Chemistry - An Asian Journal最新文献

Design of stimuli-responsive chiral polydiacetylenes (PDAs) with an innate photoswitch offers exciting opportunities toward tunable chromogenesis and chiroptical behavior as a result of E-Z photoisomerization. We designed a series of asymmetric photopolymerizable diacetylene bisamides bearing variable alkyl chains, DA_n (n = 2, 5, 10), to connect the DA with a chiral azobenzene motif. Topochemical polymerization in thin films of DA forms orange colored PDAs to furnish long-ranged fibrillar nanostructures with increasing alkyl chain lengths. The polymer nanostructures exhibit axial or lateral growth after thermal annealing due to improved ordering in the polymeric domains. The PDA self-assembly exhibits crystalline or soft-crystalline packing based on alkyl chain stacking, aromatic interactions, and hydrogen bonding. Differential molecular packing in the PDAs dictates the E to Z photoisomerization percentages, eventually resulting in diminishing chiroptical signatures and anisotropic textures. Photoisomerization-mediated dynamic disassembly in 1D nanofibers are observed in the PDAs bearing decyl chain spacers, which show prominent room temperature soft-crystalline switching behavior. Reverse photoisomerization of Z to E mediated structural reordering result recovery of the chiral packing, morphology, and birefringent patterns. Such tunable soft-crystalline PDAs provide a convenient access to soft adaptable chiroptical materials toward solid-state actuation applications.

Electrocatalytic water electrolysis is intrinsically limited by the slow kinetics of the oxygen evolution reaction (OER) at the anodic electrode. The development of highly active and stable catalysts for the OER is both essential and challenging. In this work, we employed porous metal-organic frameworks (MOFs) to synthesize Ru-etched MOF-derived CuCoO₂ nanocrystals used as an OER catalyst. The electrochemical test results revealed that the Ru-etched CuCoO₂ electrode (Ni@CCORu-3) synthesized via a 3 h RuCl₃-etching reaction exhibits superior catalytic activity (η₁₀ = 368.4 mV, Tafel slope = 81.2 mV dec⁻¹) in 1.0 M KOH electrolyte. After an 18 h OER stability test, the Ni@CCORu-3 exhibited excellent stability with a minimal overpotential degradation of approximately 30 mV. This enhancement in OER activity can be attributed to the improved specific surface area and pore structure of the MOF-derived CCORu-3 catalyst, resulting from RuCl₃ etching. Furthermore, the electron distribution on the catalyst surface is modulated by Ru species loaded onto the surface. X-Ray photoelectron spectroscopy (XPS) and ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectra results revealed that RuCl₃ etching increases the proportion of active sites and narrows the bandgap of CuCoO₂, thereby accelerating electron transfer rates during the OER process and optimizing catalytic activity. This study may provide a novel insight into enhancing the OER performance of CuCoO₂ catalysts derived from MOFs.

Metal–organic frameworks (MOFs) are promising electrocatalysts for the oxygen evolution reaction (OER), owing to their high surface areas, tailorable structures, and numerous potential active sites. Herein, we investigate the impact of flow velocity within microchannels on the crystallization rate and internal structures of Co-MOF-74 via an air–liquid segmented flow method. We demonstrate that a higher flow velocity enhances the frequency of collisions between the metal ions and the organic linkers, yielding Co-MOF-74 samples with improved crystallinity, and unique voids. Specifically, the A-Co-MOF-74-8v synthesized at high flow velocity, exhibits a smaller particle size, developed internal voids, and abundant accessible electroactive sites. These features facilitate efficient mass transport and gas release during electrolysis, leading to significantly enhanced electrocatalytic OER performance. In 1 M KOH, A-Co-MOF-74-8v achieves a low overpotential of 310 mV at 10 mA cm⁻², which is 42 mV lower than that of the solvothermally synthesized counterpart (ST-Co-MOF-74). This work provides key mechanistic insights and design principles for engineering highly efficient MOF-based electrocatalysts under precisely controlled microfluidic conditions.

Under the catalysis of p-TsOH immobilized on silica (PTS-Si), the iso-Nazarov reaction of (E)-(2-stilbenyl)methanol/(E)-(2-stilbenyl)imine tosylate bearing a styrene moiety forged the corresponding [5/6] systems with the exclusive trans relationship at the two newly formed adjacent stereogenic centers. The ensuing “interrupted” nucleophilic addition by the pendent styrenyl olefin furnished the dihydro-11H-benzo[a]fluorene with the exclusive cis stereocontrol at the two-carbon ring junction. Thus, from non-chiral starting materials, the interrupted iso-Nazarov reaction formed two rings and provided the olefin moiety, which can be functionalized to other groups/systems possessing one to two additional chiral centers. Up to five contiguous stereogenic centers on the tetrahydrobenzo[a]fluorene could be constructed efficiently.

In order to increase the photocatalytic activity of TiO₂-anchored meso-tetrakis(4-carboxyphenyl)porphyrin (H₂TCPP), TiO₂@H₂TCPP, in the aerobic oxidation of sulfides in water, KBr has been used as a source for the formation of the secondary oxidant, bromine. The change in the nature of reactive oxidant from superoxide anion radical to molecular bromine led to a significant increase in the efficiency of oxidation of the sulfide as well as the oxidative stability of the porphyrin photosensitizer. The contribution from different reactive oxygen species, hole and electron in the formation of sulfone as the sole product, has been studied using the scavengers of hydroxyl radical, superoxide anion radical, hole, electron, and singlet oxygen, and accordingly, a mechanism was proposed. Using sodium bromate instead of KBr led to a similar increase in the photocatalytic activity of TiO₂@H₂TCPP, which was attributed to the reduction of bromate to bromide under the reaction conditions.

Electrocatalytic oxidation of biomass molecules such as ethanol in hybrid alkaline water electrolysis is more thermodynamically favorable and techno-economic attractive to replace conventional pure water electrooxidation to produce green hydrogen. Herein, the flexible and binder-free hollow microtube catalyst arrays of CoS₂/CC, Ni_0.04Co_0.96S₂/CC, Fe_0.07Ni_0.04Co_0.89S₂/CC, and Fe_0.08Ni_0.10Co_0.82S₂/CC were derived from metal-organic framework arrays anchored on carbon cloth (CC). These arrays exhibited favorable performance in electrochemical water oxidation, ethanol oxidation, and hydrogen evolution processes, because of their obvious advantages in high conductivity and long-term stability. The optimized self-supporting Fe_0.08Ni_0.10 Co_0.82S₂/CC electrode composed of a 3D hollow porous microtube structure only needs a low potential of 1.412 and 1.267 V (vs. RHE) to deliver 10 mA cm⁻² current density for alkaline water and ethanol oxidation reactions, respectively. Simultaneously, the pure CoS₂/CC electrode presents excellent alkaline hydrogen production property among the series self-supporting electrodes with a low overpotential of 188 mV at 10 mA cm⁻². In this work, it is proved that the hybrid water splitting system, using Fe_0.08Ni_0.10Co_0.82S₂/CC and CoS₂/CC as anode and cathode, respectively, can effectively reduce the cell voltage to 1.479 V to deliver 10 mA cm⁻² with high pure hydrogen generation and high valued potassium acetate generation.

Bifunctional electrocatalysts for overall water splitting (OWS) is critical for sustainable hydrogen production but remains challenging due to the sluggish kinetics and leaching of metal ions. Herein, we present a kind of phosphorus and molybdenum codoped ruthenium and ruthenium oxides heterostructure (P,Mo_0.1-Ru/RuO₂) as a highly efficient bifunctional electrocatalyst for alkaline OWS. The incorporation of P facilitates the electron transfer from P to Ru, leading to the partial reduction of RuO₂ to metallic Ru. Moreover, the reduced oxidation of Ru suppresses the dissolution of RuO₂, favoring the structural stability. In alkaline media, P,Mo_0.1-Ru/RuO₂ demonstrates enhanced hydrogen evolution and oxygen evolution activities, requiring overpotentials of only 61 and 230 mV, respectively, to achieve a current density of 10 mA cm⁻². When employed as anode and cathode for OWS, the P,Mo_0.1-Ru/RuO₂ catalyst enabled a low cell voltage of 1.50 V at 10 mA cm⁻², along with an enhanced electrochemical stability. These results highlight the synergistic effect of anion and cation codoping in enhancing electrocatalytic performance, offering a promising strategy for the design of advanced bifunctional catalysts for sustainable hydrogen production.

An efficient Rh(III)-catalyzed pivaloyl-directed strategy has been developed for the C7_Ar-(acyl)alkylation of tryptophans with substituted and unsubstituted allyl alcohols, delivering tryptophan-based unnatural amino acids without compromising their chirality. The disclosed methodology showcased high tolerance of neutral, acidic, and basic amino acids, including Gly, Ala, Val, Leu, Phe, Pro, Asp, Lys, and Thr units, enabling regioselective late-stage functionalization of tryptophan units in a variety of tryptophan-containing dipeptides, tripeptides in reasonable yields.