bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metal Complexes of Thiophosphinic and Selenophosphinic Acids
Authors: Kuchen W. , Hertel H. 
Published: December 2003

AbstractThe anions of thiophosphinic and selenophosphinic acids R2P(X) YH (X = S, Se; Y = O, S, Se) can act as bidentate ligands. They combine with many metals to form complexes containing a four‐membered chelate ring, or to give coordination polymers in which they form ligand bridges. The preparation, properties, and reactions of these compounds, as well as the dielectric properties and analytical use of dithiophosphinato complexes, which are also of industrial interest, are described. Some thiophosphinato and selenophosphinato complexes exhibit concentration‐dependent association via ligand bridges. Evidence of the chelate nature of the ligands R2P(X)Y⊖ was obtained from IR spectroscopic studies. The ligand field parameters of the anion (C2H5)2P(S)S⊖ were deduced from the electronic spectra of octahedral diethyldithiophosphinato complexes, and the position of the ligand in the spectrochemical and nephelauxetic series were determined from these parameters.
Structure and Biosynthesis of the Ergot Pigments
Authors: Franck B. 
Published: December 2003

AbstractIn addition to the well known alkaloids, ergot contains two groups of yellow to red pigments, between which there is a close and novel biogenetic relation. The pigments are anthraquinonecarboxylic acids and dimeric hydroxanthone derivatives (ergochromes), the structures of which, including the absolute configurations at 80 centers of chirality, have been completely determined. The intermediates involved in the biosynthesis have been largely established by feeding with labeled precursors, and its course by model experiments.
A New Type of Corrin Synthesis
Authors: Yamada Yasuji , Miljkovic D. , Wehrli P. , Golding B. , Löliger P. , Keese R. , Müller K. , Eschenmoser A. 
Published: December 2003

AbstractWork towards a synthesis of vitamin B12 has inspired a new type of corrin synthesis. The key step is a light‐induced 1,16‐hydrogen transfer leading to an antarafacial (π→σ)‐cycloisomerization of a seco‐corrinoid metal complex. The construction of the seco‐corrinoid ligand system is achieved by coupling monocyclic ring precursors in their enamide or enamine form through the methods of sulfide‐contraction via oxidative coupling and of iminoester‐enamine condensation.
Methods and Possibilities of Nucleophilic Acylation
Authors: Seebach D. 
Published: December 2003

AbstractNucleophilic acylation is the attachment of anmagnified imagegroup to an electrophilic center. A brief discussion of the advantages offered by acylations of this type in syntheses is followed by a description of the direct methods (reactions with acylmetal compounds) and the methods proceeding via “masked” acyl anions. The latter methods are based on the use of either metalated vinyl ether derivatives or carbanions derived from acetals. Organyllithiums of sulfur‐stabilized carbanions are important reagents of this type.
Elemento‐Organic Amines and Imines
Authors: Scherer O. J. 
Published: December 2003

AbstractAmines with mixed substituents containing two or three ElN bondsEl = a higher IVa, Va, or VIa element; by IVa, Va, and VIa elements are meant elements of the IV, V, and VI main groups of the periodic system
. are relatively stable if one or two of these bonds are (CH3)3 SiN bonds. IR and 1HNMR studies indicate that the (p → d)π bond components of the element‐nitrogen bonds steadily decrease from silicon, phosphorus, and sulfur toward their higher homologs. Because of the differences in the polarities of the element‐nitrogen bonds, these substances can be used for selective insertion and cleavage reactions. The reaction of metalated N‐silylaminoarsines with methyl chloride as well as the reaction of metalated N‐trimethyl(IVa)‐element‐substituted amino‐tert‐butylphosphines with halogenotrimethyl(IVa) element compounds open new, simple routes for the conversion of elemento‐organic amine systems into imine systems. The problem of reversible and irreversible (CH3)3 El ligand migration (1,3 shift) is discussed for trimethyl(IVa)element‐substitued benzamidines, diaminophosphines, aminoiminophosphoranes, sulfinamides, and aminosulfimines.
The Coordination Number – an “Inorganic Chameleon”
Authors: Hoppe R. 
Published: December 2003

AbstractThe purpose of the present article is to describe the changing ambiguous character of the term “coordination number” and its present‐day definition in structural chemistry, particularly of typical solids (assemblies of particles with short‐range and long‐range order). An effort is made at the same time to describe the crystal structure of solids as simply as possible while also taking long‐range order into account, i.e. by determining “effective” coordination numbers by the geometrical “polyhedron method” or from MAPLE (Madelung Part of Lattice Energy) values.
Polyurethane Ionomers, a New Class of Block Polymers
Authors: Dieterich D. , Keberle W. , Witt H. 
Published: December 2003

AbstractLinear polyurethanes containing ionic centers at wide intervals are heteropolymers having a pronounced segment structure, i.e. ionomers. As a result of interactions between chains (Coulomb forces and hydrogen bonds), their properties are similar to those of crosslinked elastomers. They are strongly associated both in organic and in aqueous solutions. Polyurethane ionomers in polar organic solvents spontaneously form stable aqueous dispersions on addition of water, with the ionomer as the disperse phase. The particle size can be varied between 20 nm and 1 mm.
Organogold Chemistry
Authors: Armer Brunhilde , Schmidbaur Hubert 
Published: December 2003

AbstractOrganogold compounds having at least one Au–C δ or π bond and gold‐carborane complexes have recently received rapidly increasing attention, from the point of view of valence theory and structure as well as on practical grounds. Interesting possibilities are offered particularly in connection with the use of gold and its derivatives as heterogeneous or homogeneous catalysts for organic reactions, and new problems also arise.
The Behavior of Acid Halides Toward Lewis Acids and Lewis Bases
Authors: Lindner Ekkehard 
Published: December 2003

AbstractReactions of some typical acid halides of carbonic and trithiocarbonic acids and of orthophosphoric and sulfuric acids with Lewis acids and Lewis bases are compared. Acylium, perfluoroacylium, thioacylium, and even sulfonylium ions are obtainable with Lewis acids. It is possible by conductivity measurements and by electronic and above all IR spectroscopic investigations to determine whether the 1:1 adducts of acid halides and Lewis compounds are acylium or sulfonylium salts or donor‐acceptor complexes. In the reaction with Lewis bases, the halogen atom in the acid halide is replaced by the electron donor, generally with formation of nonpolar molecular compounds or complexes.
Inelastic Interactions of Slow Electrons with Adsorbed Particles
Authors: Menzel Dietrich 
Published: December 2003

AbstractWhen slow electrons impinge on metal surfaces which are covered with an adsorbed layer, desorption of neutral particles as well as of positive ions, partly accompanied by fragmentation of the adparticles, is observed. The mechanism of these processes is of interest in connection with existing concepts of the surface bond. The effect can also be used as a probe for the investigation of complex adsorption layers.Transfer of much smaller energies to the adsorbate can lead to vibrational excitation. This process may find application in the vibrational spectroscopic study of adsorbates. If the energy transferred in the inelastic collision is high enough to ionize low‐lying levels of the surface atoms, radiationless re‐ordering of the electron configuration (Auger‐effect) can occur subsequently. The secondary electrons of characteristic energy emitted in these processes can be used for qualitative analysis of the surface.
The Differential Calorimetric Study of the Reactivity of Unstable Compounds
Authors: Koch Erhard 
Published: December 2003

AbstractThe detection of unstable intermediates in chemical, photochemical, and radiation‐chemical reactions can be greatly facilitated by the use of thermoanalytical methods. Special advantages are offered by differential thermal analysis (DTA), since it permits fast, easy investigation, from about −150°C upward in some cases, over a wide temperature range. In this way processes that under normal conditions follow one another with immeasurable rapidity can be separated on the basis of their different temperature dependences. The great sensitivity of the method also allows the use of very dilute solutions, so that the studies can be confined to unimolecular processes.The value of the method for the determination of energetic and kinetic data is illustrated by its application to the photochemically obtanable, unstable, ozonide‐like epidioxydihydrofurans.
Electroplating of Plastics in Theory and Practice
Authors: Heymann Kurt , Riedel Wolfgang , Woldt Günter 
Published: December 2003

AbstractElectroplated plastics combine many advantages of plastics and of metals; they have the low weight and ease of shaping of plastics, together with the luster, hardness, and electrical conductivity of metals. An important part of any process for the electroplating of plastics is a pretreatment to ensure good adhesion of the metal film. Etch activation in the straight‐through method requires only six steps for pretreatment.
Recent Chemistry and Biochemistry of Bile Pigments
Authors: Rüdiger Wolfhart 
Published: December 2003

AbstractBile pigments are not merely waste products of the degradation of hemoglobin, but have specific functions in plants and lower animals, in which they occur in the form of chromoproteins (biliproteins). Chromic acid degradation under controlled conditions is particularly suitable for structural investigations. In the case of the phycobilins (bile pigments of red and blue algae), not only have the structures been established, but the linkages with the proteins have also been located.
Disorder in Solids (Ionic Crystals and Metals)
Authors: Nölting Jens 
Published: December 2003

AbstractImportant properties of crystalline solids are due to deviations from the ideal crystal structure. Lattice defects can be divided into structural defects (grain boundaries, dislocations, impurities) and intrinsic defects. The present article deals mainly with the problems and possibilities for the determination of intrinsic disorder. This disorder, which varies reversibly with temperature, plays an important role in many solid‐state processes, such as diffusion, ionic conduction, and chemical reactions in the solid phase.After an introduction to the usual physical and chemical descriptions of the state of disorder, the principal methods of investigation are discussed. Special emphasis is placed on methods of determining disorder data from “anomalous” specific heats.
Chemical Information Services
Authors: Weiske Christian 
Published: December 2003

AbstractThe definition of information services derives from the demarcation between documentation and information. The main criteria for information services are up‐to‐dateness, clarity, manageability, relevance, and flexibility. In addition to the printed information media (tables of contents, lists of titles, abstract journals) services have been offered in recent years which are prepared with the aid of data processing machines and which operate on the basis of data tapes (SDI, profile searches).
Theoretical Aspects of Communication in Chemistry
Authors: Fugmann Robert 
Published: December 2003

AbstractSuccessful searching for publications on the basis of subject obeys rules whose relations to thermodynamics are unmistakable. As a collection of literature grows, the degree of order required increases, since the patience, time, and memory used by man to compensate for lack of order cannot keep pace. The high degrees of order that are necessary nowadays in scientific literature cannot be attained by traditional documentation methods. If modern techniques are used to improve communication, the conceptual basis of such a documentation method must be revised and adapted to suit the new possibilities. The conditions in chemistry are relatively favorable for the effective use of modern technical and conceptual methods, since the terminology has been developed further than in most other sciences.
Versatile Computer Techniques for Searching by Structural Formulas, Partial Structures, and Classes of Compounds
Authors: Meyer Ernst 
Published: December 2003

AbstractThe principles of the topological encoding of formulas and machine searching are briefly described. These methods have been developed to the point where it is now possible to carry out a computer search for a given structural fragment without the risk of false drops. It is also possible to carry out searches whose requirements, while well‐defined and readily used by chemists, cannot be represented exclusively by element symbols and chemical bonds.
A System for the Documentation of Chemical Reactions
Authors: Schier Oswald , Nübling Wolfgang , Steidle Walter , Valls Jacques 
Published: December 2003

AbstractThe Documentation Ring of the chemical and pharmaceutical industries uses a punched card system to record chemical reactions. The starting materials and the end products are encoded with a fragmentation code, and the bonds that change during the reaction are recorded in the same way. Reaction modifiers and physical data can also be stored. In the case of multistage reactions, both the individual stages and various groups of stages are recorded.
Solvated and Stabilized Electrons in Radiation‐Chemical Processes
Authors: Eiben Klaus 
Published: December 2003

AbstractThe electrons solvated in metal‐ammonia solutions are relatively stable; by contrast, hydrated electrons are very unstable and have been discovered only recently during radiolysis of water. They can be regarded as the simplest radicals. Radiation chemical production of solvated electrons has proved to be a particularly elegant method for the qualitative and quantitative investigation of the reactions between these electrons and numerous compounds, whose rates are partly controlled by diffusion. It has been possible in some cases to identify optically and ESR‐spectroscopically the resulting short‐lived products (radical‐anions). The similarity between the physical and chemical properties of electrons solvated in solutions and those of electrons stabilized in the solid phase suggests that the two species are identical.
Preparative Solid State Chemistry: The Present Position
Authors: Schäfer Harald 
Published: December 2003

AbstractTwo types of reaction are distinguished in solid state chemistry: those in which high mobility of the reactants is aimed at (which can be achieved by the use of high temperatures, by the introduction of defects, by the promotion of surface diffusion, or by means of chemical transport phenomena), and those reactions in which the nature of the products is determined by existing structural elements or lattice defects of the reactants. The importance of paying more attention than hitherto to reaction pathways in preparative solid state chemistry is pointed out.
Blood Coagulation and Fibrinolysis
Authors: Heimburger Norbert , Trobisch Heiner 
Published: December 2003

AbstractAs a result of advances in protein chemistry it is now widely accepted that blood coagulation proceeds via a series of reaction steps of the nature of enzyme‐substrate reactions catalyzed by phospholipids. This also applies to the compensatory process of fibrinolysis. The factors taking part in both mechanisms as well as the inhibitors regulating the equilibrium have been shown to be proteins, some of them with a high carbohydrate content. Modern diagnostic methods and therapy are based on this knowledge.
Lac Repressor
Authors: Müller‐Hill Benno 
Published: December 2003

AbstractRepressors are proteins that interact with inducers and operators to regulate the synthesis of enzymes in the cell. Lac repressor ensures that sufficient β‐galactosidase is available to the bacterium Escherichia coli, depending upon the amount of lactose present in the culture medium. It has proved possible to isolate lac repressor from E.coli. The present progress report describes how these discoveries were made, as well as the formation and mode of action of the repressor.
Optical Activity from Asymmetric Transition Metal Atoms
Authors: Brunner Henri 
Published: December 2003

AbstractThe preparation and resolution of asymmetric organometallic compounds of the transition series with four different ligands on the metal atom are described. Some of the optically active complexes retain their configuration, while others undergo racemization in solution. Their properties and reactions are discussed. Centers of asymmetry at transition metal atoms can also be detected on the basis of the magnetic nonequivalence of diastereotopic groups. Information about the configurational stability of such compounds can be obtained by investigation of the temperature dependence of the nuclear magnetic resonance spectra.
Synthesis of Heterocyclic Ring Systems for Heat‐Resistant Plastics from Polyisocyanates
Authors: Merten Rudolf 
Published: December 2003

AbstractInvestigations on space flight and rockets carried out in particular in the United States have aroused great interest in plastics with enhanced thermal stability. It has become possible to pass far beyond the expected limits of thermal stability with organic plastics, and to synthesize plastics and polymers that can be used at temperatures between about 200 and about 500 °C, a range that formerly appeared to be the exclusive province of inorganic materials.
Generation of Carbenes by Thermal Cycloelimination
Authors: Hoffmann Reinhard W. 
Published: December 2003

AbstractThe growth of interest in carbenes has led to a need for methods that allow their generation in unimolecular decomposition processes, possible also in the gas phase, without troublesome by‐products. Besides the decomposition of diazo compounds, thermal cycloeliminations from carbocycles and heterocycles with odd numbers of ring atoms have been found to be suitable for this purpose. The problems, structural requirements, and scope of such cycloelimination reactions are discussed in the present progress report. The advantages of carbene generation by thermal cycloelimination are demonstrated with reference to dialkoxycarbenes, which are very dfficult to obtain in any other way.
Generation of Carbenes by Photochemical Cycloelimination
Authors: Griffin Gary W. 
Published: December 2003

AbstractA wide variety of shelf stable substrates undergo photochemical cycloelimination under relatively mild conditions. Suitable substrates include cyclopropanes, oxiranes, aziridines, and diazirines, as well as 3 H‐pyrazoles and 1,3‐dioxolanes. Carbenes prepared from these substrates as well as certain cyclic carbonates, sulfites, and phosphoranes behave chemically in a manner similar to divalent carbon species produced from conventional diazo precursors, namely, they react with alkenes to give cyclopropanes and undergo insertion into CH bonds of alkanes. In many cases the carbenes formed may also be detected by EPR and optical spectroscopic methods.
The Anomalous Temperature Dependence of Enzyme‐Catalyzed Reactions
Authors: Talsky Gerhard 
Published: December 2003

AbstractBreaks or curvatures in the plot of log vbr vs. 1/T have been described in the literature for a number of reactions. If sufficiently small temperature intervals are used in the investigation of the temperature dependence (STI method) a trend line is obtained instead. It is then possible to distinguish regions of linear behavior and regions of anomalous behavior. The effects of e. g. the pH, the ionic strength, and added salts as well as of the size of the enzyme and substrate molecules on the anomalies were examined. The anomalous temperature dependence of the reaction rate was found to be a particularly sensitive indicator of the reaction event on the enzyme. The course of the reaction is evidently affected even by relatively small changes in conformation, particularly in the region of the active center.
Translation of Genetic Information on the Ribosome
Authors: Schreiber Gerhard 
Published: December 2003

AbstractThe information for protein structure that is contained in the base sequence of the nucleic acids is translated on the ribosome into the amino acid sequence. This translation can be divided into chain initiation, chain growth, and chain termination. Several specific protein factors and nucleic acids are involved in each section.—For chain initiation, start complexes are formed from the initiating amino acyl‐tRNA, mRNA carrying the start signal, and the small and large subunits of a ribosome. GTP and the initiating factors are also involved in this process.—In chain elongation, one amino acid at a time is transferred, in a reaction cycle, from the linkage with tRNA into a linkage with the polypeptide chain. The amino acid to be incorporated is initially bound to the ribosome as amino acyl‐tRNA, a process for which GTP and protein factors are necessary. The subsequent formation of a peptide linkage is catalyzed by the peptidyl transferase of the large ribosomal subunit. The peptidyl‐tRNA with its newly added amino acid residue is then transferred from the amino acyl‐tRNA acceptor site A to the peptidyl donor site P of the ribosome. This requires another protein factor and cleavage of GTP into GDP and phosphate.–Ghain termination begins as soon as one of the three terminator triplets UAA, UAG, or UGA in the mRNA reaches the ribosome. The mRNA is moving in relation to the ribosome from the 5′ end to the 3′ end. Release of the completed polypeptide chain from the ribosome is dependent on release factors. Before initiation of a new polypeptide chain, the ribosomes dissociate into their subunits.
Applications of Mössbauer Spectroscopy to Problems in Solid‐State Chemistry
Authors: Greenwood Norman N. 
Published: December 2003

AbstractThe factors influencing the chemical isomer shift, quadrupole splitting and hyperfine magnetic interactions, are briefly summarized and applications to solid state systems reviewed. New results on the disordered rutile phases Fe2MgF6, FeMg2F6, and FeCoNiF2, and on the trirutile phase Li+ Fe2+ Fe3+ F6 are presented to illustrate the power of the Mössbauer technique in probing details of oxidation states, site symmetries and magnetic ordering. An extensive study on the nonstoichiometric wüstite phase Fe1−xO is also reported and analyzed in terms of diffusion broadening at high temperatures and defect clustering in quenched samples; the production of essentially stoichiometric FeO by annealing is also discussed. Recent results on the application of large external magnetic fields to diamagnetic compounds of tin are reviewed and results of a Mössbauer investigation of lunar samples returned by the Apollo 11 and 12 missions are discussed.
Bifunctional Reagents for the Crosslinking of Proteins
Authors: Fasold Hugo , Klappenberger Jürgen , Meyer Christa , Remold Heinz 
Published: December 2003

AbstractProteins can be crosslinked by chemical compounds without any accompanying change in the complicated three‐dimensional structure. Many bifunctional reagents that can react with functional groups in the side chains of the amino acids are now known. Not only can the distance between the linked amino acid residues be deduced from the known length of the bridge introduced, but information can also be obtained concerning changes in conformation during other reactions and concerning the arrangement of the components of a quaternary structure.