Process Intensification of the Continuous Synthesis of Bio-Derived Monomers for Sustainable Coatings Using a Taylor Vortex Flow Reactor

We describe the optimization and scale-up of two consecutive reaction steps in the synthesis of bio-derived alkoxybutenolide monomers that have been reported as potential replacements for acrylate-based coatings (Sci. Adv.2020, 6, eabe0026). These monomers are synthesized by (i) oxidation of furfural with photogenerated singlet oxygen followed by (ii) thermal condensation of the desired 5-hydroxyfuranone intermediate product with an alcohol, a step which until now has involved a lengthy batch reaction. The two steps have been successfully telescoped into a single kilogram-scale process without any need to isolate the 5-hydroxyfuranone between the steps. Our process development involved FTIR reaction monitoring, FTIR data analysis via 2D visualization, and two different photoreactors: (i) a semicontinuous photoreactor based on a modified rotary evaporator, where FTIR and 2D correlation spectroscopy (2D-COS) revealed the loss of the methyl formate coproduct, and (ii) our fully continuous Taylor Vortex photoreactor, which enhanced the mass transfer and permitted the use of near-stoichiometric equivalents of O2. The use of in-line FTIR monitoring and modeling greatly accelerated process optimization in the Vortex reactor. This led to scale-up of the photo-oxidation in 85% yield with a projected productivity of 1.3 kg day-1 and a space-time yield of 0.06 mol day-1 mL-1. Higher productivities could be achieved while sacrificing yield (e.g., 4 kg day-1 at 40% yield). The use of superheated methanol at 200 °C in a pressurized thermal flow reactor accelerated the second step, the thermal condensation of 5-hydroxyfuranone, from a 20 h batch reflux reaction (0.5 L, 85 g) to a space time of <1 min in a reactor only 3 mL in volume operating with projected productivities of >700 g day-1. Proof of concept for telescoping the two steps was established with an overall two-step yield of 67%, producing a process with a projected productivity of 1.1 kg day-1 for the methoxybutenolide monomer without any purification of the 5-hydroxyfuranone intermediate.

Photophysical Properties of Fluorescent 2-(Phenylamino)-1,10-phenanthroline Derivatives†

The present study details the experimental and theoretical characterization of the photophysical properties of 14 examples of 2-(phenylamino)-1,10-phenanthrolines (1). The absorption spectra of 1 are substituent-dependent but in a general manner present absorption bands at wavelengths of ~230; ~300; ~335 and a shoulder at ~380 nm. Electron-donating groups (EDG) and electron-withdrawing groups (EWG), respectively, result in bathochromic and hypsochromic shifts. Compounds 1 are highly luminescent, in contrast to phenanthroline, and emit in the region between 350 and 500 nm with substituent-dependent λ_max emission. The emission spectra show a redshift for EDG (4-OMe 62 nm; 4-Me 19 nm) and a blueshift for EWG (4-CN 41 nm; 4-CF₃ 38 nm) relative to the emission of the unsubstituted parent compound 1a. Plotting the λ max EM against Hammett σ+ constants gave an excellent linear correlation demonstrating the electron-deficient nature of the excited state and how the substituents (de)stabilize S₁ . Theoretical calculations revealed a HOMO-LUMO π-π* electronic transition to S₁ which in combination with difference (S₁ -S₀ ) in electron density maps revealed charge-transfer character. Strongly electron-withdrawing substituents switch off the charge transfer to give rise to a local excitation.

Glass wool supported ruthenium complexes: versatile, recyclable heterogeneous photoredox catalysts

Versatile and recyclable heterogeneous photocatalysts based on the use of glass wool supported ruthenium complexes and organic dyes.

A photochemical and theoretical study of the triplet reactivity of furano- and pyrano-1,4-naphthoquionones towards tyrosine and tryptophan derivatives

The photochemical reactivity of the triplet state of pyrano- and furano-1,4-naphthoquinone derivatives (1 and 2) has been examined employing nanosecond laser flash photolysis. The quinone triplets were efficiently quenched by l-tryptophan methyl ester hydrochloride, l-tyrosine methyl ester hydrochloride, N-acetyl-l-tryptophan methyl ester and N-acetyl-l-tyrosine methyl ester, substituted phenols and indole (k q ∼109 L mol-1 s-1). For all these quenchers new transients were formed in the quenching process. These were assigned to the corresponding radical pairs that resulted from a coupled electron/proton transfer from the phenols, indole, amino acids, or their esters, to the excited state of the quinone. The proton coupled electron transfer (PCET) mechanism is supported by experimental rate constants, isotopic effects and theoretical calculations. The calculations revealed differences between the hydrogen abstraction reactions of phenol and indole substrates. For the latter, the calculations indicate that electron transfer and proton transfer occur as discrete steps.

Iridium Nanoparticles for Multichannel Luminescence Lifetime Imaging, Mapping Localization in Live Cancer Cells

The development of long-lived luminescent nanoparticles for lifetime imaging is of wide interest as luminescence lifetime is environmentally sensitive detection independent of probe concentration. We report novel iridium-coated gold nanoparticles as probes for multiphoton lifetime imaging with characteristic long luminescent lifetimes based on iridium luminescence in the range of hundreds of nanoseconds and a short signal on the scale of picoseconds based on gold allowing multichannel detection. The tailor-made IrC₆ complex forms stable, water-soluble gold nanoparticles (AuNPs) of 13, 25, and 100 nm, bearing 1400, 3200, and 22 000 IrC₆ complexes per AuNP, respectively. The sensitivity of the iridium signal on the environment of the cell is evidenced with an observed variation of lifetimes. Clusters of iridium nanoparticles show lifetimes from 450 to 590 ns while lifetimes of 660 and 740 ns are an average of different points in the cytoplasm and nucleus. Independent luminescence lifetime studies of the nanoparticles in different media and under aggregation conditions postulate that the unusual long lifetimes observed can be attributed to interaction with proteins rather than nanoparticle aggregation. Total internal reflection fluorescence microscopy (TIRF), confocal microscopy studies and 3D luminescence lifetime stacks confirm the presence of bright, nonaggregated nanoparticles inside the cell. Inductively coupled plasma mass spectrometry (ICPMS) analysis further supports the presence of the nanoparticles in cells. The iridium-coated nanoparticles provide new nanoprobes for lifetime detection with dual channel monitoring. The combination of the sensitivity of the iridium signal to the cell environment together with the nanoscaffold to guide delivery offer opportunities for iridium nanoparticles for targeting and tracking in in vivo models.