bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal‐Induced Decarboxylation of Diketene—A Novel Route to Allene Complexes[1]
Authors: Herrmann Wolfgang A. , Weichmann Josef , Ziegler Manfred L. , Pfisterer Heike
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1223. DOI:10.1002/anie.198212230
Natural versus Indexing Language in Chemical Documentation
Authors: Fugmann Robert
Published: December 2003

In 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

The 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

The 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

The 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

In 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.
Stereochemistry of the Bromination of 1,6‐Methano[10]annulene
Authors: Scholl Thomas , Lex Johann , Vogel Emanuel
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1927. DOI:10.1002/anie.198219270
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

Various 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

The 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

The 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

The 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

The 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.
1‐Lithio‐1‐phenylcyclopropanes—Structure and Dynamics
Authors: Hoell Detlef , Schnieders Christoph , Müllen Klaus
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 299. DOI:10.1002/anie.198302990
Structure and Evolution of the “Atmungsferment” Cytochrome c Oxidase
Authors: Kadenbach Bernhard
Published: December 2003

Approximately 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

Classical 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

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 323. DOI:10.1002/anie.198303230
The Relative Basicities of Imidazole and Benzimidazole
Authors: Catalan Javier , Elguero José , Flammang Robert , Maquestiau André
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 411. DOI:10.1002/anie.198304110
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

The 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

The 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

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 803. DOI:10.1002/anie.198308030
Lithiumcarbamoyl‐bis(ethene)nickel(0)
Authors: Pörschke Klaus , Wilke Günther , Krüger Carl
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 786. DOI:10.1002/anie.198307860
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

The 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

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 718. DOI:10.1002/anie.198307180
Novel Surface‐Modified Solids by Topochemical Oxidation of Zintl Anions
Authors: Haushalter Robert C.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 766. DOI:10.1002/anie.198307660
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

Bilirubin 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.
Pentacarbonylrhenium Complexes with Thiazylamide Ligands
Authors: Hartmann Gabriele , Mews Rüdiger , Sheldrick George M.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 945. DOI:10.1002/anie.198309450
Synthesis of Peptide Hormones using Recombinant DNA Techniques
Authors: Wengenmayer Friedrich
Published: December 2003

Recombination 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

The 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

Following 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

“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

The 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

Carbocations 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

A 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

Fixation 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.
A “Cluster‐Centered” Acetylene‐Vinylidene Rearrangement
Authors: Bernhardt Wolfgang , Vahrenkamp Heinrich
Published: December 2003

The isomerization tBuCCH→tBuHCC was achieved on the cluster Co2Ru (CO)9. Starting material and product were charterized by X‐ray structure analysis. It appears plausible that initial migration of the acetylenic H atom to the metal leads to formation of an acetylide complex, which then tautomerizes in a second step to the vinylidene complex.—Reactions of this type are interesting, inter alia, as models for catalytic processes on solid surfaces.
Trifluoroethylidynesulfur Trifluoride, F3CCSF3
Authors: Pötter Brigitte , Seppelt Konrad
Published: December 2003

A carbon‐sulfur triple bond is present in the title compound, which has been synthesized for the first time. The compound is a colorless gas which rapidly oligomerizes. The strong, very broad band in the IR gas spectrum at 1740 cm−1 can be unequivocally assigned to the CS bond.
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Synthesis of New Amorphous Metallic Spin Glasses M2SnTe4 (MCr, Mn, Fe, Co): Solvent Induced Metal‐Insulator Transformations
Authors: Haushalter Robert C. , O'Connor Charles M. , Haushalter Jeanne P. , Umarji Arun M. , Shenoy Gopal K.
Published: December 2003

Precipitation of amorphous metallic spin glasses from solution is a novel, potentially general method. By this means, main‐group metal polyanions are oxidized by transition‐metal cations. The example which has been studied in most detail is Fe2SnTe4. This forms immediately as a black precipitate when methanolic solutions of anhydrous FeBr2 and K4SnTe4 are mixed at −20°C. The resistivity of pressed powder samples is low. In the presence of strong donor ligands, the FeTe bonds are selectively cleaved. Solid [Fe(en)2]2SnTe4 (orange) is an insulator.
“… to make Chemistry more Applicable and Generally Beneficial”—The Transition in Scientific Perspective in Eighteenth Century Chemistry
Authors: Meinel Christoph
Published: December 2003

In 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.
Protein Folding and Protein Association
Authors: Jaenicke Rainer
Published: December 2003

The biosynthesis of proteins leads to linear chain molecules with a well‐defined amino acid sequence that is unambiguously determined by a corresponding polynucleotide sequence at the level of the gene. The underlying mechanism of transcription and translation is based upon the complementarity of pyrimidine and purine bases, on the one hand, and the genetic code, on the other. As indicated by denaturation/renaturation experiments, the one‐dimensional structural information encoded in the polypeptide chain generates a unique three‐dimensional structure. In consequence, one would expect a “folding code” to exist which governs the spontaneous acquisition of the thermodynamically stable “native” structure of a given protein. The rate of folding (in vivo as well as in vitro) is fast, despite the astronomically high number of potential conformations. The mechanism of folding must therefore be kinetically controlled. Whether the native structure represents the “global” or a “local” minimum on the energy hyperspace is an open question. Above a critical size, protein molecules tend to be organized as assemblies made up of identical or non‐identical subunits. The observed uniformity of a given “quaternary structure” requires a close correlation of folding and association as well as a high specificity of subunit recognition. Both are corroborated by in vitro reconstitution experiments.
Carbene Complexes in Organic Synthesis [New Synthetic Methods (47)]
Authors: Dötz Karl Heinz
Published: December 2003

Transition metals are finding increasing use in organic synthesis on the borderline between “organic” and “inorganic” chemistry. Advantage is taken thereby of the fact that metal‐induced CC bond formation often takes place with remarkable selectivity. The rapid development that has taken place in this area of chemistry is clearly demonstrated by the carbene complexes, examples of which are now known for almost all transition elements, and which have transformed from organometallic curiosities into synthetically useful reagents in less than two decades since the first studies of E. O. Fischer. They are not only suitable as carbene‐transfer agents but also undergo interesting cycloadditions with other ligands in the co‐ligand sphere. Their manipulation requires techniques no more complicated than those for Grignard reactions. Thus, carbene complexes can also be used in the synthesis of natural products such as vitamins or antibiotics.
Red α‐Indium(III) Iodide
Authors: Kniep Rüdiger , Blees Peter
Published: December 2003

Indium(III) iodide is dimorphic: As is already well‐known, individual domains in yellow β‐InI3 transform irreproducibly into red α‐InI3 at low temperature. It has now been possible to gain information about the structure of this phase by way of the InI3InBr3 system. On cooling a melt, mixed crystals of α‐InI3−xBrx (x ≈ 1) could be grown which were suitable for X‐ray structure analysis.
Asymmetric Diels‐Alder and Ene Reactions in Organic Synthesis. New Synthetic Methods (48)
Authors: Oppolzer Wolfgang
Published: December 2003

Rapidly accumulating evidence shows the value of asymmetric Diels‐Alder and ene reactions for the syntheses of enantiomerically pure molecules. This article presents a systematic and critical treatment of various stereoface‐differentiating principles, including very recent spectacular advances. The chiral information is mainly provided by covalently bound auxiliaries, some of which are crystalline, inexpensive, and readily available from naturally occurring monoterpenes, hydroxy acids, amino acids, steroids, and sugars. Non‐destructive transfer of chirality leads to the efficient creation of up to four chiral centers with predictable relative and absolute configurations. Regenerative cleavage of the auxilary group from the diastereomerically pure adducts furnishes a range of polyfunctional, optically pure building blocks. Their synthetic potential is illustrated by strategic applications to the syntheses of physiologically interesting, chiral natural products such as prostaglandins, antibiotics, terpenoids, shikimic acid, alkaloids, and kainoids.
Elementary Steps in Catalytic 1‐Alkyne Coupling to Substituted Cyclooctatetraenes
Authors: Diercks Rainer , Stamp Lutz , Kopf Jürgen , tom Dieck Heindirk
Published: December 2003

A butadienyl bridge between two nickel atoms, which, in addition, carries N ligands of the diazadiene type, is formed on reaction of mononuclear diazadienenickel complexes with disubstituted acetylenes. The pattern of substitution of the C4‐bridge is the same as that of the octatetraene formed from the same educts. These findings are a further indication of binuclear catalysts in the formation of COT from alkynes.
Probing the Structure and Crystallinity of a Lithium Silicate Glass by 29Si Magic‐Angle‐Spinning NMR Spectroscopy
Authors: Rao C. N. R. , Thomas John M. , Klinowski Jacek , Selvaraj U. , Rao K. J. , Millward G. Robert , Ramdas Subramaniam
Published: December 2003

The short‐range order in noncrystalline and crystalline silicates can be investigated with 29Si magic‐angle‐spinning (MAS) NMR spectroscopy. Different 29Si chemical shifts are observed depending on the degree of cross‐linkage of the silicate, the SiOSi bond angles, and the interatomic distances. In this way, the distribution of SiOSi angles in glasses, the crystallinity of which lies between 0 and 100%, can be obtained.
Diamminebis(1,5‐cyclooctadiene)(μ‐1,4,10,13‐tetraoxa‐7, 16‐diazacyclooctadecane‐N7, N16)dirhodiumbis‐(hexafluorophosphate): An Example of Simultaneous First and Second Sphere Coordination
Authors: Colquhoun Howard M. , Doughty Simon M. , Slawin Alexandra M. Z. , Stoddart J. Fraser , Williams David J.
Published: December 2003

The first example of a nitrogen‐containing crown ether acting as both a first and second sphere ligand towards a transition metal is found in the rhodium complex 1. This complex contains a crystallographic center of symmetry and is stabilized by intramolecular hydrogen bridges.
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Sequencing of Short Peptides Using FAB Mass Spectrometry—Increased Information via Derivatization
Authors: Renner Dieter , Spiteller Gerhard
Published: December 2003

Structure‐specific cleavage fragments, all of which contain the amino end of the molecule and which were formed by cleavage of the peptide bond, are obtained by fast atom bombardment (FAB) mass spectrometry of N‐dansyl substituted small peptides. This derivatization thus allows an unequivocal determination of the amino acid sequence.
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Synthesis and Structure of New Potassium‐Gold‐Tellurium Polyanions: [KAu9Te7]4⊖, [K2Au4Te4(en)4]2⊖, and [K2Au4Te4(dmf)2(CH3OH)2]2⊖
Authors: Haushalter Robert C.
Published: December 2003

By extraction of tertiary KAuTe alloys, the salts 1–3, which contain new KAuTe polyanions, could be obtained. The anion of 1 can be roughly described as a derivative of an [M12X8]4⊖ cube; in 2 and 3, planar [Au4Te4]4⊖ rings are present, the sides of which are capped by K⊕.
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Consequences of Strain for the Structure of Aliphatic Molecules
Authors: Rüchardt Christoph , Beckhaus Hans‐Dieter
Published: December 2003

The chemist is accustomed to deriving structures and preferred conformations of organic compounds from rigid molecular models and standard values for bond lengths, bond angles, and torsional profiles. In the case of strained compounds, this rigid structural model has to be abandoned and replaced by a flexible one which takes individual conditions of strain into consideration. It is shown, on the basis of new experimental structure data, that the force field method is suitable and highly reliable for the calculation of structural parameters and preferred conformations of strained compounds. It is, therefore, capable of replacing the rigid molecular model. Furthermore, the systematic analysis of strain induced angle and bond deformation gives a new pivot for the development of a qualitative discussion of deformation in strained molecules and hence for improved conformational analysis. — In the course of this work we were able to isolate two rotamers of D,L‐3,4‐di(1‐adamantyl)‐2,2,5,5‐tetramethylhexane; this is the first isolation of a rotamer pair of an aliphatic hydrocarbon.
Selective Reactions Using Organoaluminum Reagents [New Synthetic Methods (54)]
Authors: Maruoka Keiji , Yamamoto Hisashi
Published: December 2003

In addition to their high oxyphilicity, organoaluminum compounds are endowed with ambiphilic character. These properties can be successfully utilized in developing new synthetic reactions with unique selectivities. Especially noteworthy are the organoaluminum‐promoted Beckmann rearrangement of oxime sulfonates, new syntheses of polyamino macrocycles via reductive cleavage of aminals and amidines by diisobutylaluminum hydride, the diastereoselective cleavage of chiral acetals by organoaluminum compounds leading to optically active secondary alcohols, allylic alcohols, and β‐substituted carbonyl compounds, and biomimetic terpene syntheses. These and other examples, which illustrate the characteristics of organoaluminum chemistry, are used to demonstrate the distinct advantages of organoaluminum reagents in selective organic synthesis.
Phosphorus‐Substituted Thioformamides and Thioformimidates: Molecular Structure and Solid State 13C‐NMR Spectra
Authors: Albert Klaus , Bruns Andreas , Förster Hans , Hiller Wolfgang , Kunze Udo
Published: December 2003

The presence of two symmetry‐independent molecules in the unit cell‐not E/Z isomerism in the crystal‐is responsible for the existence of two N‐methyl signals in the solid‐state 13C‐NMR spectrum of the thioamide 1. Even small conformational differences in the molecule in the solid state have a considerable effect on the chemical shift.
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From the Structure of Antibodies to the Diversification of the Immune Responce (Noble Lecture)
Authors: Milstein Cesar
Published: December 2003

The unimaginable variety of antibody structures is evidenced by the fact that an animal produces specific antibodies against bacteria, viruses, and other foreign substances, even against substances with which it has had no prior contact. How is this possible? In his lecture, on the occasion of accepting the 1984 Nobel Prize for Physiology and Medicine, Cesar Milstein describes work directed toward answering this question. These investigations have led to, among other things, the development of the hybridoma technique in collaboration with G. Köhler.
Derivation and Diversification of Monoclonal Antibodies (Nobel Lecture)
Authors: Köhler Georges
Published: December 2003

The trick to preparing monoclonal antibodies on a large scale consists in fusing mouse myeloma (tumor) cells with mouse spleen cells that have previously been exposed to an antigen. The hybridoma cells having the desired characteristics are immortal and secrete antibodies with a single specificity. Georges Köhler, who received the 1984 Nobel Prize for Physiology and Medicine, developed this hybridoma technique together with C. Milstein. The number of applications is legion.
Cl2CClCl⊙⊕, Cl2CClBr⊙⊕, and Br2CBrCl⊙⊕ by Gas‐Phase Decarbonylation of CX3COY⊙⊕
Authors: Drewello Thomas , Weiske Thomas , Schwarz Helmut
Published: December 2003

The long‐sought radical cation of carbon tetrachloride has been generated by decarbonylation of Cl3CCOCl⊙⊕ in the gas phase and characterized as the stable isomer Cl2CClCl⊙⊕. The theoretically predicted properties were experimentally confirmed. The dication CCl is known.
A Previously Unrecognized 1H‐Azepine Synthesis
Authors: Perst Hartwig , Massa Werner , Lumm Michael , Baum Gerhard
Published: December 2003

The 1H‐azepine derivative 1 rather than the cyclohexadienylidenamide 3 was the species obtained by Adams and Brower in 1956, as now revealed by an X‐ray analysis. Assignment of the structure on the basis of spectroscopic data was—and still is—not possible in this case. This finding opens up a simple route for the synthesis of other 2‐cyano‐1H‐azepines.
Polymeric Tris[trimethyltin(IV)]hexacyanocobaltate(III), a Compound Non‐Analogous to “Super Prussian Blue,” and Its Tris[tricyclopentadienyluranium(IV)] Homologue
Authors: Yünlü Kenan , Höck Nils , Fischer R. Dieter
Published: December 2003

The coordination polymer 1 with a three‐dimensional network of Co atoms is formed as shown below. Distorted octahedral Co(CN)6 structural units are present in 1, which are linked through SnMe3 bridges such that the partial structures …CoCN → SnMe3 ← NCCo… are formed. The Sn atoms are coordinated trigonal‐bipyramidally. Since, surprisingly, two‐thirds of the chains are nonlinear, no super Prussian blue analogue can form; such an analogue should contain cubic Co8 cages.
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New Co and Ni Clusters with Se and PPh3 as Ligands: [Co4(μ3‐Se)4(PPh3)4], [Co6(μ3‐Se)8(PPh3)6], [Co9(μ4‐Se)3(μ3‐Se)8(PPh3)6], and [Ni34(μ5‐Se)2(μ4‐Se)20(PPh3)10]
Authors: Fenske Dieter , Ohmer Johannes , Hachgenei Johannes
Published: December 2003

Four novel clusters of Co or Ni, Se, and PPh3 have been obtained in good yields from [MCl2(PPh3)2] and Se(SiMe3)2 in toluene. In all four clusters, whose structures have been elucidated, the actual core is surrounded by a sheath of phenyl groups. The empirical formulas are given in the title; the structure of the nickel complex is to be seen on the cover page of this issue. The four complexes are 60e, 98e, 137e, and 448e species, respectively.–The longer known analogous reaction with S(SiMe3)2 gave other types of products.
Error Rates of the Replication and Expression of Genetic Information
Authors: Englisch Uwe , Gauss Dieter , Freist Wolfgang , Englisch Sabine , Sternbach Hans , von der Haar Friedrich
Published: December 2003

Biological evolution is based on continual changes in the genomes of cells. If stable organisms are to develop nonetheless in the course of this process, low error rates (high accuracy) in both the replication of genes and their transcription and translation into proteins have to be assured. The overall error rates of these processes are measurable and can be estimated: they result from the error rates of the individual enzyme‐catalyzed steps. In many cases, for example in the discrimination of the amino acids valine and isoleucine during protein biosynthesis, it is not possible to achieve a sufficient accuracy only on the basis of the difference of the free energies of binding of the correct and incorrect substrates (the two amino acids differ only in a CH2 group). The necessary low error rate is maintained by an additional proofreading step, which is carried out by the enzymes involved after formation of the enzyme‐substrate complex, either during catalysis or before product release. In this step, an incorrect intermediate or product is hydrolyzed. The energy input necessary for the synthesis of the incorrect intermediate or product, which is provided by hydrolysis of adenosine or guanosine triphosphate, is the price paid for the low error rates. In this article, the proofreading mechanisms of several enzymes—mainly those involved in DNA replication and the aminoacylation of transfer RNA during protein biosynthesis—are discussed.
The Role of Hydrothermal Synthesis in Preparative Chemistry
Authors: Rabenau Albrecht
Published: December 2003

“Hydrothermal synthesis” usually refers to heterogeneous reactions in aqueous media above 100°C and 1 bar. The previously common distinction between hydrothermal conditions below and pneumatolytic conditions above the critical point is no longer made, since no discontinuities are observed upon exceeding the critical conditions. Under hydrothermal conditions, reactants otherwise difficult to dissolve go into solution as complexes, in whose formation water itself or very soluble “mineralizers” can participate. Thus, one can obtain the conditions of chemical transport reactions,[1] of which hydrothermal syntheses can be considered a special case. During recent decades in the geological sciences—in which the method is also historically rooted—it has received a strong impulse, whose effect on preparative solid state chemistry is discussed here.
Non‐Induced, Highly Diastereoselective Intramolecular Ene Reactions of 1,7‐Dienes to trans‐1,2‐Disubstituted Cyclohexanes
Authors: Tietze Lutz F. , Beifuss Uwe
Published: December 2003

The terminology of stereoselective synthesis is rapidly coming to resemble the legendary Tower of Babel. “Induced” and “non‐induced diastereoselective” are the most recent newcomers. Whether these unquestionably useful terms will find acceptance is a matter for the future to decide. They were introduced in order to explain the title reaction in which 1,2‐disubstituted cyclohexanes with a trans: cis selectivity of > 99 : 1 are formed.
Elucidation of the Structure of Epidermin, a Ribosomally Synthesized, Tetracyclic Heterodetic Polypeptide Antibiotic
Authors: Allgaier Hermann , Jung Günther , Werner Rolf G. , Schneider Ursula , Zähner Hans
Published: December 2003

A decosapeptide that is highly effective against acne has been isolated from a culture filtrate of Staphylococcus epidermidis Tü 3298. The molecule contains four disulfide bridges derived from meso‐lanthionine, β‐methyllanthionine, and the newly discovered amino acid S‐(2‐aminovinyl)‐D‐cysteine. The structure elucidation was achieved by enzymatic and hydrolytic fragmentation and desulfurization with Raney nickel followed by sequence analysis.
Bis(2,4,6‐tri‐tert‐butylphenyl)bicyclotetraphosphane
Authors: Riedel Ralf , Hausen Hans‐Dieter , Fluck Ekkehard
Published: December 2003

Only one bond of the P4 tetrahedron is opened to form the title compound 1, a derivative of P4H2. 1, along with the diphosphene derivative 2, was isolated as orange, air‐stable crystals (R2,4,6‐tri‐tert‐butylphenyl).
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[3+2] Cycloaddition Approaches to Five‐Membered Rings via Trimethylenemethane and Its Equivalents [New Synthetic Methods (55)]
Authors: Trost Barry M.
Published: December 2003

The power of cycloadditions for ring formation derives from the potential for chemo‐, regio‐, diastereo‐, and enantioselectivity. Trimethylenemethane (TMM) and its equivalents offer the possibility of extending such benefits to the synthesis of five‐membered rings. Three types of conjunctive reagents appear to be promising candidates: (1) selected 4‐alky‐lidene‐4,5‐dihydro‐3H‐pyrazoles, (2) 2‐[(trimethylsilyl)methyl]allyl esters and halides, and (3) alkylidenecyclopropanes. Thermal reactions, especially intramolecular ones, effect the cycloaddition of the pyrazoles to olefins–especially electron‐poor olefins. The latter two precursors require a catalyst, notably a palladium complex, to unlock the synthetic potential. With the 2‐[(trimethylsilyl)methyl]allyl esters, a general chemo‐, regio‐, and diastereoselective cycloaddition with typical Diels‐Alder dienophiles forms methylenecyclopentanes in both inter‐ and intramolecular fashion. A tin analogue allows extension of this cycloaddition to aldehydes, and, in a related sequence, to ketones and imines to form 3‐methylenete‐trahydrofurans and 3‐methylenepyrrolidines with excellent diastereoselectivity. The 2‐[(tri‐methylsilyl)methyl]allyl esters also serve to effect net methylenecyclopentane annulation to cyclic enols. Such adducts can further undergo three‐carbon intercalation or combined ring contraction‐spiroannulation simply by the use of either a nucleophilic or electrophilic trigger. Alkylidenecyclopropanes undergo cycloadditions to both electron‐rich and electron‐poor olefins when stimulated by metal catalysts, especially palladium. A complementary regiochemistry to the approach based upon silicon conjunctive reagents is observed. The availability of these cycloadditions provides new strategies for the synthesis of natural products.
Cluster Beam Chemistry—from Atoms to Solids
Authors: Martin T. Patrick
Published: December 2003

How do the properties of a solid gradually evolve as atoms are brought together to form increasingly larger units? In order to answer this question one must study aggregates of atoms too large to be called molecules but still too small to have even the structure of a crystal. Recent advances in both theory and experiment have made possible some first explorations in this long neglected but fascinating field of study. This review will emphasize the generation, growth, and properties of homo‐ and heteronuclear clusters in the vapor phase, particular attention being paid to mass spectrometric investigations.
2‐(2,4,6‐Tri‐tert‐butylphenyl)‐1‐arsaethyne—the First Compound Containing an Arsenic–Carbon Triple Bond
Authors: Märkl Gottfried , Sejpka Hans
Published: December 2003

An AsC bond and otherwise only C and H—that is no metal—are present in the title compound 3. It was prepared from the acid chloride 1 and the arsenide 2, which is readily accessible from tris(trimethylsilyl)arsane. 3 is pale yellow and crystalline, and melts at 114–116°C (R = 2,4,6‐tBu3C6H2).
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