Quantum Chemical Study on a New Mechanism of One-carbon Unit Transfer Reaction： The Water-assisted Mechanism

It is a theoretical study on the water-assisted mechanism of one-carbon unit transfer reaction, in which the energy barrier for each transition state lowered by about 80-100 kJ/mol when compared with the one in no-water-involved mechanism. The water-assisted path 4 is the favorite reaction way. Our results well explained the presumption from experiments.     

On the Possibility of Uphill Intramolecular Electron Transfer in Multicopper Oxidases: Electrochemical and Quantum Chemical Study of Bilirubin Oxidase

The catalytic cycle of multicopper oxidases (MCOs) involves intramolecular electron transfer (IET) from the Cu‐T1 copper ion, which is the primary site of the one‐electron oxidations of the substrate, to the trinuclear copper cluster (TNC), which is the site of the four‐electron reduction of dioxygen to water. In this study we report a detailed characterization of the kinetic and electrochemical properties of bilirubin oxidase (BOx) – a member of the MCO family. The experimental results strongly indicate that under certain conditions, e.g. in alkaline solutions, the IET can be the rate‐limiting step in the BOx catalytic cycle. The data also suggest that one of the catalytically relevant intermediates (most likely characterized by an intermediate oxidation state of the TNC) formed during the catalytic cycle of BOx has a redox potential close to 0.4 V, indicating an uphill IET process from the T1 copper site (0.7 V) to the Cu‐T23. These suggestions are supported by calculations of the IET rate, based on the experimentally observed Gibbs free energy change and theoretical estimates of reorganization energy obtained by combined quantum and molecular mechanical (QM/MM) calculations.     

The Fluorescence Properties of Hypocrellin B and its Amino‐substituted Derivative: Photinduced Intramolecular Proton Transfer and Photoinduced Intramolecular Electron Transfer¶

We report on the emission spectra and emission quantum yields of a newly synthesized hypocrellin dye, Z‐demethoxy‐ 2,3‐ethylenediamino hypocrellin B (EDAHB), and its parent HB in different solvents of varying polarity. Our results demonstrate that EDAHB is one of the few dyes that exhibit highly solvent polarity‐dependent fluorescence in the useful region (680–730 nm). Therefore, it offers some applications in the biomedical field as a fluorescent probe molecule. The solvatochromic effect of EDAHB is proposed to be due to a distinct change in the dipole moment of the dye on excitation. A photoinduced intramolecular proton transfer and a photoinduced intramolecular electron transfer process are considered relevant for the fluorescence properties of HB and EDAHB, respectively.     

Gas chromatography/mass spectrometric analysis of N,N-dialkylaminoethyl-2-chlorides and trimethylsilyl derivatives of N,N-dialkylaminoethan-2-ols for verification of the Chemical Weapons Convention

Gas chromatography/electron ionization mass spectrometry (GC/EI-MS) of N,N-dialkylaminoethyl-2-chlorides (DAAECls) and trimethylsilyl (TMS) derivatives of N,N-dialkylaminoethan-2-ols (DAAEAs) has been carried out. GC/EI-MS data of these compounds are of importance for verification of the Chemical Weapons Convention (CWC). Based on these EI mass spectra, generalized fragmentation routes are proposed that rationalize most of the characteristic ions.     

The Role of Intramolecular Hydrogen Bonds vs. Other Weak Interactions on the Conformation of Hyponitrous Acid and Its Mono- and Dithio-Derivatives

High level ab initio and density functional theory calculations have been carried out to investigate the relative stability of the different conformers of hyponitrous acid and its mono- and dithio-derivatives. Geometries and vibrational frequencies were obtained at the B3LYP/6-311+G(d,p) level and final energies through B3LYP/6-311++G(3df,2pd) single point calculations. The reliability of this theoretical scheme has been assessed by comparing these DFT results with those obtained at the G3 level of theory, for some suitable cases. The cis conformers of hyponitrous acid and its mono- and dithio-derivatives are systematically more stable than the trans ones because in the cis conformation a dative interaction between the nitrogen-lone pairs and the σ_NX^* antibonding orbital is significantly favored. Quite interestingly, in general, the conformers presenting an intramolecular hydrogen bond (IHB) are not the global minima of the corresponding potential energy surfaces and only for hyponitrous acid the conformer with a OH ⋅s O IHB is slightly more stable than the cis conformer without IHB. The low stability of the tautomers with IHB is closely related with another weak intramolecular interaction which involves the lone-pairs of the chalcogen atoms and the π_NN^* antibondig orbital, and which is significantly perturbed when the IHB is formed.     

ChemInform Abstract: Li4Ge2B as a New Derivative of the Mo2B5 and Li5Sn2 Structure Types.

Single crystals of Li₄Ge₂B are obtained by solid state reaction of stoichiometric mixtures of the elements (sealed Ta crucible, 1473 K, 15 min; rapid cooling to 25 °C).     

Simulation of Molecular Weight Distributions Obtained by Pulsed Laser Polymerization (PLP): New Analytical Expressions Including Intramolecular Chain Transfer to the Polymer

A new approach for the simulation of PLP (pulsed laser polymerization) is presented. This approach allows one to obtain new analytical solutions for different polymerization schemes, including either chain transfer to the monomer or intramolecular chain transfer to the polymer. The first results of the simulation of PLP experiments on n‐butyl acrylate at 20 °C and ambient pressure are presented.

MWDs simulated for PLP of n‐butyl acrylate, in bulk at 20 °C and ambient pressure using three models: the model with intramolecular chain transfer to the polymer (solid line), the model with chain transfer to monomer (dashed line), and the classical model (dotted line).     

Porphyrins and Their Derivatives: XXII. A New Product of Intramolecular Cyclization of 5,10,15,20-Tetraphenyl-2-formylporphyrin Copper Complex

The treatment at boiling of 5,10,15,20-tetraphenyl-2-formylporphyrin copper(II) with saturatedsolution of p-chloranil in benzene in the presence of 70% aqueous trifluoroacetic acid affords alongsideverdin (16.7%) its isomer with a keto group located in the -position of the macrocycle in 71% yield.     

Dependence of the Lifetime upon the Excitation Energy and Intramolecular Energy Transfer Rates: The 5D0 EuIII Emission Case

In many Eu^III‐based materials, the presence of an intermediate energy level, such as ligand‐to‐metal charge transfer (LMCT) states or defects, that mediates the energy transfer mechanisms can strongly affect the lifetime of the ⁵D₀ state, mainly at near‐resonance (large transfer rates). We present results for the dependence of the ⁵D₀ lifetime on the excitation wavelength for a wide class of Eu^III‐based compounds: ionic salts, polyoxometalates (POMs), core/shell inorganic nanoparticles (NPs) and nanotubes, coordination polymers, β‐diketonate complexes, organic–inorganic hybrids, macro‐mesocellular foams, functionalized mesoporous silica, and layered double hydroxides (LDHs). This yet unexplained behavior is successfully modelled by a coupled set of rate equations with seven states, in which the wavelength dependence is simulated by varying the intramolecular energy transfer rates. In addition, the simulations of the rate equations for four‐ and three‐level systems show a strong dependence of the emission lifetime upon the excitation wavelength if near‐resonant non‐radiative energy transfer processes are present, indicating that the proposed scheme can be generalized to other trivalent lanthanide ions, as observed for Tb^III/Ce^III. Finally, the proper use of lifetime definition in the presence of energy transfer is emphasized.     

茶叶中653种农药化学品残留GC-MS、GC-MS/MS与LC-MS/MS分析方法：国际AOAC方法评价预研究

选择了16个实验室,按AOAC方法评价指南对盲样进行了检测。对16个实验室的统计分析结果表明:剔除操作偏离方法的2个实验室的全部数据,剩余14个实验室GC-MS/SIM(GC-MS/MS):RSDr<8%的占100%;RSDR<16%的占57.5%,RSDR<25%的占92.5%;HorRat值小于1.0的占80.0%,HorRat值小于2.0的占97.5%。LC-MS/MS:RSDr<8%的占65.0%,RSDr<15%的占97.5%;RSDR<16%的占35.0%,RSDR<25%的占95.0%;HorRat值小于1.0的占92.5%,HorRat值小于2.0的占97.5%。建立的1 220条标准曲线中,有1 132个满足r2≥0.995的要求,占92.8%;检测目标农药离子3 600个,离子丰度符合EU要求的有3 443个,占95.6%。AOAC方法评价结果证明,该方法重现性和再现性良好,完全适用于茶叶中653农药残留的定性和定量分析。     

Adsorption of Co2B2 and Ni2B2 Clusters on the TiO2 (110) Surface: a Density Functional Study

Based on density functional theory and generalized gradient approximation calculations, the adsorption of Co2B2 and Ni2B2 clusters on the rutile TiO2 (110) surface has been investigated utilizing periodic supercell models. Unambiguously, the results demonstrate that the hollow site turns out to be preferable for Co2B2 cluster while Ti2 site is for Ni2B2 cluster to adsorb. Orbital population analysis indicates a strong interaction between Co2B2 and O atom of TiO2 surface, which can be attributed to the overlap of Co 3d and surface O 2p orbital. Similarly, for Ni2B2 , the bonding interaction occurs mostly through the interaction of Ni 3d/4s and O 2p orbitals. Note that, there is also an interaction within the Co2B2 clusters (Ni2B2) through B 2s/2p and Co 3d orbitals (Ni 3d/4s). Moreover, orbital analysis results shows that the strong bonding between Ni2B2 and Ti2 site is due to the overlap of HOMO of Ni2B2 and d-orbital of five-coordinated titanium atoms.     

仲钨酸A与仲钨酸B的化学活性及其转变速度的研究

根据ParaA和ParaB对H₂O₂反应活性的差异,提出己酸化的钨酸钠溶液经加热陈化后溶液中ParaB的测定方法(即H₂O₂-SO₂法)。求出不同Z(H⁺/W)值溶液在80℃时ParaB的形成速度,发现形成速度呈线性变化,且随Z值的增加而变慢。从ParaA和ParaB的结构解释了它们对H₂O₂活性上的差异。     

川芎水蒸气蒸馏和超临界CO2提取物化学成分的GC-MS分析鉴别

用水蒸气蒸馏和超临界CO2提取方法对川芎药材中的化学成分进行提取,用气相色谱-质谱联用技术(GC-MS)对提取物进行分析,分别鉴定出30和34个化合物,测定了其相对含量。 结果表明,水蒸气蒸馏和超临界CO2提取物的主要成分均为(Z)-藁本内酯。 超临界CO2提取方法能提取出较多的川芎药效物质,如丁基酞内酯、丁烯基酞内酯、川芎内酯A、(Z)-藁本内酯、(E)-藁本内酯和川芎内酯I。 而水蒸气蒸馏提取物中除了川芎药效物质外,还含有较多的萜烯类化合物。 结果表明,超临界CO2对川芎药效物质的提取比水蒸气蒸馏法的效率高。 通过对川芎中带不饱和侧链与饱和侧链内酯类化合物质谱裂解规律的解析归纳,鉴别了川芎中不饱和侧链内酯类化合物如(Z)-藁本内酯、(E)-藁本内酯、丁烯基酞内酯和川芎内酯I以及饱和侧链内酯类化合物如丁基酞内酯和川芎内酯A。     

Rate Study for Electron Transfer of Sml2 to the Carbonyl Compounds and the Sulfoxides

The rate constants for the electron transfer of samarium diiodide to 2-heptanal, 2-methyl valeraldehyde and diphenyl sulfoxide were obtained for the first time. The reaction is first order in these substrates and there are hints that the reaction rate has a strong steric dependence. HMPA exhibited a profound catalytic effect but t-BuOH did not. The effect of temperature on reaction rates was also obtained.     

The New Carbodiimide Li2Gd2Sr(CN2)5 Having a Crystal Structure Related to That of Gd2(CN2)3

The new carbodiimide compounds Li₂RE₂Sr(CN₂)₅ (RE = Sm, Gd, Eu, Tb) were prepared by a straight forward solid state metathesis reaction of REF₃, SrF₂, and Li₂(CN₂) at around 600 °C. The crystal structure of Li₂Gd₂Sr(CN₂)₅ was solved based on X‐ray single‐crystal diffraction data. Corresponding Li₂RE₂Sr(CN₂)₅ compounds were analyzed by isotypic indexing of their powder patterns. The crystal structure of Li₂Gd₂Sr(CN₂)₅ can be well related to that of Gd₂(CN₂)₃, because both structures are based on layered structures composed of close packed layers of [N=C=N]^2– sticks, alternating with layers of metal ions. The crystal structure of Li₂Gd₂Sr(CN₂)₅ can be considered to contain an ABC layer sequence of [N = C=N]^2– layers with the interlayer voids being occupied by (three) distinct types of cations.