Extended Hartree—Fock (EHF) theory of chemical reactions VI: hybrid DFT and post-Hartree—Fock approaches for concerted and non-concerted transition structures of the Diels—Alder reaction

Activation barrier heights for concerted and non-concerted transition structures between butadiene and ethylene have been calculated by the broken-symmetry Hartree-Fock (HF), QCISD(T), and CCSD(T) methods with and without approximate spin projection, and the spin-restricted CASCI, CASSCF UNO MP2 and MR MP2 methods. They also have been calculated by the density functional theory (DFT) and hybrid DFT (HDFT) methods such as B2LYP and B3LYP. The reliability and utility of the HDFT methods have been investigated, and compared with the post-HF and MR MP2 results. The information entropy and related electron correlation indices also have been examined in relation to the polyradical character of the transition structures. Implications of the present results are discussed concerning the applicability of HDFT to large systems.     

Complex Formation of Cyclodextrins with Various Thiophenes and their Polymerization in Water: Preparation of Poly-pseudo-rotaxanes containing Poly(thiophene)s

Cyclodextrins (α-CD, β-CD and 2,6-di-O-dimethyl-β-CD (DM-β-CD)) were found to form inclusion compounds with thiophenes (thiophene (T), bithiophene (2T)) in water and in crystalline states. The structures of α-CD–T, β-CD–2T, and DM-β-CD–2T inclusion complexes were determined by X-ray crystallography. DM-β-CD forms a 1:1 cage type complex with 2T. In contrast, β-CD formed 2:3 (CD:guest) complexes with thiophene and α-CD formed 2:3 complexes, both of the channel type. These inclusion complexes were found to polymerize by FeCl₃ in the inclusion compounds in water. The products were formed poly-pseudo-rotaxane between cyclodextrins and poly(thiophene) characterized by IR, ¹H-NMR and ¹³C CP/MAS NMR. The molecular weights of the poly-pseudo-rotaxanes with poly(thiophene) were determined by the MALDI-TOF mass spectra to be 3000–5000. In comparison between poly-pseudo-rotaxane (DM-β-CD–poly(thiophene)), authentic poly(thiophene) and the washed DM-β-CD–poly(thiophene) which was washed with DMF to dethread DM-β-CD, these poly-pseudo-rotaxane was characterized by Raman, UV–vis and fluorescence spectra. The maximum emission band of DM-β-CD–poly(thiophene) shifted to a shorter wavelength. The hypsochromic shift was derived from poly-pseudo-rotaxane with DM-β-CD.     

Theoretical investigation of magnetic parameters in two-dimensional sheets of pure organic BEDT-TTF and BETS molecules by using ab initio MO and DFT methods

The effective exchange integrals (J _ab(M)) between two cation radicals of title compounds in the Heisenberg model were calculated by ab initio molecular orbital (MO) and density functional theory (DFT) methods, together with hybrid DFT methods. The J _ab(D) values between two dimer mono-cation radicals were also estimated assuming J _ab(D) = J _ab(M)/2. It is found that the spin lattice obtained by the ab initio method is square planar and linear in BEDT-TTF and BETS planes, respectively, although other previous calculations show that spin lattice in the BEDT-TTF plane is a triangular one. The J _ab and overlap integrals (s_ab ) values by the ab initio methods were used to determine transfer integral (t_ab ) and Coulomb repulsion (U_cff ) parameters of the Hubbard model, which were compared with those of the previous results. Implications of the calculated results are discussed in relation to the spin-mediated mechanism for superconductivity.     

基于生物芯片的核酸凝胶电泳仪

为克服传统平板凝胶电泳法操作步骤繁琐,实验时间长,以及采用紫外光源可能对人体造成伤害等缺陷,该文研制了一种基于电泳芯片的快速凝胶电泳仪,仅需DNA点样于电泳芯片后,将电泳芯片置于该电泳仪便可实现DNA样品快速分离及实时在线成像检测。以20、50、100 bp DNA ladder为检测对象,在仪器内对其分离效果进行验证及优化,其最佳电泳条件为电压100 V/cm,琼脂糖质量分数分别为2. 5%、1. 0%、1. 4%。结果表明在14 min内可以实现3种DNA样品的高效分离,DNA迁移距离与分子量的相关系数均高于0. 9,且该仪器具有较高的稳定性。     

Dielectric relaxation spectrum of water studied by the site—site generalized Langevin/modified mode-coupling theory

The dielectric relaxation spectrum of water is calculated from the site-site generalized Langevin/modified mode-coupling theory. The main part of the relaxation follows the Debye-type function, and a small deviation from the Debye relaxation is found on the high-frequency side. This tendency is consistent with recent experiments, although the absolute relaxation time does not agree with the experimental value quantitatively. The time development of the longitudinal polarization function resembles the dielectric part of the memory function, and we consider that this is because the dielectric friction dominates the collective reorientation of the dipole moment of water. We performed calculations with different dielectric constants using the reference interaction-site model integral equation, and found that the large gap between the time scales of the dielectric relaxation and the longitudinal polarization relaxation causes the Debye-type dielectric relaxation in our theory when the dielectric friction is dominant in the friction on the collective reorientation of the dipole moment. Namely, the longitudinal polarization relaxation is fast enough to be considered as a white noise to the dielectric relaxation process, so that the relaxation becomes a Markov process. The large gap between the two relaxation times originates from a large local field correction owing to the large dielectric constant of water. It is also suggested that the deviation from the Debye relaxation at the high-frequency side is the manifestation of the slow memory caused by the long-time part of the longitudinal polarization relaxation in the low-wavenumber region.     

脉冲毛细管电泳分离蛋白质的研究

蛋白质是机体细胞的重要组成成分,通过分析蛋白质可获得机体的受损或病变情况,因此毛细管电泳(CE)分析蛋白质分子在临床医学中具有重要的应用价值.该文以溶菌酶、生长激素、碳酸酐酶、肌动蛋白、牛血清白蛋白和磷酸化酶B为样本,采用有效长度为6 cm和总长度为8 cm的毛细管,以羟乙基纤维素(HEC)为分离介质,首次采用脉冲电场...     

Ab initio study for static hyperpolarizabilities of several donor-π-acceptor molecules

Static molecular second hyperpolarizabilities γ of several donor-π-acceptor molecules have been examined using an ab initio molecular orbital (MO) method to evaluate the effects of substituents and molecular distortion on γ. It was found that γ values of the donor-π-acceptor compounds are affected by the degree of π electron delocalization more than the donor or acceptor strength of the substituents. Also it was found that contributions from higher order excitation process are not negligible for γ values of the donor-π-acceptor molecules.     

RbCl和CsCl水溶液结构的X射线散射及经验势结构精修模拟

采用X射线散射法研究了RbCl和CsCl水溶液的结构,利用基于经验势的结构精修(EPSR)方法获得了溶液中的水合Cl^-、Rb⁺、Cs⁺、离子缔合及本体水的对径向分布函数、配位数分布及空间密度分布(3D结构)等结构信息。在水溶液中,Cl^-具有相对稳定的6水合结构,其水合距离为0.321 nm,外加阳离子对其水合作用的影响不明显。7.3 ± 1.4个水分子与Rb⁺水合,其特征水合距离为0.297 nm,8.4 ± 1.6个水分子与Cs⁺水合其水合距离为0.312 nm。Cs⁺不具有第二水合层,而Rb⁺表现出了更强的水合能力,具有较明显的第二水合层。Cl^-、Rb⁺及Cs⁺常被认为是“结构破坏”型离子。从微观角度来看这种所谓的“结构破坏”主要体现在破坏了本体水分子的第二水合层保持四面体构型的趋势。RbCl和CsCl水溶液中部分存在着Rb-Cl和Cs-Cl直接接触离子对,在1.0 mol·dm^-3的溶液中Rb-Cl及Cs-Cl的特征距离分别为0.324和0.336 nm,溶剂分割离子对的距离则都在0.6 nm左右。相对于Cs⁺,Rb⁺与Cl^-离子之间表现出了更强的缔合能力。