Metal-Organic Framework Thin Films as Ideal Matrices for Azide Photolysis in Vacuum

Studies on reactions in solutions are often hampered by solvent effects. In addition, detailed investigation on kinetics is limited to the small temperature regime where the solvent is liquid. Here, we report the in situ spectroscopic observation of UV-induced photochemical reactions of aryl azides within a crystalline matrix in vacuum. The matrices are formed by attaching the reactive moieties to ditopic linkers, which are then assembled to yield metal–organic frameworks (MOFs) and surface-mounted MOFs (SURMOFs). These porous, crystalline frameworks are then used as model systems to study azide-related chemical processes under ultrahigh vacuum (UHV) conditions, where solvent effects can be safely excluded and in a large temperature regime. Infrared reflection absorption spectroscopy (IRRAS) allowed us to monitor the photoreaction of azide in SURMOFs precisely. The in situ IRRAS data, in conjunction with XRD, MS, and XPS, reveal that illumination with UV light first leads to forming a nitrene intermediate. In the second step, an intramolecular rearrangement occurs, yielding an indoloindole derivative. These findings unveil a novel pathway for precisely studying azide-related chemical transformations. Reference experiments carried out for solvent-loaded SURMOFs reveal a huge diversity of other reaction schemes, thus highlighting the need for model systems studied under UHV conditions.     

N=8 Armchair Graphene Nanoribbons: Solution Synthesis and High Charge Carrier Mobility**

Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky barrier in device performance. Here, we demonstrate the first solution synthesis of 8-AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor-made polymer precursor into 8-AGNRs was validated by FT-IR, Raman, and UV/Vis-near-infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho[1,2,3,4-ghi]perylene derivatives ( 1 and 2 ) as subunits of 8-AGNR , with a width of 0.86 nm as suggested by the X-ray single crystal analysis. Low-temperature scanning tunneling microscopy (STM) and solid-state NMR analyses provided further structural support for 8-AGNR . The resulting 8-AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical-pump TeraHertz-probe spectroscopy revealed charge-carrier mobility in the dc limit of ∼270 cm² V⁻¹ s⁻¹ for the 8-AGNR .     

On-Surface Synthesis and Real-Space Visualization of Aromatic P3N3

On-surface synthesis is at the verge of emerging as the method of choice for the generation and visualization of unstable or unconventional molecules, which could not be obtained via traditional synthetic methods. A case in point is the on-surface synthesis of the structurally elusive cyclotriphosphazene (P₃N₃), an inorganic aromatic analogue of benzene. Here, we report the preparation of this fleetingly existing species on Cu(111) and Au(111) surfaces at 5.2 K through molecular manipulation with unprecedented precision, i.e., voltage pulse-induced sextuple dechlorination of an ultra-small (about 6 Å) hexachlorophosphazene P₃N₃Cl₆ precursor by the tip of a scanning probe microscope. Real-space atomic-level imaging of cyclotriphosphazene reveals its planar D_3h-symmetric ring structure. Furthermore, this demasking strategy has been expanded to generate cyclotriphosphazene from a hexaazide precursor P₃N₂₁ via a different stimulation method (photolysis) for complementary measurements by matrix isolation infrared and ultraviolet spectroscopy.     

Functional Dithienopyrazines: Structure-Property Relationships**

Dithienopyrazines are only scarcely used as building blocks in organic electronic materials. Here, we report efficient preparation and investigation of syn- and anti-dithienopyrazines, which were functionalized with triaraylamine units to provide different series of donor-acceptor-donor-type materials. The characterization of the optoelectronic properties resulted in valuable structure-property relationships and allowed for the elucidation of the influence of structural effects such as core structure (syn vs anti), type of substituents (directly arylated vs ethynylated aryl), and substitution pattern (α,α’- vs β,β’- vs fourfold substitution). Finally, first application of a dithienopyrazine derivative as model for hole-transport materials tailored for organic electronic devices has been realized.     

Structure and Mechanism of an Aspartimide‐Dependent Peptide Ligase in Human Legumain

Peptide ligases expand the repertoire of genetically encoded protein architectures by synthesizing new peptide bonds, energetically driven by ATP or NTPs. Here, we report the discovery of a genuine ligase activity in human legumain (AEP) which has important roles in immunity and tumor progression that were believed to be due to its established cysteine protease activity. Defying dogma, the ligase reaction is independent of the catalytic cysteine but exploits an endogenous energy reservoir that results from the conversion of a conserved aspartate to a metastable aspartimide. Legumain’s dual protease–ligase activities are pH‐ and thus localization controlled, dominating at acidic and neutral pH, respectively. Their relevance includes reversible on–off switching of cystatin inhibitors and enzyme (in)activation, and may affect the generation of three‐dimensional MHC epitopes. The aspartate–aspartimide (succinimide) pair represents a new paradigm of coupling endergonic reactions in ATP‐scarce environments.     

Application of polymethyl methacrylate in cathode materials of lithium-ion batteries

A study of the Li₂FeSiO₄/C cathode material doped with Mn demonstrated that introduction of polymethyl methacrylate results in a substantial decrease in the particle size and increase in the specific surface area of the cathode material. Polymethyl methacrylate strongly improves the cyclic stability of the cathode material. The discharge capacity after the first cycle was 218 mA h g^–1, and that upon stabilization of the structure of the cathode material, 170 mA h g^–1.     

Metal‐Catalyzed “On‐Demand” Production of Carbonyl Sulfide from Carbon Monoxide and Elemental Sulfur

The group 6 molybdenum(II) cyclopentadienyl amidinate (CPAM) bis(carbonyl) complex [Cp*Mo{N(iPr)C(Ph)N(iPr)}(CO)₂] (Cp*=η⁵‐C₅Me₅) serves as a precatalyst for the high‐yielding photocatalytic production of COS from CO and S₈ under near‐ambient conditions (e.g., 10 psi, 25 °C). Further documented is the isolation and structural characterization of several key transition‐metal intermediates which collectively support a novel molybdenum(IV)‐based catalytic cycle as being operative. Finally, in the presence of an excess amount of a primary amine, it is demonstrated that this catalytic system can be successfully used for the “on‐demand” generation and utilization of COS as a chemical reagent for the synthesis of ureas.     

Self-penetrating and interpenetrating 3D metal-organic frameworks constructed from 4-(4-carboxyphenoxy)-phthalic acid and <Emphasis Type="Italic">N</Emphasis>-donor auxiliary ligands

Two new interesting entangled structures, namely, [Ni_1.5(L)(bpy)₂(H₂O)₃] _n · 3nH₂O (I) and [Cd₃(L)₂(bbi)₂]n · nH₂O (II)(where H₃L is 4-(4-carboxyphenoxy)-phthalic acid, bpy is 4,4′-bipyridine, and bbi is 1,1′-(1,4-butanediyl)bis(imidazole)) have been synthesized and characterized by elemental analysis (EA), infrared spectra (IR), X-ray powder diffraction (XRPD), solid fluorescence and thermogravimetric analysis (TGA). Single-crystal X-ray diffraction analysis revealed that complex I possesses a 3D self-penetrating framework constructed from ladder-like and fishbone-like subunits. Complex II shows a 3D framework of two-fold interpenetration assembled from trinuclear Cd(II) clusters bridged by bbi and L^3? ligands.     

Improvements to CO<Subscript>2</Subscript> headspace biodegradability test

This study proposes changes to the design and evaluation of the CO₂ headspace test, which is used as a simple method for assessment of the complete biodegradability of surfactants. It presents a modified equation for the calculation of biodegradation. It is proposed that the solution of 7 mol L^?1 sodium hydroxide commonly used in the process involving alkalinisation of the vial contents be replaced with 15 mol L^?1 sodium hydroxide. The use of the higher hydroxide concentration leads to a significant reduction in the value of the blank CO₂ headspace test.