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171.
Alfonso Ortiz-Acevedo 《Tetrahedron letters》2004,45(36):6795-6798
A novel approach for the synthesis of cyclic peptides that can exist in either linear or cyclized conformations is described. Synthesis of the peptides was achieved via a modified solid phase methodology. The reversible linear/cyclized (i.e., open/closed) states are controlled via the reduction/oxidation of a disulfide bond incorporated into the backbone of the peptide chain. 相似文献
172.
The ground state and the excited states of benzene, pyrimidine, and pyrazine have been examined by using the symmetry adapted cluster-configuration interaction (SAC-CI) method. Detailed characterizations and the structures of the absorption peaks in the vacuum ultraviolet (VUV), low energy electron impact (LEEI), and electron energy loss (EEL) spectra were theoretically clarified by calculating the excitation energy and the oscillator strength for each excited state. We show that SAC-CI has the power to well reproduce the electronic excitation spectra (VUV, LEEI, and EEL) simultaneously to an accuracy for both the singlet and the triplet excited states originated from the low-lying pi --> pi*, n --> pi*, pi --> sigma* and n --> sigma* excited states of the titled compounds. The present results are compared with those of the previous theoretical studies by methods, such as EOM-CCSD(T), STEOM-CCSD, CASPT2 and TD-B3LYP, etc. 相似文献
173.
174.
测量了标题配合物Ni(mnt)(phen)在多种介质中的电子吸收光谱和发射光谱, 使用密度泛函理论的B3LYP方法和分子轨道理论的PM3方法研究了其气态分子几何构型、电子结构和成键, 用ZINDO/S方法通过多组态的组态相互作用(CI)计算解释了实验光谱. 结果表明: 该配合物分子为平面结构, 对称性属于点群C2v, 基态为自旋三重态, 配位键Ni—N和Ni—S为典型的共价结合, Ni的3d电子反馈效应较显著; 可见区的吸收带和发射带(对应于基态电子组态到较低能量激发态组态的跃迁)本质上属于配体phen到mnt2-的荷移跃迁(LL'CT), 紫外区的吸收带本质上属于配体的π→π*跃迁. 相似文献
175.
用从头算和MP2方法求得亚硝酸甲酯的基态、第一和第二激发态解离为CH3O和NO自由基的解离能分別为238.14、68.99和-183.97kJ/mol,而CH3O和NO易于生成甲醛和硝酰。由CI方法求出的亚硝酸甲酯直接生成甲醛和硝酰的基态和激发态反应曲线表明,该反应难以按这种机理进行。因此,以上计算支持了实验提出的亚硝酸甲酯光反应生成甲醛和硝酰的两种机理中的光解离机制。 相似文献
176.
The electronic structures of the S2O and S3 isomers have been dealt with by the multireference double-excitation (MRD) configuration-interaction (CI) calculations, using contracted [5s3p1d] and [4s2p1d] basis functions for the S and O atoms, respectively. The ground-state geometries for the SOS (symmetric chain), S2O (symmetric ring) and SSO (unsymmetric chain) are optimized, and their vertical singlet excitation energies are calculated. It is found that SSO is the most stable of the three isomers and that the ground state (1A1) of the S2O (ring) is correlated with the excited states of SOS (21A1) and SSO (31A). The chain and ring isomers of S3 have been treated in a similar manner. Energetics for the ring closure of the O3, SO2, SSO and S3 chain molecules are discussed on a unified ground.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayPresented at the 5th International Congress on Quantum Chemistry, Montréal, August 1985 相似文献