Review of key issues and potential strategies in bio-degradation of polyolefins

Polyolefins are the most widely used plastic product and a major contributor to white pollution. Currently, studies on polyolefin degradation systems are mainly focused on microorganisms and some redox enzymes, and there is a serious black-box phenomenon. The use of polyolefin-degrading enzymes is limited because of the small number of enzymes; in addition, the catalytic efficiency of these enzymes is poor and their catalytic mechanism is unclear, which leads to the incomplete degradation of polyolefins to produce microplastics. In this review, three questions are addressed: the generation and degradation of action targets that promote the degradation of polyolefins, the different modes by which enzymes bind substrates and their application scenarios, and possible multienzyme systems in a unified system. This review will be valuable for mining or modifying polyolefin degradation enzymes and constructing polyolefins degradation systems and may provide novel ideas and opportunities for polyolefin degradation.

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Silica-Based Supported Ionic Liquid-like Phases as Heterogeneous Catalysts

Supported ionic liquid phases offer several advantages related with catalysis. Immobilization of ionic liquid on the solid support provides catalytic activity or efficient matrix for active phases, as enzymes or metal compounds. Ionic liquid can be physically adsorbed on the carrier (supported ionic liquid phase) or chemically grafted to the material surface (supported ionic liquid-like phase). The use of supported ionic liquid phases improves mass transport, reduces ionic amount in the process and, most importantly, enables effortless catalyst separation and recycling. Moreover, chemical modification of the surface material with ionic liquid prevents its leaching, enhancing length of catalyst life. Silica-based materials have become an effective and powerful matrix for supported ionic liquid-like phase due to its cost-efficiency, presence of hydroxyl groups on the surface enabling its functionalization, and specific material properties, such as the size and shapes of the pores. For these reasons, supported ionic liquid-like phase silica-based materials are successfully used in the organic catalysis.

Diversifying Arena of Drug Synthesis: In the Realm of Lipase Mediated Waves of Biocatalysis

Hydrolases, being most prominent enzymes used in industrial processes have left no stone unturned in fascinating the pharmaceutical industry. Lipases, being a part of acyl hydrolases are the ones that function similarly to esterases (except an interfacial action) wherein they generally catalyze the hydrolysis of ester bonds. Be it in terms of stereoselectivity or regioselectivity, lipases have manifested their promiscuous proficiency in rendering biocatalytic drug synthesis and intermediates thereof. Industrial utilization of lipases is prevalent since decades ago, but their distinctive catalytic competencies have rendered them suitable for maneuverability in various tides of biocatalytic industrial process development. Numbers of exquisite catalysts have been fabricated out of lipases using nanobiotechnology whereby enzyme reusability and robustness have been conferred to many of the organic synthesis procedures. This marks a considerable achievement of lipases in the second wave of biocatalysis. Furthermore, in the third wave an advent of genetic engineering has fostered an era of customized lipases for suitable needs. Be it stability or an enhanced efficacy, genetic engineering techniques have ushered an avenue for biocatalytic development of drugs and drug intermediates through greener processes using lipases. Even in the forthcoming concept of co-modular catalytic systems, lipases may be the frontiers because of their astonishing capability to act along with other enzymes. The concept may render feasibility in the development of cascade reactions in organic synthesis. An upcoming wave demands fulfilling the vision of tailored lipase whilst a far-flung exploration needs to be unveiled for various research impediments in rendering lipase as a custom fit biocatalyst in pharmaceutical industry.

Asymmetric Sulfoxidation of Thioether Catalyzed by Soybean Pod Shell Peroxidase to Form Enantiopure Sulfoxide in Water-in-Oil Microemulsions: A Kinetic Model

Esomeprazole with chiral sulfoxides structure is used to treat gastric ulcer disease. Soybean pod shell peroxidase (SPSP) is a peroxidase extracted from soybean pods shells which are one of the most abundant natural resources in the world. In the production of chiral sulfoxides catalyzed by SPSP, it is very important to establish the reaction kinetic model and explore the reaction mechanism for the development of the process, however, there is no report on the establishment of the model. Asymmetric sulfoxidation reactions catalyzed by SPSP in water-in-oil microemulsions were carried out, and the King-Altman approach was used to establish a kinetic model. A yield of 91% and e.e. value of 96% for esomeprazole were obtained at the activity of SPSP of 3200 U ml-1 and 50 °C for 5 h. The mechanism with a two-electron reduction of SPSP-I is accompanied with a single-electron transfer to SPSP-I and nonenzymatic reactions, indicating that three concomitant sub-mechanisms contribute to the asymmetric oxidation involving five enzymatic and two nonenzymatic reactions, which can represent the asymmetric sulfoxidation of organic sulfides to form enantiopure sulfoxides. With 5.44% of the average relative deviation, a kinetic model fitting experimental data was developed. The enzymatic reactions may follow ping-pong mechanism with substrate inhibition of H2 O2 and product inhibition of esomeprazole, while nonenzymatic reactions follow a power law. Those results indicate that SPSP with a lower cost and higher thermal stability may be used as an effective substitute for horseradish peroxidase.

Chemo-Enzymatic Baeyer-Villiger Oxidation Facilitated with Lipases Immobilized in the Supported Ionic Liquid Phase

A novel method for chemo-enzymatic Baeyer–Villiger oxidation of cyclic ketones in the presence of supported ionic liquid-like phase biocatalyst was designed. In this work, multi-walled carbon nanotubes were applied as a support for ionic liquids which were anchored to nanotubes covalently by amide or imine bonds. Next, lipases B from Candida antarctica, Candida rugosa, or Aspergillus oryzae were immobilized on the prepared materials. The biocatalysts were characterized using various techniques, like thermogravimetry, IR spectroscopy, XPS, elemental analysis, and SEM-EDS microscopy. In the proposed approach, a biocatalyst consisting of a lipase as an active phase allowed the generation of peracid in situ from the corresponding precursor and a green oxidant–hydrogen peroxide. The activity and stability of the obtained biocatalysts in the model oxidation of 2-adamantanone were demonstrated. High conversion of substrate (92%) was achieved under favorable conditions (toluene: n-octanoic acid ratio 1:1 = v:v, 35% aq. H₂O₂ 2 eq., 0.080 g of biocatalyst per 1 mmol of ketone at 20 °C, reaction time 4 h) with four reaction cycles without a drop in its activity. Our ‘properties-by-design’ approach is distinguished by its short reaction time at low temperature and higher thermal stability in comparison with other biocatalysts presented in the literature reports.

Outperformance in Acrylation: Supported D-Glucose-Based Ionic Liquid Phase on MWCNTs for Immobilized Lipase B from Candida antarctica as Catalytic System

This study presents a highly efficient method of a synthesis of n-butyl acrylate via esterification of acrylic acid and n-butanol in the presence of supported ionic liquid phase (SILP) biocatalyst consisting of the lipase B from Candida antarctica (CALB) and multi-walled carbon nanotubes (MWCNTs) modified by D-glucose-based ionic liquids. Favorable reaction conditions (acrylic acid: n-butanol molar ratio 1:2, cyclohexane as a solvent, biocatalyst 0.150 g per 1 mmol of acrylic acid, temperature 25 °C) allowed the achievement of a 99% yield of n-butyl acrylate in 24 h. Screening of various ionic liquids showed that the most promising result was obtained if N-(6-deoxy-1-O-methoxy-α-D-glucopyranosyl)-N,N,N-trimethylammonium bis-(trifluoromethylsulfonyl)imide ([N(CH3)3GlcOCH3][N(Tf)2]) was selected in order to modify the outer surface of MWCNTs. The final SILP biocatalyst-CNTs-[N(CH3)3GlcOCH3][N(Tf)2]-CALB contained 1.8 wt.% of IL and 4.2 wt.% of CALB. Application of the SILP biocatalyst led to the enhanced activity of CALB in comparison with the biocatalyst prepared via physical adsorption of CALB onto MWCNTs (CNTs-CALB), as well as with commercially available Novozyme 435. Thus, the crucial role of IL in the stabilization of biocatalysts was clearly demonstrated. In addition, a significant stability of the developed biocatalytic system was confirmed (three runs with a yield of ester over 90%).

A mild and chemoselective CALB biocatalysed synthesis of sulfoxides exploiting the dual role of AcOEt as solvent and reagent

A mild, chemoselective and sustainable biocatalysed synthesis of sulfoxides has been developed exploiting CALB and using AcOEt with a dual role of more environmentally friendly reaction solvent and enzyme substrate. A series of sulfoxides, including the drug omeprazole, have been synthesised in high yields and with excellent E-factors.

Optimization of chemoenzymatic Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone using response surface methodology

ε-Caprolactone (ε-CL) has attracted a great deal of attention and a high product concentration is of great significance for reducing production cost. The optimization of ε-CL synthesis through chemoenzymatic Baeyer-Villiger oxidation mediated by immobilized Trichosporon laibacchii lipase was studied using response surface methodology (RSM). The yield of ε-CL was 98.06% with about 1.2 M ε-CL concentration that has a substantial increase mainly due to both better stability of the cross-linked immobilized lipase used and the optimum reaction conditions in which the concentration of cyclohexanone was 1.22 M, the molar ratio of cyclohexanone:urea hydrogen peroxide (UHP) was 1:1.3, and the reaction temperature was 56.5°C. Based on our experimental results, it can be safely concluded that there are three reactions in this reaction system, not just two reactions, in which the third reaction is that the acetic acid formed reacts with UHP to form peracetic acid in situ catalyzed by the immobilized lipase. A quadratic polynomial model based on RSM experimental results was developed and the R² value of the equation is 0.9988, indicating that model can predict the experimental results with high precision. The experimental results also show that the molar ratio of cyclohexanone to UHP has very significant impact on the yield of ε-CL (p < .0006).

Biocatalytic synthesis of lactones and lactams

Cyclic esters and amides (lactones and lactams) are important active ingredients and polymer building blocks. In recent years, numerous biocatalytic methods for their preparation have been developed including enzymatic and chemoenzymatic Baeyer-Villiger oxidations, oxidative lactonisation of diols, and reductive lactonisation and lactamisation of ketoesters. The current state of the art of these methods is reviewed.

Lipase-mediated direct in situ ring-opening polymerization of ε-caprolactone formed by a chemo-enzymatic method

A novel method to synthesize poly(ε-caprolactone) (PCL) through a three-step, lipase-mediated chemo-enzymatic reaction from cyclohexanone using an immobilized lipase from Trichosporon laibacchii (T. laibacchii) CBS5791 was developed. The immobilized preparation with 1280 U· g^-1 used here was obtained by a method of purification and in situ immobilization where the crude intracellular lipase (cell homogenate) was subjected to partial purification by an aqueous two-phase system (ATPS) consisting of 12% (w/w) polyethylene glycol (PEG) 4000 and 13% (w/w) potassium phosphate (K₂HPO₄) and then in situ immobilization directly on diatomite from the top PEG-rich phase of ATPS. In this multi-step process, the ε-caprolactone (ε-CL) produced by lipase-mediated one-pot two-step chemo-enzymatic oxidation of cyclohexanone was directly subjected to in situ ring-opening polymerization (ROP) started by adding highly hydrophobic solvents. It is necessary to note that ε-CL synthesis and its subsequent ROP were catalyzed by the same lipase. The impact of various reaction parameters, e.g., solvent, cyclohexanone: hydrogen peroxide molar ratio, hydrogen peroxide forms and reaction temperature were investigated. Toluene was selected as a preferred solvent due to supporting the highest molecular weight (M_n = 2168) and moderate ε-CL conversion (65.42%). Through the optimization of reaction conditions, PCL was produced with a M_n of 2283 at 50 °C for 24 h. These results reveal that this lipase-mediated direct ring-opening polymerization of in situ formed ε-CL is an alternative route to the conventional synthesis of PCL.

Dimethyl carbonate as a non-innocent benign solvent for the multistep continuous flow synthesis of amino alcohols

An efficient methodology for the production and resolution of amino alcohols with a low environmental impact has been developed.

Novel chemoenzymatic oxidation of amines into oximes based on hydrolase-catalysed peracid formation

The efficient transformation of benzylamines into the corresponding oximes has been described by means of a chemoenzymatic process.

Applications of Liquid/Liquid Biphasic Oxidations by Hydrogen Peroxide with Ionic Liquids or Deep Eutectic Solvents

This Minireview focuses on recent applications of ionic liquids (ILs) and deep eutectic solvents (DESs) in biphasic oxidations in which the oxidizing agent corresponds to hydrogen peroxide. Biphasic reactions are accomplished when the substrate presents low or moderate solubility in aqueous (polar) systems and/or when separation of products and byproduct is an issue. The properties of the IL and DES allows the reaction activity to be intensified. On the other hand, the high chemical stability of the ionic solvents allows the use of hydrogen peroxide to minimize solvent degradation and unwanted byproducts. The experimental evidence presented herein shows that ILs and DESs can be used as cocatalysts, catalysts, and solvents to achieve enhanced yields and conversions. The process advantages, in terms of a reduction of volatile solvents, improve the safety and use of the oxidizing agent, which implies the possibility of developing new process improvements in the future.

Chemo-enzymatic Baeyer-Villiger oxidation of 4-methylcyclohexanone via kinetic resolution of racemic carboxylic acids: direct access to enantioenriched lactone

A new method for the asymmetric chemo-enzymatic Baeyer-Villiger oxidation of prochiral 4-methylcyclohexanone to (R)-4-methylcaprolactone in the presence of (±)-4-methyloctanoic acid, Candida Antarctica lipase B and 30% aq. H2O2 has been developed. A mechanism for the asymmetric induction based on kinetic resolution of racemic carboxylic acids is proposed.

Recent advances in exploiting ionic liquids for biomolecules: Solubility, stability and applications

The technological utility of biomolecules (e.g. proteins, enzymes and DNA) can be significantly enhanced by combining them with ionic liquids (ILs) - potentially attractive "green" and "designer" solvents - rather than using in conventional organic solvents or water. In recent years, ILs have been used as solvents, cosolvents, and reagents for biocatalysis, biotransformation, protein preservation and stabilization, DNA solubilization and stabilization, and other biomolecule-based applications. Using ILs can dramatically enhance the structural and chemical stability of proteins, DNA, and enzymes. This article reviews the recent technological developments of ILs in protein-, enzyme-, and DNA-based applications. We discuss the different routes to increase biomolecule stability and activity in ILs, and the design of biomolecule-friendly ILs that can dissolve biomolecules with minimum alteration to their structure. This information will be helpful to design IL-based processes in biotechnology and the biological sciences that can serve as novel and selective processes for enzymatic reactions, protein and DNA stability, and other biomolecule-based applications.

The effect of imidazolium cations on the structure and activity of the Candida antarctica Lipase B enzyme in ionic liquids

To understand how cations affect the enzyme structure and activity of Candida antarctica Lipase B, we performed MD simulations of CALB in four types of ionic liquids with varying sizes of cations and correlated the results with the experimental data.