The suppression of diorganogermanium compounds on the Maillard reaction of histidine(His) and glycine (Gly) with glucose has been determined by fluorescence spectrum underphysiological conditions. The title compounds ...The suppression of diorganogermanium compounds on the Maillard reaction of histidine(His) and glycine (Gly) with glucose has been determined by fluorescence spectrum underphysiological conditions. The title compounds show inhibition for the fluorescence intensity (FI) ofglycosylated andno acids stronger than Ge-132.展开更多
Chemical analysis of acid-insoluble fractions in loess and paleosols shows that concentrations of Fe and Mg were under control of wind sorting and post-depositional weathering-pedogenesis. The former caused Fe and Mg ...Chemical analysis of acid-insoluble fractions in loess and paleosols shows that concentrations of Fe and Mg were under control of wind sorting and post-depositional weathering-pedogenesis. The former caused Fe and Mg concentrated in the finer grain-size fractions, displaying synchronous variations, while the latter made Fe and Mg separated, leading to Fe retained in the weathered section and Mg leached out. Therefore, Fe/Mg ratios in the acid insoluble fraction of loess and paleosols can eliminate the effect of wind sorting and serve as an excellent proxy record on intensity of weathering-pedogenesis. Based on calculation, leaching percentage of Mg in the paleosol S1 from the Luochuan, Xifeng and Huanxian sections is 15%, 11% and 2%, respectively, and on average 9% for the paleosols S2—S14 from the Luochuan section, with the highest value amounting to 22% in S5-1, suggesting the strongest weathering-pedogenesis.展开更多
THE loess-paleosol sequences from China potentially provide one of the best terrestrial records of past climates. Studies have shown that magnetic susceptibility in the sequences represents a proxy climate index close...THE loess-paleosol sequences from China potentially provide one of the best terrestrial records of past climates. Studies have shown that magnetic susceptibility in the sequences represents a proxy climate index closely related to changes of summer monsoon intensity. Some interpretative models have been advanced to account for these magnetic variations, although unanimity of opinion has not been reached. Recent geochemical studies of chemical展开更多
A convenient and direct per(poly)fluoroalkylmethyl-introducing cyclopropanation reaction was described. In the presence of CrCl3/Fe, per(poly)fluoroalkyl iodides reacted with diethyl allylmalonate and its analogs to g...A convenient and direct per(poly)fluoroalkylmethyl-introducing cyclopropanation reaction was described. In the presence of CrCl3/Fe, per(poly)fluoroalkyl iodides reacted with diethyl allylmalonate and its analogs to give per(poly)fluoroalkylmethyl-substituted electrophilic cyclopropane derivatives in high yields. This reaction was considered to proceed by two steps: radical addition followed by cyclopropanation.展开更多
In the presence of CrCl3/Fe redox system, polyfluoropolyhaloethanes readily added to electron-deficient or electron-rich alkenes, giving the corresponding 1:1 hydropolyfluoroalkylation product or 1:1 adduct in high yi...In the presence of CrCl3/Fe redox system, polyfluoropolyhaloethanes readily added to electron-deficient or electron-rich alkenes, giving the corresponding 1:1 hydropolyfluoroalkylation product or 1:1 adduct in high yields. This reaction provided a simple and convenient method to synthesize building blocks containing a CF3 or CF2 moiety.展开更多
文摘The suppression of diorganogermanium compounds on the Maillard reaction of histidine(His) and glycine (Gly) with glucose has been determined by fluorescence spectrum underphysiological conditions. The title compounds show inhibition for the fluorescence intensity (FI) ofglycosylated andno acids stronger than Ge-132.
基金This work was supported the National Key Basic Research Project (Grant No. G1999043400) the National Natural Science Foundation of China (Grant No. 49725307).
文摘Chemical analysis of acid-insoluble fractions in loess and paleosols shows that concentrations of Fe and Mg were under control of wind sorting and post-depositional weathering-pedogenesis. The former caused Fe and Mg concentrated in the finer grain-size fractions, displaying synchronous variations, while the latter made Fe and Mg separated, leading to Fe retained in the weathered section and Mg leached out. Therefore, Fe/Mg ratios in the acid insoluble fraction of loess and paleosols can eliminate the effect of wind sorting and serve as an excellent proxy record on intensity of weathering-pedogenesis. Based on calculation, leaching percentage of Mg in the paleosol S1 from the Luochuan, Xifeng and Huanxian sections is 15%, 11% and 2%, respectively, and on average 9% for the paleosols S2—S14 from the Luochuan section, with the highest value amounting to 22% in S5-1, suggesting the strongest weathering-pedogenesis.
文摘THE loess-paleosol sequences from China potentially provide one of the best terrestrial records of past climates. Studies have shown that magnetic susceptibility in the sequences represents a proxy climate index closely related to changes of summer monsoon intensity. Some interpretative models have been advanced to account for these magnetic variations, although unanimity of opinion has not been reached. Recent geochemical studies of chemical
基金Project supported by the National Natural Science Foundation of China.
文摘A convenient and direct per(poly)fluoroalkylmethyl-introducing cyclopropanation reaction was described. In the presence of CrCl3/Fe, per(poly)fluoroalkyl iodides reacted with diethyl allylmalonate and its analogs to give per(poly)fluoroalkylmethyl-substituted electrophilic cyclopropane derivatives in high yields. This reaction was considered to proceed by two steps: radical addition followed by cyclopropanation.
基金Project supported by the National Natural Science Foundation of China.
文摘In the presence of CrCl3/Fe redox system, polyfluoropolyhaloethanes readily added to electron-deficient or electron-rich alkenes, giving the corresponding 1:1 hydropolyfluoroalkylation product or 1:1 adduct in high yields. This reaction provided a simple and convenient method to synthesize building blocks containing a CF3 or CF2 moiety.
