bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrocrystallization of Metals under Ideal and Real Conditions
Authors: Fischer Hellmuth 
Published: December 2003

AbstractIdeal conditions during electrocrystallization, which are only approximately attainable, would lead to a perfect single crystal, whereas real conditions yield a monocrystalline or polycrystalline product containing many structural defects. The electrolytic production of quasi‐ideal single crystals requires an overpotential that supplies at least the activation energy necessary for the formation of two‐dimensional nuclei, since growth otherwise proceeds via screw dislocations with formation of a “real” crystal. The potential deviation in electrocrystallization under real conditions is due to electrochemical and/or crystallization overpotential, which can be determined separately. The investigation of electrocrystallization also offers possibilities for a systematic study of the formation of imperfections in real crystals.
Lysozymes: A Chapter of Molecular Biology
Authors: Jollès P. 
Published: December 2003

AbstractHen egg‐white lysozyme was the first enzyme whose tertiary structure could be elucidated. The peptide chain of this enzyme is arranged in two sections, of approximately equal size, that are separated by a deep cleft. Substrates (and inhibitors) are bound in this cleft via hydrogen bonds and are hydrolyzed under the action of Glu 35 and Asp 52, which form the active site of the enzyme. Although the lysozymes, which occur in many species of animals and plants, exhibit differences in their chemical behavior, they have the same qualitative biological activity; quantitatively important differences have been noted which also concern the specificity. Infection of E. coli with bacteriophages gives rise to a lysozyme whose formation is controlled by the phage DNA. The fact that mutated lysozymes are produced when the phages are treated with mutagens opens new fields of research in molecular biology.
Deactivation of Excited States
Authors: Stephenson L. M. , Hammond G. S. 
Published: December 2003

AbstractNature abhors an electronically excited state and strives to convert this energy to other forms. This article is concerned with the various pathways involved in the degradation of electronic excitation to ordinary “thermal” forms, but will primarily discuss the quenching of excited states by other molecules. The authors include as examples only those phototransformations and interactions encountered in solution.
Spectroscopic Investigation of Various Phosphorus‐Sulfur Bonds
Authors: Goubeau J. 
Published: December 2003

AbstractThe results of spectroscopic investigations on phosphorus‐sulfur compounds, and particularly the force constants, reveal several factors that decisively influence the bonding. The effects of hybridization, the other bonding partners and their electronegativities, the π‐bonding components, and the ionic charge are discussed. It is shown that the PS bond, unlike the PO bond, never attains full double bond character, despite its great variability.
Phosphorus Isocyanates
Authors: Derkatsch G. I. 
Published: December 2003

AbstractCompounds containing the PNCO grouping can be obtained e.g. from phosphorus halides and silver cyanate or esters of N‐chloroiminocarbonic acid and by thermal decomposition of alkoxycarbonylimino‐phosphoranes. The phosphorus (V) isocyanates resemble the “carbon” isocyanates in their chemical properties, whereas the phosphorus (III) isocyanates resemble the phosphorus (III) chlorides. Some of the compounds discussed have insecticidal or cytostatic actions.
The Meaning and Use of the Arrhenius Activation Energy
Authors: Menzinger M. , Wolfgang R. 
Published: December 2003

AbstractThe nature of the Arrhenius activation energy and frequency factor is reexamined in terms of information now becoming available on the microscopic aspects of collisional reactions. It is pointed out that the activation energy is not generally equal to the threshold for reaction, and its correct conceptual meaning is discussed. The temperature dependence of this quantity and its relation to the threshold energy is developed for a number of representative forms of the energy dependence of the reaction cross‐section (excitation function). The uses and limitations of the activation energy as a means of evaluating thresholds, excitation functions, and the presence of tunneling processes are discussed.
Hetero Analogs of Sesquifulvalene
Authors: Seitz G. 
Published: December 2003

AbstractHeterosesquifulvalenes containing sulfur or oxygen as hetero atom may be prepared, e.g., by condensation of cyclopentadienes with thiopyrones or pyrones in acetic anhydride. Heterosesquifulvalenes containing nitrogen can be obtained from the oxygen compounds by O,N‐exchange. The ground state of all these compounds is determined mainly by the nonpolar resonance formula.
Chemical Investigations of the Molecular Origin of Biological Radiation Damage
Authors: Fahr E. 
Published: December 2003

AbstractThe radiation damage observed when UV and ionizing radiations react on biological objects is caused in many cases by changes in the nucleic acids. Exposure of these compounds to UV radiation in vitro and in vivo leads, inter alia, to dimerization of the pyrimidine bases with formation of cyclobutane derivatives, and to addition of water to the 5,6‐double bond of the pyrimidine bases to form derivatives of the 6‐hydroxyhydropyrimidine system. The structure of the irradiation products has been established. The dimerization prevents the reduplication of the DNA, and the addition of water appears to be the cause of UV mutations. Ionizing radiation in aqueous solution results e.g. in addition of H and/or HO radicals to the 5,6‐double bond of the pyrimidine bases and cleavage of the imidazole ring of the purine bases. The mutations caused by ionizing radiation are probably also due, in part, to the formation of 6‐hydroxydihydropyrimidine derivatives.
Vapor Pressure Isotope Effects
Authors: Höpfner A. 
Published: December 2003

AbstractThe vapor pressure isotope effect is a reflection of the thermodynamic relations in the condensed phase. It is possible to explain the observed effects on the basis of intermolecular vibrations, e.g. hydrogen bond vibrations, and the frequency shifts of the charateristic vibrations on condensation, though other effects must also be discussed. Information about the thermodynamics of liquids, e.g. about the degree of association or the expected positions of the lattice frequencies, can be obtained from the vapor pressure isotope effect.
Reactions with Addition Compounds Containing Activated Formic Acid
Authors: Wagner K. 
Published: December 2003

AbstractAddition compounds of formic acid with tertiary organic bases in ratios higher than that required for salt formation (3:1 and 2:1 adducts) contain formic acid in a highly activated form. In particular, the 3:1 adducts of formic acid with trimethylamine and triethylamine are liquid reducing agents that are convenient to handle and are suitable for use in many selective reductions. These addition compounds have a surprisingly strong reducing action on sulfur dioxide, which is rapidly converted, even at low concentrations, into crystalline rhombic sulfur. Sulfones and polysulfones can be prepared in good yields by three‐component reactions from activated formic acid, sulfur dioxide, and polarized vinyl compounds.
Automatic Analysis of Amino‐Acid Sequences in Proteins and Peptides
Authors: von. Wilm M. 
Published: December 2003

AbstractThe development of the widely used automatic method from Edman's manual sequence analysis of proteins and peptides has resulted from modification of the procedure and from the use of a physically novel principle. All reaction, centrifugation, extraction, and drying operations are carried out in a rotating vessel. At a minimal cost in time and material, for example, sixty amino acids have been split off consecutively from a single sample of myoglobin.
Macromolecular Chemistry and Medicine
Authors: Hastings Garth W. 
Published: December 2003

AbstractMacromolecular substances are used in medicine both as materials and as reagents. In the former category polymers serve as replacements for soft tissue, as cardiovascular and orthopedic implants, and as adhesives. When employed as reagents, macromolecules interact with living tissue and play an active part in bodily repair processes.
Pyramidal Inversion
Authors: Rauk Arvi , Allen Leland C. , Mislow Kurt 
Published: December 2003

AbstractPyramidal inversion is discussed from the point of view of recent theoretical and experimental investigations in an attempt to provide a unified description of this process. Quantum mechanical studies of pyramidal molecules indicate that the origin of the inversion barrier may be dependent on the degree of angular constraint. Effects due to the electronegativity of substituents on the inversion center, to the presence of adjacent lone pairs, and to inclusion of d‐type functions in the basis set are discussed. The utility and limitations of molecular orbital calculations, vibrational spectroscopy, microwave spectroscopy, direct kinetic measurements, and dynamic nuclear magnetic resonance (DNMR) spectroscopy as means for determining barriers to pyramidal inversion are discussed in context with a review of the highlights of experimental observations on the subject. Ambiguities that arise in the interpretation of barriers determined by DNMR are explored in detail. Factors that affect the magnitude of inversion barriers are discussed separately in four broad categories: steric effects; effects of conjugation (including (p–d)π conjugation) and hyperconjugation; effects of angular constraint; and effects of heteroatomic substitution. In the last category, critical reference is made to the question of electronegativity vs. lone pair‐lone pair repulsions, the problem of rotation vs. inversion, and the role of d orbitals.
Use of the IDC System
Authors: Lobeck Martin A. 
Published: December 2003

AbstractThe documentation system operated by the IDC Internationale Dokumentationsgesellschaft für Chemie mbH uses electronic data processing methods. It allows the storage and retrieval of structures, reactions, and nonstructural keyword information. Structures and reactions are coded as terms of a faceted classification, while keywords are stored in clear text. 900000 formulas from patent and journal publications, including many Markush formulas, have now been stored on magnetic tape. Searches in this store are carried out with IDC programs, which require an average computer time of less than 1 minute per inquiry (CPU time). The structure terms can be produced by computer from topological records. The field covered at present is low molecular weight organic chemistry, though extension to macromolecular chemistry is feasible, and is in fact planned.
The “Dokumentationsring der chemisch‐pharmazeutischen Industrie”; Aims and Methods
Authors: Nübling Wolfgang , Steidle Walter 
Published: December 2003

AbstractThe members of the Documentation Ring have chosen the “punched picture” method for coding of chemical and pharmaceutical literature. Chemical, biochemical, and medical facts gleaned from a publication are broken down into basic concepts, each of which is allocated a certain position on the punched card. This system has proved to be reliable over a period of twelve years.
Methods of Virus Formation
Authors: Sauer Gerhard 
Published: December 2003

AbstractViruses occur in a great variety of shapes and sizes, but for all their diversity in appearance they possess certain characteristics in common: all viruses contain a single nucleic acid molecule – deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) – surrounded by a protective protein coat. Among other things, the protein coat enables the genetic information stored in the nucleic acid to enter a host cell in a usable state, where it can initiate the reproduction of identical virus particles. After penetration of the cell the foreign genetic material of the virus particle first induces the synthesis of macromolecules not normally present in the cell: the viral nucleic acid undergoes replication and very many copies are produced, the protein of the virus coat is synthesized, and then these components are assembled to form a new generation of infectious virus particles. Most viruses also exhibit certain common structural features: their protein coat is built up from subunits arranged in helical or icosahedral fashion around the genetic material.
Nucleosides and Nucleotides as Potential Therapeutic Agents
Authors: Shen T. Y. 
Published: December 2003

AbstractThe present article summarizes recent progress in the study of nucleoside derivatives as antiviral and immunosuppressive agents. A number of 5′‐substituted 5′‐deoxy nucleosides have been found to be permeable and nonincorporable antimetabolites of 5′‐nucleotides. N6‐isopentenyladenosine and analogs show certain promising immunosuppressive activities. Encouraged by the antibody‐stimulating effect of oligonucleotides, we have developed a convenient synthesis of oligonucleotides using fully protected phosphorylated intermediates. A group of tetradeoxyribonucleotides, dApdApdApdX, was prepared for biological and physical evaluations. Nucleotide derivatives may prove valuable in the treatment of several immunological disorders.
Kinetic Evidence for Reactive Intermediates
Authors: Huisgen Rolf 
Published: December 2003

AbstractSpectroscopic methods have recently been developed that allow the direct detection of reactive intermediates under favorable circumstances. The most general and reliable method, however, is still the indirect one, which makes use of the priciple of kinetic competition; this method is based on the freedom of the intermediate to choose between several reaction possibilities. The following discussion is addressed less to the specialist in reaction mechanisms than to the outsider who wishes to obtain some idea of the value and limitations of the kinetic method.
Metal‐Boron Compounds – Problems and Perspectives
Authors: Schmid Günter 
Published: December 2003

Abstract“True” metal‐boron compounds have been known for about ten years. The bonding between the metal and boron atoms can vary widely in nature: Not only simple covalent bonds are encountered but also coordinate bonds and boron‐metal multicenter bonds. Furthermore, π complexes of transition metals with boron‐nitrogen systems and metal complexes containing boron(I) compounds as ligands have recently also been prepared.
Relations Between Structure and Reactivity in Free‐Radical Chemistry
Authors: Rüchardt Christoph 
Published: December 2003

AbstractAn analysis of the relations between structure and reactivity in free‐radical chemistry has shown that the usual interpretation of reactivities by means of the stability of the radicals involved is greatly simplified and often incorrect. The CX bond energies of the alkanes and simple alkyl derivatives can be explained qualitatively by strain effects in the ground state on the basis of the VSEPR theory and nonbonding interactions. To be able to explain reactivities in free‐radical chemistry, it is necessary to deduce information about the geometry of the transition states during free‐radical formation from experimental measurements. The relations between structure and reactivity in free‐radical chemistry are interpreted in terms of bond dissociation energies, as well as polar and steric effects.
Principles and Latest Developments in the Field of Metallic and Nonmetallic Hard Materials
Authors: Kieffer Richard , Ettmayer Peter 
Published: December 2003

AbstractA survey of some fundamental aspects of the theory of hardness is followed by a discussion of recent developments in the field of sintered hard metal alloys. For example, good results have been obtained by the addition of hafnium carbide to hard metals. Niobium carbide can sometimes replace the more expensive tantalum carbide; vanadium carbide can be used to inhibit grain growth, especially in the case of ultrafine carbides. A brief outline is given of the results of investigations on ternary and quaternary systems with the components TiC, HfC, NbC, TaC, and WC. The utilization of sintered nitride and carbonitride hard metals in the field of machining appears feasible. Recently developed high‐pressure/high‐temperature autoclaves permit work on nitride systems under a high nitrogen pressure. The authors comment on the latest work in the field of non‐metallic hard materials and on diamond synthesis.
1,4‐Benzodiazepines. Chemistry and Some Aspects of the Structure‐Activity Relationship
Authors: Sternbach Leo H. 
Published: December 2003

AbstractNumerous clinically used compounds having favorable tranquilizing and toxic properties possess the 1,4‐benzodiazepine skeleton. This group of active substances is readily accessible, e.g. by ring enlargement of quinazoline derivatives, by ring contraction of benzoxadiazocines, and by synthesis from aminobenzophenones, constructing the seven‐membered ring in many cases in one step. The relationships between type and position of substituents and the pharmacological properties are illustrated using 1,3‐dihydro‐5‐phenyl‐1,4‐benzodiazepin‐2‐ones as examples.
Influence of Ligands on the Activity and Specificity of Soluble Transition Metal Catalysts
Authors: Henrici‐Olivé G. , Olivé S. 
Published: December 2003

AbstractThe reaction of a covalently σ‐bonded ligand (alkyl group, hydrogen) with a molecule (olefin, CO) attached to the transition metal by a coordinate bond is the essence of many catalytic processes. The influence of the other ligands in the complex on this reaction is discussed in the present article. Various ways in which the ligands can act, e.g. by electronic effects via the σ and π electron systems of the complex and by steric effects, are first described separately and then illustrated by examples.
Bond Character of β‐Diketone Metal Chelates
Authors: Bock Bodo , Flatau Karsten , Junge Helmut , Kuhr Manfred , Musso Hans 
Published: December 2003

AbstractThe vibrational spectra of molecules labeled with 2H, 13C, and 18O show that delocalization of double and single bonds in the six‐membered ring is complete in all the metal chelates investigated of 2,4‐pentanedione (acetylacetone), but not in 2,4‐pentanedione itself. Mercury, on the other hand, is bonded to the central C atom of the ligands. The NMR spectra of the metal chelates of 3‐mesityl‐2,4‐pentanedione and 3‐anthryl‐2,4‐pentanedione show that the chelate rings have no magnetic anisotropy comparable with that of benzene. A critical appraisal is made of the questions whether it is at all justifiable to attribute any “aromatic character” to such molecules and why all comparisons with the chemical reactivity of benzene have so far led to controversial conclusions concerning the character of the bonding in the metal chelates of 2,4‐pentanedione.
The Synthesis of Antibiotic Sugars
Authors: Brimacombe J. S. 
Published: December 2003

AbstractThe term antibiotic sugar denotes the carbohydrate component of an antibiotic. Two alternative approaches are adopted for the synthesis of these neutral and amino sugars, many of which have unusual structures: One route starts from fairly simple non‐carbohydrate precursors, the other depending upon the modification of a carbohydrate precursor.
Nutmeg as a Narcotic. A Contribution to the Chemistry and Pharmacology of Nutmeg (Myristica fragrans)
Authors: Kalbhen Dieter Abbo 
Published: December 2003

AbstractThe abuse of nutmeg for narcotic purposes has led to renewed chemical and pharmacological interest in this drug. Several allylbenzene derivatives whose biological transformation products have structures resembling mescaline and amphetamine have been identified as psychotropic constituents. It is suggested that the intensity of the hallucinogenic action of these compounds is due to the possibility of simulation of LSD‐like structural elements.
Methods and Applications of Nuclear Magnetic Double Resonance
Authors: von Philipsborn Wolfgang 
Published: December 2003

AbstractIn double resonance spectra, transitions between energy levels of a nuclear spin system are measured in the presence of two (or more) oscillating magnetic fields. Experiments of this nature form the basis of what is nowadays one of the most important techniques of NMR spectroscopy. Depending on the method selected, they can be used to unravel complex spectra, to measure hidden or weak resonances, or to determine the relative signs of coupling constants, as well as in stereochemical or kinetic studies. This wide and steadily growing range of applications of double resonance is described with the aid of specifilc examples.
Imaging and Analysis of Surfaces with a Scanning Electron Microscope and Electron Spectrometer
Authors: Holm Reimer 
Published: December 2003

AbstractThe topography and the composition of a surface are in many cases of equal importance (catalysis, electroplating, pretreatment of foils and sheet metal, corrosion, passivation, adsorption, coating of fibers, etc.), and this explains the great interest in methods of investigation that reveal both. If the demands on the resolving power, the analytical possibilities, and the thickness of the surface layer are not too exacting, combined devices like the scanning electron microscope and its analytical accessories can be used. When it is necessary to avoid the compromises involved in simultaneous imaging and analysis, the investigations must be carried out with separate equipment. As an example of a method for the analysis of surfaces we consider briefly photo‐ and Auger electron spectroscopy (ESCA).
Synthesis of Naturally Occurring Polypeptides, Problems of Current Research
Authors: Wünsch Erich 
Published: December 2003

AbstractThe synthesis of naturally occurring polypeptides has recently again become a center of interest. It therefore seems appropriate to make a critical appraisal of the present state of research, and at the same time to try to eliminate much of the element of chance from the solution of the problems that face us. An attempt will be made to group the preparation methods commonly used in the past into four strategies, to point out their advantages, and to uncover their disadvantages. The ultimate aim in the synthesis of naturally occurring peptides must always be a true, clean synthesis.
The Mode of Action of Hormones
Authors: Schauer Roland 
Published: December 2003

AbstractHigher organisms having anatomically and functionally differentiated organ systems must be able to coordinate biochemical processes within and between the various organs or cells, even under rapidly changing environmental conditions. Hormones play an important part in the regulation processes: they promote numerous metabolic reactions and differentiation processes, and show considerable differences in the speed with which they act. Some hormones act almost instantaneously by stimulating adenyl cyclase and thus initiating the production of adenosine 3′,5′‐monophosphate (cyclic AMP), which passes on the hormone message (“second messenger”) to the intracellular metabolism by modifying enzyme activities. Delayed‐action hormones, mainly morphogenetic hormones, act primarily on the cell nucleus where they induce the synthesis of certain enzymes by activation of genes.