RESUMEN
Single-atom catalysts (SACs) have well-defined active sites, making them of potential interest for organic synthesis1-4. However, the architecture of these mononuclear metal species stabilized on solid supports may not be optimal for catalysing complex molecular transformations owing to restricted spatial environment and electronic quantum states5,6. Here we report a class of heterogeneous geminal-atom catalysts (GACs), which pair single-atom sites in specific coordination and spatial proximity. Regularly separated nitrogen anchoring groups with delocalized π-bonding nature in a polymeric carbon nitride (PCN) host7 permit the coordination of Cu geminal sites with a ground-state separation of about 4 Å at high metal density8. The adaptable coordination of individual Cu sites in GACs enables a cooperative bridge-coupling pathway through dynamic Cu-Cu bonding for diverse C-X (X = C, N, O, S) cross-couplings with a low activation barrier. In situ characterization and quantum-theoretical studies show that such a dynamic process for cross-coupling is triggered by the adsorption of two different reactants at geminal metal sites, rendering homo-coupling unfeasible. These intrinsic advantages of GACs enable the assembly of heterocycles with several coordination sites, sterically congested scaffolds and pharmaceuticals with highly specific and stable activity. Scale-up experiments and translation to continuous flow suggest broad applicability for the manufacturing of fine chemicals.
RESUMEN
An electrochemical sensor that can resist biofouling even when operated in complex biological medium is developed for the determination of dopamine. It is based on the use of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) that is doped with the water insoluble ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A glassy carbon electrode modified with PEDOT/IL is shown to enable accurate determination of dopamine, as a model analyte in the presence of high concentrations of proteins, and resist biological fouling even in native serum. It exhibited a low limit of detection of 33 nM for the detection of dopamine, with a wide linear range from 0.2 to 328 µM (at 0.2 V vs. saturated calomel electrode). The PEDOT/IL modified glassy carbon electrode has a porous microstructure, high electrical conductivity and good stability. The sensor can be used to quantify dopamine in human urine samples with satisfying accuracy. Graphical abstract An antifouling electrochemical sensor capable of detecting target in complex biological samples was developed based on the use of a conducting polymer (PEDOT) that was doped with a water insoluble ionic liquid.
RESUMEN
The stabilization of transition metals as isolated centres with high areal density on suitably tailored carriers is crucial for maximizing the industrial potential of single-atom heterogeneous catalysts. However, achieving single-atom dispersions at metal contents above 2 wt% remains challenging. Here we introduce a versatile approach combining impregnation and two-step annealing to synthesize ultra-high-density single-atom catalysts with metal contents up to 23 wt% for 15 metals on chemically distinct carriers. Translation to a standardized, automated protocol demonstrates the robustness of our method and provides a path to explore virtually unlimited libraries of mono- or multimetallic catalysts. At the molecular level, characterization of the synthesis mechanism through experiments and simulations shows that controlling the bonding of metal precursors with the carrier via stepwise ligand removal prevents their thermally induced aggregation into nanoparticles. The drastically enhanced reactivity with increasing metal content exemplifies the need to optimize the surface metal density for a given application. Moreover, the loading-dependent site-specific activity observed in three distinct catalytic systems reflects the well-known complexity in heterogeneous catalyst design, which now can be tackled with a library of single-atom catalysts with widely tunable metal loadings.
RESUMEN
Sensitive but with simple, inexpensive detection of disease-related biomarkers in real biological samples is of quite necessity for early diagnosis and disease surveillance. We herein first introduced high-activity Fe3O4 nanozyme as signal amplifier to develop an ultrasensitive photoelectrochemical (PEC) immunoassay, which meanwhile has the distinct merits of both simplicity and low cost compared with previously reported enzyme-labeling PEC immunoassays. In the proposal, to illustrate and describe the PEC platform, prostate-specific antigen (PSA, Ag) was used as a target model. Specifically, ZnO nanorods (ZnO-NRs) grown vertically on a bare indium-tin oxide (ITO) electrode was deposited with ZnIn2S4 nanocrystals, producing ZnIn2S4/ZnO-NRs/ITO photoelectrode as the PEC matrix to modify capture PSA antibody (Ab1). Histidine-modified Fe3O4 (his-Fe3O4) nanozyme as signal amplifier was linked with signal PSA antibody (Ab2) to form his-Fe3O4@Ab2 conjugate, and was anchored through specific sandwich immunoreaction. The labeling his-Fe3O4 nanozyme acted as a peroxidase to induce the generation of the insoluble and insulating precipitation, resulting in an evident decrease in the photocurrent signal. On account of combined effects of high catalytic efficiency of the his-Fe3O4 nanozyme and excellent PEC properties of the ZnIn2S4/ZnO-NRs/ITO photoelectrode, ultralow detection limit of 18â¯fg/mL for target Ag detection was achieved. Besides, as high-activity his-Fe3O4 nanozyme has substituted natural enzyme as signal amplifier, simplicity and low cost of the PEC immunoassay was realized.