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Keywords:

  • aldehydes;
  • cyanides;
  • enzyme catalysis;
  • gels;
  • immobilization

Abstract

Hydroxynitrile lyase from cassava, Manihot esculenta, (MeHNL) catalyzes the formation of (S)-cyanohydrins from HCN and aldehydes or ketones. Four differently immobilized MeHNLs were prepared: by noncovalent immobilization (celite R-633), covalent immobilization (cross-linked enzyme aggregates, CLEA), encapsulation [in a poly(vinyl alcohol) hydrogel Lentikats] and a combination of the above, an unusual immobilization, CLEA encapsulated in a poly(vinyl alcohol) hydrogel. A comparative study of the recyclability of each immobilized MeHNL was performed. Particular attention was paid to the stability and activity of the new immobilized MeHNL–CLEA–Lentikats and to the minimum enzyme loading required to achieve high yields and enantiomeric excesses. MeHNL–CLEA stability was slightly improved by encapsulation into Lentikats and good recyclability rates at low enzyme loading were obtained. However, MeHNL immobilized on celite R-633 exhibited the best recyclability, giving >95 % conversion and an enantiomeric excess of 99 % during 12 cycles.