bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemistry and Biology of the Acylneuraminic Acids
Authors: Schauer Roland 
Published: December 2003

AbstractAcylneuraminic acids occupy an outstanding position both sterically and with respect to biological functions in gangliosides and in many glycoprotein molecules. Acylneuraminic acids are N‐acylated and partly O‐acylated derivatives of neuraminic acid, a polyhydroxyamino keto acid that has the properties of a carbohydrate and is therefore capable of forming a glycoside linkage. The present report provides a survey of our knowledge of the chemistry and biology of the acylneuraminic acids, which occur widely in particular in the animal kingdom.
Quartz Crystals and Their Colors
Authors: Lehmann Gerhard , Bambauer Hans Ulrich 
Published: December 2003

AbstractThe many colors found in quartz crystals are always due to the presence of impurity atoms, whose concentrations rarely exceed 0.1 wt.%. The impurity atoms occupy either silicon sites in the lattice or interstitial sites in the channels parallel to the c axis of the quartz structure; very fine precipitations of foreign phases are sometimes also observed, though this is less common. In addition to intrinsic colors of transition metal ions, one also finds color centers produced by ionizing radiation. Regular distributions of impurity atoms and colors may develop in the crystals as a result of some factor connected with its growth. Most of the natural quartz colors, as well as others that do not occur in nature, have been produced in synthetic quartzes.
Bredt Compounds and the Bredt Rule
Authors: Köbrich Gert 
Published: December 2003

AbstractThe Bredt rule, which proved useful in earlier decades mainly as an exclusion criterion in the assignment of structures, has in recent years become the stimulus for efforts to synthesize strained bicyclic systems with a bridgehead double bond. On the basis of the ring‐strain forces operating in such systems, an extended Bredt rule is discussed. The “Bredt comgounds” to which this rule applies, which include bicyclic systems not prevoously consodered from this point of view (e.g. bridged methylenecyclopropanes), form a clearly circumscribed, interesting field within the chemistry of highly‐strained hydrocarbons with ring unsaturation.
Chemical Analysis of Synthetic Fibers
Authors: Nissen Dietmar , Rossbach Volker , Zahn Helmut 
Published: December 2003

AbstractThe analytical characterization of synthetic fibers has not kept pace with their development and production. Whereas the “second‐generation” fibers have already conquered the market, the chemical investigation methods used until now for the three classical fiber polymers of the polyester, polyamide, and polyacrylonitrile types are still frequently unsatisfactory. Though they satisfy the requirements of production supervision and quality control, they do not supply enough information to enable us to understand and to explain the degradation of and damage to the polymers under hydrolytic, thermal, or thermooxidative influences. This report presents methods of chemical analysis that open up new possibilities for investigations of this nature on synthetic fibers. The results reported for commercial products must not be taken as an assessment of quality. They are simply intended to show the diversity to be expected in the chemical properties and to emphasize the practical basis of the chemical analysis of synthetic fibers.
Reactive Monomeric Carbonic Acid Derivatives
Authors: Kühle Engelbert 
Published: December 2003

AbstractMonomeric carbonic acid derivatives that can react by addition or substitution are systematically discussed according to the three tabular surveys A, B, and C, from which a principle for the classification of carbonic acid derivatives can be readily deduced. For each type of compound, a brief description is given first of the principal syntheses and then of the reactions, and the heterocycles obtainable by addition, disubstitution, or coupled addition‐substitution are also considered. The carbonic acid derivatives discussed can be synthesized from very simple and in most cases cheap base chemicals.
Chemistry and Significance of the Carbohydrate Moieties of Human Serum Glycoproteins
Authors: Heide Karl , Schwick Hans‐Gerhard 
Published: December 2003

AbstractThe glycoproteins exercise important biological functions as transport proteins, inhibitors, enzymes, hormones, complement factors, and immunoglobulins. Their chemistry is characterized by a number of rules. Thus only asparagine, threonine, or serine can carry the oligosaccharide groups; for the N‐acylglycosylamine linkage involving asparagine, the grouping Asn‐X‐Thr or Asn‐X‐Ser is always present in the peptide chain. However, practically no agreement is found in the molecular weights of the glycoproteins, their carbohydrate contents, and the relative contents of the‐various sugars. The biological significance of the carbohydrate fraction has not yet been explained, but some idea of the part played by the easily removable neuraminic acid is being formed.
The Chemistry of Dichloromethylenammonium Salts (“Phosgenimonium Salts”)
Authors: Viehe Heinz Günter , Janousek Zdenek 
Published: December 2003

AbstractDichloromethylenammonium salts, particularly dichloromethylenedimethylammonium chloride, occupy a unique place as stable but reactive building blocks for synthesis. They contain three mobile chlorine atoms activated by an amino group on the same carbon atom. These salts can be regarded as chlorinated Vilsmeier or Mannich reagents and are thus at a higher oxidation level. As in the Mannich or Vilsmeier reaction, the carbon condenses here as an electrophile with formation of CC or Chetero atom bonds in a variety that is still far from being exhausted.
Oxathiazinone Dioxides—A New Group of Sweetening Agents
Authors: Clauss Karl , Jensen Harald 
Published: December 2003

Abstract1,2,3‐0xathiazin‐4(3H)‐one 2,2‐dioxides bearing lower alkyl substituents on C‐5 and C‐6 represent potential sweeteners. They are formed from chloro‐ or fluorosulfonyl isocyanate and acetylenes, ketones, β‐diketones, β‐oxo carboxylic esters, or benzyl vinyl ethers via N‐halosulfonyl β‐oxo carboxamides as common intermediates.
The “Nickel Effect”
Authors: Fischer Karl , Jonas Klaus , Misbach Peter , Stabba Reinhold , Wilke Günther 
Published: December 2003

AbstractWhereas the reaction of ethylene and triethylaluminum under pressure at 100°C yields trialkylaluminum compounds having long alkyl chains, the presence of small amounts of nickel salts induces the formation of butene. The discovery of this “nickel effect” represents the starting point for the development of the Ziegler catalysts. Comparatively little was formerly known about the nature and the mode of action of the catalytically active nickel species. A basis for the elucidation of the effect was provided by studies on the reduction of nickel compounds by organoaluminum compounds, on the occurrence and existence of nickel hydrides, and on interactions between nickel(0) and Lewis acids as well as organic compounds of main group metals. The most significant result of these studies is the recognition that multicenter bonding systems involving trialkylaluminum compounds and nickel atoms are involved. These react further with complex bonded ethylene in what is probably a concerted manner.
Structure‐Property Relationships in a Polymer
Authors: Andrews E. H. 
Published: December 2003

AbstractThe way in which polymer molecular structure controls structure on higher levels of organization in a solid polymer is briefly reviewed, as is also the way in which structure, on all levels, controls physical properties. The “line of descent” from molecular structure to physical properties is then illustrated for cis‐polyisoprene (natural rubber). It is shown how the crystalline‐amorphous morphology in the solid is controlled both by the chemical microstructure of the polymer and by the physical conditions (temperature, time, strain) under which solidification occurs. By changing these “processing conditions” great changes can be effected in the morphology.
Recent Discoveries in the Evolution of Proteins
Authors: Acher Roger 
Published: December 2003

AbstractIs it possible to reconcile the great diversity of present‐day proteins with a unitary theory of the evolution of these molecules? The mechanisms of diversification of proteins are undoubtedly not yet all known, but it is clear that the linear construction of polypeptide chains lends itself to operations such as addition, insertion, deletion, and fusion. Combinations of these modifications would explain the development of an infinite number of entirely different proteins from one ancestral molecule.
The Stable Isotopes of Oxygen in Research and Technical Applications
Authors: Staschewski Dieter 
Published: December 2003

AbstractThe stable isotopes of oxygen have proved to be efficient research tools; however, only a small fraction of the possible applications of these isotopes have been examined so far. The present progress report deals with five basic types of isotopic effects whose investigation and evaluation offer information of a new kind about physical, chemical, and biological systems and processes.
The Chemistry of Hydroxamic Acids and N‐Hydroxyimides
Authors: Bauer Ludwig , Exner Otto 
Published: December 2003

AbstractThis progress report is concerned primarily with problems relating to the structure and reactions of hydroxamic acids and N‐hydroxyimides, and also surveys some of the biological activities of these compounds. Particular significance attaches to the Lossen rearrangement of O‐acylated hydroxamic acids, which leads to isocyanates or their reaction products.
Carbon Suboxide in Preparative Organic Chemistry. New synthetic methods (1)
Authors: Kappe Thomas , Ziegler Erich 
Published: December 2003

AbstractAlthough it has been known for nearly 70 years, carbon suboxide was used almost exclusively for the preparation of simple malonic acid derivatives until about 1960. Since then, however, the significance of this unusual “bisketene” has steadily increased in synthetic chemistry (especially that of heterocyclic compounds). This progress report surveys the possible applications of C3O2 in preparative organic chemistry, including photochemical reactions.
Antimetabolites of Coenzyme Q. Their Potential Application as Antimalarials
Authors: Porter Thomas H. , Folkers Karl 
Published: December 2003

AbstractMalaria is transmitted to man by the bite of the female Anopheles mosquito, man acting as the intermediate host, and the mosquito as the definitive host for the plasmodia. Plasmodia are found to have become resistant to certain chemotherapeutic agents. A new fundamental approach to malaria chemotherapy is based on the biochemical rationale of inhibition of the electron transfer mechanism in the metabolism of plasmodia by antimetabolites of coenzyme Q, which is essential for electron transfer. Coenzyme Q refers to 2,3‐dimethoxy‐5‐methyl‐1,4‐benzoquinones with isoprenoid chains of varying length on C‐6. In this progress report a series of synthetic antimetabolites are presented together with a discussion of their action in current pharmacological tests.
Enzymatic Reduction of Ribonucleotides: Biosynthesis Pathway of Deoxyribonucleotides
Authors: Follmann Hartmut 
Published: December 2003

AbstractRibonucleotide reductases are enzymes that synthesize the deoxyribonucleotides required for the replication of DNA in dividing cells. They thus have a key function for the growth of microorganisms and of all plant and animal tissues. The enzymes reduce all four purine and pyrimidine ribonucleotides (as the 5′‐diphosphates or triphosphates) with direct substitution of the 2′‐hydroxyl group by hydrogen. The physiological reducing agents are the mercapto groups of thioredoxins, a group of small proteins, which are regenerated from the oxidized form by NADPH‐dependent thioredoxin reductases. There are two known types of ribonucleotide reductases (I and II), which catalyze hydrogen transfer with the aid of protein‐bound iron ions or of 5′‐deoxyadenosylcobalamin (coenzyme B12); free radicals can be detected in both cases. The enzymes are regulated by effector nucleotides. There may exist a homeostatic mechanism, which guarantees the supply of DNA precursors to the cell.
What Do We Know about the Deeper Layers of the Earth?
Authors: Schwab Roland G. 
Published: December 2003

AbstractIn the last twenty years modern chemical and physical methods have done much to extend our knowledge of the Earth. Some new questions have been raised, e.g. the question of the bonding relationships in the Earth's interior, which make the Earth an interesting object of research to chemists as well. This progress report attempts to give a survey of the Earth's structure as seen at the present day. Naturally, special emphasis has been placed on those aspects which concern the chemist.
Umpolung of Amine Reactivity. Nucleophilic α‐(Secondary Amino)‐alkylation via Metalated Nitrosamines
Authors: Seebach Dieter , Enders Dieter 
Published: December 2003

AbstractThere are basically two kinds of hetero atoms in organic molecules: one kind confers electrophilic character upon the carbon atom to which it is bound, and the other kind turns it into a nucleophilic site. The development of methods permitting transitions between the two resulting categories of reagents has become an important task of modern organic synthesis. The scope of such umpolung of the reactivity of functional groups is discussed for the case of amines as an example. A method of preparing masked α‐secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of the resulting nitrosamine α‐to the nitrogen, reaction with electrophiles, and subsequent denitrosation. Many examples are given for each of these steps which illustrate the wide scope of the overall synthetic operation (electrophilic substitution at the α‐C atom of the secondary amine). Preliminary applications and a method for avoiding the handling of nitrosamines are presented, and the report concludes with a brief account of the significance of nitrosamines in the study of carcinogenesis and mutagenesis.
Isomerization Polymerization of Lactams
Authors: Reimschuessel H. K. 
Published: December 2003

AbstractIsomerization polymerization affords a macromolecule whose repeating unit is derived from an isomer of the original monomer. Thus hexa‐ and heptacyclic β‐carboxymethyllactams yield polymers containing glutarimide units, whereas penta‐ and hexacyclic β‐carboxylactams furnish polymers containing succinimide units. Some dimethyl derivatives of β‐carboxylactams isomerize or rearrange, and 5‐oxopyrrolidine‐3‐acetic acid does not react at all. These observations can be explained in terms of a bicyclic intermediate.
13C Spin‐Lattice Relaxation Times and the Mobility of Organic Molecules in Solution
Authors: Breitmaier Eberhard , Spohn Karl‐Heinz , Berger Stefan 
Published: December 2003

AbstractWhile the chemical shifts and coupling constants of13C NMR belong to the most powerful tools available to the organic chemist for the solution of structural problems, increasing interest is being shown in13C spin‐lattice relaxation timesT1as structural parameters. Together with the nuclear Overhauser effects arising by proton decoupling of13C NMR spectra, theT1values of13C nuclei in a molecule permit conclusions to be drawn with regard to relaxation mechanisms. They reflect the inter‐ and intramolecular mobility of a molecule, and thus complement the results of temperature‐dependent NMR spectroscopy. TheT1differences within a molecule show, for instance, whether the molecular motion is anisotropic in solution, whether the internal motion of groups is subject to steric hindrance, the extent to which strong intermolecular or interionic interactions affect the flexibility of the molecule, and which parts of the molecule are rigid and which are flexible. Finally, differences between theT1values measured for the13C nuclei of a molecule frequently provide a reliable aid in the assignment of13C NMR spectra, particularly in cases of signal crowding and multiplet overlapping.
Investigation of Enzyme Mechanisms with Nucleoside Phosphorothioates
Authors: Eckstein Fritz 
Published: December 2003

AbstractNucleoside phosphorothioates are modified nucleotides in which an oxygen atom bound to a phosphorus atom has been replaced by a sulfur atom. These compounds are suitable for the investigation of enzyme mechanisms because, although they are bound by enzymes in many cases just as well as the natural substrate, the enzymatic reactions very often proceed considerably more slowly. Since nucleoside thiophosphate O‐esters exist as diastereomers these compounds can be used in suitable cases for information about the stereochemistry of enzymatic reactions.
New Element‐Carbon (p‐p)π Bonds
Authors: Jutzi Peter 
Published: December 2003

AbstractRecent years have seen the preparation of π systems containing novel (p‐p)π bonds between carbon and elements from the third, fourth, and fifth Main Groups of the Periodic Table; most of these compounds are predicted to be incapable of existence according to the classical concepts of the double bond. (p‐p)π. Bonds between carbon and phosphorus, arsenic, and antimony have been successfully stabilized in resonance‐stabilized colored compounds of the cyanine and triphenylmethane type, and also in aromatic systems deriving from benzene, naphthalene, and anthracene. Bismuth‐carbon and boron‐carbon (p‐p)π bonds have likewise been confirmed in aromatic systems. Silicon‐carbon and germanium‐carbon (p‐p)π bonds have been detected in extremely reactive derivatives of silaethylene and germaethylene, respectively. The present report describes characteristic reactions of the new π systems. Their bonding follows from X‐ray structure analysis, from photoelectron, UV, and NMR spectra, and from calculations. Criteria for the existence of π systems which are not allowed by the classical double bond rule are discussed; these criteria remain valid on generalization.
Spectral Evidence for Lanthanoid and Actinoid Carbonyl Compounds
Authors: Sheline Raymond K. , Slater James L. 
Published: December 2003

AbstractThe co‐condensation of actinoid or lanthanoid atoms and a mixture of argon containing small amounts carbon monoxide on a surface cooled with liquid helium leads, after annealing of the argon matrix, to a series of new binary actinoid and lanthanoid carbonyl compounds. Evidence for these new carbonyls is obtained using infrared spectroscopy. Preliminary interpretation of the IR spectra suggests that at least six complexes, M(CO)1–6, have been observed for each metal. A distinct difference in the infrared spectra is observed for the ytterbium derivative, probably associated with the fact that ytterbium lacks one electron from having entirely filled 4f orbitals. A brief description of the possible bond hybridization and its effect on the MCO bonding, which may explain the difference between ytterbium and the other lanthanoids, is presented.
The Flipping of CO Ligand Groups in Metal Carbonyl Compounds and its Frequency in Fe(CO)5
Authors: Sheline Raymond K. , Mahnke Harald 
Published: December 2003

AbstractIt has been proven qualitatively by a number of authors using variable temperature NMR experiments that most metal carbonyl complexes are nonrigid. A quantitative determination of the ligand exchange frequency veis often achieved by a line shape analysis or by measurement of the transverse relaxation timeT2using the Carr‐Purcell method. In the case of a “very fast” exchange, however, both methods prove unsuccessful. It is shown in this study that a simultaneous fit of IR or Raman spectra on the one hand and NMR spectra on the other can make possible the determination of vefor the “very fast” exchange and can also facilitate the determination of vein “slow” and “medium” exchange cases considerably. The ligand exchange frequency thus found for Fe(CO)5, 1.1 × 1010s−1, is unexpectedly high; comparison with variable temperature measurements on solid Fe(CO)5, yields similar energy barriers. A mechanism of exchange closely related to the “Berry mechanism” is proposed. Finally the consequences of this surprisingly large ligand exchange rate are discussed with respect to IR band assignments for molecular “fragments” M(CO)x(wherex=coordination number, and M is a transition metal, typically lanthanoid or actinoid).
Asymmetric Membranes: Preparation and Applications
Authors: Saier H.‐D. , Strathmann H. 
Published: December 2003

AbstractThe separation of molecular mixtures by semipermeable membranes under the driving force of hydrostatic pressure has assumed major importance in recent years. Among other factors the development of membranes with asymmetric structure which, while having the same separating properties, afford a filtration output many times greater than that of the previously known symmetrical membranes, was decisive for this method. In the present progress report the structures of asymmetric membranes are discussed, as well as their preparation from various polymers and their application to the separation of molecular mixtures.
Formation, Detection, and Reactions of Phosphinidenes (Phosphanediyls)
Authors: Schmidt Ulrich 
Published: December 2003

AbstractFormation and detection of phosphinidenes (RP̈:) in the decomposition of cyclophosphanes and in the reaction of dichlorophosphanes with metals are considered critically. Only in the thermolysis of pentaphenylcyclopentaphosphane can phenylphosphinidene be detected with certainty by pyrolysis‐mass spectroscopy. “Trapping reactions” such as “insertion” into SS or AsAs bonds, and addition reactions with 1,2‐diketones, 1,3‐dienes, or alkynes can also be interpreted without the assumption of free phosphinidenes. The pyrolysis products of cyclophosphanes add to 1,3‐dienes and alkynes, yielding five‐ and six‐membered heterocycles that contain one to three phosphorus atoms.
Painting of Ancient Ceramics
Authors: Noll Walter , Holm Reimer , Born Liborius 
Published: December 2003

AbstractThe painting of ancient ceramics has been investigated for its morphological characteristics and its elemental and phase composition with the aid of scanning electron microscopy, energy‐dispersive and in part wavelength‐dispersive X‐ray microanalysis, X‐ray diffraction, and electron spectroscopy. Some conclusions about the methods of production can be drawn from these results. It transpires that the painting of ancient ceramics constitutes an extremely important document for the history of chemical technology. The findings bring to light the wealth of experience acquired by the craftsmen and artists of the time and their knowledge of the mineral raw material and their possible utilization. The facts thus obtained are of great value for problems in archaeology and prehistory and at the same time open up new prospects for interdisciplinary collaboration.
Optical Properties of Pigments—Objective Methods for Testing and Evaluation
Authors: Völz Hans G. 
Published: December 2003

AbstractAlthough man has used pigments to impart color to his surroundings since prehistoric times, it is only in the 20th century that methods for objective testing and evaluation of their optical properties have become available. Colorimetry and color‐order systems based on principles of color perception, in particular the Adams‐Nickerson system, which form the basis of these methods are described, and are followed by a discussion of the theories of light absorption and light scattering, in particular of the Kubelka‐Munk theory. Of the important optical pigment properties chromaticity and color difference, tinting strength and lightening power (of white pigments), and the hiding power of colored and uncolored coatings are discussed on the basis of the testing methods. Sweeping developments in computer technology during recent years have contributed significantly to the present advanced status of testing practice; further progress in testing methods may be expected in the future as our understanding of the visual process improves.