bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Desorption/Ionization Mass Spectrometry of Proteins of Mass 100 000 to 250 000 Dalton
Authors: Karas Michael , Bahr Ute , Ingendoh Arndt , Hillenkamp Franz
Published: December 2003

Irradiation of proteins in a nicotinic acid matrix with the 266‐nm light of a Nd‐YAG laser allowed the first determination of molecular masses up to 250 000 daltons. Since the peaks of multiply charged molecular ions and of oligomer ions can also be used in determination of molecular mass, this method attains a precision of ca. 0.1%. Its potential is demonstrated for β‐D‐galactosidase, glucose isomerase, and catalase.
The Photosynthetic Reaction Center from the Purple Bacterium Rhodopseudomonas viridis (Nobel Lecture)
Authors: Deisenhofer Johann , Michel Hartmut
Published: December 2003

In our lecture we first describe the history and methods of membrane protein crystallization, before we show how the structure of the photosynthetic reaction center from the purple bacterium Rhodopseudomonas viridis was solved. The structure of this membrane protein complex is then correlated with its function as a light‐driven electron pump across the photosynthetic membrane. Finally, we draw conclusions on the structure of the photosystem II reaciton center of plants and discuss the aspects of membrane protein structure. Sections 1 (crystallization), 4 (conclusions on the structure of photosystem II reaction center and evolutionary aspects) and 5 (aspects of membrane protein structure) were presented and written by H. M., sections 2 (determination of the structure) and 3 (structure and function) by J. D. We have arranged the manuscript in this way in order to facilitate continuous reading.
The First PE‐Spectroscopic Investigations of Lithium, Sodium, and Potassium tert‐Butoxide
Authors: Braun Manfred , Waldmüller Delia , Mayer Bernhard
Published: December 2003

It is alway profitable to try and find out more about classical reagents in organic synthesis. The readily sublimable tert‐butoxides of lithium, sodium and potassium have therefore been investigated by photoelectron spectroscopy at 150–180°C in the gaseous state, in which they are present as oligomeric aggregates. According to MNDO calculations the degeneracy of the HOMO of monomeric LiOC(CH3)3 is lifted during transition to the dimes and hexamer, as is also demonstrated in the PE spectrum of the lithium tert‐butoxide vapor consisting of hexamers.
Metal Organic Chemical Vapor Deposition (MOCVD) Perspectives and Prospects
Authors: Williams John O.
Published: December 2003

Review: Thin film epitaxial semiconductor structures of widely varying but controlled compositions and thickness can be prepared using MOCVD. The performance of the method is gauged against molecular beam epitaxy (MBE) and spray pyrolysis, and comment is made on the direction in which this area of research is going, for example, towards the processing of high‐Tc superconductors and ferroelectric oxides.
Magnetic and Magneto‐Optic Thin Films and Multilayers in San Diego
Authors: Marinero Ernesto , Suzuki Takao
Published: December 2003

Conference Report: G. Partridge (GEC) reports on a meeting which concerned the joining of ceramics, glass, and metals and E. Marinero and T. Sizuki (IBM) on two major symposia from the spring meeting of MRS, on magnetic and magneto‐optic thin films and multilayers.
The Active Sites in Manganese‐Containing Metalloproteins and Inorganic Model Complexes
Authors: Wieghardt Karl
Published: December 2003

Manganese is an essential trace element, forming the active sites of a number of metalloproteins. Several metalloproteins contain two or more manganese ions per subunit. The structural properties of these enzymes and the experimental evidence for their proposed structures are described. Parallel to the efforts of biochemists, who are seeking to understand the function of these enzymes on a molecular level, inorganic chemists have been investigating the coordination chemistry of bi‐ and polynuclear complexes of manganese which contain O, N donor atoms and a variety of bridging O, N ligands. A large number of such complexes have been synthesized, their X‐ray structures determined and their magnetic and spectroscopic properties studied in detail. In some instances the electronic and spectroscopic properties of these model compounds are amazingly similar to those of the biomolecules. This has led to a deeper understanding of the structure and sometimes of the function of the metalloproteins. Research on manganese metalloproteins with polynuclear active sites represents a fascinating example of interdisciplinary cooperation between physicists, biochemists and inorganic chemists.
The Beginnings of Organic Photochemistry
Authors: Roth Heinz D.
Published: December 2003

Although sunlight induced photochemistry must have occurred on the planet Earth for billions of years, the chemical changes caused by light have attracted systematic scientific scrutiny only relatively recently. How did scientists first conceive the idea that the interaction of materials with light could not only cause physical phenomena, but could also alter their chemical nature? When sunlight began to be employed as a heat source for distillation, the eventual discovery of photochemical reactions was assured. One can envision three types of changes that would have aroused the curiosity of laboratory chemists: color changes; the evolution of gas bubbles (oxygen in photosynthesis); and the precipitation of a photoproduct less soluble than its precursor. Less predictable was the observation that sunlight caused crystalline santonin to burst because it is converted into a product with a different crystal lattice. In the course of the eighteenth and nineteenth centuries a variety of photochemical reactions, some observed by chance, others uncovered in carefully planned studies, ultimately led to a major systematic investigation that established photochemistry as a viable branch of chemistry.
The European Ceramic Society (ECerS)
Authors: Metselaar Rudi
Published: December 2003

Editorial Essay: The European Ceramic Society (ECerS) is a federation of ceramic societies from eleven European nations. The Society was run for the first two years of its existence by the Dutch ceramists but now control has passed over to the Germans who will direct matters for the next two years. The first president of the new Society explains its aims and constitution.
Solids: Dynamics and Kinetics in Siegen
Authors: Schmalzried Hermann
Published: December 2003

Conference Reports:Ralph Settonreports on his visit to an international symposium on graphite intercalation compounds,Hermann Schmalzriedon the Annual Meeting of the German physical chemists which this year concentrated on solid state chemistry and physics, andHans Reuteron a meeting on the sol–gel processing of ceramics.
How to Tailor Molecular Electronics or Why is Nature Taking the ‘Soft’ Approach?
Authors: Haarer Dietrich
Published: December 2003

Editorial Essay: Nature performs “molecular electronics” with astounding efficiency. Now, researchers attempt to duplicate these processes in order to produce, for example, molecular switches. The recent direction of molecular electronics work has been towards ever increasing miniaturization but this is in fact not how nature approaches the problem. The current status of human “molecular electronics” is assessed and compared with nature's highly successful version.
Surface Analysis I: Imaging Surfaces, Electric Charges and Magnetic Domains with the Atomic Force Microscope
Authors: Rabe Jürgen P.
Published: December 2003

Research News: Surface Analysis I. Atomic Force Microscopy (AFM) provides a method of imaging surfaces on an atomic scale. Closely related to STM, AFM can, however, image insulating materials such as organic molecules. The technique is described and some recent applications discussed in the first article of a regular series from Jürgen Rabe on surface analysis techniques.
Fundamentals of Silicon Chemistry: Molecular States of Silicon‐Containing Compounds
Authors: Bock Hans
Published: December 2003

Silicon and its compounds have made possible the design of new materials, which, from computers to space travel, have helped to shape the technology of our 20th century. Conversely, the demands of new technology have stimulated the fast development of silicon chemistry as part of the “renaissance” of inorganic chemistry. This article uses selected examples of predominantly organosilicon compounds to discuss in simplified terms the measurement and assignment of suitable spectroscopic “molecular fingerprints” as well as the resulting benefit for the preparative chemist. The comparison of “equivalent” states of “chemically related” molecules is emphasized, based on perturbation arguments and supporting quantum‐chemical models. Special attention is given to the relation between structure and energy, which allows us to understand and to predict the connectivity between and the spatial arrangement of silicon “building blocks”, the energy‐dependent electron distribution over the effective nuclear potentials of a molecular framework, and, especially, the partly considerable effects of “silicon substituents” on molecular properties. Future‐directed extensions and applications include polysilane band structures, Rydberg states of chromophores containing silicon centers, redox reactions and ion‐pair formation of silicon‐substituted π systems, and molecular dynamic phenomena in solution or on thermal fragmentation in the gas phase. The main objective is a set of clear and practical rules for interpreting measurements and planning experiments.
Indications of Cesium in a Higher Oxidation State
Authors: Moock Klaus , Seppelt Konrad
Published: December 2003

The notion that alkali metals might exhibit oxidation states higher than + I predates concrete evidence for the existence of noble gas compounds with oxidation states up to + VIII, but until now no such species has been positively identified. Cyclovoltammetry and polarography provide evidence for the first time of an electrochemical oxidation of [Cs⊕(Crypt. 2.2.2)]PF, which suggests the presence of higher‐valent cesium, specifically CsIII.
A New Route to Highly Conducting Polyenes
Authors: Hopf Henning , Kretschmer Olaf , Naarmann Herbert
Published: December 2003

Communication: Polymeric films synthesized by the simple heat treatment of allene (propadiene) and several terminal alkynes exhibit a 109 fold increase in electrical conductivity when doped with iodine. The new synthetic method obviates the need for catalysts and the washing process needed to remove impurities from the polymer.
Glass‐Ceramics in the Scheme of Inorganic Materials
Authors: Partridge Graham
Published: December 2003

Research News: Inorganic Materials I. Glasses, ceramics, and glass‐ceramics are examined in the first article of a regular series by Graham Partridge of GEC ALSTHOM. Their definitions, and their mechanical, electrical and thermal properties are summarized and the scene set for future articles.
NMR Microscopy—Fundamentals, Limits and Possible Applications
Authors: Kuhn Winfried
Published: December 2003

Alongside the numerous applications of NMR spectroscopy to structural elucidation in analytical chemistry, and to biochemical and morphological studies by NMR tomography, NMR microscopy makes possible a whole new range of applications. These include imaging, the investigation of biological objects such as plants and small animals, and also the observation of microscopic structures and structural changes in polymers and ceramics. NMR spectroscopy can also be conducted combinationally as volume‐selective spectroscopy, whereby it is possible to spatially resolve the NMR‐specific parameters: spin density ϱ, chemical shifts δ, and the relaxation times T1 and T2. The numerous well developed methods available make it possible to study dynamic processes by fast imaging with a temporal resolution in milliseconds. This not only allows the imaging of moving objects without incurring movement artefacts but also the measurement of diffusion constants in isotropic and anisotropic diffusion—in the latter case allowing, in principle, the determination of the complete diffusion tensor. The spatially resolved measurement of the relaxation times yields information on molecular mobility and bonding, e. g. the bonding of water, or other solvents, to polymers, the mobility of fluids in polymers or ceramics, or the three‐dimensional evaluation of pore size in porous materials. In biomedicine, NMR microscopy allows the observation of growth on the cellular level, the study of embryos, and the development of therapeutic methods in animal experiments. It can lead to a drastic reduction in the number of animal experiments, and in combination with volume‐selective spectroscopy gives valuable information on in‐vivo metabolism.
Biologically Active Analogues of the Extracellular Matrix: Artificial Skin and Nerves
Authors: Yannas Ioannis V.
Published: December 2003

Animal development starts as a single cell which proliferates into several new cells; these differentiate into highly specialized tissues, organs, and limbs; and the small but functioning organism eventually grows into its full scale. Throughout development the extracellular matrices, which are complex macromolecular networks, also undergo dramatic changes. Matrix transformations occasionally control the much more well‐studied changes in number and type of differentiating cells. Extracellular matrix (ECM) networks are typically broken down enzymatically to oligopeptides and are then resynthesized (remodeled) to form insoluble and nondiffusible macromolecular structures which confer stability of shape to multicellular systems. Mature ECM, such as skin, tendon, cartilage, and blood vessels, provides stiffness and strength to tissues and organs. Remodeling of ECM also occurs in adult organisms, during wound healing. An understanding of the role that ECM plays during development or wound healing can be obtained by use of synthetic ECM analogues. Several simple chemical ECM analogues have been synthesized and a few have been found to possess remarkable biological activity. One of these analogues has induced the partial regeneration of skin in an adult guinea pig wound model as well as in man. Peripheral nerve has been regenerated in another animal model by use of a similar ECM analogue. In all these mammalian lesions it is well‐known that regeneration does not occur spontaneously. These analogues are graft copolymers of collagen and chondroitin 6‐sulfate (a glycosaminoglycan) in the state of highly hydrated and covalently cross‐linked gels. Procedures are summarized for synthesis of copolymers with adjusted physicochemical properties, such as the rate at which they degrade enzymatically when implanted, the elements of their pore structure, and the degree of collagen crystallinity. ECM analogues have provided a novel window into the complexities of morphogenesis and regeneration and they have pointed towards entirely new directions in the medical treatment of serious organ dysfunction and organ loss. An ECM analogue has already become the basis of a new clinical treatment for massively burned patients. An interpretation of the results leads to a hypothesis about the nature of ECM during development. Since biological activity appears only when the physicochemical parameters fall within very narrow limits, it is intriguing to speculate that these experiments describe a single insoluble growth factor which is specific for skin synthesis. Such an insoluble growth factor appears to be just as essential to skin development as are the much more well‐known soluble growth factors. A different ECM analogue appears to induce nerve regeneration, possibly because each tissue requires its own developmentally active ECM.
Peptides as Conformational Switch: Medium‐Induced Conformational Transitions of Designed Peptides
Authors: Mutter Manfred , Hersperger René
Published: December 2003

The synthetic oligopeptide I undergoes a spontaneous, reversible transition from an α‐helix to a β‐sheet structure in mixtures of 45% 2,2,2‐trifluoroethanol and 55% H2O. The amphiphilic oligopeptide 1 and two isomers were expressly designed for this investigation. Such peptides, which can exist in several conformations, might find application as “switches” in the de novo design of artificial proteins.
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Active MgH2Mg Systems for Reversible Chemical Energy Storage
Authors: Bogdanović Borislav , Ritter Alfred , Spliethoff Bernd
Published: December 2003

An overview of the importance of and methods available for heat storage in the form of sensible and latent heat is followed by a discussion of the advantages and disadvantages of reversible thermochemical energy storage compared to conventional energy sources such as fuels, i.e. irreversible chemical energy carriers. Of the reversible metal‐hydride–metal systems, the MgH2Mg system is particularly attractive as a hydrogen and a high‐temperature heat storage material because of its high hydrogen content and the high energy content of the Mg–H bond. The advances made in this area over the past few years, namely in catalytic hydrogenation and the doping of magnesium powders, have led to the development of “active MgH2Mg systems” for energy storage. The first experimental results on high‐temperature heat storage (also with cooling) by coupling a MgH2Mg storage system with a low‐temperature metal hydride storage system are presented.
Nickel: An Element with Wide Application in Industrial Homogeneous Catalysis
Authors: Keim Wilhelm
Published: December 2003

The efficiency and future development of the chemical industry are closely linked to catalysis. It has been estimated, for example, that 60 to 70% of all industrial chemicals have involved the use of a catalyst at some point during their manufacture. In the past two decades the share of the market credited to homogeneous transition metal catalysis increasead to 10–15%. Besides cobalt, which is used mainly in hydroformylation reactions, nickel is the most frequently used metal. Many carbon–carbon bond formation reactions can be carried out with high selectivity if catalyzed by organonickel complexes. Such reactions include, inter alia, carbonylation reactions, cyclic and linear oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions. It was Reppe and Wilke who pioneered and shaped the field of homogeneous nickel catalysis. Great impetus was also given to the development of organonickel chemistry by Wilke and his students. Research in this area has contributed immensely towards an understanding of the reactions involved in catalysis.—This review is primarily concerned with nickel‐catalyzed reactions which are of interest both preparatively and industrially; some mechanistic aspects are also dealt with.
On the Conformation and Structure of Organometal Complexes in the Solid State: Two Studies Relevant to Chemical Synthesis
Authors: Shambayati Soroosh , Crowe William E. , Schreiber Stuart L.
Published: December 2003

Conformational preferences of two classes of organometal complexes have been surveyed by inspecting the Cambridge Structural Database (CSD). Lewis acid carbonyl complexes demonstrate a variety of coordination geometries, depending on the electronic and steric requirements of the carbonyl ligands and the nature of the Lewis acid. Similarly, the solid‐state conformation of various π‐bonding ligands in metal acyl, metal nitrosyl, metal acetylene, and metal imido complexes is revealed. These insights have stimulated the development of a conformational model that is based on considerations of π‐bond hybridization and frontier molecular orbital theory. The analyses are relevant to the mechanism and transition structures of many synthetically important transformations. A deeper understanding of the conformational properties of organometal complexes, based on accurate structural information, will likely expedite the design and improvement of metal‐mediated processes.
Synthesis and Structure of the Novel μ2‐Carbido Complex [(TPP)FeCRe(CO)4 Re(CO)5]
Authors: Beck Wolfgang , Knauer Wolfgang , Robl Christian
Published: December 2003

The title compound 2 contains an FeCReRe unit. This 1,3‐dimetallaallene is a novel example of the rare carbide‐bridged complexes. 2 is formed on reaction of the dichlorocarbene complex 1 with pentacarbonylrhenate (TPP  tetra‐phenylporphyrinate).
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Carbonyl Oxides: Zwitterions or Diradicals?
Authors: Sander Wolfram
Published: December 2003

Over the last few years new experimental and theoretical methods have made it possible to gain a more detailed insight into the chemistry of short‐lived reaction intermediates. In 1949 Criegee postulated the intermediacy of carbonyl oxides in the mechanism of ozonolysis, and since then these species have become the goal of much research effort. Even though the formation of “Criegee zwitterions” during ozonolysis and carbene oxidations was proven by scavenger experiments, the electronic structure—zwitterion or diradical—of this short‐lived species is still a subject of debate. To date no stable carbonyl oxide has been found to exist under “normal” laboratory conditions, although by using matrix isolation and laser spectroscopy, it has been possible to obtain highly resolved IR and UV/VIS spectra of carbonyl oxides as well as to determine their dipole moments experimentally. The influence of substituents, exact kinetic data on modes of formation, and the subsequent reactions of carbonyl oxides as well as their photochemistry complete the picture. In accordance with ab initio calculations carbonyl oxides, are best viewed as polar diradicals. The zwitterionic state lies at higher energies and should be stabilized by π donors.
Modern NMR Pulse Experiments: A Graphical Description of the Evolution of Spin Systems
Authors: Eggenberger Urs , Bodenhausen Geoffrey
Published: December 2003

Many modern methods designed to enhance the power of NMR spectroscopy have been widely adopted by the scientific community. Some of the best known among these techniques are one‐dimensional methods for polarization enhancement and spectral editing (“INEPT” and “DEPT”) and various two‐dimensional experiments such as correlation spectroscopy (“COSY”) and nuclear Overhauser spectroscopy (“NOESY”). Most of these methods cannot be described in terms of classical magnetization vectors, and although they can be understood with the help of the density operator formalism, this approach remains difficult for many users, in part because of its cumbersome notation, which prevents one from recognizing the important features at a glance. In this paper, a set of graphical conventions is described which allows one to represent the effect of sequences of radio‐frequency pulses on spin systems in a variety of experiments. The graphs provide a concise description of the network of spins that are coupled through scalar and dipolar interactions, of the state of a spin system expressed in terms of products of operators, and, most importantly, of the transformations from one state to another due to the effect of radio‐frequency pulses, chemical shifts, and scalar couplings. The graphical approach also allows one to represent the effect of phase‐cycling and multiple‐quantum filtration, cross‐relaxation (Overhauser effects) and cross‐correlated relaxation.
Radiation‐Induced Copolymerization of cis‐[PdCl2{CN(CH2)3‐OC(O)CHCH2}2]: A Novel Route to Organometallic Cross‐linked Copolymers Useful for Catalytic Applications
Authors: Corain Benedetto , Zecca Marco , Sam Felix Okon , Palma Giancarlo , Lora Silvano
Published: December 2003

A new polymer has been shown to be an effective hydrogenation catalyst: specifically, the polymer that results from copolymerization (through γ‐ irradiation) of the isocyanide complex 1 with dimethylacrylamide in the presence of N,N′‐methylenebisacrylamide. The PdII centers are initially pre‐hydrogenated to Pd0, after which the catalyst becomes stable, especially with respect to the loss of metallic centers.
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Se, a Bicyclic Polyselenide
Authors: Fenske Dieter , Kräuter Gertrud , Dehnicke Kurt
Published: December 2003

The structural diversity of polyselenide ions has once more been demonstrated. A decaselenadecalin anion Se can be prepared in over 70% yield by heating a polyselenide solution in dimethylformamide in the presence of [Ph3PNPPh3]Cl and a trace of iodine. The product is isolated in the form of black crystals that correspond to a [Ph3PNPPh3]⊕ salt. The two bridgehead selenium atoms in this bicyclo[4.4.0] system are coordinated in such a way as to constitute a distorted pseudo‐trigonal bipyramid, with the bonding between them being equatorial/equatorial.
Vanadium Tetrafluoride
Authors: Becker Stephan , Müller Bernd G.
Published: December 2003

Pale green single crystals of VF4 have been prepared for the first time: by treatment of pure vanadium powder with elemental fluorine in a monel autoclave. The unit cell of VF4 is monoclinic (space group P21/c), and the structure of the material is related to that of SnF4. As in the latter, there are distinct layers of octahedra joined at their vertices, corresponding to [V/2F2/1] and incorporating trans terminal F⊖ ions. Unlike SnF4, however, the layers are not planar, instead displaying undulations.
CH Activation of Acetonitrile by Alkyl Compounds of the Early Lanthanoids: Dimeric Cyanomethyl‐Lanthanoid Complexes with CH2CN Bridges
Authors: Heeres Hero J. , Meetsma Auke , Teuben Jan H.
Published: December 2003

CH2CN bridging ligands are novel. Treatment of acetonitrile with the alkyl lanthanum or cerium compounds 1 results not in the expected insertion of a nitrile group into the Ln‐C σ bond, but rather in activation of a CH bond in the methyl group, leading to the new type of complex 2. In the case of the dimeric lanthanum complex 2, where n = 2, the product has been shown to contain an eight‐membered ring in a chair conformation (Cp*  C5Me5).
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Five Decades Ago: From the “Transuranics” to Nuclear Fission
Authors: Herrmann Günter
Published: December 2003

The discovery of nuclear fission is one of the most outstanding episodes in the history of chemistry: It starts in the spring of 1934 when Enrico Fermi and his group irradiate uranium with neutrons and seem to succeed in going beyond uranium, the then heaviest known element, reaching the first transuranic element; it continues with Otto Hahn, Lise Meitner and Fritz Strassmann who believe to have found additional transuranic elements; with Irène Curie and Paul Savitch who observe an activity which somehow does not fit into that scheme; again with Otto Hahn and Fritz Strassmann who first identify this activity as radium but then on the 17th of December 1938 after rigorous chemical tests realize that the activity is instead barium, thus discovering the fission of the uranium atom into two lighter nuclei; and with Lise Meitner and Otto Robert Frisch who explain nuclear fission on the basis of an already known nuclear model; Otto Robert Frisch finally performs a physical experiment on the 13th of January 1939 which corroborates the fission of uranium. This discovery of nuclear fission is not only an event of historic dimensions, it is also an excellent example of how science evolves, not by successive logical steps but rather through strange detours.
Fast Heteronuclear 3D NMR Spectroscopy
Authors: Schmieder Peter , Kessler Horst , Oschkinat Hartmut
Published: December 2003

Carbon atom correlations become interesting in 3D NMR spectroscopy if one selects CH2 groups with an inverse DEPT sequence in such a way that the spectral breadth in two of the dimensions is limited. 3 D DEPT‐TOCSY has made it possible to obtain, within about ten hours and with a very good signal‐to‐noise ratio, a high‐resolution 13C‐resolved 3D NMR spectrum of a cyclic hexapeptide.
Solid‐State NMR Studies of the Structure and Reactivity of Metakaolinite
Authors: Rocha João , Klinowski Jacek
Published: December 2003

Si atoms in various environments, as well as tetra‐, penta‐, and hexacoordinated AI atoms, have been observed in metakaolinite by high‐resolution solid‐state NMR spectroscopy. Their ratios depend upon the calcination temperature. Studies have shown that the most reactive metakaolinite (calcination temperature 480‐500 °C) is associated with a minimum concentration of hexacoordinate and a maximum concentration of tetra‐ and pentacoordinate Al.
17O NMR Spectroscopy of Benzoyl Compounds YC6H4COX: Sensitivity to Ring Substituents as a Measure of the Electron Demand of the Carbonyl Group
Authors: Dahn Hans , Péchy Peter , Van Toan Vien
Published: December 2003

Contrary to the consensus of opinion 13C‐NMR spectroscopy is not suitable for the determination of electron density at the carbonyl C‐atom. However, by measurement of the 17O‐chemical shift in aromatic carbonyl compounds Y‐C6H4‐COX, X = CF3, H, CH3, CO2R, Br, Cl, F, OCOAryl, SR, OR, NH2, OH, O⊖, reliable statements could be made about the electrophilicity of the carbonyl C‐atom. It is gratifying that the results are in agreement with classical chemical rules. There is much to be said for 17O‐NMR spectroscopy being given more attention than hitherto.
Electrochemical Solid‐State Studies on Oligomeric p‐Phenylenes as Model Compounds for Conductive Polymers
Authors: Meerholz Klaus , Heinze Jürgen
Published: December 2003

Reversible reductions and oxidations at separated potentials are possible electro‐chemically in the solid state up to the tetraanion and tetracation respectively in the case of sexiphenyl. However, at room temperature and depending on the electrode potential the formation of more or less strongly cross‐linked polymer chains is observed during the oxidation. In addition, the measurements prove that the characteristic current plateaus in the voltammograms of conductive polymers are attributable to faradaic redox processes.
A Surface Organometallic Approach for Controlling the Pore Opening Size of Zeolites: the Case of Mordenite Modified via Grafting of Dineopentylmagnesium
Authors: Théolier Albert , Custodero Emmanuel , Choplin Agnès , Basset Jean‐Marie , Raatz Francis
Published: December 2003

The shape selectivity of zeolites toward guest molecules can be controlled by “grafting” organometallic compounds at the entrances to the pores on the surface and thus reducing the size of the pores in a defined way. For example, the adsorption capacity of a mordenite for isooctane is nearly lost upon reaction with dineopentylmagnesium, whereas its capacity for n‐hexane decreases only slightly. Zeolites modified in this way can react still further: for example, oxide coatings can be generated.
Gas Chromatographic Separation of Enantiomers on Cyclodextrin Derivatives
Authors: Schurig Volker , Nowotny Hans‐Peter
Published: December 2003

In investigations concerned with the phenomenon of molecular chirality, the use of gas chromatography for the enantiomeric analysis of stable, volatile compounds is a technique of steadily growing importance. [1] In the last three years an important breakthrough in gas‐chro‐matographic separation of enantiomers has been achieved by using alkylated cyclodextrins (α, β, and γ) as chiral stationary phases in high‐resolution capillary columns. In academic and commercial practice two different and complementary strategies have been adopted up to now. In the first, alkylated cyclodextrins are diluted with polysiloxanes and coated on glass or fused silica capillary columns. In the second, lipophilic per‐n‐pentylcyclodextrins and hydrophilic di‐n‐pentyl‐ and hydroxyalkylpermethylcyclodextrins are coated directly in the form of liquid phases onto suitably pretreated glass or fused silica surfaces. These techniques permit enantiomer separations not only for polar diols and alcohols, derivatized hydroxycarboxylic acids, amino acids, sugars, and alkyl halides, but also for nonpolar alkenes, cyclic saturated hydrocarbons, and metal π complexes. An important aspect for practical applications is that in many cases the enantiomers can be separated without previous derivatization. Whereas the resolution of racemates of unfunctionalized hydrocarbons is attributed to an enantioselective host–guest inclusion complex, some observations indicate that for polar guest molecules additional enantioselective interactions are also involved. The new chiral stationary phases can be used over a wide range of temperatures (25 to 250°C). The technique described is likely to become widely adopted as a simple, accurate and highly sensitive method for the enantiomeric analysis of chiral compounds that can be vaporized without decomposition. It will also stimulate future research aimed at finding universal cyclodextrin phases and elucidating the mechanisms of enantioselectivity.
The Directed Synthesis of Biaryl Compounds: Modern Concepts and Strategies
Authors: Bringmann Gerhard , Walter Rainer , Weirich Ralf
Published: December 2003

The preparation and utilization of specific biaryl systems, particularly those which suffer hindered rotation, is a demanding goal not only in the synthesis of natural products and Pharmaceuticals, but also for example in the discovery of new reagents for asymmetric synthesis. This article will attempt to provide a topical review of modern, efficient processes for the specific preparation of biaryls. This appears to be of particular urgency, since, under the pressure of continually increasing demand, a wealth of new or modified synthetic approaches to the ever more important biaryl systems has been realized in recent years. The high standard which has been reached in this field is impressively demonstrated by regio‐ and stereoselective syntheses of important biaryl natural products such as steganone, ancistrocladine, ancistrocladisine, and dioncophylline A. Besides the utilization of asymmetric induction in the actual coupling step, the thermodynamically or kinetically controlled torsion of biaryl axes belongs to the most important concepts discussed.
Computer Simulation of Molecular Dynamics: Methodology, Applications, and Perspectives in Chemistry
Authors: van Gunsteren Wilfred F. , Berendsen Herman J. C.
Published: December 2003

During recent decades it has become feasible to simulate the dynamics of molecular systems on a computer. The method of molecular dynamics (MD) solves Newton's equations of motion for a molecular system, which results in trajectories for all atoms in the system. From these atomic trajectories a variety of properties can be calculated. The aim of computer simulations of molecular systems is to compute macroscopic behavior from microscopic interactions. The main contributions a microscopic consideration can offer are (1) the understanding and (2) interpretation of experimental results, (3) semiquantitative estimates of experimental results, and (4) the capability to interpolate or extrapolate experimental data into regions that are only difficultly accessible in the laboratory. One of the two basic problems in the field of molecular modeling and simulation is how to efficiently search the vast configuration space which is spanned by all possible molecular conformations for the global low (free) energy regions which will be populated by a molecular system in thermal equilibrium. The other basic problem is the derivation of a sufficiently accurate interaction energy function or force field for the molecular system of interest. An important part of the art of computer simulation is to choose the unavoidable assumptions, approximations and simplifications of the molecular model and computational procedure such that their contributions to the overall inaccuracy are of comparable size, without affecting significantly the property of interest. Methodology and some practical applications of computer simulation in the field of (bio)chemistry will be reviewed.
Complexes with Substituent‐free Acyclic and Cyclic Phosphorus, Arsenic, Antimony, and Bismuth Ligands
Authors: Scherer Otto J.
Published: December 2003

Until recently, phosphorus, arsenic, antimony and bismuth ligands were nearly always understood to be molecules such as R3E, R2E(CH2)nER2, and RC[(CH2)nER2]3(E = P, As, Sb, Bi) in which the lone pair of the atom E functions as a 2e donor. Current research interests, however, increasingly involve substituent‐free En ligands (n = 1–6), the various types of which are mainly accessible via EX3 (X = F,Cl,Br,Ph), E (SiMe3)3, (RAs)n, P4S3, As4S4, gray arsenic, and especially P4 and As4; these ligands can be stabilized in the coordination spheres of certain transition metal fragments. P1, As1 and Sb1 units with multiple M‐E bonds are found in bi‐ and trinuclear complexes; E1 units can also be encapsulated (partially or completely) in cavities of a variety of metal cluster frameworks. Metallatetrahedranes with up to three E atoms are especially common. Besides E1 units, the greatest variety of coordination modes is exhibited by E4 ligands, which are found as intact tetrahedra and also as parts of chains, polycycles, cubes and a trigonal prism. The phosphorus and arsenic species cyclo‐En, isoelectronic to the carbocyclic (CH)n species, are suitable ligands for forming sandwich complexes (n =3, 4, 5) and triple‐decker sandwich complexes (n = 3, 5, 6). In addition to the wide variety of chemical reactions, remarkable parallels are found in organic chemistry as well as in solid‐state chemistry for many of these substance classes. Some of the molecules have received lively interest from theoretical chemists.
An N‐Phosphino C‐ThiophosphinoyI Nitrilimine as a Formal 1,4 Dipole: Synthesis of 1,2,3λ5‐Diaza‐ and 1,2,4,3λ5‐Triazaphosphinines
Authors: Granier Michel , Baceiredo Antoine , Nieger Martin , Bertrand Guy
Published: December 2003

No Absract.
Synthesis of Two TIIII Diacetonyl Compounds and Crystal Structure of [Tl{CH2C(0)Me}2(μ‐CF3S03)(bpy)]2
Authors: Vicente José , Abad JoséAntonio , Cara Gabriel , Jones Peter G.
Published: December 2003

No Absract.
Organometallic Host‐Guest Systems Representing Novel Charge‐Transfer “Ion Pairs” with Three‐Dimensional Electron‐Donor Networks
Authors: Eller Stefan , Adam Martin , Fisher R. Dieter
Published: December 2003

No Absract.
Stereospecific Insertion of the Carbene Ligand of a Fischer Carbene Complex into Olefinic CH Bonds
Authors: Wienand Anette , Reissig Hans‐Ulrich
Published: December 2003

No Absract.
Novel Bonding Mode for a Cyanometalate Ligand: Synthesis and Crystal Structure of the Mn4Pd4 Cluster [(OC)Pd(μ‐NC)Mn(η‐C5H4Me)(CO)2]4 Containing an Orthogonal Arrangement of Helical Units
Authors: Braunstein Pierre , Oswald Benoît , Tiripicchio Antonio , Camellini Marisa Tiripicchio
Published: December 2003

No Absract.
α‐Umpolung of Ketones via Enol Radical Cations: A Mechanistic Study
Authors: Schmittel Michael , Abufarag Ahmed , Luche Olaf , Levis Michael
Published: December 2003

No Absract.
Facile Hydrogenation of the Central Cyclohexatriene of Tris(benzocyclobutadieno)benzene: Synthesis, Structure, and Thermal and Photochemical Isomerization of all‐cis‐Tris(benzocyclobuta)cyclohexane
Authors: Mohler Debra L. , Vollhardt K. Peter C. , Wolff Stefan
Published: December 2003

No Absract.
Structure of a Synthetic Trefoil Knot Coordinated to Two Copper(I) Centers
Authors: Dietrich‐Buchecker Christiane O. , Guilhem Jean , Pascard Claudine , Sauvage Jean‐Pierre
Published: December 2003

No Absract.
Epoxidation of the PC Double Bond of Phosphaalkene Complexes: X‐Ray Crystal Structure Analysis of a Stable Oxaphosphirane Complex
Authors: Bauer Siegfried , Marinetti Angela , Ricard Louis , Mathey François
Published: December 2003

No Absract.
Fluorescence “Off–On” Signalling upon Linear Recognition and Binding of α,ω‐Alkanediyldiammonium Ions by 9,10‐Bis{(1‐aza‐4,7,10,13,16‐pentaoxacyclooctadecyl)methyl}anthracene
Authors: de Silva A. Prasanna , Sandanayake K. R. A. Samankumara
Published: December 2003

No Absract.
Chemistry for the Future—State of the Art and Perspectives
Authors: Quadbeck‐Seeger Hans‐Jürgen
Published: December 2003

A particularly close relationship exists between chemistry, the science of the transformation of matter, and developments in human living conditions. Though little more than 150 years old, chemical technology has had a greater influence on our civilization than any other technological discipline. Its roots lie not in the crafts, but in scientific research. Relationships derived from the laws of nature were taken as a basis for the systematic solution of practical problems. It is to this strategy that chemistry owes its success. New opportunities arise from new discoveries. These result from basic research at universities, research institutes, and industrial laboratories. Applied research in turn transforms the discoveries into innovative solutions to problems on an industrial scale. The objectives of applied research are oriented toward the marketplace and to the needs of mankind. Our knowledge of scientific interrelationships has been growing with unabated vigor for decades, but so too has our insight into the enormous complexity of the material world. Many of the problems that civilization faces result from the fact that our knowledge is still inadequate. Intensive research and development offer the only hope for progress. Scientists must of course act responsibly with the knowledge they acquire, and they must provide the information necessary to establish public confidence in their methods and products. This is the prerequisite for broad acceptance of technological progress, and given the extent of the world's population no alternative to progress exists. The shape of that progress is also subject to influences outside the realm of science, however, including social norms and political activities. A country that is not rich in raw materials, like the Federal Republic of Germany, must pay particular attention to these factors as well if it is to maintain its innovative strength.
The Integrating Effect of the Research Policy of the European Communities
Authors: Narjes Karl‐Heinz
Published: December 2003

The research and development policy of the European Community (EC) was raised to a more solid legal basis by means of an extension of the treaties—the Single European Act—30 years after the enactment of the treaties of Rome. Today, the EC has succeeded in creating an independent, successful continent‐wide research und development community despite rather limited budgetary means. The reasearch activities of the EC were originally restricted to EURATOM, which takes care of problems concerning civil nuclear research. EURATOM brought many experiences in the course of time, and also yielded many successes. We have learned above all how community research and national research are to be coordinated in the most efficient way. After the energy crisis of the seventies, and after many national R & D failures in various fields, high priority was given to the improvement and safeguarding of the technological competitivity of the community and the effective strengthening of its innovation potential. It was more and more generally accepted that all R & D resources had to be concentrated throughout the community in order to enable it to compete successfully, especially with the U. S. and Japan. In order to fulfill this objective a research policy with a strong integrating effect was requested in addition to the national R & D research policies. Cohesion and know‐how transfer inside the EC belong therefore to the central issues of the R & D policy of the community, as do special efforts to include small and medium‐sized institutes and enterprises (SMEs). Framework programs were introduced in the eighties in order to ensure a medium‐term disposability of the budgetary means for R & D and to secure a certain continuity. The third framework program has been agreed upon, and it provides research funding until 1994. In 1987 approximately 1 Bill. Ecu/year were spent for R & D. Today, 1, 5 Bill. Ecu/year are available, and this amount will further grow to provide approximately 2 Bill. Ecu/year in 1992/93. Issues like the difference between basic and applied research under inclusion of industry‐political viewpoints are also included in this report. Furthermore, cooperation with and delimitation to other countries or communities such as the U. S. and Japan or the EFTA and the Comecon member states will be discussed. Finally, perspectives for R & D policies of the European Community in the nineties will be presented.
Elementary Steps in Heterogeneous Catalysis
Authors: Ertl Gerhard
Published: December 2003

Despite the great importance of heterogeneous catalysis, research in this field has long been characterized by its empiricism. Now, however, thanks to the rapid development of methods in surface physics, the elementary steps can be identified at the atomic level and the underlying principles understood. Defined single crystal surfaces are employed as models, based on the analysis of the surfaces of ‘real’ catalysts. Direct images, with atomic resolution, can be obtained using scanning tunneling microscopy, while electron spectroscopic methods yield detailed information on the bonding state of adsorbed species and the influence of catalyst additives (promotors) upon them. The successful application of this approach is illustrated with reference to the elucidation of the mechanism of ammonia synthesis. The catalyst surface is usually transformed under reaction conditions, and, as the processes involved are far‐removed from equilibrium, such transformations can lead to intrinsic spatial and temporal self‐organization phenomena. In this case, the reaction rate may not remain constant under otherwise invariant conditions but will change periodically or exhibit chaotic behavior, with the formation of spatial patterns on the catalyst surface.
Mathematical Modeling of Chemical Reactors—Development and Implementation of Novel Technologies
Authors: Matros Yuri Shaevich
Published: December 2003

Mathematical modeling is an important tool for rapid and reliable reactor development and design. The models are built up from basic studies of the reaction mechanism and kinetics, the transfer processes, and the interactions within the system. A detailed understanding of the elementary processes enables the construction of powerful and complex models for dynamic and steady‐state simulation. With the aid of experimentally determined parameter values one can develop new processes or improve existing ones. Excellent results obtained in experimental work under idealized laboratory conditions can seldom be fully realized in practice. This is due to factors such as transfer resistances, local gradients, fluctuating conditions, and constructional and other limitations which lead to unsatisfactory parameter values and higher costs to compensate for these shortcomings. Some recommendations are made for circumventing these deficiencies.