Adrenaline recognition in water.
Host mol. I displays a high affinity in water towards catecholamines and esp. related structures such as b-blockers with extended arom. p-faces (up to 7*103M-1 for each single complexation step or 5*107M-2 for both steps). The amphiphilic structural design leads to an extensive self-assocn. of host mols. through their arom. flanks. Above a cmc (crit. micelle concn.) of 3*10-4M, host I forms micelles that produce a favorable microenvironment for hydrophobic interactions with the included guest mols. Electrostatic attraction of the ammonium alc. by the phosphonate anions is thus combined with hydrophobic contributions between the arom. moieties. Ionic hydrogen bonds with polar OH or NH groups of the guest enforce the non-covalent interactions, and finally lead to increased specificity. Both its affinity and its selectivity towards adrenergic receptor substrates are greatly enhanced if the receptor mol. I is transferred from water into a lipid monolayer. Catecholamines and b-blockers lead to drastically different effects at concns. approaching the micromolar regime. Esp. b-blockers with minute structural changes can be easily distinguished from each other. In both cases, extensive hydrophobic interactions with a self-assocd. and/or self-organized microenvironment are largely responsible for the obsd. high efficiency and specificity.
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