Showing papers in "Angewandte Chemie in 1998"
TL;DR: A detailed and systematic examination of many interpenetrating nets of this kind is made, and implications for crystal engineering are discussed.
Abstract: Independent one-, two-, and even three-dimensional nets interpenetrate each other in many solid-state structures of polymeric, hydrogen-bonded nets and coordination polymers. For example, the interpenetration of the adamantane units of two diamondlike nets is shown on the right. A detailed and systematic examination of many interpenetrating nets of this kind is made, and implications for crystal engineering are discussed.
4,070 citations
TL;DR: Polyvalent interactions can be collectively much stronger than corresponding monovalent interactions, and they can provide the basis for mechanisms of both agonizing and antagonizing biological interactions that are fundamentally different from those available inmonovalent systems.
Abstract: Found throughout biology, polyvalent interactions are characterized by the simultaneous binding of multiple ligands on one biological entity to multiple receptors on another (top part of the illustration) and have a number of characteristics that monovalent interactions do not (bottom). In particular, polyvalent interactions can be collectively much stronger than corresponding monovalent interactions, and they can provide the basis for mechanisms of both agonizing and antagonizing biological interactions that are fundamentally different from those available in monovalent systems.
3,669 citations
TL;DR: A new exciting interdisciplinary research field has evolved following the discovery that conjugated polymers can emit light when put into light-emitting diodes.
Abstract: A new exciting interdisciplinary research field has evolved following the discovery that conjugated polymers can emit light when put into light-emitting diodes. A myriad of light-emitting polymers (examples of which are shown below) shining in various colors have been developed through chemical intuition and structural design.
3,015 citations
TL;DR: Possible areas of application for polyelectrolyte shells range from the pharmaceutical, food, cosmetic, and paint industries to catalysis and microcrystallization.
Abstract: Exact control of the film thickness of polyelectrolyte shells (a transmission electron microscopy image is shown) is achieved by colloid-templated consecutive adsorption of polyanions and polycations followed by decomposition of the templating core. Possible areas of application for these shells range from the pharmaceutical, food, cosmetic, and paint industries to catalysis and microcrystallization.
1,768 citations
TL;DR: Oxidative addition and reductive elimination are the central steps in new palladium-catalyzed chemistry that forms C-N and C-O bonds in arylamines and ethers.
Abstract: Oxidative addition and reductive elimination are the central steps in new palladium-catalyzed chemistry that forms C–N and C–O bonds in arylamines and ethers. In the potential mechanism shown on the right the amine is formed by reductive elimination from a four-coordinate, 16-electron amido aryl complex. The use of a chelating ligand such as 1,1′-bis(diphenylphosphanyl)ferrocene (DPPF) reduces the occurrence of the competing β-hydrogen elimination. X=Br, I; R, R′=alkyl, aryl.
1,586 citations
TL;DR: The design of such a filigrane network requires the very careful control of chemical parameters and the reward is an assortment of different property profiles owing to the richness of possible variations.
Abstract: Air, air, air… and some solid skeleton; this is the basis for an interesting class of materials-the aerogels (shown schematically on the right). Can one therefore speak of "simple" chemistry? The design of such a filigrane network requires the very careful control of chemical parameters. The reward is an assortment of different property profiles owing to the richness of possible variations.
1,471 citations
TL;DR: The latest advances in the field of electroluminescence enable new displays and light generation concepts that challenge the classical areas of application of luminescent materials.
Abstract: Owing to their use in fluorescent lamps and many display applications, luminescent materials affect our daily life. Improvement of already very mature as well as development of new materials demanded by a variety of new applications are the focus of research today. The latest advances in the field of electroluminescence enable new displays and light generation concepts that challenge the classical areas of application of luminescent materials.
1,194 citations
TL;DR: Reactions based on lipase catalysis usually proceed with high regio- and enantioselectivity, and the Ca2+ antagonist diltiazem was obtained with lipase from Serratia marcescens.
Abstract: Unusually versatile substrate specificity is shown by lipases. Not only do they hydrolyze triacylglycerols-for example, in the stomach and intestine during digestion of dietary fat-and various synthetic esters and amides, but their high stability in organic solvents permits their use in transesterification reactions and ester synthesis as well. Reactions based on lipase catalysis usually proceed with high regio- and enantioselectivity. Thus, the Ca2+ antagonist diltiazem (1) was obtained with lipase from Serratia marcescens. Over 30 lipases have been cloned in the last few years. Since the tertiary structure of 12 lipases is known, there are presently significant efforts to improve this class of enzymes by protein engineering techniques, in view of their use in detergents and other fields of industrial application.
1,145 citations
TL;DR: High enantioselectivity can be achieved when chiral oxazaborolidines are used as catalysts in the reduction of ketones by borane when the two reactants are activated and held in close proximity by the catalyst.
Abstract: High enantioselectivity can be achieved when chiral oxazaborolidines are used as catalysts in the reduction of ketones by borane. In the transition state on the way to the complex chiral compounds, the two reactants are activated and held in close proximity by the catalyst, as shown below.
1,135 citations
TL;DR: Modern variants of the Mannich reaction that expand the potential of the classical intermolecular reaction significantly and enable efficient control of the regioselectivities and stereoselectivity are therefore the topic of intensive research.
Abstract: Important building blocks for the synthesis of drugs or natural products are found in Mannich bases and their derivatives Modern variants of the Mannich reaction that expand the potential of the classical intermolecular reaction significantly and enable efficient control of the regioselectivity and stereoselectivity are therefore the topic of intensive research Intramolecular reactions, in particular as part of domino reaction sequences, often afford astoundingly simple and elegant approaches to complex target compounds
967 citations
TL;DR: A long-standing challenge to synthesis can now be met through the use of new and powerful catalytic asymmetric reactions for the assembly of complex chiral molecules with quaternary stereocenters from achiral building blocks.
Abstract: A long-standing challenge to synthesis can now be met through the use of new and powerful catalytic asymmetric reactions for the assembly of complex chiral molecules with quaternary stereocenters from achiral building blocks. The reaction sequence shown below is just one example discussed in this review.
TL;DR: Most racemates, from an analytical to a preparative scale, now appear to be resolved by this technique, and the chromatogram for the enantiomeric resolution of a fullerene derivative is shown.
Abstract: The first resolution of enantiomers was performed 150 years ago-mechanically. Today a powerful method for carrying out this task is HPLC on polysaccharide derivatives as chiral stationary phases. Most racemates, from an analytical to a preparative scale, now appear to be resolved by this technique. As an example, the chromatogram for the enantiomeric resolution of a fullerene derivative is shown on the right.
TL;DR: This review presents the progess made recently in understanding key elements of this reaction and describes a solution to the often quoted Levinthal Paradox.
Abstract: The mechanism of protein folding (represented schematically below) is one of the most fascinating problems in the field of chemical reactions. This review presents the progess made recently in understanding key elements of this reaction and describes a solution to the often quoted Levinthal Paradox.
TL;DR: Especially in the field of enantioselective synthesis, vicinal diamines (1,2-diamines) 1 and compounds easily prepared from them are widely used by organic chemists and various strategies have been developed to produce these compounds selectively.
Abstract: Especially in the field of enantioselective synthesis, vicinal diamines (1,2-diamines) 1 and compounds easily prepared from them-such as 1,2-bisimines, 1,2-diamides, or imidazolidin-2-ones-are widely used by organic chemists. Various strategies have been developed to produce these compounds selectively. Many natural products and medicinal agents also contain a 1,2-diamino unit.
TL;DR: Nonlinear effects of an enantiomerically impure catalyst on an asymmetric synthesis are not only of academic interest since they have a variety of practical uses, which are highlighted in this review.
Abstract: Who would have thought before 1986 that an enantiomerically impure catalyst could give a product in an asymmetric synthesis with an enantiomeric excess higher than that of the catalyst? Until then it was assumed that the ee value of the product (eeprod ) from an asymmetric synthesis was linearly correlated to the ee value of the chiral auxiliary (eeaux )-in fact a large deviation is possible (see diagram). These nonlinear effects are not only of academic interest since they have a variety of practical uses, which are highlighted in this review.
TL;DR: Gold complexes are almost unknown in homogeneous catalysis, but can catalyze the addition of alcohols to alkynes with turnover frequencies up to 1.5 s-1 and total turnover numbers up to 105 !
Abstract: Gold complexes are almost unknown in homogeneous catalysis, and for a long time gold was even thought of as “catalytically dead”. This is clearly not the case for cationic phosphanegold(I) complexes (see reaction below), which can catalyze the addition of alcohols to alkynes with turnover frequencies up to 1.5 s−1 and total turnover numbers up to 105! R=H, alkyl, Ph, CH2OH.
TL;DR: This development provides a general solution to a long-standing limitation of this extremely powerful process-the poor reactivity of inexpensive and readily accessible aryl chlorides.
Abstract: From only commercially available reagents a wide array of Suzuki cross-couplings of aryl chlorides with arylboronic acids can be effected in excellent yield [Eq. (a)]. This development provides a general solution to a long-standing limitation of this extremely powerful process-the poor reactivity of inexpensive and readily accessible aryl chlorides. dba=dibenzylideneacetone.
TL;DR: Carbononyl-selective asymmetric hydrogenation of α,β-unsaturated ketones proceeds in the presence of these RuII catalysts, and 4-substituted cyclohexanones are selectively converted into cis alcohols.
Abstract: A turnover number (TON) of 2 400 000 and a turnover frequency (TOF) of 63 s-1 are achieved with the chiral RuII complex 1 (R=p-CH3 C6 H4 ) in the asymmetric hydrogenation of acetophenone. Carbonyl-selective asymmetric hydrogenation of α,β-unsaturated ketones proceeds in the presence of these RuII catalysts, and 4-substituted cyclohexanones are selectively converted into cis alcohols.
TL;DR: Low cross-sensitivity for other metal ions and the ability to detect nanomolar concentrations of Cu2+ ions are the exciting properties of fluorescence sensors in which a fluorophore and a chelating group are discrete subunits of the same molecule.
Abstract: Low cross-sensitivity for other metal ions and the ability to detect nanomolar concentrations of Cu2+ ions are the exciting properties of fluorescence sensors in which a fluorophore and a chelating group are discrete subunits of the same molecule. The spatial separation offers considerable flexibility in design, which is a prerequisite for the optimization of sensor properties. The activity of the “chemodosimeter” 1 of Czarnik et al. is based on the Cu2+-induced hydrolysis of the hydrazide group and the formation of fluorescent rhodamine B.
TL;DR: The different nature of carbene ligands is clearly demonstrated by the first ruthenium-based complexes 1, which contain both alkylidene and N-heterocyclic carbene moieties, which forms the basis of the high catalytic activities of these compounds in olefin metathesis reactions.
Abstract: The different nature of carbene ligands is clearly demonstrated by the first ruthenium-based complexes 1, which contain both alkylidene and N-heterocyclic carbene moieties. The latter exhibit a pronounced Lewis base behavior. Moreover, this difference forms the basis of the high catalytic activities of these compounds in olefin metathesis reactions.
TL;DR: This macrocyclization protocol is a novel and mild procedure for introducing nonnative covalent cross-links into peptide helices.
Abstract: Olefin metathesis has been successfully applied to the synthesis of macrocyclic helical peptides [Eq (a)] Carbon–carbon bond tethers between amino acid side chains were introduced by ring‐closing metathesis This macrocyclization protocol is a novel and mild procedure for introducing nonnative covalent cross‐links into peptide helices
TL;DR: New developments in alkane oxidation catalyzed by electrophilic late transition metals have provided important mechanistic insights as well as potentially practical methods for alkane transformations.
Abstract: The selective oxidation of alkanes is a topic of considerable interest to both industrial and academic chemists. While the initial discovery occurred more than 25 years ago, new developments in alkane oxidation catalyzed by electrophilic late transition metals have provided important mechanistic insights as well as potentially practical methods for alkane transformations.
TL;DR: The need to quickly and cheaply produce pure products is driving the development of new separation and purification techniques, and the modern concepts and techniques for coupling synthesis and separation are rooted in workup procedures that are as old as the art of synthesis itself.
Abstract: A dirty word in synthesis: separation! The normally unavoidable separation at the end of each reaction finds no friends among synthetic chemists and is often regarded as a technical procedure. However, the need to quickly and cheaply produce pure products is driving the development of new separation and purification techniques. Astonishingly, the modern concepts and techniques for coupling synthesis and separation are rooted in workup procedures that are as old as the art of synthesis itself.
TL;DR: A close interaction between chemistry and medicine is offered by cationic liposome research, and the problems that still have to be faced are presented here along with potential solutions.
Abstract: A close interaction between chemistry and medicine is offered by cationic liposome research. Cationic liposomes are able to deliver nucleic acids to cells and are projected to be core technology for the emerging discipline of gene therapy. The problems that still have to be faced are presented here along with potential solutions.
TL;DR: In this article, polyvalent Wechselwirkungen viel starker sein als entsprechende monovalente Wechwirthungen, and sie konnen die Basis fur das Verstandnis fordernder und hemmender biologischer Wechungungen liefern, die sich grundsatzlich von denen in monovalenten Systemen unterscheiden.
Abstract: Uberall in der Biologie kommen polyvalente Wechselwirkungen vor. Sie zeichnen sich durch die gleichzeitige Bindung mehrerer Liganden einer biologischen Einheit an mehrere Rezeptoren einer anderen biologischen Einheit aus (oberer Teil der Graphik) und haben eine Reihe von Charakteristika, die monovalenten Wechselwirkungen fehlen (unten). Besonders im Verbund konnen polyvalente Wechselwirkungen viel starker sein als entsprechende monovalente Wechselwirkungen, und sie konnen die Basis fur das Verstandnis fordernder und hemmender biologischer Wechselwirkungen liefern, die sich grundsatzlich von denen in monovalenten Systemen unterscheiden.
TL;DR: A new generation of nonionic surfactants that are widely applicable and simultaneously ecologically compatible has been developed in the alkyl polyglycosides.
Abstract: A new generation of nonionic surfactants that are widely applicable and simultaneously ecologically compatible has been developed in the alkyl polyglycosides. Their production from the renewable resources glucose and fatty alcohol and their ultimate biodegradation into carbon dioxide, water, and assimilated bacterial biomass is an example for a closed cycle. As a result of their physico-chemical properties and ecotoxicological evaluation, they have become very important as high-performance components of detergents and cosmetic preparations.
TL;DR: The combined use of several complimentary helical assembling techniques in a hierarchical process, a method used by nature, will ultimately allow the design and construction of helical architectures such as 1 with a predefined organization and function.
Abstract: From hexahelices to nanometer-sized fibers: Helical molecular, macromolecular, and supramolecular structures have moved into the forefront of chemical research in the last years. The information that determines the formation and sense of the helical architecture can be incorporated in the constituent molecular building blocks. The combined use of several complimentary helical assembling techniques in a hierarchical process, a method used by nature, will ultimately allow the design and construction of helical architectures such as 1 with a predefined organization and function.
TL;DR: In this paper, a remarkable selectivity on the basis of size is observed for the encapsulation of Et4N+ in the presence of Me4N+) and Pr4N+, by a predesigned [Ga4L6]12− homochiral tetrahedral cluster (L=bis-bidentate ligand).
Abstract: A remarkable selectivity on the basis of size is observed for the encapsulation of Et4N+ in the presence of Me4N+ and Pr4N+ by a predesigned [Ga4L6]12− homochiral tetrahedral cluster (L=bis-bidentate ligand). Immediate and quantitative stepwise replacement of R4N+ counterions in the cluster cavity is observed by 1H NMR spectroscopy (see below). The encapsulation of Et4N+ is also observed in the solid state.
TL;DR: The discovery that peptide nucleic acids (PNAs, B=nucleobase), in spite of their drastic structural difference to natural DNA, are better nucleic acid mimetics than many other oligonucleotides has resulted in an explosion of research into this class of compounds.
Abstract: The astonishing discovery that peptide nucleic acids (PNAs, B=nucleobase), in spite of their drastic structural difference to natural DNA, are better nucleic acid mimetics than many other oligonucleotides has resulted in an explosion of research into this class of compounds. The synthesis, physical properties, and biological interactions of PNAs as well as their chimeras with DNA and RNA are summarized here.
TL;DR: The principle of chemical ligation of reactive partners (see reaction scheme) has been employed to find a new, highly efficient synthesis of fused 3-aminoimidazoles.
Abstract: When general and reliable, multicomponent reactions are among the most powerful tools in modern drug discovery. The principle of chemical ligation of reactive partners (see reaction scheme) has been employed to find a new, highly efficient synthesis of fused 3-aminoimidazoles.