Abstract
A calix[4]arene ligand, in which two of the phenol functions are replaced by pyrazole units has been employed to mimic the His2–Tyr2 (His: histidine, Tyr: tyrosine) ligand sphere within the active site of the galactose oxidase (GO). The calixarene backbone forces the corresponding copper(II) complex into a see‐saw‐type structure, which is hitherto unprecedented in GO modelling chemistry. It undergoes a one‐electron oxidation that is centered at the phenolate donor leading to a copper‐coordinated phenoxyl radical like in the GO. Accordingly, the complex was tested as a functional model and indeed proved capable of oxidizing benzyl alcohol to the respective aldehyde using two phenoxyl‐radical equivalents as oxidants. Finally, the results show that the calixarene platform can be utilized to arrange donor functions to biomimetic binding pockets that allow for the creation of novel types of model compounds.
Highlights
A calix[4]arene ligand, in which two of the phenol functions are replaced by pyrazole units has been employed to mimic the His2–Tyr2 (His: histidine, Tyr: tyrosine) ligand sphere within the active site of the galactose oxidase (GO)
We were interested in exploiting calixarene-shaped binding sites in bioinorganic investigations, which required the introduction of soft donor atoms directly in place of one or more oxygen atoms of the calixarene lower rim
The GO catalyzes the oxidation of primary alcohols to the corresponding aldehydes
Summary
A calix[4]arene ligand, in which two of the phenol functions are replaced by pyrazole units has been employed to mimic the His2–Tyr2 (His: histidine, Tyr: tyrosine) ligand sphere within the active site of the galactose oxidase (GO). Only [Cu(bpzCal)] is X-band EPR active (Figure S10 in the Supporting Information) in contrast to [Ni(bpzCal)] for which the large zero-field splitting (ZFS) of the S = 1 spin state results in the absence of any observable signal.
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