Enzymes in "Green" Synthetic Chemistry: Laccase and Lipase

Enzymes play an important role in numerous natural processes and are increasingly being utilized as environmentally friendly substitutes and alternatives to many common catalysts. Their essential advantages are high catalytic efficiency, substrate specificity, minimal formation of byproducts, and low energy demand. All of these benefits make enzymes highly desirable targets of academic research and industrial development. This review has the modest aim of briefly overviewing the classification, mechanism of action, basic kinetics and reaction condition effects that are common across all six enzyme classes. Special attention is devoted to immobilization strategies as the main tools to improve the resistance to environmental stress factors (temperature, pH and solvents) and prolong the catalytic lifecycle of these biocatalysts. The advantages and drawbacks of methods such as macromolecular crosslinking, solid scaffold carriers, entrapment, and surface modification (covalent and physical) are discussed and illustrated using numerous examples. Among the hundreds and possibly thousands of known and recently discovered enzymes, hydrolases and oxidoreductases are distinguished by their relative availability, stability, and wide use in synthetic applications, which include pharmaceutics, food and beverage treatments, environmental clean-up, and polymerizations. Two representatives of those groups-laccase (an oxidoreductase) and lipase (a hydrolase)-are discussed at length, including their structure, catalytic mechanism, and diverse usage. Objective representation of the current status and emerging trends are provided in the main conclusions.

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.

Lipase-Catalyzed Synthesis of Furan-Based Oligoesters and their Self-Assembly-Assisted Polymerization

We investigate the synthesis of bio-based hydrophilic and hydrophobic oligoesters, which in turn are derived from easily accessible monomers from natural resources. In addition to the selection of renewable monomers, Novozyme 435, an immobilized lipase B from Candida antarctica was used for the oligomerization of monomers. The reaction conditions for oligomerization using Novozyme 435 were established to obtain a moderate-to-good yield. The average number of repeating units and the molecular weight distribution of hydrophilic and hydrophobic oligoester were identified by using NMR spectroscopy, gel-permeation chromatography, and MS. The oligoester derived from a hydrophilic monomer self-assembled to form a viscous solution, which upon further heating resulted in the formation of a polymer by the intermolecular Diels-Alder reaction. The viscosity of the solution and the assembly of oligoester to form a fibrous structure were investigated by using rheological studies, XRD, and SEM. The molecular weight of the cross-linked polymer was identified by using matrix-assisted laser desorption/ionization-MS. The thermal properties of the bio-based polymers were investigated by using thermogravimetric analysis and differential scanning calorimetry. For the first time, the self-assembly-assisted polymerization of an oligoester is reported using the intermolecular Diels-Alder reaction, which opens a new avenue in the field of polymer science.

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.

Enzymatic polymerization of cyclic monomers in ionic liquids as a prospective synthesis method for polyesters used in drug delivery systems

Biodegradable or bioresorbable polymers are commonly used in various pharmaceutical fields (e.g., as drug delivery systems, therapeutic systems or macromolecular drug conjugates). Polyesters are an important class of polymers widely utilized in pharmacy due to their biodegradability and biocompatibility features. In recent years, there has been increased interest in enzyme-catalyzed ring-opening polymerization (e-ROP) of cyclic esters as an alternative method of preparation of biodegradable or bioresorbable polymers. Ionic liquids (ILs) have been presented as green solvents in enzymatic ring-opening polymerization. The activity, stability, selectivity of enzymes in ILs and the ability to catalyze polyester synthesis under these conditions are discussed. Overall, the review demonstrates that e-ROP of lactones or lactides could be an effective method for the synthesis of useful biomedical polymers.