No abstract

Electrochemistry offers opportunities to promote single-electron transfer (SET) redox-neutral chemistries similar to those recently discovered using visible-light photocatalysis but without the use of an expensive photocatalyst. Herein, we introduce a microfluidic redox-neutral electrochemistry (μRN-eChem) platform that has broad applicability to SET chemistry, including radical-radical cross-coupling, Minisci-type reactions, and nickel-catalyzed C(sp2)–O cross-coupling. The cathode and anode simultaneously generate the corresponding reactive intermediates, and selective transformation is facilitated by the rapid molecular diffusion across a microfluidic channel that outpaces the decomposition of the intermediates. μRN-eChem was shown to enable a two-step gram-scale electrosynthesis of a nematic liquid crystal compound, demonstrating its practicality.

Visible-light photoredox reactions have been demonstrated to be powerful synthetic tools to access pharmaceutically relevant compounds. However, many photoredox reactions involve insoluble starting materials or products that complicate the use of continuous flow methods. By integrating a new solid-feeding strategy and a continuous stirred-tank reactor (CSTR) cascade, we realize a new solid-handling platform for conducting heterogeneous photoredox reactions in flow. Residence time distributions for single phase and solid particles characterize the hydrodynamics of the heterogeneous flow in the CSTR cascade. Silyl radical-mediated metallaphotoredox cross-electrophile coupling reactions with an inorganic base as the insoluble starting material demonstrate the use of the platform. Gram-scale synthesis is achieved in 13 h of stable operation.

Continuous handling of solids creates challenges for realizing continuous production of pharmaceuticals and fine chemicals. We present a new miniature continuous stirred-tank reactor (CSTR) cascade to handle solid-forming reactions in flow. Single-phase residence time distribution (RTD) measurements of the CSTR cascade reveal nearly ideal CSTR mixing behavior of the individual units. Consistency of experimental and predicted conversions of a Diels-Alder reaction further confirms the CSTR performance. Two solid-forming reactions, (i) glyoxal reacting with cyclohexylamine to form N,N′-dicyclohexylethylenediimine, (ii) sulfonylation of 2-octanol with methanesulfonyl chloride, demonstrate the ability of the reactor cascade to transport solid particles continuously for hours without significant signs of clogging.

bAntibiotic growth promoters (AGPs) have been used as feed additives to improve average body weight gain and feed efficiency in food animals for more than 5 decades. However, there is a worldwide trend to limit AGP use to protect food safety and public health, which raises an urgent need to discover effective alternatives to AGPs. The growth-promoting effect of AGPs has been shown to be highly correlated with the decreased activity of intestinal bile salt hydrolase (BSH), an enzyme that is produced by various gut microflora and involved in host lipid metabolism. Thus, BSH inhibitors are likely promising feed additives to AGPs to improve animal growth performance. In this study, the genome of Lactobacillus salivarius NRRL B-30514, a BSH-producing strain isolated from chicken, was sequenced by a 454 GS FLX sequencer. A BSH gene identified by genome analysis was cloned and expressed in an Escherichia coli expression system for enzymatic analyses. The BSH displayed efficient hydrolysis activity for both glycoconjugated and tauroconjugated bile salts, with slightly higher catalytic efficiencies (k cat /K m ) on glycoconjugated bile salts. The optimal pH and temperature for the BSH activity were 5.5 and 41°C, respectively. Examination of a panel of dietary compounds using the purified BSH identified some potent BSH inhibitors, in which copper and zinc have been recently demonstrated to promote feed digestion and body weight gain in different food animals. In sum, this study identified and characterized a BSH with broad substrate specificity from a chicken L. salivarius strain and established a solid platform for us to discover novel BSH inhibitors, the promising feed additives to replace AGPs for enhancing the productivity and sustainability of food animals.