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Developing bifunctional catalysts toward urea oxidation and hydrogen evolution is a huge challenge. In this study, novel MOF-derived nickel nitride on nickel foam catalysts were successfully synthesized at different temperatures (300, 350, 400 °C) (denoted as C-T, T = 300, 350, 400). C-350 was demonstrated to be a highly active and durable 3D catalyst toward urea oxidation reaction (UOR), with a required potential of 1.337 V at 10 mA/cm2. At the same time, C-350 has higher catalytic performance toward hydrogen evolution reaction (HER) than other materials with a low overpotential of 47 mV at 10 mA/cm2. Furthermore, its two-electrode alkaline electrolyzer only needs a voltage of 1.503 V to obtain 100 mA/cm2, which is 0.160 V lower than that of pure water splitting. Also, the current density can be maintained for at least 24 h, showing its potential for practical applications.

Recently, G-quadruplex/hemin (G4/hemin) complexes have been found to exhibit peroxidase activity, and this feature has been extensively exploited for colorimetric detection of various targets. To further understand and characterize this important DNAzyme, its substrate specificity, inactivation mechanism, and kinetics have been examined by comparison with horseradish peroxidase (HRP). G4/hemin DNAzyme exhibits broader substrate specificity and much higher inactivation rate than HRP because of the exposure of the catalytic hemin center. The inactivation of G4/hemin DNAzyme is mainly attributed to the degradation of hemin by H(2)O(2) rather than the destruction of G4. Both the inactivation rate and catalytic oxidation rate of G4/hemin DNAzyme depend on the concentration of H(2)O(2), which suggests that active intermediates formed by G4/hemin and H(2)O(2) are the branch point of catalysis and inactivation. Reducing substrates greatly inhibit the inactivation of G4/hemin DNAzyme by rapidly reacting with the active intermediates. A possible catalytic and inactivation process of G4/hemin has been proposed. These results imply a potential cause for the hemin-mediated cellular injury and provide insightful information for the future application of G4/hemin DNAzyme.

Biogenic polyamines participate in regulating gene expression, activating DNA synthesis and facilitating DNA-protein interaction through interaction with DNA/RNA. The interaction of polyamines with G-quadruplexes (G4s) has been reported to modulate the structure of G4s. In this paper, we investigate the effects of polyamines on one of the properties of G4s, G4/hemin peroxidase. Three polyamines (spermine, spermidine and putrescine) are found to have positive effects on different G4/hemin DNAzymes, in which spermine exhibits the strongest enhancement efficiency. CD and UV/Vis spectral analysis suggests two reasons for the strong activity enhancement: first, spermine protects hemin from rapid degradation by H 2 O 2 ; second, spermine condenses the G4 structures and provides a favorable microenvironment for the catalytic reaction. Since G4/hemin DNAzymes have been extensively applied in various chemical sensors and biosensors, this finding would be helpful for the design of G4/hemin based sensors and widen the application range of this kind of DNAzyme.