Conformations and vibrational spectra of methyl-pyrazines

Molecular geometries of 2-methyl as well as 2–3-, 2–5- and 2–6-dimethyl-pyrazine have been optimized in the MINDO/3 approximation. Potential energy barriers concerning internal rotation of the methyl groups have been computed also for each molecule and relevant periodic functions have been adjusted to fit the respective results. Finally, the theoretical spectrum for the hindered rotation in 2-methyl-pyrazine has been calculated too.     

Characterization, via ESR spectroscopy, of radical intermediates in the photooxidation of arylcarbinols by ceric ammonium nitrate

The photooxidation by ceric ammonium nitrate (CAN) of several aryl and naphthylcarbinols has been studied by means of ESR spectroscopy. For all the investigated arylcarbinols, but not for the naphthyl derivatives, it has been possible to detect radical intermediates deriving from the parent alkoxyl radicals. In particular, in the photooxidation of 1,1-diphenylethanol, a bridged-radical intermediate has been detected. The assignment has been validated through experiments with two different labeled compounds: the 1,1-[2', 3', 4', 5', 6', 2", 3", 4", 5", 6"-2H10]diphenylethanol and the 1,1-diphenyl[2, 2, 2-2H3]ethanol. A similar bridged radical has been found to be formed in the photooxidation of triphenylmethanol, while, for the 1,1-diphenylpropanol, the only detectable species has been the ethyl radical deriving from a competitive beta-scission process. Finally, for the 2-phenylpropan-2-ol (cumyl alcohol), two radical species have been identified: the methyl, deriving from the beta-scission process, and the cyanomethylene, deriving from H-abstraction of the cumyloxyl radical from the solvent. A kinetic study on the competition of the two processes has also been conducted and the parameters of the Arrhenius equation for the latter process have been estimated.     

An ab initio study of the lowest electronic states of yttrium dicarbide, YC2

The low-lying electronic states of yttrium dicarbide have been calculated using highly correlated wave functions and systematic sequences of correlation consistent basis sets. For the (2)A(1) ground electronic state, the near-equilibrium potential energy surface (PES) has been calculated using the coupled cluster method in conjunction with basis sets ranging in size from double to quintuple zeta. The relativistic effects have been taken into account by using pseudopotentials for the Y atom. After extrapolation to the complete basis set limit, additional corrections due to core-valence correlation and spin-orbit effects have also been included. The same approach has been followed for the (2)B(1), (2)B(2), and (2)A(2) states but only the C(2V) PESs have been considered in these cases. For the two (2)A(1) electronic excited states and, for comparison purposes, for the ground state, the multireference configuration interaction (MRCI) approach has been used in conjunction with double-zeta and triple-zeta basis sets for the construction of the PES. The molecular and spectroscopic properties predicted for the ground and excited states investigated in this work compare well with the available experimental data, particularly for the ground electronic state. The 0 K dissociation enthalpy of YC(2), DeltaH(Y-C2)(0 K), and its atomization enthalpy, SigmaD(0), are predicted to be 148.4 and 291.5 kcal/mol, respectively.     

量子化学的Gaussian－2理论及其应用与化合物的标准生成焓预测

本文较为全面地综述了Ｇａｕｓｓｉａｎ－１，Ｇａｕｓｓｉａｎ－２（简称Ｇ１，Ｇ２）理论以及简化的Ｇ２（ＭＰ２），Ｇ２（ＭＰ３）理论，将其主要结果进行了比较分析。关于Ｇ２理论的应用，除了较为详细地综述了几年来理论在重现实验数据、评价实验数据、预测实验数据及研究化学反应途径等方面的应用外，还结合我们近期研究结果的主要结论讨论了该理论在研究等电子－等自旋，价层等电－等旋，等旋及非等旋化学反应的能量计算中的应用情况，以及该理论在预测化合物的标准生成焓方面的应用情况。     

Structural biology of the cell adhesion protein CD2: from molecular recognition to protein folding and design

CD2 (cluster of differentiation 2) is a cell adhesion molecule expressed on T cells and is recognized as a target for CD48 (rats) and CD58 (humans). Tremendous progress has been achieved in understanding the function of CD2, the mechanism of molecular recognition and protein folding, thus, leading towards the use of this protein as a scaffold for protein design. CD2 has been shown to set quantitative thresholds in T cell activation both in vivo and in vitro. Further, intracellular CD2 signaling pathways and networks are being discovered by the identification of several cytosolic tail binding proteins. In addition, a new method for directly measuring heterophilic adhesion has been developed. The functional "hot spot" for the adhesion surface of CD2 and CD58 has been dissected. Detailed NMR studies reveal that rat CD2 weakly self-associates to form a homodimeric structure in solution. Dynamic interaction of CD2 with the GYF and SH3 domains has been investigated. CD2 has been shown to form fibrils in the presence of 2,2,2-trifluoroethanol (TFE) and at low pH. Furthermore, kinetic studies have been completed to monitor the effect of surface hydrophobic residues and intramolecular bridges on the folding pathways of CD2. Our lab has de novo designed single calcium-binding sites into domain 1 of rat CD2 (CD2-D1) with strong metal selectivity. In addition, the EF-hand motifs have been grafted into CD2 to understand the site-specific calcium-binding affinity of calmodulin and calcium-dependent cell adhesion.     

Application of molecular absorption properties of horseradish peroxidase for self-indicating enzymatic interactions and analytical methods

In this paper an in depth study is presented of the use of the horseradish peroxidase (HRP) enzyme as a self-indicating biorecognition reagent in UV-vis molecular absorption spectrometry. The HRP/H2O2 reaction mechanism in the absence of an external substrate has been clarified, and the interaction between HRP and glucose oxidase (GOx) has been studied. It has been demonstrated that GOx can act as a substrate of HRP; in both cases the kinetic constants have been obtained and mathematical models have been developed. Second, the HRP/H2O2 reaction is used to follow a H2O2-producing enzymatic reaction, the glucose reaction with GOx being used as a model. As an application of this, two methodologies have been proposed for glucose determination: with or without previous incubation of glucose with GOx. In both cases mathematical models relating HRP absorbance changes to glucose concentration have been developed and tested; both methods have been optimized, analytically characterized, and tested for glucose determination in samples. The methodology described could be applied to other heme-proteins and to other H2O2-producing enzymatic reactions. The models permit the reaction constants to be calculated. From the analytical chemistry point of view the models allow the prediction of the method sensitivity for other analytes involved in this type of reaction if the kinetic constants are known and can be used in the design of optical sensors.     

层状LiMnO_2正极材料的研究进展

层状LiMnO2 化合物的研究是目前锂离子电池正极材料锂锰氧化物研究工作的新热点 ,本文综述了近年来国内外LiMnO2 化合物的研究进展 ,主要阐述了具有层状和扭曲层状结构的m LiMnO2和o LiMnO2 的结构、电性能、合成和改性方法等方面的研究状况 ,重点介绍了离子交换法合成层状LiMnO2 的原因和机理。探索新的合成方法和掺杂其它金属离子改性以提高循环性能是今后LiMnO2 的研究趋势。     

等电子-等自旋与非等旋反应的G2(MP2)和G2研究

我们在前文［1－2］中分别用MP2－4／6－31G**／／MP2／6－31G**及MP4／6－311G（2df，Zpd）／／MP2／6－31G**研究了一些双原子氢化物、卤化物、硫化物和氧化物的化学反应的烂变·这些化学反应按如下类型分为四组，即（1）反应物与生成物之间为等电子一等自旋关系，（2）价层等电一等旅，（3）等施和（4）非等旅·结果表明，MP4／6－3fiG（2才，ZPd）对于（1），（2）和（3）类反应，基本上与实验误差小于士15kJ·mo－‘而对非等旋反应仍有较大误差；MPZ－4／6－31G””只对（1）类反应较好．由于PoPle等人近几年来创立的Gaussi…     

Ultraviolet absorption spectra of chalcone analogs containing a selenophene nucleus

The UV absorption spectra in solutions in hexane and ethanol of chalcone analogs containing, apart from 2-selenienyl, the following heterocyclic radicals-2-furyl, 2-thienyl, 2-pyrryl, 2- and 3-pyridyl, and 2-quinolyl-have been measured and discussed. Considerations on the electronic influence of the heterocycles have been put forward and the Hammett's parameters have been evaluated for some of the radicals.     

CS_2~+离子~2∑_g~+←~2∑_u~+跃迁的Franck-Condon因子计算以及与光解离谱的比较

将线性三原子分子离子CS2 的对称伸缩振动简化为SC和S之间的简谐振动,用谐振子的势能曲线和波函数对CS2 分子离子2∑g 和2∑u 电子态(对称伸缩)振动能级间跃迁的Franck-Condon因子进行了计算,得到的结果与2∑g ←2∑u 跃迁的光解离谱实验强度进行了比较,对前人给出的分子数据(转动常数、分子平衡核间距)进行了验证和分析,讨论了经由2∑g ←2∑u 电子态振动能级间跃迁的光解离机理.     

The nature of the surface species formed on Au/TiO2 during the reaction of H2 and O2: an inelastic neutron scattering study

Inelastic neutron spectroscopy (INS) has been employed to identify surface species formed during the H2-O2 reaction on Au/TiO2 catalysts. Determination of the surface intermediates formed in this reaction is crucial to develop a mechanistic understanding for the direct vapor-phase propylene epoxidation reaction and synthesis of H2O2. Although the presence of intermediate hydroperoxo species (during these reactions) has been suggested in literature, it has never been demonstrated. Our studies provide direct evidence for the formation of surface hydroperoxo species during the H2-O2 reaction.     

Bis(mu-oxo)dimetal "diamond" cores in copper and iron complexes relevant to biocatalysis

Although quite a familiar feature in high-valent manganese chemistry, the M(2)(mu-O)(2) diamond core motif has only recently been found in synthetic complexes for M=Cu or Fe. Structural and spectroscopic characterization of these more reactive Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) compounds has been possible through use of appropriately designed supporting ligands, low-temperature handling methods, and techniques such as electrospray ionization mass spectrometry and X-ray crystallography with area detector instrumentation for rapid data collection. Despite differences in electronic structures that have been revealed through experimental and theoretical studies, Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) cores exhibit analogously covalent metal-oxo bonding, remarkably congruent Raman and extended X-ray absorption fine structure (EXAFS) signatures, and similar tendencies to abstract hydrogen atoms from substrates. Core isomerization is another common reaction attribute, although different pathways are traversed; for Fe, bridge-to-terminal oxo migration has been discovered, while for Cu, reversible formation of an O-O bond to yield a peroxo isomer has been identified. Our understanding of biocatalysis has been enhanced significantly through the isolation and comprehensive characterization of the Cu(2)(mu-O)(2) and Fe(2)(mu-O)(2) complexes. In particular, it has led to the development of new mechanistic notions about how non-heme multimetal enzymes, such as methane monooxygenases, fatty acid desaturase, and tyrosinase, may function in the activation of dioxygen to catalyze a diverse array of organic transformations.     

Band Structures and Two-photon Absorption of ZnGeP2 and AgGaS2 Crystals

Band structure and bonding properties have been investigated in terms of periodic density functional theory(DFT) method,and two-photon absorption(TPA) spectra have been simulated by two-band model for ZnGeP2 and AgGaS2 crystals.It has been predicted that the AgGaS2 crystal has a wider window of nonlinear transmission,and the laser pumping energy larger than 1.02 and 1.35 eV will lead to deleterious TPA of higher nonlinear effect for ZnGeP2 and AgGaS2 crystals,respectively.Electron origin of TPA for them is also discussed.     

离子对生成反应截面的量子散射理论研究

将Miller的S-矩阵变分法推广到离子对生成反应动力学的研究。M＋X~2→M^+＋X~2^-反应体系包括共价态(M＋X~2)和离子态(M^+＋X~2^-)两个势能面及其交叉效应,本文在此两态模型下导出了生成截面公式。在矩阵元计算中,平动波函数采用分布Gauss基作展开。作为上述公式的应用,对Cs＋O~2→Cs^+＋O~2^-反应体系作了数值计算并取得了满意结果。     

Statistical modelling of NH+/ND+ + H2/HD/D2 branching ratios

In this work we study hydrogen isotope fractionation along the proposed gas-phase ammonia formation pathway at temperatures relevant to interstellar modelling. Specifically we study the isotopically substituted variants of the NH(+) + H(2) reaction, for which the primary product is NH(2)(+) + H. Adiabatic capture theory calculations have been performed for the association reaction. A new potential-energy surface has been determined for the NH(2)(+) product. An extensive set of rovibrational energy levels has been calculated for the NH(2)(+) isotopologues described by this potential-energy surface. These rovibrational energy levels have been used to determine energy- and angular-momentum-resolved numbers of accessible product states from the NH(3)(+) isotopologue intermediates, which in turn have been averaged to give statistical branching fractions for all isotopically-substituted NH(+) + H(2) reactions. It is determined that in all cases where both hydrogen and deuterium are present, the NHD(+) product is preferred.     

Matrix isolation infrared observation of HxSi(N2)y (x = 0, 1, 2 and y = 1, 2) transient species using a 121-nm vacuum ultraviolet photolysis source

Vacuum ultraviolet photolysis (121.6 nm) of silane in a nitrogen matrix at 12 K leads to the observation of several transient species, which have been characterized using Fourier transform infrared spectroscopy. Four transient species containing silicon and nitrogen have been observed (SiN2, Si(N2)2, HSiN2, and H2SiN2), and one transient species containing only silicon and hydrogen has been observed. The assignment of the infrared bands due to each of these species is accomplished by performing isotopic substitution experiments (SiD4, 15N2, and mixtures with SiH4 and 14N2), matrix annealing experiments, UV-visible photolysis experiments, by comparison with previous experimental matrix isolation frequencies, where available, and for HSiN2 and H2SiN2 by comparison to B3LYP/aug-cc-pVTZ-calculated vibrational frequencies. The observation and infrared assignment of the HSiN2 and H2SiN2 molecules in these experiments is significant in that HSiN2 has not been previously reported in the matrix isolation literature, and H2SiN2 has only been reported once previously by a different route of formation. The energetics of the overall formation pathways for the molecules observed in these experiments is discussed using B3LYP/aug-cc-pVTZ calculations.     

微波衍生-离子对高效液相-磺化四苯基卟啉光度法同时测定痕量镍、铜、锰和锌

 用磺化四苯基卟啉 (TPPS4 )作柱前衍生试剂 ,在微波作用下进行衍生反应 ,研究了衍生和分离Ni2 + ,Mn2 + ,Zn2 + 和Cu2 + 的最佳条件。在 75 0W的微波作用下衍生反应 3min ,在C18柱上采用乙腈 水 (体积比为 2 2 5∶77 5 )体系作流动相 ,四乙基溴化铵 (TEABr)作离子对试剂 ,在 415nm处检测 ,建立了微波衍生 离子对高效液相快速分离、光度检测Ni2 + ,Mn2 + ,Zn2 + 和Cu2 + 的新方法。络合物和反应试剂在 15min内出峰完毕。Zn2 + ,Cu2 + ,Ni2 + 和Mn2 + 的检测限分别为 0 0 5 μg/L ,0 0 1μg/L ,0 10 μg/L和 0 40 μg/L。     

Photomagnetic properties in a series of spin crossover compounds

The spin crossover (SC) compounds [Fe(PM-AzA)2(NCX)2] and [Fe(PM-FIA)2(NCX)2] (with PM-AzA = N-2'-pyridylmethylene-4-(phe-nylazo)aniline, PM-FIA = N-2'-pyridylmethylene-4-(2-amino)fluorene, and X = S, Se) have been prepared. The SC regimes have been deduced from variable-temperature magnetic susceptibility data. The enthalpy and entropy changes associated with the SC have been evaluated from DSC measurements. A cooperativity factor, C, has been defined, and its values for the different compounds have been deduced from the spin crossover curves. At 10 K, the light-induced excited spin state trapping (LIESST) effect has been observed within the cavity of the SQUID magnetometer. The critical temperatures Tc(LIESST) have been determined for [Fe(PM-AzA)2(NCS)2] and [Fe(PM-F1A)2(NCX)2], and the role of cooperativity has been analyzed. A linear correlation has been found between the Tc(LIESST) and C values. The kinetics of HS-->LS relaxation have been investigated; a thermally activated mechanism at elevated temperatures and a nearly temperature independent relaxation behavior at low temperatures have been found. Finally, the magnetic behavior recorded under light irradiation in the warming and cooling modes has revealed the occurrence of the light-induced thermal hysteresis (LITH) effect.     

Determination of cadmium and copper with ET-AAS after electrochemical deposition on a graphite electrode

The electrodeposition of cadmium and copper on a special graphite disk electrode has been performed at controlled potential. The electrode with the deposit has been inserted into the graphite atomizer HGA-400 by an adapted automatic sampler for the final determination by ET-ASS. The sensitivity of determination has been 0.371 (microg l(-1))(-1) for cadmium and 0.025 (microg l(-1))(-1) for copper for 2 min electrodeposition and increased linearly with the time of deposition. The limit of detection (3s(bl)) has been 7.9 ng l(-1) Cd(2+) and 0.11 microg l(-1) Cu(2+) for 2 min deposition and it has been improved with increased time of electrodeposition. The technique has been applied to the determination of both metals in seawater and to speciation in the presence of EDTA complexing agent.     

Synthesis, characterization and antiproliferative activity of transition metal complexes with 3-(4,5-diphenyl-1,3-oxazol-2-yl)propanoic acid (oxaprozin)

A series of novel Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with oxaprozin (Hoxa), a non-steroidal anti-inflammatory drug, has been synthesized. The drug and complexes have been characterized by elemental and thermogravimetric (TG) analysis, Fourier transform (FT)-IR, 1H-NMR, 13C-NMR, UV-Vis spectroscopy and magnetic susceptibility measurements. The (pseudo)octahedral geometry has been proposed for all complexes based on electronic spectra and magnetic moments. With exception of the Cu(II) complex, where bridging bidentate mode of COO groups has been found, FT-IR spectra confirmed chelately coordinated COO groups in the other complexes. The general formula of the complexes is [M(H2O)2(oxa)2 ·χH2O, with χ=2 for M=Mn, Co and Ni and χ=1.5 for Zn. The binuclear Cu(II) complex, [Cu2(H2O)2(OH)(oxa)3]·2H2O, has strong Cu-Cu interactions of antiferromagnetic type. The complexes and Hoxa did not exhibit the cytotoxic effect to peritoneal macrophages. For the first time these complexes have been tested for their in vitro antiproliferative activity against human colon and breast cancer cell lines, HCT-116 and MDA-231, respectively. For all investigated compounds significant antiproliferative effects have been observed. Ni(II) complex has been shown to be a promising antiproliferative agent exerting excellent activity against HCT-116 even in nanomolar concentrations.