The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction...The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction: decreasing the activation energy and stabilizing the C=N double bond owing to the conjugative effect of p-π-p of products and transition states.展开更多
Intra-abdominal injection of amitraz(0.25 nmol per honeybee,i.e.,approx 2.3 nmol/g)to emerging worker bees,in vivo,led to a significant hypertrehalosemia(300-400%)followed by a hyperglucosemia(≈600%).Maxima were reac...Intra-abdominal injection of amitraz(0.25 nmol per honeybee,i.e.,approx 2.3 nmol/g)to emerging worker bees,in vivo,led to a significant hypertrehalosemia(300-400%)followed by a hyperglucosemia(≈600%).Maxima were reached at 0.5 and 2h,respectively.A strong negative correlation between glucosemia and trehalosemia appeared after injection of pure phentolamine (1 nmol per bee),suggesting stimulation of trehalase activities.Simultaneous administration of the α-blocker at≥0.25 nmol per individual suppressed the hyperglycemic response of amitraz. The formamidine pesticide thus likely acts on the honeybee α-aminergic system.1989 Academic Press,Inc.展开更多
The time-course and dose-related action of amitraz (AMZ) on gut lipids of worker honeybees were examined over 3 hours following in vivo injections of 0.25, 0.5, 1 and 2 nmols of pesticide per bee. Significant decrease...The time-course and dose-related action of amitraz (AMZ) on gut lipids of worker honeybees were examined over 3 hours following in vivo injections of 0.25, 0.5, 1 and 2 nmols of pesticide per bee. Significant decreases were observed at 30-45 min with 0.25 nmols per bee, for phospholipids, fatty acids, steroids and triacylglycerols. However increases were observed either later or with higher doses. The decreasing action observed with 0.25 nmol AMZ per bee was inhibited by simultaneous injections of the a antagonist phentolamine (from 0.25 to 2.0 nmols per bee). The toxicity of AMZ to honeybees thus likely involves the mobilization of lipids from the gut, via action of this formamidine pesticide on a-adrenoceptors.展开更多
An environmentally benign and highly efficient biomimetic approach for the synthesis of N,N＇-diarylsubstituted formamidines in water catalyzed β-cyclodextrin is described under neutral condition with quantitative yi...An environmentally benign and highly efficient biomimetic approach for the synthesis of N,N＇-diarylsubstituted formamidines in water catalyzed β-cyclodextrin is described under neutral condition with quantitative yields of products.β-Cyclodextrin has been recovered and reused.展开更多
The hydrolysis mechanisms of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine (FA-3TC) in the gas phase and in aqueous solution were studied by use of the density functional theory B3LYP/6-31+G(d, p) met...The hydrolysis mechanisms of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine (FA-3TC) in the gas phase and in aqueous solution were studied by use of the density functional theory B3LYP/6-31+G(d, p) method. Two possible reaction pathways in the title reaction were considered. In one pathway water attacks the C=N double bond first (path A) while in the other water attacks the C—N single bond first (path B). The calculated results indicate that the first step in both pathways is the rate-limiting process and path A is more favorable than path B in the gas phase. The effect of solvent water on the title reaction was assessed at the B3LYP/6-31+G(d, p) level of theory based on the po-larizable continuum model (CPCM). In water the first mechanism (path A) is also favored.展开更多
Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chro- matography （HPLC） and mass spectrometry （MS） at 25 ~C. By controlling the slow reaction rate...Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chro- matography （HPLC） and mass spectrometry （MS） at 25 ~C. By controlling the slow reaction rate and choosing appropriate mobile phase, HPLC provides the unique advantages over other methods （UV-Vis, chemical separation） in species tracking and kinetic study. In addition to thiourea and formamidine sulfinic acid, two unreported products were also detected in the hy- drolysis reaction. Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyan- ogen with mass weights of 92.28 and 116,36, respectively. In the oxidation of formamidine disulfide by hydrogen peroxide, besides thiourea, formamidine sulfenic acid, formamidine sulfinic acid, thiocyanogen and urea, formamidine sulfonic acid and sulfate could be detected. The oxidation reaction was found to be first order in both forrnamidine disulfide and hydrogen per- oxide. The rate constants of hydrolysis and oxidation reactions were determined in the pH range of 1.5-3.0. It was found both rate constants are increased with the increasing of pH. Experimental curves of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation, including hydrolysis equilibrium of formamidine disulfide and irre- versible hydrolysis of formamidine sulfenic acid.展开更多
Gold dissolves easily in an alkaline thiourea solution with Na2SO3 and Na2S2O8, where the accompanied elements of Au, such as Ag, Cu, Ni and Fe can hardly dissolve. It was considered that electrochemical reduction and...Gold dissolves easily in an alkaline thiourea solution with Na2SO3 and Na2S2O8, where the accompanied elements of Au, such as Ag, Cu, Ni and Fe can hardly dissolve. It was considered that electrochemical reduction and catalytic action of SO32- prevent thiourea from decomposing irreversibly and accelerates dissolution of gold.The S2O82- as an oxidant can control the potential so that formamidine disulfide may form efficiently. The dissolution of gold is mainly through oxidation of Au by formamidine disulfide and complexation of thiourea with An+,and not direct oxidation of S2O82-. Thus,sufficient formamidine disulfide is necessary to accelerate the dissolution of gold. The reason for Ag, Cu hardly being dissoluble is that the black layers of Ag2S and Cu1.92S form on the surface of Ag and Cu. The metal Ni and Fe do not dissolve in the alkaline media due to their sulfide films passivation samely.展开更多
In current paper, the effect of different factors on extraction of silver from tailings of lead flotation plant using thiourea leaching was studied. According to the mineralogical studies and chemical analysis taken f...In current paper, the effect of different factors on extraction of silver from tailings of lead flotation plant using thiourea leaching was studied. According to the mineralogical studies and chemical analysis taken from the tailings dam, the representative sample taken from there contained 30 ppm Ag and the minerals such as calcite, dolomite, barite, microcline, galena etc. In this research, the effects of iron(III) sulfate concentration, thiourea concentration, size and temperature onextraction of silver from Ravanj flotation plant tailings were analyzed using statistics design of experiment and DX7 software;and it was determined that iron(III) sulfate concentration and temperature were the most effective factors on the extraction of silver. The results showed that the best recovery obtained in particle size of 75 microns, 1 kg/m<sup>3</sup> thiourea concentration and 1 kg/m<sup>3</sup> iron(III) sulfate concentration in the temperature of 60℃ for 2 hours.展开更多
基金Supported by the Yunnan Provincial Science and Technology Department (2003A0003M)
文摘The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction: decreasing the activation energy and stabilizing the C=N double bond owing to the conjugative effect of p-π-p of products and transition states.
文摘Intra-abdominal injection of amitraz(0.25 nmol per honeybee,i.e.,approx 2.3 nmol/g)to emerging worker bees,in vivo,led to a significant hypertrehalosemia(300-400%)followed by a hyperglucosemia(≈600%).Maxima were reached at 0.5 and 2h,respectively.A strong negative correlation between glucosemia and trehalosemia appeared after injection of pure phentolamine (1 nmol per bee),suggesting stimulation of trehalase activities.Simultaneous administration of the α-blocker at≥0.25 nmol per individual suppressed the hyperglycemic response of amitraz. The formamidine pesticide thus likely acts on the honeybee α-aminergic system.1989 Academic Press,Inc.
文摘The time-course and dose-related action of amitraz (AMZ) on gut lipids of worker honeybees were examined over 3 hours following in vivo injections of 0.25, 0.5, 1 and 2 nmols of pesticide per bee. Significant decreases were observed at 30-45 min with 0.25 nmols per bee, for phospholipids, fatty acids, steroids and triacylglycerols. However increases were observed either later or with higher doses. The decreasing action observed with 0.25 nmol AMZ per bee was inhibited by simultaneous injections of the a antagonist phentolamine (from 0.25 to 2.0 nmols per bee). The toxicity of AMZ to honeybees thus likely involves the mobilization of lipids from the gut, via action of this formamidine pesticide on a-adrenoceptors.
基金Department of Science and Technology,New Delhi for financial supportUniversity Grant Commission,New Delhi for JRF fellowship
文摘An environmentally benign and highly efficient biomimetic approach for the synthesis of N,N＇-diarylsubstituted formamidines in water catalyzed β-cyclodextrin is described under neutral condition with quantitative yields of products.β-Cyclodextrin has been recovered and reused.
基金the National Natural Science Foundation of China (Grant Nos. 20473055 and 20773089)the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (Grant No. 20071108-18-15)
文摘The hydrolysis mechanisms of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine (FA-3TC) in the gas phase and in aqueous solution were studied by use of the density functional theory B3LYP/6-31+G(d, p) method. Two possible reaction pathways in the title reaction were considered. In one pathway water attacks the C=N double bond first (path A) while in the other water attacks the C—N single bond first (path B). The calculated results indicate that the first step in both pathways is the rate-limiting process and path A is more favorable than path B in the gas phase. The effect of solvent water on the title reaction was assessed at the B3LYP/6-31+G(d, p) level of theory based on the po-larizable continuum model (CPCM). In water the first mechanism (path A) is also favored.
基金supported by the National Natural Science Foundation of China (21073232 & 50921002)the Fundamental Research Fund from the Chinese Central University (2010LKHX02)
文摘Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chro- matography （HPLC） and mass spectrometry （MS） at 25 ~C. By controlling the slow reaction rate and choosing appropriate mobile phase, HPLC provides the unique advantages over other methods （UV-Vis, chemical separation） in species tracking and kinetic study. In addition to thiourea and formamidine sulfinic acid, two unreported products were also detected in the hy- drolysis reaction. Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyan- ogen with mass weights of 92.28 and 116,36, respectively. In the oxidation of formamidine disulfide by hydrogen peroxide, besides thiourea, formamidine sulfenic acid, formamidine sulfinic acid, thiocyanogen and urea, formamidine sulfonic acid and sulfate could be detected. The oxidation reaction was found to be first order in both forrnamidine disulfide and hydrogen per- oxide. The rate constants of hydrolysis and oxidation reactions were determined in the pH range of 1.5-3.0. It was found both rate constants are increased with the increasing of pH. Experimental curves of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation, including hydrolysis equilibrium of formamidine disulfide and irre- versible hydrolysis of formamidine sulfenic acid.
文摘Gold dissolves easily in an alkaline thiourea solution with Na2SO3 and Na2S2O8, where the accompanied elements of Au, such as Ag, Cu, Ni and Fe can hardly dissolve. It was considered that electrochemical reduction and catalytic action of SO32- prevent thiourea from decomposing irreversibly and accelerates dissolution of gold.The S2O82- as an oxidant can control the potential so that formamidine disulfide may form efficiently. The dissolution of gold is mainly through oxidation of Au by formamidine disulfide and complexation of thiourea with An+,and not direct oxidation of S2O82-. Thus,sufficient formamidine disulfide is necessary to accelerate the dissolution of gold. The reason for Ag, Cu hardly being dissoluble is that the black layers of Ag2S and Cu1.92S form on the surface of Ag and Cu. The metal Ni and Fe do not dissolve in the alkaline media due to their sulfide films passivation samely.
文摘In current paper, the effect of different factors on extraction of silver from tailings of lead flotation plant using thiourea leaching was studied. According to the mineralogical studies and chemical analysis taken from the tailings dam, the representative sample taken from there contained 30 ppm Ag and the minerals such as calcite, dolomite, barite, microcline, galena etc. In this research, the effects of iron(III) sulfate concentration, thiourea concentration, size and temperature onextraction of silver from Ravanj flotation plant tailings were analyzed using statistics design of experiment and DX7 software;and it was determined that iron(III) sulfate concentration and temperature were the most effective factors on the extraction of silver. The results showed that the best recovery obtained in particle size of 75 microns, 1 kg/m<sup>3</sup> thiourea concentration and 1 kg/m<sup>3</sup> iron(III) sulfate concentration in the temperature of 60℃ for 2 hours.
