Bindung von Anionen: Selbstorganisation von Polypyrrolmakrocyclen

Molecular Engineering of Free-Base Porphyrins as Ligands-The N-H⋅⋅⋅X Binding Motif in Tetrapyrroles

The core N-H units of planar porphyrins are often inaccessible to forming hydrogen-bonding complexes with acceptor molecules. This is due to the fact that the amine moieties are "shielded" by the macrocyclic system, impeding the formation of intermolecular H-bonds. However, methods exist to modulate the tetrapyrrole conformations and to reshape the vector of N-H orientation outwards, thus increasing their availability and reactivity. Strategies include the use of porpho(di)methenes and phlorins (calixphyrins), as well as saddle-distorted porphyrins. The former form cavities due to interruption of the aromatic system. The latter are highly basic systems and capable of binding anions and neutral molecules via N-H⋅⋅⋅X-type H-bonds. This Review discusses the role of porphyrin(oid) ligands in various coordination-type complexes, means to access the core for hydrogen bonding, the concept of conformational control, and emerging applications, such as organocatalysis and sensors.

Host-guest chemistry of aromatic-amide-linked bis- and tris-calix[4]pyrroles with bis-carboxylates and citrate anion

A small library of polytopic receptors has been synthesized from meso-p- and meso-m-aminophenylcalix[4]pyrroles and p- or m-phthaloyl or trimesic chloride. Selected bis-carboxylates and the citrate anion, which either exhibit altered distribution profiles in cancerous tissues in comparison with healthy tissues or are metabolites of carcinogenic substances (for example, trans,trans-muconic acid from benzene exposure in humans) were tested as ligands. Varied affinities and binding modes were observed as a function of the number of calix[4]pyrroles and the topology of amide units present in each of the polytopic receptors. The structures of the 1:1 complexes derived by molecular modeling are in excellent agreement with the results of (1)H NMR complexation studies.