bluuebunny/crossref_metadata_2025 huggingface dataset:
Bifunctional Reagents for the Crosslinking of Proteins
Authors: Fasold Hugo , Klappenberger Jürgen , Meyer Christa , Remold Heinz
Published: December 2003

Proteins can be crosslinked by chemical compounds without any accompanying change in the complicated three‐dimensional structure. Many bifunctional reagents that can react with functional groups in the side chains of the amino acids are now known. Not only can the distance between the linked amino acid residues be deduced from the known length of the bridge introduced, but information can also be obtained concerning changes in conformation during other reactions and concerning the arrangement of the components of a quaternary structure.
Methods of Asymmetric Synthesis—Enantioselective Catalytic Hydrogenation
Authors: Izumi Yoshiharu
Published: December 2003

It is proposed that asymmetric syntheses be divided into enantioselective and diastereoselective syntheses. The enantioselective hydrogenations discussed in the present progress report were catalyzed by Raney nickel that had previously been treated with solutions of optically active compounds. Relationships exist between the enantioselectivity of the catalyst and the structure of the chiral compound used to modify it.
Signal Transducers: Terra Incognita of Molecular Biology
Authors: Delbrück Max
Published: December 2003

In this article four cases of signal transduction in biology are discussed, ranging from a case which we do understand in molecular detail (genetic induction) through two cases where the fog may be beginning to clear (vertebrate vision and bacterial chemotaxis) to a case where we are still struggling to define the participants of the play (the avoidance response of the fungus Phycomyces).—Although most of the facts presented are not brand new, the juxtaposition of them is perhaps unconventional and may be of interest at least by way of outlining an area of research of some promise. No doubt modern concepts and technologies of chemical and physical research will play a great role in this borderline area between a variety of fields, presenting great challenges to the ingenuity and versatility of the experimenter.
Stereochemistry of [2.2]Metacyclophanes
Authors: Vögtle Fritz , Neumann Peter
Published: December 2003

Increasing numbers of investigations have been carried out on bridged aromatic compounds, the independence of which was very recently acknowledged in the class name “phanes”. Special attention is being attracted by the [2.2] metacyclophanes, whose molecular architecture raises many interesting theoretical questions, mainly with regard to intramolecular steric and electronic interactions. In the present progress report, a short description of the classification and nomenclature of the phanes is followed by a discussion of new physical and chemical aspects of the stereochemistry of [2.2] metacyclophanes and a number of related [2.2] phanes with other aromatic nuclei.
The syn and anti Steric Course in Bimolecular Olefin‐Forming Eliminations
Authors: Sicher Jiři
Published: December 2003

Earlier evidence led to the view that in bimolecular olefin‐forming eliminations the anti steric course is generally preferred over the syn. Recent experiments, however, show that in some common bimolecular elimination reactions, notably those involving onium bases, syn‐ and anti‐eliminations proceed side by side, the former preferentially leading to the trans‐ and the latter to the cis‐olefins.
Chemical Plant Protection — Past, Present, and Future
Authors: Sasse Klaus
Published: December 2003

Chemical plant protection greatly contributes to ensuring good harvests and is therefore of considerable agricultural and economic importance. After thirty years of systematic research we are now in possession of powerful chemical agents active against most of the significant enemies of cultivated plants, but the constant change in nature always calls for more and better plant protection agents. These agents play a mostly well‐known part in environmental pollution and in the overall toxic situation, and one of the aims of future development is to reduce further the dangers to man and the environment.
Chemical Synthesis of Polynucleotides
Authors: Agarwal K. L. , Yamazaki A. , Cashion P. J. , Khorana H. G.
Published: December 2003

Current methodology for the chemical synthesis of short chains (up to about twenty nucleotide units) of deoxyribopolynucleotides is reviewed.
The Chemistry of Carbenoids and Other Thermolabile Organolithium Compounds
Authors: Köbrich Gert
Published: December 2003

Organolithium compounds are thermally quite stable, despite their extremely high reactivity. Thermolability, i.e. the property of undergoing irreversible changes at low temperatures without the participation of molecules of a different kind, is associated with additional functional groups, which may be readily eliminated together with the metal cation, may cause intramolecular rearrangements, or may lead to intermolecular additions and substitutions involving several molecules of the same type. Thermolabile organolithium compounds have frequently been postulated or detected as intermediates of important reactions, and are therefore of theoretical and practical interest. If certain precautions are taken, it is occasionally possible (mainly at low temperatures) to prepare them intact, and hence to release them from the constraint of the fate assigned to them as short‐lived intermediates. Investigations with this aim have for some time occupied a place of considerable importance in the chemistry of organometallic compounds.
Intermolecular Interactions: van der Waals Molecules
Authors: Ewing George E.
Published: December 2003

Recent experiments using electron diffraction techniques, optical and infrared spectroscopy and mass spectroscopy have provided convincing evidence for the existence of bound states of gaseous Ar2, (H2)2, (O2)2, (NO)2 and other simple dimers. The bond strength of these van der Waals molecules is hundreds of times weaker than ordinary chemical bonds. These experimental studies yield information on the structure and stability of van der Waals molecules and can provide new insight into weak intermolecular interactions.
Polycrystalline Inorganic Fibers—Production, Properties, Applications
Authors: Winter Gerhard
Published: December 2003

This progress report ends with the sentence: In the opinion of many experts, we are entering an “age of inorganic fibers”. An attempt is made in the article to outline the present stage of development and the outlook for one of the most interesting fields of modern materials science.
Organic Syntheses in the Plasma of Glow Discharges and Their Preparative Application
Authors: Suhr Harald
Published: December 2003

It is only during the last few years that reactions of organic substances as a result of electron collisions in the cold plasma of glow and corona discharges have been developed into a preparatively useful method with a wide range of possibilities. Its basic principles and development prospects are discussed in the present progress report on the basis of the research results that are known at present.
Energy Metabolism in Mitochondria
Authors: Heldt Hans Walter
Published: December 2003

Mitochondria are separate metabolic compartments within the cell. The functional boundary of the mitochondrial compartment is the inner membrane. This membrane contains the enzymatic apparatus for the electron transport and oxidative phosphorylation. The substrate breakdown cycles are localized in the mitochondrial matrix space. Specific carriers are responsible for the exchange of ADP, ATP, phosphate, and intermediates of the citric acid cycle between the matrix space and the extramitochondrial space. The particular importance of the adenine nucleotide transport to the regulation of the energy metabolism of the cell is discussed in detail.
Transcription of Genetic Information and Its Regulation by Protein Factors
Authors: Rüger Wolfgang
Published: December 2003

During transcription, genetic information is transferred from DNA to mRNA, the process being catalyzed by DNA‐dependent RNA polymerase. Transcription comprises binding of the RNA polymerase to DNA, initiation, elongation, and termination. The interplay of the positive and negative control elements of these processes is illustrated for bacteria and bacteriophages.
Reactions of Electron‐Rich Olefins with Proton‐Active Compounds
Authors: Hocker Jürgen , Merten Rudolf
Published: December 2003

Proton‐active substances react with certain electron‐rich olefins with cleavage of the central CC double bond to give compounds that can be formally regarded as insertion products of nucleophilic carbenes. If they satisfy certain structural conditions, they isomerize with β elimination to give open‐chain compounds. Both CH‐acidic compounds and compounds containing NH or OH groups can undergo this reaction. The mechanisms are discussed, and the importance of the intermediate products to biochemistry (thiamine, tetrahydrofolic acid) is indicated.
The Stereoselective Acylation of Racemic Secondary Alcohols with Phenyltrifluoromethylketene as an Experimental Test of the Stereochemical Analogy Model
Authors: Anders Ernst , Ruch Ernst , Ugi Ivar
Published: December 2003

Validity of the stereochemical analogy model[1,2] for stereoselective reactions is tested on acylations of racemic chiral secondary alcohols with phenyltrifluoromethylketene. The product ratios for the diastereomeric esters formed can be calculated using a formula derived from the general model for the special case, the results agreeing with the experimental data within the accuracy of the measuring method (integration of the 19F‐NMR signals).
Carbocations and Electrophilic Reactions
Authors: Olah George A.
Published: December 2003

The general concept of carbocations encompasses all cations of carbon containing compounds which can be differentiated into two distinct classes: trivalent (“classical”) carbenium ions and pentacoordinated (“nonclassical”) carbonium ions. In this paper the preparation and structural study (by NMR, IR, Raman and ESCA spectroscopy) of stable carbenium ions and carbonium ions are discussed. As is well known, trivalent carbenium ions play an important role in electrophilic reactions of π‐ and n‐donor systems. Similarly, pentacoordinated carbonium ions are the key to electrophilic reactions of σ‐donor systems (single bonds). The ability of single bonds to act as σ‐donor lies in their ability to form carbonium ions via triangular two electron, three‐center bond formation. Consequently there seems to be no principle difference between the electrophilic reactions of π‐ and σ‐bonds except that the former react more easily, even with weak electrophiles, whereas the latter necessitate more severe conditions. The role of carbocations in electrophilic reactions of π‐ and σ‐donor systems is discussed.
Polar Cycloadditions
Authors: Schmidt Richard R.
Published: December 2003

Cycloadditions with ionic components are known as “polar cycloadditions” to distinguish them from cycloadditions with dipolar and uncharged components. The structural requirements, the manner in which “polar” intermediates capable of addition are produced and their reactivity with activated and nonactivated multiple bonds, the many peculiarities of the course of the cycloaddition, and the favorable synthesis of heterocyclic systems by this reaction principle makes such a terminological distinction useful and necessary if the existing data are to be brought into order. The present review, which is the first on a field of chemistry that has not yet been very extensively investigated, deals initially with cationic and then with anionic polar cycloadditions.
Spectroscopic Properties of Organic Azo Compounds
Authors: Rau Hermann
Published: December 2003

Azo compounds are characterized by a low‐energy1(n,π*) electronic state, which gives rise to a weak band at long wavelengths in the absorption spectrum. Coupling of this state with other low‐lying molecular states is responsible for the high intensity of the “azo band” compared to other forbidden transitions, for its lack of vibrational structure, and for the inability of nearly all organic azo compounds to fluoresce.
Mechanistic Analysis of Solution Reactions by Non‐Isothermal Calorimetry
Authors: Koch Erhard
Published: December 2003

For the rapid kinetic and energetic analysis of reactions in solution (τ20°C > 10‐4s) by differential thermal analysis (DTA), the following thermogram parameters are defined as characterizing the start of the reaction: 1. initial temperature, 2. activation energy of the initiation reaction. In conjunction with the shape index (asymmetry of the DTA curve) and the half width of the DTA curve referred to standard physical conditions (cell constant, heating rate, and temperature difference), these quantities allow a simple distinction between one‐step reactions of first and second order and composite reactions. It is possible to recognize whether a process involves parallel, successive, or equilibrium reactions, or combinations of these. The reaction mechanism can be clarified in many cases by measurements at various concentrations and heating rates and by discussion of the enthalpy values. The shortened method described in this report for the evaluation of the thermograms was derived with the aid of an analog computer and checked experimentally.
Hydrazidinyl Radicals: 1 2,4,5‐Tetraazapentenyls, Verdazyls, and Tetrazolinyls
Authors: Neugebauer Franz A.
Published: December 2003

This report reviews the preparation of hydrazidinyls and their chemical and physical properties.
Chemistry and Applications of Liquid Crystals
Authors: Steinsträsser Ralf , Pohl Ludwig
Published: December 2003

Approximately 5% of all organic compounds are transformed at their melting point into liquid crystals—thermodynamically stable, anisotropic liquids which in contrast to isotropic melts appear turbid and are also known as mesophases. Such melts are classed as smectic, nematic, and cholesteric liquid crystalline phases, depending upon the arrangement of the constituent molecules. The discovery of numerous potential applications during the past ten years has awakened the study of liquid crystals from its former slumber as a physical curiosity and placed it in the limelight of the scientific stage. Uses in display systems for measured values and for computer and process data, as well as for remote controlled timetables, for windows of variable light‐transmission, etc., appear particularly promising. Not only black‐and‐white contrasts are now possible but also color production.
Recent Results in Insect Pheromone Chemistry
Authors: MacConnell John G. , Silverstein Robert M.
Published: December 2003

Pheromones are substances which are secreted to the outside by an animal, especially an insect, and received by a second individual of the same species, in which they release a specific reaction, for example, a definite behavior or developmental process. The name is derived from the Greek pherein (to bear, transmit) and hormon (impel, excite). Pheromones include, inter alia, sex attractants, warning substances, and “aggregation pheromones”. Many of these substances are effective at very low concentration. The insect pheromones are predominantly derivatives of long‐chain, slightly branched hydrocarbons.
Photoelectron Spectra of Nonmetal Compounds and Their Interpretation by MO Models
Authors: Bock Hans , Ramsey Brian G.
Published: December 2003

The results of (low energy) photoelectron spectroscopy render possible a better appreciation of the “Nature of the Chemical Bond”. The application of this new experimental method is demonstrated utilizing representative compounds of the nonmetal elements, and a close symbiosis delineated with molecular orbital models. In particular, general consequences are discussed concerning electron deficiency, σ‐ and π‐interactions, electron pair delocalization, and substituent effects or geometric perturbations. Photoelectron spectroscopic ionization energies permit evaluation of parameters for specified molecular groups, allow correlation with numerous other experimental data, and are didactically valuable in the teaching of general chemistry.
The Allylcobalt System
Authors: Bönnemann Helmut , Grard Charles , Kopp Werner , Pump Wichard , Tanaka Kenjiro , Wilke Günther
Published: December 2003

The following report describes the preparation and reactions of organocobalt compounds, especially the thermally unstable tris(π‐allyl)cobalt and cyclooctenylcobalt compounds. The stoichiometric and catalytic transformations of these highly reactive organocobalt systems give an insight into the rôle of cobalt in homogeneous catalysis involving alkenes and alkynes.
Polymers as Reagents in Organic Synthesis
Authors: Overberger C. G. , Sannes K. N.
Published: December 2003

Polymeric reagents offer a range of unique advantages. Intramolecular reactions, such as the cyclization of peptides or Dieckmann cyclizations, can be brought about by attaching the reactive molecules at remote points along a polymer chain. In contrast, if the reactive molecules are anchored in close proximity on a polymeric support then intermolecular reactions occur, as demonstrated for a ketone synthesis. Apart from such proximity effects, cooperative effects can also be exploited, e.g. in the formation of a 2:1 complex of a crown ether and an alkali metal ion. The hydrolysis of an ester with polyvinylimidazole provides a detailed illustration of hydrophobic interactions. The simple separation of polymer‐bound and low‐molecular compounds by filtration is another significant advantage.
Oxidative Coupling via Organocopper Compounds
Authors: Kauffmann Thomas
Published: December 2003

The type of reaction described here, which achieved preparative importance before the turn of the century in the form of the Glaser reaction, has found new applications in recent years: Syntheses of 1,3‐dienes, 2,3,6,7‐tetraaza‐1,3,5,7‐tetraenes, 2,3‐diaza‐1,3‐dienes, hydrazine derivatives, bis(heteroallyl) compounds, hetarenes, polyhetarenes, cyclopolyarenes, protophanes, phanes, and heteraprotophanes. The reaction, which consists in the metalation of the starting substance followed by oxidative coupling of the metal derivative, merits special preparative interest when several successive coupling processes are possible (e. g. polyyne, polyarene, cyclopolyarene, and protophane syntheses). The main factors limiting its applicability are the high thermal stability of some organic copper compounds and the disproportionation of the ligands that frequently occurs as a competing reaction. Selective asymmetric linkages are not generally possible by this method.
The Reactivity of the Porphyrin Ligand
Authors: Fuhrhop Jürgen‐Hinrich
Published: December 2003

The physical properties and the chemical reactivity of the porphyrin macrocycle, whose formation can be rationalized by a simple statistical argument, are related in many respects to those of aromatic hydrocarbons. The reactivity of the porphyrin ligand in its metal complexes varies within wide limits because of the difference in the inductive effects of different central metal ions on the conjugated π‐electron system. One‐electron reactions, phlorin formation by addition of hydrogen or oxygen to the methine bridges, and the formation of π complexes predominate. The biochemical reactivity of the porphyrin ligand largely corresponds to its in‐vitro chemistry.
The Synthesis of Unusual Organic Molecules Using Cyclic Peroxides. New synthetic methods (3)
Authors: Adam Waldemar
Published: December 2003

The photodecarboxylation of malonyl peroxides into α‐lactones[1] and the thermal conversion of the 1,4‐endo‐peroxide 4,5‐epoxy‐3,6‐epidioxy‐1‐cyclohexene into the novel benzene trioxide[2] are two recent examples of the potential of cyclic peroxides in the synthesis of unusual organic molecules. The former transformation entails a fragmentation, the latter a rearrangement process. Most reported examples fall into one of these two gross reaction types. Of the numerous examples that have been reported in the literature during the last two decades, only those shall be focused on that lead to unusual compounds or constitute efficient syntheses of known compounds, in order to stress the convenience of cyclic peroxides in the synthesis of organic compounds.
Dinitrogen‐Transition Metal Complexes: Synthesis, Properties, and Significance
Authors: Sellmann Dieter
Published: December 2003

Compared to the large number of CO complexes, N2 complexes are still rare. In certain cases they may be formed from N2 gas and metal compounds under physiological conditions, and are therefore frequently considered as possible intermediates in N2 assimilation. However, despite numerous attempts it has not yet been possible to reduce the N2 ligand of a fully characterized N2 complex to NH3. This negative evidence recently prompted the discoverers of the first dinitrogen complex, the [Ru(NH3)5N2]2⊕ ion isolated in 1965, to express doubt whether such complexes really do play a part in the enzymatic reduction of N2. The latest findings nevertheless incline toward a somewhat more optimistic view. Thus, the mild partial reduction of the N2 ligand in metal complexes with inert gas configuration, hitherto considered nonreducible, justifies the hope that a suitable system permitting the catalytic reduction of molecular nitrogen under normal conditions will one day be found. Even apart from any technical potential, the N2 complexes constitute an interesting chapter of modern inorganic chemistry.
The Helicenes
Authors: Martin Richard Henri
Published: December 2003

“Helicene” is the name introduced by Newman in 1955, to describe the benzologues of phenanthrene in which the extra ortho‐condensed rings give rise to a (regular) cylindrical helix. The pioneer work of Newman in this field cannot be overemphasized; his brillant synthesis and resolution of [6]helicene, achieved eighteen years ago, will remain as a landmark, for it opened the way to the study of a fascinating class of synthetic molecules. In the following review, an attempt is made to summarize the present state of our knowledge in this rapidly expanding field.
Fixation of Atmospheric Nitrogen by Microorganisms
Authors: Kleiner Diethelm
Published: December 2003

Research on the enzymatic assimilation of molecular nitrogen (N2 fixation) has made decisive advances in recent years. Both the purely scientific aspects of this process and its industrial implications are assuming ever‐increasing interest. Some of the results most important from the biochemical point of view have been collected in the present report.
Relationships between the Chemistry of Dispersed Metals and Chemical Syntheses with Metal Atoms
Authors: Kohlschütter Hans Wolfgang
Published: December 2003

An interesting and topical question in modern inorganic chemistry is: To what extent are the well‐known chemistry of dispersed metals and the new technique of chemical synthesis with free metal atoms interrelated? Or in other words: Where, do these two facets of metal chemistry meet? In an attempt to glean an answer to this question three important aspects are considered: metal sols, activated metals as powders, and deposits in vacuum processes (evaporation and cathodic sputtering of metals).
Prostaglandins
Authors: Bartmann Wilhelm
Published: December 2003

The prostaglandins are lipid‐soluble C20‐carboxylic acids containing a five‐membered ring, several oxygen function, and at least one double bond. They are found in animal organisms where they stimulate, inter alia, the smooth muscle. In the last decade more has been learned about the occurrence, biosynthesis, metabolism and pharmacological properties of the prostaglandins. Analytical methods for their determination, and syntheses for the naturally occurring prostglandins and their synthetic analogs have been developed. In this report, an attempt is made to show why new knowledge has dramatically stimulated pharmaceutical research in this field.
Preparation of Aryl‐Alkyl Ethers and Thioethers
Authors: Downie Ian M. , Heaney Harry , Kemp Graham
Published: December 2003

For corrigendum see DOI:10.1002/anie.197507162
Microencapsulation
Authors: Sliwka Wolfgang
Published: December 2003

Microencapsulation is the enveloping of liquid droplets or fine solid particles to form microscopic capsules 1 to 5000 μm in diameter. For the fabrication of such capsules special techniques have been developed which take into account the substance to be encapsulated and the intended use of the capsules. The envelopes, consisting of natural or synthetic polymers, may be made permeable, semipermeable, or impermeable. Thus, there are several possibilities for controlled release of an encapsulated reactive substance, for example by destruction of the envelope or by permeation: alternatively, reactions can be allowed to take place within the microcapsules. Microencapsulation facilitates delivery of many substances to their site of utilization in a novel form of preparation and novel mode of dosage, the solids being dispersed very finely and having a very large surface area.
Zeolites—Their Synthesis, Structure, and Applications
Authors: Schwochow Friedrich , Puppe Lothar
Published: December 2003

During the last 15 years zeolitic molecular sieves, which should not be confused with the amorphous aluminosilicate ion exchangers, have attained increasing importance as specific adsorbing agents and catalysts. The progress made in all sectors of the zeolite field is perhaps best appreciated from the increase in publications from 34 at the First International Conference on Molecular Sieves held in London in 1967 to 116 at the last Meeting, which was held in Zürich in 1973. The present review provides an introduction to this extensive subject which still provides stimulus to intensive research.
Heterocycles as Structural Units in New Optical Brighteners
Authors: Dorlars Alfons , Schellhammer Carl‐Wolfgang , Schroeder Joseph
Published: December 2003

Optical brighteners are used in detergents, textiles, paper, plastics, and paints. Most optical brighteners contain heterocycles such as coumarins, 2‐pyrazolines, naphthalimides, pyrazoles, triazoles, oxadiazoles, and triazines. In this article the syntheses, properties, and applications of new optical brighteners are described with references to patent literature.
Tetracyclines: Chemistry, Biochemistry, and Structure‐Activity Relations
Authors: Dürckheimer Walter
Published: December 2003

Tetracycline antibiotics continue to play an important role in human and veterinary medicine and in animal nutrition. The classical tetracyclines obtained by fermentation have been supplemented by products of partial synthesis which provide, in particular, the advantages of better pharmacokinetic properties and greater tolerance. Following a brief review of older work, the present article describes partial and total syntheses of tetracyclines, the influence of electronic, steric, and lipophilic factors and of complex formation on biological activity. The inhibition of biochemical systems invoked in interpretation of the mode of action of tetracyclines and problems involved in the development of resistance are discussed.
En Route to Multisurface Chemistry
Authors: Quinkert Gerhard
Published: December 2003

This article considers what happens when the energy required for a compound to react is supplied by an irradiation lamp instead of by a Bunsen burner. For this purpose real examples are selected from three typical groups of cases. The respective answers obtained should indicate significant moves in organic photochemistry which may be expected to affect the further development of chemistry as a whole in the near future. During this tour d'horizon particular attention is paid to photochemical processes in solids or solvent matrices, light‐induced reactions are especially emphasized as key reactions in (natural product) syntheses, and a strong case is made for interpreting the reactions of electronically excited molecules in terms of Salem correlation diagrams.
Exchange in vitro of Subunits between Enzymes from Different Organisms: Chimeras of Enzymes
Authors: Hartmann Guido R.
Published: December 2003

Most intracellular enzymes are made up of several identical or different subunits. The more remote any two organisms are phylogenetically, the greater will be the differences in amino acid sequence of a given enzyme. Nevertheless, numerous examples exist of specific association between chemically different subunits, or even of the formation of enzyme chimeras. They span not only the boundaries between related organisms but also the deep rift between prokaryotic and eukaryotic cells. Exchange of subunits between enzymes of similar activity but differing origin can be rationalized by assuming enzymes to posses functionally defined types of three‐dimensional structures.
Electro‐Deprotection—Electrochemical Removal of Protecting Groups
Authors: Mairanovsky V. G.
Published: December 2003

The reactions of electrochemical splitting may be successfully used for removal of protecting groups. Theoretical and preparative aspects of the method of electro‐deprotection are discussed, and examples of its use are given. The removal often requires high potentials. The use of modified protecting groups (“inner activation”) or of catalysts (electron carriers) which facilitate electron transfer against the standard potential gradient (“external activation”), can greatly increase the scope of the electrochemical method.
Hydrozirconation: A New Transition Metal Reagent for Organic Synthesis
Authors: Schwartz Jeffrey , Labinger Jay A.
Published: December 2003

Hydrozirconation has recently been developed as a procedure for functionalizing alkenes, alkynes, and 1,3‐dienesviaorganozirconium(IV) intermediates. These intermediates react with a variety of electrophilic reagents to give organic products in high yield. Mechanisms of reactions involved in these sequences are discussed.
Production of Oil by Hydrogenation of Coal
Authors: Schlupp K. F. , Wien H.
Published: December 2003

A survey of coal hydrogenation processes revealed that, despite a wealth of experience gathered in Germany up to 1945 some of which served as a basis for further work in the USA, there is at present no process available anywhere in the world for the commercial production of oil from coal. Approaches suitable for further development are the noncatalytic one‐step limited hydrogenation and catalytic hydrogenation. Under the most favorable conditions production of oil from coal should become technically feasible some time between the early and mid‐1980's. In view of the price of heavy fuel oil the commercial prerequisites for production of synthetic fuel oil from coal are presumably fulfilled only in those countries with low coal prices.
Elementary Processes at Gas/Metal Interfaces
Authors: Ertl Gerhard
Published: December 2003

Recent years have seen the development of several physical methods for the study of solid surfaces under ultrahigh vacuum conditions, of which the most important are discussed in this progress report. Contemporary views of the chemisorption bond and the factors affecting it are discussed against the background of the adsorption of hydrogen and of carbon monoxide on single crystal surfaces of face‐centered cubic transition metals. Catalytic oxidation of CO over palladium and the interaction of oxygen with nickel serve as examples of chemical surface reactions.
Radioimmunoassay
Authors: Eckert Hans Georg
Published: December 2003

Biologically active substances are often effective in nanogram or even smaller quantities. Investigations of their mode of action therefore require highly sensitive microanalytical methods of detection. Chemical, chromatographic or spectrometric methods frequently lack the required sensitivity; it was only after the discovery of the radioimmunoassay (RIA) that quantitative determination of minute amounts of substances in the presence of a millionfold excess of other compounds became possible. The radioimmunoassay combines the extreme sensitivity of detection of radioactively labeled substances with the high specificity of immunological reactions. The superiority of radioimmunological methods over other analytical techniques rests upon their sensitivity, specificity, facile application, and especially their broad general scope.
Structural Rules for Globular Proteins
Authors: Schulz Georg E.
Published: December 2003

Is it possible to reach a detailed understanding of the complex three‐dimensional structures of native polypeptide chains? In view of the wealth of common physicochemical and phylogenetic features discovered among proteins this question has become reasonable. The current state of discussion is presented in this report.
Experimental Electron Densities and Chemical Bonding
Authors: Coppens Philip
Published: December 2003

Some recent results of charge density analysis by X‐ray and neutron diffraction are discussed. Problems that have been studied in a number of laboratories include the nature of single, double, and triple bonds, lone‐pair hybridization, bonding in some metals, alloys, and organometallic compounds, and the derivation of physical properties from X‐ray diffraction densities. At the present stage of development of methods studies of series of related compounds are feasible and expected to find widespread application.
Polar Effects in the Addition of Alkyl Radicals to Olefins
Authors: Giese Bernd , Meister Jürgen
Published: December 2003

The presence of a negative partial charge on the benzylic carbon atom in the transition state (1) can be deduced from the experimentally determinable Hammett ϱ values. Alkyl radicals R˙ are accordingly seen to develop nucleophilic properties during addition to olefins.
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Halogenonitrosylmolybdates—Simple, Monomeric MoII Complexes
Authors: Sarkar Sabyasachi , Müller Achim
Published: December 2003

The first mononuclear coordination compounds of MoII with simple ligands have the formulas (1) to (4). The diamagnetic complexes, which are stable at room temperature, can be used for the synthesis of further MoII compounds.
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Acceptor Function of η2‐Bonded CS2 Ligands
Authors: Herberhold Max , Süss‐Fink Margot
Published: December 2003

Withdrawal of charge from a central metal is accomplished better by η2‐bonded CS2 than by CO. This follows from the IR and 1H‐NMR spectra of complexes of type (1) (L = CO or PMe3), (2), and (3) (ar = hexamethylbenzene or mesitylene).
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Isocyanide Synthesis with Diphosgene
Authors: Skorna Giselher , Ugi Ivar
Published: December 2003

An alternative dehydrating agent to the dangerous compound phosgene is urgently required for the isocyanide synthesis. Diphosgene is easy to handle and, moreover, leads to higher yields.
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Synthetic and Mechanistic Aspects of Inorganic Insertion Reactions. Insertion of Carbon Monoxide
Authors: Calderazzo Fausto
Published: December 2003

The synthetic potential and the mechanistic aspects of inorganic insertion reactions of carbon monoxide, especially into metal‐carbon σ‐bonds, are considered. Reactions of this type are encountered among most 3d, 4d, and 5d elements. In one case it has been demonstrated that the CO insertion proceeds by alkyl migration; this is likely to be a general feature of all such reactions. If an alkyl migration takes place, then insertion of CO into the MC bond is governed kinetically by the cleavage of that bond. CO abstraction from RCOM bonds most commonly proceeds by rate‐determining vacation of a coordination position. Both CO insertion and abstraction are usually highly stereospecific.
Preparation of Cyclohexasilane, Si6H12
Authors: Hengge Edwin , Kovar Dieter
Published: December 2003

The silicon analog of cyclohexane has now been prepared from the dodecaphenyl derivative. Si6H12 probably exists in the chair form.
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Synthesis of Dinuclear Complexes Containing PCl2 and PF2 Bridges
Authors: Malisch Wolfgang , Panster Peter
Published: December 2003

Stable dinuclear complexes having the partial structure M‐‐‐PCl2‐‐‐M′ (M,M′Cr, W) have now been synthesized. They can be transformed into the corresponding fluorine derivatives by treatment with AgBF4.
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Difluorooxobromine(v) Ion, BrOF
Authors: Adelhelm Manfred , Jacob Eberhard
Published: December 2003

BrO2F and PtF6 surprisingly afford the salt BrOFPtF. So far this appears to be the only case in which oxygen is partially eliminated from an oxide fluoride by PtF6.
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The Chlorofluorocarbon/Ozone Theory—A Scientific Status Report
Authors: Jesson J. Peter
Published: December 2003

In 1974 Professors Rowland and Molina of the University of California at Irvine developed a theory concerning the possible adverse impact of chlorofluorocarbons on the earth's ozone shield. These compounds are the working fluids responsible for the safety and efficiency of almost all air‐conditioning and refrigeration equipment and are used as propellants in many types of aerosol products.—The present article is divided into five sections. The first is an historical perspective of the scientific situation up to the end of 1974. The second section examines the various findings and observations on which the theory is founded and outlines new knowledge gained in this sector since early 1975. The third section is devoted to the possible consequences of ozone depletion while the fourth and fifth sections consider the question of the risk taken in delaying a decision to stop production of certain halocarbons.
Carbodiimides as Source of Isocyanide and Carbonyl Ligands
Authors: Fehlhammer Wolf Peter , Mayr Andreas , Ritter Michael
Published: December 2003

Coordination of a heterocumulene to a basic metallic center modifies the electronic properties of the former species. Thus, reaction of carbodiimides and metal carbonyl anions at −78°C affords (after treatment with phosgene) isocyanide complexes such as (1) and (after protonation) diaminocarbene complexes such as (2).
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Thioheteroanions—Unusual Metal‐Ligand Interaction and Reactions
Authors: Müller Achim , Sarkar Sabyasachi
Published: December 2003

The first reaction products of “heteroanions” such as in (1) could now be isolated. An example is the brownish‐red salt (2) which is one of the few pentacoordinate Co compounds.
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Flexible Drug Molecules and Dynamic Receptors
Authors: Williams R. J. P.
Published: December 2003

When a small flexible drug molecule binds to its likewise mobile receptor (protein, membrane etc.) the shape and function of both can change. The study of the nature and extent of these changes by several independent methods gives an insight into the mode of action of drugs. The static lock and key model will most probably have to be revised or be replaced by the nebulous concept of dynamic states.
Quantitative Trace Analysis of Metals by Field Desorption Mass Spectrometry
Authors: Lehmann Wolf Dieter , Schulten Hans‐Rolf
Published: December 2003

The quantitative determination of 6Li and 7Li in Rhine water and determination of the isotopic distribution in some commercial Li salts have been performed by FD mass spectrometry in combination with a multi‐channel analyzer. Surprisingly, the isotopic distribution in the Li salts deviates from the mean natural abundance. In contrast, the natural distribution is found in Rhine water. Using 6Li‐enriched LiF as standard, 6Li and 7Li can be determined quantitatively by the method of isotopic dilution (total error 5%).
Chemical Oscillations
Authors: Franck Ulrich F.
Published: December 2003

Under constant external conditions, chemical reactions may also proceed in a rhythmic manner. The kinetic mechanisms responsible for such oscillations prove to be unexpectedly complicated. It can nevertheless be demonstrated that chemical periodicity is caused by certain kinds of coupling between simultaneous reactions or transport processes. A general survey of the chemistry and phenomenology of the principal chemical oscillations is followed by a discussion of the situations leading to periodic reactions on the basis of the multivariable kinetics of feedback systems. Autocatalysis and autoinhibition play an important role, as also do kinetic instability and spatial propagation.
Quaternary Ammonium Salts as Catalysts of Nucleophilic Substitution Reactions in a Solid‐Liquid Two‐Phase System
Authors: Jończyk Andrzej , Ludwikow Maria , Ma̧kosza Mieczyslaw
Published: December 2003

Solid inorganic salts react with dissolved organic compounds if a lipophilic tetraalkyl‐ammonium salt is added as catalyst, e.g. Aliquat 336® (technical grade methyl‐trioctylammonium chloride). This catalyst is less expensive than crown ethers.
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Asymmetric Synthesis of α‐Alkyl‐α‐aminocarboxylic Acids by Alkylation of 1‐chiral‐Substituted 2‐Imidazolin‐5‐ones
Authors: Schöllkopf Ulrich , Hausberg Hans Heinrich , Hoppe Inga , Segal Marcos , Reiter Udo
Published: December 2003

Over 95% asymmetric induction is achieved, given favorable substituent combinations, in the key step of a new synthesis of α‐alkyl α‐amino acids (1), X=H. Chemical yields are good, and the chiral auxiliary agent can be recovered.
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Tetraphenylphosphonium Tetrakis(difluorooxosulfimidato)borate
Authors: Eisenbarth Rainer , Sundermeyer Wolfgang
Published: December 2003

Only NSOF2 ligands are present in the anion of compound (3). Tetracoordination of the boron was deduced from the 11B‐NMR spectrum.
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Quantitative Mass Spectrometry in Biochemistry and Medicine
Authors: Lehmann W. D. , Schulten H.‐R.
Published: December 2003

The current state of quantitative analysis with the mass spectrometer in biochemistry and medicine is reviewed. The basic principles of mass spectrometry, the latter's combination with chromatography, the development of sensitive, exact, and in particular specific mass‐spectrometric methods of detection, and the principle of dilution with stable isotopes are illustrated by examples. The most important fields of application are: the pharmacokinetics of drugs and active metabolites, investigation of metabolic pathways, supporting of medical diagnoses and enhancement of their specificity, and finally checking the quality of simpler quantitative processes in clinical chemistry.
Synthesis and Biological Properties of Prostaglandin Endoperoxides, Thromboxanes and Prostacyclins
Authors: Nicolaou K. C. , Gasic G. P. , Barnette W. E.
Published: December 2003

Prostaglandins continue to be a major and fast‐developing area of research in the chemical and biological sciences. Increasing evidence has recently prompted some researchers to suggest that the important physiological actions of these hormones are exerted by their unstable arachidonic acid pathway intermediates, the endoperoxides, thromboxanes, and prostacyclin. The importance of these substances in physiology and medicine and the challenge they pose to synthetic chemistry place them in the forefront of chemical and biochemical investigation. Current biological research has greatly benefited by synthetic advances which have made available large quantities of some of these naturally occurring intermediates and several analogs with increased stabilities. Following a brief review of the primary prostaglandins, the present article describes recent biosynthetic developments, partial and total syntheses of prostaglandin endoperoxide analogs, thromboxane B2, and prostacyclins, and the biological properties of these molecules.
Extremely High Electronegativities
Authors: Lentz Dieter , Seppelt Konrad
Published: December 2003

Electronegativities exceeding that of a fluorine atom are found for the groups OSeFs and OTeF5. This was deduced from attempted direct syntheses of I(OTeF5)5 and from the 19F‐NMR spectra of mixed‐substituted compounds FxI(OSeF5)5−x and FxI(OTeF5)5−x.
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Xenon Tetrakis(pentafluoroorthotellurate), Xe(OTeF5)4
Authors: Lentz Dieter , Seppelt Konrad
Published: December 2003

The chemistry of tetravalent xenon has been extended to include Xe(OTeF5)4. Its synthesis was prompted by the idea of replacing the fluorine of XeF4 by the apparently more electronegative OTeF5 group.
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What Do We Know about the Metal‐Metal Bond?
Authors: Vahrenkamp Heinrich
Published: December 2003

Almost all main group and subgroup metals are able to form metal‐metal bonds. The bond order ranges from weak interaction to a quadruple bond, and the degree of aggregation from a dinuclear entity to a three‐dimensional network. In spite of numerous physicochemical studies, not all aspects of the metal‐metal bond are understood. The ability of metal‐metal linked polynuclear complexes to serve as a reservoir for missing or excess electrons enables them to react both with nucleophilic or reducing reagents and with electrophilic or oxidizing reagents. The intermediate position occupied by clusters between simple complexes and the bulk metal is of theoretical and practical significance.
The Distribution of Charge in Complex Compounds
Authors: Chatt Joseph , Leigh G. Jeffery
Published: December 2003

The charges on metal atoms and ligands in complex compounds of transition metals may be calculated theoretically or measured empirically, but there is no reliable method of doing either. This review is concerned mainly with two experimental methods, dipole moment measurement and X‐ray photoelectron spectroscopy, applied to tertiary phosphate and such complexes of the heavier transition metals. It is concluded that the charge is rarely greater than ±0.3e and that some so‐called neutral or positive ligands, e.g. N2 or NO+, may carry more negative charge in a complex than formally anionic ligands such as H−. Small ligands of high formal charge, e.g. O2−, NR2−, and N3−, appear to carry no more negative charge than Cl−, but monoanionic ligands vary greatly in their capacity to contribute to the dipole moments. The ligands NO, CO, PF3, CH, and H− are all nearly neutral to slightly negative, whereas pyridines, tertiary phosphanes, etc. are the most strongly positively charged.
Hemoglobin—An Inspiration for Research In Coordination Chemistry
Authors: Buchler Johann Walter
Published: December 2003

Hemoglobin transports oxygen in the blood and is responsible for its red color. Being one of the most closely studied proteins, it is entitled an “honorary enzyme”. This admirable natural substance invites chemists to copy it, imitate it, and vary or modify it. The first means a total synthesis of the original molecule, but such reproduction does not increase our knowledge of its function. In the case of imitation, the biochemical effect of the “original” (i.e. hemoglobin) is achieved in full or in part with simpler molecules of similar structure, i.e. with models. Research is here directed at the function of hemoglobin. In the case of variation or modification the original molecule is changed to various extents, which reveals the factors underlying its action. In all three cases—reproduction, imitation, and modification—hemoglobin serves as an inspiration for research. The aim of the present review is to summarize recent investigations inspired by hemoglobin in the field of coordination chemistry. A brief outline of the coordination chemistry of the porphin system serves as an introduction.