Anion macropolycyclic ligands

Macropolycyclic ligands, 2,942 classification, 2,917 metal complexes binding sites, 2, 922 cavity size, 2,924 chirality, 2, 924 conformation, 2,923 dimensionality, 2, 924 electronic effects, 2, 922 shaping groups, 2,923 structural effects, 2,922 molecular cation complexes, 2,947 molecular neutral complexes, 2,952 multidentate, 2,915-953 nomenclature, 2,920 Macro tetrolide actins metal complexes, 2,973 Macrotricycles anionic complexes, 2,951 cylindrical... 

More complex organic anions and polyanions (oxalate ", malonate ", succinate ", etc.), and phosphates (ATP , ADP , AMP ", etc.) also form complexes with macrocyclic ligands. Steric constraints imposed by incorporation of the larger, more complex ions into macropolycyclic ligands lead to marked selectivity patterns. - "-" ... 

Our present aim is to summarize the results obtained in the design of coreceptors capable of performing molecular recognition. Complexation of two or more metal ions by various macropolycyclic ligands to form di- or polynuclear cryptates will not be considered here (see ref. [15]). The discussion will be limited to substrate recognition by ditopic coreceptors for polyatomic molecular cations and anions and to developments towards poly topic coreceptors. 

The complexation of various molecular anions by other types of macrocyclic ligands has been reported [3.1-3.4] in particular with cyclophane-type compounds. Two such receptors are represented by the protonated forms of the macropolycycles 40 [3.29] and 41 [3.30]. Quaternary polybipyridinium compounds also bind anionic substrates [3.31]. Progress is also being made towards the developments of neutral anion receptor molecules [3.32]. The thermodynamic and kinetic data for anion complexation by macrocyclic receptors have been reviewed [2.18c]. 

Macrocyclic systems—polyazamacrocycles. Anion complexation can only occur when over a certain range of pH the anion exists and the host ligand is in its protonated form. With the macropolycyclic systems previously described, this prerequisite for binding is obeyed for halide and azide guest anions. However, for the important classes of carboxylate and adenosine... 

Thus, cryptands (1-3) and (5) display spherical recognition towards spherical cations and anions. The special complexation properties encountered clearly result from the macropolycyclic nature of these ligands. They define a cryptate effect characterized by high stability and selectivity of complexation, slow exchange rates and efficient shielding of the bound substrate from the environment. 

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