scholarly journals Tyrosinase Nanoparticles: Understanding the Melanogenesis Pathway by Isolating the Products of Tyrosinase Enzymatic Reaction

2021 ◽  
Vol 22 (2) ◽  
pp. 734
Author(s):  
Paul K. Varghese ◽  
Mones Abu-Asab ◽  
Emilios K. Dimitriadis ◽  
Monika B. Dolinska ◽  
George P. Morcos ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Large Scale ◽  
Magnetic Beads ◽  
Enzymatic Reaction ◽  
Oculocutaneous Albinism ◽  
Transmission Electron ◽  
Hill Kinetics ◽  
Rate Limiting ◽  
Human Tyrosinase

Human Tyrosinase (Tyr) is the rate-limiting enzyme of the melanogenesis pathway. Tyr catalyzes the oxidation of the substrate L-DOPA into dopachrome and melanin. Currently, the characterization of dopachrome-related products is difficult due to the absence of a simple way to partition dopachrome from protein fraction. Here, we immobilize catalytically pure recombinant human Tyr domain (residues 19–469) containing 6xHis tag to Ni-loaded magnetic beads (MB). Transmission electron microscopy revealed Tyr-MB were within limits of 168.2 ± 24.4 nm while the dark-brown melanin images showed single and polymerized melanin with a diameter of 121.4 ± 18.1 nm. Using Hill kinetics, we show that Tyr-MB has a catalytic activity similar to that of intact Tyr. The diphenol oxidase reactions of L-DOPA show an increase of dopachrome formation with the number of MB and with temperature. At 50 °C, Tyr-MB shows some residual catalytic activity suggesting that the immobilized Tyr has increased protein stability. In contrast, under 37 °C, the dopachrome product, which is isolated from Tyr-MB particles, shows that dopachrome has an orange-brown color that is different from the color of the mixture of L-DOPA, Tyr, and dopachrome. In the future, Tyr-MB could be used for large-scale productions of dopachrome and melanin-related products and finding a treatment for oculocutaneous albinism-inherited diseases.

Electrooxidation of Methanol on Carbon Supported Gold Nanoparticles

2013 ◽  
Vol 313-314 ◽  
pp. 232-236
Author(s):  
Dan Zhang
Keyword(s):  
Gold Nanoparticles ◽  
Catalytic Activity ◽  
Competitive Adsorption ◽  
Chemical Reduction ◽  
Reduction Process ◽  
Carbon Support ◽  
Transmission Electron ◽  
Supported Gold Nanoparticles ◽  
Supported Gold

Activated carbon supported gold nanoparticles (Au/C) were prepared by a chemical reduction process using NaBH4as a reducing agent. The characterization of transmission electron microscope indicated that the Au nanoparticles (AuNPs) in the Au/C catalyst were highly well dispersed on the carbon support. The catalytic activity of the Au/C catalyst for the methanol electrooxidation (MEO) was investigated by the cyclic voltammetry (CV). The results displayed that the Au/C catalyst exhibited a favorable catalytic activity towards the MEO in alkaline solution. Moreover, the competitive adsorption between OH-and CH3OH on the surface of the AuNPs in the Au/C catalyst existed in the course of the MEO. Based on this competitive adsorption, the mechanism of the MEO on the Au/C catalyst was further investigated.

scholarly journals Characterization of hepatitis C virus pseudoparticles by cryo-transmission electron microscopy using functionalized magnetic nanobeads

2010 ◽  
Vol 91 (8) ◽  
pp. 1919-1930 ◽  
Author(s):  
Pierre Bonnafous ◽  
Marie Perrault ◽  
Olivier Le Bihan ◽  
Birke Bartosch ◽  
Dimitri Lavillette ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Membrane Fusion ◽  
Magnetic Beads ◽  
Neutral Ph ◽  
Transmission Electron ◽  
Magnetic Nanobeads

Cell entry and membrane fusion of the hepatitis C virus (HCV) depend on its envelope glycoproteins E1 and E2. HCV pseudotyped particles (HCVpps) are relevant and popular models to study the early steps of the HCV life cycle. However, no structural characterization of HCVpp has been available so far. Using cryo-transmission electron microscopy (cryo-TEM), providing structural information at nanometric resolution, the molecular details of HCVpps and their fusion with liposomes were studied. Cryo-TEM revealed HCVpps as regular 100 nm spherical structures containing the dense retroviral nucleocapsid surrounded by a lipid bilayer. E1–E2 glycoproteins were not readily visible on the membrane surface. Pseudoparticles bearing the E1–E2 glycoproteins of Semliki forest virus looked similar, whereas avian influenza A virus (fowl plague virus) haemagglutinin/neuraminidase-pseudotyped particles exhibited surface spikes. To further characterize HCVpp structurally, a novel method was designed based on magnetic beads covered with anti-HCV antibodies to enrich the samples with particles containing E1–E2. This strategy efficiently sorted HCVpps, which were then directly observed by cryo-TEM in the presence or absence of liposomes at low or neutral pH. After acidification, HCVpps looked the same as at neutral pH and closely contacted the liposomes. These are the first visualizations of early HCV membrane fusion events at the nanometer scale. Furthermore, fluorimetry analysis revealed a relative resistance of HCVpps regarding their fusion capacity when exposed to low pH. This study therefore brings several new molecular details to HCVpp characterization and this efficient strategy of virion immunosorting with magnetic nanobeads is direct, efficient and adaptable to extensive characterization of any virus at a nanometric resolution.

Synthesis and Characterization of In-Doped SnO2 (ITO) Nanowires

2007 ◽  
Vol 121-123 ◽  
pp. 209-214 ◽  
Author(s):  
Zai Yin Huang
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Large Scale ◽  
Thermal Evaporation ◽  
Critical Factor ◽  
Argon Atmosphere ◽  
Synthesis And Characterization ◽  
Transmission Electron ◽  
Scanning Electron

Large-scale synthesis of In-doped SnO2 (ITO) nanowires was achieved by direct thermal evaporation of a mixture of Sn and In powders at 900°C in an Argon atmosphere. Scanning electron microscopy and transmission electron microscopy observations show that ITO nanowires have diameter ranging from 20 to 100 nm and lengths up to several tens of micrometers. By altered the reaction temperature, we find that the temperature of the reaction is the critical factor for the morphologies and sizes of the ITO nanowires.

scholarly journals Characterization of graphene nanosheets obtained by a modified Hummer's method

2018 ◽  
Vol 23 (1) ◽  
Author(s):  
Renata Hack ◽  
Cláudia Hack Gumz Correia ◽  
Ricardo Antônio de Simone Zanon ◽  
Sérgio Henrique Pezzin
Keyword(s):  
Electron Microscopy ◽  
Large Scale ◽  
Graphene Nanosheets ◽  
Scale Production ◽  
Natural Graphite ◽  
Graphite Oxidation ◽  
Transmission Electron ◽  
Large Scale Production ◽  
High Degree

ABSTRACT Natural graphite is an inexpensive and abundant source to obtain graphene nanosheets. The most efficient method for large-scale production is the chemical method, which is based on the oxidation of natural graphite. This paper reports the synthesis and characterization of graphene obtained by the Hummers method with some modifications. The results indicate a high degree of graphite oxidation, proving that the process was efficient. Analyses of field emission scanning electron microscopy (FEG), transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetric analysis (TGA) and X-ray diffraction showed that the graphene produced presented characteristics similar to the commercial graphene.

Synthesis and Characterization of MoO2 Nanoplates Prepared by Thermal Evaporation of MoO3 and S Powders

2016 ◽  
Vol 697 ◽  
pp. 3-6
Author(s):  
Han Qing Li ◽  
Zhi Jian Peng ◽  
Jing Wen Qian ◽  
Zhen Guang Shen ◽  
Xiu Li Fu
Keyword(s):  
Electron Microscopy ◽  
Large Scale ◽  
Thermal Evaporation ◽  
Silicon Substrates ◽  
X Ray Diffraction ◽  
Super Capacitor ◽  
Transmission Electron ◽  
Composition And Structure ◽  
Battery Electrode

MoO2 has been widely used in many fields such as catalyst, gas-senor, super capacitor and Li-ion battery electrode. In this paper, MoO2 nanoplates were synthesized in high density and large scale on silicon substrates via simple thermal evaporation of MoO3 and S powders at 950 °C in a tube furnace. The morphology, composition and structure of the nanoplates were characterized by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results indicate that the as-synthesized nanoplates are of well crystalline structure, and the thickness of these nanoplates is in the range of 100-300 nm. The growth mechanism of the nanoparticles was proposed as a vapor-solid process.

scholarly journals Design and Characterization of Ag@Cu2O-rGO Nanocomposite for the p-Nitrophenol Reduction

Catalysts ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 43
Author(s):  
Chao Song ◽  
Shuang Guo ◽  
Lei Chen
Keyword(s):  
Electron Microscopy ◽  
Catalytic Activity ◽  
Catalytic Reduction ◽  
Catalytic Efficiency ◽  
Transmission Electron ◽  
Nitrophenol Reduction ◽  
Reduced Graphene ◽  
High Degree ◽  
Scanning Electron

In this paper, we designed Ag nanoparticles coated with a Cu2O shell, which was successfully decorated on reduced graphene oxide (rGO) via a solid-state self-reduction. The Cu2O, Ag@Cu2O, and Ag@Cu2O-rGO nanocomposites were synthesized and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis, and XPS to evaluate the properties of the composites. In order to compare the chemical catalytic activity, the Cu2O, Ag@Cu2O, and Ag@Cu2O-rGO nanocomposites were employed for the catalytic reduction of p-nitrophenol (4-NP) into p-aminophenol (4-AP) in aqueous solution. The Ag@Cu2O-rGO nanocomposite exhibited excellent catalytic activity due to the intense interaction and high degree of electron transfer among Ag, Cu2O, and rGO. The rGO acted as the platform to bridge the isolated nanoparticles; furthermore, the electrons could quickly transfer from the Ag core to the Cu2O shell, which improved the chemical catalytic efficiency.

Preparation and Characterization of Perovskite-Type Oxide Catalysts for Combustion of Methane

2012 ◽  
Vol 427 ◽  
pp. 77-81
Author(s):  
Gang Xue ◽  
Xue Fang Zhang ◽  
Sai Fei Wang ◽  
Chao Yue Zhao
Keyword(s):  
Electron Microscopy ◽  
Catalytic Activity ◽  
Sol Gel ◽  
Perfect Crystal ◽  
Activity Measurement ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Microscopy Techniques ◽  
Perovskite Type

A series of rare earth perovskite-type oxides La09Sr0.1Co0.9Mn0.1O3La08Sr0.2Co0.8Mn0.2O3and La05Sr0.5Co0.5Mn0.5O3were prepared along the sol-gel method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy techniques (TEM) and catalytic activity measurement for combustion of CH4. The results indicated that a perfect crystal structure of perovskite was formed and La3+and Co3+ions were partly replaced by Sr2+and Mn3+ions, respectively, and perovskite-type oxides were composed of nanocrystals with particle size of 20~50nm. The catalytic activity for the combustion of CH4 was evaluated and La05Sr0.5Co0.5Mn0.5O3exhibited best performance with the temperature of 50% and 90% conversion efficiency of 723K and 833K.

Multi- and Single-Walled Nanotubes in the B-C-N System Studied by HRTEM and EELS

2000 ◽  
Vol 6 (S2) ◽  
pp. 50-51
Author(s):  
Y. Bando ◽  
D. Golberg ◽  
L. Bourgeois ◽  
K. Kurashima ◽  
T. Sato
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Large Scale ◽  
Chemical Method ◽  
Layered Compounds ◽  
Synthesis Parameters ◽  
Transmission Electron ◽  
Wide Horizon ◽  
Bn Nanotubes

Discoveries of C multi-walled (MWNTs) and single-walled (SWNTs) nanotubes opened up a wide horizon for applications of these nanostructures as electronic and structural materials. Later on, it has been realized that the nanotubular structures are formed in other layered compounds, e.g. in the B-C-N materials. However, in contrast to the C-based nanotubes whose synthesis parameters are well-established, synthesis of B- and N-doped C and pure BN nanotubes is a challenging issue. The present paper reports on large-scale synthesis and detailed HRTEM and EELS characterization of nanotubes in the B-C-N system.MWNTs and SWNTs of B-C-N and BN were produced from C nanotube templates via a substitution chemical method through oxidation by B2O3, in a flowing N2 atmosphere at 1573- 1773 K. HRTEM of a product was carried out using a high-resolution field emission transmission electron microscope JEM-3000F (JEOL) equipped with a parallel EELS detector Gatan 666 and an ultra thin window Si(Li) EDS detector.

Structural Characterization of GaN Nanowires Fabricated via Direct Reaction of Ga Vapor and Ammonia

2001 ◽  
Vol 675 ◽  
Author(s):  
R.N. Jacobs ◽  
L. Salamanca-Riba ◽  
M. He ◽  
G.L. Harris ◽  
P. Zhou ◽  
...  
Keyword(s):  
Large Scale ◽  
Critical Role ◽  
Compositional Analysis ◽  
Direct Reaction ◽  
X Ray Diffraction ◽  
Growth Technique ◽  
X Ray ◽  
Gan Nanowires ◽  
Transmission Electron

ABSTRACTWe report structural studies of large-scale wurtzite GaN nanowires fabricated by direct reaction of Ga vapor and NH3. This recently reported growth technique [1] demonstrates processing of GaN one-dimensional structures as thin as 26 nm and up to 500 μm in length. This method is both interesting and attractive in that fabrication is carried out without the assistance of template materials as required by other methods. In this study, transmission electron microscopy (TEM) is used to characterize the nanowires, while x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) data provide supporting structural/compositional analysis. Our structural investigation reveals the presence of thin hexagonal platelets, which we believe play a critical role in the nucleation, growth, and orientation of the wires. In particular, our findings indicate that most of the wires grow along the [2110] direction, normal to the platelet edges.

scholarly journals Mutagenesis and mechanistic study of a glycoside hydrolase family 54 α-L-arabinofuranosidase from Trichoderma koningii

2006 ◽  
Vol 401 (2) ◽  
pp. 551-558 ◽  
Author(s):  
Chin-Feng Wan ◽  
Wei-Hong Chen ◽  
Cheng-Ta Chen ◽  
Margaret Dah-Tsyr Chang ◽  
Lee-Chiang Lo ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Enzymatic Reaction ◽  
Glycoside Hydrolase Family ◽  
Wild Type ◽  
Trichoderma Koningii ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Hydrolase Family ◽  
Enzyme Intermediate

A GH (glycoside hydrolase) family 54 α-L-arabinofuranosidase from Trichoderma koningii G-39 (termed Abf) was successfully expressed in Pichia pastoris and purified to near homogeneity by cation-exchange chromatography. To determine the amino acid residues essential for the catalytic activity of Abf, extensive mutagenesis of 24 conserved glutamate and aspartate residues was performed. Among the mutants, D221N, E223Q and D299N were found to decrease catalytic activity significantly. The kcat values of the D221N and D299N mutants were 7000- and 1300-fold lower respectively, than that of the wild-type Abf. E223Q was nearly inactive. These results are consistent with observations obtained from the Aspergillus kawachii α-L-arabinofuranosidase three-dimensional structure. This structure indicates that Asp221 of T. koningii Abf is significant for substrate binding and that Glu223 as well as Asp299 function as a nucleophile and a general acid/base catalyst for the enzymatic reaction respectively. The catalytic mechanism of wild-type Abf was further investigated by NMR spectroscopy and kinetic analysis. The results showed that Abf is a retaining enzyme. It catalyses the hydrolysis of various substrates via the formation of a common intermediate that is probably an arabinosyl–enzyme intermediate. A two-step, double-displacement mechanism involving first the formation, and then the breakdown, of an arabinosyl–enzyme intermediate was proposed. Based on the kcat values of a series of aryl-α-L-arabinofuranosides catalytically hydrolysed by wild-type Abf, a relatively small Brønsted constant, βlg=−0.18, was obtained, suggesting that the rate-limiting step of the enzymatic reaction is the dearabinosylation step. Further kinetic studies with the D299G mutant revealed that the catalytic activity of this mutant depended largely on the pKa values (>6) of leaving phenols, with βlg=−1.3, indicating that the rate-limiting step of the reaction becomes the arabinosylation step. This kinetic outcome supports the idea that Asp299 is the general acid/base residue. The pH activity profile of D299N provided further evidence strengthening this suggestion.

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