Redox-active Reagents Research Articles

Selenosulfones, a Meetup of Chalcogens: A Journey Into Their Recent Chemistry

AbstractA mini review focused on the chemistry of selenosulfones reported since 2019 is here presented. Initially, methods aimed to the preparation of such moiety are discussed. Successively 1,2‐, 1,3‐, 1,4‐ and 1,7‐addition reactions to C−C single and multiple bonds are illustrated. The forth chapter focuses on electrophilic aromatic substitutions. The fifth chapter deals with C−H functionalizations while the sixth one shows the reactions with aryl diazonium salts or its precursors. The radical coupling with redox active reagents, is the subject of section seventh. Selenosulfones challenged in nucleophilic substitutions and in reactions with phosphorus‐containing compounds are shown in chapter eight and nine followed by the conclusions and perspectives section.

Incorporating sulfur into redox-active reagents and materials

Small sulfur-containing heterocycles, like thianthrenes and tetrathiafulvalenes, together with their larger π-extended counterparts, represent a long-known structural motif and offer reversible redox chemistry at low potentials. Recently these motifs gained an increasing interest in a variety of fields circulating organic chemistry ranging from molecular switches and redox reagents in synthesis to supramolecular aggregates. We anticipate fruitful developments from these versatile building blocks in modern technologies based on their reversible redox properties.

A practical fluorosulfonylating platform via photocatalytic imidazolium-based SO2F radical reagent

Sulfonyl fluorides are key components in the fields of chemical biology, materials science and drug discovery. In this line, the highly active SO2F radical has been employed for the construction of sulfonyl fluorides, but the utilization of gaseous ClSO2F as radical precursor is limited due to the tedious and hazardous preparation. Meanwhile, the synthesis of sulfonyl fluorides from inert SO2F2 gas through a fluorosulfonyl radical (·SO2F) process has met with inevitable difficulties due to the high homolytic bond dissociation energy of the S(VI)-F bond. Here we report a radical fluorosulfonylation strategy for the stereoselective synthesis of alkenyl sulfonyl fluorides and functional alkyl sulfonyl fluorides with an air-stable crystalline benzimidazolium fluorosulfonate cationic salt reagent. This bench-stable redox-active reagent offers a useful and operational protocol for the radical fluorosulfonylation of unsaturated hydrocarbons with good yield and high stereoselectivity, which can be further transformed into valuable functional SO2F moieties.

Nucleophilic and Radical Heptafluoroisopropoxylation with Redox-Active Reagents.

The heptafluoroisopropyl group (CF(CF3 )2 ) is prevalent in pharmaceuticals and agrichemicals. However, heptafluoroisopropoxylated (OCF(CF3 )2 ) compounds remain largely underexplored, presumably due to the lack of efficient access to these compounds. Herein, we disclose the practical and efficient heptafluoroisopropoxylation reactions through the invention of a series of redox-active N-OCF(CF3 )2 reagents. These reagents were readily prepared from the oxidative heptafluoroisopropylation of hydroxylamines with AgCF(CF3 )2 . The substitutions on the nitrogen atom significantly affected the properties and reactivities of N-OCF(CF3 )2 reagents. Accordingly, two types of N-OCF(CF3 )2 reagents including N-OCF(CF3 )2 phthalimide A and N-OCF(CF3 )2 benzotriazolium salt O' were used as OCF(CF3 )2 anion and radical precursors, respectively. This protocol enables the direct heptafluoroisopropoxylation of a range of substrates, delivering the corresponding products in moderate to excellent yields.

Photocatalyzed Radical Relayed Regio- and Stereoselective Trifluoromethylthiolation-Boration.

Vinylboronates and alkylboronates are key components in variegated transformations in all aspects of chemical science. This work describes a sequential radical difunctionalization strategy for the construction of fluorine-containing vinylboronates and alkylboronates with the integrated redox-active reagent N-trifluoromethylthiophthalimide. This multifunctional N-S precursor offers a scalable and practical protocol for the trifluoromethylthiolation-borylation of unsaturated hydrocarbons in a highly regio- and stereoselective fashion, which can be further converted into valuable synthons via boryl migration.

Organic redox-active crystalline layers for reagent-free electrochemical antibiotic susceptibility testing (ORACLE-AST)

Rapid antibiotic susceptibility testing (AST) is critical in determining bacterial resistance or susceptibility to a particular antibiotic. Simple-to-use phenotype-based AST platforms can assist care-givers in timely prescription of the right antibiotic. Monitoring the change of bacterial viability by measuring electrochemical Faradaic current is a promising approach for rapid AST. However, the existing works require mixing redox-active reagents in the solution which can interfere with the antibiotics. In this paper, we developed a facile electrodeposition process for creating a redox-active crystalline layer (denoted as RZx) on pyrolytic graphite sheets (PGS), which was then utilized as the sensing layer for reagent-free electrochemical AST. To demonstrate the proof-of-principle, we tested the sensors with Escherichia coli (E. coli) K-12 treated with two antibiotics, ampicillin and kanamycin. While the sensors enable detection of bacterial metabolism mainly due to pH-sensitivity of RZx (∼ 53 mV/pH), secreted redox-active metabolites/compounds from whole cells are likely contributing to the signal as well. By monitoring the differential voltammetric signals, the sensors enable accurate prediction of the minimum inhibitory concentration (MIC) in 60 min (p < 0.03). The sensors are stable after 60 days storage in ambient conditions and enable analysis of microbial viability in complex solutions, as demonstrated in spiked milk and human whole blood.

Integrated redox-active reagents for photoinduced regio- and stereoselective fluorocarboborylation

Vinylboronates and alkylboronates are key components in variegated transformations in all facets of chemical science. The synthesis of vinylboronates and alkylboronates suffers from step-tedious and poor stereoselective procedures. We have developed a regulated radical difunctionalization strategy for the construction of fluorine-containing vinylboronates and alkylboronates with an integrated redox-active reagent IMDN-SO2RF. This bench-stable imidazolium sulfonate cationic salt offers a scalable and operational protocol for the fluoroalkylation-borylation of unsaturated hydrocarbons in a high regio- and stereoselective manner. The products can be further transformed into valuable fluorinated building blocks.

Phylogenetic and functional features of the plastid transcription kinase cpCK2 from Arabidopsis signify a role of cysteinyl SH‐groups in regulatory phosphorylation of plastid sigma factors

A plastidic serine/threonine protein kinase, initially named plastid transcription kinase (PTK) has been implicated in phosphorylation and redox control of chloroplast transcription. This kinase was later renamed as chloroplast casein kinase 2 (cpCK2) because of its physical and functional similarity to nucleocytosolic casein kinase 2 (ncCK2). It shares all four of its cysteine residues with ncCK2 from land plants, while only three of these residues are conserved in algal CK2-type sequences, and just two in animals. Using bacterial overexpression of cpCK2 from Arabidopsis thaliana, here we show the principal features of this enzyme and assign functional determinants of its role as a transcriptional regulator in vitro. The recombinant protein is capable of using various plant sigma transcription factors as phosphorylation substrates. Electrophoretic mobility shift DNA-binding assays reveal differential effects of sigma phosphorylation, depending on the factor and the promoter used. Treatment of the kinase with redox-active reagents indicate a critical involvement of thiol groups in both its enzymatic activity and interaction capabilities. Mutational exchanges of cysteine to serine residues, in combination with in vitro assays, have provided clues to the possible role of individual cysteines. For instance, while Cys4 but not Cys2 is essential for activity, the latter seems to be involved in the formation of intermolecular (regulatory) disulfide bonds.

Nanodiamond films growth on porous silicon substrates for electrochemical applications

Nanocrystalline diamond (NCD) films were successfully grown on micrometric porous silicon (PS) substrate in a hot filament chemical vapor deposition (HFCVD) reactor. The films were deposited at substrate temperature of 920 K and 6.5 kPa, after seeding pretreatment. The gas flow rate was set in a 50 sccm for Ar–CH 4–H 2 mixture. PS substrates were produced by anodic etching using n-type silicon wafers. The morphology, quality and electrochemical response of NCD have been analyzed by scanning electron microscopy (SEM), Raman scattering spectroscopy and cyclic voltammetry (CV) measurements. SEM images have shown faceted nanograins with average size from 30 to 50 nm and uniform surface texture covering all the supports among the pores resulting in an apparent micro honeycomb structure. Raman spectra have exhibited a shoulder at 1550 cm −1, that is NCD characteristic and have confirmed the good quality films with diamond purity around 90%. Electrochemical response and capacitance behavior of NCD/PS electrodes immersed in aqueous electrolyte solution without redox-active reagents has been explored. The work potential window remains large for NCD, in a similar way of boron doped diamond (BDD), but with a large capacitive background current compared to BDD. NCD/PS presented capacitance values from 230 to 990 μF cm −2, while such capacitance values for BDD were between 20 and 40 μF cm −2 in the potential range of −0.5 up to 1.0 V × Ag/AgCl.

The assignment of the 1H nuclear magnetic resonance spectrum of azurin. An investigation of the 1H NMR spectrum of the blue copper protein, azurin, from Pseudomonas aeruginosa, with reference to the previously determined crystal structure.

A detailed assignment of the 1H nuclear magnetic resonance spectrum of azurin has been made. Resonances associated with the single tryptophan residue, all six phenylalanine residues, one of the two tyrosine residues and all four histidine residues, as well as most of the resonances from the ring-current shifted methyl groups have been assigned. These assignments have been used to study the pH dependence of the structure of the protein and binding of analogues of redox-active reagents to the protein.