Analytical Chemistry
DOI: 10.1021/acs.analchem.3c02755
[ASAP] Cleavable Cross-Linkers Redefined by a Novel MS3-Trigger Algorithm
Analytical Chemistry
DOI: 10.1021/acs.analchem.3c01673
[ASAP] Fully Unattended Online Protein Digestion and LC–MS Peptide Mapping
Analytical Chemistry
DOI: 10.1021/acs.analchem.3c01554
A New Strategy for the Preparation of 3‐Amino‐4‐hydroxypyrrolidinone‐4‐acetic Acid, an Unusual γ‐Amino Acid found in Microsclerodermins
An original synthetic strategy is presented for the preparation of the sensitive 3-amino-4-hydroxypyrrolidinone-4-acetic acid residue which is present in the structures of the microsclerodermin natural product family. The approach relies on the use of a linear γ-amino acid surrogate derived from asparagine bearing a β-dithiolanyl group. A protected dipeptide model system is used to demonstrate that selective removal of the dithioketal protection followed by cyclization gives the target structure in single diastereoisomer form and with little or no dehydration.
An Intramolecular Enyne Metathesis Approach for the Synthesis of Cyclic 3‐Substituted Unsaturated Sulfones
Studies into the ring-closing enyne metathesis of a series of nine sulfone containing enynes is described. The readily accessible sulfone substrates were shown to undergo cyclisation to form 3-subsituted 2,5-dihydrothiophene 1,1-dioxides (sulfolenes) and one 3,6-dihydro-2H-thiopyran 1,1-dioxide. The success of this process depended on the substrate’s substitution pattern. Moderate to good yields of the products were obtained when the ene component was monosubstituted and it was found that the reactions proceeded most efficiently using the 2nd generation Grubbs catalysts, at elevated temperatures.
Plasma‐Promoted Ammonia Decomposition over Supported Ruthenium Catalysts for COx‐Free H2 Production
NH3 decomposition: The introduction of DBD plasma makes a breakthrough in the temperature of hydrogen production from ammonia decomposition catalyzed by ruthenium-based catalyst, and significantly enhances the NH3 conversion.
Abstract
The efficient decomposition of ammonia to produce COx-free hydrogen at low temperatures has been extensively investigated as a potential method for supplying hydrogen to mobile devices based on fuel cells. In this study, we employed dielectric barrier discharge (DBD) plasma, a non-thermal plasma, to enhance the catalytic ammonia decomposition over supported Ru catalysts (Ru/Y2O3, Ru/La2O3, Ru/CeO2 and Ru/SiO2). The plasma-catalytic reactivity of Ru/La2O3 was found to be superior to that of the other three catalysts. It was observed that both the physicochemical properties of the catalyst (such as support acidity) and the plasma discharge behaviours exerted significant influence on plasma-catalytic reactivity. Combining plasma with a Ru catalyst significantly enhanced ammonia conversion at low temperatures, achieving near complete NH3 conversion over the 1.5 %-Ru/La2O3 catalyst at temperatures as low as 380 °C. Under a weight gas hourly space velocity of 2400 mL gcat −1 h−1 and an AC supply power of 20 W, the H2 formation rate and energy efficiency achieved were 10.7 mol gRu −1 h−1 and 535 mol gRu −1 (kWh)−1, respectively, using a 1.5 %-Ru/La2O3 catalyst.
Hexaguanidino‐Triptycenes and Triphenylenes: Electronic Coupling in Molecules Containing Three Redox‐Active o‐Diguanidinobenzene Units Connected either Directly or Interacting Through Homoconjucation
Novel redox-active hexaguanidine molecules with multiple redox states were synthesized by connecting three o-diguanidinobenzene units. In 2,3,6,7,14,15-hexaguanidino-triptycenes, the three redox-active o-diguanidinobenzene units are connected through C-C bonds to the sp3-hybridized bridgehead C atoms, and in 2,3,6,7,10,11-hexaguanidino-triphenylenes they are directly connected. The connectivity difference leads to different electronic coupling between the three redox-active o-diguanidinobenzene units, with homoconjugation being present in the triptycene, but not in the triphenylene compounds. Motivated by the appearance of an intense low-energy electronic transition, we especially analysed the effect of homoconjugation on the electronic structure and charge delocalization in the dicationic redox state of the triptycene derivatives. Then, several trinuclear high-spin cobalt (and copper) complexes were synthesized with the triphenylene and triptycene ligands, and the magnetic coupling and redox properties analysed. By choice of the coligands (hexafluoroacetylacetonate, trifluoroacetylacetonate and acetylacetonate), oxidation could be switched between metal- and ligand-centered redox events, leading to drastic changes in the magnetic or optical properties, especially as a consequence of homoconjugation in the triptycene derivatives.
Molecular Accessibility and Diffusion of Resorufin in Zeolite Crystals
We use confocal laser scanning microscopy on the small, fluorescent resorufin dye molecule to visualize molecular accessibility and diffusion in the hierarchical, anisotropic pore structure of large (~10 µm-sized) zeolite-β crystals. The resorufin dye is widely used in life and materials science, but only in its deprotonated form because the protonated molecule is barely fluorescent in aqueous solution. In this work, we show that protonated resorufin is in fact strongly fluorescent when confined within the zeolite micropores enabling fluorescence microimaging experiments. We find that J-aggregation guest–guest interactions lead to a decrease in the measured fluorescence intensity, but is prevented by using non-fluorescent spacer molecules. By introducing resorufin from the outside solution and following its diffusion into zeolite-β crystals, we characterize the pore space. The eventual homogeneous distribution of resorufin molecules throughout the zeolite indicates a fully accessible pore network. This enables the quantification of its diffusion coefficient in the straight pores of zeolite-β without the need for complex analysis, and we find a value of 3 × 10−15 m2 s−1. Furthermore, we visualize that diffusion through the straight pores of zeolite-β is impeded when crossing the boundaries between zeolite sub-units.
Temperature‐modulated Reversible Clustering of Gold Nanorods Driven by Small Surface Ligands
Temperature-modulated colloidal phase of plasmonic nanoparticles is a convenient playground for resettable soft-actuators or colorimetric sensors. To render reversible clustering under temperature change, bulky ligands are required, especially if anisotropic morphologies are of interest. Here, we showcase thermoresponsive gold nanorods by employing small surface ligands, bis (p-sulfonatophenyl) phenyl-phosphine dihydrate dipotassium salt (BSPP) and native cationic surfactant. Temperature-dependent analysis in real-time allowed us to describe the structural features (interparticle distance and cluster size) as well as thermal parameters, melting and freezing temperatures. Our findings suggest that neither covalent Au-S bonds nor bulky ligands are required to obtain a robust thermoresponsive system based on anisotropic gold nanoparticles, paving the way to stimuli-responsive nanoparticles with a wide range of sizes and geometries.
Hydrogenation of Terminal Alkenes Catalyzed by Air‐Stable Mn(I) Complexes Bearing an N‐Heterocyclic Carbene‐Based PCP Pincer Ligand
Efficient hydrogenations of terminal alkenes with molecular hydrogen catalyzed by well-defined bench stable Mn(I) complexes containing an N-heterocyclic carbene-based PCP pincer ligand are described. These reactions are environmentally benign and atom economic, implementing an inexpensive, earth abundant non-precious metal catalyst. A range of aromatic and aliphatic alkenes were efficiently converted into alkanes in good to excellent yields. The hydrogenation proceeds at 100 oC with catalyst loadings of 0.25-0.5 mol %, 2.5 - 5 mol % base (KOtBu) and a hydrogen pressure of 20 bar. Mechanistic insight into the catalytic reaction is provided by means of DFT calculations.