A Silica Bilayer Supported on Ru(0001): Following the Crystalline‐to Vitreous Transformation in Real Time with Spectro‐microscopy

The crystalline‐to‐vitreous phase transformation of a SiO₂ bilayer supported on Ru(0001) was studied by time‐dependent LEED, local XPS, and DFT calculations. The silica bilayer system has parallels to 3D silica glass and can be used to understand the mechanism of the disorder transition. DFT simulations show that the formation of a Stone–Wales‐type of defect follows a complex mechanism, where the two layers show decoupled behavior in terms of chemical bond rearrangements. The calculated activation energy of the rate‐determining step for the formation of a Stone—Wales‐type of defect (4.3 eV) agrees with the experimental value. Charge transfer between SiO₂ bilayer and Ru(0001) support lowers the activation energy for breaking the Si?O bond compared to the unsupported film. Pre‐exponential factors obtained in UHV and in O₂ atmospheres differ significantly, suggesting that the interfacial ORu underneath the SiO₂ bilayer plays a role on how the disordering propagates within the film.     

Synthesis of Di- and Tri-Substituted Imidazole-4-carboxylates via PBu3-Mediated [3 + 2] Cycloaddition

Some new di- and trisubstituted imidazole-4-carboxylates were prepared from amidoacetic acids 3 in the present report. The key step to establish such imidazole-4-carboxylates stemmed from the PBu₃-mediated [3 + 2] cycloaddition between in situ–generated Δ2-oxazolinone 4 and ethyl cyanoformate6. Our results indicated that trisubstituted imidazoles 7–20 were afforded in better yields than those of disubstituted imidazoles 21–27.

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Decay Mechanisms of Protonated 4-Quinolone Antibiotics After Electrospray Ionization and Ion Activation

This study presents a detailed experimental investigation of charge isomers of protonated 4-quinolone antibiotics molecules formed during electrospray ionization (ESI) with proposed dissociation mechanisms after collisional activation. Piperazinyl quinolones have been previously shown to exhibit erratic behavior during tandem MS analyses of biological samples, which originated from varying ratios of two isomeric variants formed during ESI. Here, a combination of ESI-collision-induced dissociation (CID), differential ion mobility spectrometry (DMS), high resolution MS, and density functional theory (DFT) was used to investigate the underlying mechanisms of isomer formation and their individual dissociation behaviors. The study focused on ciprofloxacin; major findings were confirmed using structurally related 4-quinolones. DFT calculations showed a reversal of basicity for piperazinyl quinolones between liquid and gas phase. We provide an experimental comparison and theoretical treatment of factors influencing the formation ratio of the charge isomers during ESI, including solvent pH, protic/aprotic nature of solvent, and structural effects such as pK _a and proton affinity. The actual dissociation mechanisms of the isomers of the protonated molecules were studied by separating the individual isomers via DMS-MS, which allowed type-specific CID spectra to be recorded. Both primary CID reactions of the two charge isomers originated from the same carboxyl group by charge-remote (CO₂ loss) and charge-mediated (H₂O loss) fragmentation of the piperazinyl quinolones, depending on whether the proton resides on the more basic keto or the piperazinyl group, followed by a number of secondary dissociation reactions. The proposed mechanisms were supported by calculated energies of precursors, transition states, and products for competing pathways. Graphical Abstract

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