Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material.
activity (2007), [1] a wide range of nanomaterials (i.e., nanozymes) has been found to exhibit this property. [2][3][4][5] However, the mechanism behind those transition metal-based mimetics is not clear until recently. [6][7][8] As illustrated in Figure 1a, the redox between their surface M n+ (oxidation) and H 2 O 2 (reduction) first generates OH radicals (step (a)), which later oxidize substrates (e.g., tetramethylbenzidine (TMB)) giving a color change for the evaluation of activity (step (b)). To complete the catalytic cycle, OH radicals must oxidize other H 2 O 2 to produce HO 2 radicals (step (c)) for the regeneration of surface M n+ (step (d)). Since the later three steps are two orders of magnitude faster than step (a), the redox rate of surface M n+ with H 2 O 2 is thus the key step affecting the peroxidase-like activity of nanozymes. [6] Our recent study also suggests that the activity of a given nanozyme can be further enhanced by tuning the initial concentration of surface M n+ and its local structure for H 2 O 2 activation. [8] This mechanism is distinct from that of peroxidases. Taking horseradish peroxidase (HRP) as an example (Figure 1b), [9] its active site consists of a Fe(III)-protoporphyrin IX with His-42 and Arg-38 in the reaction pocket coactivating the OO bond of H 2 O 2 . The adsorbed H 2 O 2 first oxidizes Fe(III) (i.e., the resting state) to Fe(IV)-oxo with a radical retained on the porphyrin ring (the compound I). This reactive Single-atom catalysts have attracted attention in the past decade since they maximize the utilization of active sites and facilitate the understanding of product distribution in some catalytic reactions. Recently, this idea has been extended to single-atom nanozymes (SAzymes) for the mimicking of natural enzymes such as horseradish peroxidase (HRP) often used in bioanalytical applications. Herein, it is demonstrated that those SAzymes without constructing the reaction pocket of HRP still undergo the OH radical-mediated pathway like most of the reported nanozymes. Their positively charged single-atom centers resulting from support electronegative oxygen/nitrogen hinder the reductive conversion of H 2 O 2 to OH radicals and hence display low activity per site. In contrast, it is found that this step can be facilitated over their metallic counterparts on cluster nanozymes with much higher site activity and atom efficiency (cf. SAzymes with 100% atom utilization). Besides the mimicking of HRP in glucose detection, cluster nanozymes are also demonstrated as a better oxidase mimetic for glutathione detection.
Application of a fiber optic biosensor (FOB) to the real-time investigation of the interaction kinetics between FITC-conjugated monoclonal sheep anti-human C-reactive protein (CRP) antibody and CRP isoforms on the surface of optical fiber is described. Recently, both the native pentameric CRP (pCRP), an acute phase protein belonging to pentraxin family, and an isoform of pCRP, modified CRP (mCRP), have been suggested to have proinflammation effects on vascular cells in acute myocardial infarction (AMI). In current studies, we generate mCRP from pCRP, and use several methods including fluorescence spectral properties, circular dichroism, analytical ultracentrifuge, and Western blotting to demonstrate their differences in physical and chemical properties as well as the purity of pCRP and mCRP. In addition, we design and implement an FOB to study the real-time qualitative and quantitative biomolecular recognition of CRP isoforms. Specifically, the association and dissociation rate constants of the reaction between FITC-conjugated monoclonal sheep anti-human CRP antibody and the pCRP and mCRP are determined. The feasibility of our current approach to measure the association and dissociation rate constants of the reaction between tested CRP isoforms was successfully demonstrated.
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