bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zeolites—Their Synthesis, Structure, and Applications
Authors: Schwochow Friedrich , Puppe Lothar 
Published: December 2003

AbstractDuring 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

AbstractOptical 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

AbstractTetracycline 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

AbstractThis 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

AbstractMost 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

AbstractThe 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

AbstractHydrozirconation 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

AbstractA 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

AbstractRecent 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

AbstractBiologically 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.
Experimental Electron Densities and Chemical Bonding
Authors: Coppens Philip 
Published: December 2003

AbstractSome 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.
Synthetic and Mechanistic Aspects of Inorganic Insertion Reactions. Insertion of Carbon Monoxide
Authors: Calderazzo Fausto 
Published: December 2003

AbstractThe 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.
The Chlorofluorocarbon/Ozone Theory—A Scientific Status Report
Authors: Jesson J. Peter 
Published: December 2003

AbstractIn 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.
Flexible Drug Molecules and Dynamic Receptors
Authors: Williams R. J. P. 
Published: December 2003

AbstractWhen 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.
Chemical Oscillations
Authors: Franck Ulrich F. 
Published: December 2003

AbstractUnder 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.
Quantitative Mass Spectrometry in Biochemistry and Medicine
Authors: Lehmann W. D. , Schulten H.‐R. 
Published: December 2003

AbstractThe 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

AbstractProstaglandins 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.
What Do We Know about the Metal‐Metal Bond?
Authors: Vahrenkamp Heinrich 
Published: December 2003

AbstractAlmost 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

AbstractThe 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

AbstractHemoglobin 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.
Perfluoro Compounds as Blood Substitutes
Authors: Riess Jean G. , Le Blanc Maurice 
Published: December 2003

AbstractInconceivable as it is, it has been proved that animals can survive after having had their blood massively or even totally replaced by emulsions of perfluorinated compounds in salines. “Bloodles” rats charged with an emulsion of perfluorotri‐n‐butylamine survived a five hour period in an atmosphere containing 50% oxygen and 50% carbon monoxide, i.e. in conditions where the transport of oxygen by the red cells is entirely blocked. This review discusses: (1) the experiments which have demonstrated the capability of blood substitutes based on perfluorinated compounds to sustain life; (2) the characteristics and preparation of the relevant perfluoro compounds and the production and handling of their emulsions; (3) their “physiology”, i.e. toxicity, life‐span in the blood‐stream, effect on the organs and their functions, and excretion properties. Obstacles remaining to be overcome in order to provide a safe blood substitute for medical practice include the availability of numerous series of well‐defined pure and inert perfluorinated chemicals, the production of stable emulsions, the optimization of fluid balance, and the attainment of reasonable excretion rates. The accent is placed upon the role of the chemist in the progress of this research.
Protein Biosynthesis: The Codon‐Specific Activation of Amino Acids
Authors: Holler Eggehard 
Published: December 2003

AbstractAt the start of protein biosynthesis the amino acids are chemically activated by esterification with transfer ribonucleic acids bearing the appropriate anticodons. The esterification is catalyzed with an exceptionally high specificity by aminoacyl‐tRNA synthetases. Current knowledge of the structural properties of the reactants, the course of the reaction, and the reasons for its specificity are summarized.
Polymeric Catalysts
Authors: Manecke Georg , Storck Winfried 
Published: December 2003

AbstractThe present‐day position in the field of polymeric catalysts is outlined. The following selected groups of polymeric catalysts are discussed: synthetic hydrolases, immobilized enzymes, phase‐transfer catalysts, nucleophilically active bases, polymers with conjugated π‐systems, photosensitizers, polymers as carriers for catalytically active metals or ions, and immobilized homogeneous catalysts. Polymeric catalysts have the following valuable properties: insoluble polymeric catalysts are readily separable from reaction solutions and can often be re‐used without loss of activity; a hydrophobic matrix protects the organometallic active center from deactivation by oxygen and water; by fixation of finely divided metals on an ion exchanger, multistage reactions may be effected successively in one reactor. Polymeric carriers may influence the catalytic properties; for example, in the case of immobilized enzymes on polyionic carriers the pH of the activity maximum may be shifted.
Organometallic Syntheses with Diazoalkanes
Authors: Herrmann Wolfgang A. 
Published: December 2003

AbstractIn recent years, aliphatic diazo compounds have proved to be more and more versatile as reagents in the preparative chemistry of organometallic complexes. As readily accessible compounds, they are not only suitable for the synthesis of known kinds of metal complexes but also open fresh routes to novel complex systems. The comparatively new field of diazoalkane complex chemistry exhibits numerous unexpected and novel reactions, and introduces interesting and promising aspects into the chemistry of carbonylmetal compounds.
Polyethylene Fibrids: Preparation and Properties
Authors: Gordon Wolfgang , Leugering Hans Joachim , Cherdron Harald 
Published: December 2003

AbstractPolyethylene fibrids are small fibers having lengths of up to some millimeters, which are highly oriented and which have a morphology similar to that of cellulose fibers. The preparation of polyethylene fibrids is based on shear‐induced crystallization, a process in which the polyethylene crystallizes from solution under the influence of an elongated flow in the form of so‐called shish‐kebabs. Polymerization under shear conditions and the flash spinning of polyethylene solutions are the main processes for the preparation of PE fibrids. They may be hydrophilized by an additional process step.—Because of their cellulose‐like morphology, (hydrophilized) polyethylene fibrids have interesting properties, e.g. high adsorption capacity and the ability to form hydrogen bonds. In addition, the possibility of undertaking chemical reactions on the surface of the fibrids should be mentioned.
Physical and Chemical Properties of Dissolved Electrons (Excess Electrons)
Authors: Schindewolf Ulrich 
Published: December 2003

AbstractElectrons produced in a gaseous, liquid, or solid solvent are called dissolved electrons or excess electrons. These excess electrons can exist as quasi‐free particles of high mobility in a delocalized state, comparable with electrons in a metal; or as bound particles of low mobility they can be localized within narrow limits—in a solvent cavity formed by repulsive forces. Localized electrons can also be solvated like normal ions. Characteristically, such solvated electrons exhibit broad and extensive absorption spectra in the visible to near infrared spectral range. The localized and delocalized states of the excess electrons can be in equilibrium with each other, such that a continuous transition of the properties between the limiting extremes can be observed. The reactions of the excess electrons with suitable acceptors (substrates) are initiated by an attachment‐detachment equilibrium A + e− ⇌ A− which is followed by further chemical rearrangements. The rate constants of these reactions vary by more than 15 powers of ten depending on the substrates and the solvents. Most of the properties of excess electrons in solution can be interpreted by means of a model which is easily understandable but quantitatively evaluated only with considerable effort.
Structure and Bonding in Cyclic Sulfur‐Nitrogen Compounds
Authors: Roesky Herbert W. 
Published: December 2003

AbstractThe coordination number of sulfur is used in this review as a classification principle; cyclic sulfur‐nitrogen compounds in which the sulfur is di‐, tri‐, and tetracoordinated are discussed. Compounds with sulfur (and nitrogen) of coordination number 2 are electron‐rich combinations of elements whose π‐electrons are extensively delocalized. A correlation between the coordination number and the bond length can be observed in certain compounds containing tri‐ and tetracoordinated sulfur.
Permeability of the Outer Membrane of Bacteria
Authors: Nikaido Hiroshi 
Published: December 2003

AbstractThe outer membrane of Gram‐negative bacteria is an attractive system for the study of the structure‐function relationships in biological membranes. This membrane has, inter alia, the task of regulating the inflow of nutrients and outflow of waste products. Investigations with the aid of mutants showed that there are at least two general pathways for the diffusion of small molecules across the outer membrane: one for hydrophobic and one for hydrophilic compounds. In the case of the “hydrophobic pathway” the hydrophobic compound dissolves in the interior of the membrane and then crosses the membrane in accordance with the partition coefficient. In wild‐type forms of enteric bacteria this pathway cannot be used—presumably owing to the absence of regions with phospholipid bilayers. Small hydrophilic molecules, on the other hand, penetrate the membrane through water‐filled pores.