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Abstract:The use of α-glucosidase inhibitors is considered to be an effective strategy in the treatment of diabetes. Using a bioassay-guided fractionation technique, five Bacillus stearothermophilus α-glucosidase inhibitors were isolated from the flowers of Musa spp. (Baxijiao). Using NMR spectroscopy analysis they were identified as vanillic acid (1), ferulic acid (2), β-sitosterol (3), daucosterol (4) and 9-(4′-hydroxyphenyl)-2-methoxyphenalen-1-one (5). The half maximal inhibitory concentration (IC 50 ) values of compounds 1-5 were 2004.58, 1258.35, 283.67, 247.35 and 3.86 mg/L, respectively. Compared to a known α-glucosidase inhibitor (acarbose, IC 50 = 999.31 mg/L), compounds 3, 4 and 5 showed a strong α-glucosidase inhibitory effect. A Lineweaver-Burk plot indicated that compound 5 is a mixed-competitive inhibitor, while compounds 3 and 4 are competitive inhibitors. The inhibition constants (K i ) of compounds 3, 4 and 5 were 20.09, 2.34 and 4.40 mg/L, respectively. Taken together, these data show that the compounds 3, 4 and 5 are potent α-glucosidase inhibitors.

PurposeThe purpose of this paper is twofold: first, to clarify what specific behaviors are involved in consumers' partial switching in mobile application (app) usage, and, second, to explore the common and differential motivations of these behaviors.Design/methodology/approachThis paper specified two behaviors in consumers' partial switching in mobile app usage, trialing and combining behaviors, and conceptualized them as different types of variety seeking behaviors. A theoretical model contrasting intrinsic motivations and extrinsic motivations on the two behaviors was developed and tested with a sample of 561 mobile app users in China.FindingsThe findings showed that both trialing and combining behaviors could be motivated by intrinsic individual-related and extrinsic technology-related factors. Besides, intrinsic individual-related factors were more effective in motivating trialing behavior, whereas extrinsic technology-related factors were more effective in motivating combining behavior. All these findings are applicable and consistent in both hedonic and utilitarian apps.Originality/valueThis study extends and advances the literature on information technology switching by investigating consumer use behaviors from a new perspective of partial switching and multiple competing apps usage. This study also contributes to variety seeking literature by extending the understanding of variety seeking to the context of mobile app usage. Finally, by investigating the associations and distinctions of trialing and combining behavior, this study not only helps to fully understand the partial switching but also enriches the understanding of different types of variety seeking behaviors.

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A meroterpenoid, chevalone B, was obtained from the Cucumaria japonica-derived fungus Aspergillus sp. H30, which was collected from the South China Sea. The structure was determined by the analysis of nuclear magnetic resonance (NMR) spectroscopic and X-ray data. This is the first report of the crystallographic data and absolute stereochemistry of chevalone B, which was shown to have weak antibacterial activity.

A novel Gram-positive actinobacterium, designated WT-2-1, was isolated from a sample of petroleum-contaminated soil collected in Daqing, Heilongjiang province, China and characterised using a polyphasic taxonomic approach. The optimal growth for strain WT-2-1 was found to be at 25-35 °C and at pH 6.0-9.0 and with 0-4% (w/v) NaCl, forming blackish green-coloured colonies. Chemotaxonomic and molecular characteristics of the isolate match those described for members of the genus Geodermatophilus. The peptidoglycan was found to contain meso-diaminopimelic acid; galactose, glucose and xylose were detected as diagnostic sugars. The main phospholipids were identified as diphosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidylglycerol; MK-9(H) was the dominant menaquinone present. The major cellular fatty acids were identified as iso-C and iso-C. 16S rRNA gene sequence analysis showed that strain WT-2-1 is a member of the genus Geodermatophilus, with high sequence similarities to Geodermatophilus aquaeductus BMG801 (98.4%), Geodermatophilus saharensis CF5/5 (98.4%), Geodermatophilus bullaregiensis BMG841 (98.3%) and Geodermatophilus normandii CF5/3 (98.3%). Based on the phenotypic characteristics, phylogenetic data and DNA-DNA hybridization results, the isolate is concluded to represent a novel species of the genus Geodermatophilus, for which the name Geodermatophilus daqingensis sp. nov. is proposed. The type strain is WT-2-1 (=CGMCC 4.7381 = DSM 104001).

Cycloaddition reactions such as intramolecular Diels-Alder (IMDA) are extremely important in constructing multicyclic scaffolds with diverse bioactivities. Using MycB as a biomarker, three new polyketides-Chaetolivacines A (1), B (3), and C (4)with one known compound Myceliothermophin E (2) comprising of decalin and 4-hydroxy-2-pyridones were obtained from the culture of Chaetomium olivaceum SD-80A under the guidance of gene mining. The structures of these compounds were established using detailed 1D, 2D NMR, and high-resolution electron spray ionization mass spectroscopy (HRESIMS) analysis. The relative and absolute configurations of the compounds 1, 3, and 4 were elucidated by NOESY and ECD. The biosynthesis pathways of these compounds were proposed, which involves in three key genes ChaA [polyketide synthase-non-ribosomal peptide synthetases (PKS-NRPS)], ChaB, and ChaC. Compounds 1-4 were tested for their antimicrobial activities, and compounds 2 and 3 showed moderate bioactivity against Staphylococcus aureus (SA) and methicillinresistant S. aureus (MRSA) with MIC values of 15.8 and 27.1 µM. The results showed that configuration of C-21 in 3 and 4 is important for anti-SA and anti-MRSA activities. This study reveals the significant potential of the genus Chaetomium in producing new PKS-NRPS, therefore increasing the speed in the mining for new sources of antimicrobial agents.

Objective External events affect individuals through their cognitive process, a model on how and when negative life events are associated with depressive symptoms was tested by considering individuals’ internal and external factors based on the conservation of resource theory (COR). Methods We conducted a survey to test our hypotheses. Participants were college students who were selected with the cluster sampling method and were asked to complete the scales measuring negative life events, perceived social support, psychological capital (PsyCap), rumination, and depressive symptoms in the classroom with a unit of class. A total of 764 questionnaires were distributed and returned, and 703 valid data were obtained finally. Results The present study found that (1) the relationship between negative life events and depressive symptoms was moderated by perceived social support negatively, such that the relationship was stronger with low perceived social support; (2) the relationship between negative life events and depressive symptoms was mediated by rumination; (3) the relationship between rumination and depressive symptoms was moderated by PsyCap negatively, such that the relationship was stronger with low PsyCap; (4) the indirect relationship between negative life events and depressive symptoms through rumination was moderated by PsyCap negatively, such that the indirect relationship got stronger with low PsyCap. Conclusion Rumination is an essential process for negative life events to affect depressive symptoms, PsyCap and perceived social support help alleviate the detrimental effect of negative life events from internal and external perspectives, respectively. Our research conclusion has a theoretical and practical implementation for reducing depressive symptoms in college students.