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1.
ACS Appl Mater Interfaces ; 12(2): 2572-2580, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31860265

RESUMO

Recently, aluminum ion batteries (AIBs) have attracted great attention across the globe by virtue of their massive gravimetric and volumetric capacities in addition to their high abundance. Though carbon derivatives are excellent cathodes for AIBs, there is much room for further development. In this study, flexuous graphite (FG) was synthesized by a simple thermal shock treatment, and for the first time, an Al/FG battery was applied as a cathode for AIBs to reveal the real-time intercalation of AlCl4- into FG with high flexibility by using in-situ scanning electron microscope (SEM) measurements exclusively. Similarly, in-situ X-ray diffraction (XRD) and in-situ Raman techniques have been used to understand the anomalous electrochemical behavior of FG. It was found that FG adopts a unique integrated intercalation-adsorption mechanism where it follows an intercalation mechanism potential above 1.5 V and an adsorption mechanism potential below 1.5 V. This unique integrated intercalation-adsorption mechanism allows FG to exhibit superior properties, like high capacity (≥140 mAh/g), remarkable long-term stability (over 8000 cycles), excellent rate retention (93 mAh/g at 7.5 A/g), and extremely rapid charging and slow discharging.

2.
Sci Rep ; 9(1): 20174, 2019 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-31882825

RESUMO

Under a controlled adsorption environment, L-cysteine molecules can be chemically adsorbed to the dendritic silver (Ag-D) surface by electrochemical methods with different functional groups. It is verified by surface-enhanced Raman spectroscopy that under alkaline conditions (pH = 13.50), the two functional groups of thiol and acid are simultaneously adsorbed on the surface of Ag-D, while NH2 is far from the surface; under acidic conditions (pH = 1.67), adsorption behavior suggests that both NH3+ and COO- are oriented toward the Ag-D surface, and that SH is far from the surface. The structure of L-cysteine adsorption under acidic conditions can be further verified by the addition of an L-cysteine molecule through light-induced coupling reaction to form cystine. Finally, in-situ two-dimensional Raman scattering spectroscopy confirmed the feasibility and uniformity of the coupling reaction.

3.
Phys Chem Chem Phys ; 17(28): 18443-8, 2015 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-26106968

RESUMO

A novel surface-enhanced Raman scattering (SERS) sensing system which operates by the self-assembly of Ag nanoparticles (AgNPs) onto the nanocomposite of AgNPs and graphene oxide (AgNP-GO) in the presence of two complementary DNAs has been developed. In this system, AgNP-GO serves as a SERS-active substrate. The AgNPs with the modification of non-fluorescent 4-mercaptobenzoic acid (4-MBA) act as highly efficient Raman probes for DNA hybridization. When probe DNAs on AgNP-GO are complementary to target DNAs on AgNPs functionalized with 4-MBA, the DNA hybridization occurring directs the self-assembly of AgNPs onto AgNP-GO, leading to the creation of SERS hot spots. Due to the fact that partial 4-MBA molecules are located in the region of the hot spots, their SERS signals are greatly enhanced, indicating successful DNA hybridization. It is noteworthy that the size of AgNPs contributes significantly to the enhancement of SERS activity. The detection limit of the target DNAs at the pM level can be achieved through the self-assembly of large sized AgNPs onto AgNP-GO. More importantly, the AgNP-AgNP-GO system shows reproducible SERS signals in proportion to the logarithm of the target DNA concentrations spanning from 10(-6) to 10(-12) M and the excellent capability for multiplex DNA detection.

4.
Biophys J ; 97(2): 609-17, 2009 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-19619476

RESUMO

With Cd and Zn metal ions removed from the native rabbit-liver metallothionein upon unfolding, Cu-modified metallothioneins (Cu-MTs) were obtained during refolding in solutions containing Cu(I) or Cu(II) ions. X-ray absorption near-edge spectroscopic results confirm the respectively assigned oxidation states of the copper ions in Cu(I)-MT and Cu(II)-MT. Global and local structures of the Cu-MTs were subsequently characterized by anomalous small-angle x-ray scattering (ASAXS) and extended x-ray absorption fine structure. Energy-dependent ASAXS results indicate that the morphology of Cu(II)-MT resembles that of the native MT, whereas Cu(I)-MT forms oligomers with a higher copper content. Both dummy-residue simulation and model-shape fitting of the ASAXS data reveal consistently rodlike morphology for Cu(II)-MT. Clearly identified Cu-S, Cu-O, and Cu-Cu contributions in the extended x-ray absorption fine structure analysis indicate that both Cu(I) and Cu(II) ions are bonded with O and S atoms of nearby amino acids in a four-coordination environment, forming metal clusters smaller than metal thiolate clusters in the native MT. It is demonstrated that a combination of resonant x-ray scattering and x-ray absorption can be particularly useful in revealing complementary global and local structures of metalloproteins due to the atom specific characteristics of the two techniques.


Assuntos
Cobre/química , Cobre/metabolismo , Metalotioneína/química , Metalotioneína/metabolismo , Difração de Raios X , Absorção , Animais , Apoproteínas/química , Apoproteínas/metabolismo , Modelos Moleculares , Oxirredução , Conformação Proteica , Desnaturação Proteica , Renaturação Proteica , Coelhos , Espalhamento a Baixo Ângulo , Soluções
5.
Biophys J ; 94(12): 4828-36, 2008 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-18326641

RESUMO

Equilibrium unfolding behaviors of cytochrome c and lysozyme induced by the presence of urea (0-10 M) as well as changes in temperature (295-363 K) or pH (1.8-7) are examined via small-angle x-ray scattering and spectroscopic techniques, including circular dichroism and optical absorption. Denaturant and temperature effects are incorporated into the free energy expression for a general multigroup unfolding process. Results indicate that there are at least four unfolding groups in the temperature-, urea-, or pH-induced unfolding of cytochrome c: two of these are related to the prosthetic heme group, and the other two correspond, respectively, to the unfolding of alpha-helices and global changes in protein morphology that are largely unaccounted for by the first two groups. In contrast, the unfolding of lysozyme approximately follows a simple one-group process. A modified mean-field Ising model is adopted for a coherent description of the unfolding behaviors observed. Thermodynamic parameters extracted from simple denaturing processes, on the basis of the Ising model, can closely predict unfolding behaviors of the proteins in compounded denaturing environments.


Assuntos
Cristalografia/métodos , Citocromos c/química , Citocromos c/ultraestrutura , Modelos Químicos , Modelos Moleculares , Muramidase/química , Muramidase/ultraestrutura , Simulação por Computador , Conformação Proteica , Desnaturação Proteica , Dobramento de Proteína
6.
J Phys Chem A ; 111(38): 9286-90, 2007 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-17696324

RESUMO

The local and global structural changes of cytochrome c induced by urea in aqueous solution have been studied using X-ray absorption spectroscopy (XAS) and small-angle X-ray scattering (SAXS). According to the XAS result, both the native (folded) protein and the unfolded protein exhibit the same preedge features taken at Fe K-edge, indicating that the Fe(III) in the heme group of the protein maintains a six-coordinated local structure in both the folded and unfolded states. Furthermore, the discernible differences in the X-ray absorption near-edge structure (XANES) of these two states are attributed to a possible spin transition of the Fe(III) from a low-spin state to a high-spin state during the unfolding process. The perseverance of six-coordination and the spin transition of the iron are reconciled by a proposed ligand exchange, with urea and water molecules replacing the methionine-80 and histidine-18 axial ligands, respectively. The SAXS result reveals a significant morphology change of cytochrome c from a globular shape of a radius of gyration R(g) = 12.8 A of the native protein to an elongated ellipsoid shape of R(g) = 29.7 A for the unfolded protein in the presence of concentrated urea. The extended X-ray absorption fine structure (EXAFS) data unveil the coordination geometries of Fe(III) in both the folded and unfolded state of cytochrome c. An initial spin transition of Fe(III) followed by an axial ligand exchange, accompanied by the change in the global envelope, is proposed for what happened in the protein unfolding process of cytochrome c.


Assuntos
Citocromos c/química , Ureia/química , Água/química , Modelos Moleculares , Desnaturação Proteica , Dobramento de Proteína , Soluções/química , Espectrometria por Raios X
7.
J Synchrotron Radiat ; 14(Pt 4): 320-5, 2007 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-17587656

RESUMO

Using a superconducting-wavelength-shifter X-ray source with a photon flux density of 10(11)-10(13) photons s(-1) mrad(-1) (0.1% bandwidth)(-1) (200 mA)(-1) in the energy range 5-35 keV, three hard X-ray beamlines, BL01A, BL01B and BL01C, have been designed and constructed at the 1.5 GeV storage ring of the National Synchrotron Radiation Research Center (NSRRC). These have been designed for structure-related research using X-ray imaging, absorption, scattering and diffraction. The branch beamline BL01A, which has an unmonochromatized beam, is suitable for phase-contrast X-ray imaging with a spatial resolution of 1 microm and an imaging efficiency of one frame per 10 ms. The main beamline BL01B has 1:1 beam focusing and a medium energy resolution of approximately 10(-3). It has been designed for small-angle X-ray scattering and transmission X-ray microscopy, used, respectively, in anomalous scattering and nanophase-contrast imaging with 30 nm spatial resolution. Finally, the branch beamline BL01C, which features collimating and focusing mirrors and a double-crystal monochromator for a high energy resolution of approximately 10(-4), has been designed for X-ray absorption spectroscopy and high-resolution powder X-ray diffraction. These instruments, providing complementary tools for studying multiphase structures, have opened up a new research trend of integrated structural study at the NSRRC, especially in biology and materials. Examples illustrating the performances of the beamlines and the instruments installed are presented.

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