Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: Determination of the selenium 'dendrimer effect' origins, mechanism, catalytic cycle, and applications.

摘要

The popularity of dendrimers in materials science and organic chemistry has soared over the last ten years. One of the most common applications of dendrimers has been as scaffolds for catalytic functional groups. The dendrimer architecture can offer shape and size-selectivity, ease of recovery, or enhanced reactivity through cooperation. Very few literature examples of dendritic cooperation, leading to higher reaction rates, exist. Of those, the “dendrimer effect” observed during haloperoxidase catalysis with diorganochalcogen(II) end-capped dendrimers is the most outstanding. While the diorganotellurium(II) dendrimers exhibit the expected linear rate of reaction growth with each dendrimer generation, the diorganoselenium(II) dendrimers display an exponential increase over the analogous series. Although benzeneseleninic acid was determined to be an excellent haloperoxidase catalyst, its generation from the selenoxide syn-elimination, is not operative during the observed dendrimer catalysis. The “dendrimer effect” was shown to result from large differences in the rate-limiting step of haloperoxidase catalysis (initial diorganoselenium(II) oxidation). The autocatalytic production, and diffusion inhibition, of BrOH within the dendritic sphere, accelerates the rate-limiting step, and ultimately is the root cause of the selenium “dendrimer effect”. The diorganotellurium(II) dendrimers do not exhibit similar properties, because tellurium oxidation with H₂O₂ is rapid, and the vehicles of the selenium “dendrimer effect” are not present. Lastly, the application of diorganochalcogen(II) haloperoxidase monomers and wedges toward anti-fouling coatings is described, and exhibits promising results.