Diels–Alder modification of poly(ethylene terephthalate‐co‐anthracene‐2,6‐carboxylate) with N‐substituted maleimides

Dimethyl 2,6‐anthracene dicarboxylate is used as a comonomer in the synthesis of functional copolymers that are subject to modification with Diels–Alder reactions. The formation of poly(ethylene terephthalate‐co‐2,6‐anthracenate), containing less than 20 mol % of the anthracene‐2,6‐dicarboxylate structural units, provides materials that are tractable and soluble. The anthracene units of the copolymers undergo Diels–Alder reactions with N‐substituted maleimides. The grafting of N‐alkylmaleimides affords soluble, hydrophobic polymers, whereas grafting with maleimide‐terminated poly(ethylene glycol) affords hydrophilic polymers. Because this reaction proceeds below the melting point of the copolymers, the procedure can be applied to thin films, whereby the surface properties are modified. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3256–3263, 2002     

Zn(Ⅱ)在TiO2表面上的微观吸附模式研究

用延展X射线吸收精细结构(EXAFS)技术并结合密度泛函理论(DFT)研究了Zn(Ⅱ)在锐钛型TiO2表面上微观吸附结构。EXAFS结果表明, Zn(Ⅱ)在吸附时由自由水合状态下的Zn—O六配位八面体结构向四配位四面体结构转化, 中心Zn原子的第二配位层存在两种不同的Zn—Ti距离(R1=0.371和R2=0.332 nm). 用DFT方法对四配位水合Zn离子在簇Ti2O11H14上进行优化后发现, 四配位的Zn—O平均距离为0.200 nm; 外层Zn—Ti结合存在两种稳定的吸附模式: 单角吸附模式和更加稳定的双角吸附模式, 其Zn—Ti距离分别为0.369和0.335 nm. EXAFS结果与DFT计算结果吻合, 说明Zn(Ⅱ)在锐钛型TiO2表面上存在不同的亚稳平衡态吸附结构.     

High-sensitivity x-ray absorption fine structure investigation of arsenic shallow implant in silicon

High-sensitivity fluorescence-yield x-ray absorption fine structure spectroscopy (XAFS) has been investigated to characterize the local structure around arsenic shallow implant in silicon. Fluorescence-yield XAFS experiments were performed using a high-brilliance synchrotron radiation beam from an in-vacuum-type undulator in a third-generation light source. In addition to investigating the efficiency of high-brilliance undulator x-rays during the fluorescence-yield XAFS measurements, we compared the analytical performance of both the wavelength dispersive spectrometer (WDS) and the energy dispersive spectrometer (EDS) based on the silicon drift detector (SDD). It was confirmed that the WDS reduces the influence of scattering background due to the high spectral resolution. Another advantage of the WDS is high counting rate measurements. It was found that fluorescence-yield XAFS using undulator x-rays combined with the WDS permits superior sensitivity measurements.     

两态反应Ni2+与c-C6H12的机理及自旋-轨道耦合研究

在密度泛函理论的B3LYP方法下, 对两态反应Ni₂⁺与环己烷体系进行了较为系统的研究. 结果表明, 反应分别在第一个氢迁移(⁴IM1→⁴TS1/2), 第三个氢迁移(⁴TS15/16→⁴IM15)以及 翻转过程(⁴IM5→⁴TS5/6, ²TS11/12→²IM12)发生了二、四重态势能面的交叉, 本文运用内禀反应坐标单点垂直激发计算的方法得到势能面大致的交叉点(CP), 进一步利用Crossing2004程序获得精确的最低能量交叉点(MECP). 对MECP附近的自旋轨道耦合(SOC)常数进行了计算. MECP1～MECP4处的SOC值分别为318.01, 396.89, 268.74和306.67 cm^-1. 较大的SOC值说明不同势能面间发生了有效地跃迁并使反应沿着最低反应通道进行. 对反应通道的研究发现, 反应中同面脱氢是主要反应通道. 异面脱氢由于翻转过程中决速步骤势垒为33 kcal/mol(吸热3 kcal/mol), 只生成少量的异面脱氢产物. 计算结果解释了实验现象.     

A self‐guided search for good local minima of the sum‐of‐squared‐error in nonlinear least squares regression

Hard modeling of nonlinear chemical or biological systems is highly relevant as a model function together with values for model parameters provides insights in the systems' functionalities. Deriving values for said model parameters via nonlinear regression, however, is challenging as usually one of the numerous local minima of the sum‐of‐squared errors (SSEs) is determined; furthermore, for different starting points, different minima may be found. Thus, nonlinear regression is prone to low accuracy and low reproducibility. Therefore, there is a need for a generally applicable, automated initialization of nonlinear least squares algorithms, which reaches a good, reproducible solution after spending a reasonable computation time probing the SSE‐hypersurface. For this purpose, a three‐step methodology is presented in this study. First, the SSE‐hypersurface is randomly probed in order to estimate probability density functions of initial model parameter that generally lead to an accurate fit solution. Second, these probability density functions then guide a high‐resolution sampling of the SSE‐hypersurface. This second probing focuses on those model parameter ranges that are likely to produce a low SSE. As the probing continues, the most appropriate initial guess is retained and eventually utilized in a subsequent nonlinear regression. It is shown that this “guided random search” derives considerably better regression solutions than linearization of model functions, which has so far been considered the best‐case scenario. Examples from infrared spectroscopy, cell culture monitoring, reaction kinetics, and image analyses demonstrate the broad and successful applicability of this novel method. Copyright © 2014 John Wiley & Sons, Ltd.     

Factors Affecting the Branching Ratio of Photodissociation: Thiophenol Studied through Quantum Wavepacket Dynamics

The photodissociation dynamics of thiophenol (PhSH) excited to the 1¹ππ* state was investigated by time‐dependent quantum wavepacket propagation within two‐dimensional (2D) space consisting of the S?H bond and ?SH torsion. We systematically studied the dependence of the branching ratio ${\left( {{{{\rm{\tilde A}}} \mathord{\left/ {\vphantom {{{\rm{\tilde A}}} {{\rm{\tilde X}}}}} \right. \kern-\nulldelimiterspace} {{\rm{\tilde X}}}}} \right)}$ between the two electronic states of the phenylthiyl radical (PhS^.) on several factors of the 2D potential energy surfaces (PESs). The effect of a reduced initial barrier to the first ππ*/πσ* conical intersection (CI) was found to be marginal, whereas the effects of a reduced torsional barrier of ?SH on the excited ππ* state and the mitigated slope of the πσ* PES between the first (ππ*/πσ*) and the second (πσ*/S₀) CIs were noticeable. The effect of the slope on the branching ratio has never been previously noticed. It was shown that the branching ratio can be sufficiently above unity without pre‐excitation of the torsion mode of ?SH, which has been assumed so far.     

Antibacterial poly(ethylene terephthalate) surfaces obtained from thymyl methacrylate polymerization

Thymol, an antibacterial agent was used for the preparation of a methacrylic monomer. The conventional and atom transfer radical (ATRP) polymerizations of this monomer were studied using different conditions. Then, the functionalization of poly(ethylene terephthalate) (PET) films by “grafting from” ATRP using this monomer was investigated. In this aim, a three steps procedure was developed. The surfaces were first treated by NH₃ plasma treatment to incorporate primary amino functions. Then, in a second step, ATRP initiator was grafted by reaction with bromoisobutyryl bromide. Surface initiated ATRP of thymyl methacrylate was performed in solution in the presence of a sacrificial initiator. The efficiency of these reactions was confirmed by X‐ray photoelectron spectroscopy. Wetting properties and surface energy were found to vary systematically depending to the type of functionalization and grafting. The poly(thymyl methacrylate)‐grafted PET surfaces exhibit resistance to bacterial adhesion toward Pseudomonas aeruginosa, Listeria monocytogenes, and Staphylococcus aureus strains. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1975–1985     

Silicene,a promising new 2D material

Silicene is emerging as a two-dimensional material with very attractive electronic properties for a wide range of applications; it is a particularly promising material for nano-electronics in silicon-based technology. Over the last decade, the existence and stability of silicene has been the subject of much debate. Theoretical studies were the first to predict a puckered honeycomb structure with electronic properties resembling those of graphene. Though these studies were for free-standing silicene, experimental fabrication of silicene has been achieved so far only through epitaxial growth on crystalline surfaces. Indeed, it was only in 2010 that researchers presented the first experimental evidence of the formation of silicene on Ag(1 1 0) and Ag(1 1 1), which has launched silicene in a similar way to graphene. This very active field has naturally led to the recent growth of silicene on Ir(1 1 1), ZrB₂(0 0 0 1) and Au(1 1 0) substrates. However, the electronic properties of epitaxially grown silicene on metal surfaces are influenced by the strong silicene–metal interactions. This has prompted experimental studies of the growth of multi-layer silicene, though the nature of its “silicene” structure remains questionable. Of course, like graphene, synthesizing free-standing silicene represents the ultimate challenge. A first step towards this has been reported recently through chemical exfoliation from calcium disilicide (CaSi₂). In this review, we discuss the experimental and theoretical studies of silicene performed to date. Special attention is given to different experimental studies of the electronic properties of silicene on metal substrates. New avenues for the growth of silicene on other substrates with different chemical characteristics are presented along with foreseeable applications such as nano-devices and novel batteries.     

Optimal cloud use of quartic force fields: The first purely commercial cloud computing based study for rovibrational analysis of SiCH−

Commercial cloud computing (CCC) has the promise of an untold number of computing nodes available for the researcher as long as he or she has the financial means to absorb these costs and the administrative skills necessary to effectively utilize the resources. The key is finding how to maximize parallelization for a minimum of monetary and management costs. Previous work has shown that CCC resources are viable for use on large numbers of small‐to‐medium sized quantum chemical computations. Composite energy quartic force fields (QFFs) are a highly‐attractive platform for subsequent testing of CCC resources to find the proper balance between time savings of the cloud versus monetary expenditure. Use of this type of potential energy surface has lead to highly‐accurate rovibrational data in earlier work. QFFs use large numbers of stand‐alone energies that have to be computed for various molecular geometries. At each geometry, different methods and/or basis sets are used to efficiently generate accurate representations of the nuclear potential. For this initial study, the small molecular anion, SiCH^? of interest in astrochemistry, is chosen for analysis as it can be done cheaply on the cloud while still providing insight into the nature of CCC usage. Additionally, no rovibrational data exists for this molecule making it the first molecule quantum chemically computed purely via CCC tools. © 2015 Wiley Periodicals, Inc.