Functional and structural mimics of superoxide dismutase enzymes

摘要

Superoxide dismutase (SOD) enzymes form important defence line in living organisms. Through a dismutation reaction they transform the highly reactive superoxide radical ion to oxygen and hydrogen peroxide. The latter compound is further transformed by catalase or peroxidase enzymes to water and oxygen. The overall structure of the enzymes and those of the active sites are largely known, thus, it has been revealed that in eukaryotes Cu(II) and Zn(II) ions act as cofactors and they are connected with an imidazolate bridge and this structural unit is coordinated with amino acids. In prokaryotes the SOD enzymes contain Mn(II) or Fe(II) or Ni(II) in their active centres. In order to learn about the working mechanism of SOD enzymes at the molecular level various structural mimics were prepared and their structural transformations during the dismutation reaction was followed. Gathering adequate amount of information allowed the preparation of functional mimics that are not necessarily copies of the active sites of the enzymes, nevertheless, display considerable SOD activity. Both functional and structural mimics are comprehensively dealt with in this review. Although enzymes may seem to be attractive catalysts for promoting real-life reactions effectively with high selectivity, they can seldom if ever be used under industrial conditions, i.e. at high temperatures and pressures. The SOD enzymes for promoting oxygen transfer reactions are not durable enough under these conditions either. The complexes mimicking SOD activities perform better in this respect, however, their reusabilities are limited, because of separation problems. A solution can be the immobilisation of these SOD mimicking complexes on solid or semi-solid supports. Even if the activity is not better then the support-free complexes, the catalyst can be filtered at the end of the reaction and can easily be recycled. Attempts for immobilisation are also comprehensively reviewed and immobilised complexes with surprisingly high SOD activities are reported as well. Full characterisation of these materials is given and rationalisation of their exceptionally high activities is offered.