Molecular Recognition of Neutral and Charged Guests using Metallomacrocyclic Hosts

Mechanisms of Oxygen Binding and Activation at Transition Metal Centers

“…These sterically hindered ligands also protect end-on dioxygen adducts from oxidative decomposition via formation of peroxo-or oxo-bridged dimers: While peroxo dimer formation is sometimes reversible for cobalt complexes, it inevitably leads to further oxidations in case of iron complexes. 38 The only crystal structure for a cobalt(II) cyclidene dioxygen adduct, that of [Co(C6Cyc(O 2 )(MeIm)] 2 þ (R 1 ¼ (CH 2 ) 6 , R 2 ¼R 3 ¼R 4 ¼Me), showed that O 2 binds at an angle of 121 , as expected for coordinated superoxide, and that the hexamethylene bridge flips away from the guest. Extensive efforts to model natural oxygen carriers resulted in impressive collection of sterically hindered porphyrins 21,31,32 ; some examples of these molecules are shown in Figure 4.9.…”

“…Oxygenation of both iron(II) and cobalt(II) complexes was studied, unraveling the factors that control dioxygen binding and release. Even longer 35,38 bridges are flexible and can adopt various confirmations that allow the cleft to shrink back to its optimal width (about 7 A ). 31 Steric constrains at the O 2 binding site decrease dioxygen affinity and O 2 binding rates.…”

“…35 (Table 4.3). 38 Electronic effects on the oxygenation rates are less pronounced, although in some cases still significant. The sixcoordinate C6-and C8-iron(II) cyclidenes release the solvent molecule in the course of oxygen binding.…”

Neutral discrete metal–organic cyclic architectures: Opportunities for structural features and properties in confined spaces

“…Several general synthetic approaches to the preparation of discrete metallacycles have emerged, which include directional bonding [46,47], symmetry interactions [48,49], and weak-link approaches [50]. Many impressive examples of metallosupramolecular materials can be found in studies reported by Lehn [1,49,70], Sauvage [51], Stang [46,47], Fujita [26][27][28][29][30][31], Mirkin [50], Hupp [52][53][54][55], Lees [56][57][58][59], Lu [60,61], Jin [62,63], and others [64][65][66][67]. Lehn et al demonstrated the spontaneous self-assembly of dinuclear helicates from bipyridine and copper (I) [70].…”

Contact Ion Pairs on a Protonated Azamacrocycle: the Role of the Anion Basicity

“…In particular, this is true for the interaction of cations with anionic carboxylate groups as it influences protein association and enzymatic activity [1][2][3][4][5][6][7][8][9][10][11][12]. So far, model studies have centered mainly on the recognition of cations using synthetic host compounds, such as macrocyclic polyether [13][14][15][16] and polyamines [17]. Polyazamacrocycles, such as M (Figure 1), have been successfully employed as chiral solvating agent for monocarboxylic acids in CDCl 3 [18], but not in aqueous solutions because the strong solvation capability of water inhibits the formation of the corresponding noncovalent adducts.…”