Biomimetic models of intradiol catechol dioxygenases: Structures and properties of inclusion complexes of iron(III) centered metal complexes with beta-cyclodextrin derivatives

A series of Fe(III)-DHN complexes and inclusion complexes with beta-Cyd(s) were prepared to study the structure and the properties of intradiol catechol dioxygenase in aqueous state. beta-Cyd derivatives are employed as a mimic of a protein scaffold to stabilize the metal complexes.;For understanding the conformation of the metal complex inside of beta-Cyd(s), DHN-beta-Cyd is investigated through UV-Vis, NMR, CD and molecular modeling. Its chemical properties were studied to obtain insight on how the geometric structure and electronic properties correlate with a biological function. The spectroscopic results show the binding mode in which the upper rim of beta-Cyd is mostly involved in binding of the metal complex. The solid state structure of the inclusion complex was investigated using X-ray crystallography and used to compare with the solution state structure.;Model complexes are synthesized and investigated by spectroscopic and other analytical methods to elucidate their thermodynamic and kinetic properties: Fe(III)-DHN complexes encapsulated in a parent beta-Cyd and upper rim modified beta-Cyd(s). The results from spectroscopic and electrochemical analysis suggest that the modified beta-Cyd, DJ-70, stabilizes [Fe(III)NTA(DHN)]2- more than the parent Cyd does and DJ-70 favors the Fe(II) oxidation state whereas the parent beta-Cyd favors the Fe(III) oxidation state. Both Cyd(s) reduce the redox reaction rate.;Kinetic activities of beta-Cyd inclusion complex with [Fe(III)L(DHN)], where L is a ligand with different Lewis basicity, show that Cyd reduces the reaction rate, which indicates that Cyd protects the metal complex from oxidizing agents. The reduction is more apparent in TPA and NTA metal complexes. This fact is possibly related to the stability of the metal complexes inside beta-Cyd. The rate constants of the metal complexes without beta-Cyd follow the trend: the stronger in the Lewis acidity of the metal center, the faster the oxidative degradation rate. Mass spectra of reaction products of NTA and IDA metal complexes show that NTA favors intradiol ring cleavage while IDA favors extradiol ring cleavage.