This review offers an overview of recent synthetic strategies employing photoredox catalysis and electrochemistry in the framework of multicomponent reactions.

Multicomponent reactions (MCRs) are ideal platforms for the generation of a wide variety of organic scaffolds in a convergent and atom-economical manner. Many strategies for the generation of highly substituted and diverse structures have been developed and among these, the Petasis reaction represents a viable reaction manifold for the synthesis of substituted amines via coupling of an amine, an aldehyde and a boronic acid (BA). Despite its synthetic utility, the inherent drawbacks associated with the traditional two-electron Petasis reaction have stimulated continuous research towards more facile and tolerant methodologies. In this regard, we present the use of free alkyl BAs as effective radical precursors in this MCR through a single-electron transfer mechanism under mild reaction conditions. We have further demonstrated its applicability to photo-flow reactors, facilitating the reaction scale-up for the rapid assembly of complex molecular structures.

Catechol direct modification enables the preparation of functional coatings by imparting adhesive capability to the target molecule. The catechol precursor choice affects synthetic route and substrate compatibility, allowing for tailored strategies.

The popularity of microflow chemistry has skyrocketed in the last 20 years, more and more chemists are switching from macro-batch reactors to miniaturized flow devices. As a result, microfluidics is paving its way into the future by consolidating its position in organic chemistry not only as a trend but as a new, effective, and sustainable way of conducting chemistry, that clearly will continue to grow and evolve. This perspective highlights the most relevant examples of innovative enhancing technologies applied to microflow reactors aimed to improve and intensify chemical processes. The extensive applicability of microflow chemistry is further illustrated by briefly discussing examples of complex integrated microsystems and scale-up technologies, demonstrating ultimately that microflow chemistry has the potential to become the ideal technology for the future.

In recent years, antimicrobial hydrogels have attracted much attention in biomedical applications due to their biocompatibility and high water content. Glycyrrhizin (GA) is an antimicrobial that can form pH-dependent hydrogels due to the three carboxyl groups of GA that differ in pK_a value. The influence of GA protonation on the antimicrobial activity, however, has never been studied before. Therefore, we investigated the effect of the pH on the antimicrobial activity of GA against Pseudomonas aeruginosa, Staphylococcus aureus, MRSA, Staphylococcus epidermidis, Acinetobacter baumannii, Klebsiella pneumoniae, Klebsiella aerogenes, and two strains of Escherichia coli. In general, the antimicrobial activity of GA increases as a function of decreasing pH (and thus increasing protonation of GA). More specifically, fully protonated GA hydrogels (pH = 3) are required for growth inhibition and killing of E. coli UTI89 and Klebsiella in the suspension above the hydrogel, while the staphylococci strains and A. baumannii are already inhibited by fully deprotonated GA (pH = 6.8). P. aeruginosa and E. coli DH5α showed moderate susceptibility, as they are completely inhibited by a hydrogel at pH 3.8, containing partly protonated GA, but not by fully deprotonated GA (pH = 6.8). The antimicrobial activity of the hydrogel cannot solely be attributed to the resulting pH decrease of the suspension, as the presence of GA significantly increases the activity. Instead, this increased activity is due to the release of GA from the hydrogel into the suspension, where it directly interacts with the bacteria. Moreover, we provide evidence indicating that the pH dependency of the antimicrobial activity is due to differences in GA protonation state by treating the pathogens with GA solutions differing in their GA protonation distribution. Finally, we show by LC-MS that there is no chemical or enzymatic breakdown of GA. Overall, our results demonstrate that the pH influences not only the physical but also the antimicrobial properties of the GA hydrogels.