Exploring the Reactivity of Multicomponent Photocatalysts: Insight into the Complex Valence Band of BiOBr

The band structure of multicomponent semiconductor photocatalysts, as well as their reactivity distinction under different wavelengths of light, is still unclear. BiOBr, which is a typical multicomponent semiconductor, may have two possible valence‐band structures, that is, two discrete valence bands constructed respectively from O 2p and Br 4p orbitals, or one valence band derived from the hybridization of these orbitals. In this work, aqueous photocatalytic hydroxylation is applied as the probe reaction to investigate the nature and reactions of photogenerated holes in BiOBr. Three organic compounds (microcystin‐LR, aniline, and benzoic acid) with different oxidation potentials were selected as substrates. Isotope labeling (H₂¹⁸O as the solvent) was used to determine the source of the O atom in the hydroxyl group of the products, which distinguishes the contribution of different hydroxylation pathways. Furthermore, a spin‐trapping ESR method was used to quantify the reactive oxygen species (^.OH and ^.OOH) formed in the reaction system. The different isotope abundances of the hydroxyl O atom of the products formed, as well as the reverse trend of the ^.OH/^.OOH ratio with the oxidative resistance of the substrate under UV and visible irradiation, reveal that BiOBr has two separate valence bands, which have different oxidation ability and respond to UV and visible light, respectively. This study shows that the band structure of semiconductor photocatalysts can be reliably analyzed with an isotope labeling method.     

Giant Fullerene Polyelectrolytes Composed of C60 Building Blocks with an Octahedral Addition Pattern and Discovery of a New Cyclopropanation Reaction Involving Dibromomalonates

We report here on the facile synthetic access of a new family of bis‐, tetra‐, hexa‐, and heptafullerenes (prototypes I–IV), which can be easily converted into very water soluble polyelectrolytes with up to 60 charges located on their periphery. Their very regioselective formation is based on the use of C_2v‐symmetrical pentakisadducts 3 and hexakisadducts 2 as key intermediates. All fullerene moieties incorporated in these macromolecular structures involve a complete or partial octahedral addition pattern. Tripod‐shaped tetrafullerenes 9 a , b (type II), which can accumulate up to thirty positive or negative charges, are very soluble in acidic or basic water, respectively. Hexafullerenes 13 a , b (type III) were synthesized via isoxazolinofullerenes 10 followed by photolytic cleavage of the isoxazoline group. The giant heptafullerene 1 b (type IV) representing the anionic counterpart of the previously synthesized polyelectrolyte 1 a can store up to 60 negative charges on its periphery within a defined three‐dimensional structure. We also discovered a new cyclopropanation reaction of C₆₀ involving dibromomalonates and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU). This reaction allows even for the highly regioselective formation of hexakisadducts with an octahedral addition pattern without requiring activation with reversibly binding addends such as 9,10‐dimethylanthracene (DMA).     

High Charge Delocalization and Conjugation in Oligofuran Molecular Wires

The extent of charge delocalization and of conjugation in oligofurans and oligothiophenes was studied by using mixed valence systems comprising oligofurans and oligothiophenes capped at both ends by ferrocenyl redox units. Using electrochemical, spectral, and computational tools, we find strong charge delocalization in ferrocene‐capped oligofurans which was stronger than in the corresponding oligothiophene systems. Spectroscopic studies suggest that the electronic coupling integral (H_ab) is roughly 30–50 % greater for oligofuran‐bridged systems, indicating better energy matching between ferrocene units and oligofurans. The distance decay constant (damping factor), β, is similar for oligofurans (0.066 A^?1) and oligothiophenes (0.070 A^?1), which suggests a similar extent of delocalization in the bridge, despite the higher HOMO–LUMO gap in oligofurans. Computational studies indicate a slightly larger extent of delocalization in furan‐bridged systems compared with thiophene‐bridged systems, which is consistent with oligofurans being significantly more rigid and less aromatic than oligothiophenes. High charge delocalization in oligofurans, combined with the previously reported strong fluorescence, high mobility, and high rigidity of oligofuran‐based materials makes them attractive candidates for organic electronic applications.     

Trapped in Misbelief for Almost 40 Years: Selective Synthesis of the Four Stereoisomers of Mefloquine

Here we report the synthesis of all four stereoisomers of mefloquine. Mefloquine (Lariam) is an important anti‐malaria drug that is applied as a racemate of the erythro form. However, the (?)‐isomer induces psychosis, while the (+)‐enantiomer does not have this undesired side effect. There are six syntheses of which five lead to the wrong enantiomer without the authors of these syntheses noting that they had synthesized the wrong compound. At the same time physical chemistry investigations had assigned the absolute configuration correctly and the last enantioselective synthesis that took these results into account delivered the correct absolute configuration. Since various synthetic approaches failed to provide the correct stereoisomers in previous syntheses, we submit here a synthetic approach with a domino Sonogashira‐6π‐electrocyclisation as key step that confirmed synthetically the correct absolute configuration of all four isomers.     

Conformational Isomerism in Monomeric,Low‐Coordinate Group 12 Complexes Stabilized by a Naphthyl‐Substituted m‐Terphenyl Ligand

The synthesis and characterization of the first series of low‐coordinate bis(terphenyl) complexes of the Group 12 metals, [Zn(2,6‐Naph₂C₆H₃)₂] ( 1 ), [Cd(OEt₂)(2,6‐Naph₂C₆H₃)₂] ( 2 ) and [Hg(OEt₂)(2,6‐Naph₂C₆H₃)₂] ( 3 ) (Naph=1‐C₁₀H₇) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two‐coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three‐coordinate distorted T‐shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid‐state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution.     

Flexizyme‐Mediated Genetic Reprogramming As a Tool for Noncanonical Peptide Synthesis and Drug Discovery

Noncanonical peptides occur frequently in Nature, and often display high bioactivity. However, the lack of tractable systems for the synthesis of diverse libraries of such peptides has thus far hampered their development as drugs. Genetic reprogramming techniques, in which noncanonical amino acids may be incorporated into peptides, have largely removed this limitation. This Concept article outlines the development of these techniques with an emphasis on drug discovery.     

Homogeneous Catalytic Hydrogenation of Amides to Amines

Hydrogenation of amides in the presence of [Ru(acac)₃] (acacH=2,4‐pentanedione), triphos [1,1,1‐tris‐ (diphenylphosphinomethyl)ethane] and methanesulfonic acid (MSA) produces secondary and tertiary amines with selectivities as high as 93 % provided that there is at least one aromatic ring on N. The system is also active for the synthesis of primary amines. In an attempt to probe the role of MSA and the mechanism of the reaction, a range of methanesulfonato complexes has been prepared from [Ru(acac)₃], triphos and MSA, or from reactions of [RuX(OAc)(triphos)] (X=H or OAc) or [RuH₂(CO)(triphos)] with MSA. Crystallographically characterised complexes include: [Ru(OAc‐κ¹O)₂(H₂O)(triphos)], [Ru(OAc‐κ²O,O′)(CH₃SO₃‐κ¹O)(triphos)], [Ru(CH₃SO₃‐κ¹O)₂(H₂O)(triphos)] and [Ru₂(μ‐CH₃SO₃)₃(triphos)₂][CH₃SO₃], whereas other complexes, such as [Ru(OAc‐κ¹O)(OAc‐κ²O,O′)(triphos)], [Ru(CH₃SO₃‐κ¹O)(CH₃SO₃‐κ²O,O′)(triphos)], H[Ru(CH₃SO₃‐κ¹O)₃(triphos)], [RuH(CH₃SO₃‐κ¹O)(CO)(triphos)] and [RuH(CH₃SO₃‐κ²O,O′)(triphos)] have been characterised spectroscopically. The interactions between these various complexes and their relevance to the catalytic reactions are discussed.