Showing papers in "Angewandte Chemie in 2004"

Functional porous coordination polymers.

Abstract: The chemistry of the coordination polymers has in recent years advanced extensively, affording various architectures, which are constructed from a variety of molecular building blocks with different interactions between them. The next challenge is the chemical and physical functionalization of these architectures, through the porous properties of the frameworks. This review concentrates on three aspects of coordination polymers: 1). the use of crystal engineering to construct porous frameworks from connectors and linkers ("nanospace engineering"), 2). characterizing and cataloging the porous properties by functions for storage, exchange, separation, etc., and 3). the next generation of porous functions based on dynamic crystal transformations caused by guest molecules or physical stimuli. Our aim is to present the state of the art chemistry and physics of and in the micropores of porous coordination polymers.

Controlled microwave heating in modern organic synthesis.

Abstract: Although fire is now rarely used in synthetic chemistry, it was not until Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied to a reaction vessel in a focused manner. The Bunsen burner was later superseded by the isomantle, oil bath, or hot plate as a source for applying heat to a chemical reaction. In the past few years, heating and driving chemical reactions by microwave energy has been an increasingly popular theme in the scientific community. This nonclassical heating technique is slowly moving from a laboratory curiosity to an established technique that is heavily used in both academia and industry. The efficiency of "microwave flash heating" in dramatically reducing reaction times (from days and hours to minutes and seconds) is just one of the many advantages. This Review highlights recent applications of controlled microwave heating in modern organic synthesis, and discusses some of the underlying phenomena and issues involved.

Integrated Nanoparticle–Biomolecule Hybrid Systems: Synthesis, Properties, and Applications

Abstract: Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

In the Golden Age of Organocatalysis

Abstract: The term "organocatalysis" describes the acceleration of chemical reactions through the addition of a substoichiometric quantity of an organic compound. The interest in this field has increased spectacularly in the last few years as result of both the novelty of the concept and, more importantly, the fact that the efficiency and selectivity of many organocatalytic reactions meet the standards of established organic reactions. Organocatalytic reactions are becoming powerful tools in the construction of complex molecular skeletons. The diverse examples show that in recent years organocatalysis has developed within organic chemistry into its own subdiscipline, whose "Golden Age" has already dawned.

Colloidal carbon spheres and their core/shell structures with noble-metal nanoparticles.

Abstract: Colloidal microand nanospheres have been of continuous research interest, since their intrinsic properties can be finely tuned by changing parameters such as diameter, chemical composition, bulk structure, and crystallinity. Up to now, they have found a broad range of applications in fields such as drug delivery, biodiagnostics, combinatorial synthesis, and photonic band-gap crystals (PBG). The success of these applications strongly depends on the availability of colloidal spheres with tightly controlled size and surface properties. However, until now, only amorphous silica and some colloidal polymer spheres can be routinely prepared with satisfactorily narrow size distributions. As-prepared colloidal nanoand microspheres usually have relatively inert surfaces, which make surface modification almost unavoidable before use as supports or templates.

Metal carboxylates with open architectures.

Abstract: The field of inorganic open-framework materials is dominated by aluminosilicates and phosphates. The metal carboxylates have emerged as an important family in the last few years. This family includes not only mono- and dicarboxylates of transition, rare-earth, and main-group metals, but also a variety of hybrid structures. Some of the carboxylates possess novel adsorption and magnetic properties. Dicarboxylates and related species provide an effective means of designing novel hybrid structures with porous and other properties. In some of these structures, the dicarboxylate acts as a linker between two inorganic units. Hybrid nanocomposites are also of particular note, for example, cadmium oxalate host lattices that can accommodate extended alkali-metal halide structures. This Review discusses the synthesis, structure, and properties of various types of open-framework metal carboxylates.

Theoretical chemistry of gold.

Abstract: Gold is an element whose unique properties are strongly influenced by relativistic effects. A large body of appropriate calculations now exist and their main conclusions are summarized. The theoretical interpretation of the aurophilic attraction is discussed in detail.

G-quartets 40 years later: from 5'-GMP to molecular biology and supramolecular chemistry.

Abstract: Molecular self-assembly is central to many processes in both biology and supramolecular chemistry. The G-quartet, a hydrogen-bonded macrocycle formed by cation-templated assembly of guanosine, was first identified in 1962 as the basis for the aggregation of 5'-guanosine monophosphate. We now know that many nucleosides, oligonucleotides, and synthetic derivatives form a rich array of functional G-quartets. The G-quartet surfaces in areas ranging from structural biology and medicinal chemistry to supramolecular chemistry and nanotechnology. This Review integrates and summarizes knowledge gained from these different areas, with emphasis on G-quartet structure, function, and molecular recognition.

Palladium Oxidase Catalysis: Selective Oxidation of Organic Chemicals by Direct Dioxygen-Coupled Turnover

Abstract: Selective aerobic oxidation of organic molecules is a fundamental and practical challenge in modern chemistry. Effective solutions to this problem must overcome the intrinsic reactivity and selectivity challenges posed by the chemistry of molecular oxygen, and they must find application in diverse classes of oxidation reactions. Palladium oxidase catalysis combines the versatility of Pd(II)-mediated oxidation of organic substrates with dioxygen-coupled oxidation of the reduced palladium catalyst to enable a broad range of selective aerobic oxidation reactions. Recent developments revealed that cocatalysts (e.g. Cu(II), polyoxometalates, and benzoquinone) are not essential for efficient oxidation of Pd(0) by molecular oxygen. Oxidatively stable ligands play an important role in these reactions by minimizing catalyst decomposition, promoting the direct reaction between palladium and dioxygen, modulating organic substrate reactivity and permitting asymmetric catalysis.

A Planning Strategy for Diversity‐Oriented Synthesis

Abstract: In contrast to target-oriented synthesis (TOS) and medicinal or combinatorial chemistry, which aim to access precise or dense regions of chemistry space, diversity-oriented synthesis (DOS) populates chemical space broadly with small-molecules having diverse structures. The goals of DOS include the development of pathways leading to the efficient (three- to five-step) synthesis of collections of small molecules having skeletal and stereochemical diversity with defined coordinates in chemical space. Ideally, these pathways also yield compounds having the potential to attach appendages site- and stereoselectively to a variety of attachment sites during a post-screening, maturation stage. The diverse skeletons and stereochemistries ensure that the appendages can be positioned in multiple orientations about the surface of the molecules. TOS as well as medicinal and combinatorial chemistries have been advanced by the development of retrosynthetic analysis. Although the distinct goals of DOS do not permit the application of retrosynthetic concepts and thinking, these foundations are being built on, by using parallel logic, to develop a complementary procedure known as forward-synthetic analysis. This analysis facilitates synthetic planning, communication, and teaching in this evolving discipline.

Industrial Methods for the Production of Optically Active Intermediates

Abstract: Enantiomerically pure amino acids, amino alcohols, amines, alcohols, and epoxides play an increasingly important role as intermediates in the pharmaceutical industry and agrochemistry, where both a high degree of purity and large quantities of the compounds are required. The chemical industry has primarily relied upon established chemical methods for the synthesis of these intermediates, but is now turning more and more to enzymatic and biotechnological fermentation processes. For the industrial implementation of many transformations alternative methods are available. The advantages of the individual methods will be discussed herein and exemplified by syntheses of relevant compounds.

Chemistry in microstructured reactors.

Abstract: The application of microstructured reactors in the chemical process industry has gained significant importance in recent years. Companies that offer not only microstructured reactors, but also entire chemical process plants and services relating to them, are already in existence. In addition, many institutes and universities are active within this field, and process-engineering-oriented reviews and a specialized book are available. Microstructured systems can be applied with particular success in the investigation of highly exothermic and fast reactions. Often the presence of temperature-induced side reactions can be significantly reduced through isothermal operations. Although microstructured reaction techniques have been shown to optimize many synthetic procedures, they have not yet received the attention they deserve in organic chemistry. For this reason, this Review aims to address this by providing an overview of the chemistry in microstructured reactors, grouped into liquid-phase, gas-phase, and gas-liquid reactions.

Grid-type metal ion architectures: functional metallosupramolecular arrays.

Abstract: Recent advances in supramolecular coordination chemistry allow access to transition-metal complexes of grid-type architecture comprising two-dimensional arrays of metal ions connecting a set of organic ligands in a perpendicular arrangement to generate a multiple wiring network. General design principles for these structures involve the thermodynamically driven synthesis of complex discrete objects from numerous molecular components in a single overall operation. Such supramolecular metal ion arrays combine the properties of their constituent metal ions and ligands, showing unique optical, electrochemical, and magnetic behavior. These features present potential relevance for nanotechnology, particularly in the area of supramolecular devices for information storage and processing. Thus, a dense organization of addressable units is represented by an extended "grid-of-grids" arrangement, formed by interaction of grid-type arrays with solid surfaces.

Ionic liquids for the convenient synthesis of functional nanoparticles and other inorganic nanostructures

Abstract: Ionic liquids are a new class of organic solvents with high polarity and a preorganized solvent structure. Very polar reactions can be carried out in these liquid in the absence of or with a controlled amount of water, and crystalline nanoparticles can be synthesized conveniently at ambient temperatures. The pronounced self-organization of the solvent is used in the synthesis of self-assembled, highly organized hybrid nanostructures with unparalleled quality. The extraordinary potential of ionic liquids in materials synthesis is described in this minireview and a physicochemical explanation is given.

Reversible Switching between Superhydrophilicity and Superhydrophobicity

Abstract: Wettability is a very important property that is governed by both chemical composition and surface structure. Recently, the control of surface wettability has aroused great interest because of its wide variety of applications. In general, superhydrophobic surfaces with a water contact angle (CA) greater than 1508 can be obtained by controlling the topography of hydrophobic surfaces, while superhydrophilic surfaces with a CA about 08 can be realized through a 3D or 2D capillary effect on hydrophilic surfaces. Stimuli-responsive surfaces make it possible to reversibly control the wettability of the surface and has been demonstrated by various methods, including light-irradiation, 12] use of an electric field, 14] thermal treatment and treatment with solvent. However, reversible switching between superhydrophilicity and superhydrophobicity has never been reported. Herein we show the roughness-enhanced thermally responsive wettability of a poly(N-isopropylacrylamide) (PNIPAAm)-modified surface. 18] Reversible switching between superhydrophilicity and superhydrophobicity can be achieved in a narrow temperature range of about 10 8C, which is considered to result from the combined effect of the chemical variation of the surface, and surface roughness. Such switchable surfaces may have wide applications in functional textiles, intelligent microfluidic switching, controllable drug release, and thermally responsive filters. Surface-initiated atom-transfer radical polymerization 20] was used to fabricate thermally responsive PNIPAAm thin films on both a flat and a rough silicon substrate. Results from atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that the thickness of the PNIPAAm thin film could be well controlled by the polymerization time. Figure 1a (left) shows a typical SEM image of a rough substrate that has been modified with a PNIPAAm thin film. Compared with the smooth surface (Figure 1a right) of the flat substrate, the rough substrate exhibits a regular array of square silicon microconvexes (bright squares). The dark lines are microgrooves that are about 6 mm in width and about 5 mm in depth. These microgrooves were generated by a laser cutter (see Experimental Section) on a silicon wafer in a region of about 1 : 1 cm. The surface roughness can be adjusted by controlling the spacing between the grooves. In our experiments, different groove spacings of about 31 mm, 18 mm, 8 mm, and 6 mm were selected. The magnified image of the rough surface shows that both microconvexes and microgrooves were also rather rough (Figure 1b). Further magnified SEM images of the silicon microconvexes before (Figure 1c) and after (Figure 1d) PNIPAAm polymerization show that these

Funktionale poröse Koordinationspolymere

Abstract: Die Chemie der Koordinationspolymere hat sich in den vergangenen Jahren rasant entwickelt. Strukturen aus einer Vielzahl molekularer Bausteine mit unterschiedlichen Wechselwirkungen sind mittlerweile zuganglich. Die nachste Stufe ist die chemische und physikalische Funktionalisierung dieser Architekturen durch Einstellung ihrer Porositaten. Dieser Aufsatz konzentriert sich auf drei Aspekte von Koordinationspolymeren: 1) Anwendung von Kristall-Engineering zum Aufbau poroser Geruste aus Konnektoren und Linkern (“Nanospace-Engineering”), 2) Charakterisierung und Katalogisierung poros-struktureller Funktionalitat fur Anwendungen in Speicherungs-, Austausch-, Trennprozessen etc. und 3) poros-strukturelle Funktionalitat auf der Basis dynamischer Kristallumwandlungen durch Gastmolekule oder physikalische Reize. Ziel ist es, den aktuellen Stand der Forschung zur Chemie und Physik von und in den Mikroporen poroser Koordinationspolymere vorzustellen.

Functionalized Carbon Nanotubes for Plasmid DNA Gene Delivery

Abstract: [*] Dipl.-Chem. D. Pantarotto, Prof. M. Prato Dipartimento di Scienze Farmaceutiche Universit di Trieste 34127 Trieste (Italy) Fax: (+39)040-5272 E-mail: prato@univ.trieste.it Dipl.-Chem. R. Singh, Dipl.-Chem. D. McCarthy, Dr. K. Kostarelos Centre for Drug Delivery Research and Electron Microscopy Unit The School of Pharmacy University of London London WC1N 1AX (United Kingdom) Fax: (+39)207-7535942 E-mail: kostas.kostarelos@ulsop.ac.uk Dipl.-Chem. D. Pantarotto, Dr. J.-P. Briand, Dr. A. Bianco Institut de Biologie Mol=culaire et Cellulaire UPR9021 CNRS Immunologie et Chimie Th=rapeutiques 67084 Strasbourg (France) Fax: (+33)388-610-680 E-mail: A.Bianco@ibmc.u-strasbg.fr Dr. M. Erhardt Institut de Biologie Mol=culaire des Plantes 67084 Strasbourg (France) [**] This work was supported by the Centre National de la Recherche Scientifique (CNRS), Universit di Trieste, and Ministero dell’Istruzione, dell’ Universit e della Ricerca (MIUR; cofin 2002, prot. 2002032171). Transmission electron microscopy (TEM) analysis was performed at the microscopy facility of the Institute of Biomedical Problems and was cofinanced by CNRS, R=gion Alsace, Louis Pasteur University, and the Association de la Recherche pour le Cancer. The authors wish to acknowledge C. D. Partidos for helpful and stimulating discussions. We thank Mr. Claudio Gamboz (Centro Servizi Polivalenti di Ateneo (CSPA), Universit di Trieste) for his great help with the TEM measurements. Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Communications

Discrete Metal-Based Catalysts for the Copolymerization of CO2 and Epoxides: Discovery, Reactivity, Optimization, and Mechanism

Abstract: Most synthetic polymers are made from petroleum feedstocks. Given the non-renewable nature of these materials, there is increasing interest in developing routes to polymeric materials from renewable resources. In addition, there is a growing demand for biodegradable polymeric materials. Polycarbonates made from CO(2) and epoxides have the potential to meet these goals. Since the discovery of catalysts for the copolymerization of CO(2) and epoxides in the late 1960's by Inoue, a significant amount of research has been directed toward the development of catalysts of improved activity and selectivity. Reviewed here are well-defined catalysts for epoxide-CO(2) copolymerization and related reactions.

A Lotus‐Leaf‐like Superhydrophobic Surface: A Porous Microsphere/Nanofiber Composite Film Prepared by Electrohydrodynamics

Abstract: [*] Prof. Dr. L. Jiang, Dr. Y. Zhao, Prof. Dr. J. Zhai Center of Molecular Sciences Institute of Chemistry, Chinese Academy of Sciences Beijing 100080 (P. R. China) Dr. Y. Zhao Graduate School of the Chinese Academy of Sciences (P. R. China) Prof. Dr. L. Jiang National Center for Nanoscience and Nanotechnology Beijing 100080 (P. R. China) Fax: (+86)10-8262-7566 E-mail: jianglei@iccas.ac.cn [**] The authors thank the State Key Project for Fundamental Research (G1999064504) and the Special Research Foundation of the National Nature Science Foundation of China (29992530) for continuing financial support. The Chinese Academy of Sciences is gratefully acknowledged. Communications

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

Abstract: Herein, recent experiments on the spectroscopy and chemical reactions of molecules and complexes embedded in helium droplets are reviewed. In the droplets, a high spectroscopic resolution, which is comparable to the gas phase is achieved, while an isothermal low-temperature environment is maintained by evaporative cooling at T =0.37 K (4He droplets) or 0.15 K (3He droplets), lower than possible in most solid matrices. Thus the helium-droplet technique combines the benefits of both the gas phase and the classical matrix-isolation techniques. Most important, the superfluid helium facilitates binary encounters, and absorbs the released binding energy upon recombination. Thus the droplet can be viewed as an isothermal nanoscopic reactor, which isolates single molecules, clusters, or even a single reactive encounter at ultralow temperatures.

Tailor‐Made Polyelectrolyte Microcapsules: From Multilayers to Smart Containers

Abstract: This review addresses the fabrication and properties of novel polyelectrolyte microcapsules, with an emphasis on their mechanical and permeability properties. Ease of preparation through layer-by-layer self assembly, accurate control over wall thickness as well as flexibility in the choice of constituents make these capsules very promising for numerous applications in materials and life science. Moreover, by engineering the inner and outer interfaces, these capsules can be used as microreactors for precipitation, crystallization, and polymerization reactions, as well as enzymatic, and heterogeneous catalysis.

Platonic Gold Nanocrystals

Abstract: Thiswork was supported by the Camille and Henry Dreyfus Foundation, Beckman Foundation, the National Science Foundation (CAREER) and Department of Energy. P.Y. isan Alfred P. Sloan Research Fellow.Work at the Lawrence Berkeley National Laboratory was supported by the Office of Science, Basic Energy Sciences, Division of Materials Science of the U.S. Department of Energy. We thank the National Center for Electron Microscopy for the use of their facilities.

Noncoordinating anions--fact or fiction? A survey of likely candidates.

Abstract: A review on the available candidates in the quest for the least coordinating anion and a summary of new applications, available starting materials, and general strategies to introduce a WCA into a system. Some of the unusual properties of WCA salts such as high soly. in low dielec. media, pseudo gas-phase conditions in condensed phases, and the stabilization of weakly bound and low-charged complexes are rationalized on thermodn. grounds. Limits of the WCAs, i.e., anion coordination and decompn., are shown and a quantum chem. anal. of all types of WCAs is presented which allows the choice of a particular WCA to be based on quant. data from a wide range of different anions. [on SciFinder (R)]

The evolution of dip-pen nanolithography.

Abstract: The ability to tailor the chemical composition and structure of a surface on the 1-100 nm length scale is important to researchers studying topics ranging from electronic conduction, to catalysis, to biological recognition in nanoscale systems. Dip-pen nanolithography (DPN) is a new scanning-probe based direct-write tool for generating such surface-patterned chemical functionality on the sub-100 nm length-scale, and it is a technique that is accessible to any researcher who can use an atomic force microscope. This article introduces DPN and reviews the rapid growth of the field of DPN-related research over the past few years. Topics covered range from the development of new classes of DPN-compatible chemistry, to experimental and theoretical advances in the understanding of the processes controlling tip-substrate ink transport, to the implementation of micro-electro-mechanical system (MEMS) based strategies for parallel DPN applications.

Catalytic Markovnikov and anti-Markovnikov functionalization of alkenes and alkynes: recent developments and trends.

Abstract: The regioselective functionalization of terminal alkenes and alkynes is of utmost importance for the synthesis of a wide variety of organic products. Based on the original observation by Vladimir Markovnikov-the pioneer of this field of research-in the 19th century, the possible regioisomeric products are classified as Markovnikov or anti-Markovnikov products. Contrary to traditional belief, it is nowadays possible to control the regiochemistry of various additions of nucleophiles to alkenes and alkynes by applying different transition-metal catalysts. Recent developments in this area of selective functionalization of alkenes and alkynes are reviewed.