No abstract

Studies involving transition-metal dichalcogenides (TMDs) have been around for many decades and in recent years, many were focused on using TMDs to synthesize inorganic analogues of carbon nanotubes, fullerene, as well as graphene and its derivatives with the ultimate aim of employing these materials into consumer products. In view of this rising trend, we investigated the cytotoxicity of three common exfoliated TMDs (exTMDs), namely MoS2 , WS2 , and WSe2 , and compared their toxicological effects with graphene oxides and halogenated graphenes to find out whether these inorganic analogues of graphenes and derivatives would show improved biocompatibility. Based on the cell viability assessments using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-8) assays on human lung carcinoma epithelial cells (A549) following a 24 h exposure to varying concentrations of the three exTMDs, it was concluded that MoS2 and WS2 nanosheets induced very low cytotoxicity to A549 cells, even at high concentrations. On the other hand, WSe2 exhibited dose-dependent toxicological effects on A549 cells, reducing cell viability to 31.8 % at the maximum concentration of 400 μg mL(-1) ; the higher cytotoxicity displayed by WSe2 might be linked to the identity of the chalcogen. In comparison with graphene oxides and halogenated graphenes, MoS2 and WS2 were much less hazardous, whereas WSe2 showed similar degree of cytotoxicity. Future in-depth studies should be built upon this first work on the in vitro cytotoxicity of MoS2 and WS2 to ensure that they do not pose acute toxicity. Lastly, nanomaterial-induced interference control experiments revealed that exTMDs were capable of reacting with MTT assay viability markers in the absence of cells, but not with WST-8 assay. This suggests that the MTT assay is not suitable for measuring the cytotoxicity of exTMDs because inflated results will be obtained, giving false impressions that the materials are less toxic.

Vitamin K(1) (VK(1)) was shown by voltammetry and coulometry to undergo two chemically reversible one-electron reduction processes in acetonitrile (CH(3)CN) containing 0.2 M Bu(4)NPF(6) as the supporting electrolyte. The potential separation between the first and second electron-transfer steps diminished sequentially with the addition of water, so that at a H(2)O concentration of approximately 7 M (approximately 13% v/v) only one process was detected, corresponding to the reversible transfer of two electrons per molecule. The voltammetric behavior was interpreted on the basis of the degree of hydrogen bonding between the reduced forms of VK(1) with water in the solvent. It was found that the potential separation between the first and second processes was especially sensitive to water in the low molar levels (0.001-0.1 M); therefore, by measuring the peak separation as a function of controlled water concentrations (accurately determined by Karl Fischer coulometric titrations) it was possible to prepare calibration curves of peak separation versus water concentration. The calibration procedure is independent of the type of reference electrode and can be used to determine the water content of CH(3)CN between 0.01 and 5 M, by performing a single voltammetric scan in the presence of 1.0 mM VK(1). The voltammetry was also investigated in dichloromethane, dimethylformamide, and dimethyl sulfoxide. The reduction processes were monitored by in situ electrochemical UV-vis spectroscopy in CH(3)CN over a range of water concentrations (0.05-10 M) to spectroscopically identify the hydrogen-bonded species.

MoS₂ belong to a class of inorganic 2D nanomaterials known as transition metal dichalcogenides (TMDs) which have recently attracted a renewed and growing interest due to their interesting electronic and catalytic properties when scaled down to single or few layer sheets. Although exfoliated MoS₂ nanosheets have been proposed for numerous energy-related and biosensing applications, little is known about the toxicological impacts of using MoS₂ nanosheets. Here, we report about the in vitro toxicity of MoS₂ nanosheets that have been chemically exfoliated with different lithium intercalating agents and compared their respective cytotoxic influence. Methyllithium (Me-Li), n-butyllithium (n-Bu-Li) and tert-butyllithium (t-Bu-Li) were used for the exfoliation of bulk MoS₂ and we found the t-Bu-Li and n-Bu-Li exfoliated MoS₂ nanosheets to be more cytotoxic than MoS₂ exfoliated by Me-Li. t-Bu-Li and n-Bu-Li provide more efficient exfoliation over Me-Li, and we establish that the extent of exfoliation that MoS₂ undergo is a factor influencing their toxicity. Specifically, the more exfoliated the MoS₂ nanosheets, the stronger its cytotoxic influence, which may be due to an increase in surface area and active edge sites. The potential toxicity of these MoS₂ nanosheets should be taken into account before their employment in real world applications and we have shown the effect the amount of exfoliation can have on the toxicity of MoS₂ nanosheets, representing the first step towards a better understanding of their toxicological properties.

Voltammetry experiments were performed on the natural quinone, vitamin K(1) (VK(1)), in a range of organic solvents of varying dielectric constant that are commonly used for electrochemical measurements [dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile (MeCN), propionitrile (EtCN), butyronitrile (PrCN), 1,2-dichloroethane (DCE), dichloromethane (DCM), and 1,1,2,2-tetrachloroethane (TCE)]. The water content of the solvents was accurately measured using Karl Fischer (KF) coulometric titrations, and the voltammetric data were used to estimate the degree of hydrogen-bonding interactions between the reduced forms of VK(1) and variable levels of water, thereby allowing a ranking of water-substrate interactions in the different solvents. The voltammetric data were analyzed based on interactions that occur between reduced forms of VK(1) and the water, the solvent, and the supporting electrolyte. Calibration data were obtained that are independent of the nature of the reference electrode and allow the water content of the solvents to be calculated by performing a single voltammetric scan in the presence of VK(1) and 0.2 M supporting electrolyte (Bu(4)NPF(6)).