Chemoenzymatic Epoxidation of Limonene Using a Novel Surface-Functionalized Silica Catalyst Derived from Agricultural Waste

Improving efficiency and reducing enzyme inactivation during lipase-mediated epoxidation of α-pinene in a double-phase reaction system

Chemoenzymatic epoxidation of olefin mediated by lipase is a green and environmentally friendly alternative process. However, the mass transfer barrier and lipase deactivation caused by the traditional organic-water biphasic reaction system have always been the focus of researchers' attention. To overcome these issues, we investigated the effects of reaction temperature and two important substrates (H₂O₂ and acyl donor) on the epoxidation reaction and interfacial mass transfer. As a result, we determined the optimal reaction conditions: a temperature of 30 °C, 30 wt-% H₂O₂ as the oxygen source, and 1 M lauric acid as the oxygen carrier. Additionally, by simulating the conditions of shaking flask reactions, we designed a batch reactor and added a metal mesh to effectively block the direct contact between high-concentration hydrogen peroxide and the enzyme. Under these optimal conditions, the epoxidation reaction was carried out for 5 h, and the product yield reached a maximum of 93.2%. Furthermore, after seven repetitive experiments, the lipase still maintained a relative activity of 51.2%.

Synthesis of Biorenewable Terpene Monomers Using Enzymatic Epoxidation under Heterogeneous Batch and Continuous Flow Conditions

A commercially available Lipase B from Candida antarctica immobilized onto a macroporous support (Novozym 435) has been employed in the presence of H2O2 as a benign oxidant for the epoxidation of various biorenewable terpenes. This epoxidation protocol was explored under both heterogeneous batch and continuous flow conditions. The catalyst recyclability was also investigated demonstrating good activity throughout 10 cycles under batch conditions, while the same catalyst system could also be productively used under continuous flow operation for more than 30 h. This practical and relatively safe sustainable flow epoxidation of di- and trisubstituted alkenes by H2O2 allows for the production of gram quantities of a range of terpene epoxides. As a proof of principle, the same protocol can also be applied to the epoxidation of biobased polymers as a means to post-functionalize these macromolecules and equip them with cross-linkable epoxy groups.

Solvent screening, optimization and kinetic parameters of the biocatalytic epoxidation reaction of β-pinene mediated by Novozym®435

Monoterpenes, such as beta-pinene, are secondary metabolites widely used in the flavors and fragrance industries and can have their structure altered to enhance their applicability, such as producing epoxides, which are used as intermediaries for pharmaceuticals. Epoxides are commonly synthesized by the use of inorganic acids as catalysts, although the acid medium induces epoxide degradation. To overcome these limitations biocatalysis is shown as an alternative. Related to, this work aimed to perform the synthesis of β-Pinene epoxide using Pseudozyma antarctica lipase B (Novozym®435) as a biocatalyst, while determining the independent variables that influence the reaction using experimental design tools. Different solvent systems were evaluated (cyclohexane, acetonitrile, ethyl acetate, and dichloromethane) until 72 h reaction time, from which ethyl acetate showed higher conversion into the epoxidized product (40% in 24 h). Under the other solvents systems, several oxidized by-products were obtained, such as ketones and aldehydes. Moreover, applying metrics of green chemistry, ethyl acetate was also corroborated as the most promising solvent, with a higher atom economy (66.8%) in comparison to the others (41.3%), and a smaller E-value (1.19). Ethyl acetate was the solvent/acyl donor of choice and had the molar ratio and percentage of biocatalyst increased, which resulted in 80% of the product after 3 h of reaction. To obtain an optimized model, four independent variables (temperature, stirring, molar ratio, percentage of biocatalyst) were evaluated using experimental design tools, Fractional Factorial Design and Central Composite Rotatable Design, with conversions ranging from 23 to 95% after 3 h. All the independent variables were statistically significant (p < 0.05) and had different degrees of impact on the conversion. Kinetic parameters of the reaction were determined using the Lineweaver-Burk model (results under 30.1 mmol for Km and 10.7 mmol.min^-1 for Vmax). In conclusion, the combination of two different tools of experimental design provided the development of an optimized model for beta-Pinene epoxidation, achieving high conversion to the epoxidized product after 3 h.

Highly active heterogeneous hydrogenation catalysts prepared from cobalt complexes and rice husk waste

Highly active heterogeneous catalysts for the hydrogenation of nitro compounds were made by pyrolysis of rice husk waste impregnated with cobalt complexes followed by base-treatment. The catalysts show high selectivity and broad substrate scope.

Organic-inorganic epoxide hydrolase hybrid nanoflowers with enhanced catalytic activity: Hydrolysis of styrene oxide to 1-phenyl-1,2-ethanediol

Epoxide hydrolases are ubiquitous in nature and are utilized to catalyze the cofactor-independent hydrolysis of epoxides to their corresponding diols. These enzymes have tremendous potential and have been applied in the synthesis of bulk and fine chemical industry and utilized as chiral building blocks. Herein, we report a green, facile, and economical method for immobilization of epoxide hydrolase based on biomimetic mineralization. The organic-inorganic hybrid nanoflowers have received tremendous attention due to their higher catalytic activity and stability. The nanoflowers were synthesized, with the organic component being enzyme epoxide hydrolase and the inorganic component being Ca²⁺ ions. A unique hierarchical flower-like spherical structure with hundreds of spiked petals was observed. The synthesized nanoflowers were applied for styrene oxide hydrolysis, producing 1-phenyl-1,2-ethanediol. Further, the factors influencing the morphology, catalytic activity, and stability studies were performed to study the activity recovery of the synthesized organic-inorganic hybrid epoxide hydrolase nanoflowers. The findings will have interesting applications.

Process intensification using immobilized enzymes for the development of white biotechnology

Process intensification of biocatalysed reactions using different techniques such as microwaves, ultrasound, hydrodynamic cavitation, ionic liquids, microreactors and flow chemistry in various industries is critically analysed and future directions provided.