catalysts Article Efficient One-Step Immobilization of CaLB Lipase over MOF Support NH 2 -MIL-53(Al) Victoria Gascón-Pérez 1,2, * , Mayra Belen Jiménez 1 , Asunción Molina 1 , Rosa María Blanco 1 and Manuel Sánchez-Sánchez 1, * 1 Instituto de Catálisis y Petroleoquímica (ICP), CSIC, C/ Marie Curie, 2, 28049 Madrid, Spain; mayrabelen_jimenez@outlook.com (M.B.J.); asuncion.molina@csic.es (A.M.); rmblanco@icp.csic.es (R.M.B.) 2 Department of Chemical Sciences, Bernal Institute, University of Limerick, V94 T9PX Limerick, Ireland * Correspondence: Victoria.GasconPerez@ul.ie (V.G.-P.); manuel.sanchez@icp.csic.es (M.S.-S.) Received: 23 May 2020; Accepted: 7 August 2020; Published: 10 August 2020   Abstract: Metal-organic framework (MOF) materials possess the widest versatility in structure, composition, and synthesis procedures amongst the known families of materials. On the other hand, the extraordinary affinity between MOFs and enzymes has led to widely investigating these materials as platforms to support these catalytic proteins in recent years. In this work, the MOF material NH 2 -MIL-53(Al) has been tested as a support to immobilize by one-step methodology (in situ) the enzyme lipase CaLB from Candida antarctica by employing conditions that are compatible with its enzymatic activity (room temperature, aqueous solution, and moderate pH values). Once the nature of the linker deprotonating agent or the synthesis time were optimized, the MOF material resulted in quite efficient entrapping of the lipase CaLB through this in situ approach (>85% of the present enzyme in the synthesis media) while the supported enzyme retained acceptable activity (29% compared to the free enzyme) and had scarce enzyme leaching. The equivalent post-synthetic method led to biocatalysts with lower enzyme loading values. These results make clear that the formation of MOF support in the presence of the enzyme to be immobilized substantially improves the efficiency of the biocatalysts support for retaining the enzyme and limits their leaching. Keywords: CaLB lipase; enzyme immobilization; in situ; MOF support; nanocrystalline; NH 2 -MIL-53(Al); one-step; post-synthesis 1. Introduction Immobilized lipases are currently used in many processes, most of them related to the pharmaceutical industry due to their enantioselectivity. Among many others, typical examples are the enantiomeric esterification of captopryl (antihypertensive) or the aryl propionic analgesics such as (S)-naproxen. The immobilization of lipases to lead solid biocatalysts is essential for their applications as it allows their stabilization and easy recovery from the liquid reaction media and subsequent reuse. The discovery of permanent porosity in certain thermally-stable coordination polymers, the so-called metal-organic frameworks (MOFs) [1–4], at the end of the last century, probably gave rise to the greatest ever revolution in the field of porous materials. MOFs are nanoporous coordination polymers, generally but not always crystalline, formed by either isolated metal ions or metal clusters linked by multidentate (at least, bidentate) organic ligands given rise to structures extended along two or three spatial dimensions [5]. Indeed, more than 90,000 MOF materials have been described in two decades [6,7], involving a diverse selection of metals and numerous organic linkers. The extraordinary versatility of MOFs is not only structural or compositional but also in terms of synthesis methods [8,9], Catalysts 2020, 10, 918; doi:10.3390/catal10080918 www.mdpi.com/journal/catalysts