Effects of a triangular nanocage structure on the binding of neutral and anionic ligands to Co^II and Zn^II porphyrins

Interactions of neutral pyridine ligands and anionic benzoate with the metalloporphyrin walls M6L3 nanocages (M = [(tmeda)Pt]2+, L tetra(3-pyridyl)porphyrin-M′, M′ CoII, Co3-1; ZnII, Zn3-1) were evaluated in CD3CN. The binding to simple tetra(N-methyl-3-pyridinium)porphyrin-M′ complexes Co-2 Zn-2 was also evaluated. It found that bind generally similar strength monomeric porphyrins as outer faces corresponding cage. Coordination is enhanced inside cages for one equivalent pyridine, 3-methylpyridine, or 3,5-dimethylpyridine. In contrast, 4-(4′-methoxyphenyl)pyridine cannot cages, 4-methylpyridine shows weaker than outside. Steric effects play a complex role influencing ligand since 4-tert-butylpyridine binds more strongly 4-methylpyridine. These latter two reveal subtle allosteric effect which Zn3-1 becomes increasingly favored over external once some sites are occupied. confirmed 3,5-di-tert-butylbenzoate can coordinate M3-1, but quantitative analysis these interactions complicated by competing affinity anions other limiting detailed insight.