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We synthesized a planar macrocyclic dinuclear nickel(II) metallohost from the corresponding macrocyclic imine ligand containing two N2O2 chelate coordination sites and an O6 cation binding site like 18‐crown‐6 as well as peripheral hexyl groups. Due to the lipophilic nature of the hexyl groups, the metallohost was soluble in less polar media where its interaction with alkali metal ions was enhanced. The binding studies by NMR spectroscopy clearly showed its strong tendency to form multi‐layered structures. The metallohost formed 2 : 1 and 1 : 1 (host/guest) complexes with Na+ with the two‐step binding constants of logK1=6.6 and logK2=3.0. In contrast, its complexation with larger alkali metal ions (K+, Rb+, Cs+) preferentially gave 3 : 2 (host/guest) complexes when 2/3 equiv. of the guest was present. The three‐layered structures of these 3 : 2 complexes were well characterized by mass spectrometry and 2D COSY/ROESY experiments as well as DFT calculations, elucidating their unique structural feature with three chemically different environments due to the oppositely curved two [Ni(saloph)] moieties of the metallohost. Therefore, the three‐layered structures were preferentially formed when larger alkali metal ions (K+, Rb+, Cs+) were complexed with the metallohost. [ABSTRACT FROM AUTHOR]

The structural variability of a compound class is an important criterion for the research into phosphor host lattices for phosphor‐converted light‐emitting diodes (pc‐LEDs). Especially, nitridophosphates and the related class of imidonitridophosphates are promising candidates. Recently, the ammonothermal approach has opened a systematic access to this substance class with larger sample quantities. We present the successful ammonothermal synthesis of the imidonitridophosphate Ba4P4N8(NH)2:Eu2+. Its crystal structure is solved by X‐ray diffraction and it crystallizes in space group Cc (no. 9) with lattice parameters a=12.5250(3), b=12.5566(4), c=7.3882(2) Å and β=102.9793(10)°. For the first time, adamantane‐type (imido)nitridophosphate anions [P4N8(NH)2]8− are observed next to metal ions other than alkali metals in a compound. The presence of imide groups in the structure and the identification of preferred positions for the hydrogen atoms are performed using a combination of quantum chemical calculations, Fourier‐transform infrared, and solid‐state NMR spectroscopy. Eu2+ doped samples exhibit cyan emission (λmax=498 nm, fwhm=50 nm/1981 cm−1) when excited with ultraviolet light with an impressive internal quantum efficiency (IQE) of 41 %, which represents the first benchmark for imidonitridophosphates and is promising for potential industrial application of this compound class. [ABSTRACT FROM AUTHOR]

Transformations of solid samples under solvent‐free or minimal solvent conditions set the future trend and define a modern strategy for the production of new materials. Of the various technologies tested in recent years, the mechanochemical approach seems to be the most promising for economic and ecological reasons. The aim of this review article is to present the current state of art in solid state research on binary systems, which have found numerous applications in the pharmaceutical and materials science industries. This article is divided into three sections. In the first part, we describe the new equipment improvements, which include the innovative application of thermo‐mechanochemistry, sono‐mechanochemistry, photo‐mechanochemistry, electro‐mechanochemistry, as well as resonant acoustic mixing (RAM), and transformation under high‐speed sample spinning ("SpeedMixing"). A brief description of techniques dedicated to ex‐situ and in‐situ studies of progress and the mechanism of solid matter transformation (PXRD, FTIR, Raman and NMR spectroscopy) is presented. In the second section, we discuss the problem of cocrystal polymorphism highlighting the issue related with correlation between mechanochemical parameters (time, temperature, energy, molar ratio, solvent used as a liquid assistant, surface energy, crystal size, crystal shape) and preference for the formation of requested polymorph. The last part is devoted to the description of the processes of coformer exchange in binary systems forced by mechanical and/or thermal stimuli. The influence of the thermodynamic factor on the selection of the best‐suited partner for the formation of a two‐component stable structure is presented. [ABSTRACT FROM AUTHOR]

The structural variability of a compound class is an important criterion for the research into phosphor host lattices for phosphor‐converted light‐emitting diodes (pc‐LEDs). Especially, nitridophosphates and the related class of imidonitridophosphates are promising candidates. Recently, the ammonothermal approach has opened a systematic access to this substance class with larger sample quantities. We present the successful ammonothermal synthesis of the imidonitridophosphate Ba4P4N8(NH)2:Eu2+. Its crystal structure is solved by X‐ray diffraction and it crystallizes in space group Cc (no. 9) with lattice parameters a=12.5250(3), b=12.5566(4), c=7.3882(2) Å and β=102.9793(10)°. For the first time, adamantane‐type (imido)nitridophosphate anions [P4N8(NH)2]8− are observed next to metal ions other than alkali metals in a compound. The presence of imide groups in the structure and the identification of preferred positions for the hydrogen atoms are performed using a combination of quantum chemical calculations, Fourier‐transform infrared, and solid‐state NMR spectroscopy. Eu2+ doped samples exhibit cyan emission (λmax=498 nm, fwhm=50 nm/1981 cm−1) when excited with ultraviolet light with an impressive internal quantum efficiency (IQE) of 41 %, which represents the first benchmark for imidonitridophosphates and is promising for potential industrial application of this compound class. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a new type of the intramolecular reaction between non‐activated alkyne units and the dialkylboryl group (9‐BBN), which was previously only hypothesized and studied on a calculational level. The reaction described here can formally be classified as a 1,2‐hydroboration reaction, but, in contrast to the classical mechanism via a cyclic four‐membered transition state, the reaction proceeds by a pericyclic mechanism involving a six‐membered transition state. In practice, the reaction allows the synthesis of a new class of the borolenes fused with silole or dihydrosilole units. Thus, the heating (125 °C) of 2,3‐dihydrosiloles or 2,3‐dihydrosilolo[2,3‐b]silole bearing 9‐BBN and propargyl or dimethylpropargyl groups in positions 4 and 5, respectively, affords, in high to moderate yields, di‐ and tricyclic compounds containing a borolo[3,2‐b]silole unit. In all cases, the reactions are accompanied by an unprecedented dehydroboration of the 9‐BBN fragment, leading, in the final products, to a cyclooct‐4‐enyl group on the boron atom. The effects of the substituents on the rate and the selectivity of the reaction are discussed. The structures of all the new compounds have been determined from HRMS together with multinuclear 1D and 2D NMR spectroscopy, the results of which are in excellent agreement with DFT calculated chemical shifts. [ABSTRACT FROM AUTHOR]

Two fenestrindane‐based porous nanographenes containing four polyaromatic macrocycles in a highly twisted, basically S4–symmetric conformation were synthesized and characterized by NMR spectroscopy and mass spectrometry. Stepwise π‐extension at the periphery of the fenestrindane core by a sequence of eightfold Suzuki‐Miyaura cross‐coupling, fourfold Scholl cyclodehydrogenation and another eightfold Suzuki‐Miyaura reaction affords the porous nanographene precursors in good yields. In the last step, fourfold intramolecular Yamamoto coupling generates the porous nanographenes in 17‐18 %‐yield. Their optical and electronic properties were studied by UV/Vis and fluorescence spectroscopy and cyclic voltammetry. DFT calculations revealed structural details of the macrocycles. The surprisingly weak binding of these porous structures with chloride ions (K≈10 M−1) is attributed to their highly twisted conformation. The title compounds represent the first porous nanographenes based on the [5.5.5.5]fenestrane motif and, at the same time, they consist of a fenestrane‐like polyarylene network. [ABSTRACT FROM AUTHOR]

This study investigates the hydrogen‐bond geometry in six two‐component solid systems composed of quinoline and chloro‐nitrobenzoic acids. New X‐ray diffraction studies were conducted using both the conventional independent‐atom model and the more recent Hirshfeld atom‐refinement method, with the latter providing precise hydrogen‐atom positions. The systems can be divided into salts (the hydrogen atom transferred to the quinoline nitrogen), cocrystals (the hydrogen atom retained by the acid), and intermediate structures. Solid‐state NMR experiments corroborated the X‐ray diffraction‐derived H−N distances. DFT calculations, using five functionals including hybrid B3LYP and PBE0, showed varying energy profiles for the hydrogen bonds, with notable differences across functionals. These calculations revealed different preferences for salt or cocrystal structures, depending on the functional used. Path‐integral molecular dynamics simulations incorporating nuclear quantum effects demonstrated significant hydrogen‐atom delocalization, forming a hydrogen‐bond continuum, and provided average N−H distances in excellent agreement with experimental results. This comprehensive experimental and theoretical approach highlights the complexity of multicomponent solids. The study emphasizes that the classification into salts or cocrystals is frequently inadequate, as the hydrogen atom is often significantly delocalized in the hydrogen bond. This insight is crucial for understanding and predicting the behavior of such systems in pharmaceutical applications. [ABSTRACT FROM AUTHOR]

para‐Nitrophenyl (PNP) ethers of glycosides are important building blocks en route to functional carbohydrates. They are stable in neutral media, however, under basic conditions such as during the Zemplén deacylation of sugars, aryl migration is frequently observed. We have employed a library of O‐PNP‐substituted methyl glycosides of the manno‐, galacto‐, gluco‐ and altro‐series to study the kinetics of aryl migration in MeOH/sodium methoxide using NMR spectroscopy revealing that migration between cis‐oriented OH groups is faster than between trans‐oriented ones. The rate constants of migration decrease in the order of Alt>Man>Gal>Glc and are related to the energy barriers of chair conformation inversion. The energy profile of the 3 to 4‐PNP migration in methyl mannoside was calculated using DFT methods suggesting the Meisenheimer complex is an intermediate of PNP migration and that coordination of the sodium cation has a major impact on the energy profile. [ABSTRACT FROM AUTHOR]

The synthesis and reactivity of an air and water stable Bicyclic (alkyl)(amino)carbene (BICAAC) stabilized phosphenium cation (1) is reported. Air and water stable phosphenium cation are rare in the literature. Compound 1 is obtained by reaction of BICAAC with Ph2PCl in THF followed by anion exchange with LiOTf. The reduction and oxidation of 1 yielded corresponding α‐radical phosphine species (2) and BICAAC stabilized phosphenium oxide (3) respectively. All compounds are well characterized by single crystal X‐ray diffraction studies. The Lewis acidity of compounds 1 and 3 are determined by conducting fluoride ion affinity experiments using UV‐Vis spectrophotometry and multinuclei NMR spectroscopy. Compounds 1 and 3 exhibited selective binding to fluoride anion but did not interact with other halides (Cl− and Br−). Quantum chemical calculations were performed to understand the structure and nature of bonding interactions in these compounds, as well as to comprehend the specific bonding affinity to fluoride over other halide ions. [ABSTRACT FROM AUTHOR]

High‐resolution nuclear magnetic resonance (NMR) spectroscopy represents a key methodology for studying biomolecules and their interplay with other molecules. Recent developments in labeling strategies have made it possible to incorporate fluorine into proteins and peptides reliably, with manageable efforts and, importantly, in a highly site‐specific manner. Paired with its excellent NMR spectroscopic properties and absence in most biological systems, fluorine has enabled scientists to investigate a rather wide range of scientific objectives, including protein folding, protein dynamics and drug discovery. Furthermore, NMR spectroscopic experiments can be conducted in complex environments, such as cell lysate or directly inside living cells. This review presents selected studies demonstrating how 19F NMR spectroscopic approaches enable to contribute to the understanding of biomolecular processes. Thereby the focus has been set to labeling strategies available and specific NMR experiments performed to answer the underlying scientific objective. [ABSTRACT FROM AUTHOR]

A series of isostructural early actinide AnIV complexes was synthesized in order to investigate the influence of a conjugated framework in the ligand backbone on An bonding. Therefore, the AnIV complexes [An(pyrophen)2] (An = Th, U, Np, and Pu) with the pure N–donor ligand bis(2‐pyrrolecarbonylaldehyde)‐o‐phenylenediamine referred to as pyrophen, were synthesized and characterized. Solid state analysis via single‐crystal X‐ray diffraction (SC‐XRD) reveals two sets of ligands binding in an almost orthogonal arrangement to the actinide center. For the larger actinides Th and U, the coordination sphere allows for additional coordination by a solvent molecule. Nuclear magnetic resonance spectroscopy (NMR) studies show the presence of highly symmetrical complexes in solution in good agreement with the solvent‐free solid structures. While SC‐XRD suggests mainly ionic binding, an analysis of paramagnetic NMR contributions and quantum chemical bond analysis hint towards significant covalency in the U, Np, and Pu compounds. This series of An complexes allowed for a thorough structural and theoretical comparison of a conjugated system to a closely related N‐donor ligand (pyren)[1] as well as to the mixed N,O Schiff base ligands salophen (conjugated) and salen (non‐conjugated). [ABSTRACT FROM AUTHOR]

We present a comprehensive study on the conformational behavior of diversely substituted 4‐fluorotetrahydrothiopyran derivatives. Through quantum chemical simulations including DFT as well as NBO and NPA analysis, we elucidate the pivotal role of electrostatic interactions, occasionally complemented by hyperconjugative interactions, in stabilizing axial fluorine conformers. Less polar conformers were occasionally obtained, attributed to the interplay of electrostatic and hyperconjugative interactions. Experimental validation through NMR spectroscopy aligns with the computational analysis, thus providing a coherent understanding of the structural dynamics of these compounds. [ABSTRACT FROM AUTHOR]

Most redox processes that break/form bonds involve net 2e− changes, and many are coupled to protons. Yet most proton‐coupled electron transfer (PCET) studies focus on 1e−/1H+ reactions. Reported here is a family of molecular models that undergo tunable 2e−/2H+ redox changes. Complexes [(X2bpy)RuII(en*)2](PF6)2 and [(X2bpy)RuIV(en*‐H)2](PF6)2 have been synthesized with bpy=2,2'‐bipyridine with 4,4'‐subtitutions X=−NMe2, −OMe, −Me, −H, −CF3; and en*=2,3‐dimethyl‐2,3‐butanediamine. They have been characterized by IR, UV‐vis, and NMR spectroscopies, XRD, electrochemistry, mass spectrometry, DFT and (TD)DFT computations. The introduction of electron‐withdrawing and donating groups at the 4,4'‐position of the bpy ligand affects the complexes' redox potentials, pKa's, and Bond Dissociation Free Energies (BDFEs) of the N−H bonds in the en* ligands. The average BDFEs for the overall 2e−/2H+ PCET span over 5 kcal/mol. Notably, these complexes all show marked potential inversion over an extended range, ΔpKa>25 units and ΔE0>1.4 V. Potential inversion remains despite the electronic influence of bpy's substitutions which regulate N−H properties several bonds apart by trans‐effect over dπ‐molecular orbitals at the Ru center. The experimental and computational results presented in this work support the presence of strong coupling between electrons and protons, for modelling insights of 2e−/2H+ transfer reactivity. [ABSTRACT FROM AUTHOR]

A series of titanium μ2‐nitrido complexes supported by the triamidoamine ligand Xy‐N3N (Xy‐N3N={(3,5‐Me2C6H3)NCH2CH2}3N3−) is reported. The titanium azido complex [(Xy‐N3N)TiN3] (1‐N3), prepared by salt metathesis of the chloride complex [(Xy‐N3N)TiCl] (1‐Cl) with NaN3, reacted with lithium metal or with alkali metal naphthalenides (alkali metal M=Na, K, and Rb) in THF to give the corresponding dinuclear μ2‐nitrido complexes M[(Xy‐N3N)Ti=N‐Ti(Xy‐N3N)] (2‐M; M=Li, Na, K, Rb). Single crystal X‐ray diffraction studies of 2‐Li, 2‐Na, and 2‐K revealed alkali metal dependent structures in the solid state. While 2‐Li and 2‐K contain a μ2‐nitrido ligand with a linear Ti−N−Ti core, 2‐Na includes a μ3‐nitrido ligand as part of a T‐shape Ti2NaN fragment with the sodium cation weekly coordinated to the nitrido nitrogen atom. When the synthesis of the nitrido complexes was carried out in the presence of excess alkali metals, decomposition of the nitrido complexes was observed affording some intractable titanium species along with the trialkali metal salts [M3(Xy‐N3N)] (3‐M) (M=Li, Na, K, and Rb). These salts were also prepared by deprotonation of (Xy‐N3N)H3 with the corresponding alkali metal hexamethyldisilazide and characterized by multinuclear NMR spectroscopy as well as single crystal X‐ray diffraction. [ABSTRACT FROM AUTHOR]

Chalcogen bonds (ChB) are moderately strong, directional, and specific non‐covalent interactions that have garnered substantial interest over the last decades. Specifically, the presence of two σ‐holes offers great potential for crystal engineering, catalysis, biochemistry, and molecular sensing. However, ChB applications are currently hampered by a lack of methods to characterize and control chalcogen bonds. Here, we report on the influence of various substituents (halogens, cyano, and methyl groups) on the observed self‐complementary ChB networks of 2,1,3‐benzoselenadiazoles. From molecular electrostatic potential calculations, we show that the electrostatic surface potentials (ESP) of the σ‐holes on selenium are largely influenced by the electron‐withdrawing character of these substituents. Structural analyses via X‐ray diffraction reveal a variety of ChB geometries and binding modes that are rationalized via the computed ESP maps, although the structure of 5,6‐dimethyl‐2,1,3‐benzoselenadiazole also demonstrates the influence of steric interactions. 77Se solid‐state magic‐angle spinning NMR spectroscopy, in particular the analysis of the selenium chemical shift tensors, is found to be an effective probe able to characterize both structural and electrostatic features of these self‐complementary ChB systems. We find a positive correlation between the value of the ESP maxima at the σ‐holes and the experimentally measured 77Se isotropic chemical shift, while the skew of the chemical shift tensor is established as a metric which is reflective of the ChB binding motif. [ABSTRACT FROM AUTHOR]

The preparations of homo‐ and hetero‐bimetallic complexes as well as thiourea and selenourea derivatives of a mesoionic Janus‐type N‐heterocyclic dicarbene (diNHC) are reported. Analogues of its monocationic intermediate NHC have also been obtained for comparison. Using the main group adducts, the π‐acceptor properties of both NHCs were determined using low temperature 77Se NMR spectroscopy completing their stereoelectronic profiling. Moreover, catalytic investigations reveal that the mesoionic dipalladium Janus‐diNHC complex can be used in the sequential C2‐ and C5‐arylation of 1‐methylpyrrole for the preparation of non‐symmetrical 2,5‐diarylpyrroles. [ABSTRACT FROM AUTHOR]

Parahydrogen‐induced polarization (PHIP) is an emerging technique to enhance the signal of stable isotope metabolic contrast agents for Magnetic Resonance (MR). The objective of this study is to continue establishing 1‐13C‐pyruvate‐d3, signal‐enhanced via PHIP, as a hyperpolarized contrast agent, obtained in seconds, to monitor metabolism in human cancer. Our focus was on human pancreatic and colon tumor xenografts. 1‐13C‐vinylpyruvate‐d6 was hydrogenated using parahydrogen. Thereafter, the polarization of the protons was transferred to 13C. Following a workup procedure, the free hyperpolarized 1‐13C‐pyruvate‐d3 was obtained in clean aqueous solution. After injection into animals bearing either pancreatic or colon cancer xenografts, slice‐selective MR spectra were acquired and analyzed to determine rate constants of metabolic conversion into lactate and alanine. 1‐13C‐pyruvate‐d3 proved to follow the increased metabolic rate to lactate and alanine in the tumor xenografts. [ABSTRACT FROM AUTHOR]

Parahydrogen‐induced polarization (PHIP) is an emerging technique to enhance the signal of stable isotope metabolic contrast agents for Magnetic Resonance (MR). The objective of this study is to continue establishing 1‐13C‐pyruvate‐d3, signal‐enhanced via PHIP, as a hyperpolarized contrast agent, obtained in seconds, to monitor metabolism in human cancer. Our focus was on human pancreatic and colon tumor xenografts. 1‐13C‐vinylpyruvate‐d6 was hydrogenated using parahydrogen. Thereafter, the polarization of the protons was transferred to 13C. Following a workup procedure, the free hyperpolarized 1‐13C‐pyruvate‐d3 was obtained in clean aqueous solution. After injection into animals bearing either pancreatic or colon cancer xenografts, slice‐selective MR spectra were acquired and analyzed to determine rate constants of metabolic conversion into lactate and alanine. 1‐13C‐pyruvate‐d3 proved to follow the increased metabolic rate to lactate and alanine in the tumor xenografts. [ABSTRACT FROM AUTHOR]

Cyclisation of peptides by forming thioether (lanthionine), disulfide (cystine) or methylene thioacetal bridges between side chains is established as an important tool to stabilise a given structure, enhance metabolic stability and optimise both potency and selectivity. However, a systematic comparative study of the effects of differing bridging modalities on peptide conformation has not previously been carried out. In this paper, we have used the NMR deconvolution algorithm, NAMFIS, to determine the conformational ensembles, in aqueous solution, of three cyclic analogues of angiotensin(1–7), incorporating either disulfide, or non‐reducible thioether or methylene thioacetal bridges. We demonstrate that the major solution conformations are conserved between the different bridged peptides, but the distribution of conformations differs appreciably. This suggests that subtle differences in ring size and bridging structure can be exploited to fine‐tune the conformational properties of cyclic peptides, which may modulate their bioactivities. [ABSTRACT FROM AUTHOR]

We previously described NMR based fingerprint matching with peptide backbone resonances as a fast and reliable structural dereplication approach for Pseudomonas cyclic lipodepsipeptides (CLiPs). In combination with total synthesis of a small library of configurational CLiP congeners this also allows unambiguous determination of stereochemistry, facilitating structure‐activity relationship studies and enabling three‐dimensional structure determination. However, the on‐resin macrocycle formation in the synthetic workflow brings considerable burden and limits universal applicability. This drawback is here removed altogether by also transforming the native CLiP into a linearized analogue by controlled saponification of the ester bond. This eliminates the need for macrocycle formation, limiting the synthesis effort to linear peptide analogues. NMR fingerprints of such linear peptide analogues display a sufficiently distinctive chemical shift fingerprint to act as effective discriminators. The approach is developed using viscosin group CLiPs and subsequently demonstrated on putisolvin, leading to a structural revision, and tanniamide from Pseudomonas ekonensis COR58, a newly isolated lipododecapeptide that defines a new group characterized by a ten‐residue large macrocycle, the largest to date in the Pseudomonas CLiP portfolio. These examples demonstrate the effectiveness of the saponification‐ enhanced approach that broadens applicability of NMR fingerprint matching for the determination of the stereochemistry of CLiPs. [ABSTRACT FROM AUTHOR]

Hydrogels are of interest for a wide range of applications. The ability to control when the hydrogel degrades can provide beneficial properties such as controlled degradation in the environment or the stimulated release of drugs or cells. Self‐immolative polymers are a class of degradable polymers that undergo complete end‐to‐end depolymerization upon the application of a stimulus. They have been explored for hydrogel development, but the ability to prepare and selectively degrade self‐immolative hydrogels under neutral aqueous conditions has so far been limited. We describe here the preparation of water‐soluble polyglyoxylamides with cross‐linkable pendent azides and their cross‐linking to form hydrogels with 4‐arm poly(ethylene glycol)s having unstrained and strained alkynes using copper‐assisted and strain‐promoted azide‐alkyne click chemistry respectively. The influence of pendent azide density and solution polymer content on the resulting hydrogels was evaluated. A polyglyoxylamide with a 70 : 30 ratio of pendent hydroxyl:azide successfully provided hydrogels with compressive moduli ranging from 1.3–6.3 kPa under copper‐free conditions at 10–20 % (w/w) of polymer in phosphate‐buffered saline. Selective depolymerization and degradation of the hydrogels upon irradiation with light was demonstrated, resulting in reductions in the compressive moduli and the release of depolymerization products that were detected by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The particular reactivity of the recently discovered class of the main group element polyhedral clusters, pyramidanes, remains largely unexplored. In this communication, we report the reaction of the germapyramidane with tert‐butyllithium leading to the rather unusual organogermanium compound [Li+(thf)2]⋅2−, as the product of the formal insertion of a Ge‐apex into the C−Li bond. This reactivity mode exemplifies unusual electrophilic behaviour of a pyramidane, which is a priori considered as a nucleophilic reagent. Being highly reactive, [Li+(thf)2]⋅2− readily undergoes reactions with electrophiles (MeI, EtBr), initially forming intermediate germahousenes, which isomerize to the thermodynamically more favourable germoles. [ABSTRACT FROM AUTHOR]

We report the syntheses of tin(II) salts of the types [L1SnX]SnX3 [L1=2,6‐{(i‐PrO)2(O)P}2C5H3N: 1, X=Cl; 2, X=Br], [L2SnCl]SnCl3 [L2=2‐{(i‐PrO)Ph(O)P}‐6‐{(i‐PrO)2(O)P}C5H3N: 3], [L3SnX]SnX3 [L3=2,6‐{MeO(O)C}2C5H3N: 4, X=Cl; 5, X=Br], [L4SnX]SnX3 [L4=2,6‐{Et2N(O)C}2C5H3N: 6, X=Cl; 7, X=Br]. These compounds were obtained by addition of SnX2 to the corresponding ligand inducing autoionization of the respective tin(II) halide. The thermal stability of 1, 3, and 4 was elucidated, giving, under ester cleavage and cyclisation, the tin(II) derivatives 8–12. The reaction of [L1SnCl]SnCl3 (1) with W(CO)4(thf)2 afforded the tungsten tetracarbonyl complex [{L1SnCl}{SnCl3}W(CO)4] (13), representing the first example in which a tin(II) stannate anion and a tin(II) stannylium cation simultaneously coordinate to a transition metal centre. The compounds were characterized by single crystal X‐ray diffraction analyses and in part by elemental analyses, IR and NMR spectroscopy, electrospray ionization mass spectrometry. DFT calculations accompany the experimental work. [ABSTRACT FROM AUTHOR]

The activation of poorly reactive substrates via strong chiral acids is a central topic in asymmetric ion pair catalysis these days. Despite highly successful scaffolds such as N‐triflylphosphoramides, these catalysts either lack C2‐symmetry or provide multiple H‐bond acceptor sites, leading to lower ee values for certain reactions. We present BINOL‐based diselenophosphoric acids (DSA) as an extremely promising alternative. Using an intertwined approach of synthesis and NMR studies, we developed a synthetic approach to DSA with up to 98 % NMR yield. The obtained acids provide both very high proton donor and proton acceptor properties, a bifunctionality, which is key to catalytic applications. Indeed, first reactivity test proved the much higher acidity of DSA and its ability to initiate Mukaiyama–Mannich reaction and protodesilylation of silyl ethers. Together with their C2‐symmetry, the single donor and single acceptor situation, the decreased tendency of self‐association, and the straightforward synthesis with potential 3,3'‐substitution, the DSA provide all features ideal for the further development of ion pair catalysis. [ABSTRACT FROM AUTHOR]

The acetonitrile AgIII complex [AgIII(CF3)3(NCCH3)] (2) has been reported independently by Eujen and Naumann in the last century, albeit with intriguing NMR discrepancy. In their reports, 2 was claimed to be obtained starting from either [AgIII(CF3)3Cl]− (3⋅Cl) or [AgIII(CF3)4]− (1) via halide abstraction using AgNO3 or acidic treatment, resp. These two synthetic routes are herein reinvestigated. The feasibility of Naumann's method is demonstrated, thus providing 2 yet accompanied by its s‐triazinyl derivative [AgIII(CF3)3(C6H9N3)] (2'). The formation of 2' is unprecedented and was thereby investigated. Both 2 and 2' were isolated in pure fashion and fully characterized. In turn, halide extraction from 3⋅Cl leads to the AgIII‐ONO2 anion 5 instead of 2, as evidenced by NMR spectroscopy, EA and Sc‐XRD. [ABSTRACT FROM AUTHOR]

Quinazoline (Qz)‐linked covalent organic frameworks (COFs) have been constructed via a three‐component reaction of ortho‐acylanilines, benzaldehydes and NH4OAc. The structure of Qz‐COFs has been confirmed by solid‐state nuclear magnetic resonance spectroscopy, Fourier transform infrared and powder X‐ray diffraction patterns. The Qz‐COFs possess high chemical stability, showing good endurance to strong acid, strong base, oxidant, reductant and other conditions. Particularly, Qz‐COF‐3 can catalyze the aerobic photooxidation of toluene and other compounds containing C(sp3)−H bonds. [ABSTRACT FROM AUTHOR]

Sn3P8N16 combines the structural versatility of nitridophosphates and Sn within one compound. It was synthesized as dark gray powder in a high‐pressure high‐temperature reaction at 800 °C and 6 GPa from Sn3N4 and P3N5. The crystal structure was elucidated from single‐crystal diffraction data (space group C2/m (no. 12), a=12.9664(4), b=10.7886(4), c=4.8238(2) Å, β=109.624(1)°) and shows a 3D‐network of PN4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight‐membered rings of vertex‐sharing PN4 tetrahedra, stacked along the [001] direction. A combination of solid‐state nuclear magnetic resonance spectroscopy, 119Sn Mössbauer spectroscopy and density functional theory calculations was used to confirm the mixed oxidation of Sn. Temperature‐dependent powder X‐ray diffraction measurements reveal a low thermal expansion of 3.6 ppm/K up to 750 °C, beyond which Sn3P8N16 starts to decompose. [ABSTRACT FROM AUTHOR]

In 1977 Weiss and Grimes, by means of mass spectrometry and 1H and 11B NMR spectroscopy, proposed two structures (I and II) for the ferraborane (η5‐C5H5)Fe(B5H10), isoelectronic with ferrocene. In this work, by means of high‐level quantum‐chemical computations, we confirm the experimental structures of the two isomers with their corresponding energies, and assign the reported 1H and 11B NMR chemical shifts. A striking result from this study is the planarization (3D→2D) of the B5H10− ligand – an unknown isolated anion, isoelectronic with aromatic cyclopentadienyl anion C5H5− – when attached to the (η5‐C5H5)Fe+ moiety, thus resulting in a more stable ferraborane isomer II. [ABSTRACT FROM AUTHOR]

Sn3P8N16 combines the structural versatility of nitridophosphates and Sn within one compound. It was synthesized as dark gray powder in a high‐pressure high‐temperature reaction at 800 °C and 6 GPa from Sn3N4 and P3N5. The crystal structure was elucidated from single‐crystal diffraction data (space group C2/m (no. 12), a=12.9664(4), b=10.7886(4), c=4.8238(2) Å, β=109.624(1)°) and shows a 3D‐network of PN4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight‐membered rings of vertex‐sharing PN4 tetrahedra, stacked along the [001] direction. A combination of solid‐state nuclear magnetic resonance spectroscopy, 119Sn Mössbauer spectroscopy and density functional theory calculations was used to confirm the mixed oxidation of Sn. Temperature‐dependent powder X‐ray diffraction measurements reveal a low thermal expansion of 3.6 ppm/K up to 750 °C, beyond which Sn3P8N16 starts to decompose. [ABSTRACT FROM AUTHOR]

In 1977 Weiss and Grimes, by means of mass spectrometry and 1H and 11B NMR spectroscopy, proposed two structures (I and II) for the ferraborane (η5‐C5H5)Fe(B5H10), isoelectronic with ferrocene. In this work, by means of high‐level quantum‐chemical computations, we confirm the experimental structures of the two isomers with their corresponding energies, and assign the reported 1H and 11B NMR chemical shifts. A striking result from this study is the planarization (3D→2D) of the B5H10− ligand – an unknown isolated anion, isoelectronic with aromatic cyclopentadienyl anion C5H5− – when attached to the (η5‐C5H5)Fe+ moiety, thus resulting in a more stable ferraborane isomer II. [ABSTRACT FROM AUTHOR]

In the design of dynamic supramolecular systems used in molecular machines, it is important to understand the binding preferences between the macrocycle and stations along the thread. Here, we apply 1H NMR spectroscopy to investigate the relative stabilities of a series of linear alkylammonium templated pseudorotaxanes with the general formula [H2NRR'][Cr7CoF8(O2CCH2tBu)16] by exchanging the cation in solution. Our results show that the pseudorotaxanes are able to exchange threads via a dissociative mechanism. The position of equilibrium is dependent upon the ammonium cation and solvent used. Short chain primary ammonium cations are shown to be far less favourable macrocycle stations than secondary ammonium cations. Collision‐induced dissociation mass spectrometry (CID‐MS) has been used to look at disassembly of the pseudorotaxanes in a solvent‐free environment and stability trends compared to those in acetone‐d6. The energy needed to induce 50 % of the precursor ion loss (E50) is used and shows a similar trend to the equilibria measured by NMR. The relative stabilities of these hybrid inorganic‐organic pseudo‐rotaxanes are different to those of host‐guest compounds involving crown ethers and this may be valuable for the design of molecular machines. [ABSTRACT FROM AUTHOR]

An acyclic phosphonate‐linked nucleic acid backbone (ZNA) demonstrated the capability to support duplex formation and propagate genetic information in vivo, unveiling its potential for evolution into a synthetic genetic system (XNA). To determine the structural impact of such modification, modified Dickerson Drew DNA dodecamers (DDDs) were prepared by solid phase synthesis, each containing either an (R) or (S) isomeric form of a cytosine ZNA nucleotide. While the DDD is known to adopt a stable duplex, both duplex and hairpin forms were simultaneously observed for both modified oligonucleotides by NMR spectroscopy over a broad temperature range (5–65 °C). Diffusion‐ordered spectroscopy (DOSY) experiments allowed to separate duplex and hairpin signals based on the different diffusion constants of both conformational states. For the oligomer containing (R)‐ZNA, only the duplex form occurred at 5 °C, while it was not possible to determine by NMR a single hairpin conformation at higher temperatures. In the case of the (S)‐ZNA nucleoside modified oligomer, both hairpin and duplex forms were observable at 0 °C, while a single hairpin conformation was detected at 37 °C, suggesting a higher destabilizing effect on dsDNA. [ABSTRACT FROM AUTHOR]

The emergent properties resulting from selective supramolecular interactions are of significant importance for materials and chemical systems. For the directed use of such properties, a fundamental understanding of the interaction mechanism and the resulting mode of function is necessary for a tailored design. The self‐induced diastereomeric anisochronism effect (SIDA), which occurs in the intermolecular interaction of chiral molecules, generates unique properties such as chiral self‐recognition and nonlinear effects. Here we show that anisidine amino acid diamides lead to extraordinary signal splitting in NMR spectra through supramolecular interaction and homochiral self‐recognition. By systematic experiments we have investigated the underlying SIDA effect, explored its limits and finally successfully utilized it in the determination of enantiomeric ratios by NMR spectroscopy of chiral 'SIDA‐inactive' compounds such as thalidomide. [ABSTRACT FROM AUTHOR]

Chemical activation of the nuclear singlet state of dihydrogen, para‐hydrogen, can dramatically increase the sensitivity of magnetic resonance spectroscopy and imaging. Here, we show that the highly reversible activation of para‐hydrogen by an iridium pyridylpyrrolide complex is capable of producing this hyperpolarisation effect. Bound alkene ligands exhibit signal enhancement without reduction to alkanes, which is in contrast to the most widely used hyperpolarisation catalysts. The complex is recoverable due to the highly reversible binding and release of H2, and result in enhanced hydride signals in a wide range of coordinating and non‐coordinating deuterated solvents. Synthetic modification of the ligand substituents and the addition of co‐ligands show a strong dependence of chemical structure on reactivity, which reveals an untapped potential to exploit pyridylpyrrolides as ligands in the development of tunable para‐hydrogen induced hyperpolarisation catalysts or molecular probes. [ABSTRACT FROM AUTHOR]

While π‐complexes of C=C bonds are ubiquitous in organometallic chemistry, analogous complexes of the isoelectronic but strongly polarized B=N double bond of aminoboranes are extremely scarce. To address this gap, a diphosphine‐aminoborane ligand (PhDPBAiPr) is introduced and its coordination with group 10 metals is investigated. The B=N bond does not coordinate to the metal in Pt(0) and Pd(II) complexes. In contrast, side‐on coordination of the B=N bond is observed in the Ni(0) complex (PhDPBAiPr)Ni(NCPh), and the X‐ray crystal structure reveals B−N bond elongation compared to the free ligand. The choice of co‐ligand strongly influences the presence or absence of side‐on coordination at Ni(0) as evidenced by NMR spectroscopy. While the B=N π‐complex is geometrically similar to C=C analogues, a bonding analysis reveals that the interaction of the B=N motif with the electron‐rich Ni(0) center is best described as 3c4e hyperbond, in which Ni and N are competing for the empty orbital on B. [ABSTRACT FROM AUTHOR]

A novel class of diazonium salts is introduced for the photochemical aryl‐aryl coupling to produce (substituted) biphenyls. As common diazonium tetrafluoroborate salts fail, soluble and safe aryl diazonium trifluoroacetates are applied. In this mild synthesis route no catalysts are required to generate an aryl‐radical by irradiation with UV‐A light (365 nm). This reactive species undergoes direct C−H arylation at an arene, forming the product in reasonable reaction times. With the implementation of a continuous flow setup in a capillary photoreactor 13 different biphenyl derivatives are successfully synthesized. By integrating an inline 19F‐NMR benchtop spectrometer, samples are reliably quantified as the fluorine‐substituents act as a probe. Here, real‐time NMR spectroscopy is a perfect tool to monitor the continuously operated system, which produces fine chemicals of industrial relevance even in a multigram scale. [ABSTRACT FROM AUTHOR]

7Li nuclear magnetic resonance (NMR) spectroscopy is an ideal tool to study hierarchically assembled helicates of the form Li[Li3L6Ti2]. Internally bound and external lithium ions can be well distinguished by solution‐ or solid‐state NMR spectroscopy and dimerization constants of the monomer/dimer equilibrium can be easily determined in solution. Averaged dimerization constants can be estimated in case of statistical mixtures of helicates formed from mixtures of ligands. [ABSTRACT FROM AUTHOR]

The investigation of reaction mechanisms is a complex task that usually requires the use of several techniques. To obtain as much information as possible on the reaction and any intermediates – possibly invisible to one technique – the combination of techniques is a solution. In this work we present a new setup for combined UV/Vis and NMR spectroscopy and compare it to an established alternative. The presented approach allows a versatile usage of different commercially‐available components like mirrors and fiber bundles as well as different fixed pathlengths according to double transmission or single transmission measurements. While a previous approach is based on a dip‐probe setup for conventional NMR probes, the new one is based on a micro‐Helmholtz coil array (LiquidVoxel™). This makes the use of rectangular cuvettes possible, which ensure well‐defined pathlengths allowing for quantification of species. Additionally, very low quantities of compound can be analyzed due to the microfabrication and small cuvette size used. As proof‐of‐principle this new setup for combined UV/Vis and NMR spectroscopy is used to examine a well‐studied photochromic system of the dithienylethene compound class. A thorough comparison of the pros and cons of the two setups for combined UV/Vis and NMR measurements is performed. [ABSTRACT FROM AUTHOR]

Herein, reactivity studies of a cyclic bis‐hydridostannylene [(ADC)SnH]2 (1‐H2) (ADC=PhC{(NDipp)C}2; Dipp=2,6‐iPr2C6H3) with various unsaturated organic substrates are reported. Reactions of terminal alkynes (RC≡CH) with 1‐H2 afford mixed acetylide‐vinyl‐functionalized bis‐stannylenes via dehydrogenation and hydrostannylation. Treatment of 1‐H2 with PhC≡CCH3 gives a unique distannabarrelene via dehydrogenative C(sp3)−H stannylation and hydrostannylation of the C≡CCH3 moiety. 1‐H2 undergoes dehydrogenative [2+2]‐cycloaddition reactions with diphenylacetylene, azobenzene, acetone, benzophenone, and benzaldehyde to form the 1,4‐distannabarrelene derivatives. The elimination of H2 in these reactions suggests the masked‐diradical property of 1‐H2. In fact, these [2+2]‐cycloaddition products are also accessible on treatments of the Sn(I) diradicaloid [(ADC)Sn]2 (1) with appropriate reagents. All compounds have been characterized by multinuclear NMR spectroscopy and single crystal X‐ray diffraction. Moreover, the catalytic activity of 1‐H2 has been shown for the hydroboration of unsaturated substrates. [ABSTRACT FROM AUTHOR]

Gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(Ar)]2; Ar=2,6‐iPr2C6H3) reacts with N‐heterocyclic carbenes RNHC (RNHC=[CMeN(R)]2C; R=Me, iPr) to RNHC‐coordinated phosphinidenes RNHC→PGa(Cl)L (R=Me 2 a, iPr 2 b) and with isonitriles RNC (R=iPr, Cy) to 1,3‐phosphaazaallenes L(Cl)GaP=C=N−R (R=iPr 3 a, Cy 3 b), respectively. Quantum chemical calculations reveal that 2 a/2 b possess two localized lone pair of electrons, whereas 3 a/3 b only show one localized lone pair as was reported for gallaphosphene 1. 2 b reacts with 2.5 equivalents of a borane (THF ⋅ BH3) to the NHC‐stabilized phosphinidene‐borane complex [iPrNHC→P(BH2)]2(BH3)34 with concomitant formation of LGa(H)Cl 5. 2–5 are characterized by heteronuclear (1H, 13C{1H}, 31P{1H}) NMR and IR spectroscopy, elemental analysis, and single crystal X‐ray diffraction (sc‐XRD). [ABSTRACT FROM AUTHOR]

NMR spectroscopy techniques can provide important information about protein‐ligand interactions. Here we tested an NMR approach which relies on the measurement of paramagnetic relaxation enhancements (PREs) arising from analogous cationic, anionic or neutral soluble nitroxide molecules, which distribute around the protein‐ligand complex depending on near‐surface electrostatic potentials. We applied this approach to two protein‐ligand systems, interleukin‐8 interacting with highly charged glycosaminoglycans and the SH2 domain of Grb2 interacting with less charged phospho‐tyrosine tripeptides. The electrostatic potential around interleukin‐8 and its changes upon binding of glycosaminoglycans could be derived from the PRE data and confirmed by theoretical predictions from Poisson‐Boltzmann calculations. The ligand influence on the PREs and NMR‐derived electrostatic potentials of Grb2 SH2 was localized to a narrow protein region which allowed the localization of the peptide binding pocket. Our analysis suggests that experiments with nitroxide cosolutes can be useful for investigating protein‐ligand electrostatic interactions and mapping ligand binding sites. [ABSTRACT FROM AUTHOR]

Oligo‐ and polysiloxanes are usually prepared by condensation reactions in solvents without control of stereochemistry. Here we present a solventless thermal condensation of stable organosilanols. We investigated the condensation reactions of organosilanediols with different organic substituents, having in common at least one aromatic group. The condensation kinetics of the precursors observed by NMR spectroscopy revealed a strong dependence on temperature, time, and substitution pattern at the silicon atom. SEC measurements showed that chain length increases with increasing condensation temperature and time and lower steric demand of the substituents, which also influences the glass transition temperatures (Tg) of the resulting oligo‐ or polymers. X‐ray diffraction studies of the crystalline silanediols and their condensation products revealed a structural correlation between the substituent location in the crystalline precursors and the formed macromolecules induced by the hydrogen bonding pattern. In certain cases, it is possible to carry out topotactic polymerization in the solid‐state, which has its origin in the crystal structure. [ABSTRACT FROM AUTHOR]

In the context of a project aiming at the replacement of the 3‐substituted β‐lactam ring in classical β‐lactam antibiotics by an N(3)‐acyl‐1,3‐diazetidinone moiety, we have investigated the reaction of isocyanates with imines derived from allyl glycinate and differently substituted propionaldehydes. Imines of aromatic aldehydes with anilines have been reported to react with acyl isocyanates to give 1,3‐diazetidinones or 2,3‐dihydro‐4H‐1,3,5‐oxadiazin‐4‐ones, via [2+2] or [4+2] cycloaddition, respectively. However, neither of these products was formed with imines derived from allyl glycinate and 2‐(mono)methyl propionaldehydes. α,α‐Dimethylation of the imine enabled the [4+2] cycloaddition pathway, but the desired 1,3‐diazetidinone products were not observed. Surprisingly, the imines obtained from thioesters of 2,2‐dimethyl 3‐oxo propionic acid reacted with aryl isocyanates or with benzyl isocyanate to give 5,5‐dimethyl‐2,4‐dioxo‐6‐(aryl‐/alkylthio)tetrahydropyrimidines, via thiol displacement and re‐addition to a putative six‐membered iminium intermediate. These experimental results obtained for the reactions could be rationalized by DFT calculations. In addition, we have shown that N(3)‐acyl‐1,3‐diazetidinone and 2,3‐dihydro‐4H‐1,3,5‐oxadiazin‐4‐one products can be distinguished based on experimental IR data in combination with theoretical reference spectra employing the IR spectra alignment (IRSA) algorithm. This discrimination was not possible by means of 1H, 13C, or 15N NMR spectroscopy [ABSTRACT FROM AUTHOR]

In recent decades, many efforts have been devoted to studying reactions catalyzed in nanoconfined spaces. The most impressive aspect of catalysis in nanoconfined spaces is that the reactivity of the molecules can be smartly driven to disobey classical behavior. A green and efficient three‐component aza‐Darzens (TCAD) reaction using a catalytic amount of γ‐cyclodextrins (CDs) in water has been developed to synthesize N‐phenylaziridines. CDs effectively performed this reaction in an environmentally friendly setting, achieving good yields. The same reaction was then performed using polymeric γ‐CD such as a γ‐cyclodextrin polymer crosslinked (GCDPC) with epichlorohydrin, a sponge‐like macroporous γ‐cyclodextrin‐based cryogel (GCDC), and a γ‐cyclodextrin‐based hydrogel (GCDH). The homogeneous and heterogeneous catalyst recovery was then studied, and it was proved to be easily recycled several times without relevant activity loss. Water, as a unique and eco‐friendly reaction medium, has been utilized for the first time, to the best of our knowledge, in this reaction. The inclusion of the reagents in CDs has been studied and rationalized by NMR spectroscopy experiments and molecular modeling calculations. The credit of the presented protocol includes good yields and catalyst reusability and precludes the use of organic solvents. [ABSTRACT FROM AUTHOR]

The syntheses of novel N‐heterocyclic carbene (NHC) adducts of group 13, 14 and 15 element hydrides are reported. Salt metathesis reactions between NaPH2 and IDipp ⋅ GeH2BH2OTf (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2BH2PH2 (2 a) and IDipp ⋅ BH2GeH2PH2 (2 b); by altering the reaction conditions an almost exclusive formation of 2 b was achieved. Attempts to purify mixtures of 2 a and 2 b by re‐crystallization from THF afforded a salt [IDipp ⋅ GeH2BH2 ⋅ IDipp][PHGeH2BH2PH2BH2GeH2] (4) that contains the novel anionic cyclohexyl‐like inorganic heterocycle [PHGeH2BH2PH2BH2GeH2]−. In addition, the borane adducts IDipp ⋅ GeH2BH2PH2BH3 (3 a) and IDipp ⋅ BH2GeH2PH2BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3B ⋅ SMe2 and were studied by NMR spectroscopy. Accompanying DFT computations give insight into the mechanism and energetics associated with 2 a/2 b isomerization as well as their decomposition pathways. [ABSTRACT FROM AUTHOR]

The Zr‐based Metal Organic Framework (MOF) UiO‐66(Zr) is widely employed owing to its good thermal and chemical stabilities. Although the long‐range structure of this MOF is preserved in the presence of water during several days, little is known about the formation of defects, which cannot be detected using diffraction techniques. We apply here 17O solid‐state NMR spectroscopy at 18.8 T to investigate the reactivity of UiO‐66, through the exchange of oxygen atoms between the different sites of the MOF and water. For that purpose, we have selectively enriched in 17O isotope the carboxylate groups of UiO‐66(Zr) by using it with 17O‐labeled terephthalic acid prepared using mechanochemistry. In the presence of water at 50 °C and a following dehydration at 150 °C, we observe an overall exchange of O atoms between COO− and μ3‐O2− sites. Furthermore, we demonstrate that the three distinct oxygen sites, μ3‐OH, μ3‐O2− and COO−, of UiO‐66(Zr) MOF can be enriched in 17O isotope by post‐synthetic hydrothermal treatment in the presence of 17O‐enriched water. These results demonstrate the lability of Zr−O bonds and the reactivity of UiO‐66(Zr) with water. [ABSTRACT FROM AUTHOR]

Extracellular amyloid‐β (Aβ) plaques, primarily formed by Aβ(1‐40) and Aβ(1‐42) fibrils, are a hallmark of Alzheimer's disease. The Aβ peptide can undergo a high variety of different post‐translational modifications including formation of a pyroglutamate (pGlu, pE) at N‐terminal Glu3 or Glu11 of truncated Aβ(3‐x) or Aβ(11‐x), respectively. Here we studied structural similarities and differences between pEAβ(3‐42) and LS‐shaped Aβ(1‐42) fibrils grown under identical conditions (pH 2) using solid‐state NMR spectroscopy. We show that the central region of pEAβ(3‐42) fibrils including the turn region around V24 is almost identical to Aβ(1‐42) showing similar β‐strands also at the N‐terminus. The missing N‐terminal residues D1‐A2 along with pE3 formation in pEAβ(3‐42) preclude a salt bridge between K28‐D1' as in Aβ(1‐42) fibrils. G37 and G38 act as highly sensitive internal sensors for the modified N‐terminus, which remains rigid over ~five pH units. [ABSTRACT FROM AUTHOR]

Reliable structure elucidation of covalent organic cage compounds remains challenging as routine analysis might leave ambiguities. Diffusion‐ordered NMR spectroscopy (DOSY) allows insight into the molecular size and mass of the species present in solution, but a systematic evaluation of the diffusion behavior for cage assemblies is rarely considered. Here we report the synthesis of four series of covalent organic cages based on tribenzotriquinacenes and diboronic acids with varying geometry and exohedral substituents. We provide a guideline for the consistent measurement of diffusion coefficients from 1H‐DOSY NMR spectroscopy, which was utilized to study the diffusion behavior for the whole set of cages and selected examples from the literature. For structurally similar cages, a linear correlation between the solvodynamic volume and the molecular mass allows precise size determination. For more complex systems, multiple parameters, such as window size or rigid exohedral functionalization. further modulate cage diffusion in solution. [ABSTRACT FROM AUTHOR]

The analog of the diterpene precursor geranylgeranyl diphosphate with a double bond shifted from C14=C15 to C15=C16 (named iso‐GGPP III) has been synthesized and enzymatically converted with six bacterial diterpene synthases; this allowed the isolation of nine unnatural diterpenes. For some of the enzyme‐substrate combinations, the different reactivity implemented in the substrate analog iso‐GGPP III opened reaction pathways that are not observed with natural GGPP, resulting in the formation of diterpenes with novel skeletons. A stereoselective deuteration strategy was used to assign the absolute configurations of the isolated diterpenes. [ABSTRACT FROM AUTHOR]

Here we show that the sp‐hybridized nitrogen cation is strongly stabilized by a peri‐iodine substituent in the tetralone system. The cation is captured by anionic species such as CF3CO2−, affording hypervalent iodine(III) compounds with a short nitrogen‐iodine (N−I) bond, in which the cation serves as a Lewis acid. Notably, the O−I bond of the O‐trifluoroacetate or O‐acetate is intrinsically weaker than the N−I bond due to its more ionic character and is further weakened by protonation in trifluoroacetic acid. As a result, the oxygen ligand can dissociate in the presence of a Brønsted acid, affording a I+ cation intermediate that retains the N−I bond. We isolated the cation as the tetrafluoroborate, and characterized it experimentally by 1H NMR spectroscopy and X‐ray structure analysis, and theoretically by means of DFT calculation. The results suggest that the N−I bonded cation is intrinsically stable, and is weakly coordinated with water and the BF4 counter anion or trifluoroacetate anion. This cation can be employed as a reagent for α‐oxidation of ketones. [ABSTRACT FROM AUTHOR]