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A rationally designed dual‐purpose non‐canonical amino acid (Trz) has been synthesised and successfully incorporated into a protein scaffold by genetic code expansion. Trz contains a 5‐pyridyl‐1,2,4‐triazine system, which allows for inverse‐electron‐demand Diels–Alder (IEDDA) reactions to occur on the triazine ring and for metal ions to be chelated both before and after the click reaction. Trz was successfully incorporated into a protein scaffold and the IEDDA utility of Trz demonstrated through the site‐specific labelling of the purified protein with a bicyclononyne. Additionally, Trz was shown to successfully coordinate a cyclometallated iridium(III) centre, providing access to a bioorthogonal luminogenic probe. The luminescent properties of the Ir(III)‐bound protein blue‐shift upon IEDDA click reaction with bicyclononyne, providing a unique method for monitoring the extent and location of the labelling reaction. In summary, Trz is a new dual‐purpose non‐canonical amino acid with great potential for myriad bioapplications where metal‐based functionality is required, for example in imaging, catalysis, and photo‐dynamic therapy, in conjunction with a bioorthogonal reactive handle to impart additional functionalities, such as dual‐modality imaging or therapeutic payloads. [ABSTRACT FROM AUTHOR]

Bis‐1,2,4‐triazine ligands are amongst the most promising soft N‐donor ligands for the partitioning of trivalent actinides from trivalent lanthanides; a key separation proposed in the future reprocessing of spent nuclear fuels. In an effort to improve the extraction properties of these benchmark ligands, we propose herein a general ligand design approach that is inspired by the field of drug discovery, and we apply it to a new class of ligands in which the bidentate 3‐(2‐pyridyl)‐1,2,4‐triazine unit of the benchmark ligands is replaced by a bidentate 1,2,4‐triazine‐3‐carboxamide unit. A series of nine novel ligands were synthesized by reactions of readily available ethyl 1,2,4‐triazine‐3‐carboxylate building blocks with different polyamine cores and evaluated for their ability to extract and separate Am(III) and Cm(III) from Eu(III). One of the reported ligands can co‐extract Am(III) and Eu(III) from nitric acid into cyclohexanone, albeit with no selectivity between the metal ions. NMR titration experiments suggested that ligand 23 b formed a chiral 1 : 1 complex species with La(III) but not Lu(III) or Y(III), suggesting the coordination cavity of the ligand is sensitive to the size of the metal ion. The structures and thermodynamic parameters for the proposed complexes were further supported by DFT calculations. [ABSTRACT FROM AUTHOR]

The synthesis and evaluation of three novel bis‐1,2,4‐triazine ligands containing five‐membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1–3 containing six‐membered aliphatic rings, the distribution ratios for relevant f‐block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of AmIII and CmIII from nitric acid. The speciation of the ligands with trivalent f‐block metal ions was probed using NMR titrations and competition experiments, time‐resolved laser fluorescence spectroscopy and X‐ray crystallography. While the tetradentate ligands 8 and 10 formed LnIII complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3, significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10. The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with YIII, LuIII and PrIII are very similar to those formed by 2 and 3 with LnIII. Ligand 10 forms CmIII and EuIII 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable AnIII complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity. [ABSTRACT FROM AUTHOR]

Anaerobic degradation of polycyclic aromatic hydrocarbons has been mostly investigated with naphthalene as a model compound. Naphthalene degradation by sulphate-reducing bacteria proceeds via carboxylation to 2-naphthoic acid, formation of coenzyme A thioester and subsequent reduction to 5,6,7,8-tetrahydro-2-naphthoyl- CoA (THNCoA), which is further reduced to hexahydro-2-naphthoyl-CoA (HHNCoA) by tetrahydronaphthoyl-CoA reductase (THNCoA reductase), an enzyme similar to class I benzoyl-CoA reductases. When analysing THNCoA reductase assays with crude cell extracts and NADH as electron donor via LC-MS, scanning for putative metabolites, we could show that small amounts of the product of an HHNCoA hydratase are formed in the assays, but the downstream conversion by an NAD+-dependent ß-hydroxyacyl-CoA dehydrogenase was prevented by the excess of NADH present in those assays. Experiments with alternative electron donors indicated that 2-oxoglutarate can serve as an indirect electron donor for the THNCoA-reducing system via a 2- oxoglutarate:ferredoxin oxidoreductase. With 2-oxoglutarate as electron donor, THNCoA was completely converted and further metabolites resulting from subsequent oxidation-like reactions and hydrolytic ring-cleavage were detected. These metabolites indicate a downstream pathway with water addition to HHNCoA and ring fission via a hydrolase acting on a ß'-hydroxy-ß-oxo-decahydro-2-naphthoyl-CoA intermediate. Formation of the downstream intermediate cis-2- carboxycyclohexyl)acetyl-CoA, which is the substrate for the previously described lower degradation pathway leading to the central metabolism, completes the anaerobic degradation pathway of naphthalene. [ABSTRACT FROM AUTHOR]

The high luminescence efficiency of cyclometallated iridium(iii) complexes, including those widely used in OLEDs, is typically attributed solely to the formally spin-forbidden phosphorescence process being facilitated by spin-orbit coupling with the Ir(iii) centre. In this work, we provide unequivocal evidence that an additional mechanism can also participate, namely a thermally activated delayed fluorescence (TADF) pathway. TADF is well-established in other materials, including in purely organic compounds, but has never been observed in iridium complexes. Our findings may transform the design of iridium(iii) complexes by including an additional, faster fluorescent radiative decay pathway. We discover it here in a new dinuclear complex, 1, of the form [Ir( N^C ) 2 ] 2 (μ-L), where N^C represents a conventional N^C -cyclometallating ligand, and L is a bis- N^O -chelating bridging ligand derived from 4,6-bis(2-hydroxyphenyl)-pyrimidine. Complex 1 forms selectively as the rac diastereoisomer upon reaction of [Ir( N^C ) 2 (μ-Cl)] 2 with H 2 L under mild conditions, with none of the alternative meso isomer being separated. Its structure is confirmed by X-ray diffraction. Complex 1 displays deep-red luminescence in solution or in polystyrene film at room temperature ( λ em = 643 nm). Variable-temperature emission spectroscopy uncovers the TADF pathway, involving the thermally activated re-population of S 1 from T 1 . At room temperature, TADF reduces the photoluminescence lifetime in film by a factor of around 2, to 1 μs. The TADF pathway is associated with a small S 1 -T 1 energy gap Δ E ST of approximately 50 meV. Calculations that take into account the splitting of the T 1 sublevels through spin-orbit coupling perfectly reproduce the experimentally observed temperature-dependence of the lifetime over the range 20-300K. A solution-processed OLED comprising 1 doped into the emitting layer at 5 wt% displays red electroluminescence, λ EL = 625 nm, with an EQE of 5.5% and maximum luminance of 6300 cd m -2 ., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Novel 7-N-(beta-alanyl)aminophenoxazin-3-one salts 27a-d have been synthesized and tested as chromogenic substrates for beta-alanyl aminopeptidase, which is present in Pseudomonas aeruginosa, the most common respiratory pathogen in patients with cystic fibrosis. The biological results show that 7-N-(beta-alanyl)amino-1-pentylphenoxazin-3-one trifluoroacetate salt 27a is a chromogenic substrate for this bacterium, with a low degree of diffusion in nutrient media for growing bacterial cultures and a bright red colour, making it easily distinguishable from the agar background.