Reaction of thiocyanates with ironcyanogen compounds of silver

Silver fenocyanide as well as Silver ferricyanide are converted into silver thiocyanate by treating with thiocyanate ions, while feirocyanide ions or ferricyanide ions are formed at the same time. Silver ferrocyanide as well as silver ferricyanide are dissolved by solutions of thiocynates of higher concentrations.     

Structure and growth of self-assembling monolayers

The structural phases and the growth of self-assembled monolayers (SAMs) are reviewed from a surface science perspective, with emphasis on simple model systems. The concept of self-assembly is explained, and different self-assembling materials are briefly discussed. A summary of the techniques used for the study of SAMs is given. Different general scenarios for structures obtained by self-assembly are described. Thiols on Au(1 1 1) surfaces are used as an archetypal system to investigate in detail the structural phase diagram as a function of temperature and coverage, the specific structural features on a molecular level, and the effect of changes of the molecular backbone and the end group on the structure of the SAM. Temperature effects including phase transitions are discussed. Concepts for the preparation of more complex structures such as multi-component SAMs, laterally structured SAMs, and heterostructures, also with inorganic materials, are outlined. The growth and ways to control it are discussed in detail. Solution and gas phase deposition and the impact of various parameters such as temperature, concentration (in solution) or partial pressure (in the gas phase) are described. The kinetics and the energetics of self-assembly are analyzed. Several more complex issues of the film formation process including non-equilibrium issues are discussed. Some general conclusions are drawn concerning the impact of various molecular features on the growth behavior and concerning the relationship between growth and structural phase diagram. Finally, the potential of self-assembly as a route for the preparation of monolayers with pre-designed properties and SAMs as building blocks in heterostructures as well as application strategies are discussed.     

An Overview of the Antimicrobial Properties of Lignocellulosic Materials

Pathogenic microbes are a major source of health and environmental problems, mostly due to their easy proliferation on most surfaces. Currently, new classes of antimicrobial agents are under development to prevent microbial adhesion and biofilm formation. However, they are mostly from synthetic origin and present several disadvantages. The use of natural biopolymers such as cellulose, hemicellulose, and lignin, derived from lignocellulosic materials as antimicrobial agents has a promising potential. Lignocellulosic materials are one of the most abundant natural materials from renewable sources, and they present attractive characteristics, such as low density and biodegradability, are low-cost, high availability, and environmentally friendly. This review aims to provide new insights into the current usage and potential of lignocellulosic materials (biopolymer and fibers) as antimicrobial materials, highlighting their future application as a novel drug-free antimicrobial polymer.     

Effect of phosphate activating group on oligonucleotide formation on montmorillonite: the regioselective formation of 3',5'-linked oligoadenylates

The effects of amine structure on the montmorillonite-catalyzed oligomerization of the 5'-phosphoramidates of adenosine are investigated. 4-Aminopyridine derivatives yielded oligoadenylates as long as dodecamers with a regioselectivity for 3',5'-phosphodiester bond formation averaging 88%. Linear and cyclic oligomers are obtained and no A5'ppA-containing products are detected. Oligomers as long as the hexanucleotide are obtained using 2-aminobenzimidazole as the activating group. A predominance of pA2'pA is detected in the dimer fraction along with cyclic 3',5'-trimer; no A5'ppA-containing oligomers were detected. Little or no oligomer formation was observed when morpholine, piperidine, pyrazole, 1,2,4-triazole, and 2-pyridone are used as phosphate-activating groups. The effects of the structure of the phosphate activating group on the oligomer structure and chain lengths are discussed.     

A generalized formalism of the quantum theory of valence and bonding

General definitions of valence, degree of bonding between pairs of atoms, and atomic anisotropy and reactivity are given. They can be applied to closed- or open-shell molecular wave functions (in the semiempirical, quasi or full ab initio SCF levels), as well as to GVB ones. The properties and usefulness of the definitions are discussed as well as their relation to former empirical notions. Examples of their application are also reported.     

The use of solid sorbents for direct accumulation of organic compounds from water matrices–a review of solid-phase extraction techniques

The main principles of solid-phase extraction techniques are reviewed in this paper. Various solid sorbents can be used as a suitable trap for direct accumulation of organic compounds from aqueous solutions. The trapped analytes can be desorbed by elution with suitably chosen liquid phases. These preconcentration procedures can be considered as low performance liquid chromatography and the efficiency of the procedure can thus be related to the retention characteristics of the preconcentration column. The main sorbents used for trace enrichment purposes are also reviewed. Besides, the concise methodology, sample storage, and automation are discussed. The advantages of solid phase extraction as compared to liquid-liquid extraction are given as well as some drawbacks of this method.     

A Chemical History of Polycyclic Musks

Musk odorants are ubiquitous in fine perfumery as well as household products, and are divided into four main families, the nitromusks, the macrocyclic musks, the polycyclic aromatic musks, and the alicyclic musks, following their order of appearance on the perfumery market. This article presents the scientific and industrial adventures during the discovery of the seven commercial polycyclic musks, which invigorated the aroma chemistry corporations during the second half of the 20th century, resulting in relentless competition. Research and development strategies are exposed, and reactivity, analytical, mechanistic, and structure–activity relationships aspects are discussed as well as some biographical elements of the main scientific actors, and some fine perfumery examples are given as illustrations of their use.     

A perturbative calculation of the rovibrational energy levels of methane

The rovibrational energy levels of methane are determined from a quartic ab initio potential energy force field where the expansion coordinates are the Morse coordinates for the stretches and extension coordinates for the bends. Energies are calculated using canonical Van Vleck perturbation theory. Results are obtained for both rotation-vibration Hamiltonians expressed as functions of curvilinear and rectilinear normal coordinates. Second, fourth, and sixth order curvilinear results are compared with experimental results, and fourth order results for the rectilinear and curvilinear Hamiltonian are compared to each other. The calculated rovibrational levels are in good agreement with the experimental values for low J levels. The calculated rotational level splittings are in even better agreement with the experiment. In particular, the ground state tetrahedral splittings, which are as small as 10(-4) cm(-1), are well reproduced by our calculations at sixth order.     

Reactions of Amidoximes with Metal-Activated Nitriles

Metal-mediated reactions of amidoximes with nitrile ligands are discussed and recent works of the author are considered to allow the reader to better understand the amidoxime reactivity patterns. General routes of activation of amidoxime and nitrile substrates in the studied reactions are considered. Reactions employing amidoximes as HO- and HN-nucleophiles, as well as reactions of amidoximes with nitrile ligands leading to heterocyclic systems are discussed.     

环糊精衍生物气相色谱手性固定相研究进展

评述近年环糊精衍生物气相色谱手性固定相的研究进展,对环糊精衍生物进行分类并总结了近年来其在GC手性分离上的应用,介绍环糊精衍生物的手性分离机制及纯度问题进展,展望环糊精衍生物作GC手性固定相的应用前景。     

Theory of main chain nematic polymers with spacers of varying degree of flexibility

Main chain liquid crystal polymers are modelled as either worms or jointed rods. In reality they are composed of mesogenic units (rods) linked by spacers with varying degrees of flexibility. We present a molecular model to describe non-homogeneous nematic polymers. The model takes account of molecular parameters, such as the lengths of the mesogenic group and the spacer units, and the interactions between them. The spacers are found to have an order differing from the mesogenic units. If the spacer is not very long and thus in effect is inflexible, one end of the spacer can retain to some extent the orientation of the other end, allowing orientational correlation between spacers mediated by the intermediate mesogenic unit. This is important in giving the chain a global rod-like behaviour as the nematic field becomes strong or the temperature low. The nematic order of the two components (mesogens and spacers), the nematic-isotropic transition as well as the latent entropy are examined. Furthermore, the anisotropic conformations of the polymers are investigated, which show either rod-like or random walk behaviour. Comparison of our results with experiment is found to be satisfactory.     

Reticular chemistry of metal-organic polyhedra

Metal-organic polyhedra (MOPs), are discrete metal-organic molecular assemblies. They are useful as host molecules that can provide tailorable internal volume in terms of metrics, functionality, and active metal sites. As a result, these materials are potentially useful for a variety of applications, such as highly selective guest inclusion and gas storage, and as nanoscale reaction vessels. This review identifies the nine most important polyhedra, and describes the design principles for the five polyhedra most likely to result from the assembly of secondary building units, and provides examples of these shapes that are known as metal-organic crystals.     

Paradigms and Paradoxes: Aspects of the Energetics of Carboxylic Acids and Their Anhydrides

Making use of the enthalpies of formation of the well-established acetic acid and acetic anhydride, the energetics of other carboxylic acid anhydrides (with four or fewer carbons) are discussed. Some of these species are also well known, such as succinic and maleic anhydride. Others are less well known, such as ketene and carbon suboxide and even diatomic carbon and malonic anhydride. Still others are more evasive, such as the classical anhydrides of formic and oxalic acid.     

Analysis of molecular orbital wave functions in terms of valence bond functions for molecular fragments. I. Theory

A method of expansion of molecular orbital wave functions into valence bond (VB ) functions is extended to molecular fragments. The wave function is projected onto a basis of mixed determinants, involving molecular orbitals as well as fragment atomic orbitals, and is further expressed as a linear combination of VB functions, characteristic of structural formulas of the fragment but whose remaining bonds are frozen. Structural weights for the fragment are deduced from this expression. Delocalized molecular orbitals are used as a startpoint, as they are after an ordinary SCF calculation. Wave functions of medium-sized molecules may be analyzed with reasonable storage requirements in a computer.     

超声技术在纳米材料制备中的应用

对超声技术在纳米材料制备中的应用与研究进展作了比较全面的综述,着重介绍了与超声有关的纳米材料制备方法,包括雪声雾化－热分解法,金属有机物超声热分解法,化学沉淀法和声电化学法,并就这些方法中声化作用的机理,特点和影响因素进行了讨论。     

新型金属-TMA聚合物纳米孔材料的研究进展

本文简述了新型金属-TMA(1,3,5-三苯甲酸根)聚合物纳米孔材料的一般特征、材料设计方略、典型合成方法和潜在的应用领域,并着重介绍了这类聚合物的一维、二维、三维结构及性质,最后展望其发展趋势及前景。     

Solid-state synthesis of amphiphilic chitosan-polyethylene systems by the maleinization of both components

N-acylated chitosan modified by maleic anhydride was prepared by the method of the solid-state synthesis (Bridgman anvils, semipilot extruder). In contrast to the synthesis under homogeneous conditions, solid-state acylation is accompanied by the reaction of imidization of the formed amic acid as well as by reaction through double bonds, thus leading to the formation of derivatives of succinic anhydride. By simultaneous or subsequent interaction of chitosan modified with maleic anhydride with a PE matrix, either modified or not modified with maleic anhydride, new chitosan-polyethylene composite materials are prepared, and these composites are characterized by the combined valuable medicinal and biochemical properties of chitosan and high mechanical characteristics of the polyolefin component. The above composites are of obvious interest as amphiphilic sorbents, which are highly resistant to the action of aggressive media, as well as antimicrobial and biodegradable PE-based materials.     

Nanoclusters of Silicon and Germanium

Synthetic routes for the preparation of Si or Ge nanoclusters as gaseous species, colloids, supported composites, or as unsupported powders are reviewed along with selected characterization data. The optical properties of these and related materials, such as porous Si, are summarized with particular emphasis on photo- or electroluminescence phenomena. Research opportunities related to Si and Ge cluster chemistry are suggested.     

Interfacial dynamics and structure of surfactant layers

The present article provides current opinion on studies of the interfacial dynamics, adsorption, and structure of surfactant layers. The physical principles and applications of physicochemical methods such as tensiometry, ellipsometry, photon correlation spectroscopy, and neutron reflectivity techniques, as well as relevant theoretical aspects related to the adsorption and desorption kinetics, interfacial structure development, wetting enhancement, and the effect of adsorbed surfactant films of the interfacial dynamics, are covered in detail. In order to make the text as self-contained as possible, essential mathematical derivations are given demonstrating how raw data, such as ellipsometric angles or neutron reflectivity, are transformed into sought layer characteristics, such as thickness or density.     

Oxidation properties of β-substituted pyrroles

Pyrroles represent building blocks of conjugated poly(heterocycles) which, as organic conductors, are potential materials for organic electronics. Oxidation of β-substituted pyrroles constitutes an important first step in the process of electropolymerization. Ionization energy and the electron spin density distribution are two the most important properties regarding monomers. These properties are studied as a function of electron-withdrawing and electron-donating substituents of pyrrole ring. Evolution of molecular structure, nature of bonding, and electronic density are studied as an effect of ionization process.