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      Sol-Gel Immobilisation of Lipases: Towards Active and Stable Biocatalysts for the Esterification of Valeric Acid

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          Abstract

          Alkyl esters are high added value products useful in a wide range of industrial sectors. A methodology based on a simple sol-gel approach (biosilicification) is herein proposed to encapsulate enzymes in order to design highly active and stable biocatalysts. Their performance was assessed through the optimization of valeric acid esterification evaluating the effect of different parameters (biocatalyst load, presence of water, reaction temperature and stirring rate) in different alcoholic media, and comparing two different methodologies: conventional heating and microwave irradiation. Ethyl valerate yields were in the 80–85% range under optimum conditions (15 min, 12% m/ v biocatalyst, molar ratio 1:2 of valeric acid to alcohol). Comparatively, the biocatalysts were slightly deactivated under microwave irradiation due to enzyme denaturalisation. Biocatalyst reuse was attempted to prove that good reusability of these sol-gel immobilised enzymes could be achieved under conventional heating.

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          Immobilisation and application of lipases in organic media.

          Different methods of preparing lipases for use in organic media are critically reviewed. Solid lipase preparations can be made by typical immobilisation methods such as adsorption, entrapment, covalent coupling or cross-linking. Immobilisation is especially attractive for lipases because, in addition to the normal benefits of enzyme immobilisation, it can also lead to a considerable increase in catalytic activity, probably caused by conformational changes in the lipase molecules. Activation can be achieved, for example, using hydrophobic support materials or surfactants during the immobilisation procedure. Surfactants can also be used to solubilise lipases in organic media via the formation of hydrophobic ion pairs, surfactant-coated lipase or reversed micelles. Lipase preparation methods are discussed with regard to potential lipase inactivation and activation effects, mass transfer limitations, lipase stability and other features important for applications. The practical applications of lipases in organic media reviewed include ester synthesis, modification of triacylglycerols and phospholipids, fatty acid enrichment, enantiomer resolution, biodiesel production and acylation of carbohydrates and bioactive compounds.
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            The role of flow in green chemistry and engineering

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              Lipase catalysis in organic solvents: advantages and applications

              Lipases are industrial biocatalysts, which are involved in several novel reactions, occurring in aqueous medium as well as non-aqueous medium. Furthermore, they are well-known for their remarkable ability to carry out a wide variety of chemo-, regio- and enantio-selective transformations. Lipases have been gained attention worldwide by organic chemists due to their general ease of handling, broad substrate tolerance, high stability towards temperatures and solvents and convenient commercial availability. Most of the synthetic reactions on industrial scale are carried out in organic solvents because of the easy solubility of non-polar compounds. The effect of organic system on their stability and activity may determine the biocatalysis pace. Because of worldwide use of lipases, there is a need to understand the mechanisms behind the lipase-catalyzed reactions in organic solvents. The unique interfacial activation of lipases has always fascinated enzymologists and recently, biophysicists and crystallographers have made progress in understanding the structure-function relationships of these enzymes. The present review describes the advantages of lipase-catalyzed reactions in organic solvents and various effects of organic solvents on their activity.
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                Author and article information

                Journal
                Molecules
                Molecules
                molecules
                Molecules : A Journal of Synthetic Chemistry and Natural Product Chemistry
                MDPI
                1420-3049
                06 September 2018
                September 2018
                : 23
                : 9
                : 2283
                Affiliations
                [1 ]Organic Chemistry Department, University of Cordoba, Campus de Rabanales, Edificio Marie Curie (C-3), Ctra. Nacional IV-A, Km 396, E14014 Cordoba, Spain; b02cegas@ 123456uco.es (S.C.-G.); qo2balua@ 123456uco.es (A.M.B.); qo2ganua@ 123456uco.es (A.G.)
                [2 ]Scientific Centre for Molecular Design and Synthesis of Innovative Compounds for Medicine, Peoples Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya str., 117198 Moscow, Russia
                Author notes
                [* ]Correspondence: rafael.luque@ 123456uco.es or q62alsor@ 123456uco.es ; Tel.: +34-957-211050
                Author information
                https://orcid.org/0000-0002-8872-3400
                https://orcid.org/0000-0003-1063-8043
                https://orcid.org/0000-0003-4190-1916
                Article
                molecules-23-02283
                10.3390/molecules23092283
                6225346
                30200657
                f1a5da88-4aa2-4456-808e-646d22a16db2
                © 2018 by the author.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 31 July 2018
                : 04 September 2018
                Categories
                Article

                sol-gel biosilicification,esterification,conventional heating,microwaves

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