Halogenation of pyrrole requires strong electrophilic reagents and often leads to undesired polyhalogenated products. Biocatalytic halogenation is a highly attractive approach given its chemoselectivity and benign reaction conditions. While there are several reports of enzymatic phenol and indole halogenation in organic synthesis, corresponding reports on enzymatic pyrrole halogenation have been lacking. Here we describe the in vitro functional and structural characterization of PrnC, a flavin-dependent halogenase that can act on free-standing pyrroles. Computational modeling and site mutagenesis studies identified three key residues in the catalytic pocket. A moderate resolution map using single-particle cryogenic electron microscopy reveals PrnC to be a dimer. This native PrnC can halogenate a library of structurally diverse pyrrolic heterocycles in a site-selective manner and be applied in the chemoenzymatic synthesis of a chlorinated analog of the agrochemical fungicide Fludioxonil.

RadH is one of the flavin-dependent halogenases that has previously exhibited promising catalytic activity towards hydroxycoumarin, hydroxyisoquinoline, and phenolic derivatives. Here, we evaluated new functional homologs of RadH and expanded its specificities for the halogenation of non-tryptophan-derived, heterocyclic scaffolds. Our investigation revealed that RadH could effectively halogenate hydroxyquinoline and hydroxybenzothiophene. Assay optimization studies revealed the need to balance the various co-factor concentrations and where a GDHi co-factor recycling system most significantly improves the conversion and efficiency of the reaction. A crystal structure of RadH was also obtained with a resolution of 2.4 Å, and docking studies were conducted to pinpoint the binding and catalytic sites for substrates.

Considering the dangers and risks posed by climate change, many countries and organizations have pledged to achieve “net-zero emissions” by 2050. The present work introduces a new approach that addresses the growing global carbon emissions issue by integrating CO₂ capture and sequestration through the carbonation of recycled concrete aggregates (RCAs), producing an alternative sand (AS) product. This study explores the capture of low-concentration CO₂ and its suitability for sequestration into RCA. The integration of RCA in the process allows concrete manufacturers to reduce their reliance on mined sand, thereby minimizing its impact on the environment. A techno-economic analysis (TEA) was conducted on the CO₂ absorption and mineralization process to assess its economic viability across various processing scales, from 150 kt CO₂ per year to 1 Mt CO₂ per year. Initial bench-scale experiments show that RCA samples have a carbonation capacity of 10% by mass—these experimental results were used to conduct a TEA using Aspen Plus and an Aspen Process Economic Analyzer (APEA). The TEA results reveal a cost of 11.02 USD/t AS at the smallest scale and 8.02 USD/t AS at the largest scale.

Dioxaphosphabicyclo[2.2.2]octanes (L1–L4) have been prepared in a one-pot reaction from tris(hydroxymethyl)phosphine and various α,β-unsaturated ketones. The non-volatile phosphines oxidise very slowly in air. They possess highly upfield ³¹P chemical shifts (−59 to −70 ppm), small cone angles (121–140°) and a similar electronic parameter to PPh₃. Reaction of L1 with [Rh(acac)(CO)₂] gave the complex [Rh(acac)(CO)(L1)] with a ν_(CO) of 1981.5 cm⁻¹, whereas reaction L1 with [Rh(CO)₂Cl]₂ gave [Rh(CO)(L1)₂Cl] with a ν_(CO) of 1979.9 cm⁻¹, remarkably similar to the CO stretching frequencies reported for analogous PPh₃ complexes. The cage phosphines were explored as ligands in rhodium catalysed hydroformylation of 1-octene. All of the ligands gave a linear selectivity to n-nonanal of 68%, regardless of the substituents. However the ligand substituents had a significant effect on the catalyst activity, with increased steric bulk around the coordination environment giving a three-fold increase in aldehyde yield. The phosphines undergo ligand subsitution with [Pd(MeCN)₂Cl₂] forming square planar trans-[Pd(L)₂Cl₂] complexes. Subsequent reduction with hydrazine furnishes homoleptic tetravalent [Pd(L1)₄] which was applied as a catalyst in Suzuki–Miyaura couplings, furnishing the C–C coupled products in moderate yields.

This study introduces an innovative strategy to mitigate global carbon emissions by integrating carbon dioxide (CO₂) absorption and sequestration through the carbonation of recycled concrete aggregate (RCA). This approach not only promotes the recycling of concrete waste but also alleviates the demand for new natural resources, addressing both environmental impact and geographical challenges associated with mining. The integrated process utilizes ammonia to capture flue gas emissions from natural gas combined cycle (NGCC) power plants, employing the captured solution to carbonate RCA for effective CO₂ sequestration and to enhance the quality of RCA. The study comprehensively assesses the process’s viability, considering capture performance, energy penalty, compliance with ammonia emissions standards, and capital costs. A techno-economic analysis (TEA) highlights the potential and economic feasibility of the proposed approach. Bench-scale experiments, conducted at low CO₂ concentrations (3~5%), focused on optimizing the carbonation process. The concentration of carbonated ammonia solution and its ratio to RCA were investigated to enhance the yield of carbonated RCA, resulting in an approximate 10% CO₂ capacity when using a 5% carbonated ammonia solution with a 0.25 ratio. The design of a large-scale plant, with an annual carbonated RCA production capacity of around 150 ktonnes, was formulated, and TEA calculations using Aspen Plus® V14 indicated a cost of approximately SGD 13 per tonne of carbonated product. These findings underscore the promising potential of the proposed process in efficiently reducing carbon emissions while providing economic viability at a larger scale.