No abstract

Water splitting is one of the most promising solutions for storing solar energy in a chemical bond. Water oxidation is still the bottleneck step because of its inherent difficulty and the limited understanding of the O−O bond formation mechanism. Molecular catalysts provide a platform for understanding this process in depth and have received wide attention since the first Ru‐based catalyst was reported in 1982. RuV=O is considered a key intermediate to initiate the O−O bond formation through either a water nucleophilic attack (WNA) pathway or a bimolecular coupling (I2M) pathway. Herein, we report a Ru‐based catalyst that displays water oxidation reactivity with RuIV=(O) with the help of a redox‐active ligand at pH 7.0. The results of electrochemical studies and DFT calculations disclose that ligand oxidation could significantly improve the reactivity of RuIV=O toward water oxidation. Under these conditions, sustained water oxidation catalysis occurs at reasonable rates with low overpotential (ca. 183 mV).

Salt cress, Thellungiella halophila, is a late-flowering, halophytic plant that requires a prolonged period of vernalisation to flower. This poorly defined vernalisation requirement restricts the use of T. halophila as a model plant for the study of salt-stress tolerance. To facilitate research on T. halophila, the present study quantified the effects of seed vernalisation and photoperiod on its flowering. Imbibed seeds of T. halophila responded to a cold treatment (4°C), and flowering was optimal after 30 days of seed vernalisation. A longer vernalisation period shortened the time until the first flower appeared, increased the number of flowers and reduced expression of ThFLC (a repressor of flowering). Plants growing from seed that had been vernalised for 30 days did not flower when daylength was <9 h, and daylengths >9 h promoted flowering. Therefore, like for many plants in this clade of the Brassicaceae, vernalisation requirement and long-day response are features of T. halophila. These results will facilitate the use T. halophila as a model plant for the study of abiotic stress.

Three new polyketides myxotritones A-C (2-4), together with a new natural product 7,8-dihydro-7R,8S-dihydroxy-3,7-dimethyl-2-benzopyran-6-one (1) were obtained from the endolichenic fungus Myxotrichum sp. by using OMSAC (One Strain, Many Compounds) method. The planar structures of these new compounds were determined by NMR experiment and HRESIMS data, and the absolute configuration of 1 was established by X-ray diffraction, and the stereochemistry of the new compounds 2-4 were determined by same biosynthesis origin, and similar CD spectra with 1. Allelopathic test showed that compound 4 significantly retarded root elongation of Arabidopsis thaliana seed, indicating that this fungus might contribute to the defense of its host lichen. From the view of biosynthetic pathway, all four compounds 1-4 might be originated from Non-Reduced Polyketide synthase (NR-PKS).Lichens are combinations of a fungus (the mycobiont) and an algal partner (the photobiont or phycobiont). In addition to fungal mycobionts, some nonobligate fungi, such as endolichenic fungi, are also found to live asymptomatically in the bodies (thalli) of lichens 1 . Although endolichenic fungi inhabit the lichen thalli similarly to endophytes living in the intercellular spaces of healthy plant tissues, the chemistry of this class of fungi remained largely unexplored 2 . Analysis of a great number genome sequence from different microbes revealed that many secondary metabolite biosynthetic gene clusters are silent under common cultivation conditions, and their metabolic potentials were underestimated. To activate the cryptic gene cluster to express, different methods were innovated 3 . One easiest way is to vary the culture media to induce different cryptic gene cluster to express and then obtain new/novel secondary metabolites. This approach was termed as "One Strain, Many Compounds" first suggested by Germany natural product chemist Prof. A Zeek 4 . In our previous report, a series of citromycetin and fulvic acid with unique skeletons have been obtained from the PDB culture of endolichenic fungus Myxotrichum sp 5 (Fig. 1). To dig the metabolic potential of endolichenic fungi Myxotrichum sp., rice culture was used to activate the potentially silent gene clusters, from which three new polyketides myxotritones A-C (2-4), together with a new natural product 7, 8-dihydro-7R, 8S-dihydroxy-3, 7-dimethyl-2-benzopyran-6-one (1) were obtained. In this report, the structural elucidation, biological evaluation, and possible biosynthetic pathway were present. Results and DiscussionThe known compound 1 is identified to be as 7, 8-dihydro-7R, 8S-dihydroxy-3, 7-dimethyl-2-benzopyran-6-one based on the NMR, MS data and optical rotation [α ] D 22 = + 393.0 (c = 0.15, MeOH), which was known as a synthetic compound but never isolated from a natural specimen 6,7 (Fig. 2). Fortunately, a suitable crystal was obtained for X-ray diffraction (in MeOH) (Fig. S5). The planar structure and absolute configuration of 1 were confirmed by single-crystal X-ray diffraction analysis with C...

A high-performance liquid chromatography with electrospray ionization tandem mass spectrometry method has been developed and validated for the simultaneous quantification of eight major sweet mogrosides in different batches of the fruits of Siraitia grosvenorii and its marketed sweeteners. The sample preparation procedure and chromatographic and mass spectrographic conditions were optimized. Chromatographic separation was achieved on a reversed-phase Poroshell 120 SB C column in 10.0 min with gradient elution with acetonitrile and water, both of which contained 0.1% formic acid. The multiple reaction monitoring scanning mode was employed for quantification in the negative ion mode. The developed method was validated with acceptable linearity (r = 0.9984-0.9998) over a wide concentration range, precision (relative standard deviations = 1.09-3.91%), stability (relative standard deviations = 1.21-3.01%), and recovery in the range of 91.22-106.58% (relative standard deviations ≤ 3.79%) under optimum conditions. The proposed method was demonstrated to be simple, rapid, specific, and reliable and was successfully applied for the quality control of the fruits of S. grosvenorii and its marketed sweeteners.