Madalina Tudorache

Efficient bio-conversion of glycerol to glycerol carbonate catalyzed by lipase extracted from Aspergillus niger

A biocatalytic synthesis of glycerol carbonate (GlyC), as an added-value product of renewable glycerol, has been developed using a catalytic route in which glycerol (Gly) was reacting with dimethyl carbonate (DMC) in the presence of lipase under solvent-free conditions. The enzyme screening indicated lipase from Aspergillus niger as the most efficient biocatalyst for the GlyC synthesis. After the optimization of the reaction conditions it was established that the best results corresponded to 12% (w/w) Aspergillus nigerlipase, to a glycerol : DMC molar ratio of 1 : 10, to an incubation time of 4 h and to an incubation temperature of 60 °C. Consequently, the glycerol conversion was around 74%, the yield in GlyC of 59.3% and the selectivity to GlyC of 80.3%. Recycling experiments demonstrated that the biocatalyst can be successfully used for several reaction cycles (at least 4 times) and confirmed its very high stability under the reaction conditions.

Strategy of cross-linked enzyme aggregates onto magnetic particles adapted to the green design of biocatalytic synthesis of glycerol carbonate

A new strategy for the preparation of biocatalysts based on enzyme immobilization was explored, leading to cross-linked enzyme aggregate onto magnetic particles (CLEMPA). Lipase enzyme from Aspergillus niger was precipitated from aqueous solution followed by cross-linking of the enzyme aggregates onto magnetic particles using glutaraldehyde as cross-linker. An optimization study has been carried out for the CLEMPA approach to determine the best experimental conditions for both preparation steps (i.e. enzyme precipitation and cross-linking of the enzyme aggregates onto magnetic particles). Type and concentration of the precipitation agent, type and size of magnetic particles, ratio of lipase to magnetic particles, concentration of the cross-linker and growth time of CLEMPA clusters were the experimental factors taken under investigation. Characterization of CLEMPA biocatalyst considering the cluster size and lipase loading was performed using light scattering detection and UV-vis spectrophotometric techniques. The catalytic capacity of CLEMPA biocatalyst was tested with the “green” alternative of glycerol carbonate (GlyC) synthesis. CLEMPA catalyzed the conversion of glycerol to GlyC with an excess of dimethyl carbonate (DMC) providing solvent-free conditions for the reaction. These experiments resulted in encouraging biocatalytic performance with 61% glycerol conversion, 55% GlyC yield and 90% selectivity in GlyC. CLEMPA biocatalyst was also tested in the reaction of “crude” glycerol extracted from the biodiesel process, with similar performance results. Recycling experiments for 20 successive reaction cycles demonstrated the robustness of the prepared CLEMPA structure.

Direct synthesis of sorbitol and glycerol from cellulose over ionic Ru/magnetite nanoparticles in the absence of external hydrogen.

A sweet catalyst: A catalyst formed of Ru/functionalized silica-coated magnetite nanoparticles is highly efficient in the one-pot production of sorbitol and glycerol, starting from cellulose and in the absence of an external hydrogen source. The ease of recoverability of the catalyst from the solid residues, and its reuse without loss of activity or selectivity for several runs, is an important green element of the process.

Efficient magnetic and recyclable SBILC (supported basic ionic liquid catalyst)-based heterogeneous organocatalysts for the asymmetric epoxidation of trans-methylcinnamate

A green alternative, based on the use of an efficient and recyclable chiral ketone@SBILC@MWCNT@Fe3O4 catalytic system (Y = 35%, S = 100% and ee = 100%), was developed for the asymmetric epoxidation of trans-methylcinnamate to (2R,3S)-phenyl glycidate.

Biocatalytic designs for the conversion of renewable glycerol into glycerol carbonate as a value-added product

A comparative study of two different biocatalytic models, e.g. enzyme immobilized on magnetic particles (EIMP) and cross-linking enzyme aggregates onto magnetic particles (CLEMPA) was performed. The first model was designed as enzyme-immobilized on the magnetic particles surface (EIMP). The second model was constructed as a network structure with the enzyme aggregates and magnetic particles placed into the nodes and polyglutaraldehyde cross-linker as the network ledges. The design was called cross-linking enzyme aggregates onto magnetic particles (CLEMPA). The biocatalysts were prepared using lipase enzyme from Aspergillus niger for catalyzing the glycerol (Gly) conversion to glycerol carbonate (GlyC). The biocatalyst characteristics for both designs (EIMP and CLEMPA) were evaluated using scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis techniques. The EIMP model was strongly influenced by the composition of the polymeric layer covering the particles surface, while the size of the magnetic particles affected mostly the CLEMPA design. Also, the biocatalytic capacity of the tested models was evaluated as maximum 52% Gly conversion with 90% GlyC selectivity for EIMP, and 73% Gly conversion with 77% GlyC selectivity for CLEMPA. Both biocatalytic models were successfully used to prepare GlyC from “crude” glycerol collected directly from the biodiesel process (e.g. 49% Gly conversion with 91% GlyC selectivity for EIMP and 70% Gly conversion with 80% GlyC selectivity for CLEMPA).

Bifunctional carbohydrate biopolymers entrapped lipase as catalyst for the two consecutive conversions of α-pinene to oxy-derivatives.

Bifunctional catalysts designed as carbohydrate biopolymers entrapping lipase have been investigated for the biotransformation of a natural compound (α-pinene) to oxy-derivatives. Lipases assisted the epoxidation of α-pinene using H2O2 as oxidation reagent and ethyl acetate as both acetate-supplier and solvent affording α-pinene oxide as the main product. Further, the biopolymer promoted the isomerization of α-pinene oxide to campholenic aldehyde and trans-carenol. In this case, the biopolymers played double roles of the support and also active part of the bifunctional catalyst. Screening of enzymes and their entrapping in a biopolymeric matrix (e.g. Ca-alginate and κ-carrageenan) indicated the lipase extracted from Aspergillus niger as the most efficient. In addition, the presence of biopolymers enhanced the catalytic activity of the immobilized lipase (i.e. 13.39×10(3), 19.76×10(3)and 26.46×10(3) for the free lipase, lipase-carrageenan and lipase-alginate, respectively). The catalysts stability and reusability were confirmed in eight consecutively reaction runs.

Development of Biological Sensors Based on Screen-Printed Electrodes for Environmental Pollution Monitoring

Screen-printed electrodes modified with appropriate mediators have been used for the reliable determination of dithiocarbamate fungicides and alkylphenols. A sensor based on immobilization of aldehyde dehydrogenase on the surface of a disposable screen-printed carbon-paste electrode, chemically modified with Meldola’s blue mediator, was used for the determination of a soil fumigant, metham-sodium and its main toxic metabolite MITC. This sensor allowed us to discriminate between metham-sodium and its metabolite MITC, as metham-sodium did not inhibit AlDH, while MITC could be detected at 100 ppb levels. Further, a new nanocomposite was developed by combination of Prussian blue mediator and single-walled carbon nanotubes (SWNTs). Prussian blue and SWNTs exhibit synergistic electrocatalytic effect toward the hydrogen peroxide reduction. The nanocomposite sensor exhibited excellent sensitivity, 119.62 mA·M−1·cm−2, a detection limit of 0.64 μM, fast response time of 10 sec and a wide linear range up to 2 mM.

One-Pot Enzymatic Production of Lignin-Composites

A novel and efficient one-pot system for green production of artificial lignin bio-composites has been developed. Monolignols such as sinapyl (SA) and coniferyl (CA) alcohols were linked together with caffeic acid (CafAc) affording a polymeric network similar with natural lignin. The interaction of the dissolved SA/CA with CafAc already bound on a solid support (SC2/SC6-CafAc) allowed the attachment of the polymeric product direct on the support surface (SC2/SC6-CafAc-L1 and SC2/SC6-CafAc-L2, from CA and SA, respectively). Accordingly, this procedure offers the advantage of a simultaneous polymer production and deposition. Chemically, oxi-copolymerization of phenolic derivatives (SA/CA and CAfAc) was performed with H2O2 as oxidation reagent using peroxidase enzyme (2-1B mutant of versatile peroxidase from Pleurotus eryngii) as catalyst. The system performance reached a maximum of conversion for SA and CA of 71.1 and 49.8%, respectively. The conversion is affected by the system polarity as resulted from the addition of a co-solvent (e.g., MeOH, EtOH, or THF). The chemical structure, morphology, and properties of the bio-composites surface were investigated using different techniques, e.g., FTIR, TPD-NH3, TGA, contact angle, and SEM. Thus, it was demonstrated that the SA monolignol favored bio-composites with a dense polymeric surface, high acidity, and low hydrophobicity, while CA allowed the production of thinner polymeric layers with high hydrophobicity.