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    10 November 2015, Volume 36 Issue 11
    Content
    Preface to the Special Issue for Commemorating the 100th Anniversary of TANG Au-chin's Birthday
    ZHOU Qifeng
    2015, 36(11):  1-2. 
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    Reviews
    Computational Spectroscopy for Structure Characterization of Nanomaterials: a Case Study of Graphene Oxide
    ZHANG Wenhua, YIN Di, LU Ning, LI Zhenyu, YANG Jinlong
    2015, 36(11):  2081-2086.  doi:10.7503/cjcu20150602
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    Nowadays, first-principles electronic structure calculations can be routinely used to analyze energetics and then to obtain the ground-state structure of a specific material. However, with complicated synthesis routes, nanomaterials are not necessarily always in their thermodynamic ground states. In such situations, computational spectroscopy provides a reliable way for structure characterization. We first briefly introduced the theoretical background of spectrum simulation, focusing on infrared(IR) spectroscopy, Raman spectroscopy, optical absorption,nuclear magnetic resonance(NMR), X-ray photoemission spectroscopy(XPS), and scanning tunneling microscopy/spectroscopy(STM/STS). Then, structure characterization of graphene oxide(GO) was used as an example to demonstrate the power of computational spectroscopy. Comparing experimental spectra with simulated data from diffe-rent candidate structures, we obtained the information about GO structure.It was unambiguously revealed that experimentally obtained GO samples are in a kinetically constrained metastable state instead of the thermodynamic ground state. Based on computational spectroscopic studies, an updated Lerf model for GO structure was proposed.

    Quantum Chemistry Study of Electrochemical Surface-enhanced Raman Spectroscopy
    PANG Ran, JIN Xi, ZHAO Liubin, DING Songyuan, WU Deyin, TIAN Zhongqun
    2015, 36(11):  2087-2098.  doi:10.7503/cjcu20150747
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    Considering the study of electrochemical surface adsorption and reaction processes at the molecular level, Surface-enhanced Raman spectroscopy(SERS) shows its particular merits and provides a powerful technical method for this study. However, the mechanism of enhancement needs to be further explored. This review summarizes the systematic work on electrochemical SERS(EC-SERS) by combining quantum chemistry calculations. On the basis of these studies, we can make deep insight for extracting the physical and chemical information in EC-SERS spectra. Focusing on adsorption of pyridine on the electrochemical surface, adsorption and reactional process of water on the surface, and surface coupling reaction for p-aminothiophenol, we had illustrated the nature of the adsorption and photochemical reactions on the electrochemical surface.

    Black Nano Titania for Efficient Solar Energy Utilization
    ZHU Guilian, LIN Tianquan, HUANG Fuqiang
    2015, 36(11):  2099-2114.  doi:10.7503/cjcu20150741
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    Insufficient visible-light power conversion has been a great challenge for nanotitania photocatalysts in solar energy utilization.Recently, a new material—black TiO2 has attracted enormous attention due to its greatly enhanced solar absorption and photocatalytic activity. Our group has made tremendous contributions to the researches of black TiO2 via developing many effective preparation methods harvesting the extremely efficient black titania. Herein lie our recent progresses in researching black nanotitania, and a special emphasis on the fabrication methods, the chemical/physical properties and solar application.

    Assembly of Organosilver(I) Networks with Multinuclear Supramolecular Synthons Containing All-carbon and Carbon-rich Anionic Ligands
    Sam S. K. HAU, Ting HU, Dennis Y. S. TAM, Thomas C. W. MAK
    2015, 36(11):  2115-2133.  doi:10.7503/cjcu20150601
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    This review summarizes recent advances conducted by our group on related silver complexes of (a) all-carbon ligands C62- and C82-, (b) 1,5-hexadiyne-1,6-diide C6H42-, (c) ethynediide C22- and ethynide R—C2- assembled with phosphonic acids, (d) aryl, alicyclic and heteroaromatic ethynides, and (e) ethynides that are stabilized by different types of silver…carbon binding interactions in the crystalline state, which are further consolidated by weak intra/intermolecular forces. The effects of the solvent, bulkiness of ligands and ancillary ligands on the construction of coordination networks are also discussed.

    Biomolecule-assisted Surface-enhanced Raman Scattering(SERS) Technology and SERS Biosensing
    FU Cuicui, LIANG Lijia, QI Guohua, XU Shuping, XU Weiqing
    2015, 36(11):  2134-2147.  doi:10.7503/cjcu20150744
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    Biomolecule-assisted surface-enhanced Raman scattering(SERS) sensing is a technique using biological molecules as sensitive components or detected objects, which is one of the most important tools in the studies of biological molecules. SERS biosensing is widely used in environmental monitoring, food-safety, clinical testing, disease diagnosis, and many other areas. This paper summarizes the progresses on the application of SERS technique in the fields of the analysis and diagnosis of cancer. The contents mainly consist of three parts: (1) SERS biosensing technology based the new coupling mechanisms, involving SPR-coupling, waveguide-coupling and LSPR-PSPR coenhancement; (2) preparation and application of highly sensitive SERS chips; and (3) new SERS technology for investigating cancer cells and bio tissues.

    Application of Zwitterionic Polymers in the Treatment of Malignant Tumors
    CHEN Jie, LI Xiaozhou, TIAN Huayu, ZHU Xiaojuan, CHEN Xuesi
    2015, 36(11):  2148-2156.  doi:10.7503/cjcu20150608
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    Zwitterionic polymer is a kind of polymer both with acidic and basic groups, which exists in the form of zwitterion. Zwitterionic polymers have attracted our widespread attention because of the excellent performance of themselves, such as high hydration ability, significant anti-bacterial adhesion ability, charge conversion, be easily modified and so on. In this review, the variety of zwitterionic polymers will be classified according to the structure. The early diagnosis and treatment of malignant tumors by zwitterionic polymers were analyzed and summarized in this paper. Finally, the development of zwitterionic polymers in future is prospected.

    Letters
    Development of a New Kilowatt Microwave Plasma Torch(kW-MPT) Excitation Source for Atomic Emission Spectrometry
    JIN Wei, YU Bingwen, ZHU Dan, YING Yangwei, YU Haixiang, JIN Qinhan
    2015, 36(11):  2157-2159.  doi:10.7503/cjcu20150598
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    Based on the simulation of transmission and distribution characteristics of the electromagnetic field inmicrowave plasma torch(MPT) torches with different configurations using electromagnetic simulation software and experimental study, a new MPT torch with double resonant configuration was, for the first time, developed. The results show that the inner tube of MPT torch plays an important role in strengthening the electric field intensity at the open end of the MPT torch and redistributing the electromagnetic field in the whole torch by the formation of the double resonance. It contributes also to enhance the macroscopic stability and the self-sustaining of the plasma. The stability of the plasma was shown to be excellent when the spacer between inner and intermediate tubes is located about 20—30 mm from the top opening of the torch. Preliminary study showed that the analytical performance for 13 common elements was approaching that of traditional ICP-AES.

    Synthesis and Performance of Poly(ether ether ketone)s with Low Melt Viscosity
    LI Yunxi, YUE Xigui, JIANG Zhenhua
    2015, 36(11):  2160-2162.  doi:10.7503/cjcu20150566
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    A novel approach was presented on lowering the high processing viscosity of poly(ether ether ketone)s(PEEK). The commercial PEEK and poly(ether ether ether ketone)s-poly(ether ketone)s(PEEEK-PEK) were synthesized via a typical procedure. Compared to PEEK, PEEEK-PEK had the same molar ratio of ether and ketone linkages but in different linkage sequencing. Results of the DSC, DMA, TGA and Stress-strain tests indicated that the two copolymers performed close thermal and mechanical properties. Moreover, the rheological behavior was particularly investigated and it occurred that the melt viscosity of PEEEK-PEK exhibited around 50% lower than that of PEEK according to the dynamic shear rheological tests at the rate of 100 rad/s.

    Physical Chemistry
    Spin-orbit Coupling ab initio Investigation on the Photolysis Mechnism of CH2BrI
    SONG Yanli, LIU Yajun
    2015, 36(11):  2163-2170.  doi:10.7503/cjcu20150491
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    Based on the latest experimental results in solvents, the state-of-the-art quantum chemical calculation, i.e. the multi-state second order multiconfigurational perturbation theory in consideration of the spin-orbit coupling interaction through complete active space state interaction(MS-CASPT2/CASSI-SO) was used for investigating the spin-orbital-coupled states potential energy curves(PECs) of bromoiodomethane(CH2BrI) at 266 nm in solvents(acetonitrile, 2-butanol and cyclohexane). The calculated PECs leading to the products I(2P3/2) and I*(2P1/2) are consistent with the experimental observations. The mechanisms of the photoisomerization in solvents were studied in order to understand the effects of solvent polarity on the recombination products(CH2Br—I and CH2I—Br). The current calculation assigned the latest experimental observation, and once again evidenced the necessity of involving the spin-orbit coupling effect for heavy atoms like Br and I.

    Molecular Dynamics Simulation on Self-Assembly of Fmoc-FF Dipeptide
    GUO Kai, ZHANG Heng, SUN Jichao, YUAN Shiling, LIU Chengbu
    2015, 36(11):  2171-2178.  doi:10.7503/cjcu20150546
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    Molecular dynamics simulations were performed to investigate the self-assembly of Fmoc-FF dipeptide. The driving force of self-assembly and the effect of water bridge were investigated. During the simulation, Fmoc-FF dipeptides were first dispersed in aqueous solution and then the self-assembly occurred rapidly in a very short simulation time. At last the system reached the dynamics balance and the dipeptide could self-assemble into well-ordered cylindrical nanostructure. Computational analysis of radial distribution function(RDF) between fluorenyl rings showed a typical π-π interaction distance and some well-recognized π-π stacking geometries could be found from the nanostructures such as T-shaped and Herringbone structure. Further the interaction energy between Fmoc-FF dipeptide and water molecules and between different parts of Fmoc-FF dipeptide were calculated to make sure that the Fmoc-FF dipeptide tended to self-assemble into an aggregate and the major interaction was between fluorenyl rings. At last, the properties of hydrogen bond formed between water molecules and certain atoms of Fmoc-FF dipeptide indicated that water bridge structure could exist between two dipeptides and further stabilize the self-assembly aggregate.

    Self-assembly Morphological Control of Block Copolymers Simulated via the Combination of Dissipative Particle Dynamics and ABEEM Polarizable Force Field
    LIU Linlin, YANG Zhongzhi
    2015, 36(11):  2179-2188.  doi:10.7503/cjcu20150552
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    Mesoscopic dissipative particle dynamics(DPD) simulations and all-atom molecular dynamics simulations were combined to investigate the influence of the architecture, symmetry, molecular composition of block copolymers and temperature on final assembled structures of block copolymers. From the simulation results, these factors have an influence on the final assembled structures. This theoretical investigation provides a reference for experiments and practice to manipulate self-assembled structures.

    Computational Studies on Energetic Performance of Polynitro-substituted Uric Acid Derivatives
    CHI Weijie, TIAN Meng, LI Quansong, LI Zesheng
    2015, 36(11):  2189-2197.  doi:10.7503/cjcu20150595
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    To search for potential energetic materials with large energy density and acceptable thermodynamics and kinetics stability, fifteen nitro uric acid derivatives were investigated by density functional theory. The detonation properties of all the molecules were evaluated according to Kamlet-Jacobs equations and specific impulses. Calculated results show that there are good linear relationships between detonation heat, densities, detonation velocities, detonation pressures and the numbers of nitro groups, respectively. It is found that tri-nitro and tetra-nitro uric acid derivatives show detonation velocity of about 8.0 km/s, and a detonation pressure of 30 GPa, and most of the investigated molecules have higher specific impulse than hexahydro-1,3,5-trinitro-s-triazine(RDX). By analyzing bond dissociation energies(BDEs) of N—NO2 bonds, impact sensitivity, and the free space per molecule in the unit cell, most of the investigated molecules exhibit satisfactory stability(BDEs > 80 kJ/mol). The results of this study may provide basic information for the further study of this kind of compounds and the molecular design of novel energetic materials.

    State-to-state Quantum Dynamics of Reaction N+NH→N2+H
    HU Xixi, YANG Junying, XIE Daiqian
    2015, 36(11):  2198-2203.  doi:10.7503/cjcu20150596
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    Quantum dynamics of reaction N+NH→N2+H was investigated based on the recently constructed potential energy surface(PES) of N2H(12A') by Chebyshev real wavepacket method. The reaction probabilities, integral and diffe-rential cross sections, and ro-vibrational state distributions of the product were reported and compared with previous theoretical results. Besides, the calculated rate constants monotonically increase with the temperature from 50 K to 500 K, consistent with the available theoretical results obtained from other PESs. However, all the calculated values are significantly larger than the only experimental data at room temperature.

    Theoretical Investigation on Nonlinear Optical Properties of the Donor/Acceptor-decorated Zigzag Graphene Nanoribbons with the 5-9 Defect
    ZHANG Xueying, YU Guangtao, CHEN Wei, HUANG Xuri
    2015, 36(11):  2204-2210.  doi:10.7503/cjcu20150613
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    In view of the inevitability of forming defect in the process of nanomaterial synthesis, we investigated the structures and nonlinear optical(NLO) properties of the donor/acceptor-decorated zigzag graphene nanoribbons with the 5-9 defect(zGNR-D5-9) by means of the density functional theory computations. It is revealed that these donor/acceptor-decorated zGNR-D5-9 exhibit considerable NLO response, and the modified site of functional group can significantly impact the β0 value. Particularly, simultaneously employing donor/acceptor pair to decorate both sides of zGNR-D5-9 can achieve much larger β0 value, where the synergistic effect of donor-π-acceptor framework and the 5-9 defect should be responsible for the large first hyperpolari-zability of systems. These interesting results can provide the valuable insights and more reliable information for the design of new NLO material based on the graphene nanoribbons.

    Effect of Hydrophobicity of Threads on the Solvent-controlled Shuttling in Rotaxanes
    WANG Shuangshuang, LIU Peng, CAI Wensheng, SHAO Xueguang
    2015, 36(11):  2211-2219.  doi:10.7503/cjcu20150620
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    In order to investigate the hydrophobic effect of chain-like structures on shuttling in further, three similar rotaxanes are studied in this work. The rotaxanes are formed by an α-CD, two dodecamethylene chains(ALK) or two poly(ethylene glycol)(PEG) for stations, one bipyridinium moiety(PY) or one biphenyl moiety(PH) for linkers and large end groups at both sides. The shuttling of the rotaxanes was studied by means of molecular dynamics simulations(MD) combined with free-energy calculations in water and DMSO at room temperature. Two methods, the adaptive biasing force(ABF) method and the multiple walker ABF(MW-ABF) method, a modified version of ABF, are adopted for calculating the free-energy change characte-rizing the shuttling process. The potentials of mean force(PMFs) for the three rotaxanes are determined. The free-energy barriers of the PMFs for the PEG-rotaxane are lower than those for the the ALK-rotaxane both in water and DMSO. Furthermore, the barriers for the PEG-rotaxanes in DMSO are lower than that in water, which is in accordance with the ALK-rotaxanes. The barriers for the PH-rotaxanes are significantly lower than those for the PY-rotaxanes. Partitioning the PMFs into free-energy components suggests that change of the the charged group by an hydrophobic biphenyl moiety or decrease of the hydrophobicity of the chain-like structure in two stations from ALK to PEG reduces the free-energy barrier with respect to the stable states in the stations. In addition, comparison of the two free-energy calculation methods shows that the MW-ABF method can significantly improve the uniformity of sampling and hence increase the computational efficiency.

    Theoretical Studies on the Adsorption of Eosin Y on TiO2 and the Electron Injection from Eosin Y to Counter Electrode in Dye-sensitized Solar Cell
    HAO Li, WEI Wei, WANG Jian, ZHANG Hongxing
    2015, 36(11):  2220-2225.  doi:10.7503/cjcu20150811
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    The density functional calculations of the Eosin Y sensitized different interfaces were performed to analyze their structural, electronic, and charge properties in dye-sensitized solar cells. The obtained results indicate that Eosin Y with configuration H sensitized TiO2 shows a higher total energy above 59.7 kJ/mol than that with configuration B sensitized TiO2, while Eosin Y with configuration B sensitized TiO2 displays larger adsorption energy than that with configuration H adsobed on TiO2. Therefore, the configuration B would be more favorable for DSSCs. The electron-injection dynamics and quantitative analysis of charge transfer were simulated and computed, respectively. And the results reveal configuration B would provide more injected electrons and a faster electron injection process.

    Molecular Dynamics Simulation on the Conformational Changes of CYP2E1 Enzyme Under Different Concentrations of Ethyl Alcohol
    WANG Yan, ZHENG Qingchuan
    2015, 36(11):  2226-2235.  doi:10.7503/cjcu20150628
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    Cytochrome P450(CYP) 2E1 is a dual function monoxygenase with a crucial role in the metabolism of 6% of drugs on the market at present. The enzyme is of tremendous interest for its association with alcohol consumption, diabetes, obesity and fasting. The enzyme’s conformational changes at different ethanol concentrations have not been rationalized at the atomic level. In this regard, we have investigated the effects of different ethanol concentrations on the structural and energetic characteristics upon the complex of arachidonic acid and CYP2E1(AA-CYP2E1). The molecular dynamics(MD) simulation combined with binding free energy calculations was carried out on AA-CYP2E1 complex at different ethanol concentrations. Based on the MD simulation results, two residues, His109 and Lys243, are responsible for the binding of AA molecule. The binding ability of AA molecue is decreased at high concentrations of ethanol. This is due to the loss of certain hydrogen bond interaction. The high concentration of ethanol can also affect the surface structure of AA-CYP2E1. Our work provides detailed atomistic insights into the structure-function relationships of CYP2E1 at different ethanol concentrations under dynamics conditions. This work also provides particular explanations on how different ethanol concentrations affect the surface structure of CYP2E1. Furthermore, the mutational effects on the activity of CYP2E1 obtained in the present study are beneficial to both experiment and computation of CYPs and may allow researchers to achieve desirable changes in enzymatic activities.

    Multistate Density Function Theory and the Construction of Diabatic and Adiabatic Potential Energy Surfaces
    QU Zexing, GAO Jiali
    2015, 36(11):  2236-2240.  doi:10.7503/cjcu20150629
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    A multistate density function theory(MSDFT) based on valence bond theory was introduced. As an application, the MSDFT method was illustrated by the bond dissociation of H2 and the proton transfer between HNO3 and a water molecule. In the dissociation of H2, the MSDFT method yields a correct behavior as the two H atoms stretch to infinity, and gives a potential well in accord with second-order perturbation using complete active space(CASPT2). For the proton transfer process of HNO3, MSDFT can be used to yield both diabatic and adiabatic potential energy curves as a function of the proton transfer reaction coordinate. For the reaction barrier height, the inclusion of an ionic state in a three-state model can significantly improve the accuracy in barrier height in comparison with the high-level results.

    Theoretical Studies on Mononuclear and Binuclear Osmium Fluoroborylene Carbonyls Os(BF)(CO)n(n=4, 3) and Os2(BF)2(CO)n(n=7, 6, 5, 4)
    PENG Bin, LUO Qiong, LI Nan, ZHANG Xiuhui, LI Qianshu
    2015, 36(11):  2241-2250.  doi:10.7503/cjcu20150636
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    Mononuclear and binuclear osmium fluoroborylene carbonyls Os(BF)(CO)n(n=4,3) and Os2(BF)2(CO)n(n=7, 6, 5, 4) were investigated using MPW1PW91 and BP86 density functional theories. Twenty two isomers were obtained. For Os(BF)(CO)4, the lowest-energy structure 14-1 is a singlet C2v symmetrical trigonal bipyramid. The lowest energy structures for Os(BF)(CO)3 are derived from the trigonal bipyramidal Os(BF)(CO)4 structures by removal of a CO group. Four low energy isomers are predicted to be close in energy for Os2(BF)2(CO)7, the lowest-energy isomer, 27-1, has butterfly structure containing two bridging BF groups. For Os2(BF)2(CO)6. Two isomers, 26-1 and 26-2, are predicted to be nearly degenerated in energy. Both 26-1 and 26-2 are predicted to have two bridging BF groups. The global minimum isomer of Os2(BF)2(CO)5 and Os2(BF)2(CO)4 are similar to 26-1 with two BF groups bridging to two Os atoms. It seems that Os2(BF)2(CO)n(n=7, 6, 5, 4) are favored to form structures containing bridging fluoroborylene groups. The study of dissociation energy shows that the CO dissociation energy and dissociation energy of Os2(BF)2(CO)n(n=7, 6) into the mononuclear fragments Os(BF)(CO)4 or Os(BF)(CO)3 are large, suggesting those isomers are quite thermodynamically favorable.

    Diffusion Coefficient of Nanoparticles in Semidilute Polyelectrolyte Solutions Based on Mode Coupling Theory
    DONG Yunhong, CHEN Anpu, ZHAO Nanrong
    2015, 36(11):  2251-2255.  doi:10.7503/cjcu20150642
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    A theoretical formalism based on mode-coupling theory(MCT) was established to study the long-time diffusion coefficient of nanoparticles in polyelectrolyte solutions. By introducing an approximate summation form for Γpp (k,t), Dmicro can be calculated straightforwardly and it is necessary to investigate explicitly how D depends on the concentration c of the polymer solution and the nanoparticle size R. For illustration, the theoretical approach is taken to analyze the diffusion of polystyrene nanoparticles in semidilute polyacrylamide solutions which has been studied in detail experimentally. As a result, our theoretical results show very good quantitative agreements with the experimental data in many aspects, such as the strong dependence on c, the large deviation from Stokes-Einstein relation particularly for small particles. Such good agreements clearly demonstrate the validity of our MCT framework, which may serve as a good starting point to study many more complex dynamical behavior associated with polymer solutions.

    Nonequilibrium Solvation Theory Based on Constrained Equilibrium Principle and Its Applications
    MING Meijun, BI Tingjun, LI Xiangyuan
    2015, 36(11):  2256-2261.  doi:10.7503/cjcu20150645
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    A novel nonequilibrium solvation theory established recently by the authors was introduced. Differing from the traditional ones, the present theory was based on the constrained equilibrium principle of classical thermodynamics. The calculations of solvent reorganization energy were performed with the electron transfer system of NpO2+-NpO22+ as an example. The constrained density functional theory was adopted for the charge localization of the system and IEF-PCM was used for the gain of polarization charges in water. Both two-sphere model and numerical solution give consistent and reasonable solvent reorganization energies.

    Theoretical Studies on the Mechanism of Water-dependent Chemoselectivity in the Pt-Catalyzed Hydrative Cyclization of 2-Enynylbenzaldehydes
    GUO Jinxin, ZHU Rongxiu, ZHANG Dongju, LI Mingxia, LIU Chengbu
    2015, 36(11):  2262-2270.  doi:10.7503/cjcu20150649
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    With the aid of density functional theory(DFT) calculations, we made a detailed mechanism study on the origin of chemoselectivity in Pt-catalyzed hydrative cyclizations of 2-enynylbenzaldehydes. The calculations indicate that the formation of platinum-pyrylium intermediate is initiated by the activation of alkyne. Successive [3+2] cycloaddition with a double bond leads to the platinum-carbene complex. After that, the reaction proceeds along either pathway Ⅰ or pathway Ⅱ to yield products 3a and 4a, depending on the subsequent two-step water-assisted proton-transfer process. The calculated barrier leading to product 3a is 146.5 kJ/mol. For the formation of product 4a, the tautomerization(from enol to keto form) is the rate-determining step with a barrier of 185.8 kJ/mol when one water molecule is involved. However, when two and three water molecules are involved in catalysis, the barrier is reduced to 128.1 and 64.9 kJ/mol respectively. Therefore, the reaction preferentially proceeds along the pathway Ⅱ leading to product 4a. Water molecules that act as a cocatalyst in the tautomerization process are mainly responsible for the good selectivity. This result rationalizes well the experimental observations and provides a new insight into the Pt-catalyzed hydrative cyclizations.

    Metastable Hydrogen-bonds Featuring Negative Dissociation Energies in Protein-bound DNA in Hole Migration
    WANG Mei, WANG Jun, BU Yuxiang
    2015, 36(11):  2271-2282.  doi:10.7503/cjcu20150651
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    We theoretically investigated the properties of hydrogen bonds in the protein-bound DNA trimer(protona-ted arginine…guanine…cytosine, ArgH+-GC) units as hole migration carriers using density functional theory calculations. Results suggest these hydrogen bonds are metastable and feature considerable negative dissociation energies upon hole migration through the ArgH+-GC units of the carriers. Normally, the ArgH+ group can H-bond with the guanine-cytosine(GC) base pair in the major/minor-groove face with positive dissociation energy. However, hole trapping weakens the H-bonds to being metastable with a mild dissociation barrier and considerable negative dissociation energy. This barrier-inhibited negative dissociation energy phenomenon implies that the trimer motif can store energy(ca.108.48 kJ/mol) in its ArgH+…N7/O6 bond zone due to hole-trapping. This H-bond dissociation channel is governed by a balance between electrostatic repulsion and H-bonding attraction in the two associated moieties and different attenuations of two opposite interactions with respect to the H-bond distance. The topological properties of electron densities and the Laplacian values at the bond critical points clarify that this energetic phenomenon mainly originates from additional electrostatic repulsions between two moieties linked via high-energy H-bonds(ArgH+…N7/O6). Proton transfer from G induced by hole-trapping can expand the negative dissociation energy zone to both the ArgH+…N7/O6 and Watson-Crick(WC) H-bond zones. In addition, the placement of ArgH+ at the major/minor grooves of DNA where ArgH+ could interact with the GC unit increases its ionization potential, and thus weakens its hole-relaying ability in different degrees, depending on the separation between ArgH+ and GC. Similar phenomena can be observed in the protonated lysine-GC and protonated histidine-GC cases. Clearly, such property-tunable metastable H-bonds can regulate the hole migration mechanism. This work provides some important energetic information for understanding the protein-regulated hole migration mechanism in DNA.

    Understanding Substrate Specificity of Related Plant Methylesterases(MESs) from Computational Investigations
    QIAN Ping, ZHAO Nan, CHEN Feng, GUO Hong
    2015, 36(11):  2283-2291.  doi:10.7503/cjcu20150674
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    One of enzyme’s hallmarks is the high specificity to their natural substrates. But our understanding is still lacking concerning how enzymes could achieve high specificity and substrate discrimination. This is the case for a group of related methylesterases(MESs) identified in plants that catalyze reactions of different substrates, including methyl salicylate(MeSA), methyl jasmonate(MeJA) and methyl indole-3-acetate(MeIAA). In this work, a homology model was built for AtMES10(a MeJA esterase),and this model along with the X-ray structure of SABP2(a MeSA esterase) was used to understand their substrate specificity. It is shown that the specificity may be explained based on the simple Lock-and-Key Model(that is, the active site being complementary in shape to the substrate) along with the requirement that the —COO moiety involved in the reaction occupies a position allowing the nucleophilic attack by the catalytic serine(that is, in a reactive configuration). The active site of SABP2 appears not to be complementary in shape to MeJA, and this may lead to a low activity on MeJA. For AtMES10, certain bulky residues in SABP2 are replaced by relatively small residues, allowing the substrate to bind to the active site and to be catalyzed by the enzyme. The results are consistent with the substrate specificity of these two enzymes observed experimentally. Explanations are also provided for the lack of the activities of AtMES10 and SABP2 on MeIAA and the lack of the activity of AtMES10 on MeSA.

    Theoretical Study of Electronic Spectra of Lignite Structural Units
    HU Xue, SUN Mingjun, ZHANG Xiangfei, CAO Zexing
    2015, 36(11):  2292-2296.  doi:10.7503/cjcu20150689
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    Electronic spectra of the lignite structural units and the effects of structural modification were explored by extensive density functional calculations. Based on calibration calculations on six representative compounds by different functionals, the feasibility of both B3LYP and HSEH1PBE for this kind of systems was validated. Predicted absorption spectra indicate that the main bands appear in near Ultraviolet-Visible region, while for the lignite structural unit with the extended conjugated components the λmax absorption occurs in visible region. Note that there are quite strong absorptions in the visible region of 460—480 nm as the side conjugated chain is linked to the structural unit through CC. The types of hetero-atoms and their positions show remarkable effects on the electronic absorption features, and the frontier orbitals in the structural units with a symmetric hetero-atom are well delocalized, especially for LUMO, resulting in notable red-shifted absorption of λmax. The predicted spectroscopic properties of the lignite structural units provide a basis to understand their features of light response.

    Light Modulated Host-guest Recognition of Organic Modified Polyoxometalate Complex
    AI Hui, LI Wen, ZHANG Bin, LI Bao, WU Lixin
    2015, 36(11):  2297-2303.  doi:10.7503/cjcu20150637
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    By ion exchange method, we realized the counter ion substitution and phase transfer of an azobenzene covalently modified Anderson polyoxometalate. The photoisomerization behavior of the prepared complex was investigated through 1H NMR and UV-Vis spectra in the aqueous solution. Base on the above results, we studied the inclusion interactions between the organic modified polyoxometalate and cyclodextrin in the aqueous solution, and realized the reversible recognition and dissociation between hybrid supramolecular guest and cyclodextrin with irradiations by various wavelengths.

    Electrochemical Reduction Effects on the Morphology and Electrochemical Capacity of Carbon Paper
    YAN Pengli, LI Ailong, ZHANG Bingqing, SHI Jingying, GAN Yang, LI Can
    2015, 36(11):  2304-2310.  doi:10.7503/cjcu20150724
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    We studied the changes in the morphology and electrochemical capacity of carbon paper caused by the electrochemical reduction. SEM images show that the electrochemical reduction caused the decomposition of reduced carbon papers(rCPs) into carbon particles and rough surface. Raman spectra show the surface disorder as evidenced by higher ID/IG ratio for treating time as short as 1 min. BET tests reveal the markedly increased specific surface area caused by the electrochemical reduction of carbon paper. XPS analyses show a higher quantity of surface hydroxyl species(C—OH) on rCPs. The capacitance of rCP(treated at -1.6 V for 5 min) is 15 times that of the pristine carbon paper, and this outstanding capacitance is rather stable even after prolonged charge-discharge 1500 cycles.

    Inorganic Chemistry
    Organotemplate-free Synthesis and Proton Conduction Properties of a Layered Aluminophosphate Na4[Al4P4O18]·H2O
    WANG Ning, SUN Qiming, YAN Yan, LIU Jiancong, YU Jihong, XU Ruren
    2015, 36(11):  2311-2316.  doi:10.7503/cjcu20150685
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    In the organotemplate-free system, a layered aluminophosphate Na4[Al4P4O18]·H2O(1) was synthesized with Na+ ion as the structure-directing agent under hydrothermal condition. The structure was determined by single-crystal X-ray diffraction, and further characterized by powder X-ray diffraction(PXRD), scanning electron microscopy(SEM), inductively coupled plasma(ICP) and thermal gravimetric(TG) analyses. Compound 1 crystallizes in the monoclinic space group P21/c with a=1.00887(9) nm, b=0.86747(8) nm, c=0.97580(9) nm, V=0.77387(12) nm3, and Z=2, and its framework consists of AlO5 and PO4 units. Compound 1 possesses high thermal stability, and the crystal structure remains unchanged after calcination at 400 ℃ in air. The proton conductivity measurement gives that compound 1 possesses excellent conductivity with σ the value of 1.19×10-3 S/cm when immersed in water at 55 ℃, which is higher than those of traditional zeolitic materials.

    Analytical Chemistry
    Immunoassay of Rat Brain Tissue by Surface-enhanced Raman Spectroscopy
    YANG Jin, LIU Zhuo, SU Hongyang, PENG Ru, SONG Wei, ZHAO Bing
    2015, 36(11):  2317-2321.  doi:10.7503/cjcu20150635
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    Surface-enhanced Raman scattering(SERS) was used to develop and optimize a novel, quick and simple immunohistochemical ABC(avidin-biotin-HRP complex) assay for detecting specific skeleton protein neurofilament-200(NF-200) in the frozen sections of rat brain tissue. In this study, anti mouse NF-200 labeled colloid gold was used as immunoprobe, which was added into the frozen sections of rat brain tissue containing NF-200 protein. Intense SERS signals of p-mercaptobenzoic acid(MBA) at 1076 and 1589 cm-1 were observed clearly after the specific binding of antigen and antibody. Meanwhile, the SERS spectra and the immunohistochemical staining effect of antigen and antibody complex with different concentrations of anti NF-200 were examined. Compared with the traditional method, this assay can simplify the procedure, moreover, it showed higher sensitivity and selectivity.

    Organic Chemistry
    Synthesis of a Novel Compound and Mediated Neuro-protection in Differentiated PC12 Cells via Mitochondria Related Pathway
    HU Shuang, TENG Lirong, ZHANG Junrong, MENG Jiatong, ZHUANG Zhe, DU Mengyan, WANG Di, LIAO Weiwei
    2015, 36(11):  2322-2328.  doi:10.7503/cjcu20150723
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    The neuro-protective effect of a new synthetic compound named 3h8b on differentiated PC12(DPC12) cells against neurotoxins 6-hydroxydopamine(6-OHDA)- and L-glutamic acid(L-Glu)-induced cell injury and potential mechanisms were investigated. Data show that 3h8b significantly enhanced cell viability, improved nucleus morphological apoptotic alterations, and relieved intracellular Ca2+ overload caused by neurotoxins in DPC12 cells. The abnormal alteration of mitochondria in neurotoxins-treated cells was strongly restored by 3h8b. Further experiments demonstrate that 3h8b reverses neurotoxins-suppressed levels of B-cell lymphoma 2(Bcl-2) and Bcl-xL. All these results indicate that mitochondria related pathway is essential for the neuro-protective effect of the novel synthetic compound 3h8b against neurotoxins-induce toxicity in DPC12 cells.

    Polymer Chemistry
    Synthesis and Property of PDLA-PBS-PDLA Tri-block Copolymer
    MA Lili, SHAO Jun, YANG Chenguang, TANG Zhaohui, CHEN Xuesi
    2015, 36(11):  2329-2334.  doi:10.7503/cjcu20150633
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    Poly(D-lactide)-poly(butylene succinate)-poly(D-Lactide)(PDLA-PBS-PDLA) was synthesized by the ring-opening polymerization of D-lactide(D-LA) in the presence of Sn(Oct)2 and the pre-polymerized PBS as the macro-initiator. The PDLA-PBS-PDLA tir-block polymers were confirmed by gel permeation chromatography(GPC) and nuclear magnetic resonance(1H NMR). Results of differential scanning calorimeter(DSC) and X-ray diffraction(XRD) revealed that with the increase of Mn of PDLA blocks, the melting temperature and enthalpy of PBS blocks decreased, and the crystallites of PBS blocks could not be detected by DSC when m(D-LA):m(PBS) was set as 2.60:1. For all the samples, PDLA segment could crystallize. With the increase of the amount of PDLA in the copolymers, the melting temperature of PDLA blocks increased gradually, but the melting enthalpy of PDLA blocks increased first and then decreased. Furthermore, both PDLA and PBS blocks could crystallize separately, and the crystal structures PDLA and PBS blocks did not change with m(D-LA):m(PBS), which revealed that the microphase separation formed in the copolymers.

    Synthesis of Hyperbranched Polyethylene with Poly(ε-caprolactone) Arms and Its Self-assembly in n-Hexane
    SHI Xinbo, LI Lin, GAO Haiyang, WU Qing
    2015, 36(11):  2335-2341.  doi:10.7503/cjcu20150634
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    A novel polyolefin copolymer HBPE-PCLs with a hyperbranched polyethylene core and poly(ε-caprolactone) arms was successfully prepared via a combination of chain walking polymerization(CWP) and ring-opening polymerization(ROP). Hyperbranched polyethylene with hydroxyl ends(HBPE-OH) was firstly synthesized via the chain walking copolymerization of ethylene with 2-hydroxyethyl acrylate in the presence of Pd-α-diimine catalyst. The HBPE-OH was used as the macroinitior for ROP of ε-caprolactone to synthesize hyperbranched polyethylene copolymer HBPE-PCLs. Investigations of self-assembly of the HBPE-PCLs copolymer in n-hexane by means of transmission electron microscopy(TEM), scanning electran microscopy(SEM) and laser light scattering confirm that the copolymer formed vesicles in nonpolar organic solution. The vesicles are the organic counterparts to vesicles in aqueous solution and could potentially find analogous application in the encapsulation of drug and controlled release.

    Layer-by-layer Assembled Polymeric Films for Differential Release of Dual Drugs
    CHEN Dongdong, CHEN Jie, TIAN Huayu, CHEN Xuesi, SUN Junqi
    2015, 36(11):  2342-2348.  doi:10.7503/cjcu20150683
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    Layer-by-layer(LbL)-assembled polymeric films capable of differentially releasing dual anticancer drugs to achieve synergetic therapeutic effects were fabricated. Doxorubicin(DOX) was first conjugated to hyaluronic sodium(HA) via acid labile hydrazone bonds to produce HA-DOX prodrugs. Then HA-DOX was alternately deposited with 2-hydroxypropyltrimethyl ammonium chloride chitosan(HACC) to produce (HACC/HA-DOX)n(n is the number of deposition cycle) film. Methotrexate(MTX) was then loaded into (HACC/HA-DOX)20 film by a post-diffusion process. MTX was quickly released due to the breakage of its electrostatic interaction with film component HACC. Meanwhile, DOX was released in a sustained manner because of the slow hydrolysis of hydrazine bonds. The synergetic therapeutic effects can be achieved by fast release of cell cycle specific drug MTX to effectively inhibit the proliferation of cancer cells and by sustained release of cell cycle non-specific drug DOX to kill cancer cells. The present study provides a new way for designing polymeric films for controlled release of multiple therapeutic agents.

    In Situ Encapsulation of Cellubiase Enzyme in Magnetic Mesoporous Silica via the Nonsurfactant-templated Sol-gel Method
    ZHANG Xiang, LI Shurun, ZHAI Wentao, CAO Yingze, QI Hongxu, JI Yan, WEI Yen
    2015, 36(11):  2349-2354.  doi:10.7503/cjcu20150688
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    Nonsurfactant-templated sol-gel method is an advanced technology for enzyme encapsulation. The immobilized enzyme can be reused many times, so that can reduce the cost. It has a broad application prospect in biological catalysis. D-fructose is used as non-surfactant template to generate mesopores. The average diameter of the mesoporous silica is 3.2 nm. And they significantly improve the activity of the immobilized enzyme. The best result is 70% of free enzyme. On the other hand, the mesopores are smaller than the size of cellobiase enzyme. So the enzyme will not leach out. That can help avoiding enzyme leaching. The magnetic nanoparticles can make the separation and recycle of immobilized enzyme easier and more feasible. The incorporation of magnetic nanoparticles has little effect on the enzyme activity. The magnetic encapsulated enzyme can be easily recycled by magnet force. More than 83% remained after 10 cycles. The process is simple and biocompatible as the sol-gel reaction occurs inaqueous phase and neutral pH.