Integrated microreaction system for optical resolution of racemic amino acids

Design, Fundamental Principles of Fabrication and Applications of Microreactors

This study highlights the development of small-scale reactors, in the form of microstructures with microchannel networking. Microreactors have achieved an impressive reputation, regarding chemical synthesis ability and their applications in the engineering, pharmaceutical, and biological fields. This review elaborates on the fabrication, construction, and schematic fundamentals in the design of the microreactors and microchannels. The materials used in the fabrication or construction of the microreactors include silicon, polymer, and glass. A general review of the application of microreactors in medical, biological, and engineering fields is carried out and significant improvements in these areas are reported. Finally, we highlight the flow patterns, mixing, and scaling-up of multiphase microreactor developments, with emphasis on the more significant industrial applications.

Techniques for Preparation of Cross-Linked Enzyme Aggregates and Their Applications in Bioconversions

Enzymes are biocatalysts. They are useful in environmentally friendly production processes and have high potential for industrial applications. However, because of problems with operational stability, cost, and catalytic efficiency, many enzymatic processes have limited applications. The use of cross-linked enzyme aggregates (CLEAs) has been introduced as an effective carrier-free immobilization method. This immobilization method is attractive because it is simple and robust, and unpurified enzymes can be used. Coimmobilization of different enzymes can be achieved. CLEAs generally show high catalytic activities, good storage and operational stabilities, and good reusability. In this review, we summarize techniques for the preparation of CLEAs for use as biocatalysts. Some important applications of these techniques in chemical synthesis and environmental applications are also included. CLEAs provide feasible and efficient techniques for improving the properties of immobilized enzymes for use in industrial applications.

A novel approach to the consecutive extraction of drugs with different properties via on chip electromembrane extraction

Lab on chip electromembrane extraction coupled with HPLC was introduced for analysis of betaxolol, naltrexone and nalmefene in biological samples.

Passive Microextractor with Internal Fluid Recirculation for Two Immiscible Liquids

A microextractor comprising an inlet channel, a mixing chamber, two feedback channels, and an outlet channel and having no moving parts was designed for immiscible liquid–liquid extraction. Two liquids were mixed passively without any external energy input, and the extraction was completed in the microextractor. The extractor performance with or without a splitter was investigated by visualization and mass transfer experiments. Two mixing mechanisms were observed: (i) molecular diffusion at lower Reynolds number and (ii) chaotic advection at higher Reynolds number. The transition point between the two mechanisms was at Reynolds numbers 375.2 and 179.9 for the aqueous phase (3 mol/L HNO3 solution) and the organic phase (30% tributyl phosphate (TBP)–kerosene solution), respectively. In the chaotic advection mode, two vortexes rotating in opposite directions were formed on both sides of the main flow, which enhanced the mass transfer between the two liquids. Mass transfer between the 3 mol/L HNO3 and 30% TBP–kerosene solutions was achieved with an efficiency of 92.8% at the extractor exit when the extractor operated in the chaotic advection mode.

Novel process windows for enabling, accelerating, and uplifting flow chemistry

Novel Process Windows make use of process conditions that are far from conventional practices. This involves the use of high temperatures, high pressures, high concentrations (solvent-free), new chemical transformations, explosive conditions, and process simplification and integration to boost synthetic chemistry on both the laboratory and production scale. Such harsh reaction conditions can be safely reached in microstructured reactors due to their excellent transport intensification properties. This Review discusses the different routes towards Novel Process Windows and provides several examples for each route grouped into different classes of chemical and process-design intensification.

Microfluidic devices: useful tools for bioprocess intensification

The dawn of the new millennium saw a trend towards the dedicated use of microfluidic devices for process intensification in biotechnology. As the last decade went by, it became evident that this pattern was not a short-lived fad, since the deliverables related to this field of research have been consistently piling-up. The application of process intensification in biotechnology is therefore seemingly catching up with the trend already observed in the chemical engineering area, where the use of microfluidic devices has already been upgraded to production scale. The goal of the present work is therefore to provide an updated overview of the developments centered on the use of microfluidic devices for process intensification in biotechnology. Within such scope, particular focus will be given to different designs, configurations and modes of operation of microreactors, but reference to similar features regarding microfluidic devices in downstream processing will not be overlooked. Engineering considerations and fluid dynamics issues, namely related to the characterization of flow in microchannels, promotion of micromixing and predictive tools, will also be addressed, as well as reflection on the analytics required to take full advantage of the possibilities provided by microfluidic devices in process intensification. Strategies developed to ease the implementation of experimental set-ups anchored in the use of microfluidic devices will be briefly tackled. Finally, realistic considerations on the current advantages and limitation on the use of microfluidic devices for process intensification, as well as prospective near future developments in the field, will be presented.

Enzyme-immobilized microfluidic process reactors

Microreaction technology, which is an interdisciplinary science and engineering area, has been the focus of different fields of research in the past few years. Several microreactors have been developed. Enzymes are a type of catalyst, which are useful in the production of substance in an environmentally friendly way, and they also have high potential for analytical applications. However, not many enzymatic processes have been commercialized, because of problems in stability of the enzymes, cost, and efficiency of the reactions. Thus, there have been demands for innovation in process engineering, particularly for enzymatic reactions, and microreaction devices represent important tools for the development of enzyme processes. In this review, we summarize the recent advances of microchannel reaction technologies especially for enzyme immobilized microreactors. We discuss the manufacturing process of microreaction devices and the advantages of microreactors compared to conventional reaction devices. Fundamental techniques for enzyme immobilized microreactors and important applications of this multidisciplinary technology are also included in our topics.

Rapid and efficient proteolysis for proteomic analysis by protease-immobilized microreactor

Proteolysis is an important part of protein identification in proteomics analysis. The conventional method of in-solution digestion of proteins is time-consuming and has limited sensitivity. In this study, trypsin- or alpha-chymotrypsin-immobilized microreactors prepared by a microfluidics-based enzyme-immobilization technique were studied for rapid sample preparation in proteomic analysis. The kinetic studies for hydrolysis of substrate by microreactors revealed that immobilized proteases had higher hydrolytic efficiency than those performed by in-solution digestion. The performance of the microreactors was evaluated by digesting cytochrome c and BSA. Protein digestion was achieved within a short period of time (approximately 5 min) at 30 degrees C without any complicated reduction and alkylation procedures. The efficiency of digestion by trypsin-immobilized reactor was evaluated by analyzing the sequence coverage, which was 47 and 12% for cytochrome c and BSA, respectively. These values were higher than those performed by in-solution digestion. Besides, because of higher stability against high concentration of denaturant, the microreactors can be useful for immediate digestion of the denaturated protein. In the present study, we propose a protease-immobilized microreactor digestion method, which can utilize as a proteome technique for biological and clinical research.

Continuous-flow organic synthesis: a tool for the modern medicinal chemist

Medicinal chemists are under increasing pressure, not only to identify lead compounds and optimize them into clinical candidates, but also to produce materials in sufficient quantities for subsequent investigation. With this in mind, continuous-flow methodology presents an opportunity to reduce the time taken to, first, identify the compound and, second, scale the process for evaluation and, where necessary, production. It is therefore the aim of this review to provide the reader with an insight into the advantages associated with the use of continuous-flow chemistry through the use of strategically selected literature examples.

Asymmetric reactions in continuous flow

An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed.

The change of activation energy in microchannel laminar flow as demonstrated by kinetic analysis of the DNA duplex-coil equilibrium

This paper presents the capability of changing the activation energy of chemical reactions using microchannel laminar flow. Kinetic parameters of the duplex-coil equilibrium of DNA oligomers were studied by measuring the hysteresis between denaturation-renaturation curves using an in-house temperature-controllable microchannel-type flow cell. For this study, DNA oligomers were used because they allow physicochemical analysis and theoretical discussion. Kinetic parameters of the duplex-coil equilibrium of DNA oligomers were obtained by measuring the denaturation-renaturation hysteresis curves. Both cooling and heating curves were shifted to the high-temperature side at higher flow rates. The renaturation reaction was influenced by a slower flow rate. The effect of the slower flow rate was more pronounced for renaturation than denaturation reactions. The magnitude of the activation energies of association decreased as the flow rate increased, but that of the activation energies of the dissociation increased as the flow rate increased. Overall, these results suggest that chemical reactions' change of activation energy depends on the flow rate and the DNA molecular size.

Development of a silica monolith microbioreactor entrapping highly activated lipase and an experiment toward integration with chromatographic separation of chiral esters

Microbioreactors are effective for high-throughput production of expensive products from small amounts of substrates. Lipases are versatile enzymes for chiral syntheses, and are highly activated when immobilized in alkyl-substituted silicates by the sol-gel method. For practical application of sol-gel immobilized lipases to a flow system, a microbioreactor loaded with a macroporous silica monolith is well suited, because it can be easily integrated with a chromatographic separator for optical resolution. We attempted to develop a microbioreactor containing a silica monolith-immobilized lipase. A nonshrinkable silica monolith was first formed from a 4:1 mixture of methyltrimethoxysilane (MTMS) and tetramethoxysilane (TMOS). It was then coated with silica precipitates entrapping lipase, derived from a 4:1 mixture of n-butyltrimethoxysilane (BTMS) and TMOS. As a result, monolith treated with the BTMS-based silicate entrapping lipase exhibited approximately ten times higher activity than nontreated monolith-immobilized lipase derived from the MTMS-based silicate, in transesterification between glycidol and vinyl n-butyrate in isooctane. A commercially available chiral column was connected in series to the monolith microbioreactor, and a pulse of substrate solution was supplied at the inlet of the reactor. Successful resolution of the racemic ester produced was achieved in the chromatographic column.

Immobilization of thermophilic enzymes in miniaturized flow reactors

The exploitation of enzymes for biotransformation reactions for the production of new and safer drug intermediates has been the focus of much research. While a number of enzymes are commercially available, their use in an industrial setting is often limited to reactions that are cost-effective and they are rarely investigated further. However, the development of miniaturized flow reactor technology has meant that the cost of such research, once considered cost- and time-inefficient, would be much less prohibitive. The use of miniaturized flow reactors for enzyme screening offers a number of advantages over batch enzyme assay systems. Since the assay is performed on a miniaturized scale, enzyme, substrate and cofactor quantities are significantly reduced, thus reducing the cost of laboratory-scale investigations. Since flow reactors use microfluidic systems, where the substrate and products flow out of the system, the problems of substrate inhibition and product inhibition encountered by some enzymes are avoided. Quite often, enzymes fulfil a single-use function in biotransformation processes; however, enzyme immobilization allows enzyme reuse and often helps to increase enzyme stability. We have used an aminoacylase enzyme with potential use for industrial biotransformation reactions and have successfully immobilized it in miniaturized flow reactors. This L-aminoacylase is from the thermophilic archaeon Thermococcus litoralis. Two approaches to enzyme immobilization have been examined, both involving enzyme cross-linking. The first reactor type has used monoliths, to which the enzyme was attached, and the second contained previously cross-linked enzyme trapped using frits, in the microfluidic channels. Two different microreactor designs were used in the investigation: microreactor chips for the monoliths and capillary flow reactors for the cross-linked enzyme. These systems allowed passage of the substrate and product through the system while retaining the aminoacylase enzyme performing the catalytic conversion. The enzyme has been successfully immobilized and used to produce stable biocatalytic microreactors that can be used repeatedly over a period of several months.