bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Relationship of [(C6H5)4As]NdCl4·8H2O and NdCl3·6H2O: Transition from a Three‐Dimensional to a Layer Structure
Authors: Urland Werner , Schwanitz‐Schüller Ulrich 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1399. DOI:10.1002/anie.198313990
Nodal Nomenclature II—Specific Nomenclature for Parent Hydrides, Free Radicals, Ions, and Substituents
Authors: Lozac'h Noël , Goodson Alan L. 
Published: December 2003

AbstractNodal nomenclature is compared with classical organic nomenclature, and the procedure by which an organic compound is given a nodal name is described. Parent hydride–especially hydrocarbon–names are derived from the names of structure graphs and are modified to incorporate descriptions of heteroatoms, unsaturation, free valences, and ionic charges. It is also shown how the substitutive method, though not an integral part of the nodal system, may nevertheless be used as a way to simplify the structure graphs without impairing the logic of the nodal system. For this purpose, it is indicated how to use prefixes or suffixes generally formed according to IUPAC Rules. The rôle of substitution in organic nodal nomenclature is more restricted than in classical nomenclature because many classical substituents are treated as part of the parent hydrides. The concept of “characteristic group” is not used in nodal nomenclature for similar reasons, and the term “principal substituent” is preferred to “principal characteristic group”.
Synthesis of Anti‐Inflammatory α‐Arylalkanoic Acids by 1,2‐Aryl Shift. New Synthetic Methods (42)
Authors: Giordano Claudio , Castaldi Graziano , Uggeri Fulvio 
Published: December 2003

Abstractα‐Arylalkanoic acids have acquired importance as anti‐inflammatory agents and are now in great demand on the pharmaceutical front. Hence, the need has arisen for new and improved, economical synthetic procedures suitable for their preparation and manufacture on an industrial scale. For many years the synthetic approach to this class of compounds was restricted to the Willgerodt and Darzen reactions. More recently, several methods have been developed which are based on the 1,2‐aryl shift in acetals of α‐functionalized alkyl aryl ketones. This new approach starts from the oxythallation of alkyl aryl ketones first described by Taylor and McKillop in 1971. Asymmetric syntheses of some important arylakanoic acids have also been developed on this basis. The highly toxic thallium salts may be replaced, inter alia, by catalytically effective metal salts.
Microbial Asymmetric Catalysis—Enantioselective Reduction of Ketones [New Synthetic Methods (45)]
Authors: Sih Charles J. , Chen Ching‐Shih 
Published: December 2003

AbstractMicrobial asymmetric reduction of ketones is a method widely used for the preparation of chiral alcohols. The present progress report deals with the basic concepts that govern enantioselectivity of enzymes and intact cells. Strategies to control the stereochemical course of microbial reductions of carbonyl compounds and the relationship of substrate structure to enantioselectivity are considered.
Photochemistry of Alkyltransition‐Metal Complexes
Authors: Alt Helmut G. 
Published: December 2003

AbstractAlkyltransition‐metal complexes play an important role in catalytic processes (e.g. Ziegler‐Natta low‐pressure polymerization, hydroformylation, Fischer‐Tropsch synthesis), in the biochemistry of humans and animals (e.g. coenzyme B12), and in the classical theory of the chemical bond (e.g. multicenter bonding). The chemistry of alkyltransition‐metal complexes is 30 years old, but only with the '70s came the understanding necessary for the systematic synthesis of thermally stable representatives of this class of compounds by blocking preferred decomposition pathways—e.g. β‐hydrogen elimination—by the introduction of suitable ligands. In this article it is shown that thermally stable alkyltransition‐metal complexes can be dealkylated under mild conditions (even at 12 K) with the help of UV light, thus producing highly reactive intermediates which can be trapped and used preparatively. Some alkyl complexes which do not react thermally with unsaturated compounds, e.g. olefins, under the influence of UV light display high activity as polymerization catalysts.
DNA Methylation: Site‐Specific Methylations Cause Gene Inactivation
Authors: Doerfler Walter 
Published: December 2003

AbstractIn the molecular biology of eukaryotic organisms, the elucidation of mechanisms involved in the regulation of gene expression has assumed an important role. All cells of an organism carry the same genes, but differ in the patterns of genes they express. There is an increasing amount of evidence that cancer cells exhibit a pattern of gene expression which can be very different from that of normal cells. One of the molecular signals that has been recognized in the regulation of gene expression in eukaryotes is the modified nucleotide 5‐methylcytosine (5‐mC). Through experiments in well‐characterized eukaryotic systems, evidence has been adduced that the introduction of 5‐mC into highly specific sequences, particularly into the 5′ and promoter regions of a gene, can cause gene inactivation. Viral and other eukaryotic systems have helped in the recognition of this cause‐and‐effect relationship. Inactive genes are frequently hypermethylated in the promoter region; active genes are hypomethylated. However, these correlations are not always as simple and straightforward. The biochemical mechanisms by which site‐specific DNA methylations cause gene inactivation have not yet been determined. It is plausible to postulate that promoter methylations could somehow affect the binding of cellular enzymes involved in recognizing the promoter of a gene. Structural alterations of DNA promoter sequences arising from DNA methylations could also be important. DNA methylation is likely to represent a long‐term inactivation signal, since it is presently thought that patterns of DNA methylation can be changed only by DNA replication and specific inhibition of post‐replicative maintenance methylation.
The Dendralenes—a Neglected Group of Highly Unsaturated Hydrocarbons
Authors: Hopf Henning 
Published: December 2003

AbstractDendralenes are acyclic and cyclic cross‐conjugated polyolefins derived from 3‐methylene‐1,4‐pentadiene. This review summarizes and compares, for the first time, the methods developed for the synthesis of this class of hydrocarbons. Because of their particular arrangement of π‐electrons, the dendralenes are novel substrates for addition and rearrangement reactions, and model compounds for spectroscopic studies.
Basic Principles of Protease‐Catalyzed Peptide Bond Formation
Authors: Jakubke Hans‐Dieter , Kuhl Peter , Könnecke Andreas 
Published: December 2003

AbstractThe stereospecific formation of peptide bonds under mild conditions and without side reactions is still a formidable task in peptide synthesis. One approach that springs to mind, namely the use of the naturally occurring catalyst involved in the biosynthesis of proteins, the ribosomal peptidyl transferase, cannot be realized in practice. The fact, however, that the natural cleavage of proteins is carried out by other enzymes, namely the proteases, together with the reversibility of these cleavage reactions in principle, has led to an interesting synthetic concept. Proteases normally catalyze the enzymatic degradation of proteins and peptides by hydrolytic cleavage of the peptide bond in an exergonic reaction. The use of physicochemical principles in order to influence the equilibrium, the concentration of products, and the kinetic parameters of the reaction results in the successful application of the catalytic properties of proteases to peptide synthesis. The purpose of this review is to describe and summarize the methods used in such approaches and to attempt a systematic categorization. The principles are applied to the synthesis of such practically relevant products as aspartame and human insulin.
Reactive Organometallic Compounds Obtained from Metallocenes and Related Compounds and Their Synthetic Applications
Authors: Jonas Klaus 
Published: December 2003

AbstractProgress in the synthesis of organometallic compounds via the partial or total degradation of metallocenes and related compounds under mild reaction conditions is reviewed. These degradation reactions permit highly reactive organo‐transition metal complexes to be prepared which can in turn be used in a wide range of synthetic reactions. Examples include catalytic reactions such as the cobalt‐catalyzed hydrogenation of benzene and the manganese‐catalyzed cyclotrimerization of butadiene as well as stoichiometric syntheses of mono‐ and polynuclear transition metal complexes, some of which have novel structural features.
The Glycine Receptor of Rat Spinal Cord: Exploring the Site of Action of the Plant Alkaloid Strychnine
Authors: Betz Heinrich 
Published: December 2003

AbstractThe amino acid glycine is a major neurotransmitter in the spinal cord of all vertebrates and is involved in the control of various motor and sensory functions. By binding to specific receptors of the neuronal plasma membrane, glycine produces an increase in chloride permeability and thus a hyperpolarization, i.e., an inhibition of glycine‐sensitive neurons. This inhibitory action of glycine is reversibly blocked by the plant alkaloid strychnine. We have used strychnine for the biochemical characterization and isolation of the glycine receptor of rat spinal cord. Our results show that the glycine receptor is a large membrane protein which contains three different polypeptides. Based on the currently available data we propose a structural model of the glycine receptor and discuss its relation to other proteins of the neuronal membrane that are involved in the transmission of nerve impulses.
Applications of Synthetic Peptides
Authors: Moser Rudolf , Klauser Stephan , Leist Thomas , Langen Hanno , Epprecht Thomas , Gutte Bernd 
Published: December 2003

AbstractPeptide chemists are increasingly concerned with the synthesis of polypeptides of biological and medical interest. This article describes several important applications of synthetic peptides in biochemistry, molecular biology, immunology, and medicine. Synthetic peptides may be useful in structure‐function studies of polypeptides, as peptide hormones and hormone analogues, in the preparation of cross‐reacting antibodies, and in the design of novel enzymes. Peptide chemists can actively contribute to progress in these fields if they are aware of the current problems in the life sciences.
Mechanisms of Biological Ion Transport — Carriers, Channels, and Pumps in Artificial Lipid Membranes
Authors: Läuger Peter 
Published: December 2003

AbstractThe cell membrane contains specific systems for passive and active transport of ions between the cytoplasm and the extracellular medium. For a number of small and medium‐sized transport molecules like valinomycin and gramicidin A, extensive structural and kinetic data are available and it is possible in these cases to understand the transport function on the basis of their molecular structure. Incorporation into artificial bimolecular lipid membranes opens up the possibility of studying the kinetic properties of biological transport systems in detail.
Molecular Mechanism of Action of the Antibiotic Rifampicin
Authors: Hartmann Guido R. , Heinrich Peter , Kollenda Margit C. , Skrobranek Bernhard , Tropschug Maximilian , Weiß Wolfgang 
Published: December 2003

AbstractThe lipophilic antibiotic rifampicin is successfully used in the treatment of tuberculosis. On the molecular level it interferes with the metabolism of Eubacteria by blocking RNA synthesis. This effect is the consequence of the tight binding of the drug to a single and highly specific binding site on the DNA‐dependent RNA polymerase. The enzyme‐bound drug strongly inhibits RNA chain initiation and chain elongation. This inhibition can be explained by the influence of enzyme‐bound rifampicin on binding sites for the reaction products diphosphate and RNA. In order to reach its target the antibiotic must penetrate into the cytoplasm of the bacteria. Mutants have been discovered which are resistant to rifampicin because its uptake from the medium is significantly reduced. The gene responsible for this effect has been cloned. It confers on bacterial cells with highly sensitive RNA polymerases a remarkable resistance to the drug.
Molecular Biological Background of the Species and Organ Specificity of Influenza A Viruses
Authors: Scholtissek Christoph 
Published: December 2003

AbstractInfluenza is one of the great plagues which is not yet under control. The reason for this is the immense variability of the infecting agent, the influenza A viruses. These viruses behave like a chameleon: they adapt very rapidly to varying environments. New strains are “synthesized,” which can escape the immune response of the host, cross species barriers, and become highly pathogenic. We are beginning to understand the molecular background of this extraordinarily high variability. The genome of influenza A viruses consists of eight single‐stranded RNA segments, each of which constitutes a gene. The total base sequence of the eight RNA segments of several strains is known. If a suitable organism becomes doubly infected with two different influenza A strains, each of the RNA segments behaves like a chromosome. This means that by reassortment of the 16 RNA segments, 28 −2 = 254 new combinations (= reassortants) are theoretically possible, each having different properties. Furthermore, mutations in the various RNA segments are relatively easily tolerated. Another great problem resides in the enormous reservoir of different influenza A viruses in the animal kingdom, especially in feral waterbirds. In these birds the avian influenza A viruses normally cause at most mild symptoms, and therefore these viruses are distributed over and between continents. Bearing this in mind it appears to be necessary to develop new ideas as to how to overcome this great plague.
Physicochemical and Cytochemical Investigations on the Binding of Ethidium and Acridine Dyes to DNA and to Organelles in Living Cells
Authors: Zimmermann Herbert W. 
Published: December 2003

AbstractEthidium and acridine dyes are classical model substances for studying the binding of small, pharmacologically active molecules to DNA. Intercalation between the DNA base pairs is nearly always proposed as the most important type of binding. According to our investigations, however, there is a second type of binding, which also occurs when the concentration of the bound molecules is low and will be referred to here as external or preintercalative binding. The experimental binding isotherms show that the binding constant for intercalation KS1 is considerably smaller than that for external binding KS2 (KS1 > KS2). This surprising result is not due to the binding enthalpy (ΔH ≈ ΔH) but to the binding entropy (ΔS > ΔS). Electrostatic interactions between the dye and the DNA represent the most important contribution to both types of binding; they are supplemented by hydrogen bonds and hydrophobic interactions. The behavior of a substance in living cells, however, cannot be reliably predicted from its in vitro binding to DNA. Very few substances are bound to the DNA of the nuclear chromatin in cell culture; for example, dyes often accumulate instead in the lysosomes. In some cases the dye binds specifically and very efficiently to the mitochondria of the living cell, especially to the mitochondrial membranes, the sites of oxidative phosphorylation.
Ordering of Ionic Solutes in Dilute Solutions through Attraction of Similarly Charged Solutes—A Change of Paradigm in Colloid and Polymer Chemistry
Authors: Ise Norio 
Published: December 2003

AbstractEXAFS measurements indicate the presence of a quasi lattice‐like ordering of simple ions in dilute solutions. Small‐angle X‐ray scattering (SAXS) measurements on dilute aqueous solutions of synthetic macroions, polynucleotides, and proteins show a single broad peak; a binary mixture of synthetic macroions of different molecular weight gives a new scattering curve that is entirely different from the composite curve of the constituents before mixing. This would indicate that the macroions are distributed in a fairly regular way in the solution. The intermacroion spacing (2Dexp) obtained by the Bragg equation is found to be smaller than the average spacing (2D0) calculated from the polymer concentration. Furthermore, the 2Dexp value decreases with increasing number of charges per macroion. This finding is confirmed by studies on model systems, e. g. on monodisperse ionic latex particles, which are large enough (diameter: about 3000 Å) to be seen under the ultramicroscope. It follows, from the inequality relation 2Dexp<2D0, that there is an attraction between ionic species of like‐charge. This conclusion contradicts prevailing views in colloid chemistry; it has been pointed out that such a behavior can be explained in terms of a new theory, in which counterions between the macroions or ionic latex particles play a decisive role.
Enantiomer Separation of (R,S)‐2‐(tert‐Butyl)‐3‐methyl‐4‐imidazolidinone, a Chiral Building Block for Amino Acid Synthesis
Authors: Fitzi Robert , Seebach Dieter 
Published: December 2003

AbstractFor corrigendum see DOI:10.1002/anie.198607662
Charge Separation in Excited States of Decoupled Systems—TICT Compounds and Implications Regarding the Development of New Laser Dyes and the Primary Process of Vision and Photosynthesis
Authors: Rettig Wolfgang 
Published: December 2003

AbstractThe understanding of the dual fluorescence of certain aromatic systems has greatly advanced in recent years. The accompanying large charge separation has been shown to be linked to a twisted (or small overlap) arrangement of the chromophores. Recent theoretical models are able to describe the excited‐state twisting of both single bonds (TICT compounds) and double bonds (olefins) in a unified picture. These models can help to elucidate the photophysical behavior of many organic, inorganic, and biologically relevant compounds, and their application to laser dyes and fluorescent probes provides a route to new “tailor‐made” fluorescent materials. Applied to the primary processes of vision and photosynthesis, these models can lead to a deeper understanding of basic photobiological processes.
Biochemistry of Oxidative Stress
Authors: Sies Helmut 
Published: December 2003

AbstractAs a normal attribute of aerobic life, structural damage to organic compounds of a wide variety (DNA, proteins, carbohydrates and lipids) may occur as a consequence of oxidative reactions. Oxidative damage inflicted by reactive oxygen species has been called “oxidative stress”. Biological systems contain powerful enzymatic and nonenzymatic antioxidant systems, and oxidative stress denotes a shift in the prooxidant/antioxidant balance in favor of the former. Diverse biological processes such as inflammation, carcinogenesis, ageing, radiation damage and photobiological effects appear to involve reactive oxygen species. This field of research provides new perspectives in biochemical pharmacology, toxicology, radiation biochemistry as well as pathophysiology.
Sulfur Oxides as Ligands in Coordination Compounds
Authors: Schenk Wolfdieter A. 
Published: December 2003

AbstractDonor molecules undergo dramatic changes in their chemical properties on coordination to a transition‐metal atom. Highly reactive species can be trapped and studied as ligands. Conversely, stable compounds can be activated to undergo novel reactions. Sulfur dioxide complexes have generally been studied from a structural viewpoint, their reactivity having been somewhat neglected. The unstable sulfur oxides SO, S2O, and S2O2 are still often regarded as laboratory curiosities. Their successful stabilization in transition‐metal complexes has now made them accessible to detailed study, in the course of which many relationships to the chemistry of SO2 complexes have become apparent.
Directed Homogeneous Hydrogenation [New Synthetic Methods (65)]
Authors: Brown John M. 
Published: December 2003

AbstractStereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double‐bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face‐selectivity, and the polar substituent may be in the β‐, γ‐, or δ‐position to the double‐bond. Acyclic stereoselection ensues with β‐ or γ‐substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.
Genetic Engineering with Plants
Authors: Eckes Peter , Donn Günter , Wengenmayer Friedrich 
Published: December 2003

AbstractToday there are no longer any basic problems involved in isolating and characterizing plant genes. Our knowledge of the structure and function of the genes so far sequenced provides a beginning understanding of gene regulation in plants. In connection with the recently developed methods of gene transfer to plant cells, the most important application is the production of plants with new characteristics through genetic engineering. Since the genes can be transferred from any kind of plant—indeed even from any organism—completely new possibilities are opened up for plant breeding.
Polyphosphorus Compounds—New Results and Perspectives
Authors: Baudler Marianne 
Published: December 2003

AbstractIn contrast to the numerous known and often technically important mono‐ and diphosphorus compounds with phosphorus in its maximum oxidation state, polyphosphorus compounds led only a shadowy existence up to about twenty years ago. One of the reasons for this was the properties of such compounds, which made their handling and structural characterization difficult. This problem was solved by the development of modern preparative techniques and, especially, by the further methodological development of nuclear magnetic resonance spectroscopy. Thus, a fascinating new branch of phosphorus chemistry has been opened up in recent years. The first comprehensive review on this subject was published five years ago. Since then, research on this “element‐near” chemistry of phosphorus has produced further impressive advances with the result that a surprisingly large variety of compounds with skeletons consisting of chains or rings of phosphorus atoms is known today. However, the recent observation of the spontaneous formation of the “aromatic” pentaphosphacyclopentadienide ion, P, during the synthesis of phosphorus‐richer polyphosphides from phosphorus‐poorer compounds in solution and the discovery of the inversion of phosphorus in tetra‐ and pentacyclic organophosphanes demonstrate that this field is still capable of producing surprises.