Structural and Binding Features of Cofacial Bis-Porphyrins with Calixarene Spacers:Pac-Man Porphyrins That Can Chew

摘要

Based on the efficient combination of calixarene spacers and acety-lenic porphyrin derivatives,a new generation of cofacial bis-porphyrins has been synthesized.The first crystal structure of a cofacial bis-porphyrin-calixarene conjugate is reported.Their unique architectural features,analogous to those of pac-man-type bis-porphyrins,allow these calixarene-porphy-rin conjugates to adapt their shape to the size of bidentate guests,such as diazabicyclo[2.2.2]octane (dabco) and 1,4-pyrazine.The predefined,cofacial arrangement of the porphyrin moieties observed in the solid state and in solution results in extremely high affinities (in the range of 10~9M~(-1)) for these guests.The 1,3-alternate calixarene conformations afford "open-mouth" pac-man structures whose ability to bite on nitrogen bidentates depends on their functionalization.A cone con-former provides a much more flexible structure that exhibits the highest affinity for dabco and pyrazine.