Photochemical Evidence of Electronic Interwall Communication in Double‐Wall Carbon Nanotubes

Single‐ and double‐wall carbon nanotubes (CNTs) having dimethylanilino (DMA) units covalently attached to the external graphene wall have been prepared by the reaction of the dimethylaminophenylnitronium ion with the corresponding CNT. The samples have been characterized by Raman and XPS spectroscopies, thermogravimetry, and high‐resolution transmission electron microscopy in which the integrity of the single or double wall of the CNT and the percentage of substitution (one dimethylanilino group every 45 carbons of the wall for the single‐ and double‐wall samples) has been determined. Nanosecond laser flash photolysis has shown the generation of transients that has been derived from the charge transfer between the dimethylanilino (as the electron donor) to the CNT graphene wall (as the electron acceptor). Importantly, the lifetime of the double‐wall CNT is much shorter than that monitored for the single‐wall CNT. Shorter‐lived transients were also observed for the pentyl‐esterified functionalized double‐wall CNT with respect to the single‐wall analogue in the presence of hole (CH₃OH) and electron quenchers (O₂, N₂O), which has led to the conclusion that the inner, intact graphene wall that is present in double‐wall CNT increases the charge mobility significantly, favoring charge recombination processes. Considering the importance that charge mobility has in microelectronics, our finding suggests that double‐wall CNT or two‐layer graphene may be more appropriate to develop devices needing fast charge mobility.     

Application and Mechanistic Studies of a Water‐Oxidation Catalyst in Alcohol Oxidation by Employing Oxygen‐Transfer Reagents

By using a dimeric ruthenium complex in combination with tert‐butyl hydrogen peroxide (TBHP) as stoichiometric oxidant, a mild and efficient protocol for the oxidation of secondary benzylic alcohols was obtained, thereby giving the corresponding ketones in high yields within 4 h. However, in the oxidation of aliphatic alcohols, the TBHP protocol suffered from low conversions owing to a competing Ru‐catalyzed disproportionation of the oxidant. Gratifyingly, by switching to Oxone (2 KHSO₅ ? KHSO₄ ? K₂SO₄ triple salt) as stoichiometric oxidant, a more efficient and robust system was obtained that allowed for the oxidation of a wide range of aliphatic and benzylic secondary alcohols, giving the corresponding ketones in excellent yields. The mechanism for these reactions is believed to involve a high‐valent Ru^V–oxo species. We provide support for such an intermediate by means of mechanistic studies.     

Dipole Field Guided Orientated Attachment of Nanocrystals to Twin‐Brush ZnO Mesocrystals

Mesocrystals of ZnO were synthesized hydrothermally by using gum arabic as a structure‐directing agent. Their hierarchical structure has a unique twin‐brush form consisting of vertically aligned nanorods in a single‐crystal‐like porous form. The formation mechanism of the twin‐brush ZnO was investigated by quenching a series of samples at different times and examining them by TEM, SEM, and XRD. The alignment of ZnO crystal units can be modulated by adding simple salts such as KCl to change the units from nanorods to nanoplates. This can be explained by screening the dipolar force of the polar crystal. Local cathodoluminescence of twin‐brush ZnO was used to follow the local structure changes.     

Phosphorylated 3‐Heteroarylcoumarins and Their Use in Fluorescence Microscopy and Nanoscopy

Photostable and bright fluorescent dyes with large Stokes shifts are widely used as markers in far‐field optical microscopy, but the variety of useful dyes is limited. The present study introduces new 3‐heteroaryl coumarins decorated with a primary phosphate group (OP(O)(OH)₂) attached to C‐4 in 2,2,4‐trimethyl‐1,2‐dihydroquinoline fragment fused with the coumarin fluorophore. The general synthetic route is based on the Suzuki reaction of 3‐bromocoumarines with hetarylboronic acids followed by oxidation of the methyl group at the C?C bond with SeO₂ (to an aldehyde), reduction with NaBH₄ (to an alcohol), and conversion into a primary phosphate. The 4 position in the coumarin system may be unsubstituted or bear a methyl group. Phosphorylated coumarins were found to have high fluorescence quantum yields in the free state and after conjugation with proteins (in aqueous buffers). In super‐resolution light microscopy with stimulated emission depletion (STED), the new coumarin dyes provide an optical resolution of 40–60 nm with a low background signal. Due to their large Stokes shifts and high photostability, phosphorylated coumarins enable to combine multilabel imaging (using one detector and several excitation sources) with diffraction unlimited optical resolution.     

Unusual Regenerable Porous Metal–Organic Framework Based on a New Triple Helical Molecular Necklace for Separating Organosulfur Compounds

Desulfurization of fuels is receiving more and more attention all over the world due to the increase of stringent environmental regulations and fuel specifications. The metal–organic framework (MOF) is a new class of crystalline materials, and high porosity, one of the most important properties of MOFs, plays a central role in the functional properties. However, the investigation of MOFs, being employed as sorbents for adsorptive desulfurization, is still scarce. In this regard, we have constructed a new 3D porous compound 1 by using rigidly designed carboxylate ligands, which, for the first time, exhibit an unusual triple molecular necklace‐like helix. The N₂ sorption isotherms of 1 show that it has a large Brunauer–Emmett–Teller (BET) surface area and pore volume. With the stable pore structure and appropriate pore sizes, compound 1 has been used as a sorbent for adsorptive desulfurization. The results indicate that compound 1 shows an excellent adsorption property and, more importantly, displays excellent stability, repeatability, and regenerability. Thus, the design and synthesis of targeted MOFs with appropriate pore size and increased interactions between organosulfur compounds and ligands/metals from MOFs is crucial for adsorptive desulfurization, which might be an effective guide to find an efficient and green adsorbent for desulfurization.     

Accurate localization and relative quantification of arginine methylation using nanoflow liquid chromatography coupled to electron transfer dissociation and drbitrap mass spectrometry

Protein arginine (Arg) methylation serves an important functional role in eucaryotic cells, and typically occurs in domains consisting of multiple Arg in close proximity. Localization of methylarginine (MA) within Arg-rich domains poses a challenge for mass spectrometry (MS)-based methods; the peptides are highly charged under electrospray ionization (ESI), which limits the number of sequence-informative products produced by collision induced dissociation (CID), and loss of the labile methylation moieties during CID precludes effective fragmentation of the peptide backbone. Here the fragmentation behavior of Arg-rich peptides was investigated comprehensively using electron-transfer dissociation (ETD) and CID for both methylated and unmodified glycine-/Arg-rich peptides (GAR), derived from residues 679–695 of human nucleolin, which contains methylation motifs that are widely-represented in biological systems. ETD produced abundant information for sequencing and MA localization, whereas CID failed to provide credible identification for any available charge state (z=2–4). Nevertheless, CID produced characteristic neutral losses that can be employed to distinguish among different types of MA, as suggested by previous works and confirmed here with product ion scans of high accuracy/resolution by an LTQ/Orbitrap. To analyze MA-peptides in relatively complex mixtures, a method was developed that employs nano-LC coupled to alternating CID/ETD for peptide sequencing and MA localization/characterization, and an Orbitrap for accurate precursor measurement and relative quantification of MA-peptide stoichiometries. As proof of concept, GAR-peptides methylated in vitro by protein arginine N-methyltransferases PRMT1 and PRMT7 were analyzed. It was observed that PRMT1 generated a number of monomethylated (MMA) and asymmetric-dimethylated peptides, while PRMT7 produced predominantly MMA peptides and some symmetric-dimethylated peptides. This approach and the results may advance understanding of the actions of PRMTs and the functional significance of Arg methylation patterns.