Synergy of Microfluidics and Ultrasound

Rivas, David Fernández; Kuhn, Simon

doi:10.1007/s41061-016-0070-y

Cited by 83 publications

(64 citation statements)

References 142 publications

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“…Even initially homogeneous reactions where solid intermediates or products are formed are difficult due to clogging of the microchannels [24][25][26]. While some tricks exist to deal with clogging (e.g., sonication [27]), this is constant source of trouble for flow chemists. However, such processes are important in modern chemistry,…”

Section: Multiphasic Systems In Continuous-flow Photochemistrymentioning

confidence: 99%

Flow Photochemistry: Shine Some Light on Those Tubes!

Sambiagio

Noël

2020

Trends in Chemistry

316

223

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Continuous-flow chemistry has recently attracted significant interest from chemists in both academia and industry working in different disciplines and from different backgrounds. Flow methods are now being used in reaction discovery/methodology, in scale-up and production, and for rapid screening and optimization. Photochemical processes are currently an important research field in the scientific community and the recent exploitation of flow methods for these methodologies has made clear the advantages of flow chemistry and its importance in modern chemistry and technology worldwide. This review highlights the most important features of continuous-flow technology applied to photochemical processes and provides a general perspective on this rapidly evolving research field. Microflow Technology and Photochemistry: A Perfect MatchThe use of light to promote chemical reactions has been exploited since the 18th century, but only recently a resurgence has been observed in synthetic organic chemistry, in particular due to the development of visible-light photoredox catalysis [1-5]. All transformations involving light (e.g., Figure 1A-D) must consider, besides classical chemical parameters (i.e., reaction conditions), the photophysical aspects of the sensitizer (see Glossary)/photocatalyst (when used), and the reactor design. The latter, although often neglected by chemists, is a critical aspect for the outcome of the studied chemical transformation. This includes, for example, the size, shape, and material of the reaction vessel, the characteristics and positioning of the light source(s), and heat-transfer properties, particularly when high-intensity lamps are used [6,7]. The engineering and technological aspects of photochemical processes are often at the basis of the irreproducibility and non-scalability of such transformations.According to the Beer-Lambert law, light transmittance decreases exponentially with the distance from the light source ( Figure 1F). For a standard batch reactor (diameter at least in the centimeter range), light intensity decreases considerably from the flask walls to the middle of the reaction mixture, resulting in slow reactions and nonhomogeneous irradiation of the reaction mixture. Performing photochemical reactions in microchannels (ID < 1 mm) allows a higher and more homogeneous photon flux, resulting in shorter reaction times and consequently less side-product formation due to over-irradiation, often observed in batch [8,9]. Another advantage of microflow chemistry, correlated with the large surface:volume ratio, is improved heat and mass transfer, with the possibility to perform mass-transfer-limited multiphasic reactions efficiently [10]. Reactive chemicals and intermediates can be handled more safely in flow than in batch, as no accumulation of dangerous components occurs within the confined reactor volume due to the continuous nature of the process. Together, these result in often faster, safer, and higher-yielding reactions, with the possibility to perform reactions under condition...

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Section: Multiphasic Systems In Continuous-flow Photochemistrymentioning

confidence: 99%

Flow Photochemistry: Shine Some Light on Those Tubes!

Sambiagio

Noël

2020

Trends in Chemistry

316

223

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“…4,5 Clearly, given the electron's much larger γ, considerably higher ε values can be achieved by applying a similar principle to the electron−nucleus spin pairs; this is the basic idea behind DNP. Such hyperpolarization of nuclear spins can potentially elicit NMR signal enhancements of ε = γ el /γ 1H ≈ 660 or γ el /γ 15N ≈ 6500, which translates to time savings of (660) 2 and (6500) 2 , respectively. In practice, the technique relies upon saturation of the electron paramagnetic resonance (EPR) line of unpaired electrons by microwave (MW) irradiation and subsequent transfer of polarization to the material's nuclei of interest.…”

Section: Dnp Ssnmrmentioning

confidence: 99%

Dynamic Nuclear Polarization Solid-State NMR in Heterogeneous Catalysis Research

et al. 2015

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A revolution in solid-state nuclear magnetic resonance (SSNMR) spectroscopy is taking place, attributable to the rapid development of high-field dynamic nuclear polarization (DNP), a technique yielding sensitivity improvements of 2-3 orders of magnitude. This higher sensitivity in SSNMR has already impacted materials research, and the implications of new methods on catalytic sciences are expected to be profound. Disciplines Chemistry CommentsReprinted (adapted) with permission from ACS Catalysis 5 (2015): 7055,

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“…This resulting quadrupole interaction (QI) has been demonstrated to have significant importance in the characterization of a diverse array of systems. [27][28][29][30][31] At the same time, as SSNMR experiments are typically (and most conveniently) performed on powdered samples, the orientation-dependence of the QI-perturbed Zeeman interaction in a powdered sample results in NMR signal broadening. This creates a situation where the feeble 43 Ca NMR signal becomes distributed over a range of frequencies and hence could be buried in the noise.…”

Section: Introductionmentioning

confidence: 99%

Calcium-43 chemical shift and electric field gradient tensor interplay: a sensitive probe of structure, polymorphism, and hydration

Widdifield

Moudrakovski

Bryce

2014

Phys. Chem. Chem. Phys.

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Calcium is the 5th most abundant element on earth, and is found in numerous biological tissues, proteins, materials, and increasingly in catalysts. However, due to a number of unfavourable nuclear properties, such as a low magnetogyric ratio, very low natural abundance, and its nuclear electric quadrupole moment, development of solid-state (43)Ca NMR has been constrained relative to similar nuclides. In this study, 12 commonly-available calcium compounds are analyzed via(43)Ca solid-state NMR and the information which may be obtained by the measurement of both the (43)Ca electric field gradient (EFG) and chemical shift tensors (the latter of which are extremely rare with only a handful of literature examples) is discussed. Combined with density functional theory (DFT) computations, this 'tensor interplay' is, for the first time for (43)Ca, illustrated to be diagnostic in distinguishing polymorphs (e.g., calcium formate), and the degree of hydration (e.g., CaCl2·2H2O and calcium tartrate tetrahydrate). For Ca(OH)2, we outline the first example of (1)H to (43)Ca cross-polarization on a sample at natural abundance in (43)Ca. Using prior knowledge of the relationship between the isotropic calcium chemical shift and the calcium quadrupolar coupling constant (CQ) with coordination number, we postulate the coordination number in a sample of calcium levulinate dihydrate, which does not have a known crystal structure. Natural samples of CaCO3 (aragonite polymorph) are used to show that the synthetic structure is present in nature. Gauge-including projector augmented-wave (GIPAW) DFT computations using accepted crystal structures for many of these systems generally result in calculated NMR tensor parameters which are in very good agreement with the experimental observations. This combination of (43)Ca NMR measurements with GIPAW DFT ultimately allows us to establish clear correlations between various solid-state (43)Ca NMR observables and selected structural parameters, such as unit cell dimensions and average Ca-O bond distances.

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Synergy of Microfluidics and Ultrasound

Cited by 83 publications

References 142 publications

Flow Photochemistry: Shine Some Light on Those Tubes!

Flow Photochemistry: Shine Some Light on Those Tubes!

Dynamic Nuclear Polarization Solid-State NMR in Heterogeneous Catalysis Research

Calcium-43 chemical shift and electric field gradient tensor interplay: a sensitive probe of structure, polymorphism, and hydration

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