Cobalt and nitrogen co-doped mesoporous carbon for electrochemical hydrogen peroxide sensing: the effect of graphitization.

In this study, a facile strategy for the scalable synthesis of cobalt and nitrogen co-doped mesoporous carbon (Co-N/C) is reported. Structural characterization demonstrated that Co and N were successfully co-doped in the highly porous carbon. Graphitization of porous carbon was achieved by the introduction of cobalt species. The degree of graphitization of Co-N/C could be further promoted by increasing the calcination temperature. By taking advantage of the excellent mass and electron transfer kinetics attributed to the high specific surface area, high porosity and high graphitization, the obtained Co-N/C exhibited good electrochemical activity towards H2O2 reduction and excellent sensing performance for the electrochemical detection of H2O2. The Co-N/C-950 catalyst obtained at 950 °C showed good electrochemical sensing performance with a detection limit of 2 µM and a wide linear response over the concentration range from 0.03 mM to 13 mM. Meanwhile, Co-N/C exhibited high selectivity toward the detection of H2O2 in the presence of possible interferences during the applications such as NaCl, glucose, ascorbic acid and so on. The results confirm that Co-N/C could be used as an efficient electrocatalyst to fabricate electrochemical sensing devices.

Mechanism of the Oxidation of 3,3',5,5'-Tetramethylbenzidine Catalyzed by Peroxidase-Like Pt Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes: A Kinetic Study.

Experimental and kinetic modelling studies are presented to investigate the mechanism of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by hydrogen peroxide (H2 O2 ) catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes (SPB-Pt). Due to the high stability of SPB-Pt colloidal, this reaction can be monitored precisely in situ by UV/VIS spectroscopy. The time-dependent concentration of the blue-colored oxidation product of TMB expressed by different kinetic models was used to simulate the experimental data by a genetic fitting algorithm. After falsifying the models with abundant experimental data, it is found that both H2 O2 and TMB adsorb on the surface of Pt nanoparticles to react, indicating that the reaction follows the Langmuir-Hinshelwood mechanism. A true rate constant k, characterizing the rate-determining step of the reaction and which is independent on the amount of catalysts used, is obtained for the first time. Furthermore, it is found that the product adsorbes strongly on the surface of nanoparticles, thus inhibiting the reaction. The entire analysis provides a new perspective to study the catalytic mechanism and evaluate the catalytic activity of the peroxidase-like nanoparticles.

Novel porous ceramic sheet supported metal reactors for continuous-flow catalysis.

A novel porous ceramic sheet supported nickel particles reactor was obtained by an in-situ preparation method. This reactor was then used to investigate continuous-flow catalysis of nitroaromatic compounds and methyl orange. The details of the structure and morphology were characterized by XRD, SEM, XPS, Raman, element mapping, mercury intrusion method and Archimedes principle. The porous ceramic sheet supported Ni particles reactor exhibited excellent catalytic performance in the catalytic reduction of p-nitrophenol and methyl orange by sodium borohydride at room temperature. Both the conversion of p-nitrophenol (5 mM) and methyl orange (0.3 mM) reached nearly 100% at the injection speed of 2.67 mL·min-1. In addition, it maintained conversions of 100% after 10 recycling time since the porous ceramic sheet could reduce the aggregation for Ni particles. Furthermore, the chemisorbed oxygen, and the strong interaction between Ni and porous ceramic sheet resulted in a highly efficient, recoverable, and cost-effective multifunctional reactor. All of these advantages present new opportunities to be implemented in the field of waste water treatment and environmental toxicology. Ultimately, the porous ceramic sheet could also support other metal nanomaterial, and used in other fields of environmental catalysis.

Kinetic analysis of the reduction of 4-nitrophenol catalyzed by Au/Pd nanoalloys immobilized in spherical polyelectrolyte brushes.

We present a detailed study of the catalytic activity of Au/Pd nanoalloys with Au : Pd molar ratio 75 : 25 synthesized using spherical polyelectrolyte brushes (SPB) as carrier system. The reduction of 4-nitrophenol (Nip) by sodium borohydride (BH4(-)) has been used as a model reaction. This reaction proceeds in two steps: 4-nitrophenol is first reduced to 4-hydroxylaminophenol which in a second step is reduced to the final product 4-aminophenol. Both steps of the reaction proceed on the surface of the nanoparticles (Langmuir-Hinshelwood-mechanism). We use this model to analyze the experimental data obtained by catalysis with the Au/Pd-nanoalloys. Good agreements between theory and experiments were found up to 30% conversion of Nip. The kinetic parameters were compared with the data derived from neat Au and Pd nanoparticles immobilized in the same SPB carrier system. The addition of 25% molar ratio of Pd to the nanoalloys increases the reaction rate of the first step nearly 10 times compared with that of SPB-Au and 60 times compared with that of SPB-Pd. Analysis of the nanoalloy by high-resolution transmission electron microscopy suggests that the surface defects of the nanoalloys play an important role for the enhanced catalytic activity.

Effects of angiotensin-converting enzyme inhibitor, captopril, on bone of mice with streptozotocin-induced type 1 diabetes.

There are contradictory results about the effect of angiotensin-converting enzyme inhibitors (ACEIs) on bone. This study was performed to address the skeletal renin-angiotensin system (RAS) activity and the effects of the ACEI, captopril, on the bone of streptozotocin-induced type 1 diabetic mice. Histochemical assessment on bone paraffin sections was conducted by Safranin O staining and tartrate-resistant acid phosphatase staining. Micro-computed tomography was performed to analyze bone biological parameters. Gene and protein expression were determined by real-time polymerase chain reaction and immunoblotting, respectively. Type 1 diabetic mice displayed osteopenia phenotype and captopril treatment showed no osteoprotective effects in diabetic mice as shown by the reduction of bone mineral density, trabecular thickness and bone volume/total volume. The mRNA expression of ACE and renin receptor, and the protein expression of renin and angiotensin II were markedly up-regulated in the bone of vehicle-treated diabetic mice compared to those of non-diabetic mice, and these molecular changes of skeletal RAS components were effectively inhibited by treatment with captopril. However, treatment with captopril significantly elevated serum tartrate-resistant acid phosphatase 5b levels, reduced the ratio of osteoprotegerin/receptor activator of nuclear factor-κB ligand expression, increased carbonic anhydrase II mRNA expression and the number of matured osteoclasts and decreased transforming growth factor-ß and osteocalcin mRNA expression in the tibia compared to those of diabetic mice. The present study demonstrated that the use of the ACEI, captopril, has no beneficial effect on the skeletal biological properties of diabetic mice. However, this could be attributed, at least partially, to its suppression of osteogenesis and stimulation of osteoclastogenesis, even though it could effectively inhibit high activity of local RAS in the bone of diabetic mice.

Salt-Supported Nickel Oxides for Boosted Hydrogen Production: The Critical Role of Halogen.

Hydrogen production from organic waste by gasification and reforming technologies offers major benefits to both the environment and climate. The long-term stability and regeneration of the reforming catalyst are still the biggest challenges because of carbon deposition. Here we report a recyclable salt-supported nickel oxide NiO/NaX (X: F, Cl, Br) catalyst for effective autothermal reforming of the oxygenated volatile organic compound (OVOC) ethyl acetate to hydrogen. The optimal hydrogen selectivity achieved 82.0% at 650 °C and the durability reached 43 h. Interestingly, with the decreasing of halogen electronegativity (F > Cl > Br) in NaX, the corresponding hydrogen selectivity of the catalysts decreased. Although NiO/NaX catalysts possess a very small specific surface area and a dense microstructure, their catalytic performance is better than that of normal Ni-based catalysts loaded on high-specific-surface-area supports. Detailed investigations revealed the critical roles played by halogen during the reforming reaction. First, the strong electronegative halogen in NaX induced the formation of hydrogen bonds with the reactants and reaction intermediates, which may prolong the surface residence time of such species, thus ensuring efficient hydrogen production over small-specific-surface-area catalysts under high-temperature conditions. Second, the halogen of the support NaX weakening the Ni-O bonds of the exposed Ni atoms in NiO/NaX made it easier for NiO to be reduced to Ni0, thus reducing the reaction activation energy and prompting the rapid catalytic reaction. The strength of such metal-support interaction can be easily modulated by varying the halogen electronegativity. This study provides a new prospect for the design of innovative recyclable heterogeneous catalysts with low specific surface area but high activity.

Involvement of the skeletal renin-angiotensin system in age-related osteoporosis of ageing mice.

The local tissue-specific renin-angiotensin system (RAS) was identified. The aim of this study was to investigate the role of local bone RAS in the osteoporosis of aging mice. Twelve-month-old and two-month-old male mice were respectively assigned to the ageing and young groups. The tibias and femurs were collected for an analysis of histomorphology, bone mass, and gene and protein expression. H&E staining and micro-CT measurement showed a loss of the trabecular bone network and decrease of bone mineral density in the proximal tibial metaphysis of the aged mice. The PCR results indicated the significant up-regulation of renin and angiotensinogen (AGT) mRNA expression in both the tibia and femur of the ageing mice. Western blotting data showed that the tibial angiotensin II protein expression was significantly increased in the ageing group. The enhancement of renin and AGT expression in the bone tissue resulted in the increased production of angiotensin II which plays an important role in the pathology of age-related osteoporosis.

Early molecular responses of bone to obstructive nephropathy induced by unilateral ureteral obstruction in mice.

AIM: This study was performed to address the bone injury and the early molecular responses of bone to obstructive nephropathy induced by unilateral ureteral obstruction in mice. METHODS: The male mice were subjected to unilateral ureteral obstruction (UUO, n = 10) or sham operation (n = 10). All mice were killed on day 7 after the surgical operation. Hematoxylin and eosin and tartate-resistant acid phosphatase staining were performed on paraffin-embedded bone sections. Expression of genes and proteins was analyzed by reverse transcription-polymerase chain reaction, and Western blotting and immunohistochemistry staining, respectively. RESULTS: The serum calcium level was significantly reduced in UUO mice compared with that of Sham mice. The proximal tibia of UUO mice exhibited the increased expansion of chondrocytes zone, the reduction of osteoid content, and the increased separation and disconnection of woven bones. Reverse transcription-polymerase chain reaction results showed the downregulation of Cbfa1 and Col mRNA expression and the upregulation of Tgf-ß, CtsK, CaII, Opg and Rankl mRNA expression in tibia of UUO mice compared to those of Sham mice. The ratio of Opg and Rankl was unchanged between Sham and the UUO group. Local protein expression of angiotensin II and its type 2 receptor was dramatically upregulated in tibia of UUO mice. CONCLUSION: Together, it is concluded that the obstructive nephropathy has defective effects on bone, and the underlying mechanisms are the reduction of bone formation and the increase of bone resorption, which is mediated, at least partially through local angiotensin II signalling.

Changes of renal vitamin D metabolic enzyme expression and calcium transporter abundance in obstructive nephropathy.

The effects of urinary-tract obstruction on renal function have been clarified. However, there is little known about the change of renal vitamin D metabolic enzyme expression and vitamin D-dependent calcium transporting proteins expression in obstructive nephropathy. The male mice were subjected to unilateral ureteral obstruction (n = 10) or sham operation (n = 10). All mice were killed on day 7 after the surgical operation. Kidney sections were stained with Masson's trichrome and gene expression was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. The obstructed kidney exhibited interstitial fibrosis as shown by the strong collagen deposition in the interstitium. Quantitative PCR results showed the increase of 1-OHase (P < 0.001) mRNA expression and the decrease of 24-OHase (P < 0.01), CaBP-9k (P < 0.01) and CaBP-28k (P < 0.01) mRNA expression in obstructed kidney as compared to that of the Sham group. In addition, the mRNA expression of 1-OHase and CaBP-9k was significantly increased and decreased, respectively, in obstructed kidney as compared to that of the contra-lateral kidney in unilateral ureteral obstruction (UUO) mice. Together, the present finding supports the hypothesis that the ureteral obstruction leads to the alteration of renal vitamin D metabolic enzyme expression and calcium transporter abundance, which may secondarily induce the abnormality of vitamin D endocrine system and bone health.

Enhanced Catalytic Activity of Gold@Polydopamine Nanoreactors with Multi-compartment Structure Under NIR Irradiation.

Photothermal conversion (PTC) nanostructures have great potential for applications in many fields, and therefore, they have attracted tremendous attention. However, the construction of a PTC nanoreactor with multi-compartment structure to achieve the combination of unique chemical properties and structural feature is still challenging due to the synthetic difficulties. Herein, we designed and synthesized a catalytically active, PTC gold (Au)@polydopamine (PDA) nanoreactor driven by infrared irradiation using assembled PS-b-P2VP nanosphere as soft template. The particles exhibit multi-compartment structure which is revealed by 3D electron tomography characterization technique. They feature permeable shells with tunable shell thickness. Full kinetics for the reduction reaction of 4-nitrophenol has been investigated using these particles as nanoreactors and compared with other reported systems. Notably, a remarkable acceleration of the catalytic reaction upon near-infrared irradiation is demonstrated, which reveals for the first time the importance of the synergistic effect of photothermal conversion and complex inner structure to the kinetics of the catalytic reduction. The ease of synthesis and fresh insights into catalysis will promote a new platform for novel nanoreactor studies.

Effects of angiotensin II type 1 receptor blocker on bones in mice with type 1 diabetes induced by streptozotocin.

INTRODUCTION: This study was performed to address the pathological roles of the skeletal renin-angiotensin system (RAS) in type 1 diabetes-induced osteoporosis and the effects of the angiotensin II type 1 receptor blocker losartan on bones in diabetic mice. MATERIALS AND METHODS: Bone histomorphology was detected by H&E staining, Safranin O staining and X-ray radiography. Micro-CT was performed for the analysis of bone parameters. Gene and protein expression were determined by RT-PCR and immunoblotting. RESULTS: Type 1 diabetic mice displayed osteopenia phenotype, and losartan treatment had no osteoprotective effects on diabetic mice as shown by the reduction of bone mineral density and microarchitectural parameters at the proximal metaphysis of the tibia. The mRNA expression of AGT, renin receptor and ACE, and protein expression of renin and AT1R were markedly up-regulated in the bones of vehicle-treated diabetic mice compared to those of non-diabetic mice. The treatment with losartan further significantly increased the expression of AGT, renin, angiotensin II and AT1R, and reduced the expression of AT2R receptor as compared to those of diabetic mice. CONCLUSION: Local bone RAS functionally played a role in the development of type 1 diabetic osteoporosis, and losartan had no bone-sparing function in diabetes mice because of enhance skeletal RAS activity.

Trabecular bone deterioration at the greater trochanter of mice with unilateral obstructive nephropathy.

Our previous study showed the early molecular responses of bone in response to obstructive nephropathy in a unilateral ureteral obstruction (UUO) mouse model. Here, we addressed the changes in trabecular bone properties at greater trochanter, the proximal and the distal metaphysis of femur in UUO mice. The male mice were subjected to UUO (n=10) or sham operation (n=10). All mice were killed on day 7 after the surgical operation. The micro-computed tomography (micro-CT) analysis for different femoral trabecular bone sites demonstrated pathological alterations of trabecular bone mass and micro-networks at greater trochanter as shown by decreases in bone mineral density/bone volume (P<0.05) and trabecular number (P<0.05) and increases in trabecular separation (P<0.01) and bone surface/bone volume (P<0.05) in UUO mice. The present study demonstrates that UUO-induced unilateral obstructive nephropathy has markedly detrimental effects on the trabecular trochanter of the femur.