Helvetica Chimica Acta最新文献

Supported nanoparticles (NPs) are an intense field of research in industry and academia due to their unique catalytic properties. Yet, establishing relationships between structure and activity is challenging due to multiple possible compositions, interfaces, and alloy formation. This is especially pronounced for bimetallic NPs used in the CO₂-hydrogenation-to-methanol, where the structure responds dynamically to the chemical potential of the reactants and products, resulting in distinct surface structures depending on the exact reaction conditions. These phenomena have been highlighted by combining ab initio Molecular Dynamics (AIMD) and Metadynamics (MTD) with in situ X-ray absorption spectroscopy, chemisorption, and CO-IR. Here, we aim to understand how particle size and simulation temperature influence the structure and dynamics of small Cu NPs using the diffusion coefficients and the radial distribution function/atomic pair density function as descriptors using AIMD simulations. We found that decreasing the particle size or increasing the simulation temperature results in increased atom mobility, highlighted by the increased metal diffusion and resulting in reduced particle crystallinity. We also find that alloying Cu with Ga significantly increases the diffusion of both elements in the particle compared to the monometallic ones. In contrast, such diffusion lies in between the individual elements composing the CuZn particles.

Despite their synthetic interest and potential attractive properties, the preparation of heteroleptic U(III) complexes containing monodentate ligands remains challenging. Here we report the synthesis, structure and magnetic properties of three heteroleptic U(III) complexes containing two siloxide donors in the coordination sphere. The bis-siloxide monoiodide complex [U(OSi(O^tBu)₃)₂I(thf)₃], 1 provides a very attractive precursor for accessing heteroleptic complexes and rationally modify the binding angle between the two strongly donating siloxide ligands. Here we reacted 1 with macrocyclic ligands to yield complexes [[U(OSi(O^tBu)₃)₂(crypt)]I, 3 and [[U(OSi(O^tBu)₃)₂(18c6)]I, 4. Magnetic studies of these compounds offer a snapshot on how the SMM properties depend on the local symmetry in the presence of siloxide ligands. The static and dynamic magnetic properties of these compounds reveal a weak dependence of their single-molecule magnet behavior on the local symmetry.

The incorporation of methyl groups into aza-arene frameworks not only often improves their biological activity as the “magic methyl” effect, but also notably affects their solid-state electronic properties by modulating π-π stackings, which makes them promising candidates for developing organic electronic materials. This study focuses on the iron-catalyzed C−H annulation of ketones with 2-butyne via their oxime ethers, offering an efficient pathway to synthesizing methylated π-extended aza-arenes. The reactions utilize isobutyl aluminum(III) catecholate as a base and Triphos (bis(2-diphenylphosphinoethyl)phenylphosphine) as a ligand. Reported C−H activation methods using rhodium catalysis proved less effective with π-conjugated substrates. Regioselective C−H aza-annulation with 1-(trimethylsilyl)propyne following desilylation provides also mono-methylated azaarenes. The reactions also generate tetra-methylated aza-arene products by two-fold C−H aza-annulation on chromeno[3,2-a]xanthene-13,14-dione and quinacridone. These methylated aza-arenes exhibit strong π-π stacking, a narrow emission band, and tunable photophysical properties, indicating their potential applications as electronic materials.

Amoxicillin is a frequently used beta-lactam antibiotic and at the same time a fragile analyte. Aim of this work was to investigate the sensitive properties of amoxicillin in biological samples and validate a quantification method for amoxicillin in soft tissue samples. Simple protein precipitation and 2D-High performance liquid chromatography coupled to tandem mass spectrometry was used for sample preparation and analysis. The formation of a covalent amoxicillin methanol-adduct could be observed in varying extents depending on matrix and sample preparation method. In-Source Products (ISPs) were investigated in plasma, soft tissue, and water and no differences could be observed. We successfully validated a method for amoxicillin determination in tissue samples using the sum of 2 ISPs of amoxicillin for quantification. 37 study samples of different deep-seated infections could be analyzed. Measured amoxicillin concentrations ranged from below 0.5 mg/kg up to 87 mg/kg. Concentrations in abscesses were lower than in other infections.

We report a study on the photoionization of the C₆H₆ isomer 3,4-dimethylenecyclobutene, DMCB. The molecule is an intermediate in the formation of benzene from the propargyl radical self-reaction, a suggested first step in the formation of polycyclic aromatic hydrocarbons and soot. From a threshold photoelectron spectrum we determine an adiabatic ionization energy of 8.75 eV. The geometry change upon ionization is associated with considerable vibrational activity, which is assigned to a symmetric in-plane bending mode of the =CH₂ groups. A breakdown diagram shows that the dissociative photoionization resembles the one observed for benzene. Computations reveal that DMCB cation isomerizes to the benzene cation and dissociates from there.

We designed, synthesized, and investigated a new chiral carbon nanohoop that formally incorporates a benzothiadiazole and [5]helicene units into the structure of [6]cycloparaphenylene. The connection of these units in the chiral nanohoop is designed to allow for π-electron conjugation between the benzothiadiazole chromophore and the chirality-inducing [5]helicene. We resolved the enantiomers of the highly fluorescent, near-IR light emitting benzothiadiazole helicene nanohoop. Electronic circular dichroism spectroscopy then allowed us to investigate whether the selected molecular design leads to an increase in the lowest singlet excited state delocalization to improve the compound's electronic dissymmetry factor in comparison to the previously studied benzothiadiazole carbon nanohoop with planar chiral [2.2]paracyclophane unit with pseudo-meta connection.

Controlling the charge state of biomolecules in high vacuum enables experiments in molecular physics and physical chemistry, particularly in applications of mass spectrometry, trapping and cooling, spectroscopy and matter-wave interferometry. Here we investigate the synthesis, verification and gas phase photolysis of nitrodibenzofuranmethyl aryl ether derivatives. These photocages are chosen because their absorption maximum can be tuned to near 355 nm, where intense pulsed laser light is available. We demonstrate efficient gas-phase cleavage of a photoactive nitrodibenzofuranmethyl aryl ether derivative, both free and attached to oxytocin. This enables the neutralization of a polypeptide derivative in high vacuum using a wavelength outside the absorption spectrum of natural amino acids.

Functional molecular electronics require molecular design that provides integrity and stability. In this work, we explored two types of single molecule devices differing in anchoring to the conducting leads. Single molecule conductance was measured by STM break junction method and the molecular conductor was composed of the redox active anthraquinone center (switching element) containing either 4-pyridyl or p-phenylene thioacetate anchoring groups. The experimental results were supported by quantum chemical charge transport calculations. Molecular junctions containing 4-pyridyl anchors displayed two stable configurations with conductance values of 4.9 nS and 20 pS, respectively. Molecules anchored via p-phenylene thioacetate groups led to one main junction configuration with conductance of 0.1 nS. Junctions employing 4-pyridyl anchoring groups had higher junction formation probability, which in combination with lower conductance makes them better candidates for switching purposes.

Oligoprolines adopt the well-defined polyproline II (PPII) helical conformation, even at a short chain length of six residues. These rigid peptides are versatile molecular rulers and scaffolds, yet there has been great difficulty in obtaining single crystals for X-ray crystal structure analysis to probe their conformation in the solid state. Here, we report a crystal structure of an oligoproline hexamer bearing an N-terminal terephthalic acid moiety. Comparison with that of a previously obtained crystal structure of a closely related hexaproline revealed influence of the terminal functional groups and the solvent on the crystal packing.