Hydrogels with immobilized
enzymes are increasingly applied in
biocatalytic industrial processes. Here, polymer hydrogels containing
2-hydroxyethyl methacrylate (HEMA), itaconic acid (ITA), (2-((2-(ethoxycarbonyl)prop-2-en-1-yl)oxy)ethyl)
phosphonic acid (ECPPA), and N,N′-diethyl-1,3-bis(acrylamido)propane (BAAP) as the cross-linker
are synthesized by UV-initiated radical polymerization. Laccase from Trametes versicolor (LAC) is modified by reaction
with itaconic anhydride (ITAn) yielding the LAC-immobilized monomer
ITA-LAC with enhanced enzyme activity. ITA-LAC paves the way to an in situ method for enzyme immobilization. Hydrogels with
HEMA, ECPPA, and BAAP with stepwise varied chemical composition and
functionalization are prepared. The influence of the composition on
the morphology, the swelling behavior, the mechanical stability, and
the enzymatic activity is studied. The polymerization is monitored
by the conversion of double bonds with in situ attenuated
total reflection Fourier transform infrared (ATR-FTIR) spectroscopy.
The polymerization of HEMA is complete after 10 min of UV exposure,
whereas hydrogels of HEMA/ITA/ECPPA (85/5/10) with 5 mol % cross-linker
require 30 min. These hydrogels are compared with those containing
ITA-LAC instead of ITA. The covalent binding of LAC is proven by ATR-FTIR
spectroscopy and results in an enhanced enzyme activity. The incorporation
of ECPPA induces pH-dependent swelling with an equilibrium degree
of swelling of up to 6 at pH 8. Only a weak influence of temperature
on the degree of swelling is found. The morphology strongly depends
on the hydrogel composition. LAC-ITA hydrogels are characterized by
an open morphology providing access to catalytic centers. The enzyme-immobilized
hydrogels are used as granules as well as coatings on porous Al2O3 ceramic substrates as biocatalysts to convert
models for organic trace compounds [bisphenol A (BPA), diclofenac, p-chlorophenol (pCP), 17α-ethinylestradiol
(EED), triclosan, paracetamol, and 4-tert-octylphenol].
The highest conversion after 24 h in water is achieved for triclosan
(>90%), while pCP, BPA, and EED reach a conversion
between 60% and 70%. The conversions are even higher in citrate buffer.