Synergistic effect of supercritical CO2 and organic solvent on exfoliation of graphene: experiment and atomistic simulation studies.

In this work, experiments and molecular dynamics (MD) simulations are carried out to explore the synergistic effect of supercritical CO2 (scCO2) and organic solvent on intercalation and exfoliation of graphene. Experimental characterizations via transmission electron microscopy, atomic force microscopy and Raman spectroscopy indicate that by combining scCO2 and organic solvent (N-methylpyrrolidone, NMP), few-layer graphene is successfully exfoliated from graphite, among which over 30% is 1-4 layers, and 55% is 5-8 layers. Systematic experiments have shown that compared with pure scCO2 or NMP, the mixed scCO2 and NMP can significantly increase the amount of graphene and the rate of few-layer graphene, and the optimum volume fraction of NMP is 25%. Parallel MD simulations indicate that the scCO2 molecules first diffuse into the interlayer of graphite, and then the larger NMP molecules insert as wedges and further expand interlayer spacing, promoting intercalation and exfoliation. The iteration of scCO2 diffusion and the NMP wedge can generate positive feedback to improve the exfoliation productivity and efficiency. This work explores the synergistic effect of scCO2 and NMP on the exfoliation of graphene, which may provide useful insights for exfoliation of other two dimensional materials.

Aanat Knockdown and Melatonin Supplementation in Embryo Development: Involvement of Mitochondrial Function and DNA Methylation.

Aims: In addition to pineal gland, many cells, tissues, and organs also synthesize melatonin (N-acetyl-5-methoxytryptamine). Embryos are a group of special cells and whether they can synthesize melatonin is still an open question. However, melatonin application promoted embryo development in many species in in vitro condition. The purpose of this study was to investigate whether embryos can synthesize melatonin; if it is so, what are the impacts of the endogenously produced melatonin on embryo development and the associated molecular mechanisms. These have never been reported previously. Results: Melatonin synthesis was observed at different stages of embryonic development. Aanat (aralkylamine N-acetyltransferase), a rate-limiting enzyme for melatonin production, was found to mostly localize in the mitochondria. Aanat knockdown significantly impeded embryonic development, and melatonin supplementation rescued it. The potential mechanisms might be that melatonin preserved mitochondrial intact and its function, thus providing sufficient adenosine 5'-triphosphate for the embryo development. In addition, melatonin scavenged intracellular reactive oxygen species (ROS) and reduced the DNA mutation induced by oxidative stress. In the molecular level, Aanat knockdown reduced tet methylcytosine dioxygenase 2 (Tet2) expression and DNA demethylation in blastocyst and melatonin supplementation rescued these processes. Innovation: This is the first report to show that embryos synthesize melatonin, and its synthetic enzyme Aanat was located in the mitochondria of embryos. An effect of melatonin is to maintain Tet2 expression and normal methylation status, and thereby promote embryonic development. Conclusion: Embryos can produce melatonin that reduces ROS production, preserves mitochondrial function, and maintains Tet2 expression and the normal DNA methylation.

Responses of Transgenic Melatonin-Enriched Goats on LPS Stimulation and the Proteogenomic Profiles of Their PBMCs.

The anti-inflammatory activity of melatonin (MT) has been well documented; however, little is known regarding endogenously occurring MT in this respect, especially for large animals. In the current study, we created a MT-enriched animal model (goats) overexpressing the MT synthetase gene Aanat. The responses of these animals to lipopolysaccharide (LPS) stimulation were systematically studied. It was found that LPS treatment exacerbated the inflammatory response in wild-type (WT) goats and increased their temperature to 40 °C. In addition, their granulocyte counts were also significantly elevated. In contrast, these symptoms were not observed in transgenic goats with LPS treatment. The rescue study with MT injection into WT goats who were treated with LPS confirmed that the protective effects in transgenic goats against LPS were attributed to a high level of endogenously produced MT. The proteomic analysis in the peripheral blood mononuclear cells (PBMCs) isolated from the transgenic animals uncovered several potential mechanisms. MT suppressed the lysosome formation as well as its function by downregulation of the lysosome-associated genes Lysosome-associated membrane protein 2 (LAMP2), Insulin-like growth factor 2 receptor (IGF2R), and Arylsulfatase B (ARSB). A high level of MT enhanced the antioxidant capacity of these cells to reduce the cell apoptosis induced by the LPS. In addition, the results also uncovered previously unknown information that showed that MT may have protective effects on some human diseases, including tuberculosis, bladder cancer, and rheumatoid arthritis, by downregulation of these disease-associated genes. All these observations warranted further investigations.