The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, Bernhard Kräutler gives his story on cobalt.

Crystallization and biocatalysis: In situ product crystallization is a powerful technique to overcome fundamental limitations in biocatalytic reactions, for example, unfavorable reaction equilibria or product inhibitions (see figure). This Minireview presents basic process considerations within (early) process development and illustrates the high potential of crystallization with selected examples.

The elucidation of substrate–protein interactions is an important component of the drug development process. Photoaffinity labeling (PAL) is a versatile technique that can provide insight into ligand–target interactions. Among the commonly employed photoreactive groups, diazirines have emerged as the gold standard. In this Minireview, recent developments in the field of diazirine-based PAL are discussed, with emphasis on their applications in proteomic studies.

Squeeze in! The catalytic abilities of a hexameric capsule are reminiscent of the modus operandi of natural enzymes. Inside the cavity of the capsule, reagents are confined in a restricted space in close proximity, such that they react faster with regio- and stereoselectivity (see figure). The hexameric cage shows substrate selectivity, stabilization of transition states and intermediates through secondary interactions, and inhibition by competitive guests.

Carbene-phosphinidenide complexes: New potassium-containing molecular or ionic compounds were obtained starting from the phosphinidenide SIMesPK [SIMes: 1,3-bis-(2,4,6-trimethylphenyl)-imidazolidine-2-ylidene]. For example, recrystallisation of SIMesPK with KOtBu yields the barrel-like cage compound [K₆(SIMesP)₂(OtBu)₄].

Flower power: A facile, rapid and room-temperature strategy for the synthesis of Pd HBNDs is described. using N,N′-methylenebisacrylamide (MBAA) as the simultaneous coordinating agent, reducing agent and structure-directing agent for intramolecular coordination and self-reduction. Due to plentiful and ultrafine branches, porosity, and superficial bumpy atomic steps, the Pd HBNDs show remarkable catalytic activity and durability toward the ORR.

Boron-doped diamonds: The first electrochemical impedance spectroscopy studies in anhydrous HF have been conducted to understand the reactions taking place during electrochemical oxidation of Ag^I to Ag^II. Preparative electrosynthesis of dark brown AgF₂ magnetic semiconductor was successfully carried out in both galvanostatic and potentiostatic condition (see scheme).

Oxidized Ni species in-depth: An in situ generated oxidation species of the nickel quinolinylpropioamide intermediate was produced. Characterization by XANES and EPR provided complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved.

Living on the edge: Single Pt–Pd nanoparticle (NPs) electrode was fabricated by an electro-deposition method using a single nanopore electrode as a template, which was controlled by the “edge effect.” The prepared single Pt–Pd NPs exhibit excellent electrocatalytic activity towards methanol oxidation reaction, which can be used to screen electrocatalysts with high efficiency for utility in the energy field.

Activation time! The asymmetric fragmentation of a spiro[chromane-2,3′-cyclobutanol] proceeds smoothly and with high levels of stereocontrol in the presence of a chiral iridium catalyst. This opened a new strategy for the (2R)-selective synthesis of α-tocopherol (i.e., vitamin E).

Selective synthesis of ketones can be achieved by extremely fast 1:1 micromixing of acid halides and organolithiums using a flow microreactor system. Moreover, the chemoselective reactions of acid chlorides bearing electrophilic functional groups with functionalized organolithiums were also carried out in this controlled system to give the corresponding functionalized ketones (see scheme).

All swell that end swell: 3D Hansen solubility space is used to explain why the ability of binary mixtures of two solvents to swell crosslinked resins does not vary linearly with the solvent mole fractions. The applicability of this methodology to both solid-phase peptide synthesis and linear polymer dissolution is demonstrated

Controlling DNA binding: Sequence-specific small peptide–DNA major and minor groove interactions can be controlled by irradiation. Specifically, photoswitchable azobenzene moieties were implemented in the peptide backbone or turn region of transcriptionally active peptides. DNA binding affinity was affected by photochemical isomerization, which provides promising tools for DNA modulation.

Three new dithienogermole derivatives with bulky aryl substituents were prepared, which show photoenergy transfer properties between the dithienogermole core and the substituents. In addition to the photoenergy transfer, an electron transfer was also observed depending on the energy level of the aryl substituents on the Ge atom.

[n]Radialenes analogues substituted with strongly electron-donating 1,3-dithiol-2-ylidenes (DTs) are of significant interest as a novel class of multistep redox systems. Among them, [5]radialene derivatives with strongly electron-donating 1,3-dithiol-2-ylidenes (DTs) have potential application in organic electronic materials. This work reports the hydration of tetracationic [5]radialene derivative, molecular structures of its products, the possible reaction mechanism, and their electronic properties.

The anisotropy barrier in a triplesalen-based single-molecule magnet has been rationally increased by using a triplesalalen ligand. The triplesalen ligand of heteroradialene character transmits only antiferromagnetic interactions, while the rationally designed aromatic triplesalalen transmits ferromagnetic interactions by an efficient spin-polarization mechanism. This stabilizes the SMM spin ground state, reduces M_S mixing and quantum tunneling and thus yields overall better SMM characteristics.

Finer electrodes: Sub-nanometer, ultrasmall iron oxide nanosheets on reduced graphene oxide sheets were prepared by means of controlled crystallization kinetics (see figure) and investigated as anode materials for energy-storage devices. SU-Fe₂O₃-rGO exhibits high specific capacitance and superb capacitance retention, both of which are superior to those of other reported asymmetric supercapacitors based on iron oxides.

PDQ synthesis of PQDs: The passivation strategy reported herein is to use organic molecules linear alkyl phosphonic acids (PAs) and (3-aminopropyl)triethoxysilane (APTES) as ligands. The PAs and APTES produce R−PO₂(OH)⁻, R−PO₃²⁻, and R−NH₃⁺ to effectively passivate the charged surface defects of CH₃NH₃PbBr₃ perovskite quantum dots (PQDs) due to dangling bonds related to species such as MA⁺, Pb²⁺ and X⁻, respectively (see figure).

Winning ribbon: Graphene ribbon networks can effectively improve electron/ion transfer to enhance the battery performance of hybrids, especially at high mass loading. Ultra-fine Fe₂O₃ nanowires uniformly anchored on interconnected graphene ribbon networks are successfully synthesized, and exhibit high rate and long cycle life performance.

Between the sheets: Graphitic carbon nitride (g-C₃N₄) nanosheets rich in nitrogen defects were obtained by one-step tartaric acid-assisted thermal polymerization of dicyandiamide. The defects in g-C₃N₄ act as charge trapped states to prolong the lifetime of charge carriers, and the decreased interlayer distance caused by nitrogen vacancies favors of charge transport and mobility to the surface (see figure). Deficient g-C₃N₄ exhibits the enhanced photocatalytic activity in CO₂ reduction.

Ag seeds for Li nucleation: A graphene aerogel homogeneously decorated with Ag nanoparticles has been prepared by a facile hydrothermal method and used as a freestanding Li metal anode. The G-Ag aerogel displays a high coulombic efficiency (over 93.5 %) and a long cycle life (1589 h) over 200 cycles (see graphic).

Morphological storage matters: Nanoporous ZnMn₂O₄ nanorods have been successfully synthesized by calcining β-MnO₂/ZIF-8 precursors. The remarkable lithium-storage performance is attributed to the one-dimensional nanoporous structure, and thus, these nanoporous ZnMn₂O₄ nanorods have the potential to be candidates for commercial anode materials in lithium-ion batteries (see scheme).

Hard facts: The “Covalent metal” compound, TaB, possess the merits of strong covalent boron chains and metallic tantalum bilayers, which give this structure high hardness and electrical conductivity.

Bimetallic photocatalysts: Bimetallic AgPd nanoparticles are loaded on g-C₃N₄ for photocatalytic H₂ evolution. The resultant AgPd/g-C₃N₄ shows superior activity to the monometallic Ag/g-C₃N₄ and Pd/g-C₃N₄. The interfacial interaction between the metals is beneficial in accelerating photogenerated electron transfer, H₂O molecule adsorption, and H₂O dissociation, leading to enhanced photocatalytic H₂O reduction to H₂.

Stepping on the surface: The self-assembly of sexiphenyl-dicarbonitrile on highly oriented pyrolytic graphite and graphene on Cu(111) was studied using scanning tunneling microscopy. The close-packed networks exhibit a peculiar shift every four or five molecules (see figure). This shift is a unique feature induced by the graphitic substrates.

A chemoenzymatic cascade: By combining enzymatic decarboxylation and subsequent diimide-mediated C=C double bond reduction optically pure short-chain 2-methylalkanoic acids are formed (see Scheme). This route exploits the outstanding enantioselectivity and capacity of bacterial arylmalonate mutants to produce both enantiomers in pure form.

Heteroatom-containing metallacycles: New metal-bridged osma-1,3-thiazine derivatives were generated by a formal [4+2] cyclization reaction between osmacyclopentadiene derivatives and isothiocyanates (see scheme).

It takes two: A combined spectroscopy and computational study on engineered iron(IV)-oxo complexes identified a second-coordination sphere effect that enables better positioning of the iron(IV)-oxo and higher reactivity.