Esterification of lauric acid with lauryl alcohol using cross-linked enzyme crystals: Solvent effect and kinetic study

Optimization of the Enzymatic Synthesis of Pentyl Oleate with Lipase Immobilized onto Novel Structured Support

The term biorefinery is related to the sustainable production of value-added bioproducts and bioenergy from biomass. Esters from fatty acids are important compounds synthesized from by-products of the oleochemical industry. In agreement with the biorefinery concept, it is important to search for catalysts that reduce the consumption of energy and water, using moderate operation conditions and low reaction times. In this work, response surface methodology (RSM) was used to optimize the enzymatic synthesis of pentyl oleate using Candida antarctica lipase B (CALB) immobilized on a polyethylene-aluminum structured support. A factorial design was employed to evaluate the effects of several parameters on the ester yield. To obtain a model with a good fit, an approach to reaction mechanism and enzyme kinetics was taken into consideration. Experimental findings were correlated and explained using equations of a ping-pong bi-bi kinetic model and considering the inhibitory effects of both substrates. The developed model was consistent with the experimental data predicting an increase in pentyl oleate production with increasing temperature and a decrease with higher oleic acid amounts and alcohol to acid molar ratios. This model could be useful in a future industrial application of CALB/LLDPE/Al to minimize the costs in oleochemical biorefineries.

Biocatalytic synthesis of diaryl disulphides and their bio-evaluation as potent inhibitors of drug-resistant Staphylococcus aureus

Staphylococcus aureus is a WHO Priority II pathogen for its capability to cause acute to chronic infections and to resist antibiotics, thus severely impacting healthcare systems worldwide. In this context, it is urgently desired to discover novel molecules to thwart the continuing emergence of antimicrobial resistance. Disulphide containing small molecules has gained prominence as antibacterials. As their conventional synthesis requires tedious synthetic procedure and sometimes toxic reagents, a green and environmentally benign protocol for their synthesis has been developed through which a series of molecules were obtained and evaluated for antibacterial activity against ESKAPE pathogen panel. The hit compound was tested for cytotoxicity against Vero cells to determine its selectivity index and time-kill kinetics was determined. The activity of hit was determined against a panel of S. aureus multi-drug resistant clinical isolates. Also, its ability to synergize with FDA approved drugs was tested as was its ability to reduce biofilm. We identified bis(2-bromophenyl) disulphide (2t) as possessing equipotent antimicrobial activity against S. aureus including MRSA and VRSA strains. Further, 2t exhibited a selectivity index of 25 with concentration-dependent bactericidal activity, synergized with all drugs tested and significantly reduced preformed biofilm. Taken together, 2t exhibits all properties to be positioned as novel scaffold for anti-staphylococcal therapy.

Engineering aspects of immobilized lipases on esterification: A special emphasis of crowding, confinement and diffusion effects

Cross-linked enzyme crystal (CLEC) and sol-gel entrapped pseudomonas sp. lipase were investigated for the esterification of lauric acid with ethanol by considering the effects of reaction conditions on reaction rate. The activation energy for the reaction was estimated to be 1097.58 J/mol and 181.75 J/mol for sol-gel and CLEC entrapped lipase respectively. CLEC lipase exhibited a marginal internal diffusion effect on reaction rate over sol-gel lipases and found to be interesting. The overall reaction mechanism was found to conform to the Ping Pong Bi Bi mechanism. The higher efficiency of sol-gel lipases over CLEC lipases in esterification reaction is mainly due to the combined effects of crowding, confinement and diffusional limitations.

Organic Solvent Effects in Biomass Conversion Reactions

Transforming lignocellulosic biomass into fuels and chemicals has been intensely studied in recent years. A large amount of work has been dedicated to finding suitable solvent systems, which can improve the transformation of biomass into value-added chemicals. These efforts have been undertaken based on numerous research results that have shown that organic solvents can improve both conversion and selectivity of biomass to platform molecules. We present an overview of these organic solvent effects, which are harnessed in biomass conversion processes, including conversion of biomass to sugars, conversion of sugars to furanic compounds, and production of lignin monomers. A special emphasis is placed on comparing the solvent effects on conversion and product selectivity in water with those in organic solvents while discussing the origins of the differences that arise. We have categorized results as benefiting from two major types of effects: solvent effects on solubility of biomass components including cellulose and lignin and solvent effects on chemical thermodynamics including those affecting reactants, intermediates, products, and/or catalysts. Finally, the challenges of using organic solvents in industrial processes are discussed from the perspective of solvent cost, solvent stability, and solvent safety. We suggest that a holistic view of solvent effects, the mechanistic elucidation of these effects, and the careful consideration of the challenges associated with solvent use could assist researchers in choosing and designing improved solvent systems for targeted biomass conversion processes.