1,721,028 research outputs found
Carbon-Based Single-Atom Catalysts for Advanced Applications
No full textCarbon-based materials are widely employed as metal-free catalysts or supports in catalysis, energy, and ecological applications because of their interesting properties. Generally, their high surface areas, size, shape, porosity, and the possibility of incorporating additional moieties through chemical functional designs are believed to be essential for enriching the catalytic activity of carbon-containing materials. Lately, the new field of single-atom catalysts (SACs) has emerged as the finest alternative for not only homogeneous but also heterogeneous catalysts used in various kinds of catalytic applications. Among a variety of SACs, carbon-based SACs are widely investigated catalysts because of their extraordinary features such as tunable morphologies, ordered porosity, and effortless immobilization through various metals (noble and non-noble), making them highly efficient single-atom catalysts for numerous important catalytic applications. Herein, we intend to report on the progress achieved in researching carbon-based single-atom catalysts, including primarily metals such as Co, Cu, Zn, Pd, Ni, Pt, among others, embedded in carbon matrices and applied to applications in organic catalysis, photocatalysis, and electrocatalysis. It is important to point out that the main focus of this Review is directed to the activity and applications of single-atom catalysts, which are discussed in detail; thus, characterization and rationalization are excluded. Finally, we provide a future perspective on the development and progress made on a carbon-based single metal atom for catalysis
Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications
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Enzyme-iron nanoparticle direct interactions: complex formation and application for a coulometric biosensor for aminoaldehydes
No full textRecombinant aminoaldehyde dehydrogenase from tomato (LeAMADH1) was used as a model protein for studying the intimate interaction at the interface between proteins and surface active maghemite nanoparticles (SAMNs). SAMNs represent a new class of maghemite nanoparticles, displaying great colloidal behavior and specific surface chemical properties, as well as, peculiar electrochemical characteristics and specificity toward protein binding [1-2]. A potential anchor zone was individuated in a carboxylic rich surface area of the protein structure by molecular modeling. LeAMADH1 was successfully bound to the surface of bare SAMNs and its enzymatic activity was preserved, leading to a magnetic drivable enzymatic hybrid (SAMN@LeAMADH1). The catalytic parameters of SAMN@LeAMADH1 were determined, and exploited for the construction of a coulometric biosensor for the determination of aminoaldehydes in alcoholic beverages. A suspension of SAMN@LeAMADH1, used inside a low volume (1 μL) electrochemical flow cell, fabricated in-house, led to the complete oxidation of aminoaldehydes, producing a correspondent amount of NADH. The hybrid nanomaterial was magnetically removed after the enzymatic reaction allowing its reutilization. At the same time, a SAMN modified carbon paste electrode, inserted in the microcell was used for the direct electro-oxidation of NADH, leading to the coulometric determination of NADH produced during the enzymatic process. The novel biosensor showed a series of peculiarities: a) SAMN modified carbon paste electrode was used for NADH electro-oxidation; b) the complete enzymatic oxidation of sample aminoaldehydes, producing NADH, was carried out in a colloidal suspension, inside a low volume electrochemical flow cell, optimizing reactant diffusion; c) NADH, produced during the complete enzymatic oxidation of aminoaldehydes, was coulometrically determined at the SAMN modified lectrode; d) the capture of the hybrid, by the application of an external magnet, makes it reusable. 1)Baratella et al., Biosensors and Bioelectronics, 2013, 45, 13–18. 2)Magro et al., Biosensors and Bioelectronics, 2014, 52, 159–165
Colloidal maghemite nanoparticles with oxyhydroxide-like interface and chiroptical properties
No full textMagnetic nanoparticles, mainly constituted of magnetite and maghemite, are widely used for environmental, biomedical and biotechnological applications. Herein, the synthesis and properties of maghemite nanoparticles characterized by chiroptical activity, representing an unprecedented feature for iron oxide nanoparticles, is described in detail. Among nanosized iron oxides, these maghemite nanoparticles stand out for the excellent colloidal stability in water and the witnessed ability to specifically bind selected molecules. The surface properties of nanoparticles were probed with AsIII and AsV oxyacids, studied by x-ray photoelectron spectroscopy and correlated to circular dichroism. The dichroic signal of nanoparticles was differently influenced by the coordination of ligands. Crystalline vacancies on the nanomaterial surface were identified as the chiral centers responsible of the dichroic behavior and the selectivity toward ligands. The latter was correlated with the ability of restructuring the nanomaterial at the crystal truncation. Furthermore, surface binding sites emerged for bearing labile coordination water in analogy with iron oxyhydroxides. The present report, besides enriching the colloidal chemistry of iron oxide based nanomaterials, can stimulate further research on inorganic systems expressing intrinsic chiral properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A water-dispersible, carboxylate-rich carbonaceous solid: Synthesis, heavy metal uptake and EPR study
No full textThermal oxidation of Na-cholate hydrate at 300 °C in air results in a carbonaceous solid (SC-30) nanomaterial bearing a steroid interior and a significant fraction of carboxylate sites. Electron Paramagnetic Resonance spectroscopy reveals that SC-30 bears a significant concentration of stable C-based radicals located at the interior of the steroid carbonaceous matrix. H-binding, determined by potentiometric acid-base titrations show that the SC-30 contains three types of H-binding sites. One type with pKa = 4.2 corresponds to surfacial metal-binding COOH groups. A second type of sites with pKa = 6.2 corresponds to COOH buried at the interior of the SC-30 carbon matrix, which are inactive in metal binding. A third type with pKa = 8.5-is also inactive in metal binding-originates from aggregated stacked-states like those observed for cholate in solution. The surfacial COO - carboxylate groups, confer the solid hydrophilic character, therefore it can be easily dispersed in water at high concentrations providing clear aqueous colloids. pH-edge metal uptake experiments and Surface Complexation Modelling show that SC-30 is an efficient heavy metal adsorbent in aqueous solution for Pb 2+ and Cu 2+ ions at pH 5-8. A structural/functional model is discussed based on the heterogeneous character of the SC-30 material. © 2011 Springer Science+Business Media, LLC
Avidin functionalized maghemite nanoparticles and their application for recombinant human biotinyl-SERCA purification
No full textWe report on the surface characterization, functionalization and application of stable water suspensions of novel surface active maghemite nanoparticles (SAMNs), characterized by a diameter of 11 ± 2 nm and possessing peculiar colloidal properties and surface interactions. These features permitted the acquisition of titration curves and aqueous UV-Vis spectrum and suggested a role played by surface under-coordinated iron atoms. This new class of nanoparticles was obtained through an easy, inexpensive, one-step, green procedure and functionalized with ligands of high biotechnological interest, such as biotin and avidin, by simple incubation in aqueous solution. Bound avidin was determined by measuring the disappearance of free avidin absorbance at 280 nm, as a function of nanoparticle increasing concentration, showing the presence of 10 ± 3 avidin molecules per nanoparticle. The biological activity of SAMN@avidin complex was evaluated and the number of available biotin binding sites was determined, using biotinyl-fluorescein as a probe, showing that each bound avidin molecule is able to bind 2.8 ± 0.8 biotin molecules, confirming the maintenance of biological activity and excellent binding capacity of SAMN@avidin complex. Furthermore Langmuir isotherm model was used to describe the biomolecule specific monolayer adsorption onto the particle surface, and, in the case of avidin, the maximum adsorption capacity was 100 ± 27 μg avidin/mg SAMN, while the binding constant is 45.18 μL μg-1. The SAMN@avidin complex was characterized by UV-Vis spectroscopy, quartz crystal microbalance, FTIR spectroscopy and transmission electron microscopy. Finally, SAMN@avidin was applied for the large scale purification of recombinant biotinylated human sarco/endoplasmic reticulum Ca2+-ATPase (hSERCA-2a), expressed by Saccharomyces. cerevisiae. The protein was magnetically purified and about 500 μg of a 70% pure hSERCA-2a were recovered from 4 liters of yeast culture, with a purification yield of 64%
Electrochemical determination of hydrogen peroxide production by isolated mitochondria: a novel nanocomposite carbon-maghemite nanoparticle electrode
No full textA simple carbon paste electrode modified with novel maghemite (-Fe2O3) nanoparticles, characterized by a mean diameter of about 10 nm and specific surface properties (called surface active maghemite nanoparticles, SAMNs) has been developed. The electrode is able to catalyze the electro-reduction of hydrogen peroxide at low applied potentials (-0.1 V vs. SCE). In order to improve the electrocatalytic properties of the modified electrode and to protect electrode surface from fouling due to the presence of biological materials, a surfactant, namely cetyltrimethylammonium bromide, was introduced, as monomolecular layer, on electrode surface. At -0.1 V, the sensitivity of the modified nanocomposite electrode was 58 nA μM-1cm-2, with a detection limit of 2.78 μM, in the 0.01–1.5 mM H2O2 concentration range, revealing to be one of the most sensitive electrodes described in literature. The resulting electrode was used to determine native monoamine oxidase activity on intact mitochondria suspensions, allowing the determination of catalytic parameters of the enzyme. Following this new electrochemical methodology, we implemented a novel electrochemical assay for the investigation of aerobic metabolism in preparations of isolated mitochondria revealing active H2O2 production by respiring rat liver mitochondria. The present work demonstrates the feasibility of these novel maghemite nanoparticles modified electrode as efficient hydrogen peroxide electro-catalyst, for the application on biological samples at low applied potentials
Magnetic Nanoparticles with Covalently Bound Self-Assembled Protein Corona for Advanced Biomedical Applications
No full textNovel surface active maghemite nanoparticles (SAMNs) possessing peculiar colloidal properties and surface characteristics are able to covalently bind biomolecules. The interactions of SAMNs and rhodamine derivatized SAMNs (SAMN@RITC) with proteins from cell culture medium were studied by gel electrophoresis and mass spectrometry. Among the 3000 proteins present in fetal calf serum, SAMNs and SAMN@RITC give rise to the formation of a self-assembled corona shell with 22 selected proteins, representing minor plasma proteins, among which α-2-HS- glycoprotein stands out. Bovine serum albumin (BSA), representing 80% of the total serum proteins, shows negligible absorption on the SAMN surface. Nevertheless, SAMNs are able to bind BSA, upon incubation in pure BSA solutions. The interaction between SAMNs and BSA was investigated by optical spectroscopy, circular dichroism, Fourier transform infrared spectroscopy, and transmission electron microscopy. BSA binding resulted a time-consuming process, nevertheless experimental results showed the interaction of 6 ± 2 BSA molecules per nanoparticle, and optical spectra indicate remarkable changes in SAMN optical features, as well as circular dichroism proved secondary structure alteration of bound BSA, suggesting that the protein needs to adapt its structure to adhere to nanoparticle surface. The selectively bound protein corona shell, formed upon SAMNs incubation in calf serum, was responsible for the characteristic behavior when SAMNs were tested for cell internalization and cytotoxicity on HeLa cells. Cytotoxicity of SAMN preparations was extensively studied, and was negligible up to 100 μg mL -1. Moreover, nanoparticle uptake proceeded for long times, suggesting a correlation between internalization and stability of covalently bound self-assembled protein corona, representing a unique example of magnetic nanoparticle opsonization via covalent binding. We suggest that SAMN based nanobiocomposites can be employed for the preparation of self-assembled opsonized nanoparticles as future candidates for biomedical applications
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