Highly Conductive Anion‐Exchange Membranes from Microporous Tröger's Base Polymers

The development of polymeric anion‐exchange membranes (AEMs) combining high ion conductivity and long‐term stability is a major challenge for materials chemistry. AEMs with regularly distributed fixed cationic groups, based on the formation of microporous polymers containing the V‐shape rigid Tröger's base units, are reported for the first time. Despite their simple preparation, which involves only two synthetic steps using commercially available precursors, the polymers provide AEMs with exceptional hydroxide conductivity at relatively low ion‐exchange capacity, as well as a high swelling resistance and chemical stability. An unprecedented hydroxide conductivity of 164.4 mS cm^?1 is obtained at a relatively a low ion‐exchange capacity of 0.82 mmol g^?1 under optimal operating conditions. The exceptional anion conductivity appears related to the intrinsic microporosity of the charged polymer matrix, which facilitates rapid anion transport.     

Inexpensive Hole‐Transporting Materials Derived from Tröger's Base Afford Efficient and Stable Perovskite Solar Cells

The synthesis of three enamine hole‐transporting materials (HTMs) based on Tröger's base scaffold are reported. These compounds are obtained in a three‐step facile synthesis from commercially available materials without the need of expensive catalysts, inert conditions or time‐consuming purification steps. The best performing material, HTM3, demonstrated 18.62 % PCE in PSCs, rivaling spiro‐OMeTAD in efficiency, and showing markedly superior long‐term stability in non‐encapsulated devices. In dopant‐free PSCs, HTM3 outperformed spiro‐OMeTAD by a factror of 1.6. The high glass‐transition temperature (T_g=176 °C) of HTM3 also suggests promising perspectives in device applications.     

Configurational Lability of Imino‐Substituted Ethano Tröger Bases. Insight on the Racemization Mechanism

Polycyclic indoline‐benzodiazepines are afforded in one step by the reaction of Tröger bases with N‐sulfonyl‐1,2,3‐triazoles under Rh(II) catalysis. After α‐imino carbene formation, the process involves a cascade of [1,2]‐Stevens rearrangement, Friedel‐Crafts, Grob fragmentation, and aminal formation reactions. It is highly diastereoselective (d.r. >49:1, four stereocenters incl. two bridgehead N‐atoms). However and in contrast with other reported carbene additions to these moieties, full racemization occurs when enantiopure Tröger bases are used as substrates. To pinpoint the origin of this unexpected behavior, a key elemental step of the mechanism was evaluated and tested. Interestingly, it is not only the initial ring‐opening but also the latter reversible Mannich reaction of the imino‐substituted ethano Tröger base intermediate that is responsible for the loss of enantiospecificity.     

An Easy and Efficient Synthesis of Bisindolylmethanes and Tetraindolylmethane Tröger's Base Catatlyzed by AgBF4

This work presents a highly efficient and simple method for the synthesis of bisindolylmethanes, catalyzed by AgBF₄, with excellent yields. Various substituted aldehydes and ketones with indole under this reaction condition is elucidated. This reaction occurs efficiently under mild reaction conditions, such as are applied with methoxy or furfural, which commonly undergoes cleavage under strongly acidic reaction conditions. The presented approach was suitable for the synthesis of complex systems, such as tetraindolylmethane Tröger's Base.     

Catalytic Stereoselective 1,4‐Addition Reactions Using CsF on Alumina as a Solid Base: Continuous‐Flow Synthesis of Glutamic Acid Derivatives

A novel methodology using CsF⋅Al₂O₃ as a highly efficient, environmentally benign, and reusable solid‐base catalyst was developed to synthesize glutamic acid derivatives by stereoselective 1,4‐addition of glycine derivatives to α,β‐unsaturated esters. CsF⋅Al₂O₃ showed not only great selectivity toward 1,4‐addtion reactions by suppressing the undesired formation of pyrrolidine derivations by [3+2] cycloadditions, but also offered high yields for the 1,4‐adduct with excellent anti diastereoselectivities. The catalyst was well characterized by using XRD, ¹⁹F MAS‐NMR and ¹⁹F NMR spectroscopy, FT‐IR, CO₂‐TPD, and XPS. And highly basic F from Cs₃AlF₆ was identified as the most probable active basic site for the 1,4‐addition reactions. Continuous‐flow synthesis of 3‐methyl glutamic acid derivative was successfully demonstrated by using this solid‐base catalysis.     

Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations

The influence of segmental chain motion on the gas separation performance of thermally rearranged (TR) polymer membranes is established for TR polybenzoxazoles featuring Tröger's base (TB) monomer subunits as exceptionally rigid sites of contortion along the polymer backbone. These polymers are accessed from solution‐processable ortho‐acetate functionalized polyimides, which are readily synthesized as high‐molecular‐weight polymers for membrane casting. We find that thermal rearrangement leads to a small increase in d‐spacing between polymer chains and a dramatic pore‐network reconfiguration that increases both membrane permeability and O₂/N₂ selectivity, putting its performance above the 2015 upper bound.     

Ion‐Mobility Spectrometry Can Assign Exact Fucosyl Positions in Glycans and Prevent Misinterpretation of Mass‐Spectrometry Data After Gas‐Phase Rearrangement

The fucosylation of glycans leads to diverse structures and is associated with many biological and disease processes. The exact determination of fucoside positions by tandem mass spectrometry (MS/MS) is complicated because rearrangements in the gas phase lead to erroneous structural assignments. Here, we demonstrate that the combined use of ion‐mobility MS and well‐defined synthetic glycan standards can prevent misinterpretation of MS/MS spectra and incorrect structural assignments of fucosylated glycans. We show that fucosyl residues do not migrate to hydroxyl groups but to acetamido moieties of N‐acetylneuraminic acid as well as N‐acetylglucosamine residues and nucleophilic sites of an anomeric tag, yielding specific isomeric fragment ions. This mechanistic insight enables the characterization of unique IMS arrival‐time distributions of the isomers which can be used to accurately determine fucosyl positions in glycans.     

Uncovering the Stoichiometry of Pyrococcus furiosus RNase P,a Multi‐Subunit Catalytic Ribonucleoprotein Complex,by Surface‐Induced Dissociation and Ion Mobility Mass Spectrometry

We demonstrate that surface‐induced dissociation (SID) coupled with ion mobility mass spectrometry (IM‐MS) is a powerful tool for determining the stoichiometry of a multi‐subunit ribonucleoprotein (RNP) complex assembled in a solution containing Mg²⁺. We investigated Pyrococcus furiosus (Pfu) RNase P, an archaeal RNP that catalyzes tRNA 5′ maturation. Previous step‐wise, Mg²⁺‐dependent reconstitutions of Pfu RNase P with its catalytic RNA subunit and two interacting protein cofactor pairs (RPP21⋅RPP29 and POP5⋅RPP30) revealed functional RNP intermediates en route to the RNase P enzyme, but provided no information on subunit stoichiometry. Our native MS studies with the proteins showed RPP21⋅RPP29 and (POP5⋅RPP30)₂ complexes, but indicated a 1:1 composition for all subunits when either one or both protein complexes bind the cognate RNA. These results highlight the utility of SID and IM‐MS in resolving conformational heterogeneity and yielding insights on RNP assembly.