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. 2022 Nov 8;38(44):13382-13391.
doi: 10.1021/acs.langmuir.2c01630. Epub 2022 Oct 26.

Enzyme Immobilization on Metal Organic Frameworks: the Effect of Buffer on the Stability of the Support

Kim Shortall  1 , Fernando Otero  1 , Simon Bendl  1 , Tewfik Soulimane  1 , Edmond Magner  1
Affiliations

Enzyme Immobilization on Metal Organic Frameworks: the Effect of Buffer on the Stability of the Support

Kim Shortall et al. Langmuir. .

Abstract

Metal organic frameworks (MOFs) have been used to encapsulate an array of enzymes in a rapid and facile manner; however, the stability of MOFs as supports for enzymes has not been examined in detail. This study examines the stability of MOFs with different compositions (Fe-BTC, Co-TMA, Ni-TMA, Cu-TMA, and ZIF-zni) in buffered solutions commonly used in enzyme immobilization and biocatalysis. Stability was assessed via quantification of the release of metals by inductively coupled plasma optical emission spectroscopy. The buffers used had varied effects on different MOF supports, with incubation of all MOFs in buffers resulting in the release of metal ions to varying extents. Fe-BTC was completely dissolved in citrate, a buffer that has a profound destabilizing effect on all MOFs analyzed, precluding its use with MOFs. MOFs were more stable in acetate, potassium phosphate, and Tris HCl buffers. The results obtained provide a guide for the selection of an appropriate buffer with a particular MOF as a support for the immobilization of an enzyme. In addition, these results identify the requirement to develop methods of improving the stability of MOFs in aqueous solutions. The use of polymer coatings was evaluated with polyacrylic acid (PAA) providing an improved level of stability. Lipase was immobilized in Fe-BTC with PAA coating, resulting in a stable biocatalyst with retention of activity in comparison to the free enzyme.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Storage stability of a selection of MOFs in 10 mM buffer (citrate and acetate pH 5, potassium phosphate pH 7, and Tris–HCl pH 9) over 24 h, demonstrating % of metal ions leached with respect to total metal content. Determined by ICP-OES analysis. The error bars refer to different experiments.
Figure 2
Figure 2
Visualization of Fe-BTC storage samples in citrate pH 5, potassium phosphate pH 7, and Tris–HCl pH 9. (A) Fe-BTC before storage. Fe-BTC samples following 24 h of shaking incubation in (B) 10 mM buffer and (C) 100 mM buffer. The pH of the buffers is listed.
Figure 3
Figure 3
Activity of ALDHTt@MOF using hexanal at 25 °C. (A) Plot of absorbance vs time for blank (Fe-BTC) and ALDHTt@MOF samples following the production of NADH by the enzyme at 340 nm. (B) Comparison of activity of soluble ALDHTt and ALDHTt@MOF. The error bars refer to different measurements.
Figure 4
Figure 4
Stability of Fe-BTC under enzymatic assaying conditions in 100 mM buffer monitored at 340 nm (A) varying pH at 25 °C. The inset demonstrates the associated slopes. (B) Varying temperatures in 100 mM potassium phosphate, pH 7.
Figure 5
Figure 5
Enhanced stability of Fe-BTC by the addition of polymers to the storage solution of 10 mM citrate at pH 5. Quantification of Fe3+ release after 24 h of storage for control and polymer samples of 4 and 8% v/v for demonstration of stabilizing effects of each polymer. The error bars refer to different experiments.
Figure 6
Figure 6
Lip@MOF activity using p-NPA on the addition of PAA at different concentrations. The error bars refer to different measurements.
See this image and copyright information in PMC

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