Operando Spectroscopic Analysis of Axial Oxygen-Coordinated Single-Sn-Atom Sites for Electrochemical CO2 Reduction.

Sn-based materials have been demonstrated as promising catalysts for the selective electrochemical CO2 reduction reaction (CO2RR). However, the detailed structures of catalytic intermediates and the key surface species remain to be identified. In this work, a series of single-Sn-atom catalysts with well-defined structures is developed as model systems to explore their electrochemical reactivity toward CO2RR. The selectivity and activity of CO2 reduction to formic acid on Sn-single-atom sites are shown to be correlated with Sn(IV)-N4 moieties axially coordinated with oxygen (O-Sn-N4), reaching an optimal HCOOH Faradaic efficiency of 89.4% with a partial current density (jHCOOH) of 74.8 mA·cm-2 at -1.0 V vs reversible hydrogen electrode (RHE). Employing a combination of operando X-ray absorption spectroscopy, attenuated total reflectance surface-enhanced infrared absorption spectroscopy, Raman spectroscopy, and 119Sn Mössbauer spectroscopy, surface-bound bidentate tin carbonate species are captured during CO2RR. Moreover, the electronic and coordination structures of the single-Sn-atom species under reaction conditions are determined. Density functional theory (DFT) calculations further support the preferred formation of Sn-O-CO2 species over the O-Sn-N4 sites, which effectively modulates the adsorption configuration of the reactive intermediates and lowers the energy barrier for the hydrogenation of *OCHO species, as compared to the preferred formation of *COOH species over the Sn-N4 sites, thereby greatly facilitating CO2-to-HCOOH conversion.

Rapid identification of efavirenz metabolites in rats and humans by ultra high performance liquid chromatography combined with quadrupole time-of-flight tandem mass spectrometry.

An in vivo study of efavirenz metabolites in rats and human patients with ultra high performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry combined with MetabolitePilot(MT) software is reported for the first time. Considering the polarity differences between the metabolites, solid-phase extraction and protein precipitation were both applied as a part of the sample preparation method. The structures of the metabolites and their fragment ions were identified or tentatively characterized based on the accurate mass and MS(2) data. As a result, a total of 15 metabolites, including 11 from rat samples and 13 from human samples, were identified or tentatively characterized. Two metabolites and several new metabolism pathways are reported for the first time. This study provides a practical approach for identifying complicated metabolites through the rapid and reliable ultra high performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry technique, which could be widely used for the investigation of drug metabolites.

Screening of bioactive compounds in Radix Salviae Miltiorrhizae with liposomes and cell membranes using HPLC.

A new method employing HPLC, LC-MS, liposomes and cell membranes for the screening of bioactive compounds in traditional Chinese medicines (TCMs) has been proposed. We hypothesized that exposure of the TCM extracts to liposome membranes or cell membranes should decrease the concentration of membrane-permeable compounds in the solution. Using this approach, the permeability of the compounds in Radix Salviae Miltiorrhizae was investigated. By comparing chromatograms of samples prepared both before and after interaction with liposome membranes, erythrocyte membranes and cardiac myocyte membranes, 12 permeable compounds of Radix Salviae Miltiorrhizae were identified, and they were proven to be biologically active, with the exception of vanillic acid. There was a good correlation between the liposome model and the erythrocyte membranes, which was determined by comparing the binding degree of the permeable compounds (n=0.9059). Additionally, it was found that dihydrotanshinone I, cryptotanshinone, tanshinone I, tanshinone IIA combined specifically with cardiac myocyte membranes, which might indicate a useful approach for revealing the cardiovascular effects of Radix Salviae Miltiorrhizae. Based on these results, this method could be a novel approach for identifying potentially bioactive components in other TCMs.

Cancer risk assessment from trihalomethanes in drinking water.

This study intends to calculate the lifetime cancer risks resulting from intakes of trihalomethanes (THMs) in drinking water based on the presence of each THM species. The slope factors for each THM species are used, combined with exposure model and Monte Carlo simulations, to calculate the cancer risks with consideration of different exposure routes (oral ingestion, inhalation and dermal absorption). The results revealed that the highest risk comes from the inhalation exposure to chloroform during showers, which also dominates the total risk associated with chloroform exposure. For dichlorobromomethane and chlorodibromomethane, inhalation exposure also plays an important role for total risks; however, contribution from the oral consumption cannot be ignored for these two compounds. Bromoform contributes the least cancer risk among the four THM species, with a risk factor two orders of magnitude smaller than the other three THM species. For all of the four THM species, exposure from dermal absorption is not significant when compared with oral ingestion and inhalation exposures. This study also uses the THMs data collected from Taiwan to calculate the cancer risks associated with THM exposures in different areas of Taiwan. Due to the variations of the THMs compositions, it is observed that higher concentrations of total THMs do not necessarily lead to higher cancer risks. Areas with higher bromide concentration in raw water and often with higher total THM concentration may actually give lower cancer risk if the THMs formed shift to bromoform. However, this also leads to the violation of THM standards since bromoform has much higher molecular weight than chloroform. Based on the results of the cancer risks calculated from each THM species, the regulatory issue of the THMs was also discussed.