Miniemulsion as efficient system for enzymatic synthesis of acid alkyl esters

Responsive Emulsions for Sequential Multienzyme Cascades

Multienzyme cascade biocatalysis is an efficient synthetic process, avoiding the isolation/purification of intermediates and shifting the reaction equilibrium to the product side.. However, multienzyme systems are often limited by their incompatibility and cross-reactivity. Herein, we report a multi-responsive emulsion to proceed multienzyme reactions sequentially for high reactivity. The emulsion is achieved using a CO2 , pH, and thermo-responsive block copolymer as a stabilizer, allowing the on-demand control of emulsion morphology and phase composition. Applying this system to a three-step cascade reaction enables the individual optimal condition for each enzyme, and a high overall conversion (ca. 97 % of the calculated limit) is thereby obtained. Moreover, the multi-responsiveness of the emulsion allows the facile and separate yielding/recycling of products, polymers and active enzymes. Besides, the system could be scaled up with a good yield.

Biodegradable Polyester Synthesis in Renewed Aqueous Polycondensation Media: The Core of the New Greener Polymer-5B Technology

An innovative enzymatic polycondensation of dicarboxylic acids and dialcohols in aqueous polymerization media using free and immobilized lipases was developed. Various parameters (type of lipases, temperature, pH, stirring type and rate, and monomer carbon chain length) of the polycondensation in an oil-in-water (o/w) miniemulsion (>80% in water) were evaluated. The best results for polycondensation were achieved with an equimolar monomer concentration (0.5 M) of octanedioic acid and 1,8-octanediol in the miniemulsion and water, both at initial pH 5.0 with immobilized Pseudozyma antarctica lipase B (PBLI). The synthesized poly(octamethylene suberate) (POS) in the miniemulsion is characterized by a molecular weight of 7800 g mol−1 and a conversion of 98% at 45 °C after 48 h of polycondensation in batch operation mode. A comparative study of polycondensation using different operation modes (batch and fed-batch), stirring type, and biocatalyst reutilization in the miniemulsion, water, and an organic solvent (cyclohexane:tetrahydrofuran 5:1 v/v) was performed. Regarding the polymer molecular weight and conversion (%), batch operation mode was more appropriate for the synthesis of POS in the miniemulsion and water, and fed-batch operation mode showed better results for polycondensation in the organic solvent. The miniemulsion and water used as polymerization media showed promising potential for enzymatic polycondensation since they presented no enzyme inhibition for high monomer concentrations and excellent POS synthesis reproducibility. The PBLI biocatalyst presented high reutilization capability over seven cycles (conversion > 90%) and high stability equivalent to 72 h at 60 °C on polycondensation in the miniemulsion and water. The benefits of polycondensation in aqueous media using an o/w miniemulsion or water are the origin of the new concept strategy of the green process with a green product that constitutes the core of the new greener polymer-5B technology.

Miniemulsion in biocatalysis, a new approach employing a solid reagent and an easy protocol for product isolation applied to the aldol reaction by Rhizopus niveus lipase

Miniemulsion systems presented a great potential for biocatalytic reactions. However, different limitations jeopardized the applications of this non-conventional medium. In this work, miniemulsion systems (emulsion reactors) were applied for the first time to the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde by Rhizopus niveus lipase allowing a decrease in the catalyst concentration from 20 mg mL^-1 to 6 mg mL^-1 in comparison with organic solvents. Moreover, the yield increased from ~25% to ~65% for 48 h reactions and the enantiomeric excess increased from ~10% to ~30% for (R,S)-anti-aldol product, showing the potentiality of this non-conventional reaction medium. The advances reported in this work expands the possibilities of the miniemulsion reaction medium to a whole new level, increasing the scope to solid reagents and products, and also different reactions (biocatalytic or not) that requires pH control by buffers with a simple product isolation procedure, enabling future applications of this poorly studied reaction medium.

Scale Effect on the Interface Reaction between PDMS-E Emulsion Droplets and Gelatin

In this study, the scale effect on the interface reaction between PDMS-E emulsion droplets and gelatin was studied systematically. The monodisperse α-[3-(2,3-epoxy-propoxy)propyl]-ω-butyl-polydimethylsiloxane (PDMS-E) emulsion droplets on different scales were prepared using a Shirasu porous glass (SPG) membrane with a 0.5 μm pore size. The zeta potential results showed that the surface charge density of PDMS-E droplets decreased with the droplet scale, and the variation went through three stages, which corresponded to the diameter ranges of 100-450, 450-680, and 670-800 nm, respectively. The results of Raman spectra indicated that the distribution concentration of head groups in surfactants decreased but the polar epoxy groups tend to be exposed on the interface with the increase in the droplet scale. This was conducive to the nucleophilic attack of amino groups in gelatin on the epoxy group. Thus, the conversion of amino groups was related to the scale of the PDMS-E droplet. This study might provide a proper way to control the rate of interfacial reaction between immiscible macromolecule monomers.

CaLB Catalyzed Conversion of ε-Caprolactone in Aqueous Medium. Part 1: Immobilization of CaLB to Microgels

The enzymatic ring-opening polymerization of lactones is a method of increasing interest for the synthesis of biodegradable and biocompatible polymers. In the past it was shown that immobilization of Candida antarctica lipase B (CaLB) and the reaction medium play an important role in the polymerization ability especially of medium ring size lactones like ε-caprolactone (ε-CL). We investigated a route for the preparation of compartmentalized microgels based on poly(glycidol) in which CaLB was immobilized to increase its esterification ability. To find the ideal environment for CaLB, we investigated the acceptable water concentration and the accessibility for the monomer in model polymerizations in toluene and analyzed the obtained oligomers/polymers by NMR and SEC. We observed a sufficient accessibility for ε-CL to a toluene like hydrophobic phase imitating a hydrophobic microgel. Comparing free CaLB and Novozym® 435 we found that not the monomer concentration but rather the solubility of the enzyme, as well as the water concentration, strongly influences the equilibrium of esterification and hydrolysis. On the basis of these investigations, microgels of different polarity were prepared and successfully loaded with CaLB by physical entrapment. By comparison of immobilized and free CaLB, we demonstrated an effect of the hydrophobicity of the microenvironment of CaLB on its enzymatic activity.

Heck Reactions in Aqueous Miniemulsions

Carrying out organic reactions in water-based nanoreactors represents a ‘green’ method for the preparation of organic compounds. This process eliminates the need for solvents, thus reducing the effect of high volumes of solvent on the environment. In this work, we demonstrate a successful Heck cross-coupling reaction, one of the most used approaches to form C–C bonds using a palladium catalyst, in a miniemulsion. The miniemulsion droplet sizes were small (25 to 42 nm), and the reactions resulted in high conversions of three different products with high trans stereoisomers.