Copper- and Nitrogen-Codoped Graphene with Versatile Catalytic Performances for Fenton-Like Reactions and Oxygen Reduction Reaction

Copper- and nitrogen-codoped reduced graphene oxide material (Cu/N-rGO) was prepared with a hydrothermal method. Its versatile catalytic performances were demonstrated toward the oxidative degradation of rhodamine B (RhB) and oxygen reduction reaction (ORR). The Cu and N codoping of graphene enhanced not only its activation ability toward H2O2, but also its electrocatalytic ability for ORR. It was observed that the use of 3%Cu/N-rGO together with 40 mmol·L−1 H2O2 and 4 mmol·L−1 Na2CO3 could remove more than 94% of the added RhB (30 mg·L−1) in 20 min through a catalytic Fenton-like degradation. Quenching experiments and electron paramagnetic resonance (EPR) measurements indicated that the main reactive species generated in the catalytic oxidation process were surface-bound •OH. The modified graphene also showed good electrocatalytic activity for ORR reaction in alkaline media through a four-electron mechanism. On the electrode of Cu/N-rGO, the ORR reaction exhibited an onset potential of −0.1 V and a half-wave potential of −0.248 V, which were correspondingly close to those on a Pt/C electrode. In comparison with a Pt/C electrode, the 3%Cu/N-rGO electrode showed much greater tolerance to methanol. Such outstanding catalytic properties are attributed to the abundant active sites and the synergism between Cu and N in Cu/N-rGO

Pyrite Morphology as an Indicator of Paleoredox Conditions and Shale Gas Content of the Longmaxi and Wufeng Shales in the Middle Yangtze Area, South China

Pyrite is the most common authigenic mineral preserved in many ancient sedimentary rocks. Pyrite also widely exists in the Longmaxi and Wufeng marine shales in the middle Yangtze area in South China. The Longmaxi and Wufeng shales were mainly discovered with 3 types of pyrites: pyrite framboids, euhedral pyrites and infilled framboids. Euhedral pyrites (Py4) and infilled framboids (Py5) belong to the diagenetic pyrites. Based on the formation mechanism of pyrites, the pyrites could be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. Under a scanning electron microscope (SEM), the syngenetic pyrites are mostly small framboids composed of small microcrystals, but the diagenetic pyrites are variable in shapes and the diagenetic framboids are variable in sizes with large microcrystals. Due to the deep burial stage, the pore space in the sediment was sharply reduced and the diameter of the late diagenetic framboids that formed in the pore space is similar to the diameter of the syngenetic framboids. However, the diameter of the syngenetic framboid microcrystals is suggested to range mainly from 0.3 µm to 0.4 µm, and that of the diagenetic framboid microcrystals is larger than 0.4 µm in the study area. According to the diameter of the pyrite framboids (D) and the diameter of the framboid microcrystals (d), the pyrite framboids could be divided into 3 sizes: syngenetic framboids (Py1, D < 5 µm, d ≤ 0.4 µm), early diagenetic framboids (Py2, D > 5 µm, d > 0.4 µm) and late diagenetic framboids (Py3, D < 5 µm, d > 0.4 µm). Additionally, the mean size and standard deviation/skewness values of the populations of pyrite framboids were used to distinguish the paleoredox conditions during the sedimentary stage. In the study area, most of the pyrite framboids are smaller than 5 µm, indicating the sedimentary water body was a euxinic environment. However, pyrite framboids larger than 5 µm in the shales indicated that the sedimentary water body transformed to an oxic-dysoxic environment with relatively low total organic carbon (TOC: 0.4–0.99%). Furthermore, the size of the framboid microcrystals could be used to estimate the gas content due to thermochemical sulfate reduction (TSR). The process of TSR occurs with oxidation of organic matter (OM) and depletes the H bond of the OM, which will influence the amount of alkane gas produced from the organic matter during the thermal evolution. Thus, syngenetic pyrites (d ranges from 0.35 µm to 0.37 µm) occupy the main proportion of pyrites in the Wufeng shales with high gas content (1.30–2.30 m3/t), but the Longmaxi shales (d ranges from 0.35 µm to 0.72 µm) with a relatively low gas content (0.07–0.93 m3/t) contain diagenetic pyrites. Because of TSR, the increasing size of the microcrystals may result in an increase in the value of δ13C1 and a decrease in the value of δ13C1-δ13C2. Consequently, the size of pyrite framboids and microcrystals could be widely used for rapid evaluation of the paleoredox conditions and the gas content in shales

Folate Receptor-Targeted and GSH-Responsive Carboxymethyl Chitosan Nanoparticles Containing Covalently Entrapped 6-Mercaptopurine for Enhanced Intracellular Drug Delivery in Leukemia

For enhanced intracellular accumulation of 6-mercaptopurine (6-MP) in leukemia, a folate receptor-targeted and glutathione (GSH)-responsive polymeric prodrug nanoparticle was made. The nanoparticles were prepared by conjugating 6-MP to carboxymethyl chitosan via a GSH-sensitive carbonyl vinyl sulfide linkage, ultrasonic self-assembly and surface decoration with folate. The TEM graphs shows that the as-synthesized nanoparticles are spherical with a particle size of 170~220 nm. In vitro drug release of nanoparticles demonstrated acceptable stability in PBS containing 20 μM GSH at pH 7.4. However, the cumulative drug release rate of the samples containing 20 mM and 10 mM GSH medium reached 78.9% and 64.8%, respectively, in pH 5.0 at 20 h. This indicated that this nano-sized system is highly sensitive to GSH. The inhibition ratio of folate-modified nanoparticles compared to unmodified nanoparticles was higher in cancer cells (human promyelocytic leukemia cells, HL-60) while their cytotoxicity was lower in normal cells (mouse fibroblast cell lines, L929). Furthermore, in vitro cancer cell incubation studies confirmed that folate-modified nanoparticles therapeutics were significantly more effective than unmodified nanoparticles therapeutics. Our results suggest that folate receptor-targeting and GSH-stimulation can significantly elevate tumour intracellular drug release. Therefore, folate-modified nanoparticles containing chemoradiotherapy is a potential treatment for leukemia therapy

Folate Receptor-Targeted and GSH-Responsive Carboxymethyl Chitosan Nanoparticles Containing Covalently Entrapped 6-Mercaptopurine for Enhanced Intracellular Drug Delivery in Leukemia

For enhanced intracellular accumulation of 6-mercaptopurine (6-MP) in leukemia, a folate receptor-targeted and glutathione (GSH)-responsive polymeric prodrug nanoparticle was made. The nanoparticles were prepared by conjugating 6-MP to carboxymethyl chitosan via a GSH-sensitive carbonyl vinyl sulfide linkage, ultrasonic self-assembly and surface decoration with folate. The TEM graphs shows that the as-synthesized nanoparticles are spherical with a particle size of 170~220 nm. In vitro drug release of nanoparticles demonstrated acceptable stability in PBS containing 20 μM GSH at pH 7.4. However, the cumulative drug release rate of the samples containing 20 mM and 10 mM GSH medium reached 78.9% and 64.8%, respectively, in pH 5.0 at 20 h. This indicated that this nano-sized system is highly sensitive to GSH. The inhibition ratio of folate-modified nanoparticles compared to unmodified nanoparticles was higher in cancer cells (human promyelocytic leukemia cells, HL-60) while their cytotoxicity was lower in normal cells (mouse fibroblast cell lines, L929). Furthermore, in vitro cancer cell incubation studies confirmed that folate-modified nanoparticles therapeutics were significantly more effective than unmodified nanoparticles therapeutics. Our results suggest that folate receptor-targeting and GSH-stimulation can significantly elevate tumour intracellular drug release. Therefore, folate-modified nanoparticles containing chemoradiotherapy is a potential treatment for leukemia therapy.This article is published as Wei, Xuan, Jianhong Liao, Zahra Davoudi, Hua Zheng, Jingru Chen, Dan Li, Xiong Xiong et al. "Folate receptor-targeted and GSH-responsive carboxymethyl chitosan nanoparticles containing covalently entrapped 6-mercaptopurine for enhanced intracellular drug delivery in leukemia." Marine Drugs 16, no. 11 (2018): 439. DOI:10.3390/md16110439. Copyright 2018 by the authors. Attribution 4.0 International (CC BY 4.0). Posted with permission