Nonenzymatic Catalysts Research Articles

The development of titanium dioxide nanotube-supported CdTe catalysts for photocatalytic enzymatic glucose fuel cell and response surface methodology optimization

Energy is one of the critical needs for human life and well-being. Alternative energy sources are essential due to the increase in energy demand with the rise in population the development of industrialization, and the damage caused by fossil fuels to the environment. Fuel cells, an alternative energy source, are a clean and environmentally friendly technology that converts chemical energy into electrical energy. In this study, titanium dioxide (TiO2) nanotube (TNT)-support CdTe catalysts were synthesized by the wet impregnation (WI) method. Glucose oxidase (GOD) and laccase (LAC) enzymes were modified by incubation on CdTe/TNT catalysts. These enzymatic and non-enzymatic catalysts were characterized by scanning electron microscope-energy dispersive X-ray (SEM-EDX) and mapping, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscope (TEM) analyses. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) analyses were used to examine the activity, resistance, and stability of catalysts for enzymatic photocatalytic glucose electrooxidation. The 3 % CdTe(50-50)-TNT-GOD/GCE electrode exhibited the highest activity, resistance, and stability under UV illumination compared to other electrodes. The modification parameters of the electrodes, incubation time, amount of catalyst ink, and drying time were found to be 136.96 min, 8.94 µL, and 21.30 min with response surface method (RSM) analysis, respectively. The estimated specific activity value was obtained as 0.754 mA/cm2 under optimized conditions.

Chronobiological approach to study microsymbiont catalase activity in female reproductive tract

Catalase is a heme-containing enzyme belonging to protection factors that destroys peroxide compounds. The presence of catalase activity is an important ability of microorganisms that allows them to be protected from unfavorable factors as well as adapt to macroorganism conditions. Catalase along with superoxide dismutase plays an important role in pathogen resistance to phagocyte oxygen-dependent bactericidal mechanisms. The aim of the study was to investigate microsymbiont catalase activity from female reproductive tract in normocenosis and candidiasis dysbiosis using the chronobiological approach. The study was conducted on clinical isolates, isolated from female reproductive tract microsymbiocenosis. The catalase activity was determined by spectrophotometry based on 24 hour-long hydrogen peroxide reduction with 3-hours interval in winter season. Dynamic hydrogen peroxide was assessed in 3–5 experiment replicates. In some Lactobacillus spp., catalase was found containing no heme group — pseudocatalase. Chronobiological approach allowed to reveal enzyme activity from all microsymbionts. The dominant and associative microbiota isolated from healthy females was characterized by circadian (24 hours) rhythms of catalase activity early in the morning — 5 a.m. (р 0.05). Hydrogen peroxide decomposes spontaneously or via non-enzymatic catalysts, and microorganisms cope with this situation under such conditions. In microsymbionts characteristic of female reproductive tract dysbiosis, and usually found in large numbers along with decreased Lactobacillus spp. ultradian rhythms with 12- and 8-hour harmonics of catalase activity with acrophase were recorded in the morning (8 a.m.) and evening hours (8 p.m.). The minimum values of enzyme production in all cultures were recorded at 12 p.m. and 5 p.m. Therefore, the contribution of the rhythm of the studied parameter at varying degree of vaginal sterility reflects the adaptive pathogen capabilities to the conditions of existence and can be the basis for studying related regulatory mechanisms. Mesor and amplitude phase stability are universal rhythmometric parameters used to evaluate patient’s condition independent of species assignment.

Electrocatalytic Conversion of Glucose into Hydrogen and Value-Added Compounds on Gold and Nickel Catalysts

Fine chemistry historically relies on the fossil fuel industry, implying oil extraction and refining [1]. The rarefaction of this resource and adverse environmental consequences of its extraction motivate research for alternative sources of chemicals. Low carbon footprint chemicals can be synthesized from nonedible biomass waste [2]; cellulose extracted from biomass can therefore play an important role, being a clean and widely accessible carbon source. One can extract D-Glucose (units that constitute cellulose) from cellulose and obtain numerous chemicals of interest, such as sorbitol [3][4] or gluconic acid [5][6] (gluconate in alkaline media), respectively by selective reduction or oxidation.Searching for high-performance non-enzymatic catalysts to perform such reactions brought us to study the activity and selectivity of gold and nickel in alkaline media. At the anode, results from differential electrochemical mass spectrometry (DEMS) seem to indicate that the glucose oxidation on a gold surface initiates by its dissociative adsorption (dehydrogenation): the dihydrogen (H2) produced likely originates from the formation of metastable H adsorbates (Had) [7] that diffuse onto the surface [8] and recombine into H2. In parallel, the adsorbed glucose oxidizes into value-added products such as gluconic acid, through a mechanism proposed from in situ (Fourier Transform InfraRed spectroscopy, FTIR) and ex situ (products analysis by High Performance Liquid Chromatography, HPLC) observations, and on the evaluation of the number of exchanged electrons using the rotating ring disk electrode (RRDE). Confronting the experimental data to a microkinetics model enables to validate the proposed mechanism and to estimate the kinetics rate constants. At the cathode, the glucose reduction reaction (GRR) into sorbitol competes with the hydrogen evolution reaction (HER). The HER activity of nickel strongly depends on its surface oxidation state [9], which can be tuned to search the best selectivity towards sorbitol. Combining high value-added compounds production with H2 as by-product allows to improve the overall energy efficiency of this electrolysis.[1] P. G. Levi and J. M. Cullen, “Mapping global flows of chemicals: from fossil fuel feedstocks to chemical products,” Environ. Sci. Technol., vol. 52, no. 4, pp. 1725–1734, 2018, doi: 10.1021/acs.est.7b04573.[2] D. Saygin, D. J. Gielen, M. Draeck, E. Worrell, and M. K. Patel, “Assessment of the technical and economic potentials of biomass use for the production of steam, chemicals and polymers,” Renew. Sustain. Energy Rev., vol. 40, pp. 1153–1167, 2014, doi: 10.1016/j.rser.2014.07.114.[3] B. García, J. Moreno, G. Morales, J. A. Melero, and J. Iglesias, “Production of sorbitol via catalytic transfer hydrogenation of glucose,” Appl. Sci., vol. 10, no. 5, 2020, doi: 10.3390/app10051843.[4] X. Guo et al., “Selective hydrogenation of D-glucose to D-sorbitol over Ru/ZSM-5 catalysts,” Chinese J. Catal., vol. 35, no. 5, pp. 733–740, May 2014, doi: 10.1016/S1872-2067(14)60077-2.[5] H. S. Isbell, H. L. Frush, and F. J. Bates, “Manufacture of calcium gluconate by electrolytic oxidation of dextrose,” Ind. Eng. Chem., vol. 24, no. 4, pp. 375–378, 1932, doi: 10.1021/ie50268a003.[6] S. Anastassiadis and I. Morgunov, “Gluconic acid production,” Recent Pat. Biotechnol., vol. 1, no. 2, pp. 167–180, May 2007, doi: 10.2174/187220807780809472.[7] M. M. Jaksic, B. Johansen, and R. Tunold, “Electrochemical behaviour of gold in acidic and alkaline solutions of heavy and regular water,” Int. J. Hydrogen Energy, vol. 18, no. 2, pp. 91–110, Feb. 1993, doi: 10.1016/0360-3199(93)90196-H.[8] J. Cornejo-Romero, A. Solis-Garcia, S. M. Vega-Diaz, and J. C. Fierro-Gonzalez, “Reverse hydrogen spillover during ethanol dehydrogenation on TiO2-supported gold catalysts,” Mol. Catal., vol. 433, pp. 391–402, 2017, doi: 10.1016/j.mcat.2017.02.041.[9] A. G. Oshchepkov et al., “Nanostructured nickel nanoparticles supported on vulcan carbon as a highly active catalyst for the hydrogen oxidation reaction in alkaline media,” J. Power Sources, vol. 402, no. June, pp. 447–452, 2018, doi: 10.1016/j.jpowsour.2018.09.051. Figure 1

Metal-organic framework functionalized bipolar electrodes for bulk electroenzymatic synthesis

Electrochemical regeneration of the cofactor nicotinamide adenine dinucleotide (NADH) is crucial for the enzymatic synthesis of a variety of valuable chemicals. [Rh(Cp*)(bpy)Cl]+ has been reported as one of the most efficient non-enzymatic catalysts for electrochemical regeneration of NADH, but the efficiency of the existing systems is still far from satisfying. Here we propose to suspend metal–organic framework functionalized glassy carbon beads in a bipolar electrochemical cell under mechanical stirring for bulk electroenzymatic synthesis. The beads are modified with a metal–organic framework NU-1000 shell, in which [Rh(Cp*)(bpy)Cl]+ catalyst is incorporated via the solvent-assisted ligand incorporation approach. Enzymatically active 1,4-NADH is electrochemically regenerated, and finally bipolar electrochemical bulk conversion of pyruvate into L-lactate is performed in the presence of NADH dependent L-lactate dehydrogenase as a model system. The very high turnover frequency (TOF) of 3100 ± 106 h−1 opens up promising perspectives for employing this concept also for various other electroenzymatic bulk processes.

Flexible Nonenzymatic Electrochemical Sensor for the Analysis of Urea in Artificial Sweat

Recently, wearable and flexible electrochemical sensors have attracted tremendous attention due to health monitoring and diagnostics for humans [1]. Such wearable devices will be able to provide low-cost, easy-to-use, and mass production for in-situ detection or point-of-care applications. Urea is an essential biomarker for the diagnosis of healthy kidneys because urea, a protein metabolite, is formed by the function of kidneys and is excreted into the urine. An abnormal concentration of urea can indicate potential kidney dysfunction. Although most urea sensors are based on the enzyme, the electrochemical sensors to use the nonenzymatic urea oxidation can provide higher stability, biocompatibility, and nontoxicity if nonenzymatic urea sensors address the hurdles such as high conductivity, a narrow range of urea reactions, and limited catalytic activities [2-4]. In addition, a sweat-based urea sensor may show good anti-interference performances for urea detection as the urea concentration in the sweat is 3.6 times higher than that of serum [5].Herein, we report a sensitive and selective nonenzymatic urea sensor [6]. Flexible and wearable platforms were fabricated using electrospinning polystyrene (PS) containing carbon nanotube as a conductive component. For nonenzymatic catalysts, Ni-Cu alloys were co-sputtered on the PS substrate and transformed to a Ni-Cu oxyhydroxide form by cyclic voltammetry treatment. Such an electrode structure with porous PS is believed to provide sufficient active sites, easy access to reactants, and adequate water wettability for effective charge transfer. The fabricated sensor presented an excellent linear response of 2.00-30.00 mM with a high sensitivity of 10.72 μAmM–1 cm–2 and 4.67 μM LoD for urea detection in neutral pH solution and artificial sweat. The dynamic bending test via 200 times and up to 150° angle bending showed excellent mechanical tolerance where bending deformation of the sensor platform does not affect electrochemical performance.References Bariya, Mallika, et al. “Wearable sweat sensors.” Nature Electronics 1, 160-171 (2018).Debata, Suryakanti, et al. "Design of CdV2O4-V6O13 micro flowers for non-enzymatic electrochemical detection of urea." In AIP Conference Proceedings, vol. 2115, no. 1, p. 030058. AIP Publishing LLC (2019).Yoon, Jaesik, et al. “Silver-Nanoparticle-Decorated NiOOH Nanorods for Electrocatalytic Urea Sensing.” ACS Applied Nano Materials 3, 7651-7658 (2020).Yoon, Jaesik, et al. “Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea.” Electroanalysis 31, 17-21 (2019).Thudichum, J. L. W. "On the analysis of urea in urine for clinical purposes." British medical journal 1, 38, 788 (1857).Yoon, Jaesik, et al. “Flexible Electrochemical Sensor Based on NiCu(OOH) for Monitoring Urea in Human Sweat.” Journal of Electrochemical Society 168, 117510 (2021).

Finite Element Method Study of Nanostructured Metal Oxide Based on NiO for Nonenzymatic Urea Sensors

Urea electrooxidation has attracted increasing attention because urea is an essential biomarker for diagnosing kidney conditions. Most urea sensors are based on the enzyme; however, enzyme-based sensors have a moderately complicated assembling method [1] due to poor stability. Different from the bulk diffusion of urea in the enzymatic urea oxidation [2], the nonenzymatic urea oxidation has reactions between the reductive and oxidative at the electrode surface [3]. Moreover, in order to use nonenzymatic urea sensors in a biomedical application area, high conductivity and catalytic activities are required. Therefore, a study of nonenzymatic urea sensor on a nanostructured electrode is of substantial interest.For urea detection, various metal oxides, such as ZnO [4], CuO [5], and NiO [6], have been broadly proposed. Practically, NiO catalysts were studied extensively for urea electrooxidation due to successful long-term operation [7]. Typical nonenzymatic catalysts for urea electrooxidation mainly focused on designing new nanostructures and maximizing their catalytic ability. However, quantitative models integrating the physical, chemical, and geometrical design properties still need improvement to develop sensor devices. The urea reaction occurs on the surface of nanostructured metal oxide. Thus, the effect of electrode geometry on the electrochemical reactions is motivated to explore urea sensors application.In the present study, we studied three different NiO structures such as nanorods, nanoflakes, and nanoparticles, for the nonenzymatic electrochemical sensor. Additionally, we developed a new analytical model to understand the nonenzymatic urea sensor using the finite element method. To further adjust the model, the morphology and the composition of the NiO catalysts were investigated using transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The NiO catalysts showed remarkable electrochemical achievement with acceptable linear sensitivity and selectivity to urea electrooxidation. Comprehensive information of the modeling concerning NiO as a catalyst in the nonenzymatic urea sensor will be given.References FATEMA, Kamrun Nahar, et al. “New Design of Active Material Based on YInWO4-G-SiO2 for a Urea Sensor and High Performance for Nonenzymatic Electrical Sensitivity.” ACS Biomaterials Science & Engineering, 2020.Debata, Suryakanti, et al. "Design of CdV2O4-V6O13 micro flowers for non-enzymatic electrochemical detection of urea." In AIP Conference Proceedings, vol. 2115, no. 1, p. 030058. AIP Publishing LLC, 2019.YOON, Jaesik, et al. “Silver-Nanoparticle-Decorated NiOOH Nanorods for Electrocatalytic Urea Sensing.” ACS Applied Nano Materials, 2020, 3.8: 7651-7658.YOON, Jaesik, et al. “Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea.” Electroanalysis, 2019, 31.1: 17-21.Goda, M. A., et al. “Enhanced Electrocatalytic Oxidation of Urea at CuOx-NiOx Nanoparticle-Based Binary Catalyst Modified Polyaniline/GC Electrodes.” Journal of The Electrochemical Society, 2020 167(6), 064522.Tyagi, Manisha, et al. "NiO nanoparticle-based urea biosensor." Biosensors and Bioelectronics 2013, 41:110-115.BARAKAT, Nasser AM, et al. “Influence of nitrogen doping on the electrocatalytic activity of Ni-incorporated carbon nanofibers toward urea oxidation.” International Journal of Hydrogen Energy, 2017, 42.34: 21741-21750.

Synthetic glycosidases for the precise hydrolysis of oligosaccharides and polysaccharides.

Glycosidases are an important class of enzymes for performing the selective hydrolysis of glycans. Although glycans can be hydrolyzed in principle by acidic water, hydrolysis with high selectivity using nonenzymatic catalysts is an unachieved goal. Molecular imprinting in cross-linked micelles afforded water-soluble polymeric nanoparticles with a sugar-binding boroxole in the imprinted site. Post-modification installed an acidic group near the oxygen of the targeted glycosidic bond, with the acidity and distance of the acid varied systematically. The resulting synthetic glycosidase hydrolyzed oligosaccharides and polysaccharides in a highly controlled fashion simply in hot water. These catalysts not only broke down amylose with similar selectivities to those of natural enzymes, but they also could be designed to possess selectivity not available with biocatalysts. Substrate selectivity was mainly determined by the sugar residues bound within the active site, including their spatial orientations. Separation of the product was accomplished through in situ dialysis, and the catalysts left behind could be used multiple times with no signs of degradation. This work illustrates a general method to construct synthetic glycosidases from readily available building blocks via self-assembly, covalent capture, and post-modification. In addition, controlled, precise, one-step hydrolysis is an attractive way to prepare complex glycans from naturally available carbohydrate sources.

Silk Fibroin-Based Materials for Catalyst Immobilization.

Silk fibroin is a widely and commercially available natural protein derived from silkworm cocoons. Thanks to its unique amino acid composition and structure, which lead to localized nanoscale pockets with limited but sufficient hydration for protein interaction and stabilization, silk fibroin has been studied in the field of enzyme immobilization. Results of these studies have demonstrated that silk fibroin offers an important platform for covalent and noncovalent immobilization of enzymes through serving as a stabilization matrix/support with high retention of the biological activity of the enzymes of interest. In the hope of providing suggestions for potential future research directions, this review has been written to briefly introduce and summarize key advances in silk fibroin-based materials for immobilization of both enzymes/biocatalysts (including alkaline phosphatase, β-glucosidase, glucose oxidase, lipase, urease, uricase, horseradish peroxidase, catalase, xanthine oxidase, tyrosinase, acetylcholinesterase, neutral protease, α-chymotrypsin, amylase, organophosphorus hydrolase, β-galactosidase, carbonic anhydrase, laccase, zymolyase, phenylalanine ammonia-lyase, thymidine kinase, and several others) and non-enzymatic catalysts (such as Au, Pd, Fe, α-Fe2O3, Fe3O4, TiO2, Pt, ZnO, CuO, Cu2O, Mn3O4, and MnO2).

Glucose electro-oxidation on Pt(100) in phosphate buffer solution (pH 7): A mechanistic study

Glucose is an important biomolecule that participates as a main source of energy in living organism reactions. Considering its biological importance, the electrochemical investigation about glucose electro-oxidation has attracted attention with the aim to develop non-enzymatic catalysts able to achieve the complete oxidation of glucose to be used as fuel in Direct Glucose Fuel Cells (DGFC). However, there are some challenges related to the oxidation of this relatively large, complex molecule, such as product distributions, adsorbed species, surface poisoning and structure sensitivity that must be understood. The use of well-defined surfaces, as single crystals, is a helpful tool to progress in this knowledge. In this context, the goal of this manuscript is the elucidation of the glucose electro-oxidation reaction in phosphate buffered solution (pH 7) on Pt(100) using cyclic voltammetry and in situ FTIR techniques at room temperature. It was observed that the reaction product distribution depends on glucose concentration. The maximum current density was reached with 2 × 10−2 mol dm−3 glucose (~2.04 mA cm−2) and then decreases with the increase of glucose concentration, because the reaction becomes dominated by the formation of strongly adsorbed species. In situ FITR experiments on Pt(100) show that the reaction proceeds through a complex mechanism, involving CO2, COL, COB, cyclic carbonate, γ-lactone, δ-lactone and carboxylic acids as intermediates and/or oxidation products. CO2 is generated mainly from COB and cyclic carbonate. Adsorbed CO seems to be the poisoning species responsible of the decrease of the catalytic activity on Pt(100), especially in the linear configuration, at higher glucose concentration.

A Disposable Paper-Based Urea Sensor Using Metal Oxides

The level of urea in urine can be a crucial biomarker to detect kidney failure, dehydration, renal function, and hepatic failure. [1] Thus, rapid and accurate sensing of urea is essential in a diagnostic clinic, especially for point-of-care testing devices (POCT). Paper-based analytical devices have been demonstrated as POCT due to its disposability, portability, low cost, and environmental-friendly quality. [2] In order to measure urea, electrochemical biosensors based on the enzyme were explored, but the application of enzyme has its limitations due to low shelf-life, complicated immobilization procedure, high cost, and complicate operating condition which is not fit to POCT application. [3] To overcome the limitations of enzyme, non-enzymatic urea sensor have attracted from researchers due to advantages such as good stability, re-usability, high sensitivity, redox flexibility, simplicity, and low cost. [4]As a non-enzymatic catalyst, nano metal oxides such as NiO, SnO2, and Fe2O3, exhibited catalytic activity on urea by the formation of the redox couple on the sensor surface.[5] [6] [7] To utilize non-enzymatic catalysts with comparable properties of enzyme, the development to increase reaction surface area has been emphasized by using nanomaterial, hierarchical structure, and support matrix.[8] [9] However, those processes involve complicate fabrication steps and often need additional post-process to remove the template leading to poisoning of the catalyst. As a potential approach for template-free process, paper can be used for an electrochemical sensor substrate. Paper has a complex fiber matrix that can provide pore pathways for the electrolyte to infiltrate inside, and by distributing catalyst uniformly within the paper, which formsmore reaction sites. Therefore, enhancement of performance and simplification of the fabrication can be achieved with the use of paper.In this study, the simple, disposable paper-based device was developed for urea electro-oxidation by using paper matrix as support. The paper-based electrode was fabricated by a screen printing method with filter paper, and different combinations of nano-metal oxides, NiO, SnO2, and Fe2O3. The metal oxide catalysts were loaded on the working electrode area and compared the performance. Structure and morphology of paper-based electrode were characterized by XRD and SEM. Investigation of selectivity and LOD was conducted by potentiostat. A detailed description of the fabrication of paper-based electrode and sensing performances will be presented.

Non-Enzymatic Electrooxidation of Urea with a Disposable Paper-Based Sensor Using Hierarchical NiO Hollow Sphere

Urea in the urine, protein metabolism, is present in the final product of human. The level of urea is a crucial biomarker that can assess the metabolic activity of humans such as the liver and renal function. [1] A high level of urea in the urine can result in kidney failure, dehydration, and gastrointestinal bleeding, while a low level can lead to nephritic syndrome, hepatic failure, etc. [2] Therefore, accurate and rapid sensing of urea is essential in a diagnostic clinic. Recently, paper-based analytical devices (PAD) are gaining its popularity as a manageable device for point-of-care equipment due to its inexpensive, portable, disposable, and environmentally-friendly qualities.[3] The majority of electrochemical biosensors rely on enzymes, such as urease; yet, utilization of enzyme is limited due to its high cost, poor reproducibility, and most of all, thermal and chemical instability which can influence the duration of sensor that depends on storage conditions such as temperature, pH, and humidity.[4] In addition, non-enzymatic biosensors has been attracted with the advantage of simplicity, redox flexibility, stability, and low cost. As a non-enzymatic metal-based material, Ni-based nanomaterials exhibited excellent catalytic activity over urea originated from catalytic effect for the formation of the redox couple of Ni(II) and Ni(III) on the surface. [5] When compared to enzymatic-based sensors, non-enzymatic catalysts tend to present lower sensitivity and higher limit of detection corresponding to lower performances of urea biosensor. To address this limit, there have been efforts to modify nanostructures with various shapes such as nanofiber, nanoparticle, and nanoflake arrays. Here we investigated a hollow sphere structure with nanosheet building block by using a hydrothermal method. The hollow sphere structure can increase the selectivity and sensitivity for urea biosensor by providing facile transport channels through electrolyte that exploits its inner and outer surfaces as the active site with maintaining the structural stability of the catalyst. Integration of non-enzymatic hierarchical catalyst on disposable PAD will lead to a high potential for the development of point-of-care testing devices. In this study, a non-enzymatic electrochemical paper-based sensor using hollow structure NiO was developed and demonstrated for the determination of urea. PADs were fabricated by sputtering on cotton paper, and hollow NiO was synthesized by hydrothermal method. Structure and morphologies of hierarchical NiO on PAD were characterized by XRD and SEM. Electrochemical properties such as selectivity and LOD were conducted by using a potentiostat with urea solution. A detailed description of the fabrication process and discussion of structure formation and sensing performances of hollow nickel oxide catalyst will be presented.

Non-Enzymatic Urea Biosensor Based on Silver-Nickel Oxyhydroxide Nanorods Composite Electrode

Urea is an end-product of the metabolism of nitrogenous compounds, which can be detected in the blood as well as urine [1]. Ammonia catabolized by protein metabolism is converted into urea by liver and kidneys [2]. Consequently, the concentration of urea in the urine or blood is a suitable biomarker that monitors liver and kidney function. If a sensor platform can immediately determine the level of urea in the biological fluid, it will be valuable for many patients when estimating the concentration of urea in the blood. Investigation on urea biosensors has been mainly guided out the advancement of enzyme-based catalysts [3]. However, the limitations such as denaturation of enzyme and mobilization to the catalysts lead to the lack of stability. Consequently, the improvement of non-enzyme-based catalysts can work the constraints mentioned above, thereby allowing the progression of urea biosensors. Many non-enzymatic catalysts have been investigated to catch urea molecules, including noble metals, transition metals, and metal hydroxide [4]-[6]. With them, the Ni-based catalysts are the most encouraging suggestion, because it gives excellent electrocatalytic efficiency, biocompatibility, nontoxicity, and high electron transfer. [7]. Although nickel-based catalysts are admitted being an excellent facilitator for the urea electrooxidation, published investigations are few in the nickel-based catalysts for biosensor applications. The inadequacy of research in the biosensor area is related to the mechanism of nickel-based catalysts in alkaline medium. Ni(OH)2 (Ni2+) is electrochemically oxidized to NiOOH (Ni3+) before electrocatalytic urea oxidation. However, since the pH of human blood is neutral (7.35-7.45), it is necessary to develop catalysts as a biomarker for urea electrooxidation which does not depend on pH. Therefore, the nickel-based catalysts intrinsically involving Ni3+ ion will more efficiently improve the electrooxidation performance of the urea. In this study, A composite catalyst based on silver-nickel oxide hydroxide nanorods (Ag-NiOOH) was synthesized for non-enzymatic urea detection. The Ag-NiOOH was characterized by energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. The morphology and the structure of the Ag-NiOOH were investigated using scanning electron microscopy. The Ag-NiOOH coated carbon paper was employed to fabricate a new electrochemical sensor for urea detection. The Ag-NiOOH/carbon paper electrode showed a very high sensitivity of 177 μAmM−1cm−2, a low detection limit of 5 μM and a response time of 1.5 s. Detailed discussion on the performance of Ag-NiOOH and the role of inherent Ni3+ ions as a catalyst in urea biosensor will be given. References Coll, Elisabeth, et al. "Serum cystatin C as a new marker for noninvasive estimation of glomerular filtration rate and as a marker for early renal impairment." American journal of kidney diseases 36.1 (2000): 29-34.Jakhar, Seema, et al. "Preparation, characterization and application of urease nanoparticles for construction of an improved potentiometric urea biosensor." Biosensors and Bioelectronics 100 (2018): 242-250.Liu, Baohong, et al. "Studies on a potentiometric urea biosensor based on an ammonia electrode and urease, immobilized on a γ-aluminum oxide matrix." Analytica chimica acta 341.2-3 (1997): 161-169.Boggs, Bryan et al. "Urea electrolysis: direct hydrogen production from urine." Chemical Communications 32 (2009): 4859-4861.Chen, Sheng, et al. "Size Fractionation of Two‐Dimensional Sub‐Nanometer Thin Manganese Dioxide Crystals towards Superior Urea Electrocatalytic Conversion." Angewandte Chemie International Edition 55.11 (2016): 3804-3808.Wu, Mao-Sung, et al. "Hydrothermal growth of vertically-aligned ordered mesoporous nickel oxide nanosheets on three-dimensional nickel framework for electrocatalytic oxidation of urea in alkaline medium." Journal of power sources 272 (2014): 711-718.Li, Chengchao, et al. "A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose." Talanta 77.1 (2008): 455-459. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.

Biosynthetically Inspired Transformation of Iboga to Monomeric Post-iboga Alkaloids

Summary Organisms have evolved to produce various natural products from a common precursor as a means of maximizing the number of secondary metabolites, thus acquiring selectional advantages. By adopting nature's divergent biosynthetic strategy, we transformed (+)-catharanthine to various iboga and post-iboga alkaloids, including (−)-conodusine A, (+)-conodusines B and C, (−)-voatinggine, (−)-tabertinggine, and (+)-dippinine B. Well-orchestrated oxidations and reorganizations of catharanthine derivatives enabled chemical access to these natural products.

High-performance non-enzymatic catalysts based on 3D hierarchical hollow porous Co3O4 nanododecahedras in situ decorated on carbon nanotubes for glucose detection and biofuel cell application.

In this work, high-performance non-enzymatic catalysts based on 3D hierarchical hollow porous Co3O4 nanododecahedras in situ decorated on carbon nanotubes (3D Co3O4-HPND/CNTs) were successfully prepared via direct carbonizing metal-organic framework-67 in situ grown on carbon nanotubes. The morphology, microstructure, and composite of 3D Co3O4-HPND/CNTs were characterized by scanning electron microscopy, transmission electron microscopy, micropore and chemisorption analyzer, and X-ray diffraction. The electrochemical characterizations indicated that 3D Co3O4-HPND/CNTs present considerably catalytic activity toward glucose oxidation and could be promising for constructing high-performance electrochemical non-enzymatic glucose sensors and glucose/O2 biofuel cell. When used for non-enzymatic glucose detection, the 3D Co3O4-HPND/CNTs modified glassy carbon electrode (3D Co3O4-HPND/CNTs/GCE) exhibited excellent analytical performance with high sensitivity (22.21mAmM-1cm-2), low detection limit of 0.35μM (S/N = 3), fast response (less than 5s) and good stability. On the other hand, when the 3D Co3O4-HPND/CNTs/GCE worked as an anode of a biofuel cell, a maximum power density of 210μWcm-2 at 0.15V could be obtained, and the open circuit potential was 0.68V. The attractive 3D hierarchical porous structural features, the large surface area, and the excellent conductivity based on the continuous and effective electron transport network in 3D Co3O4-HPND/CNTs endow 3D Co3O4-HPND/CNTs with the enhanced electrochemical performance and promising applications in electrochemical sensing, biofuel cell, and other energy storage and conversion devices such as supercapacitor. Graphical abstract High-performance non-enzymatic catalysts for enzymeless glucose sensing and biofuel cell based on 3D hierarchical hollow porous Co3O4 nanododecahedras anchored on carbon nanotubes were successfully prepared via direct carbonizing metal-organic framework-67 in situ grown on carbon nanotubes.

Applications of Nonenzymatic Catalysts to the Alteration of Natural Products.

The application of small molecules as catalysts for the diversification of natural product scaffolds is reviewed. Specifically, principles that relate to the selectivity challenges intrinsic to complex molecular scaffolds are summarized. The synthesis of analogues of natural products by this approach is then described as a quintessential "late-stage functionalization" exercise wherein natural products serve as the lead scaffolds. Given the historical application of enzymatic catalysts to the site-selective alteration of complex molecules, the focus of this Review is on the recent studies of nonenzymatic catalysts. Reactions involving hydroxyl group derivatization with a variety of electrophilic reagents are discussed. C-H bond functionalizations that lead to oxidations, aminations, and halogenations are also presented. Several examples of site-selective olefin functionalizations and C-C bond formations are also included. Numerous classes of natural products have been subjected to these studies of site-selective alteration including polyketides, glycopeptides, terpenoids, macrolides, alkaloids, carbohydrates, and others. What emerges is a platform for chemical remodeling of naturally occurring scaffolds that targets virtually all known chemical functionalities and microenvironments. However, challenges for the design of very broad classes of catalysts, with even broader selectivity demands (e.g., stereoselectivity, functional group selectivity, and site-selectivity) persist. Yet, a significant spectrum of powerful, catalytic alterations of complex natural products now exists such that expansion of scope seems inevitable. Several instances of biological activity assays of remodeled natural product derivatives are also presented. These reports may foreshadow further interdisciplinary impacts for catalytic remodeling of natural products, including contributions to SAR development, mode of action studies, and eventually medicinal chemistry.

非酵素触媒を用いる糖類の位置選択的官能基化に関する最近の動向

複雑な化合物の全合成研究において、保護基の着脱操作は欠かせない手法の一つである。一方で、これら操作は合成を行う上で本来不必要な操作であり、特定の位置に官能基を自由自在に導入することができれば、合成工程の短縮化が期待できる。そのような試みは、Baranらに代表されるように、近年の天然物合成においてしばしば報告されているが（1）、配糖体天然物や糖鎖のような複数のヒドロキシ基を有するポリオール化合物の合成では、現在でも必ず保護基の着脱操作が行われている。また、これらポリオールを直接官能基化する非酵素的手法も存在しない。これは、配糖体天然物や糖鎖のようなポリオールだけでなく、その一構成部位である単糖が有する複数のヒドロキシ基の中から、特定のヒドロキシ基を精密に見分ける手法が十分に発達してこなかったためである。本稿では、この課題に対処すべく行われてきた非酵素触媒の開発およびそれを用いる糖の位置選択的官能基化に関する最近の国内外における動向と併せて、われわれの最新の取り組みについて紹介する。

Recent Advances in the Regioselective Functionalization of Carbohydrates Using Non-Enzymatic Catalysts

Protection–deprotection strategies are one of the most essential techniques in the synthesis of complex compounds. However, if a functional group can be freely introduced onto a particular position of a compound without interference from other functionalities, some protection–deprotection steps in the synthesis can be eliminated. Though some advances have been recently reported for the removal of these steps in natural product synthesis by groups such as Baran et al. (1), the use of protecting groups is still necessary in the synthesis of polyols such as glycosides and polysaccharides. Additionally, no non-enzymatic methods are available to directly functionalize these polyols because methods to selectively recognize a particular OH group in polyols or monosaccharides, which is a unit of polyols, have not been sufficiently developed. In this review, we report recent advances in this field from the literature and our own approaches for the regioselective functionalization of carbohydrates employing non-enzymatic catalysts.

Catalytic role of traditional enzymes for biosynthesis of biogenic metallic nanoparticles: a mini-review.

Although the formation mechanism of biogenically metallic nanoparticles is broadly associated to enzyme mediation, major attention has been given to the role of proteins and peptides in oxido-reduction of metallic ions leading to these nanostructures. Among the wide range of biomolecules that can act not only as capping agents but also as non-enzymatic agents to form nanoparticles, disulphide bridge-containing peptides and amino acids particularly stand out. The literature proposes that they actively participate in the process of nanoparticles' synthesis, with thiols groups and disulphide bridge moieties as the reaction catalytic sites. Similarly, denaturated enzymes containing exposed S-S or S-H moieties are also able to reduce metallic ions to form nanoparticles. This mini-review is focused on the biogenic synthesis of metallic nanoparticles such as gold, silver, copper, platinum, palladium, lead and selenium, in which proteins, peptides, reductases and even oxido-reductases act as non-enzymatic catalysts of the reduction reaction, opening economically and ecologically favourable perspectives in the nanoparticles synthesis field.

Ultrasensitive electrochemical cancer cells sensor based on trimetallic dendritic Au@PtPd nanoparticles for signal amplification on lab-on-paper device

A trimetallic dendritic Au@PdPt nanparticles (Au@PdPt NPs) with intrinsic peroxidase-like catalytic activity were fabricated by a facile method. Au@PdPt NPs catalyzed the reduction of H2O2 with the help of the electron mediator (thionine), which produced the electrochemical signals dramatically amplified. A sandwiched sensor was designed and implemented in the paper chip device for the determination of K-562 cells. The surface of dendritic Au@PtPd NPs was linked with folic acid by click chemistry. Folic acid was attached to the folate receptor (FR) of cell surface with high affinity. So, K-562 cells could be assayed based on folic acid-functionalized Au@PtPd NPs. On the other hand, folic acid-functionalized Au-paper working electrode on origami electrochemical device was fabricated, which could be used to capture K-562 cells. The twice utilization of folic acid for the capture of K-562 cells as well as the attachment of dendritic Au@PtPd NPs nanoprobe, which enhanced the selectivity of sensor for the determination of cells. The proposed biosensor exhibited excellent analytical performance toward the cytosensing of K562 cells with a wide detection linear range from 1.0×102 to 2.0×107 cellsmL−1 and a detection limit of 31 cellsmL−1. Further, the proposed electrochemical sensor was applied to monitor cells. Au@PtPd NPs nonenzymatic catalysts could be used as signal-amplifying nanoprobes for ultrasensitive electrochemical sensing.

Primordial chemistry and enzyme evolution in a hot environment

Ever since the publication of Darwin's Origin of Species, questions have been raised about whether enough time has elapsed for living organisms to have reached their present level of complexity by mutation and natural selection. More recently, it has become apparent that life originated very early in Earth's history, and there has been controversy as to whether life originated in a hot or cold environment. This review describes evidence that rising temperature accelerates slow reactions disproportionately, and to a much greater extent than has been generally recognized. Thus, the time that would have been required for primordial chemistry to become established would have been abbreviated profoundly at high temperatures. Moreover, if the catalytic effect of a primitive enzyme (like that of modern enzymes) were to reduce a reaction's heat of activation, then the rate enhancement that it produced would have increased as the surroundings cooled, quite aside from changes arising from mutation (which is itself highly sensitive to temperature). Some nonenzymatic catalysts of slow reactions, including PLP as a catalyst of amino acid decarboxylation, and the Ce(IV) ion as a catalyst of phosphate ester hydrolysis, have been shown to meet that criterion. The work reviewed here suggests that elevated temperatures collapsed the time required for early evolution on Earth, furnishing an appropriate setting for exploring the vast range of chemical possibilities and for the rapid evolution of enzymes from primitive catalysts.