87,036 research outputs found
F-doped TiO2 prepared by flame spray pyrolysis: effect on the photoelectrochemical performance
No full textPhotoelectrochemical water splitting performed with semiconductor materials has attracted attention due to potential clean energy production, achievable utilizing light. In this context, TiO2 is the most investigated semiconductor, though characterized by i) low rate of photopromoted e- transfer and ii) high recombination rate of photoproduced charge carriers (e-/h+ pairs). Doping with non-metal elements is often suggested as a valuable remediation to limit the occurrence of these two drawbacks.
In line with this, a series of fluorine-doped TiO2 samples (with F/O ratio varying in the 1–10 at.% range) were synthesized, in single step, by flame spray pyrolysis starting from organic solutions containing titanium tetra-isopropoxide (Ti(OC3H7)4) and hexafluorobenzene (C6F6) as titanium and fluorine precursors, respectively.
By means of the selected synthesis technique, doping can be conveniently carried out by co-dissolving the dopant source, along with the TiO2 precursor, directly in the employed solvent (i.e., xylene), with a precise engineering of dopant concentration during synthesis.
Quantitative crystalline phase analysis, performed by applying the Rietveld refinement method to XRPD data, highlighted the presence of both anatase and rutile phases in all the prepared samples, with the former being always predominant. Accordingly, all samples exhibited a UV-vis absorption edge at λ = ca. 400 nm.
The prepared powders were then deposed on fluorine-doped tin oxide (FTO) glass by means of the doctor-blade technique, to investigate the effect of F-doping on the photoelectrochemical activity of TiO2. Incident Photon-to-Current Efficiency (IPCE), reflecting the semiconductor’s ability of generating and transferring photopromoted e-/h+ under irradiation and suitable applied voltage, was found to increase with increasing the F-dopant concentration, up to a F/O ratio of 5 at.%.
This finding pointed to an improved separation of photopromoted electron-hole pairs, ascribed to the formation of intra-band gap states, induced by fluorine doping and able to efficiently trap photoproduced charge carriers. Conversely, when the amount of F-doping exceeded the optimum value, structural defects acting as e-/h+ recombination centers were formed, reasonably yielding lower photocurrent
Effect of axial coordination on the kinetics of assembly and folding of the two halves of horse heart cytochrome C.
No full textThe kinetics of the assembly of two complementary fragments of oxidized horse heart cytochrome c (cyt c), namely the heme-containing fragment-(1-56) and the fragment-(57-104), have been characterized at different pH values. At neutral pH the fragment-(1-56) is hexacoordinated and has two histidines axially ligated to the heme-Fe(III) (Santucci, R., Fiorucci, L., Sinibaldi, F., Polizio, F., Desideri, A., and Ascoli, F. (2000) Arch. Biochem. Biophys. 379, 331-336), thus mimicking what occurs in the folding intermediate of cyt c. The kinetics of the formation of the complex between the two fragments are characterized at pH 7.0 by a slow rate constant that is independent of the concentration of the reactants; conversely, at a low pH the kinetics are much faster and depend on the concentration of the fragments. This behavior suggests that the rate-limiting step observed in the recombination process of the fragments at neutral pH (that leads to the final coordination of Met-80) has to be ascribed to the detachment of the "misligated" histidine. Thus, the faster recombination rate at a low pH can be related to the fact that histidine is protonated and not able to coordinate to the metal. Furthermore, the independence of the rate constant on the concentration of the reactants observed at pH 7.0 can be accounted for by the occurrence of a conformational transition, which takes place immediately after the two fragments collapse together, likely simulating what induces the detachment of the misligated histidine during cytochrome folding
Effect of axial coordination on the kinetics of assembly and folding of the two halves of horse heart cytochrome c
No full textThe kinetics of the assembly of two complementary fragments of oxidized horse heart cytochrome c (cyt c), namely the heme-containing fragment-(1-56) and the fragment-(57-104), have been characterized at different pH values. At neutral pH the fragment-(1-56) is hexacoordinated and has two histidines axially ligated to the heme-Fe(III) (Santucci, R., Fiorucci, L., Sinibaldi, F., Polizio, F., Desideri, A., and Ascoli, F. (2000) Arch. Biochem. Biophys. 379, 331-336), thus mimicking what occurs in the folding intermediate of cyt c. The kinetics of the formation of the complex between the two fragments are characterized at pH 7.0 by a slow rate constant that is independent of the concentration of the reactants; conversely, at a low pH the kinetics are much faster and depend on the concentration of the fragments. This behavior suggests that the rate-limiting step observed in the recombination process of the fragments at neutral pH (that leads to the final coordination of Met-80) has to be ascribed to the detachment of the "misligated" histidine. Thus, the faster recombination rate at a low pH can be related to the fact that histidine is protonated and not able to coordinate to the metal. Furthermore, the independence of the rate constant on the concentration of the reactants observed at pH 7.0 can be accounted for by the occurrence of a conformational transition, which takes place immediately after the two fragments collapse together, likely simulating what induces the detachment of the misligated histidine during cytochrome folding
Cytochrome c: An extreme multifunctional protein with a key role in cell fate
No full textCytochrome c, a protein that belongs to class 1 of the c-type cytochrome family, exerts different functions depending on its cellular localization and the conditions in which it operates; therefore, it can be defined as ‘extreme multifunctional’ protein. It mediates electron-transfer in the respiratory chain and acts as a detoxifying agent to dispose of ROS. In addition, cytochrome c plays a role in cell apoptosis. After its release into the cytosol, the protein binds to APAF-1, activates pro-caspase 9, and triggers an enzymatic cascade leading to cell death. The interaction with cardiolipin, one of the phospholipids making up the mitochondrial membrane, is essential to start apoptosis; the binding partially unfolds cytochrome c, alters the heme pocket region, and facilitates detachment of Met80 from the sixth coordination position of the heme iron. These events change the function of cytochrome c from an electron-transfer shuttle to a peroxidase-like hemoprotein, capable to trigger the process that leads to cell death. This review provides an overview of the key role played by the cytochrome c-cardiolipin interaction in apoptosis. This is not only important per se, it provides interesting perspectives for applications in clinical diagnostics that use the protein as a biomarker
"Liquid chromatographic resolution of enantiomers on chiral amine derivative-bonded silica gel"
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Cytochrome c Interaction with Cardiolipin Plays a Key Role in Cell Apoptosis: Implications for Human Diseases
No full textIn the cell cytochrome, c performs different functions depending on the environment in which it acts; therefore, it has been classified as a multifunction protein. When anchored to the outer side of the inner mitochondrial membrane, native cytochrome c acts as a Schweitzer-StennerSchweitzer-Stenner that transfers electrons from cytochrome c reductase to cytochrome c oxidase in the respiratory chain. On the other hand, to interact with cardiolipin (one of the phospholipids making up the mitochondrial membrane) and form the cytochrome c/cardiolipin complex in the apoptotic process, the protein reorganizes its structure into a non-native state characterized by different asymmetry. The formation of the cytochrome c/cardiolipin complex is a fundamental step of the apoptotic pathway, since the structural rearrangement induces peroxidase activity in cytochrome c, the subsequent permeabilization of the membrane, and the release of the free protein into the cytoplasm, where cytochrome c activates the apoptotic process. Apoptosis is closely related to the pathogenesis of neoplastic, neurodegenerative and cardiovascular diseases; in this contest, the biosynthesis and remodeling of cardiolipin are crucial for the regulation of the apoptotic process. Since the role of cytochrome c as a promoter of apoptosis strictly depends on the non-native conformation(s) that the protein acquires when bound to the cardiolipin and such event leads to cytochrome c traslocation into the cytosol, the structural and functional properties of the cytochrome c/cardiolipin complex in cell fate will be the focus of the present review
A preconditioned compressible flow solver for numerical simulation of 3D cavitation phenomena
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