Artificial Metalloesterases Constructed by Site-Directed Attachment of Oximinato Metal Centers to Poly(ethylenimine) Containing β-Cyclodextrin

In an effort to establish a methodology for construction of active sites of artificial enzymes, site-directed attachment of 2,6-diacetylpyridineketoxime (III) to poly(ethylenimine) (PEI) containing β-cyclodextrin (CD) was attempted. The site-directed functionalization exploited at-butylphenyl ester (I) of a carboxylic acid containing a precursor ofIII.Anchoring of thet-butylphenyl group ofIby the CD portion followed by transfer ofIIImoiety to an amino group located in the vicinity of the CD moiety would lead to introduction ofIIIin proximity to the CD moiety. By acylation in DMSO of CD-PEI with the phenyl ester (II), instead of thet-butylphenyl ester,IIIwas introduced randomly to CD-PEI. In the presence of the Ni(II) or Zn(II) complex of theIII-containing CD-PEI prepared by either the site-directed or the random functionalization method, ester hydrolysis of 4-(4′-acetoxy-phenylazo)-benzenesulfonate (IV) was considerably enhanced. Analysis of the kinetic data measured at various pHs revealed thatkcatfor the PEI derivative prepared by site-directed modification was three to six times greater than that by random modification. The results were taken to indicate thatItransferredIIIto the vicinity of the CD moiety of CD-PEI, but that orientation ofIIIand the CD cavity in the resulting PEI derivative was not very productive for deacylation ofIVcomplexed by the CD cavity.