New insights into the interactions between dark blue pigment from Vaccinium bracteatum Thunb leaves and digestive enzymes

The dark blue pigment from Vaccinium bracteatum Thunb.leaves(VBTL)is a healthy ingredient for controlling postprandial blood glucose during the stage of dietary carbohydrate digestion.Our previous study has proved that the dark blue pigment has an inhibition effect on pancreaticα-amylase.However,the influence on other digestive enzymes(α-glucosidases,trypsin,andα-chymotrypsin)is still unclear.Therefore,this research evaluated the impact of this dark blue pigment on the three digestive enzymes during in-vitro digestion.The effects of dark blue pigment on the activities and conformations of theα-glucosidase,trypsin,andα-chymotrypsin were confirmed by multi-spectroscopic techniques and molecular docking.The results showed that this pigment possessed a higher inhibition ability on theα-glucosidase.The complexes of three enzymes and the pigment all resulted in the changes in fluorescence quenching and secondary structures of these complexes.However,the interactions between two proteolytic enzymes and pigment slightly impacted their activities.Additionally,molecular docking suggested that the complex betweenα-glucosidase and pigment formed hydrogen bonds and hydrophobic interactions in the substrate-binding pocket.These findings provide creative insight into the VBTL dark blue pigment controlling postprandial hyperglycemia without side effects on the proteolytic enzymes.

Chemical Compositions and Distribution Characteristics of Cements in Longmaxi Formation Shales, Southwest China

Shale gas resources have been regarded as a viable energy source, and it is of great significance to characterize the shale composition of different cements, such as quartz and dolomite. In this research, chemical analysis and the multifractal method have been used to study the mineral compositions and petrophysical structures of cements in shale samples from the Longmaxi Formation, China. X-ray diffraction, electron microprobe, field emission scanning electron microscopy, cathodoluminescence microscopy and C-O isotope analyses confirmed that cements in the Longmaxi Formation shales are mainly composed of Fe-bearing dolomite and quartz. Fe-bearing dolomite cements concentrate around dolomite as annuli, filling micron-sized inorganic primary pores. Quartz cements in the form of nanoparicles fill primary inter-crystalline pores among clay minerals. Theoretical calculation shows that the Fe-bearing dolomite cements formed slightly earlier than the quartz cements, but both were related to diagenetic illitization of smectite. Moreover, multifractal analysis reveals that the quartz cements are more irregularly distributed in pores than the Fe-bearing dolomite cements. These results suggest that the plugging effect of the quartz cements on the primary inoraganic pore structures is the dominant factor resulting in low interconnected porosity of shales, which are unfavorable for the enrichment of shale gas.

Geochemical Characteristics of Selenium and Its Correlation to Other Elements and Minerals in Selenium-Enriched Rocks in Ziyang County,Shaanxi Province,China

Ziyang County, Shaanxi Province, China is a world known selenium（Se）-enriched area, and a severe selenosis incident was reported in Naore Village during the 1990 s. This study investigated the geochemical characteristics of Se and its fractions in Se-enriched rocks from Ziyang. Se distribution is uneven, ranging from 0.23 to 57.00 μg/g（17.29±15.52 μg/g）. Se content is higher in slate than chert, and even lower in carbonate rocks. Cd, As and V are enriched but Pb is depleted in Se-enriched strata. Se has different correlations both with TS（total sulfur）（R^2=0.59 for chert） and TC（total carbon）（R^2=0.77 for slate, R^2=0.87 for carbonate）. Se has significant positive correlations with V（r=0.65）, As（r=0.485）, Cd（r=0.459） and Pb（r=0.405）. The Se level correlates with mineral content, positively with pyrite, chlorite and illite, negatively with albite. Se associated with sulfide/selenide and elemental Se are the predominant fractions of total recovered Se, suggesting that a reducing environment and the formation of sulfides were significant to Se deposition during its geochemical cycle. Although low concentration of bio-available Se（average 5.62%±3.69%） may reduce the risk of Se poisoning in the target area, utilization of Se-rich rock as natural fertilizer should be restricted.