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Highlights: The single-atom Cu species with S = 0 spin ground state in CuIII-HHTP have been fabricated. The CuIII-HHTP exhibits remarkable performance with a high urea yield of 7.780 mmol h−1 g−1 with the corresponding Faradaic efficiency of 23.09% at − 0.6 V (vs. RHE). Low spin state and empty ( d x 2 -y 2 0 ) orbitals are favorable to enhance the production urea of C–N coupling process. The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for electrocatalytic urea via a coordination strategy in a metal–organic frameworks: CuIII-HHTP and CuII-HHTP. CuIII-HHTP exhibits an improved urea production rate of 7.78 mmol h−1 g−1 and an enhanced Faradaic efficiency of 23.09% at − 0.6 V vs. reversible hydrogen electrode, in sharp contrast to CuII-HHTP. Isolated CuIII species with S = 0 spin ground state are demonstrated as the active center in CuIII-HHTP, different from CuII with S = 1/2 in CuII-HHTP. We further demonstrate that isolated CuIII with an empty d x 2 -y 2 0 orbital in CuIII-HHTP experiences a single-electron migration path with a lower energy barrier in the C–N coupling process, while CuII with a single-spin state ( d x 2 -y 2 1 ) in CuII-HHTP undergoes a two-electron migration pathway. [ABSTRACT FROM AUTHOR]

A turn-on fluorometric method is described for the determination of adenosine-5′-triphosphate (ATP). It is based on the displacement of a dye-labeled oligonucleotide from a cobalt(II) based layered double hydroxide (LDH). Due to the electrostatic and ligand exchange interaction, the FAM-labeled DNA is readily adsorbed on the LDH. This leads to complete and fast quenching of the green fluorescence of the label. However, on addition of ATP, the DNA is detached from the LDH because of the stronger affinity of ATP for LDH. This results in the restoration of the green fluorescence. The effect was used to design a sensitive assay that has a linear response in the 0.5–100 μM ATP concentration range and a 0.23 μM lower detection limit. It was applied to the determination of ATP in spiked serum samples. Graphical abstract Schematic presentation of a fluorometric ATP assay based on the displacement of a dye-labeled oligonucleotide from a layered double hydroxide (LDH). [ABSTRACT FROM AUTHOR]