Supramolecular perspectives in colloid science

Supramolecular chemistry puts emphasis on molecular assemblies held together by non-covalent bonds. As such, it is very close in spirit to colloid science which also focuses on objects which are small, but beyond the molecular scale, and for which other forces than covalent bonds are crucial. We discuss in this review the preparation and properties of new colloidal systems which borrow on the one hand from classical topics in colloid science, such as micellization, and on the other hand from concepts in supramolecular chemistry, such as reversible supramolecular polymers.     

Review and Future of Ionic Polymerization with Special Emphasis on Carbonyl Polymerization

Ionic polymerization received prominence about 35 years ago when isobutylene was commercially polymerized by two processes which, with some modifications, are still used today [1]. One process uses aluminum chloride as the initiator and the other uses boron trifluoride; both cationic polymerization processes are carried out at low temperatures. A number of additional commercial processes based on cationic and anionic polymerization have since been developed. Cyclic ethers, most prominently tetrahydrofuran, are polymerized cationically to relatively low molecular weight hydroxyl terminated polyethers which have found important uses in polyurethanes. Trioxane is copolymerized with a small amount of ethylene oxide to form a useful copolymer of polyoxymethylene. Other products which are of interest are the polymers of caprolactone and epichlorohydrin and polymers of various epoxides, mainly those of glycidyl ethers which are most commonly known as epoxy resins. Anionic polymerization on a commercial scale has developed along the lines of styrene and isoprene polymers. Stereorubber, stereoregular 1,4-cis isoprenes, are based on lithium initiators and were introduced in the middle 1950s. Triblock polymers based on A-B-A block polymers of isobutylene with styrene as endblocks and prepared from living polymers have been known since the early 1960s.     

Synthesis and solid-state organization of coil-ring-coil block copolymers

Shape-persistent macrocycles based on the phenyl-ethynyl-butadienyl backbone containing two extraannular hydroxyl groups were prepared by the oxidative coupling of the appropriate phenylethynyl oligomers. Carbodiimide-directed coupling with independently synthesized polystyrene carboxylic acid oligomers led to ABA coil-ring-coil block copolymers in which the central macrocycle serves as rigid and the polystyrene oligomers as flexible elements. Depending on the size of the coil blocks, these structures aggregate in cyclohexane into supramolecular hollow cylindrical brushes in which the rigid core is surrounded by the flexible matrix. However, in the solid state it is not possible to identify a morphology in which isolated channels based on aggregated macrocycles are embedded in a matrix of polystyrene. Detailed X-ray and electron diffraction studies on samples prepared from a solution in cyclohexane under equilibrium conditions show that the material adopts a lamellar morphology in the solid state in which columns of macrocycles are aggregated into layers which are separated by polystyrene.     

Studies on the growth of ice crystal templates during the synthesis of a monolithic silica microhoneycomb using the ice templating method

Porous materials with a wide variety of functions can be obtained through sol-gel synthesis. Recently, we found that sol-gel based materials can be molded into a monolithic microhoneycomb structure by simply freezing their parent hydrogels unidirectionally. The main feature of the monoliths obtained through this method, which we named the Ice Templating Method, is that they have straight and aligned macropores, the sizes of which are in the micrometer range. As these macropores are the traces of the ice crystals which are formed during freezing and which practically act as the template, the sizes as well as the shape of them depend on how the template ice crystals are formed and how they grow. Therefore in this work, the growth behavior of the ice crystals formed during the unidirectional freezing of a silica hydrogel was examined and the influences of this growth behavior on the properties of the resulting monoliths were verified.     

Kinetic evaporation and condensation rates and their coefficients

The origins and properties of evaporation and condensation coefficients are described, and results of their measurement are surveyed for water and liquid metals. Contrasts are drawn as to whether their values are likely to limit practical transfer rates at plane surfaces and on aerosols, and between evaporation and condensation. Existing theories which express condensation and evaporation rates in terms of the coefficients are described. Their failure to satisfy energy and momentum conservation as well as mass conservation at the interface is remedied by constructing a new theory which also starts with vapor molecules in Maxwell-Boltzmann distributions. The resulting rates are shown to be close to those predicted by more accurate theories in which the Boltzmann transport equation is solved.     

纳米金属铁降解有机卤化物的研究进展

有机卤化物是一种毒性强、难生物降解的环境污染物,传统处理技术存在着降解不完全、效率低等不足。纳米技术的发展给有机卤化物的处理带来了一种新的颇具潜力的方法,即应用纳米金属/双金属颗粒对有机卤化物进行脱卤。目前,以Fe(Ⅱ) 和 Fe(Ⅲ)等常见原料合成纳米铁颗粒的技术已经成熟,纳米颗粒对有机卤化物也显示出高效的降解性能。更重要的是,其可灵活应用于地下水和土壤的原位和异位修复,尤其适用于原位修复。本文综述了纳米铁颗粒降解有机卤化物的研究进展,包括纳米铁颗粒的合成与修饰, 降解效能、降解机理、降解动力学、示范工程等,以及发展前景和今后的研究方向。     

Surface supramolecular organization of a terbium(III) double-decker complex on graphite and its single molecule magnet behavior

The two-dimensional self-assembly of a terbium(III) double-decker phthalocyanine on highly oriented pyrolitic graphite (HOPG) was studied by atomic force microscopy (AFM), and it was shown that it forms highly regular rectangular two-dimensional nanocrystals on the surface, that are aligned with the graphite symmetry axes, in which the molecules are organized in a rectangular lattice as shown by scanning tunneling microscopy. Molecular dynamics simulations were run in order to model the behavior of a collection of the double-decker complexes on HOPG. The results were in excellent agreement with the experiment, showing that-after diffusion on the graphite surface-the molecules self-assemble into nanoscopic islands which align preferentially along the three main graphite axes. These low dimension assemblies of independent magnetic centers are only one molecule thick (as shown by AFM) and are therefore very interesting nanoscopic magnetic objects, in which all of the molecules are in interaction with the graphite substrate and might therefore be affected by it. The magnetic properties of these self-assembled bar-shaped islands on HOPG were studied by X-ray magnetic circular dichroism, confirming that the compounds maintain their properties as single-molecule magnets when they are in close interaction with the graphite surface.     

Mass spectrometric studies on gibberellins

Based on the element maps of twenty-two gibberellin methyl esters fragmentations are discussed, which are characteristic of the common structural features as well as structural modification in gibberellin homologues.     

Quantitation of trace betamethasone or dexamethasone in dexamethasone or betamethasone active pharmaceutical ingredients by reversed-phase high-performance liquid chromatography

Adequate separation is essential for the quantitation of trace amounts of dexamethasone that are typically found in betamethasone active pharmaceutical ingredients and vice versa. In this paper, we describe three simple and efficient high-performance liquid chromatography methods from which true baseline separations between betamethasone and dexamethasone are achieved even when the concentration ratios between these two epimers are larger than 2000:1. One method is developed on a 5 cm ACE C8 column that uses water and acetonitrile as the mobile phase and 20 mM beta-cyclodextrin as the mobile phase additive. The resolution factor between betamethasone and dexamethasone is 3.3. The second method is developed on a 10 cm ACE C8 column that uses water and acetonitrile as the mobile phase, in which the resolution factor between the epimers is 2.7. The third method is developed on a 10 cm ACE C8 column using water and tetrahydrofuran as the mobile phase, in which the resolution factor between the epimers is 3.1. Preliminary validation studies are carried out for the second and third methods.     

Microcins, gene-encoded antibacterial peptides from enterobacteria

Microcins are gene-encoded antibacterial peptides, with molecular masses below 10 kDa, produced by enterobacteria. They are secreted under conditions of nutrient depletion and exert potent antibacterial activity against closely related species. Typical gene clusters encoding the microcin precursor, the self-immunity factor, the secretion proteins and frequently the post-translational modification enzymes are located either on plasmids or on the chromosome. In contrast to most of the antibiotics of microbial origin, which are non-ribosomally synthesized by multimodular enzymes termed peptide synthetases, microcins are ribosomally synthesized as precursors, which are further modified enzymatically. They form a restricted class of potent antibacterial peptides. Fourteen microcins have been reported so far, among which only seven have been isolated and characterized. Despite the low number of known representatives, microcins exhibit a diversity of structures and antibacterial mechanisms. This review provides an updated overview of microcin structures, antibacterial activities, genetic systems and biosyntheses, as well as of their mechanisms of action.     

A miniaturized electrode configuration for isoelectric focusing

An electrode configuration is described which allows fast isoelectric focusing (IEF) with conventional IEF systems. The equipment, which can be fixed on the cooling plate of a conventional IEF system, consists of a base plate on which flappable electrode holders are fastened. The handling is simple and needs only little time. Graphite rods are used as electrodes, thus avoiding the use of buffer strips. Samples are applied with special applicator strips--permitting the analysis of up to 19 samples on a 50 x 40 mm polyacrylamide gel and up to 44 samples on a 100 x 70 mm gel. Only 30 min are needed for one IEF run.     

Electrospun nanofiber pyropolymer electrodes for fuel cells on polybenzimidazole membranes

After the deposition of Pt on their surface, the carbon nanofiber materials synthesized by sequential oxidation and pyrolysis of electrospun nanofiber mats based on polyacrylonitrile are used as the gas-diffusion electrodes for high-temperature hydrogen–air fuel cells on a polybenzimidazole (PBI) proton-conducting membranes. In contrast to the traditional methods of electrode preparation in which the catalyst (Pt) nanoparticles are localized on the surface of carbon black which is applied as “ink” on the conducting support (carbon paper or tissue), in this study the Pt nanoparticles are being deposited and developed on the surface carbon nanofibers to form a combined gas-diffusion material. In the tests, the resulting electrodes demonstrate good efficiency within hydrogen-air fuel cells on the PBI membrane.     

1,2-Migration of phosphorus-centered anions on ate-type copper carbenoids and its application for the synthesis of new potent phosphine ligands

[chemical reaction: see text]. Diorganophosphide anions, which usually function as nontransferable ligands on mixed cuprates, undergo smooth 1,2-migration on ate-type copper carbenoids. Phosphinodisilylmethylcoppers prepared by this protocol are converted into the corresponding phosphines, which can be used as bulky, highly basic and air-stable ligands.     

Mining invertebrate natural products for future therapeutic treasure

This review focuses on biologically active entities from invertebrate sources, especially snails. The reader will encounter several categories of compounds from snails including glycosaminoglycans, peptides, proteins (glycoproteins), and enzymes which possess diverse biological activities. Among glycosaminoglycans, acharan sulfate which was isolated from a giant African snail Acahtina fulica is reviewed extensively. Conotoxins which are also called conopeptides are unique peptide mixtures from marine cone snail. Conotoxins are secreted to capture its prey, and currently have the potential to be highly effective drug candidates. One of the conotoxins is now in the market as a pain killer. Proteins as well as glycoproteins in the snail are known to be involved in the host defense process from an attack of diverse pathogens. Carbohydrate-degrading enzymes characterized and purified in snails are introduced to give an insight into the applicability in glycobiology research such as synthesis and structure characterization of glycoconjugates. It seems that simple snails produce very complicated biological compounds which could be an invaluable source in future therapeutics as well as research areas in natural medicine.     

Integrated decision support for assessing chemical liabilities

Chemical liabilities, such as adverse effects and toxicity, have a major impact on today's drug discovery process. In silico prediction of chemical liabilities is an important approach which can reduce costs and animal testing by complementing or replacing in vitro and in vivo liability models. There is a lack of integrated, extensible decision support systems for chemical liability assessment which run quickly and have easily interpretable results. Here we present a method which integrates similarity searches, structural alerts, and QSAR models which all are available from the Bioclipse workbench. Emphasis has been placed on interpretation of results, and substructures which are important for predictions are highlighted in the original chemical structures. This allows for interactively changing chemical structures with instant visual feedback and can be used for hypothesis testing of single chemical structures as well as compound collections. The system has a clear separation between methods and data, and the extensible architecture enables straightforward extension via addition of more plugins (such as new data sets and computational models). We demonstrate our method on three important safety end points: mutagenicity, carcinogenicity, and aryl hydrocarbon receptor (AhR) activation. Bioclipse and the decision support implementation are free, open source, and available from http://www.bioclipse.net/decision-support .     

Molecular photonic logic gates

The possibility of performing logical operations at the molecular level is being actively investigated at present with the aim of developing molecular logic gates, which can be used in information technologies. In this minireview, the design algorithm of molecular logic gates is considered and the requirements on molecular systems for use as logic gates are specified. Examples of molecular logic gates performing different logical operations are given. Attention is focused on all-photonic molecular logic gates, in which light is used as an input signal for transferring the system from one state to another and for reading the output signal by absorption or luminescence. In addition, optoelectronic devices with light as the input signal and electric current as the output signal are briefly discussed.     

Correlated atomic motions in liquid deuterium fluoride studied by coherent quasielastic neutron scattering

The collective dynamics of liquid deuterium fluoride are studied by means of high-resolution quasielastic and inelastic neutron scattering over a range of four decades in energy transfer. The spectra show a low-energy coherent quasielastic component which arises from correlated stochastic motions as well as a broad inelastic feature originating from overdamped density oscillations. While these results are at variance with previous works which report on the presence of propagating collective modes, they are fully consistent with neutron diffraction, nuclear magnetic resonance, and infrared/Raman experiments on this prototypical hydrogen-bonded fluid.     

Reactivity within a confined self-assembled nanospace

Confined nanospaces in which reactions can take place, have been created by various approaches such as molecular capsules, zeolites and micelles. In this tutorial review we focus on the application of self-assembled nanocapsules with well-defined cavities as nanoreactors for organic and metal catalysed transformations. The self-assembly of nanocapsules based on noncovalent bonds such as hydrogen bonds and metal-ligand interactions is discussed to introduce the properties of the building blocks and capsules thereof. We will elaborate on the encapsulation effects that can be expected when reactions are carried out in a capsule-protected environment. Subsequently, literature examples will be described in which self-assembled nanocapsules are applied as nanoreactors, for various types of organic and metal catalysed reactions.