entire field of carbohydrate-recognition in any organized system. Many excellent papers have already been devoted to supramolecular systems such as cyclodextrins, podands, coronands or cryptants able to entrap carbohydrate molecules [1]. This article only deals with the molecular recognition of mono and oligosaccharides in organized self-assemblies of amphiphilic carbohydrates (possibly blended with other lipids) in aqueous medium i.e. in assemblies mimicking the cell membrane. 

Fig. 35. The structure of the water complex of the bipyridino dilactam coronand 8 S)...

As stated above, systematic names of macrocyclic host molecules were absurdly complicated for routine discussions [22]. Therefore Vogtle proposed the name coronand for crown ethers, and that of coronates for their complexes while cryptand complexes were called cryptates . The corresponding noncyclic analogues are podands such as 64 [23] and podates, respectively. The cumbersome name podando-coronands (and correspondingly podando-coronates ) was proposed for lariat ethers [24] having at least one sidearm like 65. Examples of hemispherands 66 [25], cavitands 25 [26] and those of some other hosts are discussed in Chapter 7 in some detail, whilst the exceptional stability of fragile guests 4 [2a] and 67 [27] in the hemicarcerand 5 cavity are discussed in Chapters 1 and Section 7.3. 

Multidentate ligands, both acyclic and cyclic, are now abundant and herein the nomenclature used will follow that recently proposed by Vogtle and Weber.33 Coronands are taken to mean macromonocyclic compounds having any heteroatoms present as potential donors, with crown ethers being reserved for compounds of the same type having only oxygen atoms present as... 

Alkali Metals and Group IIA Metals 23.5.1 Crown Ethers and Coronands... 

Coronands containing pyridinyl, thiophenyl and furanyl head units have been prepared,33 and their complexation studied. The coronand (109 Figure 13) gives a 1 1 complex with KNCS in which the metal is coordinated centrally by the six ring donor atoms the keto groups are not involved in the coordination.448... 

---