Probing the Determinants of Porosity in Protein Frameworks: Co-crystals of Cytochrome c and an Octa-anionic Calix[4]arene

Sulfonato-calix[n]arenes (sclxn) are promising tools to generate crystalline protein frameworks. Two crystal structures of an octa-ionic calix[4]arene (sclx4mc) in complex with yeast or horse heart cytochrome c (cytc) are reported. Highly porous honeycomb or tubular assemblies were obtained with yeast or horse cytc, respectively. Related frameworks were obtained previously with sclx8 and sclx6 but not with sclx4, suggesting that the ligand charge is a contributing factor.