bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural versus Indexing Language in Chemical Documentation
Authors: Fugmann Robert 
Published: December 2003

AbstractIn any literature searh one must be able to predict which modes of expression have been used to represent the concepts of interest in the search file. It is these lingual expressions which will be looked up or will constitute the search parameters in a mechanized search. In the case of general concepts and statements, uncontrolled natural language lacks the required representational predictability, as is demonstrated, for example, for classes of chemical compounds and for types of reactions. Hence, considerable loss of relevant information is bound to occur in searches for these concepts in free text files, regardless of how advanced a computer program may be. By restricting the modes of expression as is achieved by means of an indexing language and its reliable employment, predicability is increased and, consequently, information loss is drastically reduced.—In contrast, the modes of expression for individual concepts (e.g. individual chemical substances, authors, institutions) are, by their vary nature, often sufficiently predictable in uncontrolled natural language. In these cases, the value of translating them into indexing‐language expressions is often questionable. This holds true in particular if an indexing language does not (yet) provide adequate expressions to represent the concepts, and also in the case of ambiguous natural language expressions. Here, preserving the original, uncontrolled terms in the search file is advisable, at least in addition to an attempted translation into the indexing language.—The weaknesses of uncontrolled natural language files become apparent only at a rather late stage in the continual expansion of an information system. In its early stages the necessity of predictability is reduced through the effectiveness of human memory and the—initially—relatively high homogeneity of the experts' linguistic usage during that short period of time. Furthermore, loss of relevant information as a consequence of the lack of predictability will at first be minimal and will not yet be noticed as a steadily increasing source of search failure. Nor does the steady rise in costs for excogitating and phrasing queries with more and more alternatives become apparent at this stage. It is largely for these reasons that uncontrolled natural language systems have unjustifiably frequently been preferred. The typical weakness and strengths of both kinds of language suggest combining them so that their inherent strengths are retained and utilized as far as possible.
5‐Pivaloyl‐2H‐isoindole—An Isolable and Crystallizable o‐Quinonoid Heteroarene
Authors: Kreher Richard , Kohl Norbert , Use Götz 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1460. DOI:10.1002/anie.198214600
Facile Preparation of N‐Acyl‐2‐(diethoxyphosphoryl)glycine Esters and Their Use in the Synthesis of Dehydroamino Acid Esters
Authors: Schmidt Ulrich , Lieberknecht Albrecht , Schanbacher Ute , Beuttler Thomas , Wild Jochen 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1682. DOI:10.1002/anie.198216820
α‐Linked Disaccharides from O‐(β‐D‐Glycopyranosyl) Trichloroacetimidates using Trimethylsilyl Trifluoromethanesulfonate as Catalyst
Authors: Schmidt Richard R. , Grundler Gerhard 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1707. DOI:10.1002/anie.198217070
Organometallic Intramolecular π‐Olefin‐Metal Coordination Compounds
Authors: Omae Iwao 
Published: December 2003

AbstractIn this review article complexes of the type XnM—R are dealt with in which a σ‐bonded organic ligand R is additionally linked by a π‐bond with the metal M. In other words, the complexes contain metallacycles with three and a half, four and a half, five and a half members, etc. Well‐Known five and a half membered ring systems are those with 4‐pentenyl, 1,4‐pentadienyl, norbornyl norbornenyl, cyclooctenyl, and endo‐dicyclopentadienyl ligands. Metallacycles of this size are strain‐free and stable. Donor ligands such as amines and phosphanes can displace the coordinated double bond of the π‐ligand from the metal. This CC double bond is lengthened from ca. 133 pm to 136–146 pm by the coordination.
Molecular Mechanics Calculations in Organic Chemistry: Examples of the Usefulness of this Simple Non‐Quantum Mechanical Model
Authors: Ōsawa Eiji , Musso Hans 
Published: December 2003

AbstractVarious problems arising in experimental organic chemistry can be clarified by molecular mechanics or force field calculations: molecular dynamics (conformational analysis and internal rotation), the search for the most stable isomer of various polycyclic hydrocarbons, reactivity calculations, including solvolysis of bridgehead substituted systems. Such calculations are shown to be useful in elucidating the mechanism of multistep carbonium ion rearrangement, for predicting the structure and stability of anti‐Bredt olefins, and also offer an explanation for the selectivity observed in the hydrogenolysis of strained polycyclic smallring hydrocarbons, for the identification of long bonds and electronic effects, for the analysis of late transition states, and for the product distribution in complex reactions.
O‐Glycopeptide Synthesis using 9‐Fluorenylmethoxycarbonyl (Fmoc)‐Protected Synthetic Units
Authors: Schultheiss‐Reimann Petra , Kunz Horst 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 39. DOI:10.1002/anie.198300390
The First 13C‐ENDOR Investigation of an Organic Triradical in the Quartet State; Synthesis of a Triply 13C‐Labeled Trisgalvinol
Authors: Schubert Klemens , Kirste Burkhard , Kurreck Harry 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 128. DOI:10.1002/anie.198301280
Metal‐Induced Carbonylation of a Phosphane‐Stabilized “Carbyne Ligand”: Conversion of a Phosphorus Ylide‐Carbonylmetal Adduct into an η1‐Ketenyl Complex
Authors: Voran Siegfried , Malisch Wolfgang 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 114. DOI:10.1002/anie.198301140
Linear Control of Temperature with Time—A New Approach to Reaction Kinetics
Authors: Koch Erhard 
Published: December 2003

AbstractThe temperature dependence of the rate of chemical reactions has been known for a long time; very often it is characterized by the Arrhenius plot. However, kinetic methods that take this phenomenon into account in one measurement in a planned manner have been applied to reactions in solution only in isolated examples‐with the exception of the temperature jump method developed by Eigen et al. for fast reactions, based on a stepped temperature program. A mathematical analysis, however, reveals to the chemist that from the point of view of information theory the course of the reaction rate versus time under conditions of constantly increasing temperature is the measured signal which should lead to the most effective understanding of the reaction mechanism. Analysis of the measured peaks, which may overlap, allows the characterization of reactions either in the solid state or in solution by “mechanistic coordinates”, which extend the concept of reaction order. Their behavior allows further experiments to be planned, enabling elementary steps to be eliminated. Each reacting system can be characterized kinetically by one series of experiments using different starting concentrations for each reactant and additionally, using different heating rates. The experimental verification of these considerations can be seen in ca. 1400 DTA and UV experiments for ca. 120 different systems. Furthermore, the example of the oscillating Belousov‐Zhabotinsky reaction shows that “fast” reactions frequently may also be recognized. A test for proposed reaction mechanisms is provided by integration programs which allow immediate comparison between experimental and theoretical signal curves.
Structure and Evolution of the “Atmungsferment” Cytochrome c Oxidase
Authors: Kadenbach Bernhard 
Published: December 2003

AbstractApproximately 50 years ago, Otto Warburg received the Nobel Prize for his fundamental work on the “Atmungsferment”. But not until the end of the fifties was it possible to isolate this complicated membrane enzyme, which is necessary for respiration and energy production in most living organisms on earth. Since then, intensive research has been performed to elucidate the mechanism of reduction of oxygen to water and the coupled translocation of protons across the membrane which is involved in ATP synthesis. Until now the results have been unsatisfactory because the four catalytic heavy‐metal redox centers are bound to proteins, the structures of which have begun to be studied only recently. In the course of this research, it was discovered that cytochrome c oxidase from bacteria contains only two or three, whereas the enzyme complex from animals contains thirteen different protein components. The present article analyzes the possible functions of the various protein subunits and, using the example of cytochrome c oxidase, shows that biochemical evolution proceeds in such a way as to increase regulatory capacity.
Proximity Effects in Organic Chemistry—The Photoelectron Spectroscopic Investigation of Non‐Bonding and Transannular Interactions
Authors: Martin Hans‐Dieter , Mayer Bernhard 
Published: December 2003

AbstractClassical structural formulas often convey the impression only those relationships between the atoms are of importance which hold a molecule together as symbolized by the chemical bonds. However, many interactions between atoms or groups of atoms are not adequately denoted in this manner. Nevertheless, their existence can have important consequences for ground state energies (cis‐difluoroethylene is more stable than trans‐difluoroethylene), conformations (the syn form of methyl vinyl ether is more stable than the anti form), reactivities (an endo cyclopropane ring in 7‐anti‐norbornyl derivatives accelerates solvolysis by a factor of 1014), UV spectra (“superposition” of the π‐systems of acridine and purine‐bonded through a four‐membered chain‐results in hypochromism), CD spectra (the inherently symmetrical but dissymmetrically perturbed chromophore of 2‐deuterionorbornadiene allows the observation of three transitions in the near UV), and ESR spectra (the long‐range coupling with H‐4 in the bridgehead bicyclo[2.1.1]hex‐1‐yl radical equals 22.5 G). Since orbital interactions are involved in most intramolecular effects of this kind, photoelectron spectroscopy has proven an informative and valuable extension to other methods.
[Fe2{o‐(SCH2)2C6H4}2{SC6H5}2]2− and [Fe2{o‐(SCH2)2C6H4}3]2−: Binuclear Thiolatoiron(II) Anions with Tetrahedral FeS4‐Coordination
Authors: Henkel Gerald , Tremel Wolfgang , Krebs Bernt 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 323. DOI:10.1002/anie.198303230
cis‐1,2‐Di(9‐anthryl)ethylene: Photochemical Isomerization by Intramolecular Diels‐Alder Reaction
Authors: Becker Hans‐Dieter , Sandros Kjell , Andersson Kjell 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 609. DOI:10.1002/anie.198306090
The Crystal and Molecular Structure of Bis(1,8‐naphthalenedioxy)silane—A Contribution to the Controversy over Planar, Four‐Coordinated Silicon in Orthosilicic Acid Esters
Authors: Bibber W. , Barnes C. L. , van der Helm D. , Zuckerman Jerold J. 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 668. DOI:10.1002/anie.198306680
Photolysis of the cyclopentadienyl(hydrido) Complexes C5H5M(CO)3H (M = Cr, Mo, W) in Matrices and in Solution: Characterization of [C5H5W(CO)2H]2 and [C5Me5W(CO)2H]2
Authors: Alt Helmut G. , Mahmoud Khalil A. , Rest Antony J. 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 803. DOI:10.1002/anie.198308030
Deuteroporphyrin‐IX Dimethyl Ester: Assignment of the 1H‐NMR Spectrum by NOE Measurements in Presence of a Diamagnetic Shift Reagent
Authors: Witthohn Klaus , Brockmann Hans 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 778. DOI:10.1002/anie.198307780
Synthesis and Structure of [{[CH3C(CH2PPh2)3]IrP3}3Cu5Br4]CuBr2A 21 Atom Ir/Cu/P/Br Cluster
Authors: Cecconi Franco , Ghilardi Carlo A. , Midollini Stefano , Orlandini Annabella 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 718. DOI:10.1002/anie.198307180
Solution Conformations, Photophysics, and Photochemistry of Bile Pigments; Bilirubin and Biliverdin, Dimethyl Esters and Related Linear Tetrapyrroles
Authors: Braslavsky Silvia E. , Holzwarth Alfred R. , Schaffner Kurt 
Published: December 2003

AbstractBilirubin and biliverdin dimethyl esters (BRE and BVE, respectively) and related linear tetrapyrroles have been studied using a combination of photochemical and spectroscopic techniques, the latter including absorption, fluorescence fluorescence excitation, medium‐induced circular dichroism, and proton magnetic resonance. Both types of tetrapyrroles form mixtures of different topological isomers in very dilute solutions. In the case of the bilirubins the heterogeneity of the solutions is caused by two coexisting conformers with different orientations of the A/B and C/D pyrromethenone moieties with repect to each other. The spectral properties of one conformer resemble the isolated parent pyrromethenone, whereas those of the other result from electronic coupling of the two subchromophores presumably held in a “ridge tile” ‐like orientation. CC rotations at the C‐5 and C‐15 bridges substantially compete in both components with the photochemical channels (E→Z isomerization and lumirubin formation) for the radiationless deactivation of the excited singlet state. The more rigid “ridge tile” component additionally undergoes hydrogen bond‐mediated deactivation, and it photoisomerizes more efficiently. The situation is markedly more complex with the biliverdins. In order to obtain a more detailed insight into the mechanisms of the radiationless excited‐state processes, time‐resolved optoacoustic spectroscopy and ultrafast absorption (pump‐probe) and fluorescence detection (single‐photon‐timing) techniques were used to supplement the stationary methods. The solution mixtures are composed of a (family of) helically coiled all‐Z, all‐syn species, and of species differing from the former by stretched arrangements of the rings B and C around the central C‐10 bridge (E‐anti, E‐syn, and Z‐anti). Two excited singlet states with picosecond lifetimes are attributed to either one or two coiled ground‐state forms, and two remarkably long‐lived nanosecond excited states arise each from a stretched ground state. The radiationless deactivation of the shorter‐lived of the picosecond states is brought about by ultrafast intramolecular proton transfer between the B/C nitrogen atoms, in addition to the CC rotational modes operative in both. Z→E photoisomerization is also an appreciable deactivation channel of excited biliverdin dimethyl ester. It is confined to the central C‐10 double bond and selectively affords a stretched isomer (10E‐anti), which thermally reforms the coiled starting meterial at room temperature via a sequence of tautomerization and CC rotation. Heating or ultrasonic treatment can reverse this sequence and drive it farther to populate another stretched isomer (10E‐syn) which is thermally stable at room temperature. This stretched form aggregates (presumably to dimers) already at concentrations at which the coiled species still appears to be fully monomeric.
Synthesis of Peptide Hormones using Recombinant DNA Techniques
Authors: Wengenmayer Friedrich 
Published: December 2003

AbstractRecombination of genetic material enables the creation of new bacterial strains which can synthesize specific proteins in large amounts. Such bacteria permit the production of previously inaccessible proteins. They can therefore be used as starting materials for the production of drugs which will open up new paths for therapy. Several proteins produced by bacteria after DNA recombination are presently undergoing clinical trials while others are already being produced on a large scale. Thus, in the area of recombinant DNA techniques the transition from the research laboratory to industrial exploitation has occurred much faster than was anticipated several years ago. The methods, possibilities and problems encountered in the synthesis of peptide hormones by bacteria after DNA recombination are outlined, using insulin, somatostatin, and growth hormone as examples. Great emphasis is placed on the molecular biological aspects of this approach.
Valence Isomerization of Phane‐Bridged cis‐Trioxatris‐o‐homobenzenes
Authors: Stöbbe Michael , Behrens Ulrich , Adiwidjaja Gunadi , Gölitz Peter , de Meijere Armin 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1221. DOI:10.1002/anie.198312210
Rhodium Catalysts for Enantioselective Hydrosilylation—A New Concept in the Development of Asymmetric Catalysts
Authors: Brunner Henri 
Published: December 2003

AbstractFollowing a survey of the asymmetric hydrogenation of prochiral olefins with transition metal/phosphane catalysts, the problem of chirality transfer from the optically active ligands of the catalyst to the substrate is discussed. A new concept for this chirality transfer is introduced; the conformational analysis of model compounds as well as the development of catalysts for enantioselective hydrosilylation demonstrate the usefulness of this concept.
The Electrochemistry of Black Carbons
Authors: Besenhard Jürgen O. , Fritz Heinz P. 
Published: December 2003

Abstract“Modifications” of carbon—as long as they predominantly have the layered graphite structure—exhibit the following properties: (1) electrical conductance, (2) the ability to accomodate ions or molecules between the layers of the lattice, and (3) the ability to reactviafunctional groups at their surfaces (largely at the layer edges). The first of these properties has led to carbon being used as an “inert” electrode material; this aspect will not be considered in this article. The combination of the first and second properties leads to the possibility of electrochemical intercalation. This aspect of black carbon's properties will be described, using both literature data and our own results, in terms of both the basic information and the methodology associated with its uses. In addition to the formation of graphite salts the origin of graphite oxide and the various methods which have been used to analyze these materials will be reviewed. The functional groups [(cf. 3) above] can also be reacted electrochemically. Here, particular emphasis will be placed on detailed results obtained from chemically modified carbon electrodes and also from surface oxides and fluorides. Reference will be made to the technological uses of surface oxidized carbon fibers in composite materials and also generally to possible future uses of graphite based compounds.
Addition of Methylene to Multiple Bonds between Ligand‐Free, Main‐Group Elements and Transition Metals—A General Reaction
Authors: Herrmann Wolfgang A. , Weichmann Josef , Küsthardt Ulrich , Schäfer Adolf , Hörlein Rolf , Hecht Christian , Voss Erdmuthe , Serrano Ricardo 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1543. DOI:10.1002/anie.198315430
Destabilized Carbocations
Authors: Tidwell Thomas T. 
Published: December 2003

AbstractCarbocations are intrinsically reactive species, and in early studies of their generation and properties the more accessible with stabilizing influences were naturally the prime objects of interest. Now, however, it is possible to extend the scope of these studies to include factors which tend to destabilize carbocations. By using the carbocations CH and C2H as reference ions, such destabilizing factors can be defined; these include various structural factors, antiaromaticity effects, and the presence of electron‐withdrawing substituents. Such factors can be studied by their effect on the thermodynamics of carbocations, their effect on reactivities, and by the spectroscopic properties of long‐lived carbocations. Destabilized carbocations of this type are receiving increasing attention and promise to remain an active subject of investigation.
Metal‐Carbon and Metal‐Metal Multiple Bonds as Ligands in Transition‐Metal Chemistry: The Isolobal Connection
Authors: Stone F. Gordon A. 
Published: December 2003

AbstractA new domain for synthesis has developed following recognition that the metal‐carbon and metal‐metal multiple bonds present in certain low‐valent transition‐metal complexes are reactive centers for the attachment of metal‐ligand fragments. The products contain metal‐metal bonds which may be homo‐or heteronuclear in nature. If bridging carbon atoms are present, leading to dimetallacyclopropane or ‐cyclopropene structures, the organic groups (alkylidene or alkylidyne) have an extensive chemistry. The isolobal connection, developed by Hoffmann et al., relating the frontier orbitals of organic groups with those of metal‐ligand fragments, has been crucial in guiding the preparative work.
Routes to Functional Vesicle Membranes without Proteins
Authors: Fuhrhop Jürgen‐Hinrich , Mathieu Joachim 
Published: December 2003

AbstractFixation of reaction partners at appropriate distances from one another is a structural prerequisite for vectorial reactions and reaction sequences. In biological systems (e.g. the photosynthetically active thylakoid membrane or membrane receptors) the positions of the reaction centers are fixed by membrane‐protein complexes, but little is known about the structure of these complexes. Ordered reactive systems in synthetic vesicle membranes were first obtained by employing amphiphiles with reactive head groups as building units, by regioselective incorporation of foreign molecules into the membrane, by alignment of bolaamphiphiles with two head groups of differing solubility or size, and by the formation of domains. Chiral superstructures have also been observed in membranes, and the first stereoselective reactions have been performed in vesicle membranes. The report concludes with a brief discussion of membranes constructed from non‐amphiphilic building blocks and problems which still have to be solved.
“… to make Chemistry more Applicable and Generally Beneficial”—The Transition in Scientific Perspective in Eighteenth Century Chemistry
Authors: Meinel Christoph 
Published: December 2003

AbstractIn 1751, the Swedish chemist Johan Gottschalk Wallerius first differentiated between “pure” and “applied” chemistry, a distinction which was quickly adopted by the other branches of science. Behind this was a new scientific concept of chemistry which emphasized the importance of applying chemistry's accumulated knowledge and its capabilities of providing for the general economic benefit. It also provided chemistry with a new position within the hierarchy of the sciences as well as with a new function in society. The reasons behind and causes of the change in scientific perspective associated with this concept point to the social and institutional conditions under which this field has developed into an independent academic discipline.