Spatially resolved in situ determination of reaction progress using microfluidic systems and FT-IR spectroscopy as a tool for biocatalytic process development

In situ spatiotemporal characterization and analysis of chemical reactions using an ATR-integrated microfluidic reactor

Determining kinetic reaction parameters with great detail has been of utmost importance in the field of chemical reaction engineering. However, commonly used experimental and computational methods however are unable to provide sufficiently resolved spatiotemporal information that can aid in the process of understanding these chemical reactions. With our work, we demonstrate the use of a custom designed single-bounce ATR-integrated microfluidic reactor to obtain spatiotemporal resolution for in situ monitoring of chemical reactions. Having a single-bounce ATR accessory allows us to individually address different sensing areas, thereby providing the ability to obtain spatially and temporally resolved information. To further enhance the spatial resolution, we utilize the benefits of synchrotron IR radiation with the smallest beam spot-size ∼150 μm. An on-flow modular microreactor additionally allows us to monitor the chemical reaction in situ, where the temporal characterization can be controlled with the operational flowrate. With a unique combination of experimental measurements and numerical simulations, we characterize and analyse a model SN2 reaction. For a chemical reaction between benzyl bromide (BB) and sodium azide (SA) to produce benzyl azide (BA), we successfully show the capability of our device to determine the diffusion coefficients of BB and SA as 0.367 ± 0.115 10-9 m2 s-1 and 1.17 ± 0.723 10-9 m2 s-1, respectively. Finally, with the above characteristics of our device, we also calculate a reaction rate of k = 0.0005 (m3s-1mol-1) for the given chemical reaction.

Polymeric microfluidic continuous flow mixer combined with hyperspectral FT-IR imaging for studying rapid biomolecular events

Early reaction intermediates in protein folding, such as those resulting in β-amyloid formation due to transient misfolding, emerge within a few hundred microseconds. Here, we report a method to obtain sub-millisecond temporal resolution and molecular structural information of protein (mis-)folding events by using a microfluidic continuous-flow mixer (MCFM) in combination with Fourier transform infrared (FT-IR) imaging. The MCFMs are made out of cyclic olefin copolymer (COC) films, because this approach allows for rapid prototyping of different mixer designs. Furthermore, COC offers high IR transparency between 1500 and 2500 cm^-1, thus maximizing the signal to noise ratio of the IR data obtained from a sample of interest. By combining narrow and wide channel widths in MCFM design, the platform provides fast mixing (460 μs) to induce protein (mis-)folding, and it maximizes the residence time in the observing area, so a wide range of reaction timescales can be captured in a single image. We validated the platform for its ability to induce and observe sub-millisecond processes by studying two systems: (i) the mixing of H₂O and D₂O and (ii) the mixing induced deprotonation of carboxylic acid. First, we observed excellent agreement between simulated and experimental data of the on-chip mixing of H₂O and D₂O, which verifies the distance-reaction time relationships based on simulation. Second, deprotonation of carboxylic acid by on-chip mixing with sodium hydroxide solution validates the ability of the platform to induce rapid pH jump that is needed for some biomolecular reactions. Finally, we studied the methanol-induced partial-unfolding of ubiquitin to show that our platform can be used to study biomolecular events 'on-pathway' using FT-IR imaging. We successfully extracted kinetic and structural details of the conformational changes along the channel. Our results are in agreement with prior studies that required more elaborate stopped flow approaches to acquire data for different time points. In summary, the reported method uses an easy-to-fabricate microfluidic mixer platform integrated with hyperspectral FT-IR imaging for rapid acquisition of structural details and kinetic parameters of biomolecular reactions. This approach does not need stopped flow or molecular imaging probes, as required respectively for alternative FT-IR spectroscopy and fluorescence approaches.

The application of reaction engineering to biocatalysis

Biocatalysis is a growing area of synthetic and process chemistry with the ability to deliver not only improved processes for the synthesis of existing compounds, but also new routes to new compounds.