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In Situ Labeling and Distance Measurements of Membrane Proteins in E. coli Using Finland and OX063 Trityl Labels

In Situ Labeling and Distance Measurements of Membrane Proteins in E. coli Using Finland and OX063 Trityl Labels

Observing membrane proteins in the cellular environment is a difficult task and PELDOR/DEER spectroscopy is a versatile tool for this purpose. The nitroxide spin labels suffer from poor stability and sensitivity in cellular environments. Trityls are emerging as promising tags for in situ PELDOR/DEER. Here we show that FTAM and OX063 labels provide superior sensitivity and selectivity for distance measurements of membrane proteins in E. coli.

Abstract

In situ investigation of membrane proteins is a challenging task. Previously we demonstrated that nitroxide labels combined with pulsed ESR spectroscopy is a promising tool for this purpose. However, the nitroxide labels suffer from poor stability, high background labeling, and low sensitivity. Here we show that Finland (FTAM) and OX063 based labels enable labeling of the cobalamin transporter BtuB and BamA, the central component of the β‐barrel assembly machinery (BAM) complex, in E coli. Compared to the methanethiosulfonate spin label (MTSL), trityl labels eliminated the background signals and enabled specific in situ labeling of the proteins with high efficiency. The OX063 labels show a long phase memory time (TM) of ≈5 μs. All the trityls enabled distance measurements between BtuB and an orthogonally labeled substrate with high selectivity and sensitivity down to a few μm concentration. Our data corroborate the BtuB and BamA conformations in the cellular environment of E. coli.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Sophie Ketter, Aathira Gopinath, Olga Rogozhnikova, Dmitrii Trukhin, Victor M. Tormyshev, Elena G. Bagryanskaya, Benesh Joseph
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004606

A Xanthene‐Based Mono‐Anionic PON Ligand: Exploiting a Bulky, Electronically Unsymmetrical Donor in Main Group Chemistry

A Xanthene‐Based Mono‐Anionic PON Ligand: Exploiting a Bulky, Electronically Unsymmetrical Donor in Main Group Chemistry

The application of a sterically demanding mono‐anionic PON ligand in gallium chemistry has been probed, revealing a highly unsymmetrical donor profile towards GaI and structural features reminiscent of one‐coordinate gallium amides. Oxidation at the metal leads to a marked increase in the donor capabilities of the phosphine donor, although the transient gallanone formed by O‐atom transfer still undergoes facile C−H activation across the Ga−O bond.

Abstract

The synthesis of a novel mono‐anionic phosphino‐amide ligand based on a xanthene backbone is reported, togetherr with the corresponding GaI complex, (PON)Ga (PON = 4‐(di(2,4,6‐trimethylphenyl)phosphino)‐5‐(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene). The solid‐state structure of (PON)Ga (obtained from X‐ray crystallography) reveals very weak O⋅⋅⋅Ga and P⋅⋅⋅Ga interactions, consistent with a R2NGa fragment which closely resembles those found in one‐coordinate amidogallium systems. Strong N‐to‐Ga π donation from the amido substituent is reflected in a very short N−Ga distance (1.961(2) Å), while the P⋅⋅⋅Ga contact (3.076(1) Å) is well outside the sum of the respective covalent radii. While the donor properties of the PON ligand towards GaI are highly unsymmetrical, oxidation to GaIII leads to much stronger coordination of the pendant phosphine as shown by P−Ga distances which are up to 20 % shorter. From a steric perspective, the PON ligand is shown to be significantly bulkier than related β‐diketiminate systems, a finding consistent with reactions of (PON)Ga towards O‐atom sources that proceed without oligomerization. Despite this, the enhanced P‐donor properties brought about by oxidation at gallium are not sufficient to quench the reactivity of the highly polar Ga−O unit. Instead, intramolecular benzylic C−H activation is observed across the Ga−O bond of a transient gallanone intermediate.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Xiongfei Zheng, Andreas Heilmann, Caitilín McManus, Simon Aldridge
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004741

Chemical and Genetic Studies on the Formation of Pyrrolones During the Biosynthesis of Cytochalasans

Chemical and Genetic Studies on the Formation of Pyrrolones During the Biosynthesis of Cytochalasans

Curiouser and curiouser: The long‐proposed intermediacy of 1,5‐dihydro pyrrol‐2‐ones, which are required during cytochlasan biosynthesis, is called into question. An enzyme involved in this formal Knoevenagel step (PyiE) is identified and a potential mechanism suggested.

Abstract

A key step during the biosynthesis of cytochalasans is a proposed Knoevenagel condensation to form the pyrrolone core, enabling the subsequent 4+2 cycloaddition reaction that results in the characteristic octahydroisoindolone motif of all cytochalasans. In this work, we investigate the role of the highly conserved α,β‐hydrolase enzymes PyiE and ORFZ during the biosynthesis of pyrichalasin H and the ACE1 metabolite, respectively, using gene knockout and complementation techniques. Using synthetic aldehyde models we demonstrate that the Knoevenagel condensation proceeds spontaneously but results in the 1,3‐dihydro‐2H‐pyrrol‐2‐one tautomer, rather than the required 1,5‐dihydro‐2H‐pyrrol‐2‐one tautomer. Taken together our results suggest that the α,β‐hydrolase enzymes are essential for first ring cyclisation, but the precise nature of the intermediates remains to be determined.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Haili Zhang, Verena Hantke, Pia Bruhnke, Elizabeth J. Skellam, Russell J. Cox
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004444

The Reactivity of Isomeric Nitrenium Lewis Acids with Phosphines, Carbenes, and Phosphide

The Reactivity of Isomeric Nitrenium Lewis Acids with Phosphines, Carbenes, and Phosphide

Isomers of nitrenium cations [C6H4N2(tBu)C(C12H8)][BF4], 1 and 2, react with carbenes and phosphines and phosphide. Small donors form N‐bound Lewis adducts. Larger donors attack at the aryl carbon para‐to N, where phosphines induces proton migration ring opening the N2C3 ring, while carbene prompt loss of H. affording radical cation salts. Reactions of 1 and 2 with KPPh2 effects electron transfer affording (PPh2)2 and persistent radical products.

Abstract

Alkylation of spiro[fluorene‐9,3’‐indazole] at N(1) and N(2) with tBuCl affords the nitrenium cations [C6H4N2(tBu)C(C12H8)][BF4], 1 and 2, respectively. Compound 1 converts to 2 over the temperature range 303–323 K with a free energy barrier of 28±5 kcal mol−1. Reaction of 1 with PMe3 afforded the N‐bound phosphine adduct [C6H4N(tBu)N(PMe3)C(C12H8)]BF4] 3. However, phosphines attack 2 at the para‐carbon atom of the aryl group with concurrent cleavage of N(2)−C(1) bond and proton migration to C(1) affording [(R3P)C6H3NN(tBu)CH(C12H8)][BF4] (R=Me 4, nBu 5). Analogous reactions of 1 and 2 with the carbene SIMes prompt attack at the para‐carbon with concurrent loss of H. affording the radical cation salts [(SIMes)C6H3N(tBu)NC(C12H8).][BF4] 6 and [(SIMes)C6H3NN(tBu)C(C12H8).][BF4] 7, whereas reaction of 2 with BAC gives the Lewis acid‐base adduct, [C6H4N(BAC)N(tBu)C(C12H8)][BF4] 8. Finally, reactions of 1 and 2 with KPPh2 result in electron transfer affording (PPh2)2 and the persistent radicals C6H4N(tBu)NC(C12H8). and C6H4NN(tBu)C(C12H8).. The detailed reaction mechanisms are also explored by extensive DFT calculations.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Diya Zhu, Zheng‐Wang Qu, Jiliang Zhou, Douglas W. Stephan
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004798

[2]Catenane Synthesis via Covalent Templating

[2]Catenane Synthesis via Covalent Templating

A covalent template strategy for the synthesis of mechanically interlocked molecules has been successfully employed to give a [2]catenane. This approach results in a [2]catenane devoid of supramolecular recognition sites. An inverted spiro intermediate is formed due to the action of a covalent template, which enforces an otherwise unfavorable macrocyclization. The trapped thread could be clipped into a second macrocycle giving a precatenane and, upon cleavage of the covalent templating linkages, the [2]catenane architecture.

Abstract

After earlier unsuccessful attempts, this work reports the application of covalent templating for the synthesis of mechanically interlocked molecules (MiMs) bearing no supramolecular recognition sites. Two linear strands were covalently connected in a perpendicular fashion by a central ketal linkage. After subsequent attachment of the first strand to a template via temporary benzylic linkages, the second was linked to the template in a backfolding macrocyclization. The resulting pseudo[1]rotaxane structure was successfully converted to a [2]catenane via a second macrocyclization and cleavage of the ketal and temporary linkages.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Simone Pilon, Steen Ingemann Jørgensen, Jan H. Maarseveen
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004925

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2Ti3O7 in Na‐Ion Batteries

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2Ti3O7 in Na‐Ion Batteries

A safe, controllable and affordable method using urea at mild temperatures to synthesise a series of sodium titanate samples with different levels of oxygen vacancies is reported. The formation of oxygen vacancies leads to the reduction of Ti4+ to Ti3+ ions in NTO, together with the formation of hydroxyl groups and a secondary phase, Na2Ti6O13.The urea‐treated samples showed superior electrochemical performance at high rates with respect to pristine NTO.

Abstract

Na2Ti3O7 (NTO) is considered a promising anode material for Na‐ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na+/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na2Ti6O13. The enhanced electrochemical performance agrees with the higher Na+ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Sara I. R. Costa, Yong‐Seok Choi, Alistair J. Fielding, Andrew J. Naylor, John M. Griffin, Zdeněk Sofer, David O. Scanlon, Nuria Tapia‐Ruiz
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003129

Filling the Gap in the Metallacrown Family: The 9‐MC‐3 Chromium Metallacrown

Filling the Gap in the Metallacrown Family: The 9‐MC‐3 Chromium Metallacrown

Metalacycles: In this work, we report on the synthesis and characterization of the long sought chromium metallacrown (MC) complex {CrIII(μ2‐piv)3[9‐MCCr(III)N(shi)‐3](morph)3}MeOH. The MC with a 9‐MC‐3 cavity of kinetically inert chromium(III) ions was finally successful synthesized by a solvothermal reaction (see figure).

Abstract

In this work, we report on a long‐sought missing complex in the metallacrown family. We synthesized and characterized the novel chromium metallacrown (MC) complex {CrIII(μ2‐piv)3[9‐MCCr(III)N(shi)‐3](morph)3}MeOH (in which shi3−=salicyl hydroxamate, piv=pivalate, and morph=morpholine). The MC with a 9‐MC‐3 cavity of kinetically inert chromium(III) ions was synthesized by a solvothermal reaction. Magnetization measurements reveal a high spin ground state.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Anne Lüpke, Luca M. Carrella, Eva Rentschler
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004947

Similarities and Differences between Crystal and Enzyme Environmental Effects on the Electron Density of Drug Molecules

Similarities and Differences between Crystal and Enzyme Environmental Effects on the Electron Density of Drug Molecules

The polarization of a drug molecule in an enzyme environment can be approximated by the polarization of the same molecule in its small‐molecule crystal structure. The degree of similarity is quantified in this study for a model compound of the protease inhibitor loxistatin acid in its interaction with cathepsin B by using interaction densities and interaction electrostatic potentials.

Abstract

The crystal interaction density is generally assumed to be a suitable measure of the polarization of a low‐molecular weight ligand inside an enzyme, but this approximation has seldomly been tested and has never been quantified before. In this study, we compare the crystal interaction density and the interaction electrostatic potential for a model compound of loxistatin acid (E64c) with those inside cathepsin B, in solution, and in vacuum. We apply QM/MM calculations and experimental quantum crystallography to show that the crystal interaction density is indeed very similar to the enzyme interaction density. Less than 0.1 e are shifted between these two environments in total. However, this difference has non‐negligible consequences for derived properties.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Florian Kleemiss, Erna K. Wieduwilt, Emanuel Hupf, Ming W. Shi, Scott G. Stewart, Dylan Jayatilaka, Michael J. Turner, Kunihisa Sugimoto, Eiji Nishibori, Tanja Schirmeister, Thomas C. Schmidt, Bernd Engels, Simon Grabowsky
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003978

A Fast and General Route to Ketones from Amides and Organolithium Compounds under Aerobic Conditions: Synthetic and Mechanistic Aspects

A Fast and General Route to Ketones from Amides and Organolithium Compounds under Aerobic Conditions: Synthetic and Mechanistic Aspects

SNAc with organolithiums under air: Aliphatic and (hetero)aromatic ketones are quickly (20 s reaction time) obtained in up to 93 % yield in a straightforward and chemoselective manner and with a broad substrate scope by reacting organolithium reagents with a variety of amides at ambient temperature under air in the environmentally friendly cyclopentyl methyl ether (CPME). Gram‐scale preparations and recyclability of the reagents are also successfully demonstrated.

Abstract

We report that the nucleophilic acyl substitution reaction of aliphatic and (hetero)aromatic amides by organolithium reagents proceeds quickly (20 s reaction time), efficiently, and chemoselectively with a broad substrate scope in the environmentally responsible cyclopentyl methyl ether, at ambient temperature and under air, to provide ketones in up to 93 % yield with an effective suppression of the notorious over‐addition reaction. Detailed DFT calculations and NMR investigations support the experimental results. The described methodology was proven to be amenable to scale‐up and recyclability protocols. Contrasting classical procedures carried out under inert atmospheres, this work lays the foundation for a profound paradigm shift of the reactivity of carboxylic acid amides with organolithiums, with ketones being straightforwardly obtained by simply combining the reagents under aerobic conditions and with no need of using previously modified or pre‐activated amides, as recommended.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Simone Ghinato, Davide Territo, Andrea Maranzana, Vito Capriati, Marco Blangetti, Cristina Prandi
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004840

The Aggregation Pattern of Aβ1–40 is Altered by the Presence of N‐Truncated Aβ4–40 and/or CuII in a Similar Way through Ionic Interactions

The Aggregation Pattern of Aβ1–40 is Altered by the Presence of N‐Truncated Aβ4–40 and/or CuII in a Similar Way through Ionic Interactions

Converging mechanisms: The similar effect of Aβ4–40 and substoichiometric CuII on the kinetic parameters of Aβ1–40 aggregation and fibril morphology correlates with the increased positive charge at the Aβ N terminus induced by CuII complexation or N truncation at position 4, thus providing a unifying mechanistic concept for the biological aggregation of coexisting Aβ species (see figure).

Abstract

Alzheimer’s disease (AD) is one of the most common of the multifactorial diseases and is characterized by a range of abnormal molecular processes, such as the accumulation of extracellular plaques containing the amyloid‐β (Aβ) peptides and dyshomeostasis of copper in the brain. In this study, we have investigated the effect of CuII on the aggregation of Aβ1–40 and Aβ4–40, representing the two most prevalent families of Aβ peptides, that is, the full length and N‐truncated peptides. Both families are similarly abundant in healthy and AD brains. For either of the studied peptides, substoichiometric CuII concentrations accelerated aggregation, whereas superstoichiometric CuII inhibited fibril formation, likely by stabilizing the oligomers. The addition of either Aβ4–40 or substoichiometric CuII affected the aggregation profile of Aβ1–40, by yielding shorter and thicker fibrils; amorphous aggregates were formed in the presence of a molar excess of CuII. The similarity of these two effects can be attributed to the increase in the positive charge on the Aβ N terminus, caused both by CuII complexation and N truncation at position 4. Our findings provide a better understanding of the biological Aβ aggregation process as these two Aβ species and CuII coexist and interact under physiological conditions.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Ewelina Stefaniak, Elena Atrian‐Blasco, Wojciech Goch, Laurent Sabater, Christelle Hureau, Wojciech Bal
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004484

Mimicking Photosystem I with a Transmembrane Light Harvester and Energy Transfer‐Induced Photoreduction in Phospholipid Bilayers

Mimicking Photosystem I with a Transmembrane Light Harvester and Energy Transfer‐Induced Photoreduction in Phospholipid Bilayers

A transmembrane dye and an energy accepting dye were implemented in lipid bilayers of liposomes and giant vesicles. Light‐induced energy transfer and transmembrane arrangement can be observed with luminescence spectroscopy, dynamic light scattering and confocal microscopy, supported by time‐dependent DFT calculations and molecular dynamics simulation. More information can be found in the Full Paper by A. Pannwitz, S. Bonnet, et al. (DOI: 10.1002/chem.202003391).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Andrea Pannwitz, Holden Saaring, Nataliia Beztsinna, Xinmeng Li, Maxime A. Siegler, Sylvestre Bonnet
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004122

Iminoboronates as Dual‐Purpose Linkers in Chemical Probe Development

Iminoboronates as Dual‐Purpose Linkers in Chemical Probe Development

Iminoboronate chemistry enables the synthesis of chemical probes that selectively label proteins of interest from 2‐formylphenylboronic acid reactive groups and hydrazide‐functionalized ligands. The reversibility of the iminoboronate linkage is exploited to detect the labeled proteins by ligand‐fluorophore exchange. Remarkably, the fast iminoboronate chemistry even allows probe formation within protein mixtures.

Abstract

Chemical probes that covalently modify proteins of interest are powerful tools for the research of biological processes. Important in the design of a probe is the choice of reactive group that forms the covalent bond, as it decides the success of a probe. However, choosing the right reactive group is not a simple feat and methodologies for expedient screening of different groups are needed. We herein report a modular approach that allows easy coupling of a reactive group to a ligand. α‐Nucleophile ligands are combined with 2‐formylphenylboronic acid derived reactive groups to form iminoboronate probes that selectively label their target proteins. A transimination reaction on the labeled proteins with an α‐amino hydrazide provides further modification, for example to introduce a fluorophore.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Antonie J. Zouwen, Aike Jeucken, Roy Steneker, Katharina F. Hohmann, Jonas Lohse, Dirk J. Slotboom, Martin D. Witte
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005115

Direct Trifluoromethylation of Alcohols Using a Hypervalent Iodosulfoximine Reagent

Direct Trifluoromethylation of Alcohols Using a Hypervalent Iodosulfoximine Reagent

Trilfuoromethylethers made easy! An operationally simple method using the new hypervalent iodosulfoximine reagent alongside minimal amounts of a zinc catalyst gives access to a variety of different trifluoromethylethers, in under 2 h for most cases.

Abstract

The direct trifluoromethylation of a variety of aliphatic alcohols using a hypervalent iodosulfoximine reagent afforded the corresponding ethers in moderate to good yields (14–72 %). Primary, secondary, and even tertiary alcohols, including examples derived from natural products, underwent this transformation in the presence of catalytic amounts of zinc bis(triflimide). Typical reaction conditions involved a neat mixture of 6.0 equivalents of the alcohol with 1.0 equivalent of the reagent, with the majority of reactions complete within 2 h with 2.5 mol % of the Lewis acid catalyst. Furthermore, experimental evidence was provided that the C−O bond‐forming process occurred via the coordination of the alcohol to the iodine atom and subsequent reductive elimination.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Jorna Kalim, Thibaut Duhail, Ewa Pietrasiak, Elsa Anselmi, Emmanuel Magnier, Antonio Togni
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005104

Simple Synthesis of a Heterocyclophane Exhibiting Anti‐c‐Met Activity by Acting as a Hatch Blocking Access to the Active Site

Simple Synthesis of a Heterocyclophane Exhibiting Anti‐c‐Met Activity by Acting as a Hatch Blocking Access to the Active Site

Rapidly synthesis of suitable drug candidates using both a simple cyclophane synthesis and the fragmap method of SILCS in computational chemistry is reported in this work. The cover image depicts cyclophane synthesis using a waffle‐making device so that it is easy to imagine that cyclophane derivatives can be quickly synthesized by heat. More information can be found in the Full Paper by H. Sasaki et al. (DOI: 10.1002/chem.202001382).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Tatsuya Takimoto, Hideaki Sasaki, Hirohito Tsue, Hiroki Takahashi, Alexander D. MacKerell, Ayumi Nakamura, Katsuya Nakano, Eori Okazaki, Tatsuki Betsuyaku, Ryosuke Tachibana, Kazuhito Hioki, Ozge Yoluk, Sunhwan Jo
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004973

Self‐Assembled FeSe2 Microspheres with High‐Rate Capability and Long‐Term Stability as Anode Material for Sodium‐ and Potassium‐Ion Batteries

Self‐Assembled FeSe2 Microspheres with High‐Rate Capability and Long‐Term Stability as Anode Material for Sodium‐ and Potassium‐Ion Batteries

Microsphere anode materials: Self‐assembled FeSe2 microspheres are synthesized through a facile solvothermal method. The FeSe2 microspheres exhibit superior rate performance and long cycle stability in both sodium‐ and potassium‐ion batteries.

Abstract

Sodium‐ and potassium‐ion batteries have attracted intensive attention recently as low‐cost alternatives to lithium‐ion batteries with naturally abundant resources. However, the large ionic radii of Na+ and K+ render their slow mobility, leading to sluggish diffusion in host materials. Herein, hierarchical FeSe2 microspheres assembled by closely packed nano/microrods are rationally designed and synthesized through a facile solvothermal method. Without carbonaceous material incorporation, the electrode delivers a reversible Na+ storage capacity of 559 mA h g−1 at a current rate of 0.1 A g−1 and a remarkable rate performance with a capacity of 525 mA h g−1 at 20 A g−1. As for K+ storage, the FeSe2 anode delivers a high reversible capacity of 393 mA h g−1 at 0.4 A g−1. Even at a high current rate of 5 A g−1, a discharge capacity of 322 mA h g−1 can be achieved, which is among the best high‐rate anodes for K+ storage. The excellent electrochemical performance can be attributed to the favorable morphological structure and the use of an ether‐based electrolyte during cycling. Moreover, quantitative study suggests a strong pseudocapacitive contribution, which boosts fast kinetics and interfacial storage.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Wen Xin, Nan Chen, Zhixuan Wei, Chunzhong Wang, Gang Chen, Fei Du
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004069

Stuffed Tridymite Structures: Synthesis, Structure, Second Harmonic Generation, Optical, and Multiferroic Properties

Stuffed Tridymite Structures: Synthesis, Structure, Second Harmonic Generation, Optical, and Multiferroic Properties

Getting stuffed: New members of the stuffed tridymite structure, Ba(Zn/Co)1−xSi1−xM2xO4 (M=Al3+ and Fe3+), are studied for multiferroic behavior and inorganic colored materials. The compounds were second harmonic generation (SHG) active and exhibit moderate ferroelectric behavior. The co‐substitution of Co2+ and Fe3+ in the structure gives rise to a weak ferromagnetic behavior. The presence of transition metal elements in these oxides gives rise to brilliantly colored materials, rendering them attractive candidates for new inorganic pigments.

Abstract

The stuffed tridymite structure Ba(Zn/Co)1−xSi1−xM2xO4 (M=Al3+ and Fe3+) is explored for the possible multiferroic behavior and to develop new inorganic colored materials. The compounds were synthesized by employing conventional solid‐state chemistry methods in the temperature range 1100–1175 °C for 24 h. The powder X‐ray diffraction (PXRD) and Rietveld refinement studies indicate that the compounds stabilize in the P63 space group (no. 173). The refinement results were also rationalized by employing Raman spectroscopic studies. The compounds were found to be second harmonic generation (SHG) active and show weak ferroelectric behavior. The co‐substitution of Co2+ and Fe3+ in the structure gives rise to a weak ferromagnetic behavior to the compound, BaCo0.75Si0.75Fe0.5O4, making it a multiferroic material. The optical studies on the prepared compounds exhibited blue color (Co2+ in Td geometry), purple color (Ni2+ in Td geometry), and simultaneous substitution of Co2+ and Fe3+ gives rise to blue‐green color owing to metal‐to‐metal charge transfer (MMCT) effect.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Anupam Bhim, Jean‐Pascal Sutter, Jagannatha Gopalakrishnan, Srinivasan Natarajan
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004078

A Local D4h Symmetric Dysprosium(III) Single‐Molecule Magnet with an Energy Barrier Exceeding 2000 K**

A Local D4h Symmetric Dysprosium(III) Single‐Molecule Magnet with an Energy Barrier Exceeding 2000 K**

Building single‐molecule magnets: A compressed octahedral dysprosium(III) single‐molecule magnet with local D4h symmetry exhibits an energy barrier over 2000 K.

Abstract

Three six‐coordinate DyIII single‐molecule magnets (SMMs) [Dy(OtBu)2(L)4]+ with local D4h symmetry are obtained by optimizing the equatorial ligands. One of the compounds with L=4‐phenylpyridine shows an energy barrier (Ueff) of 2075(11) K, which is the third largest Ueff, and the first Ueff>2000 K for SMMs with axial‐type symmetry so far. Ab initio analysis indicates that the exceptional uniaxial magnetic anisotropy is deeply related to the axially compressed octahedral geometry. This work provides a new insight into the local D4h symmetry for high‐performance SMMs.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Xia‐Li Ding, Yuan‐Qi Zhai, Tian Han, Wei‐Peng Chen, You‐Song Ding, Yan‐Zhen Zheng
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003931

Synthesis of Unprecedented 4d/4f‐Polypnictogens

Synthesis of Unprecedented 4d/4f‐Polypnictogens

Ring up: By reduction of [{CptMo(CO)2}2(μ,η2:2‐E2)] (E=As, Sb; Cpt=tBu substituted cyclopentadienyl) with different samarocenes, new d/f‐polyarsenides and unprecedented 4d/4f‐polypnictogens were obtained. The latter feature for the first time a planar Sb4‐ring, which shows a rare analogy to cyclobutadiene, as ligand in organometallic chemistry.

Abstract

A series of 4d/4f‐polyarsenides, ‐polyarsines and ‐polystibines was obtained by reduction of the Mo‐pnictide precursor complexes [{CptMo(CO)2}2(μ,η2:2‐E2)] (E=As, Sb; Cpt=tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*2Sm] and [(CpMe4nPr)2Sm]. For the reductive conversion of the Mo‐stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo‐arsenide a tetraarsacyclobutadiene and a second species with a side‐on coordinated As22− anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Niklas Reinfandt, Christoph Schoo, Luis Dütsch, Ralf Köppe, Sergey N. Konchenko, Manfred Scheer, Peter W. Roesky
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003905

Iron Coordination Properties of Gramibactin as Model for the New Class of Diazeniumdiolate Based Siderophores

Iron Coordination Properties of Gramibactin as Model for the New Class of Diazeniumdiolate Based Siderophores

The sequestration properties of gramibactin as a prototype for the new class of diazeniumdiolate siderophores is presented and compared with siderophores derived from catecholates and hydroxamates. According to pFe and pL0.5 values, gramibactin is a considerably more potent sequestering agent than the known class of phytosiderophores and approximately reaches the ability of typical hydroxamates like desferrioxamines.

Abstract

Gramibactin (GBT) is an archetype for the new class of diazeniumdiolate siderophores, produced by Paraburkholderia graminis, a cereal‐associated rhizosphere bacterium, for which a detailed solution thermodynamic study exploring the iron coordination properties is reported. The acid‐base behavior of gramibactin as well as its complexing ability toward Fe3+ was studied over a wide range of pH values (2≤pH≤11). For the latter the ligand‐competition method employing EDTA was used. Only two species are formed: [Fe(GBT)] (pH 2 to 9) and [Fe(GBT)(OH)2]3− (pH≥9). The formation of [Fe(GBT)] and its occurrence in real systems was confirmed by LC‐HRESIMS analysis of the bacteria culture broth extract. The sequestering ability of gramibactin was also evaluated in terms of the parameters pFe and pL0.5. Gramibactin exhibits a higher sequestering ability toward Fe3+ than EDTA and of the same order of magnitude as hydroxamate‐type microbial siderophores, but smaller than most of the catecholate‐type siderophores and much higher than the most known phytosiderophores.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Sofia Gama, Ron Hermenau, Mariachiara Frontauria, Demetrio Milea, Silvio Sammartano, Christian Hertweck, Winfried Plass
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003842

Synthesis of Unprecedented 4 d/4 f‐Polypnictogens

Synthesis of Unprecedented 4 d/4 f‐Polypnictogens

A kind of “street art lab‐journal” on a graffiti wall is depicted in the cover image. The left side shows a table where the already obtained d/f‐polypnictides (P, As) are ticked, while Sb is still marked as an unsolved task. According to this, the right side shows the reaction equation, which represents the pathway to the solution of the task and finally the resulting, artistically highlighted, compound. On the bottom you can see the ′spray cans of the elements′, which are required for this compound. More information can be found in the Communication by P. W. Roesky et al. (DOI: 10.1002/chem.202003905).

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Niklas Reinfandt, Christoph Schoo, Luis Dütsch, Ralf Köppe, Sergey N. Konchenko, Manfred Scheer, Peter W. Roesky
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005347

A Domino Fusion of an Organic Ligand Depended on Metal‐Induced and Oxygen Insertion, Unraveled by Crystallography, Mass Spectrometry, and DFT Calculations

A Domino Fusion of an Organic Ligand Depended on Metal‐Induced and Oxygen Insertion, Unraveled by Crystallography, Mass Spectrometry, and DFT Calculations

Dominoes under investigation: Tandem application of crystallography and mass spectrometry unraveled a competitive in situ domino solvothermal reaction to tetrabenzimidazol‐pyrazine within [Co2(3)Cl4] in seven steps and to a deprotonated imide anion L2′′ within 1D chain ([Co1.5(L2′′)]n) in six steps.

Abstract

Herein, the reaction of (1‐methyl‐1 H‐benzo[d]imidazol‐2‐yl)methanamine (L1) with Co(H2O)6Cl2, in CH3CN at 120 °C, leading to the 2,3,5,6‐tetrakis(1‐methyl‐1 H‐benzo[d]imidazol‐2‐yl)pyrazine (3), isolated as a dimeric cluster {[CoII2(3)Cl4]2 CH3CN} (2), is reported. When O2 and H2O are present, (1‐methyl‐1 H‐benzo[d]imidazole‐2‐carbonyl)amide (HL1′) is first formed and crystallized as [CoIII(L1)2(L1′)]Cl22 H2O (4) before fusion of HL1′ with L1, giving 1‐methyl‐N‐(1‐methyl‐1 H‐benzo[d]imidazol‐2‐carbonyl)‐1 H‐benzo[d]imidazol‐2‐carboxamide (HL2′′) forming a one‐dimensional (1D) chain of [CoII3(L2′′)2Cl4]n (5). The combination of crystallography and mass spectrometry (ESI‐MS) of isolated crystals and the solutions taken from the reaction as a function time reveal seven intermediate steps leading to 2, but six steps for 5, for which a different sequence takes place. Control and isotope labeling experiments confirm the two carbonyl oxygen atoms in 5 originate from both air and water. The dependence on the metals, compared with FeCl36 H2O leading to a stable triheteroarylmethyl radical, is quite astounding, which could be attributed to the different oxidation states of the metals and coordination modes confirmed by DFT calculations. This metal and valence dependent process is a very useful way for selectively obtaining these large molecules, which are unachievable by common organic synthesis.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Jin‐Ming Chen, Liang Peng, Fu‐Fang Zhou, Bin Liu, Cheng Hou, Jia‐Wei Li, Zhou Huang, Mohamedally Kurmoo, Ming‐Hua Zeng
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004396

Design Approach of Lifetime Extending Thermally Activated Delayed Fluorescence Sensitizers for Highly Efficient Fluorescence Devices

Design Approach of Lifetime Extending Thermally Activated Delayed Fluorescence Sensitizers for Highly Efficient Fluorescence Devices

Efficient TADF sensitizer: Three thermally activated delayed fluorescence (TADF) materials having fast reverse intersystem crossing rate were developed for TADF sensitizer. Among these, two TADF materials include tert‐butyl blocking group to manage the Dexter energy transfer. TADF sensitized fluorescent devices with blocking groups show high maximum external quantum efficiencies. In addition, the device operational lifetime is extended by adding blocking groups.

Abstract

In this work, a design approach of three thermally activated delayed fluorescence (TADF) emitters to extend the device lifetime of the TADF sensitized fluorescent devices was studied. Three TADF materials, 5‐{4,6‐bis[4‐(tert‐butyl)phenyl]‐1,3,5‐triazin‐2‐yl}‐2‐(10,15‐diphenyl‐10,15‐dihydro‐5H‐diindolo[3,2‐a:3′,2′‐c]carbazol‐5‐yl)benzonitrile (tTCNTruX), 4‐[3‐cyano‐4‐(10,15‐diphenyl‐10,15‐dihydro‐5H‐diindolo[3,2‐a:3′,2′‐c]carbazol‐5‐yl)phenyl]‐2,6‐diphenylpyrimidine‐5‐carbonitrile (PCNTruX) and 4‐(4‐{10,15‐bis[4‐(tert‐butyl)phenyl]‐10,15‐dihydro‐5H‐diindolo[3,2‐a:3′,2′‐c]carbazol‐5‐yl}‐3‐cyanophenyl)‐2,6‐diphenylpyrimidine‐5‐carbonitrile (PCNtTruX), were synthesized as sensitizers for TADF‐sensitized fluorescent organic light‐emitting diodes. The two tTCNTruX and PCNtTruX TADF emitters were designed to have Dexter energy transfer with blocking groups either in the donor or acceptor unit of the donor–acceptor‐type TADF sensitizer. The TADF materials showed small singlet–triplet energy splitting and a high reverse intersystem crossing (RISC) rate for effective sensitization of the fluorescent emission of the fluorescent emitter. tTCNTruX‐ and PCNtTruX‐sensitized fluorescent devices showed maximum external quantum efficiencies (EQEs) of 17.7 % and 11.5 % in the yellow and red devices, respectively, which were higher than those of TADF‐sensitized devices with the corresponding TADF sensitizer without a blocking group. Moreover, the device lifetime was also extended by employing the tTCNTruX and PCNtTruX sensitizers. This work demonstrated that the tTCNTruX and PCNtTruX sensitizers are effective to improve the maximum EQE and device lifetime of TADF‐sensitized fluorescent devices.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Sung Joon Yoon, Ji Han Kim, Won Jae Chung, Jun Yeob Lee
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004042

Lanthanoid Complexes as Molecular Materials: The Redox Approach

Lanthanoid Complexes as Molecular Materials: The Redox Approach

The redox‐activity of lanthanoid complexes can arise from metal, ligand or rarely, both components. Harnessing the synergy between metal and ligand redox‐activity will ultimately facilitate the development of new molecular materials with novel and enhanced functionality.

Abstract

The development of molecular materials with novel functionality offers promise for technological innovation. Switchable molecules that incorporate redox‐active components are enticing candidate compounds due to their potential for electronic manipulation. Lanthanoid metals are most prevalent in their trivalent state and usually redox‐activity in lanthanoid complexes is restricted to the ligand. The unique electronic and physical properties of lanthanoid ions have been exploited for various applications, including in magnetic and luminescent materials as well as in catalysis. Lanthanoid complexes are also promising for applications reliant on switchability, where the physical properties can be modulated by varying the oxidation state of a coordinated ligand. Lanthanoid‐based redox activity is also possible, encompassing both divalent and tetravalent metal oxidation states. Thus, utilization of redox‐active lanthanoid metals offers an attractive opportunity to further expand the capabilities of molecular materials. This review surveys both ligand and lanthanoid centered redox‐activity in pre‐existing molecular systems, including tuning of lanthanoid magnetic and photophysical properties by modulating the redox states of coordinated ligands. Ultimately the combination of redox‐activity at both ligands and metal centers in the same molecule can afford novel electronic structures and physical properties, including multiconfigurational electronic states and valence tautomerism. Further targeted exploration of these features is clearly warranted, both to enhance understanding of the underlying fundamental chemistry, and for the generation of a potentially important new class of molecular material.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Moya A. Hay, Colette Boskovic
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003761

Evaluation of the DNA Alkylation Properties of a Chlorambucil‐Conjugated Cyclic Pyrrole‐Imidazole Polyamide

Evaluation of the DNA Alkylation Properties of a Chlorambucil‐Conjugated Cyclic Pyrrole‐Imidazole Polyamide

Targeted alkylation: The DNA alkylation properties of a cyclic pyrrole‐imidazole polyamide that was conjugated with the DNA‐alkylator chlorambucil are reported. The conjugate shows good alkylation ability in vitro and anticancer effects against cancer cells.

Abstract

Hairpin pyrrole‐imidazole polyamides (hPIPs) and their chlorambucil (Chb) conjugates (hPIP‐Chbs) can alkylate DNA in a sequence‐specific manner, and have been studied as anticancer drugs. Here, we conjugated Chb to a cyclic PIP (cPIP), which is known to have a higher binding affinity than the corresponding hPIP, and investigated the DNA alkylation properties of the resulting cPIP‐Chb using the optimized capillary electrophoresis method and conventional HPLC product analysis. cPIP‐Chb conjugate 3 showed higher alkylation activity at its binding sites than did hPIP‐Chb conjugates 1 and 2. Subsequent HPLC analysis revealed that the alkylation site of conjugate 3, which was identified by capillary electrophoresis, was reliable and that conjugate 3 alkylates the N3 position of adenine as do hPIP‐Chbs. Moreover, conjugate 3 showed higher cytotoxicity against LNCaP prostate cancer cells than did conjugate 1 and cytotoxicity comparable to that of conjugate 2. These results suggest that cPIP‐Chbs could be novel DNA alkylating anticancer drugs.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Yuki Hirose, Kaori Hashiya, Toshikazu Bando, Hiroshi Sugiyama
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004421

Rational Design of High‐Relaxivity EuII‐Based Contrast Agents for Magnetic Resonance Imaging of Low‐Oxygen Environments

Rational Design of High‐Relaxivity EuII‐Based Contrast Agents for Magnetic Resonance Imaging of Low‐Oxygen Environments

Rigid, but relaxed: EuII‐containing complexes have potential use as responsive imaging agents for hypoxia. A rigid, dimetallic EuII‐containing cryptate was investigated as a high‐efficiency contrast agent for magnetic resonance imaging. NMR dispersion studies indicate that this agent exhibits higher relaxometric efficiency than either a flexible dimetallic agent or analogous small‐molecule agents.

Abstract

Metal‐based contrast agents for magnetic resonance imaging present a promising avenue to image hypoxia. EuII‐based contrast agents have a unique biologically relevant redox couple, EuII/III, that distinguishes this metal for use in hypoxia imaging. To that end, we investigated a strategy to enhance the contrast‐enhancing capabilities of EuII‐based cryptates in magnetic resonance imaging by controlling the rotational dynamics. Two dimetallic, EuII‐containing cryptates were synthesized to test the efficacy of rigid versus flexible coupling strategies. A flexible strategy to dimerization led to a modest (114 %) increase in contrast enhancement per Eu ion (60 MHz, 298 K), but a rigid linking strategy led to an excellent (186 %) increase in contrast enhancement despite this compound′s having the smaller molecular mass of the two dimetallic complexes. We envision the rigid linking strategy to be useful in the future design of potent EuII‐based contrast agents for magnetic resonance imaging.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Matthew D. Bailey, Guo‐Xia Jin, Fabio Carniato, Mauro Botta, Matthew J. Allen
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004450