Isoscalar factors for tetragonal,orthorhombic, monoclinic and triclinic shubnikov point groups

The relations between isoscalar factors for corepresentations of antiunitary magnetic point groups are discussed in the case of associated corepresentations. The tables of the isoscalar factors for the single- and double-valued corepresentations of all tetragonal, orthorhombic, monoclinic, and triclinic Shubnikov point groups are given. Some peculiarities of the calculation method of the isoscalar factors for corepresentations are considered.     

Photodissociation dynamics of 1,2-butadiene at 157 nm

Photodissociation dynamics of 1,2-butadiene at 157 nm has been investigated using a molecular beam apparatus based on photoionization using vacuum ultraviolet synchrotron radiation. Six dissociation pathways have been observed. The observed channels are C4H5+H, C4H4+H2, C3H3+CH3, C2H3+C2H3, C2H4+C2H2, and C4H4+H+H. Among all the dissociation channels, the C3H3+CH3 channel is found to be the dominant process. The product kinetic energy distributions of all dissociation channels have been determined from simulating the experimental time-of-flight spectra. Relative branching ratios for all observed dissociation channels were also estimated based on all detected products.     

MX3(-) superhalogens (M = Be, Mg, Ca; X = Cl, Br): a photoelectron spectroscopic and ab initio theoretical study

Gas-phase alkaline earth halide anions, MgX3(-) and CaX3(-) (X = Cl, Br), were produced using electrospray and investigated using photoelectron spectroscopy at 157 nm. Extremely high electron binding energies were observed for all species and their first vertical detachment energies were measured as 6.60 +/- 0.04 eV for MgCl3(-), 6.00 +/- 0.04 eV for MgBr3(-), 6.62 +/- 0.04 eV for CaCl3(-), and 6.10 +/- 0.04 eV for CaBr3(-). The high electron binding energies indicate these are very stable anions and they belong to a class of anions, called superhalogens. Theoretical calculations at several levels of theory were carried out on these species, as well as the analogous BeX3(-). Vertical detachment energy spectra were predicted to compare with the experimental observations, and good agreement was obtained for all species. The first adiabatic detachment energies were found to be substantially lower (by about 1 eV) than the corresponding vertical detachment energies for all the MX3(-) species, indicating extremely large geometry changes between MX3(-) and MX3. We found that all the MX3(-) anions possess D3h ((1)A1') structures and are extremely stable against dissociation into MX2 and X-. The corresponding neutral species MX3, however, were found to be only weakly bound with respect to dissociation toward MX2 + X. The global minimum structures of all the MX3 neutrals were found to be C2v ((2)B2), which can be described as (X2(-))(MX+) charge-transfer complexes, whereas the MX2...X (C2v, (2)B1) van der Waals complexes were shown to be low-lying isomers.     

Theoretical Studies on Substituent Effect of the Reaction of Amide and Formaldehyde

The thermodynamic properties of the reaction of amide and formaldehyde were calculated via B3LYP method when substituents chosen included CH3,CH2CH3,CH2CH2CH3,CH2CH2CH2CH3,CH(CH3)2,CH2CH(CH3)2,CH(CH3)CH2CH3 and C(CH3)3.Based on the optimization of the structures for reactants and products,the thermodynamic functions of all the species for an actual state were obtained.The thermodynamic data and the equilibrium constants were investigated within a temperature range of 300―343.15 K.The calculated results show that the reaction is exothermic and spontaneous.The trends of all thermodynamic properties are consistent with the temperature.The preferential order of the substituent effect is CH2CH(CH3)2CH(CH3)CH2CH3CH2CH2CH2CH3 CH2CH2CH3CH2CH3≈CH(CH3)2C(CH3)3≈CH3.     

Structure and bonding in silver halides. A quantum chemical study of the monomers: Ag(2)X, AgX, AgX(2), and AgX(3) (X = F, Cl, Br, I)

The molecular structure of all silver halide monomers, Ag(2)X, AgX, AgX(2), and AgX(3), (X = F, Cl, Br, I), have been calculated at the B3LYP, MP2, and CCSD(T) levels of theory by using quasirelativistic pseudopotentials for all atoms except fluorine and chlorine. All silver monohalides are stable molecules, while the relative stabilities of the subhalides, dihalides, and trihalides considerably decrease toward the larger halogens. The ground-state structure of all Ag(2)X silver subhalides has C(2)(v)() symmetry, and the molecules can be best described as [Ag(2)](+)X(-). Silver dihalides are linear molecules; AgF(2) has a (2)Sigma(g) ground state, while all of the other silver dihalides have a ground state of (2)Pi(g) symmetry. The potential energy surface (PES) of all silver trihalides has been investigated. Neither of these molecules has a D(3)(h)() symmetric trigonal planar geometry, due to their Jahn-Teller distortion. The minimum energy structure of AgF(3) is a T-shaped structure with C(2)(v)() symmetry. For AgCl(3), AgBr(3), and AgI(3), the global minimum is an L-shaped structure, which lies outside the Jahn-Teller PES. This structure can be considered as a donor-acceptor system, with X(2) acting as donor and AgX as acceptor. Thus, except for AgF(3), in the other three silver trihalides, silver is not present in the formal oxidation state 3.     

Averaging the closest two out of three observations

The average of 3 observations is the standard method of estimating the location of their distribution. The average of the closest 2 out of 3 observations, although often used, has more variability than the average of all 3 observations for a standard normal distribution. One statistic uses a threshold to decide when to use the average of all 3 observations rather than the closest 2. With the standard normal, this statistic still has more variability than the average of all 3 observations.     

The nature of the surface site for isocyanate produced in the reaction of ammonia and carbon monoxide over supported catalysts

The reaction of CO and NH₃ was performed over M/X (M=Rh, Ru, Pd; X=Al₂O₃, SiO₂, TiO₂) films. Infrared spectroscopy was used to monitor the formation of surface intermediates. Isocyanate (NCO) was detected for all of the metals when the support was Al₂O₃ or SiO₂, but not for TiO₂. The NCO resided on the Al₂O₃ support for all M/Al₂O₃ catalysts, but on the metal when the support was SiO₂. It was concluded that the formation and location of the NCO was dependent upon the extent of NH₄⁺ formation on the various supports.     

Kinetic isotope effects implicate two electrophilic oxidants in cytochrome p450-catalyzed hydroxylations

Intramolecular kinetic isotope effects (KIEs) were determined for cytochrome P450-catalyzed hydroxylation reactions of methyl-dideuterated trans-2-phenylcyclopropylmethane-d2 (1-d2), which gives two products from oxidation of the methyl group, trans-2-phenylcyclopropylmethanol (2) and 1-phenyl-3-buten-1ol (3). In oxidations of each enantiomer of 1-d2 with three P450 enzymes (CYP2B1, CYPDelta2E1, and CYPDelta2E1 T303A), the apparent intramolecular KIEs were different for products 2 and 3 in all cases and different for each enzyme-substrate combination. In oxidations of each enantiomer of undeuterated 1-d0 and trideuteriomethyl 1-d3 by CYP2B1 and CYPDelta2E1, the ratio of products 2/3 decreased for 1-d3 in comparison to 1-d0 in all cases. The results require multiple pathways for P450-catalyzed hydroxylation and are consistent with the "two-oxidants" model, where hydroxylation is effected by both the hydroperoxy-iron species and the iron-oxo species. The results are not consistent with predictions of the "two-states" model for P450-catalyzed hydroxylations, where oxidations occur from a low-spin state and a high-spin state of iron-oxo.     

Cobalt(II) complexes of biologically active glutathione: spectroscopic and molecular modeling studies

Cobalt(II) complexes of reduced glutathione (GSH) of general composition Na[Co(L)(X)].nH2O (where H2L = GSH; X = Cl-, NO3-, NCS-, CH3CO2-, HCO2-, ClO4- and n = 0-4) have been synthesized and characterised by elemental analyses, vibrational spectra, electronic spectra, magnetic susceptibility measurements, thermal studies and molecular modeling studies. Electronic spectra indicate planar geometry for all the complexes. Infrared spectra indicate the presence of H2O molecules (except perchlorate complex) in the complexes that has been supported by TG/DTA. The room temperature magnetic moment values for all complexes lie in the range of 2.60-2.80 BM range indicating departure from spin only values due to second order Zeeman effect. Thermal decomposition of all the complexes proceeds via first order kinetics. The Na[Co(L)(Cl)].2H2O complex has the minimum activation energy and Na[Co(L)(CH3CO2)].3H2O has the maximum activation energy. The molecular modeling calculation for energy minimization optimizes geometry of the metal complexes.     

Synthesis, characterization, and catalytic properties of new half-sandwich zirconium(IV) complexes

A number of new half-sandwich zirconium(IV) complexes bearing N,N-dimethylaniline-amido ligands with the general formula Cp*ZrCl(2)[ortho-(RNCH(2))(Me(2)N)C(6)H(4)] [R = 2,6-Me(2)C(6)H(3) (1), 2,6-(i)Pr(2)C(6)H(3) (2), (i)Pr (3), (t)Bu (4)] were synthesized by the reaction of Cp*ZrCl(3) with the corresponding ortho-(Me(2)N)C(6)H(4)CH(2)NRLi. All new zirconium complexes were characterized by (1)H and (13)C NMR, elemental analyses and single crystal X-ray diffraction analysis. The molecular structural analysis reveals that the NMe(2) group does not coordinate to the zirconium atom in all cases. Complexes 1-4 all have a pseudo-tetrahedral coordination environment in their solid state structures and adopt a three-legged piano stool geometry for the zirconium atoms with the amide N atom and the two Cl atoms being the three legs and the Cp* ring being the seat. Variable-temperature (1)H NMR experiments for all complexes 1-4 were performed to investigate the possible intramolecular interaction between the N atom in the NMe(2) group and the central zirconium atom in solution. Upon activation with Al(i)Bu(3) and Ph(3)CB(C(6)F(5))(4), complexes 1-4 all exhibit moderate to good catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing linear polyethylene or poly(ethylene-co-1-hexene) with moderate molecular weight and reasonable 1-hexene incorporation.     

Stereodivergent syntheses of anisomycin derivatives from D-tyrosine

[structures: see text] Enantiomerically pure 2-alkyl-3-acetoxy-4-iodopyrrolidines with all groups cis, and all adjacent groups trans (10 and 17), important precursors for the synthesis of pyrrolidinediols, have been prepared from D-tyrosine through regio- and diastereoselective reduction of a vinyl ketone and subsequent iodoamidation controlled by minimization of nonbonding steric interactions. Highly stereodivergent Woodward-Prevost methodology, applied to both iodopyrrolidines, yielded enantiomerically pure (2R,3R,4R)-, (2R,3R,4S)-, and (2R,3S,4R)-deacetylanisomycin (3, 4, and 5), each in excellent de. Incorporation of differential protection of the hydroxyl groups led to a one-pot synthesis of (2R,3R,4R)-anisomycin 2.     

Reactive uptake of NO3, N2O5, NO2, HNO3, and O3 on three types of polycyclic aromatic hydrocarbon surfaces

We investigated the reactive uptake of NO3, N2O5, NO2, HNO3, and O3 on three types of solid polycyclic aromatic hydrocarbons (PAHs) using a coated wall flow tube reactor coupled to a chemical ionization mass spectrometer. The PAH surfaces studied were the 4-ring systems pyrene, benz[a]anthracene, and fluoranthene. Reaction of NO3 radicals with all three PAHs was observed to be very fast with the reactive uptake coefficient, gamma, ranging from 0.059 (+0.11/-0.049) for benz[a]anthracene at 273 K to 0.79 (+0.21/-0.67) for pyrene at room temperature. In contrast to the NO3 reactions, reactions of the different PAHs with the other gas-phase species (N2O5, NO2, HNO3, and O3) were at or below the detection limit (gamma 相似文献   

Probing the effect of local structure on the thermodynamic redox properties of V(+5): a comparison of V2O5 and Mg3(VO4)2

Coulometric titration, an electrochemical method for measuring oxidation isotherms, has been used to characterize the redox properties of V2O5 and Mg3(VO4)2 between 823 and 973 K. V2O5 shows distinct regions in the isotherms corresponding to equilibrium with mixtures of V2O3 and V2O4 and of V2O4 and V2O5. From this data, the enthalpies for oxidation of V2O3 to V2O4 and for V2O4 to V2O5 are shown to be -380 +/- 10 and -285 +/- 20 kJ mol-1 O2, respectively. Oxidation isotherms for Mg3(VO4)2 exhibit a single step between the oxidized sample (all V+5) and a completely reduced sample (all V+3). The enthalpy of oxidation is found to increase with the oxidation state of the sample, from -370 +/- 30 kJ mol-1 O2 at an O:V ratio of 1.5 to -460 +/- 10 kJ mol-1 O2 at an O:V ratio of 2.5.     

Synthesis of Aminoalkyl-substituted Polymethoxychalcone Derivatives and Their Antiproliferative Activities Against Three Human Cancer Cell Lines

Two novel series of sixteen aminoalkyl-substituted polymethoxychalcone derivatives 2a-2h and 3a-3h were synthesized from 2'-hydroxy-3,4,5,4',6'-pentamethoxy chalcone(1) through extending alkoxy side chain at the 2'-position, and introducing amine hydrogen bond receptor at the end of the side chain. The structures of all the synthesized compounds were confirmed by ¹H NMR, ¹³C NMR and MS techniques. Furthermore, all the compounds were tested for antiproliferative activities in vitro against a panel of three human cell lines(HeLa, HCC1954 and SK-OV-3) via CCK-8 assay. The results show that all the target compounds exhibit antiproliferative activities against the three human cancer cells with IC₅₀ values of 4.62-48.21 μmol/L, except compound 2h against SK-OV-3 cells. Most of these compounds were more active when compared to the positive control cis-Platin.     

键长和电子效应共同调控的β-二酮Dy(Ⅲ)配合物的合成、结构与磁性

以N-乙基-3-吲哚三氟甲基β-二酮(EIFD)为主配体,分别以乙二醇单甲醚(EM)、乙二醇二甲醚(EDM)、二缩三乙二醇(TEG)为辅助配体,与DyCl3·6H2O反应合成了一系列Dy(Ⅲ)配合物[Dy(EIFD)3(EM)]·CH2Cl2(1)、[Dy(EIFD)3(EDM)]·CH2Cl2(2)和[Dy(EIFD)3(TEG)](3)。X射线单晶衍射分析表明,3个配合物都是八配位的单核结构,配位构型分别为双帽三棱柱、正十二面体和双帽三棱柱,分别具有C2v、D2d和C2v对称性。磁学性质显示了配合物1~3具有慢弛豫现象,能垒分别为95.1 K (1)、40.5 K (2)、53.8和13.4 K (3),且配合物1和3有明显的蝴蝶状磁滞回线。进一步讨论了配合物中Dy-O键长和含氧辅助配体的电子效应对配合物有效翻转能垒的影响。     

Solvation of copper ions by acetone. structures and sequential binding energies of Cu+(acetone)x,x = 1-4 from collision-induced dissociation and theoretical studies

Collision-induced dissociation of Cu+(acetone)(x), x = 1-4, with Xe is studied as a function of kinetic energy using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed is endothermic loss of one acetone molecule. The primary cross section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-neutral collisions, internal energy of the complexes, and dissociation lifetimes. Density functional calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes and provide molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical bond dissociation energies are determined from single point calculations at the B3LYP/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) levels, using the B3LYP/6-31G* optimized geometries. The experimental bond energies determined here are in good agreement with previous experimental measurements made in a high-pressure mass spectrometer for the sum of the first and second bond energy (i.e., Cu+(acetone)2 --> Cu+ + 2 acetone) when these results are properly anchored. The agreement between theory and experiment is reasonable in all cases, but varies both with the size of the cluster and the level of theory employed. B3LYP does an excellent job for the x = 1 and 3 clusters, but is systematically low for the x = 2 and 4 clusters such that the overall trends in sequential binding energies are not parallel. In contrast, all MP2 values are somewhat low, but the overall trends parallel the measured values for all clusters. The trends in the measured Cu+(acetone), binding energies are explained in terms of 4s-3d sigma hybridization effects and ligand-ligand repulsion in the clusters.     

Quinolactacins revisited: from lactams to imide and beyond

Chemical analysis of a solid phase fermentation of an Australian Penicillium citrinum strain has returned all known examples of a rare class of N-methyl quinolone lactams, quinolactacins A2 (1), B2 (2), C2 (3) and A1 (4), together with the new quinolactacins B1 (5), C1 (6), D1 (7) and D2 (8), and the novel derivatives quinolonimide (9) and quinolonic acid (10). Complete stereostructures were assigned to all these compounds by detailed spectroscopic analysis and chemical interconversion. Carefully controlled and monitored decomposition studies have confirmed that quinolactacins readily undergo C-3 epimerization and oxidation, and under appropriate conditions convert to quinolonimide and quinolonic acid. Mechanisms for key transformations are proposed. The decomposition studies suggested that only quinolactacins A2 (1) and B2 (2) are genuine natural products, with all other isolated compounds being decomposition artefacts. Quinolactacins C1 (6), C2 (3), and the racemic mixture of quinolactacins D1/D2 (8/7) all displayed notable cytotoxic activity.     

Ab initio study of the interaction of CHX3 (X = H, F, Cl, or Br) with benzene and hexafluorobenzene

In this paper, the results of a study of the interaction of methane, fluoroform, chloroform, and bromoform with benzene and hexafluorobenzene are presented. The benzene complexes were studied at the MP2/6-31G(d) and MP2/6-311++G(2d,p) levels, and the hexafluorobenzene complexes were only studied at the MP2/6-31G(d) level. The optimized geometries, stabilization energies, potential energy surfaces, harmonic frequencies, and vibrational intensities are reported. A net attraction is predicted for all four benzene complexes, whereas for the CHX3.C6F6 complexes, it was found that MP2/6-31G(d) predicts a net attraction for the CH4, CHCl3, and CHBr3 complexes and does not predict a stable complex for CHF3.C6F6. The three complexes with net attractions all have blue-shifts of the CHX3 CH stretching wavenumber and a slight contraction (0.001-0.003 A) of the CH bond in CHX3. The MP2/6-31G(d) level predicts that the intensity of the CHX3 CH stretch will vary widely. For CH4.C6H6 and CHF3.C6H6, it is predicted that the intensity will be smaller for the complexes than the free molecules, whereas for the other complexes, anywhere from a 30% increase to an increase of 87 times is predicted. The atoms in molecules analysis showed that only three of the eight criteria for normal hydrogen bonding are satisfied for all eight complexes studied. Criterion 3 (value of the Laplacian at the bond critical point) is not satisfied for any of the eight complexes.     

Crystal Structures and Characterizations of Bis(1-benzoyl-methyl-benzotriazole-N~3)dichoro Metal(II) Complex:[MCl_2-(C_6H_4N_3CH_2COPh)_2][M=Zn(II),Co(II)]

Introduction Recently, the compounds containing 1H-1,2,4-tria-zole group have attracted much interest because of their exhibiting some fungicidal activity and plant growth regulating activity,1 and showing antibacterial activity against Puccinia recondite and roots growth regulation for cucumber.2 Triazole nuclei appear frequently in the structures of various natural products and biologically active compounds, notably thiamine (vitamin B), peni-cillins, antibiotics such as micrococcin,3 and m…     

Coulomb potentials in two and three dimensions under periodic boundary conditions

A method to sum over logarithmic potential in two-dimensions (2D) and Coulomb potential in three dimensions (3D) with periodic boundary conditions in all directions is given. We consider the most general form of unit cells, the rhombic cell in 2D and the triclinic cell in 3D. For the 3D case, this paper presents a generalization of Sperb's work [R. Sperb, Mol. Simulation 22, 199 (1999)]. The expressions derived in this work converge extremely fast in all region of the simulation cell. We also obtain results for slab geometry. Furthermore, self-energies for both 2D as well as 3D cases are derived. Our general formulas can be employed to obtain Madelung constants for periodic structures.