The stable configurations and hydrogen bond nature of （H2O）n clusters （n = 3-6） have been investigated by the B3LYP method at the 6-31＋＋g^＊＊ level. Upon calculation, four conclusions have been drawn： （1） In...The stable configurations and hydrogen bond nature of （H2O）n clusters （n = 3-6） have been investigated by the B3LYP method at the 6-31＋＋g^＊＊ level. Upon calculation, four conclusions have been drawn： （1） In the （H2O）3-5 clusters, cyclic configurations were confirmed to be the most stable. But in the （H2O）3-4 ones, only cyclic configurations could be observed. From n = 5 （（H2O）5 clusters）, three-dimensional configuration could be found： （2） In the （H2O）6 clusters, all configurations are inclined to be three-dimensional except the most stable configuration which is cyclic; （3） The stable order of （H2O）6 clusters indicates that it is the arrangement of hydrogen bond that plays a decisive role in the cluster stabilities, the zero-point energy is also important, and cluster stabilities are independent on the number of hydrogen bonds; （4） There exist strong cooperativity and superadditivity in the （H2O）n clusters.展开更多
The structures of the complexes formed between N-methylol ethanone （model molecule of ceramide） and azacyclopentane-2-one （the model molecule of azone） have been fully optimized at the B3LYP/6-311＋＋G＊＊ level. ...The structures of the complexes formed between N-methylol ethanone （model molecule of ceramide） and azacyclopentane-2-one （the model molecule of azone） have been fully optimized at the B3LYP/6-311＋＋G＊＊ level. The intermolecular hydrogen bonding interaction energies have been calculated by using the B3LYP/6-311＋＋G＊＊, B3LYP/6-311＋＋G（2df,2p）, MP2（full）/6-311 ＋＋G＊＊ and MP2（full）/6-311 ＋＋G（2df,2p） methods, respectively. The results show that strong O-H…O=C, N-H…O=C and C-H…O=C hydrogen bonds could exist between azacyclopentane-2-one and N-methylol ethanone. The formation of the complexes might change the conformation of ceramide molecule and thus cause better percutaneous permeation for the drugs. This is perhaps the origin of the permeation enhances the activity of azone for medicament, as is in accordance with the experimental results. The hydrogen-bonding interactions follow the order of （a） 〉 （c） 〉 （b） 〉 （d） 〉 （g） ≈ （e） ≈ （i） 〉 （h） 〉 （f）. The analyses of frequency, NBO, AIM and electron density shift are used to further reveal the nature of the complex formation. In the range of 263.0- 328.0 K, the complex is formed via an exothermic reaction, and the solvent with lower temperature and dielectric constant is favorable to this process.展开更多
基金Project supported by the Natural Science Foundation of Tangshan Teacher’s College (No. 04C06)
文摘The stable configurations and hydrogen bond nature of （H2O）n clusters （n = 3-6） have been investigated by the B3LYP method at the 6-31＋＋g^＊＊ level. Upon calculation, four conclusions have been drawn： （1） In the （H2O）3-5 clusters, cyclic configurations were confirmed to be the most stable. But in the （H2O）3-4 ones, only cyclic configurations could be observed. From n = 5 （（H2O）5 clusters）, three-dimensional configuration could be found： （2） In the （H2O）6 clusters, all configurations are inclined to be three-dimensional except the most stable configuration which is cyclic; （3） The stable order of （H2O）6 clusters indicates that it is the arrangement of hydrogen bond that plays a decisive role in the cluster stabilities, the zero-point energy is also important, and cluster stabilities are independent on the number of hydrogen bonds; （4） There exist strong cooperativity and superadditivity in the （H2O）n clusters.
文摘The structures of the complexes formed between N-methylol ethanone （model molecule of ceramide） and azacyclopentane-2-one （the model molecule of azone） have been fully optimized at the B3LYP/6-311＋＋G＊＊ level. The intermolecular hydrogen bonding interaction energies have been calculated by using the B3LYP/6-311＋＋G＊＊, B3LYP/6-311＋＋G（2df,2p）, MP2（full）/6-311 ＋＋G＊＊ and MP2（full）/6-311 ＋＋G（2df,2p） methods, respectively. The results show that strong O-H…O=C, N-H…O=C and C-H…O=C hydrogen bonds could exist between azacyclopentane-2-one and N-methylol ethanone. The formation of the complexes might change the conformation of ceramide molecule and thus cause better percutaneous permeation for the drugs. This is perhaps the origin of the permeation enhances the activity of azone for medicament, as is in accordance with the experimental results. The hydrogen-bonding interactions follow the order of （a） 〉 （c） 〉 （b） 〉 （d） 〉 （g） ≈ （e） ≈ （i） 〉 （h） 〉 （f）. The analyses of frequency, NBO, AIM and electron density shift are used to further reveal the nature of the complex formation. In the range of 263.0- 328.0 K, the complex is formed via an exothermic reaction, and the solvent with lower temperature and dielectric constant is favorable to this process.
基金supported by the National Natural Science Foundation of China(21002006,20452002)Special Program for Key Basic Research of the Ministry of Science and Technology,China(2004-973-36)~~
