ABSTRACT
Chirality on the molecular or nanometer scale is particularly significant in chemistry, materials science, and biomedicine. Chiral electrochemical reactions on solid surfaces are currently a hot research topic. Herein, a chiral solid surface is constructed in aqueous solutions by mixing chiral molecules, d- and l-glutamic, with γ-Fe2O3 and Fe3O4 nanoparticles (NPs) and MnFe2O4 colloidal nanocrystal assembly (CNA). Cyclic voltammetry and differential pulse voltammetry measurements are conducted in a phosphate buffer solution (PBS) containing ascorbic acid (AA) or isoascorbic acid (IAA), and a chiral effect appears on the electroreduction of ferric ions of amino acid-modified magnetic samples. A negative or positive potential shift is observed, respectively, for magnetic structures modified by l- and d-glutamic acid in aqueous AA electrolyte, while the opposite is observed for these samples in IAA electrolyte. The reduction peak current increases by 0.8-1.2 times for the electrodes modified with l- and d-glutamate molecules, improving the electron transport efficiency. The chiral effect is absent when the electrolytes contain achiral uric acid or dopamine, or even chiral l-/d-/ld-tartaric acid. The chiral recognition between d-/l-glutamic acid and AA/IAA at the electrochemical interface is suggested to be related to their spinal configurations. These observations will be helpful for the rational design of inorganic functional chiral micro/nanostructures.
ABSTRACT
Synthesizing alloyed bimetallic electrocatalysts with a three-dimensional (3D) structure assembly have arouse great interests in electrocatalysis. We synthesized a class of alloyed Pd3Pb/Pd nanosheet assemblies (NSAs) composed of a two-dimensional (2D) sheet structure with adjustable compositions via an oil bath approach at a low temperature. Both the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the successful formation of the nanosheet structure, where the morphology of Pd3Pb/Pd NSAs can be regulated by adjusting the atomic mole ratio of Pb and Pb metal precursors. The power X-ray diffraction (XRD) pattern shows that Pd3Pb/Pd NSA catalysts are homogeneously alloyed. Electrochemical analysis and the density functional theory (DFT) method demonstrate that the electrocatalytic activity of the alloyed Pd3Pb/Pd NSAs can be improved by the doping of the Pb element. As a result of the addition of element Pb and change of the electron structure, the electrocatalytic activity toward ethanol oxidation of alloyed Pd3Pb/Pd-15 NSA can reach up to 2886 mA mg-1, which is approximately 2.8 times that of the pure Pd NSA counterpart (1020 mA mg-1). The Pd3Pb/Pd NSAs are favorable in a high catalytic temperature, high KOH concentration, and high ethanol concentration.
ABSTRACT
The synthesis of metal nanometer electrocatalysts with a two-dimensional (2D) structure or rich active sites has become a research hotspot in electrocatalysis. In this work, surfactant hexadecyltrimethylammonium bromide (CTAB) was used to assist the synthesis and assembly of Pd ultrathin nanosheet with the help of Mo(CO)6 in the start system. Pd nanochain composed of nanoparticles is obtained under the same condition, replacing CTAB with carrageenan only. Electrochemical measurements showed that the catalytic peak current density for the electrooxidation of ethanol can reach 2145 mA mg-1 for the Pd nanosheet assembly (NSA) and 1696 mA mg-1 for Pd nanochains. Pd nanosheet assembly also has a lower electron-transfer barrier, better catalytic stability, and antipoisoning performance than that of Pd nanochains. The mechanism of Pd nanosheets and nanochains catalysts the enhanced electrocatalytic activity toward ethanol oxidation has been discussed based on the experimental data.
ABSTRACT
This study is to investigate the expression of matrix metalloproteinase-9 (MMP-9), cyclooxygenase-2 (COX-2) and vascular endothelial growth factor (VEGF) in gastrointestinal stromal tumor (GIST). Immunohistochemistry was performed to detect the expression of MMP-9, COX-2 and VEGF. The expression of MMP-9, COX-2 and VEGF was compared among different clinicopathological features of GIST. Spearman rank correlation analysis was conducted to analyze the correlation among MMP-9, COX-2 and VEGF. The positive expression rates of MMP-9, COX-2 and VEGF were 76.9%, 84.6% and 82.7%. The expression levels of MMP-9, COX-2 and VEGF were significantly different among the clinicopathological features of growth pattern, tumor diameter, metastasis, mitotic count and central necrosis (P < 0.05). Their expression levels were higher in GIST tissues with higher levels of malignancy, tumor size, metastasis, mitotic count and central necrosis. However, their expression levels were not significantly different among age, gender, primary tumor site or CD117 expression. Additionally, there were positive correlations between COX-2 and VEGF (r = 0.612, P < 0.01), between COX-2 and MMP-9 (r = 0.592, P < 0.05), and between MMP-9 and VEGF (r = 0.690, P < 0.01). MMP-9, COX-2 and VEGF expression levels are increased in GIST tissues and related with clinicopathological features of GIST.
