Dalton Transactions最新文献

Phenoxazinone synthase (PHS) is a multi-copper oxidase that catalyzes the oxidative coupling of o-aminophenol (OAP) to form phenoxazinone chromophores, a crucial step in the biosynthesis of the anticancer agent, Actinomycin D. Inspired by the structural and functional diversity of the copper sites in native PHS, three mononuclear copper(II) complexes (1, 2, and 3) were designed bearing tunable axial donor atoms (N, O, and S respectively). These complexes emulate the diversity in the coordination motifs of the different types of copper centers present in PHS and were fully characterized by multiple spectroscopic techniques. Substitution of the axial donor atom induced systematic changes in geometry, redox potential, and catalytic efficiency toward OAP oxidation. The Jahn–Teller distortion was most pronounced in the N4 and N3S systems, while complex 2 (N3O) exhibited a nearly centrosymmetric geometry and superior substrate binding affinity. All complexes catalyzed the aerial oxidation of OAP to 2-amino-3H-phenoxazin-3-one (APX) under physiological conditions without external oxidants, with the catalytic efficiency following the order 2 > 3 > 1. Density functional theory (DFT) and time-dependent DFT (TDDFT) studies corroborated the experimental observations. The optimized geometries closely matched the crystal structures, and the computed spin densities indicated greater Cu–ligand covalency in the N3O complex compared to the N4 and N3S analogues. The combined experimental and computational results highlight how subtle modifications in the primary coordination sphere influence the electronic structure, redox behaviour, and catalytic performance of the bio-inspired copper systems, thus providing a mechanistic rationale for phenoxazinone synthase activity.

Formulating environmentally friendly and sustainable protocols for catalytic transfer hydrogenation (CTH) utilizing non-noble metal catalysts presents a considerable difficulty owing to their diminished activity relative to noble metals. This study presents a highly effective NiAl layered double hydroxide (LDH) catalyst produced by a traditional co-precipitation technique and activated in situ by isopropanol (IPA), functioning as both a hydrogen donor and a reducing agent. The CTH of benzaldehyde to benzyl alcohol proceeds efficiently under base-free conditions. Notably, during the reaction, a unique in situ transformation of Ni²⁺ species in the LDH to metallic Ni⁰ particles was observed, fundamentally shifting the reaction mechanism. Initial cycles proceed via a Meerwein–Ponndorf–Verley (MPV) pathway mediated by Lewis acidic and basic sites of the LDH. However, upon repeated use, the formation of Ni⁰ introduces a new metal-hydride-based pathway, wherein IPA dehydrogenation and aldehyde hydrogenation are facilitated by metallic Ni⁰ and Lewis acidic sites. This dual mechanistic pathway results in the dynamic evolution of the catalyst during the reaction. Control and poisoning studies further confirm the pivotal role of basic sites in the initial CTH process. This protocol provides an environmentally friendly and chemoselective method for synthesizing aromatic alcohols, demonstrating exceptional substrate tolerance and advantageous environmental metrics.

We report a facile synthetic strategy for crafting unique trimetallic PdAuAg nanoplates with an abundant in-plane branching structure, termed “2D nanobranches”. This distinctive architecture combines the benefits of a two-dimensional morphology with a highly dendritic, high-surface-area framework. Physicochemical characterization confirms the successful formation of the ternary alloy and the intricate branched structure. When assessed for the ethanol oxidation reaction (EOR) in an alkaline medium, the PdAuAg 2D nanobranches demonstrate enhanced specific activity, reaction kinetics, and cycling retention compared to a commercial Pd/C benchmark. In situ surface-enhanced Raman spectroscopy (SERS) reveals that the catalyst selectively promotes the C2 pathway for ethanol oxidation to acetic acid, with no detectable C–C bond cleavage, thereby elucidating the origin of its high operational efficiency. Furthermore, density functional theory (DFT) simulations suggest that a higher surface coverage of hydroxyl radicals (OH) in the alkaline environment makes a key reaction step in this pathway more energetically favorable. The enhanced performance is attributed to the synergistic interplay of the ternary composition, which modulates the electronic structure, and the unique 2D branched morphology, which provides a high density of active sites and facilitates mass transport. This work highlights the profound impact of morphological control in conjunction with multimetallic engineering for advancing electrocatalyst design.