Composite Particles of Novozyme 435 and Silicone: Advancing Technical Applicability of Macroporous Enzyme Carriers

Abstract

The mechanical and leaching stability of enzymes adsorbed on macroporous carriers is an important issue for the technical applicability of such biocatalysts. Both can considerably benefit from the deposition of silicone coating on the carrier surface. The coating of the immobilized lipase Novozyme 435 (NZ435), as a model enzyme preparation, with different silicone loadings was studied in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as by energy‐dispersive X‐ray spectroscopy (EDX) and BET isotherms, and offers explanations and prerequisites for its stabilizing effects. The deposition of silicone on the poly(methyl methacrylate) (PMMA) carrier was found to form an interpenetrating network composite rather than the anticipated core‐shell structure. The silicone precursors homogeneously wet the carrier surface including all inner pores and gradually fill the complete carrier. In parallel, the surface area of NZ435 decreases from an initial value of 89 m2g−1to 0.2 m2g−1after silicone loading. A visible layer of silicone on the outer surface of the carrier was only observed at a silicone concentration of 54 % w/w and more. Maximum leaching stability corresponds to the formation of this layer. The mechanical stability increases with the amount of deposited silicone. It can be expected that stabilization against leaching and/or mechanical stress by formation of silicone composites can easily be transferred to a whole range of alternative biocatalytic systems. This should considerably advance their general technical applicability and overall implementation of biocatalysts in chemical synthesis.

Enabling Industrial Biocatalytic Processes by Application of Silicone‐Coated Enzyme Preparations

“…For lipase B and alcalase a residual activity above 60 % was observed, which is in the same range as for NZ435 [12] and therefore offers good prospects for a future application to technical synthesis. In contrast, esterase and laccase revealed only low residual activity after transfer to a silcoat-catalyst.…”

“…However, severe damage to the enzyme carrier was apparent, which is in agreement with the previously reported disintegration of NZ435 under mechanical stress. [11,12] As a consequence, during catalyst removal the filter was blocked by NZ435 fragments and abrasion, reducing the filtration efficiency and preventing the recovery of catalyst. In the end, a TTN of 100 g MM /g NZ435 could be obtained, a half-life time could not be determined.…”

“…[11] This involves the combination of native NZ435 with up to 54% (w/w) silicone to form distinct composite particles with a residual activity of approximately 60% of the initial NZ435 activity towards the lab-scale synthesis of propyl laurate. [12] Promising features of this approach with regard to industrial implementation are the non-toxicity, low price and largescale availability of silicone as coating material, the established polymer formation via hydrosilylation and the possibility to adapt the physicochemical properties of the material to specific needs by varying the polymer chain length, the degree of cross-linking and the number of modifications. [14] Thus, it is clearly advantageous over the reported alternative entrapment of carrier-bound enzymes in sol-gel, [13] which in addition form a brittle material with only low stability against carrier disintegration in standard industrial reactors such as STR.…”

Mesoporous Organosilicas With Large Cage‐Like Pores for High Efficiency Immobilization of Enzymes

“…These results confi rm that cage-like mesoporous oragnosilicas are superior to amorphous silica with respect to leaching and activity. Other strategies, such as covalent attachment, the formation of crosslinked enzyme aggregates, [ 9 c] or the use of a recently published silicon coating technique [ 28 ] may be used in future studies to further suppress leaching. Studies are underway to evaluate these materials under more pratically relevant conditions involving shaping into larger beads, application of mechanical forces (shear stress), and more realistic reaction media.…”

In Situ Microscopy for Online Monitoring of Enzyme Supports and Two‐Phase Systems

“…Aus diesem Grund eigenen sich Blasensäulen oder Festbettreaktoren besser für Reaktionen mit Enzymträgern, da die Scherbeanspruchung hier geringer ist [1]. Trotzdem wird generell nach Möglichkeiten gesucht, die mechanische Stabilität von Enzymimmobilisaten beispielsweise durch die Beschichtung mit Silikon zu verbessern [2,3].…”