bluuebunny/crossref_metadata_2025 huggingface dataset:
Luciferins, Bioluminescent Substances
Authors: Goto T. , Kishi Y.
Published: December 2003

The bioluminescence of the American firefly Photinus is due to the reaction of 2‐(6‐hydroxybenzothiazol‐2‐yl)‐Δ2‐1,3‐thiazoline‐4‐carboxylic acid (“firefly luciferin”) with the enzyme luciferase in the presence of ATP and magnesium ion. In the crustacean Cypridina, on the other hand, the bioluminescence is due to the reaction of a luciferase with 8‐(3‐guanidinopropyl)‐6‐indol‐3‐yl‐2‐(1‐methylpropyl)‐3,7‐dihydroimidazo[1,2‐a]‐pyrazin‐3‐one (“Cypridina luciferin”). The luciferin in Latia is 1,3,3‐trimethyl‐2‐(4‐formyloxy‐3‐methyl‐3‐butenyl)‐1‐cyclohexene and that in Renilla is a tryptamine derivative that has not yet been accurately identified; the luciferins of other luminescent organisms are not yet known. A review is given of the investigations which have been carried out on the above luciferins and the course of the luciferin‐luciferase reaction is examined. Numerous spectral data obtained during the examination of these compounds are included in the text.
Dodecacarbonyltriruthenium
Authors: Bruce M. I. , Stone F. G. A.
Published: December 2003

Since the pioneering work of Mond and his coworkers the metal carbonyls and their derivatives have been under active study, and, as in other areas of inorganic chemistry, research activity has greatly increased in the last twenty years. Whereas hitherto our knowledge of the carbonyls of the heavier transition metals has been seriously hampered by a lack of good methods of synthesis, new preparative methods have recently been developed for Ru3(CO)12, and many new ruthenium carbonyl complexes are being discovered as its chemistry is explored.
The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds
Authors: Bartlett Neil
Published: December 2003

Some of the transition metal hexafluorides demonstrate an astonishing oxidizing power. In particular may be mentioned PtF6, which is capable of oxidizing molecular oxygen or xenon, a process requiring an electron affinity, E(PtF6), > −156 kcal·mole−1. From a comparative study of all of the hexafluorides of the third transition series the electron affinity is seen to increase regularly in the sequence WF6 < ReF6 < OsF6 < IrF6 < PtF6. The increase in E with unit increase in atomic number of M appears to be ≈ −20 kcal·mole−1. On the other hand the ability of the hexafluorides to accept F− decreases along this series. This effect enables IrF6 to be more effective than PtF6 in the generation of nitrogen oxide trifluoride, ONF3, by the oxidative fluorination of nitrosyl fluoride, ONF. Both PtF6 and IrF6 interact spontaneously with ONF or O2NF to generate fluorine, at or below room temperature. The decrease in F− ‐acceptor ability along the series, which stands in sharp contrast to the increase in electron affinity, suggests that ligand crowding increases sharply across the series from WF6 to PtF6. This accords with the observed decrease in molecular volume along the series, both in the hexafluorides and in the MF6− salts. It is clear from this comparison that the species IrF6 and PtF6 are close to a minimum volume for this series. The oxide pentafluorides ReOF5 and OsOF5 are similar in oxidizing ability to their respective hexafluorides but are poorer F− acceptors. Evidently the ligand crowding in MOF5 molecules is greater than in MF6.
Cyclobutenediylium Dyes
Authors: Sprenger H.‐E. , Ziegenbein W.
Published: December 2003

In agreement with the aromaticity and electrophilic behavior of squaric acid, a cyclobutenediyliumtetroxide ion is formulated as a limiting form of the squarate dianion. These views are confirmed by the structure of a series of new compounds that are readily obtainable from squaric acid or its derivatives, and most of which are deeply colored. The compounds contain the cyclobutenediyliumdioxide grouping as the chromophore, and form a new class of dyes, for which the name cyclobutenediylium dyes is proposed.
Small Antiaromatic Rings
Authors: Breslow R.
Published: December 2003

According to quantum mechanical calculations, systems with 4n π electrons ought to have anti‐aromatic character, i.e. be destabilized by resonance. This prediction is examined for the case of cyclopropenyl anion, the simplest system having 4n π electrons (n = 1). Isolation of compounds containing the cyclopropenyl anion has not, as yet, been achieved; however, kinetic measurements indicate the existence of the ion and confirm the unusual properties predicted.
Synthesis of Cyclopropyl Ethers and Cyclopropanols by Carbene Transfer – Acetolysis of Cyclopropyl p‐Toluenesulfonates
Authors: Schöllkopf U.
Published: December 2003

The reaction of chloromethyl phenyl ether with butyllithium in olefins yields phenoxy‐cyclopropanes. 1‐Chloro‐1‐phenoxycyclopropanes can be prepared in a similar manner, though the yields are poor. Alkoxycyclopropanes are formed when dichloromethyl alkyl ethers are treated with methyllithium/lithium iodide in the presence of olefins. Cyclopropanols can be obtained in good yields by reaction of (β‐chloroethoxy)cyclopropanes either with butyl‐ or ethyllithium or with bases. – As was shown by acetolysis experiments with cyclopropyl p‐toluenesulfonates having a known steric configuration, the rearrangement of a cyclopropyl derivative into an allyl cation proceeds in accordance with the Woodward‐Hoffmann‐DePuy rule. The solvolysis of exo‐bicyclo[n.1.0]alkyl p‐toluene‐sulfonates is assumed to proceed via “semi‐open” intermediates, which are somewhere between an allyl cation and a cyclopropyl cation.
Recent Developments in the Adhesives Field
Authors: Matting A. , Brockmann W.
Published: December 2003

The applications of adhesives have been greatly extended by the use of synthetic organic high polymers. It is possible nowadays to bond, not only wood, leather, and paper, but also glass, high‐strength plastics, and metals with adhesives of this type. They give satisfactory adhesion, flexibility, and mechanical properties even at high temperatures. A particularly important advance was the introduction of chemically or mechanically blocked polymer systems, which can reduce the cost of curing equipment when used as adhesives.
Nucleophilic Reactions of Metal Carbonyl Anions with Fluorocarbons
Authors: Bruce M. I. , Stone F. G. A.
Published: December 2003

This article describes the formation of carbon‐metal bonds by reacting carbonylmetalate ions with fluorocarbons. Complex formation depends on the nucleophilic behavior of the anions, and the susceptibility of fluorocarbons to this form of attack.
Trends in Radiation Polymerization
Authors: Potter R. C. , Schneider Christel , Ryska M. , Hummel D. O.
Published: December 2003

Previously it was generally assumed that high energy radiation could only initiate radical polymerization in solutions of monomers. However, examples of radiation‐induced polymerization have recently become known that proceed via an ionic mechanism. Thus, solutions of a monomer can be polymerized ionically, preferably in the presence of a solid, at low temperatures. Suprisingly, this may also be accomplished with ultra‐pure, mainly anhydrous systems, even at room temperature. The nature of the ions has not yet been fully elucidated.
Kinetic Studies on Substitution Reactions of Carbonylmetal Complexes
Authors: Werner H.
Published: December 2003

Kinetic studies of substitution reactions of carbonylmetals and of carbonylmetal derivatives in which other ligands (n or π donors) besides CO are bound to the metal atom have recently attracted great interest, and the results of these investigations throw a new light on theoretical and preparative problems. The substitution mechanism is determined mainly by steric and electronic factors.
The Catalytic Activity of Transition Metal Compounds in the Liquid‐Phase Oxidation of Hydrocarbons
Authors: Emanuel N. M. , Maizus Z. K. , Skibida I. P.
Published: December 2003

The way in which dissolved transition metal compounds affect the liquid‐phase oxidation of hydrocarbons is demonstrated for compounds of cobalt, copper, and manganese. Kinetic investigations on model systems and comparisons with the non‐catalyzed reaction show that the catalysts participate in all the oxidation steps.
Crystal Structure Analysis by Neutron Diffraction I
Authors: Will Georg
Published: December 2003

Neutron diffraction is a valuable complement to X‐ray diffraction methods for the determination of crystal structures. A description of the principles of the method is followed by specific examples of the additional information obtained from neutron diffraction experiments: in the structural analysis of benzene, oxalic acid dihydrate, vitamin B12, ferrites, metal cyanides and carbides; and in studies of hydrogen bonding, ferroelectric effects, and thermal vibrations in crystals. Anomalous dispersion in neutron diffraction is also discussed.
Preparation of Enamino Dinitriles and Pyridines by Reduction of Geminal Dinitriles with LiAIH4
Authors: Sieveking H. U. , Lüttke W.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196906171
Thiiranium Ions as Reaction Intermediates
Authors: Mueller Wolfgang H.
Published: December 2003

The addition of sulfenvl chlorides or sulfur dichloride to unsaturated compounds proceeds via thiiranium ions. The present article reviews the electronic and steric factors influencing the nature of these ions and their effects on subsequent ring opening and product formation. For the purpose of this discussion results primarily from electrophilic ring opening have been chosen to illustrate these factors. Solvent and temperature effects have been disregarded.
Mechanisms and Stereochemistry of Heterolytic Fragmentation
Authors: Grob C. A.
Published: December 2003

Heterolytic fragmentation can proceed by several mechanisms. A study of the solvolysis of γ‐aminoalcohol derivatives NCCCX, where X equals halogen or OSO2R, shows that fragmentation may occur by a one‐step mechanism or by several multi‐step mechanisms depending on structural, electronic, and steric factors. The one‐step synchronous mechanism has rigorous stereoelectronic requirements. It is associated with an increased reaction rate as evidenced by the “frangomeric” effect. Ketoxime derivatives RR′CNX may undergo Beckmann fragmentation by the synchronous mechanism or by prior rearrangement depending on their α‐substituents. Fragmentation is frequently accompanied by conventional substitution, elimination, and rearrangement reactions. Under such circumstances knowledge of all possible mechanisms of a given substrate is essential to bring about a desired transformation.
The Ene Reaction
Authors: Hoffmann H. M. R.
Published: December 2003

The ene reaction is defined as the indirect substituting addition of a compound with a double bond (enophile) to an olefin with an allylic hydrogen (ene). For a long time the reaction has been neglected and has remained overshadowed by the related Diels‐Alder addition. It is shown that the ene reaction possesses wide scope and applicability ranging from industrial to biosynthetic processes. Preparative aspects are summarized and current views on the mechanism are discussed.
Sorption Promotors in Biopharmaceutics
Authors: Ritschel W. A.
Published: December 2003

The absorption of drugs depends on the physico‐chemical properties of the constituent substances. Drugs that are absorbed only with difficulty or only slowly, or even not at all, can be made to penetrate into the skin and the mucous membrane (penetration) or to pass through them (permeation) with the aid of “sorption promotors”. The search for substances of this type and the elucidation of their principles of action form part of the field of biopharmaceutics.
Transfer Ribonucleic Acids
Authors: Zachau H. G.
Published: December 2003

Transfer ribonucleic acids (tRNAs)

Abbreviations used according to IUPAC‐IUB convention: tRNA = transfer ribonucleic acid; tRNAyeast = mixture of tRNAs from yeast; tRNAPhe = phenylalanine specific tRNA; Phe‐tRNA = tRNA esterified (“charged”) with Phe; mRNA = messenger RNA; DNA = deoxyribonucleic acid; U = uridine; A = adenosine; C = cytidine; G = guanosine; pA = 5′‐adenylic acid; Ap or A‐ = 3′‐adenylic acid; m2′G = 2′‐O‐methyl guanosine; m7G = 7‐methyl guanosine; mG = N(2)‐dimethyl guanosine; other methylated nucleosides are abbreviated analogously; abbreviations of other odd nucleosides are given with Fig. 2; p or – signifies phosphate; RNase = ribonuclease; DEAE = diethylaminoethyl; fMet = N‐formayl methionine.

occur in all living organisms. In biological protein synthesis they accept activated amino acids which are then transferred to growing peptide chains. With molecular weights lying between 25000 and 30000, tRNAs are easily within the reach of today's physical, chemical, and biochemical methods. The primary structures of several tRNAs as well as some relationships between structure and function have been elucidated. Three‐dimensional structure, specificity, and mechanism of action are the subjects of present research efforts.
Organic Dyes in Laser Technology
Authors: Schäfer F. P.
Published: December 2003

Laser technology has been developed to a very high level since 1960. Significant advances have been made possible only by the use of organic dyes as optical shutters for the production of giant pulses. Ultrashort pulses in the picosecond range were first produced in 1966; their measurement was greatly facilitated by the use of organic dyes. Probably the most important recent advance in the laser field is the dye laser, which was first described in 1966, and in which the active medium is a solution of an organic dye.
Chlorosulfenylated Carbonic Acid Derivatives
Authors: Zumach G. , Kühle E.
Published: December 2003

The present article deals first with the synthesis of chlorocarbonylsulfenyl chloride and its imino analogs. The chemical behavior of these bifunctional compounds is illustrated for selected examples. Special attention is given to the syntheses of five‐membered heterocycles containing sulfur, oxygen, and/or nitrogen.
Structure of the Solvation Shell of Dissolved Particles
Authors: Hertz H. G.
Published: December 2003

The first part of the article deals with the structure of the solvation shell of simple ions, particularly those with the inert gas structure, in aqueous and non‐aqueous solution. It is nowadays possible in favorable cases, to determine the solvation number or the coordination number in the first sphere. The solvation shells appear to be “more liquid” than was formerly believed. The hydration of neutral inert particles in aqueous solution is discussed in the second part. Caution is advised in the postulation of particular structural arrangements in the solution.
Magnetic Resonance of Paramagnetic Complexes
Authors: Keller Heimo J. , Schwarzhans Karl E.
Published: December 2003

The line width of the ESR and NMR signals of paramagnetic transition metal complexes is determined mainly by the electron spin‐lattice relaxation time τe. Values of τe greater than 10−9 lead to ESR spectra that are readily resolved, while values smaller than 10−11 give NMR spectra having small line widths. Since fast relaxation processes are effective in nearly all transition metal complexes with several unpaired electrons and in all complexes having an orbitally degenerate ground state, the NMR method has a wider scope. The sign and magnitude of the electron‐nucleus coupling can be determined with great sensitivity from the NMR spectra, whereas only the magnitude of this interaction can be determined from the ESR spectra. Free spin densities can be found very accurately from the NMR shifts, and the method can therefore be advantageously applied to kinetic measurements, e.g. on short‐lived contact complexes.
Structure and Immunogenicity of Synthetic Antigens
Authors: Rüde Erwin
Published: December 2003

Synthetic antigens are often valuable tools in immunological research. They are usually linear or branched polypeptides, prepared by polymerization of N‐carboxy‐α‐amino acid anhydrides or by polymerization of defined oligopeptides. Owing to their great variability, these simple antigens allow a systematic study of the chemical and physical parameters involved in immunogenicity, i.e. the ability of a substance to initiate an immune response in higher animals. The study of very simple synthetic antigens made possible the first detailed analysis of genetic factors controlling the immunogenicity of a substance. The results have led to a better understanding of many immunological phenomena, and have helped to explain the complex processes initiated by antigens that lead to a specific immune response.
Problems and Possibilities of the Free‐Radical Addition of Thiols to Unsaturated Compounds
Authors: Griesbaum Karl
Published: December 2003

In view of the growing importance of photochemically initiated reactions in industry, the use of free‐radical additions of thiols to unsaturated compounds also seems promising. The present article is intended to demonstrate the possibilities and limitations of reactions of this type in organic synthesis.
Some Aspects of the Active Transport of Amino Acids
Authors: Ring Klaus
Published: December 2003

Active transport is the transport of substances against their activity gradients. In the cell, metabolic processes provide the energy for active transport through the membrane, during which amino acids are coupled with a carrier system located in the membrane. Some of the proteins involved in the translocation of amino acids have now been isolated from E. coli.
Development of and Problems in the Chemistry of Mercury‐Nitrogen Compounds
Authors: Breitinger Dietrich , Brodersen Klaus
Published: December 2003

There have been few recent additions to the group of mercury‐nitrogen compounds. Current developments in this field are mainly concerned with the elucidation of the structures of these compounds. The structures of coordination‐polymeric Hg–N compounds may be considered from the point of view of their relationship with silicates. The bond parameters of the Hg–N grouping are compared with the parameters of bonds between mercury and elements adjacent to nitrogen in the periodic system.
Phototropic Glass
Authors: Gliemeroth Georg , Mader Karl‐Heinz
Published: December 2003

Phototropic glass darkens on exposure to light and returns to its original state in the absence of light. The most extensively investigated of these glasses contain grains of silver halide having sizes > 50 Å. A discussion of theoretical principles is followed by a review of the very broad scope of the phenomenon.
Present‐Day Communication in Chemistry – Problems and Posibilities
Authors: Kresze Günter
Published: December 2003

This article deals with the problems and possibilities in the present‐day communication of chemical results and opinions. Personal communications as well as primary and secondary literature have to be supplemented in the future by documentation and information services which use modern electronic data processing equipment.
TOSAR – A Topological Method for the Representation of Synthetic and Analytical Relations of Concepts
Authors: Fugmann Robert , Nickelsen Herbert , Nickelsen Ingeborg , Winter Jakob H.
Published: December 2003

In mechanized systems used for searching in literature stores there is a steadily growing necessity not only to be able to formulate concepts as a search condition but also the characteristic connections under which these concepts appear in the inquiry. In this way the precision of the mechanized literature search is considerably increased. TOSAR has been developed in order to improve computerized literature searching in this respect.
CCBF – A System for the Computer Processing of Chemical and Biological Facts
Authors: Ohnacker Gerhard , Kalbfleisch Werner
Published: December 2003

A computer‐based system for the documentation of company research results in drug research is described. The system stores the numerous results of standardized biological tests and processes chemical formulas by topological techniques. The stored material is processed to provide computer‐printed card indexes and lists on chemical and/or biological topics. The programs enable searches to be made for any desired substructure and for pharmacophoric groups, thus providing highly effective assistance in the search for structure‐activity relationships.
Regulation of Glutamine Synthetase by Enzyme Catalyzed Structural Modification
Authors: Shapiro Bennett M.
Published: December 2003

A highly sophisticated mechanism for the regulation of glutamine metabolism in Escherichia coli involves the modification of the enzyme glutamine synthetase by the covalent attachment and release of adenylyl residues. Separate enzymes catalyze the adenylylation and deadenylylation reactions, and these enzymes are reciprocally controlled by the state of nitrogen nutrition of the cell. The resultant structural alterations in glutamine synthetase enable it to change its catalytic potential greatly in response to varying cellular demands, in order to maintain nitrogen homeostasis.
Recent Results in Carbanion Chemistry
Authors: Schöllkopf Ulrich
Published: December 2003

The Wittig rearrangement of ethers metalated in the alpha position with alkali metals is a 1,2‐shift to an atom with a lone pair of electrons. The alkyl shift proceeds with racemization (and partial retention) at the migrating carbon atom. The experimental observations suggest a cleavage‐recombination mechanism involving a radical pair, as must also be assumed for the ylide rearrangements. In the allyl migration, the double bond is displaced within the migrating residue (allyl inversion). This is readily explained by a one‐step S′ mechanism, the transition state of which is allowed on symmetry grounds. In the case of benzyl 2‐butynyl ether metalated on the butynyl residue, the ortho isomerization (corresponding to the Sommelet rearrangement) predominates. – α‐Metalated alkyl isocyanides can react with carbonyl compounds to form olefins and metal cyanate (carbonyl olefination). Isocyanoacetic esters occupy a special place; they react with aldehydes and ketones to form β‐substituted α‐formylaminoacrylates (formylaminoalkoxycarbonylmethylenation), which can enter into a wide range of reactions. β‐Hydroxyalkyl isocyanides or 2‐oxazolines can be isolated as intermediates in the carbonyl olefination. α‐Metalated isocyanides react with acylating agents to form β‐ketoalkyl isocyanides, which cyclize to give oxazoles.
Chemical Lasers
Authors: Kompa K. L.
Published: December 2003

Chemical lasers are based on the new principle of obtaining energy in the form of coherent radiation from chemical reactions. Since the discovery of the first laser of this type in 1965, laser emission has been investigated in a considerable number of fast gasphase reactions. In physical chemistry such lasers provide a diagnostic tool for the detailed investigation of the energy distribution in elementary reactions. The barrier to technological use has probably also been overcome by the recent continuous operation of a chemical hydrogen fluoride laser. An attempt is made in the present article to trace the development of this still youthful field and to demonstrate the possibilities and limitations of the generation of energy with chemical lasers.
The Ionization (Heterolysis) of Covalent Compounds as a Coordination‐Chemical Phenomenon
Authors: Gutmann Viktor
Published: December 2003

The ionization of a covalent compound into a cation and an anion is a coordination‐chemical phenomenon. The ions are formed with coordination either by nucleophilic attack of an electron pair donor or by electrophilic attack of an electron pair acceptor. The dielectrically controlled component of the ionization affects only the degree to which it occurs. It is shown that the ionization generally increases with increasing donor strength of the donor or with increasing acceptor strength of the acceptor. For a given M, the ease of ionization of the MX bond increases in the order X = fluoride < chloride < bromide < iodide. These general aspects are discussed with the aid of examples.
Modern Industrial Microbiological Fermentations and Their Effects on Technical Developments
Authors: Rehm H.‐J.
Published: December 2003

Owing to the development of many new processes and techniques, the production of primary and secondary metabolites with the aid of microorganisms has not only expanded greatly, but has also been simplified in many details, and has therefore become more widely feasible on the industrial scale. The present article surveys the principal fermentation processes and the main types of equipment, which shows a trend toward continuous processes and increasing automation. Some recent developments observed e.g. in the cultivation of animal cells or the production of electrical energy, and particularly in the production of proteins by microorganisms, are also described.
NMR Spectroscopy of Paramagnetic Complexes
Authors: Schwarzhans Karl E.
Published: December 2003

Serviceable NMR spectra can, with a few exceptions[1,6], be recorded for paramagnetic complexes in solution. These spectra provide information about the structure of the complexes and the distribution of the unpaired electrons, and hence also about reactive centers in the molecule. The elucidation of intermolecular and intramolecular exchange phenomena, e.g. the determination of ligand exchange rate constants, the determination of rotation barriers, and the detection of contact complexes in solution, or even of occupation equilibria of the electrons, is possible in this way. It can be seen, therefore, that NMR studies on paramagnetic complexes can be a rich source of information.
Nuclear Energy Reserves and Long‐Term Energy Requirements
Authors: Zimen K. E.
Published: December 2003

In this article the world's potential energy reserves are summarized on the basis of available estimates, and the future energy consumption is estimated with the aid of a working hypothesis relating to the growth of the world's population (P) and the energy consumption per capita (γ). According to this estimate, the energy requirements in 30 years will be about seven times and in 80 years about fifty times as high as they are today, and all the concentrated energy sources will be exhausted in about 120 to 160 years. – The energy requirements in the steady state (Pγ = const.) could be of the order of 1013 MWh per year and could be met out of magmatic rocks (U,Th) and sea water (U,D). High priority should be given to research and development work on the construction, reliability, and safety of breeder and fusion reactors, the chemical treatment and final disposal of radioactive waste, the extraction of uranium, thorium, and deuterium from the “primitive” raw materials, the relevant problems relating to protection of the environment, and the worldwide control of the excess birthrate.
Some Aspects of Chemical Mutagenesis in Man and in Drosophila
Authors: Obe Günter , Sperling Karl , Belitz Hans J.
Published: December 2003

Since mutations produced by chemicals are, like spontaneous mutations, generally transmitted by recessive factors, i. e. as they are only expressed after several generations, depending on the circumstances, it is extremely difficult to trace the true cause of such mutations, which are almost always unfavorable. However, it is possible to study the mutagenic action of chemicals in test systems, e.g. in Drosophila in vivo or in human chromosomes in vitro. Alkylating agents which damage DNA indirectly have a particularly severe mutagenic action. The present progress report contains, among other things, a comprehensive list of substances that produce aberrations in human chromosomes.
Bis(trimethylsilyl)diimine: Preparation, Structure, and Reactivity
Authors: Wiberg Nils
Published: December 2003

The highly reactive compound bis(trimethylsilyl)diimine (BSD), which was first prepared by oxidation of lithium tris(trimethylsilyl)hydrazide, is light blue, sensitive to thermolysis and hydrolysis, and ignites spontaneously in air. On the basis of electron transfer, acid‐base, or free‐radical reactions, it acts in particular as a (preparatively useful) redox system and as an agent for the introduction of azo groups. Redox reactions lead by oxidation or reduction of the other reactant through two oxidation stages to hydrazine derivatives or molecular nitrogen, and in the case of electrochemical reduction, to BSD radical‐anions. Azo‐group transfers, on the other hand, yield new inorganic azo compounds with no change in the oxidation state of the diimine group.
Biological Membranes
Authors: Gross Werner
Published: December 2003

Membranes are essential components of living cells. They act as barriers and pumps, as enzyme supports, and also as a means of protection. Their chemical makeup from proteins, lipids, carbohydrates, ribonucleic acids, and water is well known, but there is as yet no generally accepted model for their structure. It is also by no means certain that all membranes have the same structural plan.
Synthesis and Reactions of Ketenimines
Authors: Krow Grant R.
Published: December 2003

Ketenimines R1R2CCNR3 were first reported in 1919, but the development of the chemistry of these compounds is of relatively recent origin. These heterocumulenes are becoming of increasing interest as a dehydrating agent for peptide syntheses, as a coreagent in dimethyl sulfoxide oxidations, and as a substrate in the synthesis of heterocycles by condensation with polar multiple bonds and dipolar systems. The cycloadditions are of special interest from the viewpoint of orbital symmetry considerations. Some unusual organometallic complexes of ketenimines have also been synthesized. Recently some triaryl ketenimines have been found to have insecticidal and miticidal activity. Polymeric ketenimines have been implicated as molecular precursors of life.
Approaches to Total Synthesis of Heterocyclic Steroidal Systems
Authors: Huisman H. O.
Published: December 2003

In heterocyclic steroids the carbon atoms of the steroid skeleton (positions I to 17) are replaced in part by hetero atoms. The term generally denotes compounds containing one or two nitrogen, oxygen, and/or sulfur atoms. The part of the molecule containing the hetero atom is either introduced as a preformed unit or is constructed by stepwise synthesis. The examples given in the present article contain the hetero atoms in ring A, ring B, between rings A and B, and/or between rings C and D.
Chemical Bonding in Solids
Authors: Hartmann Hermann
Published: December 2003

The most important of the current quantum‐mechanical models of solids can be divided into one‐electron (band) models and incomplete polyelectron theories. There are no complete polyelectron theories at present. However, the interatomic exchange forces become less important in lattices with high coordination numbers; a theory of metallic phases can therefore be developed, in principle, on the basis that the antisymmetrization is only local in atoms or groups of atoms.
The Present Position of Hemoglobin Research
Authors: Buse Gerhard
Published: December 2003

Up to the present time hemoglobin has enjoyed pride of place among the objects of study in molecular biology. Investigations on this molecule have culminated in the complete description of its atomic structure in various functional states and point the way for future research on other biopolymers. However, more than just a knowledge of the anatomy of this protein is required before we can make quantitative predictions about its function.
Non‐rigid Molecular Skeletons—Berry Pseudorotation and Turnstile Rotation
Authors: Gillespie Paul , Hoffman Peter , Klusacek Hans , Marquarding Dieter , Pfohl S. , Ramirez Fausto , Tsolis E. A. , Ugi Ivar
Published: December 2003

Molecules rearrange by regular and irregular processes. The former occur with preservation of bonds and coordination numbers while the latter involve rupture and reformation of bonds via states possessing different coordination numbers. For molecules with skeletons that carry n ligands both processes can be represented by permutation operators belonging to the symmetrical group Sn. These operators are obtained from the descriptors of the particular molecules in a simple manner; the conceivable reaction mechanisms correspond to the skeletal symmetry subclasses of Sn. Regular rearrangements—e.g. of phosphorane derivatives with a monocentric skeleton, including their analogs, or of ethane derivatives with a dicentric skeleton—all submit themselves to classification based upon skeletal non‐rigidity. Flexible molecular skeletons are representable by a collection of rigid skeletal models which can be interconverted by deformations of bond angles and/or some form of internal rotation. To accomplish mechanistic understanding of these regular processes, it is useful to represent the symmetries of the rigid skeletal models and the existent ligand equivalencies by subgroups of Sn and consider the dependence of the skeletal flexibility upon the given ligand set. This procedure is based on the ideas of Polya and Longuet‐Higgins. The former introduced separation of permutational molecular symmetry into skeletal symmetry and ligand set symmetry, which, combined with the total molecular symmetry concept developed by Longuet‐Higgins for the treatment of non‐rigid symmetric molecules, yield the foundation for the following classification of regular pentacoordinate rearrangements and related processes. It will be shown that with the given quantum chemical properties of the pentacoordinate phosphorus bond system, including participation of the P3d orbital set, not only the BPR‘2’ mechanism but also single and multiple TR[2] processes must be considered in the interpretation of the observed phenomena. Although some experimental observations can be interpreted by either of the two mechanisms, and certain other regular rearrangements can be explained only by invoking the TR mechanism, no regular processes are known, as yet, that can be explained solely by the BPR mechanism.
Active Transport of Na+ and K+ through Animal Cell Membranes
Authors: Schoner Wilhelm
Published: December 2003

The transport of Na+ out of the cell and K+ into the cell against a concentration gradient is catalyzed by a (Na+ + K+)‐activated ATPase. The way in which the cations pass through the cell membrane has not yet been elucidated. Studies on the ATP hydrolysis revealed a Na+‐dependent phosphorylation of the enzyme protein; the conformation of the enzyme also appears to change. The energy required for transport of the cations against their concentration gradients is probably provided by K+‐dependent hydrolysis of the enzyme‐bound phosphate. The enzyme can synthesize ATP from inorganic phosphate and ADP on reversal of the cation concentration gradient. By keeping the enzyme in a particular conformation, the cardiac glycoside ouabain specifically inhibits the Na+ pump.
Ternary Fission
Authors: Brandt Reinhard
Published: December 2003

In this review paper, ternary fission is defined as the break‐up of heavy nuclei into three fragments of approximately equal mass. This relatively new type of nuclear decay has been investigated intensively during the last decade. Muga has studied ternary fission induced by thermal neutrons in uranium. The results of his experiments are discussed in detail. Ternary fission can definitely be observed and studied in the interaction of heavy target elements with 39 MeV alpha particles, 20 GeV protons, and 300—400MeV argon ions. The ratio of binary‐to‐binary fission for uranium is approximately 10−4: 100 in the interaction of 39 MeV alpha particles, approximately 0.1:100 for 20 GeV protons, and 3:100 for 400MeV argon ions. A theoretical model for the interpretation of ternary fission, the “cascade model”, is described. The paper concludes with a discussion of the possible connection of ternary fission with the production and decay of still undiscovered super‐heavy elements (Z = 114).
The Electronic Properties of Diradicals
Authors: Salem Lionel , Rowland Colin
Published: December 2003

A review of the various possible definitions of diradicals leads the authors to describe these systems as having two odd electrons in degenerate or nearly‐degenerate molecular orbitals. A study of the wave‐function for the two odd electrons shows that its form depends entirely on whether the diradical is homo‐ or heterosymmetric. Energy schemes are given in these two cases, as well as in the intermediate “non‐symmetric” case. The extent of zwitterionic character in diradical states is also investigated. This is followed by a discussion of intersystem crossing between singlet and triplet diradical states via spin‐orbit coupling and other mechanisms. The electronic matrix elements for spin‐orbit coupling are calculated and evaluated numerically for various model cases. It is then possible to establish general rules for favorable (electronic) intersystem crossing. In 1,3 or 1,4 diradicals its efficiency is estimated to be comparable with that in aromatics. The role of the electron‐nuclear hyperfine interaction in mixing singlet and triplet states, particularly in CIDNP, is explained.

Finally the question of whether diradicals actually occur as secondary minima on potential energy surfaces is examined. Recent quantum‐mechanical calculations, in contradiction to some thermochemical and kinetic evidence, lead to flat singlet surfaces without significant minima.
Advances in Acoustical Holography
Authors: Preston K.
Published: December 2003

The most recent branch of holography, acoustical holography employing acoustical radiation, presents a variety of new and highly interesting possible applications: Thus objects can be imaged in a turbid liquid medium (marine research); the technique can be used for non‐destructive investigations of the internal structure of objects that are opaque to light (testing of materials) and is possibly also a potential tool for the three‐dimensional imaging of biological structures (biomedical diagnosis).
Genetic Aspects of Hemoglobin Synthesis
Authors: Schmidt Berthold
Published: December 2003

The blood pigment hemoglobin (Hb) occurs in red blood cells in a higher concentration than the other proteins which are present. It is therefore particularly suitable for the investigation of genetically induced changes in protein molecules. Unlike the monomeric myoglobin (Mb) of muscle, the blood pigment is tetrameric. Several types of subunits are known that can tetramerize to hemoglobins having different properties. The information for all hemoproteins probably originated from the same primary gene. Doublets of this primary gene have developed differently, and now code different protein species. It is possible to establish from the Hb molecule the possible consequences of a mutation to the conformation and function of a protein molecule.
The Study of Prehistoric Metallurgy
Authors: Hartmann Axel , Sangmeister Edward
Published: December 2003

The puzzle we have to solve is: How did prehistoric man live? Archeologists and scientists, chemists and prehistorians have now joined forces in applying much imagination and pains taking effort to the search for a solution. Some of the fruits of their cooperation are presented in this progress report.
Decomposition of Organometallic Complexes in the Mass Spectrometer
Authors: Müller Jörn
Published: December 2003

The reliable interpretation of mass spectra for the determination of molecular constitutions requires systematic studies on the fragmentation behavior of classes of compounds, since the large number of kinetic and energy parameters that determine the decomposition of excited polyatomic ions makes ab‐initio predictions of spectra almost impossible. In this progress report, a number of general rules for the decomposition of organometallic complexes upon electron impact are discussed; a classification into decomposition types is also presented, and is illustrated by selected examples.
Cooperative Conformational Changes in Globular Proteins
Authors: Pohl Fritz M.
Published: December 2003

In globular proteins, the complicated steric arrangement of the polypeptide chain is determined by several interdependent cooperative interactions. These macromolecules are capable of reacting to changes in the environmental conditions such as temperature and pressure or the concentration of a wide range of compounds by changing their conformation and hence their biological and chemical properties. They are thus suitable for regulation processes or information storage in solution with a wide range of time constants. Environmental effects of this kind can be followed and explained in part at the molecular level by investigation of the time‐dependent reversible unfolding of a number of proteins that can be described to a good approximation by a strongly cooperative “all‐or‐none” transition between two states.
Crystal Chemistry of Complex Carbides and Related Compounds
Authors: Nowotny Hans
Published: December 2003

Numerous metal carbides can be discussed in a rather uniform way by means of structural features, mainly characterized by the mode of linking of octahedral and occasionally trigonal prismatic [M6C] groups (M = transition element). From this point of view perovskite carbides (M3M′C, M′ = another transition or A‐group element) and derivatives, β‐Mn carbides (M3M′2C), κ‐carbides, carbides with V3AsC‐ and Cr2AlC type structures and derivatives, η‐carbides (M3M′3C) and carbides having the filled Mn5Si3 type structure will be treated. The high stability of these complex carbides is due to the strong bonding MC and additional bonding of MM′ atoms forming an ordered parent lattice. Besides the interstitial principle of filling of lattice holes (by isolated carbon atoms), substitution with A‐group elements may also take place. Thus in borocarbides extended structural elements occur.
New Reactions with Cyanic Esters
Authors: Grigat Ernst
Published: December 2003

The reactions of cyanic esters with acylating agents and the reactions of the resulting N‐acyliminocarbonic ester halides are surveyed, and syntheses of heterocycles with cyanic esters and their reaction products are then reported.
Growth Processes due to Reactions in Swellable Cellular Matrixes
Authors: Wagner Kuno , Dahm M.
Published: December 2003

In matrix reactions in swellable cellular matrixes, the solids formed are oriented in space and arranged in the form of cells in strong three‐dimensional growth processes. Open‐cell, flexible, elastic polyurethanes have a particularly good matrix action. The principle is of general validity, and can be realized with a wide variety of matrixes and reaction types. The dimensional changes, which are always symmetrical, are largely determined by the chemical constitution of the matrix, segment structure, degree of crosslinking, and solvation and hydration behavior. One‐component reactions having high rates give sigmoid growth curves and exhibit parallels with growth curves of plant cell walls containing cellulose.
Semiempirical Use of Chirality Functions for the Description of the Optical Activity of Methane Derivatives in the Transparent Region
Authors: Richter Wolf Jürgen , Richter Bernd , Ruch Ernst
Published: December 2003

The optical activity can provide detailed information about the configuration and conformation of methane derivatives if the chirality function is resolved, according to the theory of chirality functions[3] and the quantum mechanical theory of the optical activity of methane derivatives[4], into its components which are compared with experimental data. A first step in this direction is undertaken in the present article and it will be shown that the second approximation method for determining the conformationally independent contribution to the optical activity yields quantitatively good results. Description of the overall optical rotation by this component is expectedly poor where interactions between ligands, e. g. hydrogen bonding, tend to favor specific conformations. A quantitative understanding of such additional effects appears promising in conjunction with analyses of the kind described.
Structure and Function of Ferritin
Authors: Crichton Robert R.
Published: December 2003

Ferritin is the major iron storage protein of mammals and consists of up to 4500 atoms of ferric iron surrounded by a shell of protein subunits. The protein component, apoferritin, consists of 24 identical polypeptide chains each of molecular weight 18500. The function of ferritin is to store iron in a soluble form from which it can be readily mobilized. Recent results concerning the structure of the protein are reported, and progress in the elucidation of the mechanisms whereby iron is introduced into apoferritin and released from ferritin is reviewed.
Displacement Reactions of Phosphorus(V) Compounds and Their Pentacoordinate Intermediates
Authors: Gillespie Paul , Ramirez Fausto , Ugi Ivar , Marquarding Dieter
Published: December 2003

Reactions of phosphorus(v) compounds involving the mutual interconversion of tetra‐ and pentacoordinate species are discussed in a critical review emphasizing stereochemical implications of the reaction mechanism. This discussion includes the formation and decomposition of the stable oxyphosphoranes, the Michaelis‐Arbusov, Perkov, and Wittig reactions, interconversions of phosphines and their oxides, and the nucleophilic displacements on phosphonium compounds. Reactions of phosphate esters and related compounds receive particular attention. All chemical arguments are derived by considering the effect of factors determining the relative stabilities of phosphorane derivatives, their rates of formation, decomposition and rearrangement by bond deformation or rupture and recombination processes, considerations which are uniformly applied on the basis of concepts developed in a preceding communication[2]. It is shown that a comprehensive mechanistic interpretation of the foregoing reactions requires substantial addition to available conceptual foundations such that, in many cases, present concepts and mechanisms must be revised.
Toxicological Problems Relating to Changes in the Environment
Authors: Henschler D.
Published: December 2003

Assessment of the toxicological risk from foreign substances in the environment is based on the determination of action thresholds below which effects injurious to health no longer occur, even with life‐long intake. According to the latest theories it is likely that such thresholds exist even for “irreversible” (carcinogenic, mutagenic) effects. However, the difficulties besetting the determination of threshold values by experimental or epidemiological methods still appear to be virtually insuperable. The problems are both quantitative (excessive numbers of animals and observations required) and qualitative (poor predictability of effects owing to substantial differences in biological reactivity between species). Neither animal experiments nor experience with human subjects can guarantee total security from toxic effects. Legislative measures designed to restrict the introduction of chemical substances into the environment must therefore be based on compromise. Scientists must be consulted, but ultimately the decisions must be political, and politicians have to assume the responsibility for them.
Molecular Hysteresis and Its Cybernetic Significance
Authors: Neumann Eberhard
Published: December 2003

The general foundations for a thermodynamic analysis of hysteresis phenomena in solutions and suspensions of polyelectrolyte systems are presented using examples of molecular hysteresis in biopolymers and membranes. The fundamental cybernetic significance of metastable states and molecular hysteresis for a physical interpretation of phenomena of life such as memory recording and biological rhythms is discussed.
Very Low‐Pressure Pyrolysis (VLPP); A Versatile Kinetic Tool
Authors: Golden D. M. , Spokes G. N. , Benson S. W.
Published: December 2003

The theory and applications of the very low‐pressure pyrolysis technique to the study of the rates and mechanisms of unimolecular reactions, radical‐radical, and radical‐molecule bimolecular reactions, surface recombination of atoms, heterogeneous reactions, and vibrational energy transfer are reviewed.