bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Characterization of Non‐Oxide Chalcogenide Glasses using Solid State NMR
Authors: Eckert Hellmut 
Published: December 2003

AbstractIn spite of the long‐standing importance of non‐oxide chalcogenide glasses in infrared optics and semiconductor technology, concepts describing the structural principles governing glass formation in these systems are just emerging. Most recently, modern quantitative solid state NMR techniques have offered new unique insights into the structural organization of these systems. In this review, we discuss the basic principles of various experimental approaches and their application to boron‐silicon, ‐and phosphorus chalcogenide glasses.
Starburst Dendrimers: Molecular‐Level Control of Size, Shape, Surface Chemistry, Topology, and Flexibility from Atoms to Macroscopic Matter
Authors: Tomalia Donald A. , Naylor Adel M. , Goddard William A. 
Published: December 2003

AbstractStarburst dendrimers are three‐dimensional, highly ordered oligomeric and polymeric compounds formed by reiterative reaction sequences starting from smaller molecules—“initiator cores” such as ammonia or pentaerythritol. Protecting group strategies are crucial in these syntheses, which proceed via discrete “Aufbau” stages referred to as generations. Critical molecular design parameters (CMDPs) such as size, shape, and surface chemistry may be controlled by the reactions and synthetic building blocks used. Starburst dendrimers can mimic certain properties of micelles and liposomes and even those of biomolecules and the still more complicated, but highly organized, building blocks of biological systems. Numerous applications of these compounds are conceivable, particularly in mimicking the functions of large biomolecules as drug carriers and immunogens. This new branch of “supramolecular chemistry” should spark new developments in both organic and macromolecular chemistry.
Chemiluminescence Techniques for the Characterization of Materials [New Analytical Methods (41)]
Authors: Mendenhall G. David 
Published: December 2003

AbstractPhotons are emitted at low levels from a wide variety of organic materials at wavelengths ranging from the visible to infrared. This light emission accompanies free‐radical autoxidation and charge‐recombination processes and is particulary useful in assessing thermal oxidation and radiation damage as well as polymer curing reactions. IR chemiluminescence, which offers advantages because of reduced self‐absorption, has been shown to mark the end of induction periods in inhibited systems. With the introduction of sensitive solid‐state devices, the chemiluminescence technique has been extended to two‐dimensional imaging and presentation.
Two‐Dimensional Model Networks
Authors: Rehage Heinz , Veyssié Madeleine 
Published: December 2003

AbstractThis article is concerned with the structure and dynamic properties of thin films that have been chemically stabilized by polymerization and cross‐linking reactions. By using different types of monomers it is possible to construct networks with rubber‐like elasticity or with glassy properties, or temporary networks, in the interfacial region between oil and water. The systematic study of these ultrathin membrances offers new insights into aspects of current research, and opens up a wide range of potential new applications.
Stereocontrolled Construction of Complex Cyclic Ketones via Oxy‐Cope Rearrangement
Authors: Paquette Leo A. 
Published: December 2003

AbstractConvergency is a highly serviceable aspect of organic synthesis, particularly when its application is accompanied by high levels of chirality transfer and regiocontrol. A reaction that is notably well suited to these objectives is the oxy‐Cope rearrangement. In addition, the benefits that can accrue from suitable condensation of β γ‐unsaturated ketones with a vinyl organometallic and subsequent [3,3] sigmatropic shift are substantive enhancement in structural complexity and the ability to generate a myriad of polycyclic frameworks. Another profitable feature is the complementary regeneration of the carbonyl group in a new structural context. In view of the pivotal role played by the carbonyl functionality in synthetic transformations, reacquisition of such a reaction site translates into heightened chemical versatility. The trajectories followed by vinyl organometallics as they engage in 1,2 addition to ketones are gradually being understood. Proper diastereoselective control of this bond‐making process, when coupled with full awareness of the chair or boat topography adopted during the ensuing oxy‐Cope electronic reorganization, provides for exciting new strategy‐level dimensions not often available in other contexts. The use of this two‐step sequence as a prelude to a third chemical event clearly serves to expand the possibilities for molecular construction still more. While a considerable amount of the work to date has focused on the preparation of rather elaborate carbocyclic molecules, principally with a view to gaining access to complex natural products, the possibilities for heterocyclic synthesis are currently being accorded increased attention.
Complexes of Carbon Monoxide and Its Relatives: An Organometallic Family Celebrates Its Birthday
Authors: Werner Helmut 
Published: December 2003

AbstractNickel tetracarbonyl was discovered one hundred years ago. Its hundredth birthday deserves to be celebrated not only by metal carbonyl chemists. The pioneering work of Mond, Langer, and Quincke has led to developments which, particularly in the last 30 years, have had consequences in many areas outside that of metal carbonyl chemistry. The parent ligand of the family, CO, has been joined by a series of relatives which are isoelectronic with it and which in some cases are even more effective as π acceptors. These are in the main extremely reactive molecules such as CS, CNH, and C= CH2, which, though very short‐lived in the free state, form very stable complexes with transition metals. This article documents the family relationships by structure and reactivity comparisons; attention is also drawn to the synthetic potential of the metal carbonyl analogues, which is still virtually untapped. The final section ventures a look towards the next 100 years, which promise to be just as exciting as the past century.
[(Ph3P)2N]2[Os18Hg2C2(CO)42] a Photochemically Generated High‐Nuclearity Cluster Which Reversibly Incorporates Metallic Mercury into Its Metal Core
Authors: Charalambous Eleni , Gade Lutz H. , Johnson Brian F. G. , Kotch Thomas , Lees Alistair J. , Lewis Jack , McPartlin Mary 
Published: December 2003

AbstractNo Absract.
What Does the Chemical Industry Expect from Physical and Industrial Chemistry?
Authors: Jentzsch Wolfgang 
Published: December 2003

AbstractProcess innovation—the systematic optimization of raw materials, energy consumption and product yields—is a constant challenge for those operating plants producing vital basic and intermediate chemicals. The production processes, rather than the products themselves, exhibit life cycles and determine the profitability of downstream manufacturing. The ongoing task of interdisciplinary teams of experts is not just to develop new process routes, but, more commonly, to improve individual process steps. The impulse for this innovation arises from changes in the price and availability of raw materials, economic and environmental considerations and, last but not least, scientific and technological progress. This paper illustrates the opportunities available using examples which have already been put into practice as well as problems not yet resolved. Questions such as the use of alternative feedstocks and the switch to catalytic processes arc addressed and used to suggest novel ideals for basic research. Worthwhile projects are identified in the area of industrial oxidation, both catalytic and non‐catalytic. A highly developed, systematic, computer‐based method for optimizing the integration of energy flows within a plant is presented and novel measurement techniques for efficient production control and product quality are. discussed. The successful realization of such concepts requires the ability and the willingness to think in terms of new approaches to problem solving, making this an important objective for university education geared to future needs.
Specific Interactions of Proteins with Functional Lipid Monolayers—Ways of Simulating Biomembrane Processes
Authors: Ahlers Michael , Müller Wolfgang , Reichert Anke , Ringsdorf Helmut , Venzmer Joachim 
Published: December 2003

AbstractThe interplay between molecular self‐organization and molecular recognition leads to the construction of functional supramolecular systems in which order and mobility are combined and whose function is based on their organization. These fascinating phenomena, for which the living cell is a perfect example, can be understood only if a wide range of scientific disciplines work together. For this purpose, synthetic supramolecular systems can be used to simulate natural biomembrane processes. One example of this is the specific recognition and interaction between membrane‐bound ligands and receptor proteins. Thus, the specific interaction of vitamin H (biotin) with the tetrafunctional protein streptavidin in the monolayer leads to 2D crystallization of the protein. Structural analysis shows that the protein is attached to the lipid membrane by two biotin‐binding sites, leaving two still free. The opportunity this allows for biotinylated molecules to dock to the protein leads to interesting possibilities for constructing protein‐containing functional multilayers. Another example for the simulation of biomembrane processes is the function of enzymes which is coupled to the recognition process. In the interaction of phospholipase A2 with lecithin monolayers, specific recognition between enzyme and substrate is followed by an active phase of lipid cleavage and then by aggregation of the enzyme to give domains of regular morphology. Fluorescence microscopy can be used to follow this process directly: an enzyme caught in action. Der Witz ist der Finder und der Verstand der Beobachter. Georg Christoph Lichtenberg“Wit is the finder and intelligence the observer” [1a].
Polyoxometalate Chemistry: An Old Field with New Dimensions in Several Disciplines
Authors: Pope Michael T. , Müller Achim 
Published: December 2003

AbstractInorganic metal–oxygen cluster anions form a class of compounds that is unique in its topological and electronic versatility and is important in several disciplines. Names such as Berzelius, Werner, and Pauling appear in the early literature of the field. These clusters (so‐called isopoly‐ and heteropolyanions) contain highly symmetrical core assemblies of MOx units (M = V, Mo, W) and often adopt quasi‐spherical structures based on Archimedean and Platonic solids of considerable topological interest. Understanding the driving force for the formation of high‐nuclearity clusters is still a formidable challenge. Polyoxoanions are important models for elucidating the biological and catalytic action of metal–chalcogenide clusters, since metal–metal interactions in the oxo clusters range from very weak (virtually none) to strong (metal–metal bonding) and can be controlled by choice of metal (3d, 4d, 5d), electron population (degree of reduction), and extent of protonation. Mixed‐valence vanadates, in particular, show novel capacities for unpaired electrons, and the magnetic properties of these complexes may be tuned in a stepwise manner. Many vanadates also act as cryptands and clathrate hosts not only for neutral molecules and cations but also for anions, whereby a remarkable “induced self‐assembly process” often occurs. Polyoxometalates have found applications in analytical and clinical chemistry, catalysis (including photocatalysis), biochemistry (electron transport inhibition), medicine (antitumoral, antiviral, and even anti‐HIV activity), and solid‐state devices. These fields are the focus of much current research. Metal–oxygen clusters are also present in the geosphere and possibly in the biosphere. The mixed–valence vanadates contribute to an understanding of the extremely versatile geochemistry of the metal. The significant differences between the chemistry of the polyoxoanions and that of the thioanions of the same elements is of relevance to heterogeneous catalysis, bioinorganic chemistry, and veterinary medicine.
Pulsed Electron Spin Resonance Spectroscopy: Basic Principles, Techniques, and Examples of Applications [New Analytical Methods (43)]
Authors: Schweiger Arthur 
Published: December 2003

AbstractElectron spin resonance (ESR) Spectroscopy has recently undergone a major innovative advance, which is described by the magical phrase pulsed ESR. To the spectroscopist who rubs this Aladdin's lamp there now opens up the mysterious world of spin acrobatics with its many novel and surprising phenomena. The use of pulse techniques makes it possible to reduce measurement times, increase sensitivity, improve resolution and simplify spectra. This article describes the most important pulse techniques used in ESR spectroscopy. Mathematical descriptions are kept to a minimum, space being devoted instead to examples of applications in various areas of chemical research.
Bonding Patterns in Intermetallic Compounds
Authors: Nesper Reinhard 
Published: December 2003

AbstractIntermetallic phases have long been among the black sheep in the family of chemical compounds. Their chemical bonding has eluded description by the valence rules, which otherwise are extremely effective. As a result, understanding of the structure–bonding relationships in these phases to date has remained nebulous, even though they form the largest group of inorganic compounds. Their broad industrial applicability and richly varied structural chemistry call for new approaches for explaining their structures, electronic structures, and physical properties. A combination of new experimental and theoretical investigations has revealed interesting local aspects of chemical bonding in metals and thereby pointed to a route from the valence compounds, through the cluster and electron‐deficient compounds, to the intermetallic phases.
Chemistry and Biology of the Enediyne Anticancer Antibiotics
Authors: Nicolaou K. C. , Dai W.‐M. 
Published: December 2003

AbstractNovel, biologically active substances from nature often provide excitement, stimulation, challenges, and opportunities for the scientific and medical communities. Experience and wisdom dictate investigation of their chemistry and pursuit of their chemical synthesis for more often than not, the rewards for both chemistry and medicine are great. The enediyne anticancer antibiotics are a rapidly emerging class of such compounds derived from bacterial sources. Combining unprecedented and highly unusual molecular architecture, phenomenal biological activities and fascinating modes of action, these DNA cleaving compounds burst onto the scene in the latter half of the 1980s when their structures became known, and they rapidly moved to center stage. Today the enediyne family includes the neocarzinostatin chromophore, the calicheamicins, the esperamicins, and the dynemicins, and soon the number of family members is certain to increase. These molecules elicited extensive research activities in chemical, biological, and biomedical circles and inspired the design of a number of novel molecular assemblies to probe and mimic their chemical and biological actions. A new body of synthetic technology and several novel synthetic strategies have already been devised to address the challenges posed by these molecules, and several new DNA cleaving agents have been designed and synthesized. This article summarizes the chemistry and biology of the enediynes and discusses mechanistic, synthetic, molecular design, and DNA cleavage aspects associated with the field.
New Forms and Functions of Tellurium: From Polycations to Metal Halide Tellurides
Authors: Beck Johannes 
Published: December 2003

AbstractMetal chalcogenides and metal chalcogenide halides are distinguished by their structural diversity and by their very different physical properties. Therefore, the synthesis of novel compounds from this class is always a rewarding goal for the preparatively oriented solid‐state chemist. Over the past few years, many syntheses and structural investigations have stimulated the field. The emphasis of the research has been placed on selenium‐rich and tellurium‐rich compounds, which are characterized by directed covalent bonds between the chalcogen atoms. Compounds with novel chalcogen polycations have also become accessible during the past few years by reacting the chalcogen elements with transition metal halides, or from chemical vapor deposition in the sense of chemical transport reactions. In these compounds, tellurium differs from its lighter homologues by a pronounced tendency towards greater covalence. This article attmepts to provide an overview of new developments in the field of compounds with chalcogen polycations and of metal chalcogenide halides, with an emphasis on compounds containing molybdenum and tungsten as the transition metals and tellurium as the chalcogen.
Protein Structure Determination with Three‐ and Four‐Dimensional NMR Spectroscopy
Authors: Oschkinat Hartmut , Müller Thomas , Dieckmann Thorsten 
Published: December 2003

AbstractStructural biology has made important contributions to the understanding of biological processes. In recent years an increasing amount of structural information has also been derived from NMR spectroscopic studies, often with special emphasis on dynamic aspects. The introduction of three‐ and four‐dimensional techniques has greatly simplified protein structure determination by NMR Spectroscopy, which has in fact become routine. In the past it was more of an art to interpret the complicated NOESY spectra of proteins, but the application of three‐dimensional techniques now makes the interpretation of protein spectra straightforward.In this review we discuss the most important multidimensional NMR techniques along with suitable applications. The emphasis is put less on the discussion of individual pulse sequences than on their application to the structure determination of proteins.
Template Syntheses
Authors: Hoss Ralf , Vögtle Fritz 
Published: December 2003

AbstractAlthough the principle of template synthesis has been known since the sixties, surprising discoveries and new applications in the field of supramolecular chemistry over the last decade have provoked a boom in the subject. The synthesis of supramolecular species has been made much more efficient, or even in some cases possible, by the introduction of template ions or molecules. It is not just metal ions that can act as templates. Neutral molecules, electrostatic interactions, and hydrogen bonds also support the formation of binary and tertiary complexes. Energetically favorable conformations then lead to the formation of a specific desired product in high yield. In addition to the discussion of metal ions and neutral molecules as templates, covalent, positive, and negative templates are differentiated. Kinetic and thermodynamic aspects will also be considered in this review, together with the influence of templates on the phenomenon of self‐organization. Further developments and applications include the synthesis of oligonucleotides, peptide blocks capable of forming secondary structure, and template polymers. Template synthesis of defined molecular cavities ultimately leads to “inclusion chemistry on a nanometer scale.”
Stereocontrolled Synthesis of Oligo(nucleoside phosphorothioate)s
Authors: Stec Wojciech J. , Wilk Andrzej 
Published: December 2003

AbstractEncouraging results obtained for modulation of gene expression by antisense oligonucleotides and their analogues have kindled hopes for a new generation of therapeutics against viral infections, cancer, and many other diseases. Among such analogues, oligo(nucleoside phosphorothioate)s (Oligo‐S) have generally shown the highest efficacy in inhibiting the biosynthesis of “unwanted” proteins. The first clinical trials of antisense agents are now in progress using Oligo‐S against genital warts and acute myeloid leukemia, and tests of Oligo‐S against AIDS should follow soon. Nevertheless, their mechanism of action, internalization, cellular trafficking, subcellular localization, and interaction with cellular proteins is still poorly understood. It is assumed a priori that application involves rapid and efficient molecular recognition of target RNA by Oligo‐S; however, the effects of the chirality of Oligo‐S have so far been unappreciated, because Oligo‐S has not yet been synthesized with stereocontrol. Indeed, the diastereomeric composition of Oligo‐S has never been determined, primarily because of the lack of appropriate analytical methods. Since each of the diastereomers is a stereochemically unique chemical entity, questions arise as to which diastereomer is responsible for an observed biological response, including positive (curative) or possibly negative (toxic) side effects.In this review we intend provide a perhaps somewhat speculative assessment of the problems associated with the stereo‐controlled synthesis of Oligo‐S and to discuss the state‐of‐the‐art in this field including strategies that may lead to Oligo‐S of predetermined chirality. This article is not intended to discourage researchers from further studies of dia‐steromeric mixtures of Oligo‐S as potential pharmaceuticals. Throughout the history of medicinal chemistry numerous useful medicines were discovered, developed, and employed without the detailed knowledge of their structure. Indeed, the composition of the vaccines discovered by Pasteur is a subject of vigorous study still today.
Cyclodextrins as Building Blocks for Supramolecular Structures and Functional Units
Authors: Wenz Gerhard 
Published: December 2003

AbstractCyclodextrins are frequently used as building blocks, because they can be linked both covalently and noncovalently with specificity. Thus one, two, three, seven, fourteen, eighteen, or twenty substituents have been linked to one β‐cyclodextrin molecule in a regioselective manner. Furthermore, Cyclodextrins may serve as organic host molecules. Their internal cavity is able to accommodate one or two guest molecules. Conversely, suitable guest molecules can be used to thread one, two, or many (one hundred or more) cyclodextrin rings. The resulting supramolecular structures are often formed in solution, which allows characterization by high‐resolution spectroscopic methods. Chemical conversion of these structures provides molecular architectures such as catenanes, rotaxanes, polyrotaxanes, and tubes, which are not readily prepared by other methods. The particular properties of Cyclodextrins can also be employed, for example, for the chromatographic separation of complex mixtures of substances, even racemates, by molecular recognition. Cyclodextrins and their derivatives have been found to be remarkably active catalysts as well. Finally, since Cyclodextrins can favorably influence the release of drugs, many new applications will certainly be developed in the near future.