Mikrochemische Apparate

Ohne Zusammenfassung     

Origin of Ferromagnetism and Magnetic Anisotropy in a Family of Copper(II) Triangles

Previously reported ferromagnetic triangles (NnBu₄)₂[Cu₃(μ₃-Cl)₂(μ-4-NO₂-pz)₃Cl₃] ( 1 ), (PPN)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] ( 2 ), (bmim)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] ( 3 ) and newly reported (PPh₄)₂[Cu₃(μ₃-Cl)₂(μ-4-Ph-pz)₃Cl₃] ( 4 ) were studied by magnetic susceptometry, electron paramagnetic resonance (EPR) spectroscopy and ab initio calculations to assess the origins of their ferromagnetism and of the magnetic anisotropy of their ground S=3/2 state (PPN⁺=bis(triphenylphosphine)iminium, bmim⁺=1-butyl-3-methylbenzimidazolium, pz⁻=pyrazolate). Ab initio studies revealed the d character of the magnetic orbitals of the compressed trigonal bipyramidal copper(II) ions. Ferromagnetic interactions were attributed to weak orbital overlap via the pyrazolate bridges. From the wavefunctions expansions, the ratios of the magnetic couplings were determined, which were indeterminate by magnetic susceptometry. Single-crystal EPR studies of 1 were carried out to extend the spin Hamiltonian with terms which induce zero-field splitting (zfs), namely dipolar interactions, anisotropic exchange and Dzyaloshinskii–Moriya interactions (DMI). The data were treated through both a giant-spin model and through a multispin exchange-coupled model. The latter indicated that ≈62 % of the zfs is due to anisotropic and ≈38 % due to dipolar interactions. The powder EPR data of all complexes were fitted to a simplified form of the multispin model and the anisotropic and dipolar contributions to the ground state zfs were estimated.     

Fast and Cysteine-Specific Modification of Peptides,Proteins and Bacteriophage Using Chlorooximes

This work reports a novel chlorooxime mediated modification of native peptides and proteins under physiologic conditions. This method features fast reaction kinetics (apparent k₂=306±4 M⁻¹s⁻¹ for GSH) and exquisite selectivity for cysteine residues. This cysteine conjugation reaction can be carried out with just single-digit micromolar concentrations of the labeling reagent. The conjugates show high stability towards acid, base, and external thiol nucleophiles. A nitrile oxide species generated in situ is likely involved as the key intermediate. Furthermore, a bis-chlorooxime reagent is synthesized to enable facile Cys-Cys stapling in native peptides and proteins. This highly efficient cysteine conjugation and stapling was further implemented on bacteriophage to construct chemically modified phage libraries.     

Alkynylgold(I) C3-Chiral Concave Complexes: Aggregation and Luminescence

Chiral gold(I) acetylide trinuclear complexes 1 – 3 based on the cyclotribenzylene platform and terminal PR₃ ligands (R=Ph, Et, and Cy, respectively), were characterized and their light emission studied. They exhibited long-lived blue phosphorescence in CHCl₃ and a weak fluorescence in the UV. In MeOH/CHCl₃ mixtures of >1:1 volume ratio, 1 and 2 exhibited a new emission band at ca. 540 nm that developed at the expense of the UV emission. DLS studies demonstrated the presence of molecular aggregates of Ø 30–80 nm. The green emission observed in MeOH-rich solvent mixtures was therefore induced by aggregation, and could originate from Au⋅⋅⋅Au interactions. The AIE spectrum of 3 was observed only in solutions containing 99 % of MeOH, and correlated with its solid state emission. The AIE profiles of the enantiomers of 1 differed from that of rac- 1 , suggesting that the latter is a true racemate.     

Microbial synthesis of natural,semisynthetic, and new-to-nature tetrahydroisoquinoline alkaloids

The tetrahydroisoquinoline (THIQ) moiety forms the backbone of several natural, synthetic, and semisynthetic drugs approved for the treatment of cancer, pain, gout, and various neurodegenerative diseases. Plants synthesize up to 3000 THIQ structures constituting the benzylisoquinoline, phenethylisoquinoline, Amaryllidaceae, and ipecac alkaloid classes. This review outlines the ongoing surge in activity surrounding the production of natural, semisynthetic, and new-to-nature THIQ metabolites in engineered microbial systems. These efforts have accelerated THIQ pathway discovery and engineering, unlocked new domains of chemical space, and spurred the development of highly productive microbial strains synthesizing unprecedented yields of THIQ precursors. Consolidating these advancements into a single bioprocess holds potential to outcompete crop-based manufacturing and total synthesis for the production of high-value THIQ pharmaceuticals at scale.     

Atomic Partitioning of the MPn (n = 2, 3, 4) Dynamic Electron Correlation Energy by the Interacting Quantum Atoms Method: A Fast and Accurate Electrostatic Potential Integral Approach

Recently, the quantum topological energy partitioning method called interacting quantum atoms (IQA) has been extended to MPn (n = 2, 3, 4) wave functions. This enables the extraction of chemical insight related to dynamic electron correlation. The large computational expense of the IQA-MPn approach is compensated by the advantages that IQA offers compared to older nontopological energy decomposition schemes. This expense is problematic in the construction of a machine learning training set to create kriging models for topological atoms. However, the algorithm presented here markedly accelerates the calculation of atomically partitioned electron correlation energies. Then again, the algorithm cannot calculate pairwise interatomic energies because it applies analytical integrals over whole space (rather than over atomic volumes). However, these pairwise energies are not needed in the quantum topological force field FFLUX, which only uses the energy of an atom interacting with all remaining atoms of the system that it is part of. Thus, it is now feasible to generate accurate and sizeable training sets at MPn level of theory. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.     

Magic-angle-spinning-induced local ordering in polymer electrolytes and its effects on solid-state diffusion and relaxation NMR measurements

Magic-angle-spinning (MAS) enhances sensitivity and resolution in solid-state nuclear magnetic resonance (NMR) measurements. MAS is obtained by aerodynamic levitation and drive of a rotor, which results in large centrifugal forces that may affect the physical state of soft materials, such as polymers, and subsequent solid-state NMR measurements. Here, we investigate the effects of MAS on the solid-state NMR measurements of a polymer electrolyte for lithium-ion battery applications, poly(ethylene oxide) (PEO) doped with the lithium salt LiTFSI. We show that MAS induces local chain ordering, which manifests itself as characteristic lineshapes with doublet-like splittings in subsequent solid-state ¹ H, ⁷ Li, and ¹⁹ F static NMR spectra characterizing the PEO chains and solvated ions. MAS results in distributions of stresses and hence local chain orientations within the rotor, yielding distributions in the local magnetic susceptibility tensor that give rise to the observed NMR anisotropy and lineshapes. The effects of MAS were investigated on solid-state ⁷ Li and ¹⁹ F pulsed-field-gradient (PFG) diffusion and ⁷Li longitudinal relaxation NMR measurements. Activation energies for ion diffusion were affected modestly by MAS. ⁷Li longitudinal relaxation rates, which are sensitive to lithium-ion dynamics in the nanosecond regime, were essentially unchanged by MAS. We recommend that NMR researchers studying soft polymeric materials use only the spin rates necessary to achieve the desired enhancements in sensitivity and resolution, as well as acquire static NMR spectra after MAS experiments to reveal any signs of stress-induced local ordering.     

Chiral Supramolecular Nanotubes of Single-Chain Magnets

We report a single-chain magnet (SCM) made of a terbium(III) building block and a nitronyl-nitroxide radical (NIT) functionalized with an aliphatic chain. This substitution is targeted to induce a long-range distortion of the polymeric chain and accordingly it gives rise to chains that are curled with almost 20 nm helical pitch. They self-organize as a chiral tubular superstructure made of 11 chains wound around each other. The supramolecular tubes have a 4.5 nm internal diameter. Overall, this forms a porous chiral network with almost 44 % porosity. Ab initio calculations highlight that each Tb^III ion possesses high magnetic anisotropy. Indeed, notwithstanding the supramolecular arrangement each chain behaves as a SCM. Magnetic relaxation with both finite and infinite-size regimes is observed and confirms the validity of the Ising approximation. This is associated with quite strong coercive field and magnetic remanence (H_c=2400 Oe M_R=2.09 μ_B at 0.5 K) for this class of compounds.