Structural and Morphological Investigation of Ce0.6Zr0.4O2 Oxides Synthesized by Sol-Gel Method: Influence of Calcination and Redox Treatments

Ceria-zirconia mixed oxides of nominal composition Ce_0.6Zr_0.4O₂ were prepared by sol-gel method. The structural and morphological modifications of these materials due to calcination and redox treatments up to 1000°C were studied by X-ray diffraction (XRD) and Rietveld refinements, specific surface area measurements (BET), oxygen storage capacity (OSC), TEM and SEM analyses. The materials maintain high OSC after several hours of treatments at 1000°C in oxidizing and reducing atmosphere, showing good resistance to the thermal ageing. An improvement of the OSC is manifested after repetitive redox cycles, even though textural characterization shows that reduction/oxidation processes induce sintering of the crystallites.     

Toward the rational design of functionalized pentacenes: reduction of the impact of functionalization on the reorganization energy.

For the widely studied high-carrier-mobility species, pentacene, it is found that perfluorination turned it into an n-type organic field-effect transistor (OFET), but doubled the internal reorganization energy (lambda) of the electron/hole hopping. Here, Cl- and N-functionalized pentacenes are designed to test two strategies that may reduce the impact of functionalization on lambda. Calculation results show that the strategies are feasible. Moreover, combined with crystal-structure data of Cl- and N-functionalized aromatic compounds, it is concluded that compared to fluorination, the presence of Cl and N atoms in pentacene not only reduces the influence of functionalization on lambda and affords a larger window for tuning HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies, but also provides the opportunity to promote pi-stacked structures through ClCl and C--HN interactions.     

生物体系中电子转移机理的理论研究Ⅰ: 一种计算电子转移 的方法及在螺环化 合物中的应用

应用“相应轨道变换”和“广义”密度矩阵的方法,向MOPAC程序包中加入了新的功能,使其能处理电子转移反应中的部分参数.然后用此程序包中AMI方法对具有螺环结构的分子进行处理,计算了化合物在不同外加电场强度下的势能面、反应热ΔE,重组能λ及电子转移矩阵元V_(AB),结果表明,λ,V_(AB)受外加电场的影响较小,而ΔE则与之成正比.对标题化合物1的计算结果也同ab initio法的结果进行了比较,发现其变化趋势完全一致,这说明本方法在计算电子转移方面是可靠的.与ab initio方法相比,本程序不仅适用于计算较大体系(如生物大分子),而且还具有速度快,耗时少的优点.     

A Joint Theoretical and Experimental Study of the Behavior of the DIDS Inhibitor and its Derivatives

4,4′‐Diisothiocyanostilbene‐2,2′‐disulfonic acid (DIDS) is a well‐known ion‐exchange inhibitor targeting cardiac functions and indirectly impeding both radio‐ and chemo‐resistance. A joint computational and experimental study is presented to provide deeper insights into DIDS and other members of this family of compounds. To this end, we applied state‐of‐the‐art density functional theory (DFT) and time‐dependent DFT methods, in addition to measuring the optical properties. The experimental data show that such compounds are highly sensitive to their environment and that the optical properties change within as little time as 7 h. However, the optical properties of DIDS are similar in various acidic/basic environments, which were confirmed by pK_a computations on both cis and trans isomers. The protonation analysis also highlights that the singly protonated form of DIDS behaves like a proton sponge compound. The experimentally observed redshift that can be seen when going from water to DMSO was reproduced solely by using the solvation model based on density, although the polarization continuum model and implicit/explicit hybrid schemes were also tested. The characteristic broadening of the absorption peak in water and the vibronic fine structure in DMSO were also reproduced thanks to vibronic coupling simulations associated with the solvent reorganization energy. For other stilbene derivatives, a correlation is found between the maximum absorption wavelength and the Hammett parameters.     

Hybrid Functional and Plane Waves based Ab Initio Molecular Dynamics Study of the Aqueous Fe2+/Fe3+ Redox Reaction**

Kohn-Sham density functional theory and plane wave basis set based ab initio molecular dynamics (AIMD) simulation is a powerful tool for studying complex reactions in solutions, such as electron transfer (ET) reactions involving Fe²⁺/Fe³⁺ ions in water. In most cases, such simulations are performed using density functionals at the level of Generalized Gradient Approximation (GGA). The challenge in modelling ET reactions is the poor quality of GGA functionals in predicting properties of such open-shell systems due to the inevitable self-interaction error (SIE). While hybrid functionals can minimize SIE, standard plane-wave based AIMD at that level of theory is typically 150 times slower than GGA for systems containing ∼100 atoms. Among several approaches reported to speed-up AIMD simulations with hybrid functionals, the noise-stabilized MD (NSMD) procedure, together with the use of localized orbitals to compute the required exchange integrals, is an attractive option. In this work, we demonstrate the application of the NSMD approach for studying the Fe²⁺/Fe³⁺ redox reaction in water. It is shown here that long AIMD trajectories at the level of hybrid density functionals can be obtained using this approach. Redox properties of the aqueous Fe²⁺/Fe³⁺ system computed from these simulations are compared with the available experimental data for validation.     

MALDI-ToF investigation of furanic polymer foams before and after carbonization: Aromatic rearrangement and surviving furanic structures

A MALDI-ToF investigation of furanic foams before and after carbonization at 900 °C has been carried out. Comparison between MALDI-ToF spectra, before and after carbonization, shows how original building blocks of the network are modified, rearranged or survived during the process. Even if most of the constituents are transformed to more stable aromatic structures, some of the starting compounds resist intact the process of carbonization. The results appeared to indicate that some furanic oligomers are particularly stable and unaffected by carbonisation. The hypothesis that these may be cyclic furanic oligomers has been checked by molecular mechanics calculation of their relative energies.     

Thermodynamics for nonequilibrium solvation and numerical evaluation of solvent reorganization energy

This work presents a thermodynamic method for treating nonequilibrium solvation. By imposing an extra electric field onto the nonequilibrium solvation system, a virtual constrained equilibrium state is prepared. In this way, the free energy difference between the real nonequilibrium state and the con-strained equilibrium one is simply the potential energy of the nonequilibrium polarization in the extra electronic field, according to thermodynamics. Further, new expressions of nonequilibrium solvation energy and solvent reorganization energy have been formulated. Analysis shows that the present formulations will give a value of reorganization energy about one half of the traditional Marcus theory in polar solvents, thus the explanation on why the traditional theory tends to overestimate this quantity has been found out. For the purpose of numerical determination of solvent reorganization energy, we have modified Gamess program on the basis of dielectric polarizable continuum model. Applying the procedure to the well-investigated intramolecular electron transfer in biphenyl-androstane-naphthyl and biphenyl-androstane-phenanthryl systems, the numerical results of solvent reorganization energy have been found to be in good agreement with the experimental fittings.     

A combined experimental and theoretical study on photoinduced intramolecular charge transfer in trans-ethyl p-(dimethylamino)cinamate

Intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino)cinamate (EDAC) in various solvents has been studied by steady-state absorption and emission, picosecond time-resolved fluorescence spectroscopy and femtosecond transient absorption experiments as well as time-dependent density functional theory (TDDFT). Large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The energy for 0,0 transition (ν_0,0) for EDAC shows very good linear correlation with static solvent dielectric property. The relaxation dynamics of EDAC in the excited state can be effectively described by a “three state” model where, the locally excited (LE) state converts into the ICT state within 350 ± 100 fs. A combination of solvent reorganization and intramolecular vibrational relaxation within 0.5–6 ps populates the relaxed ICT state which undergoes fluorescence decay within few tens to hundreds of picoseconds.     

Intramolecular reorganization 2. The Brønsted correlation for a series of gas-phase reactions of deprotonation of <Emphasis Type="Italic">para</Emphasis>-substituted toluene derivatives with the CH<Subscript>2</Subscript>CN<Superscript>−</Superscript> anion

A proton-transfer model proposed earlier that includes equalization of energies of the reactant and product by an intramolecular mechanism was used to study gas-phase reactions of deprotonation of para-substituted toluene derivatives (substituents were NH₂, OH, CH₃, H, Cl, NC, CN, and NO₂) with the CH₂CN^? anion. The energy parameters of the reactions were determined from ab initio calculations. The Brønsted correlation based on the results obtained was analyzed in the framework of conventional quantum chemical formalism (the Marcus equation). The problem of disbalance of the changes in the geometry of the activated complex relative to its position on the reaction coordinate was considered taking some geometric parameters of the system as examples.     

有机共轭体系电子转移反应的溶剂重组能

应用Marcus双球模型计算溶剂重组能λs时,在AM1法优化给受体几何构型基础上,提出了共轭体系电子云分布的扁球模型,并用统计的方法求出了rD/A.同时依照Miller等的处理办法,结合其他理论及实验证据将电子转移交叉反应中联苯分子的扭转能计入溶剂重组能λs中,从而用实验速率常数拟合出含扭转能的λs值.此实验拟合值与扁球法得到的λs计算值吻合得很好.通过比较理论值与实验值,发现了给受体间距的大小、受体分子的变化、溶剂的不同对λs计算值相对λs实验值的偏差的影响,直接证实了电子给受体的耦合作用,溶剂分子参与的超交换电子转移及溶质溶剂分子表面相互作用等量子因素造成的实际反应体系对溶剂经典连续介质模型的偏离.