Structure Sensitivity of CO Dissociation on Rh Surfaces

Using periodic self-consistent density functional calculations it is shown that the barrier for CO dissociation is 120 kJ/mol lower on the stepped Rh(211) surface than on the close-packed Rh(111) surface. The stepped surface binds molecular CO and the dissociation products more strongly than the flat surface, but the effect is considerably weaker than the effect of surface structure on the dissociation barrier. Our findings are compared with available experimental data, and the consequences for CO activation in methanation and Fischer–Tropsch reactions are discussed.     

Coherent Vibrational Wave Packet Dynamics in Femtosecond Laser Excitation of Diatomic Molecules

A scheme is discussed for real-time observation of a finite vibrational motion of diatomic molecules. Observation schemes based on the Franck-Condon principle, i.e., the “persistence” of a coordinate wave packet in an ultrashort excitation, are proposed.     

Theory of Diatomic Photodissociation to Atomic Hyperfine Structure States

We present a general theory of the photodissociation of diatomic molecules to the hyperfine sublevels of open-shell atomic fragments. The hyperfine interactions affect the fragment hyperfine sublevel populations, polarizations, etc., either when the fragment atomic hyperfine sublevels are optically resolved, when resonances possess hyperfine splittings, or both. The case of hyperfine splittings in resonances is of particular interest for states whose principle parentage is singlet, but which exhibit hyperfine splitting due to nonadiabatic mixing with close-lying triplet states. Such resonances have been observed in the photodissociation of SiH⁺ (Sarre, P.J. et al., Phil. Trans. R. Soc. London, 1988, A324 : 233). We also show how our nonadiabatic theory in the presence of hyperfine interactions reduces to the general theory of diatomic photodissociation to open-shell atoms of Singer et al. (J. Chem. Phys., 1983, 79 : 6060) when resonance hyperfine splittings or hyperfine structure states of the fragments are not resolved in particular experiments.     

Tailoring Small Molecules for an Allosteric Site on Procaspase‐6

Although they represent attractive therapeutic targets, caspases have so far proven recalcitrant to the development of drugs targeting the active site. Allosteric modulation of caspase activity is an alternate strategy that potentially avoids the need for anionic and electrophilic functionality present in most active‐site inhibitors. Caspase‐6 has been implicated in neurodegenerative disease, including Huntington’s and Alzheimer’s diseases. Herein we describe a fragment‐based lead discovery effort focused on caspase‐6 in its active and zymogen forms. Fragments were identified for procaspase‐6 using surface plasmon resonance methods and subsequently shown by X‐ray crystallography to bind a putative allosteric site at the dimer interface. A fragment‐merging strategy was employed to produce nanomolar‐affinity ligands that contact residues in the L2 loop at the dimer interface, significantly stabilizing procaspase‐6. Because rearrangement of the L2 loop is required for caspase‐6 activation, our results suggest a strategy for the allosteric control of caspase activation with drug‐like small molecules.     

Site Selective Detection of Methane Dissociation on Stepped Pt Surfaces

Topics in Catalysis - We report a combined experimental and theoretical study comparing methane dissociation on three different platinum surfaces Pt(111), Pt(211), and...     

Surface Force Field as a Factor Promoting the Dissociation of X2 Molecules

The dissociation of X₂ molecules in the surface layer of a condensed phase is governed by the surface-force energy, which is positive and arises from the interaction of particles of different kinds.     

Optical Properties of Diatomic Glasses

The ability of elements to form glasses, the leading part played by the elements of Group VI (O, S, Se, and Te), and the possible influence of the elements of Group VII (F, Cl, Br, and I) are discussed. New glasses suggested by previous work were melted and the refractive index ( n ) and coefficient of dispersion ( v ) of some of them were measured. Inspection of the n, v plots of oxide, sulfide, selenide, and telluride glasses shows that the area corresponding to them extends toward high values of refractive index ( n _max= 5.3) and low values of dispersion coefficient ( v _min=4).     

Dissociation Energies of S2, SO,Te2, SeO and P2 Molecules

The ground state dissociation energies of S₂, SO, Te₂, SeO and P₂ molecules have been estimated by fitting the Szöke and Baitz electronegativity potential energy curves to the experimental RKRV curves. The estimates of dissociation energies obtained have been compared with earlier calculations.     

Molecular Glue for RNA: Regulating RNA Structure and Function through Synthetic RNA Binding Molecules

We introduce the concept of molecular glues for RNA, in which specific RNA-binding small molecules induce designed structural changes in target functional RNAs, resulting in modulation of the functions. (Z)-NCTS is an RNA-mismatch-binding small molecule that recognizes 5′-r(XGG)-3′/5′-r(XGG)-3′ sequences (X=U or A) and acts as a molecular glue for RNA. The binding of (Z)-NCTS brings two distinct 5′-r(XGG)-3′ domains into contact with each other, and this can result in higher-order structural changes of target RNAs. We applied (Z)-NCTS to induce the formation of a proposed tertiary structure of a ribozyme together with activation of RNA-cleaving ability. The concept of a molecular glue could inspire new small-molecule-based strategies for regulating biological functions: a synthetic small molecule targeting functional RNAs could regulate the RNA structure and function.     

Relationships between Impact Sensitivity and Molecular Electronic Structure

A very simple calculational procedure is used to investigate the electronic structure of several classes of organic explosives (polynitroaliphatics with trinitromethyl or fluorodinitromethyl groups, polynitroaromatics, polynitroaliphatic nitramines and aliphatic nitrate esters). The method utilizes a bond electronegativity equalization principle. It is shown that atom charges, bond electronegativities and charge transferred in a bond are all potential indicator quantities for predicting impact sensitivity trends for the various classes. Specifically it is shown that charge transferred to the nitro group through a trigger linkage (C NO₂, N NO₂, O NO₂) can classify and correlate impact sensitivity trends in the compounds studied here. The results also indicate that electronic structure is not sufficient by itself to understand the phenomenon. This work in conjunction with previous work⁽¹⁾ shows that both a global quantity (i.e. related to the whole molecule) and a local quantity (i.e. related to the trigger linkage) are needed to understand impact sensitivity behavior.     

加强无机化学教学内容的针对性

根据我院新设应用化学本科专业的学科特点和人才培养目标,我们对大一开设的无机化学教学内容进行了调整,增加了实用性、针对性和目的性,使无机化学教学改革与应用化学本科专业建设同步发展。本文就如何加强我院无机化学教学内容针对性的具体实施及意义进行了相关的思考。     

External Effects on the Structure and Dynamics of Molecules in Oriented Polyolefins

Abstract

Oriented polyethylene samples are investigated mechanically, thermally and by oxidation. A complicated character of changes in mobility of molecules on static loading of oriented polyolefins is studied. The influence of deformation, stretching, molecular mass and its distribution on the value and sign of this change is found. The regularities of structural changes in the course of ozone oxidation are revealed. It is shown that the initial stage of oxidation is followed by a considerable improvement of mechanical properties. At a greater extent of oxidation the dependence of molecular mobility on reversible deformation of highly oriented samples of medium molecular weight (MW) and narrow molecular weight distribution (MWD) is reversed. A relaxational transition is observed over the temperature range of from 40°C to 60°C for polyethylene and from 60°C to 70°C for polypropylene. After ozone oxidation at a temperature above 90°C and oxidation under load and subsequent annealing (at the temperature of relaxational) transition the latter is not observed.     

无机化学中原子结构与分子结构的教学探讨

原子结构及分子结构是学生在无机化学学习中的较难理解的章节.本文根据教师在原子结构教学中的学生容易错误理解的问题进行了分析,对问题的解决提出了自己的看法.在无机化学的讲授中,还要注重科学精神的培养.     

Molecules for charge-based information storage

The inexorable drive to miniaturize information storage and processing devices has fueled the dreams of scientists pursuing molecular electronics: researchers in the field envisage exquisitely tailored molecular materials fulfilling the functions now carried out by semiconductors. A bottom-up assembly of such all-molecular devices would complement, if not supplant, the present top-down lithographic procedures of modern semiconductor fabrication. Short of these grand aspirations, a more near-term objective is to construct hybrid architectures wherein molecules are incorporated in semiconductor-based devices. Such a combined approach exploits the advantages of molecules for selected device functions while retaining the well-developed lithographic approaches for fabrication of the overall chip. In this Account, we survey more than a decade of results from our research programs to employ porphyrin molecules as charge-storage elements in hybrid semiconductor-molecular dynamic random access memory. Porphyrins are attractive for a variety of reasons: they meet the stability criteria for use in real-world applications, they are readily prepared and tailored synthetically, they undergo read-write processes at low potential, and they store charge for extended periods (up to minutes) in the absence of applied potential. Porphyrins typically exhibit two cationic redox states. Molecular architectures with greater than two cationic redox states are achieved by combinations of porphyrins in a variety of structures (for example, dyads, wherein the porphyrins have distinct potentials, triple deckers, and dyads of triple deckers). The incorporation of porphyrins in hybrid architectures has also required diverse tethers (alkyl, alkenyl, alkynyl, aryl, and combinations thereof) and attachment groups (alcohol, thiol, selenol, phosphonate, and hydrocarbon) for linkage to a variety of surfaces (Au, Si, SiO(2), TiN, Ge, and so forth). The porphyrins as monolayers exhibit high charge density and are robust to high-temperature excursions (400 °C for 30 min) under inert atmosphere conditions. Even higher charge densities, which are invaluable for device applications, were achieved by in situ formation of porphyrin polymers or by stepwise growth of porphyrin-imide oligomers. The various molecular architectures have been investigated by diverse surface characterization methods, including ellipsometry, atomic force microscopy, FTIR spectroscopy, and X-ray photoelectron spectroscopy, as well as a variety of electrochemical methods. These studies have further revealed that the porphyrin layers are robust under conditions of deposition of a top metal contact. The results to date indicate the superior features of selected molecular architectures for molecular electronics applications. The near-term utilization of such materials depends on further work for appropriate integration in semiconductor-based devices, whereas ultimate adoption may depend on advances that remain far afield, such as the development of fully bottom-up assembly processes.     

Structure Sensitivity of the Catalytic Oxidation of Ethene by Silver

The partial oxidation of ethene to produce ethene oxide using silver catalysts has received considerable attention because it is the basis of a several billion dollar per year industry. It is also of fundamental interest because silver is the only metal to catalyze the production of ethene oxide in economic yields. It is not surprising to find that the mechanism of the catalytic reaction and the reactor engineering associated with the commercial process have been extensively reviewed.     

Structure Sensitivity of the Catalytic Oxidation of Ethene by Silver

The partial oxidation of ethene to produce ethene oxide using silver catalysts has received considerable attention because it is the basis of a several billion dollar per year industry. It is also of fundamental interest because silver is the only metal to catalyze the production of ethene oxide in economic yields. It is not surprising to find that the mechanism of the catalytic reaction and the reactor engineering associated with the commercial process have been extensively reviewed.     

受限于碳纳米管中水分子微观结构的分子动力学模拟研究

利用分子动力学模拟研究受限于不同管径中水分子的微观结构,改变温度,做出受限水分子的径向分布函数图,并对比说明。通过做水分子在碳纳米管内的均方位移与时间关系图,利用Einstein法算出不同管径中水分子的扩散系数,与利用Knudsen扩散公式计算出的水分子的扩散系数进行比较。