Special Issue "Flow Chemistry"
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A special issue of Molecules (ISSN 1420-3049).
Deadline for manuscript submissions: closed (30 May 2012)
Special Issue Editor
Guest Editor
Dr. Jean Jacques Vanden Eynde
Laboratory of Organic Chemistry (FS), University of Mons-UMONS, Place du parc, 20, B-7000 Mons, Belgium
Website: http://w3.umons.ac.be/~jjvde/lso.htm
E-Mail: jjvde@umons.ac.be
Phone: +32 65 373337
Interests: heterocycles; microwave-induced synthesis; solvent-free reactions; polymer (insoluble and soluble)-assisted syntheses; combinatorial chemistry; prodrugs
Special Issue Information
Dear Colleagues,
Traditionally chemical reactions are performed by mixing reagents and catalysts in a solvent contained in a flask or a reactor. The mixture is the stirred and eventually heated or cooled until complete disappearance, as far as possible, of the starting materials. Alternatively the reaction medium can be flowed into a tube, which is eventually heated or cooled. In that case, the progress of the reaction will be dependent on the rate of displacement of the mixture in the tube and on its dimensions (diameter and length). The purpose of this special issue of Molecules is to draw attention on recent developments in the area of flow chemistry at the laboratory scale as well as at the industrial scale.
Dr. Jean Jacques Vanden Eynde
Guest Editor
Submission
Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.
Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed Open Access monthly journal published by MDPI.
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Keywords
- flow chemistry
- microreactors
- continuous flow
- stop-flow
- purification
Published Papers (7 papers)
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Received: 18 July 2011; in revised form: 16 August 2011 / Accepted: 17 August 2011 / Published: 25 August 2011
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Abstract: We describe a new method using flow-injection analysis with spectro-photometric detection, suitable for the determination of N-acetyl-L-cysteine (NAC). The proposed method is appropriate for the determination of NAC in reaction with Pd2+ ions in the concentration range from 1.0 × 10−5 mol L−1 to 6.0 × 10−5 mol L−1. The detection limit NAC was 5.84 × 10−6 mol L−1 and the recorded relative standard deviation of the method is in the range from 1.67 to 4.11%. NAC and Pd2+ form complexes of Pd2+:NAC molar ratios of 1:1 and 1:2, depending on the ratio of their analytical concentrations. The cumulative conditional stability constant for the Pd(NAC)22+ complex is β12' = 2.69 × 109 L2 mol−2. The proposed method was compared with the classic spectrophotometric determination of NAC, using the same reagent, PdCl2, and had shown certain advantages: a) shorter analysis time; b) the use of smaller volumes of sample and reagents, which make the proposed method cheaper and faster for NAC determination in real samples without sample pretreatment.
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Received: 12 August 2011; in revised form: 31 August 2011 / Accepted: 31 August 2011 / Published: 5 September 2011
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Abstract: This review summarizes recent advances in microflow photochemical technologies and transformations. The portfolio of reactions comprises homogeneous and heterogeneous types, among them photoadditions, photorearrangements, photoreductions, photodecarboxylations, photooxygenations and photochlorinations. While microflow photochemistry is most commonly employed as a micro-scale synthesis tool, scale-up and technical production processes have already been developed.
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Received: 1 August 2011; in revised form: 1 September 2011 / Accepted: 6 September 2011 / Published: 9 September 2011
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Abstract: The kinetics of CO2 uptake by the cis-[Cr(C2O4)(BaraNH2)(OH2)2]+ complex cation and the acid hydrolysis of the cis-[Cr(C2O4)(BaraNH2)OCO2]− complex anion (where BaraNH2 denotes methyl 3-amino-2,3-dideoxy-b-D-arabino-hexopyranoside) were studied using the stopped-flow technique. The reactions under study were investigated in aqueous solution in the 288–308 K temperature range. In the case of the reaction between CO2 and cis-[Cr(C2O4)(BaraNH2)(OH2)2]+ cation variable pH values (6.82–8.91) and the constant ionic strength of solution (H+, Na+, ClO4− = 1.0) were used. Carbon dioxide was generated by the reaction between sodium pyruvate and hydrogen peroxide. The acid hydrolysis of cis-[Cr(C2O4)(BaraNH2)OCO2]− was investigated for varying concentrations of H+ ions (0.01–2.7 M). The obtained results enabled the determination of the number of steps of the studied reactions. Based on the kinetic equations, rate constants were determined for each step. Finally, mechanisms for both reactions were proposed and discussed. Based on the obtained results it was concluded that the carboxylation (CO2 uptake) reactions of cis-[Cr(C2O4)(BaraNH2)(OH2)2]+ and the decarboxylation (acid hydrolysis) of the cis-[Cr(C2O4)(BaraNH2)OCO2]− are the opposite of each other.
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Received: 9 August 2011; in revised form: 21 September 2011 / Accepted: 28 September 2011 / Published: 30 September 2011
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Abstract: 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.
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Received: 16 December 2011; in revised form: 16 February 2012 / Accepted: 17 February 2012 / Published: 22 February 2012
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Abstract: This study conducts an experimental study concerning the improvement of nozzle/diffuser micropump design using some novel no-moving-part valves. A total of three micropumps, including two enhancement structures having two-fin or obstacle structure and one conventional micro nozzle/diffuser design, are made and tested in this study. It is found that dramatic increase of the pressure drops across the designed micro nozzles/diffusers are seen when the obstacle or fin structure is added. The resultant maximum flow rates are 47.07 mm3/s and 53.39 mm3/s, respectively, for the conventional micro nozzle/diffuser and the added two-fin structure in micro nozzle/diffuser operated at a frequency of 400 Hz. Yet the mass flow rate for two-fin design surpasses that of conventional one when the frequency is below 425 Hz but the trend is reversed with a further increase of frequency. This is because the maximum efficiency ratio improvement for added two-fin is appreciably higher than the other design at a lower operating frequency. In the meantime, despite the efficiency ratio of the obstacle structure also reveals a similar trend as that of two-fin design, its significant pressure drop (flow resistance) had offset its superiority at low operating frequency, thereby leading to a lesser flow rate throughout the test range.
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Received: 16 May 2012; in revised form: 9 July 2012 / Accepted: 11 July 2012 / Published: 26 July 2012
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Abstract: An amperometric flow biosensor for oxalate determination in urine samples after enzymatic reaction with oxalate oxidase immobilized on a modified magnetic solid is described. The solid was magnetically retained on the electrode surface of an electrode modified with Fe (III)-tris-(2-thiopyridone) borate placed into a sequential injection system preceding the amperometric detector. The variables involved in the system such as flow rate, aspired volumes (modified magnetic suspension and sample) and reaction coil length were evaluated using a Taguchi parameter design. Under optimal conditions, the calibration curve of oxalate was linear between 3.0–50.0 mg·L−1, with a limit of detection of 1.0 mg·L−1. The repeatability for a 30.0 mg·L−1 oxalate solution was 0.7%. The method was validated by comparing the obtained results to those provided by the spectrophotometric method; no significant differences were observed.
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Received: 30 May 2012; in revised form: 27 July 2012 / Accepted: 9 August 2012 / Published: 15 August 2012
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Abstract: Bacterial biofilms—aggregations of bacterial cells and extracellular polymeric substrates (EPS)—are an important subject of research in the fields of biology and medical science. Under aquatic conditions, bacterial cells form biofilms as a mechanism for improving survival and dispersion. In this review, we discuss bacterial biofilm development as a structurally and dynamically complex biological system and propose microfluidic approaches for the study of bacterial biofilms. Biofilms develop through a series of steps as bacteria interact with their environment. Gene expression and environmental conditions, including surface properties, hydrodynamic conditions, quorum sensing signals, and the characteristics of the medium, can have positive or negative influences on bacterial biofilm formation. The influences of each factor and the combined effects of multiple factors may be addressed using microfluidic approaches, which provide a promising means for controlling the hydrodynamic conditions, establishing stable chemical gradients, performing measurement in a high-throughput manner, providing real-time monitoring, and providing in vivo-like in vitro culture devices. An increased understanding of biofilms derived from microfluidic approaches may be relevant to improving our understanding of the contributions of determinants to bacterial biofilm development.
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Last update: 18 May 2012
