化学•材料最新文献

The sustainable development of efficient and stereocontrolled catalytic strategies for the synthesis of biologically relevant glycosides is of paramount importance in modern glycoscience. Herein, we report an operationally simple and scalable catalytic system employing an easily accessible, highly stable, and inexpensive pyridinium tetrafluoroborate salt as an effective organocatalyst for the stereoselective synthesis of β-O- and N-glycosides. The protocol utilizes readily available glycosyl trichloroacetimidates (TCAs) as donors and accommodates a broad range of aliphatic alcohols (including sugar and non-sugar derivatives) as well as challenging arylamines as acceptors, delivering the corresponding O- and N-glycosides in good to excellent yields with high to exclusive β-anomeric selectivity under mild reaction conditions. Mechanistic investigations suggest that the catalyst facilitates selective glycosylation through non-covalent interactions (NCIs) between catalyst and acceptor, which contribute to both donor activation and stereochemical control. The utility and robustness of the methodology are further demonstrated through gram-scale synthesis and the construction of trisaccharide.

CO₂ capture and reduction (CCR) to CO using dual-functional materials (DFMs) has recently attracted significant attention as a promising strategy for carbon capture and utilization. However, most of the DFMs for CO production reported to date require high-temperature (> 500 °C) and O₂-free conditions. Herein, we used spectroscopic characterization under operating conditions for a detailed investigation of the Pt-Na/Al₂O₃ DFM reported in our previous work that can capture CO₂ and produce CO by selective hydrogenation at moderate reaction temperatures (350 °C) in the presence of O₂. In situ X-ray absorption spectroscopy measurements revealed that the Pt nanoparticles of Pt-Na/Al₂O₃ were more oxidized and electron-deficient than those of Pt/Al₂O₃, even during the reduction step. In situ IR measurements confirmed that the CO and hydrogen species on Pt-Na/Al₂O₃ desorbed at lower temperatures than those on Pt/Al₂O₃. In addition, modulation excitation infrared spectroscopy (ME-IR) revealed the formation of Pt-H and HCOO^- intermediates. The Pt-Na/Al₂O₃ material was used for the first time in a system integrating membrane-based direct air capture (m-DAC) and a CCR system for CO production and showed excellent performance. CO selectivity of 93% and CO production concentrations of 1000-2500 ppm were achieved under continuous operation, demonstrating its practical applicability.

In our work with a Au thiolate nanocluster (Au₂₀(SG)₁₆, where SG is the tripeptide glutathione), we noticed that it underwent a self-photooxidation reaction in the presence of white light and oxygen. We now report on mechanistic studies using photophysical, photochemical, theoretical, and indirect trapping methods. We find rapid total quenching of singlet oxygen (¹O₂) by ground-state Au₂₀(SG)₁₆, with evidence of dioxygen insertion into the nanocluster. Supported by analyses with IR, ESI-MS, and density functional theory, we propose the formation of Au-O-O-SG bonds in the Au nanocluster. The expansion of the staple motif from dioxygen insertion is attributed to heightened lability and blebbing (a protrusion) arising from the O-O group. We then demonstrated that the self-photooxidized Au₂₀(SG)₁₆ undergoes oxygen-atom transfer to a phosphine trap in the dark.

Several bacterial pathogens secrete multidomain enzymes known as lytic polysaccharide monooxygenases (LPMOs) that are important for virulence. One example is the Vibrio cholerae virulence factor GbpA (VcGbpA), in which an N-terminal LPMO domain is followed by two domains of unknown function called GbpA2 and GbpA3, and a C-terminal chitin-binding domain called CBM73. In-depth functional characterization of full-length and truncated variants of VcGbpA and a homologue from V. campbellii (previously V. harveyi, VhGbpA) showed that the catalytic LPMO domains of these proteins exhibit properties similar to natural single-domain LPMOs with established roles in chitin degradation. Interestingly, binding to chitin and efficient degradation of this substrate were affected by the presence of the GbpA2 and GbpA3 domains. Combined with structural predictions and analyses of sequence conservation, our data show that GbpA3 has evolved to interact with the reduced catalytic copper site in the LPMO domain to prevent off-pathway reactions in the absence of substrate. Substrate binding by CBM73 weakens this interaction, enabling the activation of the LPMO only when substrate is present. These observations shed new light into the functionality of these multidomain LPMOs and uncover a novel mechanism for regulating LPMO activity.