2014 Vol. 27, No. 2

Content
Article
The wavelength dependence of photoelectron angular distributions (PADs) of two-photon de-tachment of Cu- has been directly studied by using the photoelectron map imaging. Results show that for the laser field intensity of 6.0×1010 W/cm2, PADs exhibit dramatic change with the external field wavelength. Comparison between the experimental observation and the lowest-order perturbation theory prediction indicates that the pattern of PADs can be explained by the interference of the s and d partial waves in the final state. Relative contri-butions of s and d partial waves in the two-photon detachment at different laser wavelengths are obtained.
The structure, electrostatic properties, and Raman spectra of aflatoxin B1 (AFB1) and AFB1-Ag complex are studied by density functional theory with B3LYP/6-311G(d,p)/Lanl2dz basis set. The results show that the surface-enhanced Raman scattering (SERS) and pre-resonance Raman spectra of AFB1-Ag complex strongly depend on the adsorption site and the excitation wavelength of the incident light. The SERS factors are found to enhance 102-103 order compared to normal Raman spectrum of AFB1 molecule due to the larger static polarizabilities of the AFB1-Ag complex, which directly results in the stronger chemical enhancement in SERS spectra. The pre-resonance Raman spectra of AFB1-Ag complex are explored at 266, 482, 785, and 1064 nm incident light wavelength, in which the enhancement factors are about 102-104, mainly caused by the charge-transfer ex-citation resonance. The vibrational modes are analyzed to explain the relationship between the vibrational direction and the enhanced Raman intensities.
The Doppler-limited absorption spectrum of 16O2+-1 by optical heterodyne velocity modulation absorption spectroscopy (OH-VMS). The transitions were assigned to the (2, 19), (3, 20), and (5, 21) bands in the second negative system (A2u-X2g). All the available lines measured using OH-VMS were global fitted in a nonlinear least-squares fitting procedure, and precise molecular con-stants (Bv, Av, Dv, pv, qv, γv) were obtained for the involved levels.
Quantum mechanics and molecular dynamics are used to simulate guanidinium ionic liquids. Results show that the stronger interaction exists between guanidine cation and chlorine anion with interaction energy about 109.216 kcal/mol. There are two types of spatial distribution for the title system: middle and top. Middle mode is a more stable conformation according to energy and geometric distribution. It is also verified by radial distribution function. The continuous increase of carbon dioxide (CO2) does not affect the structure of ionic liquids, but CO2 molecules are always captured by the cavity of ionic liquids.
The photophysics of 3-dimethylamino-2-methyl-propenal (DMAMP) after excitation to the S2(ππ*) electronic state was studied using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The transition barriers of the ground state tautomerization reactions between DMAMP and its three isomers were determined at B3LYP/6-311++G(d,p) level of theory. The vibrational spectra were assigned. The A-band resonance Raman spectra were obtained in acetonitrile with excitation wavelengths in resonance with the first intense absorption band to probe the structural dynamics of DMAMP. The B3LYP-TD computation was carried out to determine the relative A-band resonance Raman intensities of the fundamental modes, and the result indicated that the vibronic-coupling existed in Franck-Condon region. Complete active space self-consistent field (CASSCF) calculations were carried out to determine the excitation energies of the lower-lying singlet and triplet excited states, the conical intersection points and the inter-system crossing points. The A-band short-time structural dynamics and the corresponding decay dynamics of DMAMP were obtained by analysis of the resonance Raman intensity pattern and CASSCF computations. It was found that a sudden de-conjugation between C1=O6 and C2=C3 occurred at the Franck-Condon region of the S2(ππ*) state, while the enhancement of the conjugation interaction between C3 and N(CH3)2, and between C1 and C2 evolutions shortly after the wavepacket leaves away the Franck-Condon region via the excited state charge redistribution. The de-conjugation interaction between C1=O6 and C2=C3 made the rotation of C3=N(CH3)2 group around the C2-C3 bond much easier, while the enhanced conjugation between C1 and C2, and between C3 and N(CH3)2 made the rotation around the C1-C2 bond and C3-N5 more difficult. It was revealed that the initial structural dynamics of DMAMP was predominantly towards the CI-1(S2/S0) point, while the opportunities towards either CI-2(S2/S0) or CI-3(S2/S0) point were negligible. Two decay channels of DMAMP from S2,FC(ππ*) to S0 or T1,min via various CIs and ISCs were proposed.
Theoretical studies on the electronic and geometric structures, the trend in DNA-binding affinities as well as the the structure-activity relationship (SAR) of a series of water-soluble Ru(II) methylimidazole complexes, i.e. [Ru(MeIm)4iip]2+ (1) (MeIm=1-methylimidazole, iip=2-(1H-imidazo-4-group)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(MeIm)4tip]2+ (2) (tip=2-(thiophene-2-group)-1H-imidazo[4,5-f][1,10]phenanthroline), and [Ru(MeIm)42ntz]2+ (3) (2ntz=2-(2-nitro-1,3-thiazole-5-group)-1H-imidazo[4,5-f][1,10]phenanthroline), were car-ried out using the density functional theory (DFT). The electronic structures of these Ru(II) complexes were analyzed on the basis of their geometric structures optimized in aqueous solution, and the trend in the DNA-binding constants (Kb) was reasonably explained. The results show that the replacement of imidazole ligand by thiophene ligand can effectively improve the DNA-binding affinity of the complex. Meanwhile, it was found that introduc-ing the stronger electronegative N atom and NO2 group on terminal loop of intercalative ligand can obviously reduce the complex's LUMO and HOMO-LUMO gap energies. Based on these findings, the designed complex [Ru(MeIm)42ntz]2+ (3) can be expected to have the greatest Kb value in complexes 1-3. In addition, the structure-activity relationships and antitumor mechanism were also carefully discussed, and the antimetastatic activity of the designed complex 3 was predicted. Finally, the electronic absorption spectra of this series of complexes in aqueous solution were calculated, simulated and assigned using DFT/TDDFT methods as well as conductor-like polarizable continuum model (CPCM), and were in good agreement with the experimental results.
The potential energy surfaces (PES) of unimolecular dissociation reactions for di-ethyl beryl-lium and di-t-butyl beryllium are investigated by B3LYP, CCSD(T), and G3B3 approaches. Possible reaction pathways through either the radical or transition state (TS) of the molecules are considered. The geometries, vibrational frequencies and relative energies for various sta-tionary points are determined. From the study of energetics, the TS pathways arising from concerted molecular eliminations are indicated to be the main dissociation pathways for both molecules. The PES differences of the dissociation reactions are investigated. The activa-tion energies and rate constants will be helpful for investigating the predictive ability of the reaction in further theoretical and experimental research.
Based on spin-unrestricted hartree fock theory, we present the spin unrestricted multi-configuration time dependent hartree fock theory (UMCTDHF) to describe the electron correlation dynamics of systems interacting with laser field. The positive spin orbitals and the negative spin orbitals are propagated in their own subspace respectively. The spin orbital in the spin-down subspace acts with that in the spin-up subspace by the reduced density matrix and mean field operator. The ground energy is acquired by propagating the trial wave function in the imaginary time by using spin-restricted MCTDHF (RMCTDHF) and UMCTDHF respectively. Then the ionization probabilities and the electrons energies are calculated by using RMCTDHF and UMCTDHF when the laser field is present. The ion-ization probability calculated with UMCTDHF agrees with the previous theoretical reports very well. The UMCTDHF method is accurate and applicable for open shell system beyond the capability of the RMCTDHF method.
Conformations and reaction energetics are important for understanding the interactions be-tween biomolecules and metal ions. In this work, we report a systematic ab initio study on the conformations and metal ion affinities of glutamine (Gln) binding with alkali and alkaline earth metal ions. An efficient and reliable method of searching low energy conformations of metalated Gln is proposed and applied to the complexes of Gln.M+/++ (M+/++=Li+、Na+、K+、Rb+、Cs+、Be++、Mg++、Ca++、Sr++和Ba++). In addition to all conformers known in literatures, many new important conformations are located, demonstrating the power of the new method and the necessity of the conformational search performed here. The metal coordination modes, relative energies, dipole moments, and equilibrium distribu-tions of all important conformations of Gln.M+/++ are calculated by the methods of B3LYP, BHandHLYP, and MP2. IR spectra and metalation enthalpies and free energies are also pre-sented and compared with the available experiments. The results form an extensive database for systematic examination of the metalation properties of Gln.
The metal complex 5-(4-aminophenyl)-10,15,20-triphenylporphyrin copper (CuAPTPP) was covalently linked on the surface of TiO2 microspheres by using toluene disocyanate (TDI) as a bridging bond unit. The hydroxyl group (-OH) of TiO2 microspheres surface and the amino group (-NH2) of CuAPTPP reacted respectively with the active -NCO groups of TDI to form a surface conjugated microsphere CuAPTPP-TDI-TiO2 that was confirmed by FT-IR spectra. The CuAPTPP-TDI-TiO2 microspheres were characterized with UV-visible, elemental analysis, XRD, SEM, and UV-Vis diffuse reflectance spectra. The effect of amounts of linked TDI on the performance of photocatalytic microspheres was discussed, and the optimal molar ratio of TDI:TiO2 was established. The photocatalytic activity of CuAPTPP-TDI-TiO2 was evaluated using the photocatalytic degradation of methylene blue (MB) under visible-light irradiation. The results showed that, TDI, as a bond unit, was used to form a steady chemical brigdging bond linking CuAPTPP and the surface of TiO2 microspheres, and the prepared catalyst exhibited higher photocatalytic activity under visible-light irradiation for MB degradation. The degradation rate of 20 mg/L MB could reach 98.7% under Xe-lamp (150 W) irradiation in 120 min. The degradation of MB followed the first-order reaction model under visible light irradiation, and the rate constant of 5.1×10-2 min-1 and the half-life of 11.3 min were achieved. And the new photocatalyst can be recycled for 4 times, remaining 90.0% MB degradation rate.
Bi4Ti3O12 (BIT) crystals were controllably synthesized via a facile hydrothermal process without adding any surfactant or template. The morphologies of BIT with nanosphere, nanoplate, nanobelt, and nanosheet can be selectively obtained by adjusting the pH value of the reactant. The formation mechanisms of these distinctive morphologies were then discussed based on the structural analysis of samples obtained at different pH values. BIT sample prepared at pH=1 showed the highest photocatalytic activity under visible light irradiation. The photocatalytic activities difference for the BIT samples synthesized at different pH values was studied based on their shape, size, and the variation of local structure.
γ-Al2O3 supported Ni-Mn bimetallic catalysts for CO2 reforming of methane were prepared by impregnation method. The reforming reactions were conducted at 500-700 oC and atmospheric pressure using CO2/CH4/N2 with feed ratio of 17/17/2, at total flow rate of 36 mL/min. The catalytic performance was assessed through CH4 and CO2 conversions, synthesis gas ratio (H2/CO) and long term stability. Catalytic activity and stability tests revealed that addition of Mn improved catalytic performance and led to higher stability of bimetallic catalysts which presented better coke suppression than monometallic catalyst. In this work, the optimum loading of Mn which exhibited the most stable performance and least coke deposition was 0.5wt%. The fresh and spent catalysts were characterized by various techniques such as Brunauer-Emmett-Teller, the temperature programmed desorption CO2-TPD, thermogravimetric analysis, X-ray diffraction, scanning electron microscope, EDX, and infrared spectroscopy.
Lignin is the only nature renewable resource which can provide large quantities of aromatic compounds. In the work, transformation of lignin into benzene, toluene, and xylenes (BTX) was investigated over the HZSM-5, HY, and MCM-22 catalysts, and the HZSM-5 catalyst showed the highest carbon yield of BTX. The reaction condition, including temperature, the gas flow rate, and the catalyst/lignin ratio, was also investigated. The carbon yield of BTX reached about 25.3 C-mol% over HZSM-5 catalyst under T=550 oC, f(N2)=300 cm3/min, and catalyst/lignin ratio of 2.
NiSAPO-34 and NiSAPO-34/HZSM-5 were prepared and evaluated for the performance of dimethyl ether (DME) conversion to light olefins (DTO). The processes of two-stage light olefin production, DME synthesis and the following DTO, were also investigated using biosyngas as feed gas over Cu/Zn/Al/HZSM-5 and the optimized 2%NiSAPO-34/HZSM-5. The results indicated that adding 2%Ni to SAPO-34 did not change its topology structure, but resulted in the forming of the moderately strong acidity with decreasing acid amounts, which slightly enhanced DME conversion activity and C2=-C3= selectiv-ity. Mechanically mixing 2%NiSAPO-34 with HZSM-5 at the weight ratio of 3.0 further prolonged DME conversion activity to be more than 3 h, which was due to the stable acid sites from HZSM-5. The highest selectivity to light olefins of 90.8% was achieved at 2 h time on stream. The application of the optimized 2%NiSAPO-34/HZSM-5 in the second-stage reactor for DTO reaction showed that the catalytic activity was steady for more than 5 h and light olefin yield was as high as 84.6 g/m3syngas when the biosyngas (H2/CO/CO2/N2/CH4=41.5/26.9/14.2/14.6/2.89, vol%) with low H/C ratio of 1.0 was used as feed gas.
A series of mixed oxide catalysts with different composition of Co-M-Al and Co-M-Ce-Al (M=Zn, Ni, Cu) were prepared by co-precipitation method from hydrotalcite-like com-pounds. The experimental results revealed the catalytic activity of Co-Ni-Al is slightly higher than that of Co-Zn-Al and much higher than that of Co-Cu-Al for direct decomposition of N2O. Moreover, addition of small amounts of CeO2 improved the catalytic activity signif-icantly and made the decomposition temperatures at which the N2O conversion was 50% and 90% (T50 and T50) both decreased 80 oC than those of Co-M-Al catalysts without CeO2 added. Further, potassium-load also promoted the catalytic activity, and the decomposi-tion temperatures of T50 and T90 both decreased approximately 50 oC. It is significant for decomposing N2O from industries and reducing carbon emission from atmosphere.
According to the nonequilibrium solvation theory studies, a constrained equilibrium prin-ciple is introduced and applied to the derivations of the nonequilibrium solvation energy, and a reasonable expression of the spectral shift of the electronic absorption spectra is de-duced. Furthermore, the lowest transition of p-nitroaniline (pNA) in water is investigated by time-dependent density functional theory method. In addition, the details of excited state properties of pNA are discussed. Using our novel expression of the spectral shift, the value of -0.99 eV is obtained for π-π* transition in water, which is in good agreement with the available experimental result of -0.98 eV.
Accurate chemical shifts of hydrogen atoms in CH groups are difficult to obtain. To solve this problem, relative chemical shifts are introduced. Internal and external standard methods were used to measure the chemical shifts in a whole-concentration of N-methylacetamide-water system. Determination of the chemical shifts of hydrogen atoms, especially those of CH groups, according to the two methods yielded significant differences. Relative chemical shifts were proven to be independent of the reference and may be applied to other systems.
The thermal behaviors and burning characteristics of reconstituted tobacco (RT) are strongly related with evolved gaseous products. The effect of ammonium polyphosphate (APP) as an additive of RT on the pyrolysis behavior and CO evolution was studied, emphasizing the role of heating velocity in reducing CO delivery of the mainstream smoke by APP. Thermogravimetric analysis (TGA) was employed to investigate the influence of APP on RT thermal behavior. Slow and flash pyrolysis of RT were compared to discuss the role of heating rate in decreasing CO by APP. TGA results demonstrated that, in dependence on APP concentration, APP influenced exothermal amount and weight loss rate during RT thermal decomposition, promoted the formation of char and retarded the thermal decomposition of RT. In addition, APP had a considerable influence on the evolution of gaseous products during thermal decomposition of RT. Both CO delivery per cigarette and that per puff in the smoking process were significantly reduced in dependence on APP content in RT. Comparative analysis of CO evolution patterns in the flash and slow pyrolysis elucidated that heating rate played a key role in decreasing CO evolution by APP. The results suggest that APP is a potential burning additive for controlling CO delivery in mainstream smoke of RT.
Chinese abstract