Macrobicyclic solvation

Finally, a macrobicyclic or [2]-cryptate effect is found by comparing the stability of the K+ complex of 30 with that of 22, where the solvation shell is completed by solvent molecules (a better model would be a ligand of type 22 bearing a — CH2CH2OCH2CH2OCH3 chain on one nitrogen) a stability increase of more than 105 (in methanol/water, 95/5) is found on introduction of the third bridge. 

Process b) seems to occur in valinomydn (134). Process a) is more likely to operate in the case of the more rigid macrobicyclic ligand 30, which is probably not flexible enough to progressively compensate substituted solvation molecules by binding sites. The decrease in association rates from Ba2+ to Ca2+ is also in accord with such a picture since water molecules are more difficult to remove from the solvation shell of Ca2+ than from that of Ba2+ (144). 

Both macrocyclic and macrobicyclic ligands allow preparation of alkali metal solutions, but the former yield mainly M-, whereas solvated electrons are obtained with the [2]-cryptates (162,163). The enhancement of anion reactivity should also useful for activating anionic polymeriza-... 

Under LL-PTC conditions, the anions associated with bulky lipophilic cations (quaternary onium salts, macro-cyclic and macrobicyclic polyethers, etc.) are extracted into the organic medium specifically solvated by a limited number (1-11 moles per mol of Q Y") of water molecules. Furthermore, two additional molecules of water are found to accompany the cyclic polyethers 5, 10, as both free and complexed ligands. This hydration sphere, characteristic of each anion, always reduces, more or less remarkably, anionic reactivity. As shown in Table 4, when changing from LL-PTC to anhydrous homogeneous... 

Classic PTC requires the presence of an aqueous-organic two-phase solution. As discussed previously, the catalyst (a quaternary salt, a macrocyclic or macrobicyclic polyether as a complex, and in general whatever kind of PTC catalyst, see Sect. 5) extracts some water into the apolar organic phase, mostly as specific solvation sphere of the anion. The amount of water transported, though scare, may affect the reaction to give undesired side effects. 

The practical and effective synthesis of photoactive lanthanide cryptates (1), capable of effective light conversion, has found application in the design of novel fluorescent immunoassay systems. The macrobicyclic bipyridyl cryptands prevent the normal solvation quenching of these cations. Remarkably effective DNA cleavage was accomplished using intercalators (2) based on 2,7-diazapyrenium cations. 

---