Linear response time-dependent density functional theory for van der Waals coefficients

A linear response time-dependent density functional theory is described and used to calculate the dynamic polarizabilities and van der Waals C(6) coefficients of complex atom pairs. We present values of C(6) for dimers of main group atoms and the first row of transition metal atoms.     

大黄素的吸附溶出伏安研究

研究了大黄素在甲醇、二氧六环和水的混合溶剂中以１％硼砂为支持电解质在静汞电极上的吸附伏安行为。建立了用微分脉冲吸附溶出伏安法测定其含量的新方法。在－０３０Ｖ（ｖｓＡｇ／ＡｇＣｌ）电位下吸附富集，可得一灵敏的还原溶出峰，峰电位－０７５Ｖ，浓度在５×１０－８～５×１０－９ｍｏｌ／Ｌ范围内与峰电流具有良好的线性关系，最低检出限为１×１０－９ｍｏｌ／Ｌ。该法用于含有大黄素体系的测定简便、快速、可靠。     

Comparison between the symmetry-correlation examination and the perturbation method

A comparison between the construction of symmetry-correlation diagrams and the perturbation method for studying chemical reactions is carried out. The perturbation method consists of decomposing the system Hamiltonian H into a sum, H = H₀ + H′. Various symmetry correlation schemes appearing in the literature may be explained by the nonuniqueness of the decomposition scheme. All symmetry selection rules may be viewed as the varieties. By examining the symmetry-correlation diagrams, processes under investigation may be called “forbidden” or “allowed,” depending on the topological feature. Of particular importance is the topology associated with the “avoided crossing.” By making the comparison, we can establish the correspondence of the two methods and conclude that the perturbation order furnishes the origin of the “forbiddenness” of a process.     

Avoided crossing and intermediate states in certain photochemical reactions

An attempt to classify various types of avoided surface crossings originally discussed by Salem and co-workers is presented. From the present scheme, an order-of-forbiddenness criterion regarding reactivity is established from a consideration of electron and orbital counting. Since the new classification is qualitatively related to the energy gap created in the avoided crossing, the classification appears to be more systematic and informative. Energy transfer processes involved in electronically excited states may also be rationalized by such an application. Three major mechanistic types are distinguished: concerted two-electron process, concerted one-electron process, and stepwise one-electron process involving an ionic-pair intermediate.     

Synthesis of 4,12-dihydro-4-oxoquino-[1,8a,8-a,b]quinoxaline-5-carboxylic acid derivatives

The synthesis and antibacterial activity of 1-substituted amino-2-fluoro-4,12-dihydro-4-oxoquino[1,8a,8-a,b]quinoxaline-5-carboxylic acid derivatives are described. The synthetic route includes a carbon homologation and two intramolecular nucleophilic displacement cyclization reactions leading to the novel 4,12-dihydro-4-oxoquino[1,8a,8-a,b]quinoxaline-5-carboxylic acid heterocycle.     

Crystal Structure of a Supramolecular Complex Formed between 1-bromo-2-iodo-tetrafluoroethane and N,N,N′,N′-tetramethyl-ethylenediamine

X-ray analysis has revealed that N,N,N′,N′-tetramethyl-ethylenediamine 1 form donor–acceptor complex 3 with 1-bromo-2-iodo-tetrafluoroethane 2, in which the N X (X = Br, I) distances are longer than the average covalent bond length between X and N, but are also definitively shorter than the sum of the corresponding van der Waals radii of X and N, thus that indicating weak interactions between the nitrogen and bromine or iodine atoms. In our experimental section, a valuable method for recrystallization and collect X-ray data from crystals that easily exhibit decay and can be cracked is reported.     

Synthesis and pharmacological analysis of high affinity melatonin receptor ligands

We report the synthesis and radioligand binding analysis of a series of naphthalenic melatonin receptor ligands, N-[2-(7-alkoxy-2-methoxy-1-naphthyl)ethyl]propionamide. This series of ligands exhibits subpicomolar binding affinity to both MT1 and MT2 melatonin receptors expressed in chinese hamster ovary (CHO) cells.     

A new differential scanning calorimetry based approach for the characterization of peracid resin

Differential scanning calorimetry was used to trace the heat of decomposition of the peracid groups (ΔH_d) in the oxidized EVA-g-AA resin. From the correlation between ΔH_d and the oxidation capacity measured by iodometry, it was found that 35 ± 5 cal of energy evolved per miliequivalent of peracid group decomposed. The ΔH_d values are also useful in finding the optimum condition for oxidation of acid groups and can be used to investigate the distribution of active peracid groups across the matrix. The stability and the activation energy of decomposition of grafted type peracid resin were also studied, where the activation energy of decomposition was calculated to be 13.4 kcal/mol.     

Detection of ClSO with time-resolved Fourier-transform infrared absorption spectroscopy

ClSO was produced as an intermediate upon irradiating a flowing mixture of Cl2SO and Ar with a KrF excimer laser at 248 nm. A step-scan Fourier-transform infrared spectrometer coupled with a small multipass absorption cell was employed to detect time-resolved absorption spectrum of ClSO. A transient spectrum in the region 1120-1200 cm(-1), which diminished on prolonged reaction, is assigned to the S-O stretching (nu1) mode of ClSO. A spectrum with a resolution of 0.3 cm(-1) partially reveals rotational structure with the Q-branch at 1162.9 cm(-1). Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predict the geometry, vibrational, and rotational parameters of ClSO. An IR absorption spectrum of ClSO simulated based on predicted rotational parameters agrees satisfactorily with experimental results. ClSO produced from photolysis of Cl2SO at 248 nm is internally hot.     

A New Convenient Method for the Resolution of 1, 1''''-Binaphthalene-2, 2''''-diol Via a Phosphite Using (-)-Menthol as Resolving Agent

Optically active 1,1-binaphthalene-2, 2-diol has become a quite important chiral source in different fields of chirotechnology, especially in asymmetric synthesis1. Its synthesis and resolution has been extensively studied and various resolution methods have been reported2. Among the reported resolution methods, the following three, namely, via the formation of phosphoric acid derivatives3, boric acid derivatives4 and inclusion complexes5, are the most important. OHOH+_( )-1(-)-(S)-1(+)-(R)…