采用密度泛函理论(DFT)的B3LYP方法对Ti_2^+活化环己烷的同面脱氢机理进行理论计算,分别得到反应中涉及到的驻点、优化构型及相关的构型参数,并简单绘制了反应势能图,从而对反应机理进行详细的分析。对环己烷与Ti_2^+反应的同面脱氢机...采用密度泛函理论(DFT)的B3LYP方法对Ti_2^+活化环己烷的同面脱氢机理进行理论计算,分别得到反应中涉及到的驻点、优化构型及相关的构型参数,并简单绘制了反应势能图,从而对反应机理进行详细的分析。对环己烷与Ti_2^+反应的同面脱氢机理进行研究,研究结果表明环己烷与Ti_2^+的同面脱氢过程中三次脱氢机理相似,反应发生在混合势能面上,最终产物是二、四重态的混合物,且放热分别为54.85、28.74 k J/mol。展开更多
Primary biliary cirrhosis(PBC) is an autoimmune disease of the liver characterized by progressive bile duct destruction eventually leading to cirrhosis and liver failure.The serological hallmark of the disease is the ...Primary biliary cirrhosis(PBC) is an autoimmune disease of the liver characterized by progressive bile duct destruction eventually leading to cirrhosis and liver failure.The serological hallmark of the disease is the presence of circulating antimitochondrial antibodies(AMA).These reflect the presence of autoreactive T and B cells to the culprit antigens,the E2 subunits of mitochondrial 2-oxo-acid dehydrogenase enzymes,chiefly pyruvate dehydrogenase(PDC-E2).The disease results from a combination of genetic and environmental risk factors.Genetic predisposition is indicated by the higher familial incidence of the disease particularly among siblings and the high concordance rate among monozygotic twins.Environmental triggering events appear crucial to disrupt a pre-existing unstable immune tolerance of genetic origin allowing,after a long latency,the emergence of clinical disease.Initiating mimetopes of the vulnerable epitope of the PDC-E2 autoantigen can be derived from microbes that utilize the PDC enzyme or,alternatively,environmental xenobiotics/chemical compounds that modify the structure of native proteins to make them immunogenic.A further alternative as a source of antigen is PDC-E2 derived from apoptotic cells.In the effector phase the biliary ductular cell,by reason of itsproclivity to express the antigen PDC-E2 in the course of apoptosis,undergoes a multilineage immune attack comprised of CD4+ and CD8+ T cells and antibody.In this article,we critically review the available evidence on etiopathogenesis of PBC and present interpretations of complex data,new developments and theories,and nominate directions for future research.展开更多
AIM： To test the hypothesis that the variant UDP- glucuronosyltransferase 1A1 （UGT1A1） gene, glucose-6- phosphate dehydrogenase （G6PD） deficiency, and thalassemia influence bilirubin metabolism and play a role in...AIM： To test the hypothesis that the variant UDP- glucuronosyltransferase 1A1 （UGT1A1） gene, glucose-6- phosphate dehydrogenase （G6PD） deficiency, and thalassemia influence bilirubin metabolism and play a role in the development of cholelithiasis. METHODS： A total of 372 Taiwan Chinese with cholelithiasis who had undergone cholecystectomy and 293 healthy individuals were divided into case and control groups, respectively. PCR and restriction fragment length polymorphism were used to analyze the promoter area and nucleotides 211, 686, 1 091, and 1 456 of the UGT1A1 gene for all subjects and the gene variants for thalassemia and G6PD deficiency. RESULTS： Variation frequencies for the cholelithiasis patients were 16.1%, 25.8%, 5.4%, and 4.3% for A（TA）6 TAA/A（TA）TTAA （6/7）, heterozygosity within the coding region, compound heterozygosity, and homozygosity of the UGT1A1 gene, respectively. Comparing the case and control groups, a statistically significant difference in frequency was demonstrated for the homozygous variation of the UGT1A1 gene （P = 0.012, Z2 test）, but not for the other variations. Further, no difference was demonstrated in a between-group comparison of the incidence of G6PD deficiency and thalassemia （2.7% vs 2.4% and 5.1% vs 5.1%, respectively）. The bilirubin levels for the cholelithiasis patients with the homozygous variant-UGT1A1 gene were significantly different from the control analog （18.0±6.5 and 12.7±2.9 μmol/L, respectively; P〈0.001, Student＇s ttest）.CONCLUSION： Our results show that the homozygous variation in the UGT1A1 gene is a risk factor for the development of cholelithiasis in Taiwan Chinese. 2005 The WJG Press and Elsevier Inc. All rights reserved展开更多
Based on the Residual Oil Hydrodesulfurization Treatment Unit (S-RHT), the n-order reaction kinetic model for residual oil HDS reactions and artificial neural network (ANN) model were developed to determine the sulfur...Based on the Residual Oil Hydrodesulfurization Treatment Unit (S-RHT), the n-order reaction kinetic model for residual oil HDS reactions and artificial neural network (ANN) model were developed to determine the sulfur content of hydrogenated residual oil. The established ANN model covered 4 input variables, 1 output variable and 1 hidden layer with 15 neurons. The comparison between the results of two models was listed. The results showed that the predicted mean relative errors of the two models with three different sample data were less than 5% and both the two models had good predictive precision and extrapolative feature for the HDS process. The mean relative error of 5 sets of testing data of the ANN model was 1.62%—3.23%, all of which were smaller than that of the common mechanism model (3.47%— 4.13%). It showed that the ANN model was better than the mechanism model both in terms of fitting results and fitting difficulty. The models could be easily applied in practice and could also provide a reference for the further research of residual oil HDS process.展开更多
Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in const...Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes. AD reactions also can be utilized for hydrogen production from biomass or its fermentation products (mainly alcohols). Reversible hydrogenation/ dehy-drogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage. In this article, we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments. These reactions include acceptorless alcohol dehydrogenations, reversible dehydrogenation/hydrogenation of nitrogen heterocycles, dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds, and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds. For the catalysts possessing metal-ligand bifunctional active sites (such as 28, 45, 86, 87, and 106 in the paper), the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted-H elimination mechanism. However, methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene, catalyzed by the iridium complex 121, takes place via the-H elimination mechanism, because the Lewis basicity of either the-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity. Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.展开更多
文摘采用密度泛函理论(DFT)的B3LYP方法对Ti_2^+活化环己烷的同面脱氢机理进行理论计算,分别得到反应中涉及到的驻点、优化构型及相关的构型参数,并简单绘制了反应势能图,从而对反应机理进行详细的分析。对环己烷与Ti_2^+反应的同面脱氢机理进行研究,研究结果表明环己烷与Ti_2^+的同面脱氢过程中三次脱氢机理相似,反应发生在混合势能面上,最终产物是二、四重态的混合物,且放热分别为54.85、28.74 k J/mol。
文摘Primary biliary cirrhosis(PBC) is an autoimmune disease of the liver characterized by progressive bile duct destruction eventually leading to cirrhosis and liver failure.The serological hallmark of the disease is the presence of circulating antimitochondrial antibodies(AMA).These reflect the presence of autoreactive T and B cells to the culprit antigens,the E2 subunits of mitochondrial 2-oxo-acid dehydrogenase enzymes,chiefly pyruvate dehydrogenase(PDC-E2).The disease results from a combination of genetic and environmental risk factors.Genetic predisposition is indicated by the higher familial incidence of the disease particularly among siblings and the high concordance rate among monozygotic twins.Environmental triggering events appear crucial to disrupt a pre-existing unstable immune tolerance of genetic origin allowing,after a long latency,the emergence of clinical disease.Initiating mimetopes of the vulnerable epitope of the PDC-E2 autoantigen can be derived from microbes that utilize the PDC enzyme or,alternatively,environmental xenobiotics/chemical compounds that modify the structure of native proteins to make them immunogenic.A further alternative as a source of antigen is PDC-E2 derived from apoptotic cells.In the effector phase the biliary ductular cell,by reason of itsproclivity to express the antigen PDC-E2 in the course of apoptosis,undergoes a multilineage immune attack comprised of CD4+ and CD8+ T cells and antibody.In this article,we critically review the available evidence on etiopathogenesis of PBC and present interpretations of complex data,new developments and theories,and nominate directions for future research.
基金Supported by a grant from the Cathay Medical Research Center, Taipei, Taiwan, China
文摘AIM： To test the hypothesis that the variant UDP- glucuronosyltransferase 1A1 （UGT1A1） gene, glucose-6- phosphate dehydrogenase （G6PD） deficiency, and thalassemia influence bilirubin metabolism and play a role in the development of cholelithiasis. METHODS： A total of 372 Taiwan Chinese with cholelithiasis who had undergone cholecystectomy and 293 healthy individuals were divided into case and control groups, respectively. PCR and restriction fragment length polymorphism were used to analyze the promoter area and nucleotides 211, 686, 1 091, and 1 456 of the UGT1A1 gene for all subjects and the gene variants for thalassemia and G6PD deficiency. RESULTS： Variation frequencies for the cholelithiasis patients were 16.1%, 25.8%, 5.4%, and 4.3% for A（TA）6 TAA/A（TA）TTAA （6/7）, heterozygosity within the coding region, compound heterozygosity, and homozygosity of the UGT1A1 gene, respectively. Comparing the case and control groups, a statistically significant difference in frequency was demonstrated for the homozygous variation of the UGT1A1 gene （P = 0.012, Z2 test）, but not for the other variations. Further, no difference was demonstrated in a between-group comparison of the incidence of G6PD deficiency and thalassemia （2.7% vs 2.4% and 5.1% vs 5.1%, respectively）. The bilirubin levels for the cholelithiasis patients with the homozygous variant-UGT1A1 gene were significantly different from the control analog （18.0±6.5 and 12.7±2.9 μmol/L, respectively; P〈0.001, Student＇s ttest）.CONCLUSION： Our results show that the homozygous variation in the UGT1A1 gene is a risk factor for the development of cholelithiasis in Taiwan Chinese. 2005 The WJG Press and Elsevier Inc. All rights reserved
文摘Based on the Residual Oil Hydrodesulfurization Treatment Unit (S-RHT), the n-order reaction kinetic model for residual oil HDS reactions and artificial neural network (ANN) model were developed to determine the sulfur content of hydrogenated residual oil. The established ANN model covered 4 input variables, 1 output variable and 1 hidden layer with 15 neurons. The comparison between the results of two models was listed. The results showed that the predicted mean relative errors of the two models with three different sample data were less than 5% and both the two models had good predictive precision and extrapolative feature for the HDS process. The mean relative error of 5 sets of testing data of the ANN model was 1.62%—3.23%, all of which were smaller than that of the common mechanism model (3.47%— 4.13%). It showed that the ANN model was better than the mechanism model both in terms of fitting results and fitting difficulty. The models could be easily applied in practice and could also provide a reference for the further research of residual oil HDS process.
基金supported by the Chinese Academy of Sciencesthe National Natural Science Foundation of China (20973197 and 21173263)
文摘Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes. AD reactions also can be utilized for hydrogen production from biomass or its fermentation products (mainly alcohols). Reversible hydrogenation/ dehy-drogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage. In this article, we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments. These reactions include acceptorless alcohol dehydrogenations, reversible dehydrogenation/hydrogenation of nitrogen heterocycles, dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds, and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds. For the catalysts possessing metal-ligand bifunctional active sites (such as 28, 45, 86, 87, and 106 in the paper), the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted-H elimination mechanism. However, methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene, catalyzed by the iridium complex 121, takes place via the-H elimination mechanism, because the Lewis basicity of either the-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity. Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.
