scispace - formally typeset
Search or ask a question

Showing papers in "Angewandte Chemie in 1999"


PatentDOI
TL;DR: A very broad, additional spectrum of possible applications for intelligent polymers that covers an area from minimally invasive surgery, through high-performance textiles, up to self-repairing plastic components in every kind of transportation vehicles.
Abstract: Shape memory polymer compositions, articles of manufacture thereof, and methods of preparation and use thereof are described. The shape memory polymer compositions can hold more than one shape in memory. Suitable compositions include at least one hard segment and at least one soft segment. The Ttrans of the hard segment is preferably between -30 and 270 °C. At least one of the hard or soft segments can contain a cross-linkable group, and the segments can be linked by formation of an interpenetrating network or a semi-interpenetrating network, or by physical interactions of the blocks. Objects can be formed into a given shape at a temperature above the Ttrans of the hard segment, and cooled to a temperature below the Ttrans of the soft segment. If the object is subsequently formed into a second shape, the object can return to its original shape by heating the object above the Ttrans of the soft segment and below the Ttrans of the hard segment. The compositions can also include two soft segments which are linked via functional groups which are cleaved in response to application of light, electric field, magnetic field or ultrasound. The cleavage of these groups causes the object to return to its original shape.

2,837 citations


Journal ArticleDOI
TL;DR: A blueprint for the design of oxide materials is provided by nature and members of the ever-expanding class of polymeric coordination complex cations, novel molybdenum oxide substructures, such as the one shown, may be prepared.
Abstract: A blueprint for the design of oxide materials is provided by nature. By borrowing from nature's ability to influence inorganic microstructures in biomineralization processes and in the hydrothermal synthesis of complex minerals, a new class of materials in which organic components exert a role in controlling inorganic microstructure is evolving. By employing members of the ever-expanding class of polymeric coordination complex cations, novel molybdenum oxide substructures, such as the one shown, may be prepared.

2,371 citations


Journal ArticleDOI
TL;DR: Aluminosilicate zeolites such as UTD-1 belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange.
Abstract: Aluminosilicate zeolites such as UTD-1 (structure shown) belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange. During the last decade, the rate of discovery of new open-framework materials based, for example, on phosphates, sulfides, halides, nitrides, and coordination compounds has increased dramatically. The synthesis, structures, and properties of this remarkable class of materials are reviewed.

2,205 citations


Journal ArticleDOI
TL;DR: The unique structure of MCM-41 silicates has provided for extremely attractive properties such as uniform pore sizes greater than 20 A, surface areas exceeding 1000 m2 g−1, and long-range ordering of the pores.
Abstract: The unique structure of MCM-41 silicates (shown in the picture) has provided for extremely attractive properties—uniform pore sizes greater than 20 A, surface areas exceeding 1000 m2 g−1, and long-range ordering of the pores. Recent research in supramolecular-templated mesoporous materials has led to a wide range of compositions, to uses in a variety of catalytic reactions, and to a better control of bulk morphologies.

1,923 citations


Journal ArticleDOI
TL;DR: Even late transition metal complexes function as active and selective catalysts for α-olefin polymerization, and an intense search has developed for new-generation catalysts, in both academic and industrial research laboratories.
Abstract: Even late transition metal complexes function as active and selective catalysts for α-olefin polymerization. The discovery of a highly active family of catalysts 1 based on iron, a metal that had no previous track record in this field, has highlighted the possibilities for further new catalyst discoveries. As a result, an intense search has developed for new-generation catalysts, in both academic and industrial research laboratories. R1=H, Me; R2=Me, iPr; R3=H, Me, iPr; R4=H, Me; X=halide.

1,737 citations


Journal ArticleDOI
TL;DR: Despite the small differences in sequence between the two peptides studied, the simulations correctly predict a left-handed 31-helical fold for the beta-heptapeptide and a right-handed helical Fold for thebeta-hexapeptides.
Abstract: Accurate reproduction of the mechanism of peptide folding in solution and conformational preferences as a function of amino acid sequence is possible with atomic level dynamics simulations. For example, the simulations correctly predict a left-handed 31-helical fold for the β-heptapeptide 1 (the molecular model is shown in the picture) and a right-handed helical fold for the β-hexapeptide 2, as was confirmed by NMR spectroscopy.

1,689 citations


Journal ArticleDOI
TL;DR: Fast identification of binding activity directly from mixtures of potential ligands is possible with the NMR method described, which is based on saturation transfer to molecules in direct contact to a protein.
Abstract: Fast identification of binding activity directly from mixtures of potential ligands is possible with the NMR method described, which is based on saturation transfer to molecules in direct contact to a protein. In addition, the ligand's binding epitope is easily identified. High sensitivity and ease of use are the principal advantages of this method. The picture shows the normal 1D NMR spectrum of a mixture and the spectrum obtained by applying the STD method, which exclusively shows signals from molecules with binding affinity.

1,432 citations


Journal ArticleDOI
TL;DR: C-C coupling by transition metal catalyzed C-H activation has developed into a diverse area of research, and the variety of products obtained range from basic chemicals to pharmaceuticals and building blocks for carbon networks.
Abstract: C−C coupling by transition metal catalyzed C−H activation has developed into a diverse area of research. The applicable catalysts are manifold, and the variety of products obtained range from basic chemicals to pharmaceuticals and building blocks for carbon networks. One reaction, in which several C−C bonds are formed under C−H activation of a methyl group, is the conversion of ortho-iodoanisole according to Equation (1).

916 citations


Journal ArticleDOI
TL;DR: The development of structure-property relationships for monodisperse oligomers has been extremely useful to rationalize the properties of high molecular weight linear π-conjugated polymers.
Abstract: The development of structure-property relationships for monodisperse oligomers has been extremely useful to rationalize the properties of high molecular weight linear π-conjugated polymers. A great variety of spectacular molecular architecture has been generated, culminating in the recent preparation of molecular wires such as 1 with lengths exceeding 10 nm that have potential applications in molecular electronics.

839 citations


Journal ArticleDOI
TL;DR: The optimization of low-potency leads into drugs is often accompanied by an increase in molecular weight and lipophilicity, as a consequence of affinity enhancement, shown schematically by the distributions of M(r) for a leadlike library, oral drugs, and a typical combinatorial chemistry library.
Abstract: The optimization of low-potency leads into drugs is often accompanied by an increase in molecular weight (M(r)) and lipophilicity, as a consequence of affinity enhancement. Hits with affinity at µM levels discovered by screening leadlike libraries allow scope for this optimization process, as shown schematically by the distributions of M(r) for a leadlike library (1), oral drugs (2), and a typical combinatorial chemistry library (3). y=percentage with a particular molecular weight.

742 citations


Journal ArticleDOI
TL;DR: In the fight against cancer cisplatin, one of the world's best selling anticancer drugs, is being joined by other platinum, titanium, and ruthenium complexes, and metal-targeted organic agents show exciting clinical potential.
Abstract: Not only the 24 or so essential elements, but also nonessential and even radioactive elements have enormous potential for applications in medicine. In the fight against cancer cisplatin, one of the world's best selling anticancer drugs, is being joined by other platinum, titanium, and ruthenium complexes. Gadolinium(III) complexes can be safely injected as magnetic resonance imaging contrast agents, and ligand design allows targeting of paramagnetic ions as well as radiodiagnostic (e.g. 99mTc) and radiotherapeutic isotopes (e.g. 186Re). Manganese superoxide dismutase mimics, vanadium insulin mimics, ruthenium nitric oxide scavengers, lanthanide-based photosensitizers, and metal-targeted organic agents show exciting clinical potential.

Journal ArticleDOI
TL;DR: A unique combination of a clearly defined particle structure and a very highly functionalized surface is offered by the topical dendrimers and an MRI contrast agent based on dendedrimers that facilitate the visualization of bloodstreams is developed.
Abstract: A unique combination of a clearly defined particle structure and a very highly functionalized surface is offered by the topical dendrimers. Many groups work on this unusual molecular architecture to develop new applications. The most advanced progress in this respect is an MRI contrast agent based on dendrimers (see schematic representation) that facilitate the visualization of bloodstreams.

Journal ArticleDOI
TL;DR: Specific, designed, nonperiodic arrangements of gold nanocrystals that are 5 and 10 nm in diameter can be prepared with double-stranded DNA serving as a template.
Abstract: Specific, designed, nonperiodic arrangements of gold nanocrystals that are 5 and 10 nm in diameter can be prepared with double-stranded DNA serving as a template (see drawing; A' and B' denote oligonucleotide sequences complementary to sequences A and B). The methods described should be applicable to nanocrystals composed of various materials.

Journal ArticleDOI
TL;DR: A systematic look at the available data on C-C bond activation in solution provides some answers to questions about the ligated metal center and the possible mechanisms of C- C bondactivation in various reaction systems.
Abstract: What kind of ligated metal center is necessary for insertion into the "hidden" C-C bond? How can one tune the metal center for C-C bond activation by variation of the steric and electronic properties of ligands? What are the possible mechanisms of C-C bond activation in various reaction systems? A systematic look at the available data on C-C bond activation in solution provides some answers to these questions.

Journal ArticleDOI
TL;DR: Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems.
Abstract: Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality.

Journal ArticleDOI
TL;DR: A unique combination of steric and electronic properties appears to determine the effectiveness of phosphanyl-substituted biphenyls as ligands in palladium-catalyzed aminations and Suzuki coupling of aryl chlorides at room temperature.
Abstract: A unique combination of steric and electronic properties appears to determine the effectiveness of phosphanyl-substituted biphenyls as ligands in palladium-catalyzed aminations and Suzuki coupling of aryl chlorides at room temperature [Eq. (1)]. The oxidative addition step is greatly accelerated, and transmetalation (or Pd-N bond formation) and reductive elimination processes are facilitated. Use of these ligands allows for Suzuki coupling at very low catalyst loadings (as little as 10(-6) mol % Pd). R"=cyclohexyl, tert-butyl.

Journal ArticleDOI
TL;DR: Cooperative phenomena, described by one-dimensional statistical physical methods, are observed between the enantiomeric characteristics of monomeric materials and the polymers they produce, offering the possibility of developing chiral catalysts and chiral chromatographic materials in which the burden of large enantiomersic excess or content may be considerably alleviated.
Abstract: Cooperative phenomena, described by one-dimensional statistical physical methods, are observed between the enantiomeric characteristics of monomeric materials and the polymers they produce. The effect of minute energies associated with this amplified chirality, although currently not interpretable, can be easily measured. Nonlinear relationships between enantiomeric excess or enantiomeric content and polymer properties may offer the possibility of developing chiral catalysts and chiral chromatographic materials in which the burden of large enantiomeric excess or content may be considerably alleviated. New approaches to information and sensor technology may become possible.

Journal ArticleDOI
TL;DR: The war against infectious bacteria is not over!
Abstract: The war against infectious bacteria is not over! Although vancomycin and glycopeptide antibiotics have provided a strong last line of defence against many drug-resistant bacteria, their overuse has given rise to more dangerous strains of bacteria. An understanding of the chemistry and biology of these highly complex glycopeptides are destined to play a crucial role in the discovery of new antibiotics.

Journal ArticleDOI
TL;DR: A chemically advanced template search based on topological pharmacophore models has been developed as a technique for virtual screening and has successfully identified novel potent Ca(2+) antagonists in a library of several hundred thousand compounds on the basis of a correlation vector representation.
Abstract: A chemically advanced template search (CATS) based on topological pharmacophore models has been developed as a technique for virtual screening. This technique has successfully identified novel potent Ca(2+) antagonists (such as 2) that have a similar activity to 1 (a known T-channel blocking agent) in a library of several hundred thousand compounds on the basis of a correlation vector representation.

Journal ArticleDOI
TL;DR: In the gas phase, the structures of oxirane small middle dots small middle dot small middle node small middle point (SMSD) and oxiranes small middle points small middle nodes small middle positions (SMPD) have been shown to have similar properties to those of B small middle matrices as discussed by the authors.
Abstract: Similar and yet also notably different are the B small middle dot small middle dot small middle dotXY and B small middle dot small middle dot small middle dotHX complexes in the gas phase, where B is a simple Lewis base, XY is a homo- or heterodihalogen molecule, and HX is a hydrogen halide. This is demonstrated, for example, by the structures of oxirane small middle dot small middle dot small middle dotClF and oxirane small middle dot small middle dot small middle dotHCl (see picture). Both bonds are dominated by simple electrostatic interactions, but differ in terms of their propensity for nonlinearity.

Journal ArticleDOI
TL;DR: Extraordinarily stable, monodisperse noble metal nanoparticles can be prepared by using dendrimers as both templates and stabilizers, and the catalytic activity and selectivity of these materials can be controlled by adjusting the d endrimer generation.
Abstract: Extraordinarily stable, monodisperse noble metal nanoparticles can be prepared by using dendrimers as both templates and stabilizers. Dendrimer-encapsulated Pd nanoparticles (see the schematic representation) exhibit high catalytic activity for the hydrogenation of alkenes in water. The catalytic activity and selectivity of these materials can be controlled by adjusting the dendrimer generation.

Journal ArticleDOI
TL;DR: Monitoring with a fluorescence microscope should allow direct identification of intracellular production and location of NO.
Abstract: The membrane-permeating indicator DAF-FM DA is transformed by intracellular esterases into the highly water-soluble dye DAF-FM, which traps NO produced by NO synthase (NOS) to yield a highly fluorescent triazole compound in cells (see schematic diagram). Monitoring with a fluorescence microscope should allow direct identification of intracellular production and location of NO.

Journal ArticleDOI
TL;DR: Wound healing properties of plant extracts that contain the naphthoquinone natural products alkannin and shikonin have been known for many centuries and their production both by cell cultures and chemical synthesis has been studied extensively.
Abstract: Wound healing properties of plant extracts that contain the naphthoquinone natural products alkannin (1) and shikonin (2) have been known for many centuries. More recently, the biological properties of 1, 2, and related derivatives have been demonstrated experimentally, and their production both by cell cultures and chemical synthesis has been studied extensively.

Journal ArticleDOI
TL;DR: This work shows many examples of how, through the choice of ligand, the configuration of a metal center or the chirality of a helicate can be predetermined.
Abstract: Asymmetric synthesis in coordination chemistry was described very clearly by Smirnoff in 1920, but, contrary to the development in organic chemistry, it was almost completely neglected for several decades. The interest in chirality in coordination chemistry (see the stereoview of [Ru(bpy)3 ]2+ ) has increased rapidly in recent times as a consequence of developments in several fields where chirality is important (polynuclear systems, supramolecular structures, and enantioselective catalysis). Here we show many examples of how, through the choice of ligand, the configuration of a metal center or the chirality of a helicate can be predetermined.

Journal ArticleDOI
TL;DR: In this paper, Pillared-layer-type coordination networks [Cu2(pzdc)2(L)n] are used to build up stable tunable channels.
Abstract: Stable tunable channels are formed by pillared-layer-type coordination networks [{Cu2(pzdc)2(L)}n] (pzdc = pyrazine-2,3-dicarboxylate; L = pyrazine, 4,4′-bipyridine, N-(4-pyridyl)isonicotinamide). Not only their channel sizes, shapes, and chemical environments are systematically built up by tuning the pillar ligands, but also the porosity is maintained in the absence of the included guest molecules. These compounds can adsorb methane, and the amount of gas adsorption is controllable by the type of pillar ligands.

Journal ArticleDOI
TL;DR: After forever changing the drug discovery process in the pharmaceutical industry, combinatorial chemistry methodologies are increasingly being applied to the discovery and optimization of more efficient catalysts and materials.
Abstract: After forever changing the drug discovery process in the pharmaceutical industry, combinatorial chemistry methodologies are increasingly being applied to the discovery and optimization of more efficient catalysts and materials (see picture). With the advent of new combinatorial synthesis and screening technologies, coupled with integrated data management systems, the application of these technologies to materials science and catalyst research holds tremendous potential and brings high expectations to this new and exciting field.

Journal ArticleDOI
TL;DR: Not "from above", but "from the side": Configuration-retaining β-glycosidases protonate their substrate either anti or syn to the endocyclic C1-O bond as the first step in the enzymic cleavage of the glycosidic bond.
Abstract: Not "from above", but "from the side": Configuration-retaining β-glycosidases protonate their substrate either anti or syn to the endocyclic C1-O bond as the first step in the enzymic cleavage of the glycosidic bond (see schematic drawing). Insights into the mechanism of action of glycosidases have been gained by a combination of the synthesis of inhibitors, the study of the kinetics of their inhibition, and the analysis of the crystal structures of glycosidases and glycosidase-ligand complexes.

Journal ArticleDOI
TL;DR: Acentric three-dimensional coordination polymers bis(isonicotinato)zinc and bis(4-pyridylacrylato)cadmium⋅H2 O (2) were synthesized under hydro(solvo)thermal conditions and exhibit remarkable thermal stability.
Abstract: Acentric three-dimensional coordination polymers bis(isonicotinato)zinc (1) and bis(4-pyridylacrylato)cadmium⋅H2 O (2) were synthesized under hydro(solvo)thermal conditions; they exhibit a threefold (see picture) and fivefold diamondoid structure, respectively. Both 1 and 2 are active for second harmonic generation and exhibit remarkable thermal stability.

Journal ArticleDOI
TL;DR: The statistical analysis of the structures of the natural and synthetically derived compounds has shown conspicuous variations in structural types in the natural products derived from different natural sources, which can be utilized in the search for individual active substances.
Abstract: The potential of new natural products as an important source for the exploration and development of new drugs and crop protection products is a long way from being exhausted. The statistical analysis of the structures of the natural and synthetically derived compounds has shown conspicuous variations in structural types in the natural products derived from different natural sources, which can be utilized in the search for individual active substances. The occasionally voiced prepossession that natural products have already been sufficiently examined and therefore no more innovations are to be expected can definitely be rejected.

Journal ArticleDOI
TL;DR: Kinetic control of crystal growth in the presence of a coordinating ligand is critical for the formation of a new structure of elemental cobalt (ε-cobalt, the unit cell with the two different types of cobalt atoms is shown), which was discovered upon analyzing the metallic powder produced by the thermal decomposition of [Co2 (CO)8 ] in solution in the absence of trioctylphosphane oxide.
Abstract: Kinetic control of crystal growth in the presence of a coordinating ligand is critical for the formation of a new structure of elemental cobalt (e-cobalt, the unit cell with the two different types of cobalt atoms is shown), which was discovered upon analyzing the metallic powder produced by the thermal decomposition of [Co2 (CO)8 ] in solution in the presence of trioctylphosphane oxide [TOPO, Eq. (1)].