Synthetic strategies of multifunctional porphyrins as receptors

Abstract
A series of multi-functional porphyrins 1-10 were prepared as a model receptor to clarify the mechanism of electron transfer reaction mediated by molecular recognition between reductase and mobile ubiquinone in membrane. Formation of complementary face-to-face complex is performed by multi-point hydrogen bonding between benzoquinones substituted with methoxy groups and particular porphyrins. Fluorescence from photo-chemically excited porphyrin is efficiently quenched by quinone derivative in the face-to-face adduct. Binding constants and thermodynamic parameters are discussed with structural changes in both quinones and host porphyrins. Newly prepared intrinsic chiral porphyrins with C2 symmetry have been examined as a model receptor for amino acid esters. Thermodynamic investigation on the intermolecular interaction of chiral and reference porphyrins with amino acids enables us to estimate contribution of the respective interactions such as hydrogen bonding, coordination to the metal, and van der Waals contact. The host having the chiral cavity above and below the porphyrin plane shows high diastereomeric selectivity towards amino acids with bulky residue.