Ultrasound enhances lipase-catalyzed synthesis of poly (ethylene glutarate)

Effects of sound energy on proteins and their complexes

Mechanical energy in the form of ultrasound and protein complexes intuitively have been considered as two distinct unrelated topics. However, in the past few years, increasingly more attention has been paid to the ability of ultrasound to induce chemical modifications on protein molecules that further change protein-protein interaction and protein self-assembling behavior. Despite efforts to decipher the exact structure and the behavior-modifying effects of ultrasound on proteins, our current understanding of these aspects remains limited. The limitation arises from the complexity of both phenomena. Ultrasound produces multiple chemical, mechanical, and thermal effects in aqueous media. Proteins are dynamic molecules with diverse complexation mechanisms. This review provides an exhaustive analysis of the progress made in better understanding the role of ultrasound in protein complexation. It describes in detail how ultrasound affects an aqueous environment and the impact of each effect separately and when combined with the protein structure and fold, the protein-protein interaction, and finally the protein self-assembly. It specifically focuses on modifying role of ultrasound in amyloid self-assembly, where the latter is associated with multiple neurodegenerative disorders.

Recent Advances in the Enzymatic Synthesis of Polyester

Polyester is a kind of polymer composed of ester bond-linked polybasic acids and polyol. This type of polymer has a wide range of applications in various industries, such as automotive, furniture, coatings, packaging, and biomedical. The traditional process of synthesizing polyester mainly uses metal catalyst polymerization under high-temperature. This condition may have problems with metal residue and undesired side reactions. As an alternative, enzyme-catalyzed polymerization is evolving rapidly due to the metal-free residue, satisfactory biocompatibility, and mild reaction conditions. This article presented the reaction modes of enzyme-catalyzed ring-opening polymerization and enzyme-catalyzed polycondensation and their combinations, respectively. In addition, the article also summarized how lipase-catalyzed the polymerization of polyester, which includes (i) the distinctive features of lipase, (ii) the lipase-catalyzed polymerization and its mechanism, and (iii) the lipase stability under organic solvent and high-temperature conditions. In addition, this article also focused on the advantages and disadvantages of enzyme-catalyzed polyester synthesis under different solvent systems, including organic solvent systems, solvent-free systems, and green solvent systems. The challenges of enzyme optimization and process equipment innovation for further industrialization of enzyme-catalyzed polyester synthesis were also discussed in this article.

Chemical modification of lipases: A powerful tool for activity improvement

The demand for adequate and ecologically acceptable procedures to produce the most differentiated products has been growing in recent decades, with enzymes being excellent examples of the advances achieved so far. Lipases are astonishing catalysts with a vast range of applications including the synthesis of esters, flavours, biodiesel, and polymers. The broad specificity of the substrates, as well as the regio-, stereo-, and enantioselectivity, are the differentiating factors of these enzymes. Structural modification is a current approach to enhance the activity of lipases. Chemical modification of lipases to improve catalytic performance is of great interest considering the increasingly broad fields of application. Together with the physical immobilization onto solid supports, different strategies have been developed to produce catalysts with higher activity and stability. In this review, practical insights into the different strategies developed in recent years regarding the modification of lipases are described. For the first time, the impact of the modifications on the activity and stability of lipases, as well as on the biotechnological applications, is fully compiled. This article is protected by copyright. All rights reserved.

Effect of ultrasound on protein functionality

The review focus on the effect of ultrasound on protein functionality. The presence of transient ultrasonic mechanical waves induce various sonochemical and sonomechanical effects on a protein. Sonochemical effects include the breakage of chains and/or the modification of side groups of aminoacids. Sonomechanical modifications by enhanced molecular agitation, might lead to the transient or permanent modification of the 3D structure of the folded protein. Since the biological function of proteins depends on the maintenance of its 3D folded structure, both sonochemical and sonomechanical effects might affect its properties. A protein might maintain its 3D structure and functionality after minor sonochemical effects, however, the enhanced mass transfer by sonomechanical effects might expose internal hydrophobic residues of the protein, making protein unfolding to an irreversible denatured state. Ultrasound enhanced mass transport effects are unique pathways to change the 3D folded structure of proteins which lead to a new functionality of proteins as support shield materials during the formation microspheres. Enzymes are proteins and their reactions should be conducted in a reactor set-up where enzymes are protected from sonic waves to maximize their catalytic efficiency. In this review, focused examples on protein dispersions/emulsions and enzyme catalysis are given.

Prospects of Using Biocatalysis for the Synthesis and Modification of Polymers

Trends in the dynamically developing application of biocatalysis for the synthesis and modification of polymers over the past 5 years are considered, with an emphasis on the production of biodegradable, biocompatible and functional polymeric materials oriented to medical applications. The possibilities of using enzymes not only as catalysts for polymerization but also for the preparation of monomers for polymerization or oligomers for block copolymerization are considered. Special attention is paid to the prospects and existing limitations of biocatalytic production of new synthetic biopolymers based on natural compounds and monomers from biomass, which can lead to a huge variety of functional biomaterials. The existing experience and perspectives for the integration of bio- and chemocatalysis in this area are discussed.

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.

Dextran degradation by sonoenzymolysis: Degradation rate, molecular weight, mass fraction, and degradation kinetics

To study dextran degradation by sonoenzymolysis, the degradation rate, the change of molecular weight, the mass fractions of fragments of certain molecular weight, and the degradation kinetics were analyzed and compared with the corresponding parameters under ultrasonic and enzymolysis treatments. The degradation rate improved greatly and the time required to stabilize the rate was shortened compared with ultrasonic treatment, for example, more than 120 min was needed at 4 W/mL for ultrasonic treatment before stabilization with the degradation rate of 77.41%, whereas 80 min was needed for sonoenzymolysis treatment with the degradation rate of 91.44%. A lower molecular weight limit was established (7.15 × 10⁴ Da at 4 W/mL for sonoenzymolysis treatment compared with 19.61 × 10⁴ Da at 4 W/mL for ultrasonic treatment), with decreased time to approach the new limiting molecular weight (80 min compared with more than 120 min). The mass fraction of 10⁴-10⁵ Da fragment increased (61.02% at 4 W/mL for sonoenzymolysis treatment compared with 42.98% at 4 W/mL for ultrasonic treatment) and the dextran degradation kinetics for sonoenzymolysis under lower ultrasonic intensity fitted the Malhotra model well. Sonoenzymolysis treatment at the ultrasonic intensity of 4 W/mL for 80 min resulted in more 10⁴-10⁵ Da fragments in a shorter time. The results indicated that sonoenzymolysis can be applied as an efficient method to obtain clinical dextran.

Engineering a Microbial Consortium Based Whole-Cell System for Efficient Production of Glutarate From L-Lysine

Glutarate is an important C5 platform chemical produced during the catabolism of L-lysine through 5-aminovalerate (5-AMV) pathway. Here, we first established a whole-cell biocatalysis system for the glutarate production from L-lysine with the engineered Escherichia coli (E. coli) that co-expressed DavAB and GabDT. However, the accumulation of intermediate 5-AMV was identified as one important factor limiting glutarate production. Meanwhile, the negative interaction of co-expressing DavAB and GabDT in a single cell was also confirmed. Here, we solved these problems through engineering a microbial consortium composed of two engineered E. coli strains, BL21-22AB and BL21-YDT, as the whole-cell biocatalysts, each of which contains a part of the glutarate pathway. After the optimization of bioconversion conditions, including temperature, metal ion additives, pH, and cell ratio, 17.2 g/L glutarate was obtained from 20 g/L L-lysine with a yield of 95.1%, which was improved by 19.2% compared with that in a single cell. Little accumulation of 5-AMV was detected. Even at the high substrate concentration, the reduced 5-AMV accumulation and increased glutarate production were achieved. This synthetic consortium produced 43.8 g/L glutarate via a fed-batch strategy, the highest titer reported to date.

Strategies for the synthesis of fluorinated polyesters

In this work we synthetized three fluorinated polyesters from dimethyl tetrafluorosuccinate (DMTFS), dimethyl hexafluoroglutarate (DMHFG), and dimethyl octafluoroadipate (DMOFA) and ethylene glycol. The influence of parameters like monomer's size, temperature, vacuum, ultrasound and catalyst, on the polyesters synthesis was evaluated. The conversion rates were assessed considering ¹H NMR data and the results disclose the role of ultrasound (US) as crucial to attain high reaction conversion rates (≈20% of increase relatively to the reactions performed in absence of US). The effect of US was more relevant for the higher molecular weight monomers (DMHFG and DMOFA). The use of Candida antarctica lipase (immobilized CALB) marginally favors the synthesis reactions when fixing the other conditions. The size of the starting monomers influenced greatly the reaction conversion rates, as shorter monomers gave rise to high amount of product recovering. All the produced polyesters were isolated and fully characterized by NMR (¹H and ¹⁹F), FTIR, TGA and MALDI-TOF.

In this work we synthetized three fluorinated polyesters from dimethyl tetrafluorosuccinate (DMTFS), dimethyl hexafluoroglutarate (DMHFG), and dimethyl octafluoroadipate (DMOFA) and ethylene glycol.

Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology

Biobased polymers have seen their attractiveness increase in recent decades thanks to the significant development of biorefineries to allow access to a wide variety of biobased building blocks. Polyesters are one of the best examples of the development of biobased polymers because most of them now have their monomers produced from renewable resources and are biodegradable. Currently, these polyesters are mainly produced by using traditional chemical catalysts and harsh conditions, but recently greener pathways with nontoxic enzymes as biocatalysts and mild conditions have shown great potential. Bacterial polyesters, such as poly(hydroxyalkanoate)s (PHA), are the best example of the biotic production of high molar mass polymers. PHAs display a wide variety of macromolecular architectures, which allow a large range of applications. The present contribution aims to provide an overview of recent progress in studies on biobased polyesters, especially those made from short building blocks, synthesized through step-growth polymerization. In addition, some important technical aspects of their syntheses through biotic or abiotic pathways have been detailed.

Ultrasound-assisted biosynthesis of novel methotrexate-conjugates

New methotrexate-acylglycerols and methotrexate-cyclodextrins (α, β and γ-CD) conjugates were obtained via esterification or transesterification reactions. All reactions were catalysed by esterases namely immobilized Lipase from Candida antarctica B and Lipase from Thermomyces lanuginosus. The use of ultrasound to assist the reactions revealed to be a key factor to obtain high conversion yields on both MTX conjugates. Transesterification reactions including long chain triacylglycerols were only successful when ultrasound was applied. In cyclodextrins esterification a higher number of MTX molecules was also linked to cyclodextrins when ultrasound was used. All the conjugates were characterized by MALDI-TOF and NMR spectroscopy.

Structural insights into pH-responsive drug release of self-assembling human serum albumin-silk fibroin nanocapsules

Inflammation processes are associated with significant decreases in tissue or lysosomal pH from 7.4 to 4, a fact that argues for the application of pH-responsive drug delivery systems. However, for their design and optimization a full understanding of the release mechanism is crucial. In this study we investigated the pH-depending drug release mechanism and the influence of silk fibroin (SF) concentration and SF degradation degree of human serum albumin (HSA)-SF nanocapsules. Sonochemically produced nanocapsules were investigated regarding particle size, colloidal stability, protein encapsulation, thermal stability and drug loading properties. Particles of the monodisperse phase showed average hydrodynamic radii between 438 and 888 nm as measured by DLS and AFM and a zeta potential of -11.12 ± 3.27 mV. Together with DSC results this indicated the successful production of stable nanocapsules. ATR-FTIR analysis demonstrated that SF had a positive effect on particle formation and stability due to induced beta-sheet formation and enhanced crosslinking. The pH-responsive release was found to depend on the SF concentration. In in-vitro release studies, HSA-SF nanocapsules composed of 50% SF showed an increased pH-responsive release for all tested model substances (Rhodamine B, Crystal Violet and Evans Blue) and methotrexate at the lowered pH of 4.5 to pH 5.4, while HSA capsules without SF did not show any pH-responsive drug release. Mechanistic studies using confocal laser scanning microscopy (CLSM) and small angle X-ray scattering (SAXS) analyses showed that increases in particle porosity and decreases in particle densities are directly linked to pH-responsive release properties. Therefore, the pH-responsive release mechanism was identified as diffusion controlled in a novel and unique approach by linking scattering results with in-vitro studies. Finally, cytotoxicity studies using the human monocytic THP-1 cell line indicated non-toxic behavior of the drug loaded nanocapsules when applied in a concentration of 62.5 µg mL^-1. Based on the obtained release properties of HSA-SF nanocapsules formulations and the results of in-vitro MTT assays, formulations containing 50% SF showed the highest requirements arguing for future in vivo experiments and application in the treatment of inflammatory diseases.

Ultrasound-assisted lipase catalyzed hydrolysis of aspirin methyl ester

The ultrasound-assisted hydrolysis of aspirin methyl ester (AME) was investigated using immobilized Candida antarctica lipase B (CALB) (1%) in the presence of solvents like triolein, chloroform (CHCl₃) and dichloromethane (DCM). The effect of ultrasound and the role of water on the conversion rates have also been investigated. Proton nuclear magnetic resonance spectroscopic (¹H NMR) was chosen to calculate hydrolysis convertion rates. We observed that lipase-ultrasound assisted hydrolysis of AME in the presence of triolein and water showed the highest hydrolysis conversion rate (65.3%). Herein low water amount played an important role as a nucleophile being crucial for the hydrolysis yields obtained. Lipase activity was affected by the conjugated action of ultrasound and solvents (35.75% of decrease), however not disturbing its hydrolytic efficiency. It was demonstrated that lipase is able to hydrolyse AME to methyl 2-hydroxy benzoate (methyl salicylate), which applications include fragrance agents in food, beverages and cosmetics, or analgesic agent in liniments.

De Novo Biosynthesis of Glutarate via α-Keto Acid Carbon Chain Extension and Decarboxylation Pathway in Escherichia coli

Microbial based bioplastics are promising alternatives to petroleum based synthetic plastics due to their renewability and economic feasibility. Glutarate is one of the most potential building blocks for bioplastics. The recent biosynthetic routes for glutarate were mostly based on the l-lysine degradation pathway from Pseudomonas putida that required lysine either by feeding or lysine overproduction via genetic manipulations. Herein, we established a novel glutarate biosynthetic pathway by incorporation of a "+1" carbon chain extension pathway from α-ketoglutarate (α-KG) in combination with α-keto acid decarboxylation pathway in Escherichia coli. Introduction of homocitrate synthase (HCS), homoaconitase (HA) and homoisocitrate dehydrogenase (HICDH) from Saccharomyces cerevisiae into E. coli enabled "+1" carbon extension from α-KG to α-ketoadipate (α-KA), which was subsequently converted into glutarate by a promiscuous α-keto acid decarboxylase (KivD) and a succinate semialdehyde dehydrogenase (GabD). The recombinant E. coli coexpressing all five genes produced 0.3 g/L glutarate from glucose. To further improve the titers, α-KG was rechanneled into carbon chain extension pathway via the clustered regularly interspersed palindromic repeats system mediated interference (CRISPRi) of essential genes sucA and sucB in tricarboxylic acid (TCA) cycle. The final strain could produce 0.42 g/L glutarate, which was increased by 40% compared with the parental strain.

An investigation of lipase catalysed sonochemical synthesis: A review

Ultrasonic irradiation has recently gained attention of researchers for its process intensification in numerous reactions. Earlier ultrasound was known for its application either to deactivate enzyme activity or to disrupt the cell. However, in recent years, practice of ultrasonic irradiation began to emerge as a tool for the activation of the enzymes under mild frequency conditions. The incorporation of ultrasound in any of enzymatic reactions not only increases yield but also accelerates the rate of reaction in the presence of mild conditions with better yield and less side-products. To attain maximum yield, it is crucial to understand the mechanism and effect of sonication on reaction especially for the lipase enzyme. Thus, the influence of ultrasound irradiation on reaction yield for different parameters including temperature, enzyme concentration, mole ratio of substrates, solvents ultrasonic frequency and power was reviewed and discussed. The physical effect of cavitation determined by bubble dynamics and rate of reaction through kinetic modelling also needs to be assessed for complete investigation and scale up of synthesis. Thus, prudish utilisation of ultrasound for enzymatic synthesis can serve better future for sustainable and green chemistry.

Ultrasound assisted enzymatic hydrolysis of starch catalyzed by glucoamylase: Investigation on starch properties and degradation kinetics

The present work investigates the synergistic impact of glucoamylase and ultrasound on starch hydrolysis. The extent of starch hydrolysis at different reaction parameters (ultrasonic intensity, temperature, reaction time) was analyzed. The hydrolysis extent increased with the reaction time and reached a maximum value under ultrasonic intensity of 7.20W/mL at 10min. Ultrasound did not alter the optimum enzymatic temperature but speeded up the thermal inactivation of glucoamylase. The evaluation of enzymatic kinetics and starch degradation kinetics indicated a promotion of the reaction rate and enzyme-substrate affinity. According to the thermodynamic results, sonoenzymolysis reactions require less energy than enzymolysis reactions. The measurement of molecular weight, solubility, thermal properties, and structures of the substrates revealed that sonoenzymolysis reaction generated greater impacts on starch properties. The molecular weight and radii of gyration decreased by 80.19% and 90.05% respectively while the starch solubility improved by 136.50%.

Ultrasound-assisted hydrolysis of waste cooking oil catalyzed by homemade lipases

This study aimed to evaluate the waste cooking oil (WCO) hydrolysis in ultrasonic system using lipase as catalyst. Lipase was produced by the fungus Aspergillus niger via solid state fermentation (SSF) using canola meal as substrate. Prior to the hydrolysis reaction, the lipase behavior when subjected to ultrasound was evaluated by varying the temperature of the ultrasonic bath, the exposure time and the equipment power. Having optimized the treatment on ultrasound, the WCO hydrolysis reaction was carried out by evaluating the oil:water ratio and the lipase concentration. For a greater homogenization of the reaction medium, a mechanical stirrer at 170rpm was used. All steps were analyzed by experimental design technique. The lipase treatment in ultrasound generated an increase of about 320% in its hydrolytic activity using 50% of ultrasonic power for 25min. at 45°C. The results of the experimental design conducted for ultrasound-assisted hydrolysis showed that the best condition was using an oil:water ratio of 1:3 (v:v) and enzyme concentration of 15% (v/v), generating 62.67μmol/mL of free fatty acids (FFA) in 12h of reaction. Thus, the use of Aspergillus niger lipase as a catalyst for hydrolysis reaction of WCO can be considered as a possible pretreatment technique of the oil in order to accelerate its degradation.

Advances in Green Organic Sonochemistry

Over the past 15 years, sustainable chemistry has emerged as a new paradigm in the development of chemistry. In the field of organic synthesis, green chemistry rhymes with relevant choice of starting materials, atom economy, methodologies that minimize the number of chemical steps, appropriate use of benign solvents and reagents, efficient strategies for product isolation and purification and energy minimization. In that context, unconventional methods, and especially ultrasound, can be a fine addition towards achieving these green requirements. Undoubtedly, sonochemistry is considered as being one of the most promising green chemical methods (Cravotto et al. Catal Commun 63: 2-9, 2015). This review is devoted to the most striking results obtained in green organic sonochemistry between 2006 and 2016. Furthermore, among catalytic transformations, oxidation reactions are the most polluting reactions in the chemical industry; thus, we have focused a part of our review on the very promising catalytic activity of ultrasound for oxidative purposes.

On the Effect of Microwave Energy on Lipase-Catalyzed Polycondensation Reactions

Microwave energy (MWe) is, nowadays, widely used as a clean synthesis tool to improve several chemical reactions, such as drug molecule synthesis, carbohydrate conversion and biomass pyrolysis. On the other hand, its exploitation in enzymatic reactions has only been fleetingly investigated and, hence, further study of MWe is required to reach a precise understanding of its potential in this field. Starting from the authors’ experience in clean synthesis and biocatalyzed reactions, this study sheds light on the possibility of using MWe for enhancing enzyme-catalyzed polycondensation reactions and pre-polymer formation. Several systems and set ups were investigated involving bulk and organic media (solution phase) reactions, different enzymatic preparations and various starting bio-based monomers. Results show that MWe enables the biocatalyzed synthesis of polyesters and pre-polymers in a similar way to that reported using conventional heating with an oil bath, but in a few cases, notably bulk phase polycondensations under intense microwave irradiation, MWe leads to a rapid enzyme deactivation.

Synthesis of macromolecular systems via lipase catalyzed biocatalytic reactions: applications and future perspectives

This review highlights the application of lipases in the synthesis of pharmaceutically important small molecules and polymers for diverse applications.