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Concept Article (concept + article)
Selected AbstractsPolymerization of ,-Hydroxy Acids by RibosomesCHEMBIOCHEM, Issue 17 2008Atsushi Ohta Abstract Over 30 years ago, Fahnestock and Rich reported intriguing data showing the capability of the ribosome to polymerize phenyllactic acid. Although the polymerization was initiated and terminated randomly on polyuridic acids, the given data convincingly suggested that the generated polymer was composed of an approximately 7:3 mixture of phenyllactic acid and phenylalanine. Despite the fact that Fahnestock's conclusion was very likely correct, there have been no reports to follow up the ribosome-catalyzed polymerization of ,-hydroxy acids until very recently. At the end of 2007, we reported messenger RNA (mRNA)-directed polyester synthesis by using the new emerging method of genetic-code reprogramming in which , -hydroxy acids with various kinds of side-chains are assigned to arbitrarily chosen codons. In this work, we have achieved the ribosomal synthesis of polyesters with the sequence composition and length in a fully controlled manner according to the sequence of mRNA. This Concept article describes the background of the method development and its application to the synthesis of polyesters. [source] Recent Synthetic Applications of Manganese in Organic SynthesisCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2008Abstract While the organometallic compounds derived from many metals have found a broad application in organic synthesis, the use of organomanganese compounds has only recently been developed due to the passivity exhibited by commercial Mn in the direct metalation of organic compounds. In this Concept article, we highlight the potential of manganese and its organometallic compounds in organic synthesis by illustration of the studies previously reported by others and our laboratory in this field. Based on the transformations reported herein, organomanganese compounds could become important tools in the future of the organic synthesis, due to their high selectivity. [source] Metal-Mediated Formation of Carbon,Halogen BondsCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2008Arkadi Vigalok Prof. Dr. Abstract Organic halides represent basic starting materials for numerous metal-catalyzed organic transformations. Generally, the carbon,halogen is broken in the first step, that is, an oxidative addition reaction, of the catalytic cycle. On the other hand, very little is known about the reverse reaction, carbon,halogen reductive elimination from a transition-metal center. In this Concept article, we describe the examples of C(sp3)halide and C(sp2)halide reductive-elimination reactions which demonstrate that this type of reactivity can be quite common in organometallic chemistry. Although the thermodynamic driving force for the formation of carbon,halogen bonds is relatively small, the kinetic barrier for these reactions can also be low. Thus, Chalide reductive elimination can compete favorably with the more established organic transformations, such as CC reductive elimination. [source] Flow-Guided Assembly ProcessesCHEMPHYSCHEM, Issue 7 2008Shengnian Wang Dr. Abstract This Concept article focuses on capillary, hydrodynamics and electrokinetic flow-guided assembly processes that can produce patterned or gradient functional surfaces either on solid surfaces or in deep micro- and nanoscale channels. This concept has the potential to produce low-cost nanostructures, internal surface modifications, and devices in nanomedicine. [source] Star Mesogens (Hekates),Tailor-Made Molecules for Programming Supramolecular FunctionalityCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Matthias Lehmann Abstract Hekates: Modular synthesis of star-shaped molecules affords mesogens with various functional units and incompatible peripheral chains (see figure). The supramolecular order in the complex, soft, liquid-crystalline, functional materials can be programmed by variation of the elements of diversity at a meso- and nanoscale. This concept article focuses on the simplest branched liquid crystalline (LC) molecules,the three-armed mesogens with arms symmetrically linked to the core. They are basic but fascinating mesogens for the exploration of self-assembling processes into complex, functional, soft materials. Quite a large number of elements of diversity provide the possibility to synthetically program such star-shaped molecules and to control phase formation, if aggregation processes are fully understood. Recently, ABC-cores opened the way to non-symmetric mesogens and, therefore, to the concept of multifunctional materials with defined nanostructures. In the article this outstanding family of mesogens is classified, their peculiar molecular structure and self-assembly are discussed and potential applications are presented, in which this type of mesogen may be beneficial. Dieser Konzeptbeitrag stellt die einfachsten verzweigten flüssigkristallinen Moleküle in den Mittelpunkt,dreiarmige Mesogene mit symmetrisch um einen Kern angeordneten Armen. Diese schlichten, aber faszinierenden Mesogene eignen sich hervorragend für das Studium von Selbstorganisationsprozessen zu komplexen, funktionalen, weichen Materialien. Die große Zahl von Diversitätselementen, der modular aufgebauten Mesogene, ermöglicht das synthetische Programmieren der sternförmigen Moleküle und die Kontrolle der Anordnung in LC Phasen, falls die Aggregationsprozesse völlig verstanden werden. Die kürzlich vorgestellten ABC-Kerne erlauben die Synthese von unsymmetrischen Mesogenen und folglich die Umsetzung des Konzepts der multifunktionalen Materialien mit definierten Nanostrukturen. In diesem Artikel wird diese außergewöhnliche Mesogenfamilie klassifiziert und deren besondere Struktur und Selbstorganisation diskutiert. Schließlich werden mögliche Anwendungen vorgestellt, für die diese Art der Mesogene vorteilhaft sein kann. [source] Structure Formation Principles and Reactivity of Organolithium CompoundsCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2009Viktoria Abstract Organolithium chemistry! An overview of the structure formation principles and the strong structure,reactivity relationship of lithium organics is given. By means of the commonly used lithium bases the deaggregation of the oligomeric parent structures to small adducts is presented (see examples) and compared to the related chemistry of lithiosilanes. The structure,reactivity relationship is an important feature of organolithium compounds. The knowledge of the structure of reactive species is crucial for the elucidation of reaction mechanisms and the understanding of observed selectivities. This concept article gives an overview over the structural principles of lithium organics and their Lewis base coordinated complexes in the solid state. The transition from the oligomeric parent structures to smaller adducts, such as dimers and monomers, as well as special degrees of aggregation is presented. Besides the commonly used alkyllithium compounds, a short overview over the structural principles of the higher homologous silyllithium compounds is given. Moreover, the structure,reactivity relationship is depicted by means of the reactivity of the Lewis bases towards intramolecular decomposition reactions with the organolithium compound. Selected examples confirm the importance of structure elucidation for the understanding of mechanistic pathways and selectivities. [source] Processing Energy and Signals by Molecular and Supramolecular SystemsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2008Vincenzo Balzani Prof. Abstract Any kind of device or machine requires a substrate, energy, and information signals. If we wish to operate at the nanometer scale, we must use molecules as substrates. Energy- and signal-processing at a molecular level relies on cause/effect relationships between the input supplied and the kind of process obtained. We have classified energy- and signal-processing at the molecular level according to the nature of the input (electronic, photonic, or chemical) and the nature of the obtained effect (electronic, photonic, or chemical process that follows). By coupling the three kinds of inputs with the three types of resulting processes, nine types of molecular-based processes (electronic, photonic, chemionic, electrophotonic, electrochemionic, photoelectronic, photochemionic, chemiophotonic, and chemioelectronic) can be identified. In this concept article, looking at molecular transformations in an unconventional way, we have tried to give a flavor of some of the new features that project the old science of chemistry towards novel achievements. [source] Going to Extremes: "Super" Armed Glycosyl Donors in Glycosylation ChemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2007Henrik Abstract This concept article gives an overview of stereoelectronic effects in monosaccharide systems and how these can be used to dramatically enhance the reactivity of glycosyl donors in oligosaccharide synthesis. [source] Synthetically Tailored Excited States: Phosphorescent, Cyclometalated Iridium(III) Complexes and Their ApplicationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2006Michael S. Lowry Abstract Phosphorescent iridium(III) complexes are being widely explored for their utility in diverse photophysical applications. The performance of these materials in such roles depends heavily on their excited-state properties, which can be tuned through ligand and substituent effects. This concept article focuses on methods for synthetically tailoring the properties of bis-cyclometalated iridium(III) materials, and explores the factors governing the nature of their lowest excited state. [source] | ||||||||||