bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Hormonal System of Plants
Authors: Linser H. 
Published: December 2003

AbstractHigher plants generate active substances, termed phytohormones, having the character of tissue hormones. Some of these compounds have been isolated and identified, namely ethylene, heteroauxins, and gibberellic acids. Cell‐elongation inhibitors have been detected, but not yet isolated or identified. Natural and synthetic substances with hormone‐analogous effects and those with a hormone‐antagonistic effect have become known; evidently, they act on the hormonal system of plants which regulates growth, differentiation, and development and can serve as model substances for as yet unknown phytohormones. Certain physiological phenomena suggest the existence of additional phytohormones.
Complex Formation and Flower Colors
Authors: Bayer Ernst , Egeter H. , Fink A. , Nether K. , Wegmann K. 
Published: December 2003

AbstractThe pigment of the blue cornflower, protocyanin, is a complex of high molecular weight. Iron(III) and aluminum ions combine with the anhydro base of the cyanin to form deep‐blue complexes, which are stable in the physiological pH range. Complexes of this type also have been synthesized. Alkali metal salts play no part in blue flower pigments. Formation of blue complexes can be prevented by sequestration of the metal ions with stronger complexing agents, e.g. flavonols. The variation of flower colors can be explained to a large extent on the basis of the complex formation of anthocyanins. In delphinidin glycosides, the color base or anhydro base is stable even in slightly acidic media.
Evolutionary Aspects of the Structure of Proteins
Authors: Acher R. 
Published: December 2003

AbstractThe evolution of protein structures is discussed using cytochrome c, hemoglobin, and neurohypophyseal hormones as examples. Although these substances have different biological functions, their evolution is controlled by the same general rules: their primary structures vary at the level of the species, order, or class, but this variation is restricted by the fact that the biological activity of the protein must not be impaired. Alterations (i.e. substitutions, deletions, or additions of amino acid residues) can therefore occur only in certain positions of the peptide chains, although with different frequencies. The total number of alterations thus represents only the final state of a protein and does not take into account successive substitutions which may have taken place at the affected sites. It can therefore give only a rough indication of the phylogenetic distance between two species. The nature of the substituting residues, on the other hand, is a useful guide to zoological cognateness, since it allows the identification of transition molecules which simultaneously contain amino acid residues from the protein of the protein of the evolutionary ancestor and from the protein of the evolutionary descendant.
A New Group of Antischistosomal Compounds
Authors: Schmidt Paul , Wilhelm Max 
Published: December 2003

AbstractA number of compounds containing the 5‐nitro‐2‐thiazolyl group are suitable for the treatment of schistosomiasis; 1‐(5‐nitro‐2‐thiazolyl)‐2‐imidazolidinone is particularly effective. The compounds are taken up selectively by the schistosomes causing the disease and by their eggs, and destroy both. – A review of earlier attempts to control this tropical disease is also presented in this communication.
Recent Syntheses and Reactions of Cyclic Imidic Esters
Authors: Seeliger W. , Aufderhaar E. , Diepers W. , Feinauer R. , Nehring R. , Thier W. , Hellmann H. 
Published: December 2003

AbstractΔ2‐Oxazolines and 4H‐5,6‐dihydrooxazines are readily obtainable from carboxylic acids and 2‐ or 3‐amino alcohols by gas‐phase dehydration, and 4H‐dihydrooxazines can also be obtained by condensation of N‐(hydroxymethyl) carboxamides with olefins. These cyclic imidic esters undergo reactions in which the ring is cleaved; these reactions include a new type of polymerization. The behavior of alkyl groups in position 2 and the cyclodditions in the 2,3‐position also have been studied. Reactions in side chains on position 2 and addition experiments on the sulfur analogues of the cyclic imidic esters are also reported. A table shows the principal infrared bands of substituted Δ2‐oxazolines.
Syntheses and Derivatives of Squaric Acid
Authors: Maahs G. , Hegenberg P. 
Published: December 2003

AbstractSquaric acid (dihydroxycyclobutenedione), the dianion of which may be regarded as a novel aromatic system, has recently become readily accessible by simple syntheses. The acidic character of squaric acid manifests itself in the formation of salts and of lower alkyl esters, which can be converted into the amides. Squaric acid dichloride shows in its reactions typical acyl chloride behavior. Condensation of squaric acid with pyrrole, phenol, and azulene derivatives yields cyclotrimethine dyes.
Spin Density Distribution in 2,4,6‐Triphenylphenoxyl
Authors: Dimroth K. , Berndt A. , Bär F. , Schweig A. , Volland R. 
Published: December 2003

AbstractThe distribution of the unpaired electron over the oxygen and the 24 carbon atoms in the free 2,4,6‐triphenylphenoxy radical was determined by electron spin resonance spectroscopy and quantum‐mechanical approximation methods. The hyperfine splitting was evaluated with the aid of the spectra of triphenylphenoxyls deuterated in some or all of the substituent phenyl groups. The results of the quantum‐mechanical approximations were checked by recording the ESR spectra of triphenylphenoxyls labeled with 13C in positions 1,2,3, or 4 of the central ring. The spin density distribution permits a first discussion of the 17O‐coupling constants of correspondingly labeled triphenylphenoxyl and other organic free radicals.
Chemistry of Stable α‐Halogenoorganolithium Compounds and the Mechanism of Carbenoid Reactions
Authors: Köbrich G. , Akhtar A. , Ansari F. , Breckoff W. E. , Büttner H. , Drischel W. , Fischer R. H. , Flory K. , Fröhlich H. , Goyert W. , Heinemann H. , Hornke I. , Merkle H. R. , Trapp H. , Zündorf W. 
Published: December 2003

AbstractSome years ago we found that α‐halogenoorganolithium compounds (carbenoids) previously postulated as transient intermediates in organolithium‐initiated α‐eliminations can be obtained in a stable form. The present paper is a review of the methods for their preparation and of their reactivity. They possess both nucleophilic and electrophilic properties, which can be utilized singly or combained for the synthesis of substances of very different types. Their thermolability, which is considerably reduced (with only one known exception) by the solvent tetrahydrofuran, is due to electrophilic secondary reactions, in which carbenes evidently do not occur as intermediates. A mechanism is proposed which fits the experimental data for various carbenoid reactions.
Chemistry of the Incandescent Lamp
Authors: Rabenau A. 
Published: December 2003

AbstractHalogen lamps have been on the market for some time; they are replacing the conventional lamp in many fields except general service (domestic) applications. Their relatively small bulbs contain small amounts of halogen is addition to an inert gas. The mode of action of the iodine lamp, which depends on the presence of traces of oxypgen, has been elucidated. Tungsten evaporating from the filament is returned to it by a cyclic process involving a tungsten oxide and WO2I2. No tungsten is ever deposited on the bulb wall of such a lamp. A regenerative cycle in which the vaporized tungsten is deposited on the hottest (and hence most vulnerable) parts of the filament can, in principle, be realized by the use of fluorine compounds.
Chemical Effects of Nuclear Transformations in Solids
Authors: Müller Horst 
Published: December 2003

AbstractNuclear reactions and radioactive transformations offer the possibility of investigating the chemical reactions of “bare” nuclei. The interest in such chemical processes following nuclear transformations has already led to two international symposia[1,2]. In solids, the chemical reactions of recoil nuclei having energies lower than 1 keV proceed not via molten states, but via regions of little disorder.
Hydrophobic Interactions
Authors: Némethy G. 
Published: December 2003

AbstractRecent advances in theoretical and experimental studies of hydrophobic interactions are reviewed. The theory of water structure as applied to hydrophobic bonding, theoretical estimates for the free energy of unfolding of proteins, and the statistical mechanical theory of hydrophobic bonding in polyamino acids are summarized. Experimental estimates of the thermodynamic parameters of the hydrophobic bond can be obtained from solubility and dimerization data of low molecular weight compounds. Recent studies of the interaction of proteins with nonpolar solutes are discussed. Hydrophobic bonds can also be important in various other kinds of interactions involving proteins. The observed effect of urea is mentioned, although no theoretical interpretation of this effect is available yet. In conclusion the methods available for the detection of hydrophobic interactions are reviewed.
Synthesis and Reactions of Cyanic Esters
Authors: Grigat E. , Pütter R. 
Published: December 2003

AbstractIn 1963, it was found that sterically unhindered esters of cyanic acid, which had previously been considered unobtainable, could be easily prepared from phenols and cyanogen halides. Another synthesis, involving the thermolysis of thiatriazole derivatives, was discovered in 1964. The aryl cyanates in particular have since been found to have many uses as starting materials for the preparation of numerous new classes of compounds [e.g. derivatives of esters of imidocarbonic acid (esters, amides, imides, hydrazides, hydroxylamides, sulfamides, sulfhydrazides, semicarbazides); esters of imidocarboxylic acids; s‐triazines, pyrimidines, tetrazoles, triazoles, triazolones, oxadiazoles, thiadiazoles, benzoxazinones, etc.], mainly by addition of nucleophilic or 1,3‐dipolar reactants, or as aids e.g. in the elimination of H2O or H2S or in the transfer of CN groups.
The Action of Carbon Disulfide and Sulfur on Enamines, Ketimines, and CH Acids
Authors: Mayer Roland , Gewald K. 
Published: December 2003

AbstractThe reaction of sulfur, carbon disulfide, and enamines at room temperature leads mainly or exclusively to 3H‐1,2‐dithiole‐3‐thiones; these are occasionally accompanied by 2H‐1,3‐dithiole‐2‐thiones, which can also be prepared by a modified procedure. Many enamines react with sulfur at room temperature to form thioamides. At about 50°C, enamines of acetophenone give 2‐benzylidene‐4‐phenyl‐2H‐1,3‐dithiol. The action of isothiocyanates and sulfur on enamines leads to the formation of thiazolidine‐2‐thiones. 2H‐Thiopyran‐2‐thiones can be prepaAred from enamines or dienamines with carbon disulfide at room temperature. The reaction of ketimines (Schiff bases) with carbon disulfide and sulfur yields 3H‐1,2‐dithiole‐3‐thiones or isothiazoline‐5‐thiones. The reaction of alkynes with sulfur and carbon disulfide leads to 2H‐1,3‐dithiole‐2‐thiones. Nitriles containing active methylene groups react with carbon disulfide and sulfur to form 5‐amino‐3H‐1,2‐dithiole‐3‐thiones. When isothiocyanates are used instead of CS2, the reaction leads to δ4‐4‐amino‐thiazoline‐2‐thiones.
The Formation of CC Bonds with the Aid of α‐Halogeno Ethers, Sulfides, and Amines
Authors: Gross H. , Höft E. 
Published: December 2003

Abstractα‐Halogeno ethers, sulfides, and amines are reactive compounds which can be used for the formation of new CC bonds, either as nucleophilic or as electrophilic reagents, or by α‐elimination. The use of these compounds in the synthesis of many classes of organic compounds is reviewed.
Electron‐Impact Induced Rearrangement Reactions of Organic Molecules
Authors: Brown P. , Djerassi C. 
Published: December 2003

AbstractHydrogen migrations accompany many mass spectrometric fragmentation processes and a detailed study of these migrations, largely by means of deuterium labeling, has shed much light on electron‐impact induced bond fissions. More recently, it has been found that groups other than hydrogen, such as alkyl, aryl, hydroxyl, etc., also can migrate after electron bombardment and the present article is concerned with a discussion of such molecular rearrangements among organic compounds. These observations are not only of intrinsic mechanistic interest, but a detailed knowledge of the occurrence of such migration reaction is crucial to the proper interpretation of mass spectra and to the avoidance of misinterpretations in “element mapping”.
The Chemistry of Bunte Salts
Authors: Distler H. 
Published: December 2003

AbstractBunte salts can be obtained, not only from alkyl halides and sodium thiosulfate, but also from compounds containing activated multiple bonds, and sodium thiosulfate. The Bunte salts prepared by the new method, contrary to earlier observations, are cleaved by alkalis into the unsaturated starting compounds and sodium thiosulfate. This reaction, which is used for the fixation of unsaturated compounds (e.g. to cellulose), and other reactions of the Bunte salts are discussed. The industrial applications and biological properties of the Bunte salts are also mentioned.
Investigation of Inorganic Systems at High Temperature by Mass Spectrometry
Authors: Drowart J. , Goldfinger P. 
Published: December 2003

AbstractHigh‐temperature mass spectrometry (hitherto at temperatures between 1000 and 2500 °K and at pressures between 10−3 and 10−12 atm) has already made possible the identification of many previously unknown and unpredicted diatomic and polyatomic molecular species. The present paper deals with the investigation of many oxides, of halides, and of carbon molecules and intermetallic molecules. An apparatus for the production and investigation of molecular beams is described. Knudsen cells permit the production of molecular beams under equilibrium conditions; in special cases the “double‐oven” type of Knudsen cell is used. Thermodynamic and kinetic quantities such as ΔH values, dissociation energies, and ionization cross sections of the species investigated are given.
Acetylcholinesterase
Authors: Engelhard N. , Prchal K. , Nenner M. 
Published: December 2003

AbstractAcetylcholinesterase plays a vital part in the functioning of nerves, and serious physiological damage arises from its blockage by esters of phosphonic and phosphoric acid used e. g. in pesticides. The properties and the mechanism of action of acetylcholinesterase, which show many similarities to those of other hydrolases, are described. Therapeutic agents (reactivators) for the toxic phosphorus compounds specified are also discussed.
A Topological Approach to the Problem of Ring Structures
Authors: Fugmann R. , Dölling U. , Nickelsen H. 
Published: December 2003

AbstractIn the mechanized documentation of chemical literature, the definition of structural concept is very important. The usual for definitions for ring structures are inadequate. Essential ring structures are sometimes not recognized on the basis of these definitions and are therefore missed in a literature search. This is particularly true of bridged ring systems. The ring concept and ring condensation types are now redefined on a topological basis in the closest possible analogy to the intuitive approach of the chemist. In complicated molecular structures, these “fundamental rings” can be easily determined, either manually or by means of a programmed computer. The concept of the “ring complex” is defined and suggested as a preliminary screen in literature searches for ring structures. This will save machine time, and so reduce the cost of searches.
Synthesis and Reactions of the Alkynylamines
Authors: Viehe H. G. 
Published: December 2003

AbstractAlkynylamines RCCNR have been known for only a few years. They are stable compounds, some of which have now become commercially available. Their high reactivity toward electrophiles as well as toward nucleophiles (particularly on acid catalysis) makes them very versatile starting materials. An interesting practical application is their use as condensing agents in peptide syntheses. They are superior to dicycloexylcarbodiimide as dehydrating agents for organic acids. They condense with polar multiple bonds and dipolar systems to form cyclic structures.
The Active Species in Homogeneous Ziegler‐Natta Catalysts for the Polymerization of Ethylene
Authors: Henrici‐olivé G. , Olivé S. 
Published: December 2003

AbstractCp2TiCl2 and Cp2TiEtCl (Cp = cyclopentadienyl, Et = ethyl), in combination with aluminum alkyls, have been studied as model catalyst systems for the polymerization of ethylene in toluene. The activity of these systems resides in the presence of a complex molecule involving an alkylated Ti(IV) and an alkylated Al species, linked together by chlorine bridge bonds. The environment of the Ti is of octahedral symmetry with one vacant site available for the coordination of ethylene. The bridged Al‐alkyl causes a destabilization of the Ti‐alkyl bond (“trans effect”), thus rendering it active for polymerization. The reduction Ti(IV) → Ti(III), inevitable in these systems, involves the irreversible change from octahedral to tetrahedral symmetry with loss of the catalytic activity. Polymerization and reduction are supposed to occur at the same catalyst site. Magnetic methods (susceptibility and EPR) as well as the kinetics of polymerization were used in the investigation of these catalyst systems.
Electron‐Pair Repulsions and Molecular Shape
Authors: Gillespie R. J. 
Published: December 2003

AbstractThe theory described in this article emphasizes the importance of interactions between the electron pairs in the valence shell of a central atom in determining stereochemistry and it assumes that interactions between the ligands are generally of lesser importance although sufficiently bulky groups, or chelate ligands, may play an important role in determining the stereochemistry. If lone‐pair electrons are present in the valence shell of the central atom then the two theories (the theory of interaction of electron pairs and the theory of interaction between ligands) predict different structures. In the great majority of cases the determined structures are those expected if it is assumed that lone pairs are stereochemically active, i.e. if repulsions between electron pairs in the valence shell determine stereochemistry.
Potential and Charge Distribution at Semiconductor‐electrolyte Interfaces
Authors: Memming R. , Schwandt G. 
Published: December 2003

AbstractThe present article deals with the basic concepts of charge and potential distribution at semiconductor‐electrolyte interfaces. The authors use examples to show how external polarization and the variation of the electrolyte composition can change the potential drop across the space‐charge region in the semiconductor and in the Helmholtz double layer at the interface. The article also contains a detailed discussion of the effects exerted by surface properties and by injection of carries on the distribution of charge and potential.
Syntheses with ketones, sulfur, and ammonia or amines at room temperature
Authors: Asinger F. , Offermanns H. 
Published: December 2003

AbstractA large number of preparatively interesting compounds have become readily available by the simultaneous action of sulfur and ammonia or amines on ketones. Direct syntheses of Δ3‐thiazolines, Δ3‐imidazoline‐5‐thiones, 5,6‐dihydro‐4H‐1,4‐thiazines, and the 1,2,3,4,5,6‐hexathiocane system from ketones, sulfur, and ammonia or amines, and further possibilities for the synthesis of these heterocyclic systems have been proposed. Other heterocycles containing N or N and S (thiazoles, thiophenes, thiazolidines, tetrahydrothiazolo[2,3‐c]‐1,4‐thiazines, thiomorpholines, 4‐amino‐2H‐imidazoles, etc.) are readily obtainable by further reactions of these compounds. Hydrolysis of the Δ3‐thiazolines yields α‐mercapto ketones, which are the starting materials for other syntheses. Most of the syntheses described proceed at room temperature and at normal pressure.
The Concept of Hard and Soft Acids and Bases as Applied to Multi‐Center Chemical Reactions
Authors: Saville B. 
Published: December 2003

AbstractMany chemical bonds of differing types and strengths have recently been regarded by Pearson[1] as representing partnerships between (Lewis) acids and (Lewis) bases. Most acceptor molecules or ions (acids) can be placed in one or other of two categories, graphically termed “Hard” and “Soft”. There are also two broad categories of donor molecules or ions (bases) which can also be termed Hard and Soft. On the whole, strong chemical bonds are partnerships between either a Hard base and a Hard acid or a Soft base and Soft acid, whereas weaker bond types most usually result in cases of either Hard base‐Soft acid or Soft base‐Hard acid interactions. The present paper shows how this concept of acidity and basicity can be applied in the interpretation of multi‐center chemical reactions involving interconnected acid‐base relationships. In particular, fourcenter substitutions and additions involving cooperative attack by nucleophiles and electrophiles at various chemical bonds have been examined, and a conclusion is reached that especially reactive patterns of reactants can be developed if the substrates contain bonds between either a hard acid and a soft base, or a soft acid and a hard base. Indeed, the arguments can be elaborated to provide two distinct Rules which should be of interest in the interpretation of metal‐ion assisted reactions and in the design of novel syntheses.
Nucleophilic Reactivity of the Thiophosphoryl Group
Authors: Teichmann H. , Hilgetag G. 
Published: December 2003

AbstractThe difference in the nucleophilic reactivities of the and groups can be satisfactorily explained on the basis of Pearson's acid‐base concept[21]. The thiophosphoryl sulfur is a typical “soft base”, and reacts preferentially with sub‐group B metals, halogens, and sp3 hybridized carbon, whereas it is largely inert to “hard acids” such as protons, carbonyl carbon, and tetrahedral phosphorus. Since a nucleophilic attack by the thiophosphoryl sulfur leads to a decrease in the charge density of the phosphorus atom, the latter (or the α‐carbon atom in O‐alkyl esters) becomes more open to nucleophilic attack. This reaction principle forms the basis of sulfur exchange, dealkylation, isomerization, and the Pistschimuka and Michalski reactions.
Structure and Mechanism of Action of the Active Center of Yeast Pyruvate Decarboxylase
Authors: Schellenberger A. 
Published: December 2003

AbstractKinetic studies have shown that the two low molecular‐weight components of yeast pyruvate decarboxylase (thiamine pyrophosphate and Mg2⊕ ions) first add rapidly and reversibly to the apoenzyme in binary equilibria. The resulting adduct then “cyclizes” in a rate‐determining, practically irreversible reaction to form the thermodynamically stable holoenzyme. These results were supplemented and extended by the testing of numerous analogues of thiamine pyrophosphate in enzyme experiments and then used for the interpretation of the enzyme reaction.
Hexamethylphosphoramide
Authors: Normant H. 
Published: December 2003

AbstractGrowing interest is being shown in the role of the solvent (particularly polar solvents) in chemical reactions[1–4]. The most remarkable polar aprotic solvent appears to us to be the hexamethylated triamide of orthophosphoric acid, OP(N(CH3)2)3, which is known as hexamethylphosphoramide or tris(dimethylamino)phosphine oxide. Hexamethylphosphoramide[5–7] has recently been studied with respect to its solvent properties for gases[5], for many organic and inorganic salts[7], and for polymers[5], as well as its use as a polymerization co‐catalyst. However, these aspects are not considered in the present paper, which deals with the physical and chemical properties of hexamethylphosphoramide, and in particular with its use as a reaction medium. Our own work on hexamethylphosphoramide began in 1961, and until then very little work had been done on this compound. Even in a paper published by Parker[1b] in 1965, very little reference is made to hexamethylphosphoramide.