Electron Transfer Budgets and Kinetics of Abiotic Oxidation and Incorporation of Aqueous Sulfide by Dissolved Organic Matter

The reactivity of natural dissolved organic matter toward sulfide and has not been well studied with regard to electron transfer, product formation, and kinetics. We thus investigated the abiotic transformation of sulfide upon reaction with reduced and nonreduced Sigma-Aldrich humic acid (HA), at pH 6 under anoxic conditions. Sulfide reacted with nonreduced HA at conditional rate constants of 0.227–0.325 h^–1. The main transformation products were elemental S (S⁰) and thiosulfate (S₂O₃^2–), yielding electron accepting capacities of 2.82–1.75 μmol e^– (mg C)⁻¹. Native iron contents in the HA could account for only 6–9% of this electron transfer. About 22–37% of S reacted with the HA to form organic S (S_org). Formation of S_org was observed and no inorganic transformation products occurred for reduced HA. X-ray absorption near edge structure spectroscopy supported S_org to be mainly zerovalent, such as thiols, organic di- and polysulfides, or heterocycles. In conclusion, our results demonstrate that HA can abiotically reoxidize sulfide in anoxic environments at rates competitive to sulfide oxidation by molecular oxygen or iron oxides

Cytotoxic lignans from the barks of <i>Juglans mandshurica</i>

<p>Phytochemical investigation of the barks of <i>Juglans mandshurica</i> Maxim led to the isolation, purification, and identification of one new lignan named Juglansol A (<b>1</b>), along with nine known compounds (<b>2–10</b>). Their structures were determined by the results of UV, IR, CD, HRESIMS, 1D, and 2D NMR spectroscopic analysis. Compounds <b>1–10</b> were evaluated for their cytotoxicities against A549, HepG2, Hep3B, Bcap-37, and MCF-7 cell lines. The results showed that compound <b>2</b> possessed stronger cytotoxicities against the tested tumor cell lines compared with positive control 5-fluorouracil.</p

Metabolomics Analysis Reveals that Ethylene and Methyl Jasmonate Regulate Different Branch Pathways to Promote the Accumulation of Terpenoid Indole Alkaloids in <i>Catharanthus roseus</i>

The medicinal plant <i>Catharanthus roseus</i> accumulates large numbers of terpenoid indole alkaloids (TIAs), including the pharmaceutically important vinblastine, vincristine, ajmalicine, and serpentine. The phytohormone ethylene or methyl jasmonate (MeJA) can markedly enhance alkaloid accumulation. The interaction between ethylene or MeJA in the regulation of TIA biosynthesis in <i>C. roseus</i> is unknown. Here, a metabolomics platform is reported that is based on liquid chromatography (LC) coupled with time-of-flight mass spectrometry to study candidate components for TIA biosynthesis, which is controlled by ethylene or MeJA in <i>C. roseus</i>. Multivariate analysis identified 16 potential metabolites mostly associated with TIA metabolic pathways and seven targeted metabolites, outlining the TIA biosynthesis metabolic networks controlled by ethylene or MeJA. Interestingly, ethylene and MeJA regulate the 2-<i>C</i>-methyl-d-erythritol 4-phosphate (MEP) and acetate-mevalonate (MVA) pathways through <i>AACT</i> and <i>HMGS</i> and through <i>DXS</i>, respectively, to induce TIA biosynthesis in <i>C. roseus</i>. Overall, both nontargeted and targeted metabolomics, as well as transcript analysis, were used to reveal that MeJA and ethylene control different metabolic networks to induce TIA biosynthesis