Influence of receptor flexibility on intramolecular H-bonding interactions

摘要: Atropisomers of a series zinc tetraphenyl porphyrins were synthesized and used as supramolecular receptors. Rotation around the porphyrin-meso phenyl bonds is restricted by installing ortho-chlorine substituents on groups. The chlorine allowed chromatographic separation atropisomers, which did not interconvert at room temperature. porphyrin meso groups also equipped with phenol groups, led to formation intramolecular H-bonds when bound pyridine ligands ester or amide side arms. Binding conformationally locked chloroporphyrins was compared corresponding unsubstituted porphyrins, are more flexible. association constants 150 porphyrin–pyridine complexes measured in two different solvents, toluene 1,1,2,2-tetrachloroethane (TCE). These then construct 120 chemical double mutant cycles quantify influence substitution free energy formed between arms ligands. Conformational restriction leads increases stability some decreases others variations contribution due H-bonding −5 +6 kJ mol−1.