bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and Function of Chromosomal Nucleohistones
Authors: Zimmermann Eberhard 
Published: December 2003

AbstractThe progress made in molecular biology has provided definite evidence that DNA is the genetic material of all cellular organisms. It is mainly localized within the cell nuclei and, in association with histones and acidic proteins, forms the fundamental structure of the chromosomes. The DNA‐protein complex, called nucleohistone or chromatin, represents the sum of all existing genes of one cell type and can be considered as a functional genetic unit. All genetic structures contain this fundamental element and only their steric arrangement or multiplicity determine the species‐specific differences in chromosomal morphology. The preservation of the three‐dimensional structure seems to be the function of histones which, in general, are associated with densely packed and metabolically inactive DNA sequences. The lysine‐rich histone I probably has a specific regulatory function since it inhibits the transcription of certain genes. Acidic proteins are mainly to be found in stretched chromosomal structures of high metabolic activity which accentuate the correlation between structure and function of nucleohistones. Approximately 50% of the DNA of the nucleohistone complex is not masked by proteins though only a small percentage of the free nucleotide sequences can be transcribed by RNA polymerase. The “open” structure of nucleohistones finds a plausible explanation in the fact that amino acid sequence analysis of several histones revealed an asymmetric distribution of charged groups and that therefore only these protein fractions can interact with DNA. In Crick's recently published model of the chromosomal organization the unique structure of histones is taken into account and it is assumed that the histone‐rich heterochromatin contains multiple but untranscribable control elements. Functional genes are represented by a single stranded DNA duplex within the interbands which utilize a special protein to preserve this unique conformation.
Structural Principles of Biomembranes
Authors: Kreutz Werner 
Published: December 2003

AbstractThe determination of the electron density distribution of the membrane cross sections of nerve myelin and the discs of the outer segments of retinal rods by a new X‐ray evaluation method indicates, as in the case of the cross‐sectional structure of the photosynthetic membrane, an “asymmetric” mass distribution. In connection with the detection of planar protein lattices in the membranes of photosynthetic bacteria, the chloroplasts of higher plants, erythrocytes, and retinal discs as well as the detection of a new category of lipid characteristics, comprising isothermal confromational and phase changes by specific ligand binding, a basis is established for the development of a general concept of biomembrane structure.
Conformational Analysis in Heterocyclic Systems: Recent Results and Applications
Authors: Eliel Ernest L. 
Published: December 2003

AbstractThis review deals with the following aspects of conformational analysis in saturated heterocyclic systems: 1. Conformational equilibria in 2‐aryl and 2‐ethynyl‐1,3‐dioxanes in various solvents. 2. The generalized anomeric effect in perhydro‐1,3‐diazines and its origin. 3. Unexpected conformational equilibria in 5‐heterosubstituted 1,3‐dioxanes. 4. Normal and anomalous solvent effects in conformational equilibria of 1,3‐dioxanes with heteroatoms at C‐5. Calculation of solvent effects. Correlation of ΔG0 as a function of solvent with solvatochromic transition energy ET (30); a new scale of “solvent polarity”. 5. Interplay of hydrogen bonding with dipolar, non‐bonded and eclipsing interactions in 5‐hydroxymethyl‐ 1,3‐dioxanes. 6. Highly stereoselective H‐D exchanges in anancomeric 1,3‐dithianes. 7. Potential distortion of a cyclohexane or 1,3‐dioxane ring by a tert‐butyl substituent. Evidence from 1H‐NMR and 13C‐NMR investigations and from X‐ray structure analysis.
1H‐NMR Spectra of the AA′XX′ and AA′BB′ Type – Analysis and Classification
Authors: Günther Harald 
Published: December 2003

AbstractIt is shown how the secular determinant for the general four‐spin case can be greatly simplified in the case of NMR spectra of the AA′XX′ and AA′BB′ type on the basis of molecular symmetry and with the aid of the so‐called X approximation. The methods for the direct analysis of these spectra are presented, and the relations between the type of spectrum and the chemical structure are discussed in detail for selected examples. In an appendix, parallels are pointed out between the formalism of the Hückel MO theory and the calculation of the eigenvalues and eigenfunctions of nuclear spin systems.
Structure Determinations of Nitrogen Compounds with the Aid of NQR, NMR, and ESCA Spectroscopy
Authors: Fitzky Hans G. , Wendisch Detlef , Holm Reimer 
Published: December 2003

AbstractSince it is often necessary or desirable to determine the structures of compounds containing nitrogen directly via the nitrogen atoms, the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) as well as the photoelectron and the Auger‐electron spectroscopy (ESCA) of nitrogen are becoming increasingly important. A comparative review of these three methods on the basis of measurement effect, information obtainable, applications, and limitations forms the subject of this article.
The Chemistry of Phenylcyclobutenediones
Authors: Ried Walter , Schmidt Arthur H. 
Published: December 2003

AbstractPhenylcyclobutenediones are easily obtainable and very stable. Depending on the nature of the substituent R in position 3, they may be formally regarded as vinylogous carboxylic acid derivatives (Rhalogen, OCH3, OH, SH) or as α,β‐unsaturated diketo compounds (RH, alkyl, aryl). Their behavior in reactions justifies this approach. Ring contraction, ring expansion, and ring cleavage reactions are described.
Industrial Application of the Semiconductor Properties of Dyes
Authors: Meier Hans , Albrecht Wolfgang , Tschirwitz Ulrich 
Published: December 2003

AbstractEffects of industrial interest have been detected in investigations on the dark conductivity and photoconductivity of dyes. For example, it was found that organic dyes can be used in the same way as inorganic photoconductors in vidicon television pickup tubes for the reproduction of images. Among other things, pointers were obtained to the formation of rectifying and photoelectrically sensitive pn junctions, to relatively high thermoelectromotive forces of doped and polymeric dyes, to the possibility of use in reprography, and to a high catalytic activity connected with the conductivity, which is already being utilized in fuel cells.
Thermally Reversible Photoisomerizations
Authors: Quinkert Gerhard 
Published: December 2003

AbstractThis article consists of a programmatic part and a pragmatic one. The programmatic aspects are the establishment of photochemistry, in the broadest definition of its scope, as a developing field directed toward the elucidation of photobiological phenomena, and an appeal for the wide development of the hitherto neglected dimension of electronically excited states. The pragmatic part is the detailed description of the photochemistry of linearly conjugated cyclohexadienones as an example of a thermally reversible photoisomerization system. The logical use of methods for obtaining information about the formal kinetics of light‐induced reactions and for the identification of short‐lived transients by low‐temperature spectroscopy is of value to both parts.
The Loose Connection between Electron Configuration and the Chemical Behavior of the Heavy Elements (Transuranics)
Authors: Jørgensen Christian Klixbüll 
Published: December 2003

AbstractThere is no straightforward relation between the ground electron configuration of the neutral atom and the chemistry of a given element. In particular, the choice of oxidation state depends on the comparison between consecutive ionization energies of the gaseous ions and the hydration energy or Madelung energy which by preference stabilizes increased oxidation numbers. Special ligands, such as oxide, may introduce unexpectedly high oxidation numbers. The baricenters of electron configurations are discussed with vanadium and thorium as specific examples. The chemistry of the elements with Z = 101, 102, 103, 104, 105, and 112 (of which some thousand atoms have been reported) and the (yet unknown) elements with Z=108, 109, 114, 126, 164, and 184 is discussed.
Semiempirical Use of Chirality Functions for the Description of the Optical Activity of Allene Derivatives in the Transparent Region
Authors: Ruch Ernst , Runge Wolfgang , Kresze Günter 
Published: December 2003

AbstractA comparison of calculated and experimental data shows that the optical rotatory power of phenylallenecarboxylic acids is quantitatively described by the polynomial expression developed in (1). The Td component of this expression, the only relevant one for the case of methane derivatives turns out to be negligibly small in the case of allene derivatives. Therefore, and because allene derivatives belong to category a[16] the sequence of the λ‐parameter values of the ligands may be used to determine the configuration and the sign of rotation.
The Perturbation Treatment of Chemical Reactivity
Authors: Hudson Robert F. 
Published: December 2003

AbstractThe perturbation method of treating chemical reactions is discussed in a simple manner, by invoking the general hypothesis that the initial perturbation determines the course of a reaction. This approach is used to develop a general theory, as an alternative to the transition state theory. Such apparently diverse concepts as the symmetry rules for cyclic processes, and hard and soft acids and bases can be derived by this treatment, which is applied to radical reactions and aliphatic and aromatic substitution.
Chemistry and Biosynthesis of the Hypothalamic Releasing and Inhibiting Neurohormones
Authors: Folkers Karl , Johansson Nils‐Gunnar , Hooper Fred , Currie Bruce , Sievertsson Hans , Chang Jaw‐Kang , Bowers Cyril Y. 
Published: December 2003

AbstractThe hypothalamus secretes hormones which in turn affect the release of hormones from the anterior lobe of the pituitary gland. Evidence has so far been adduced for the existence of seven hypothalamic releasing hormones and three inhibiting hormones. These neurohormones are all oligopeptides and occur in only nanogram amounts in the hypothalamus. The study of synthetic analogs has provided valuable information regarding their mechanism of action.
Repair Processes on Deoxyribonucleic Acid
Authors: Berndt J. 
Published: December 2003

AbstractMany cells have the ability to recognize and eliminate damage to their DNA, particularly thymine dimers formed by UV light. The elimination of this damage may be achieved by enzymatic, light‐dependent cleavage of the dimers into the monomers (photoreactivation) or more frequently by dark repair, in which the damaged part is completely removed from the, DNA. In this repair process, the DNA is incised by an endonuclease in the immediate vicinity of the thymine dimers. Oligonucleotides containing the thymine dimer are removed hydrolytically from the DNA by the 5→3′ exonuclease activity of DNA polymerase I (Kornberg enzyme). The resulting gaps are immediately closed by a de novo synthesis with the aid of the same DNA polymerase I, the complementary strand serving as a template (excision repair). The final step is the formation of the phosphodiester bond between the newly synthesized DNA fragment and the old DNA strand by a DNA ligase. Xeroderma pigmentosum patients lack the endonuclease as a result of a genetic defect; they therefore cannot eliminate thymine dimers from their DNA, and are extremely sensitive to sunlight. All information so far suggests that genetic recombination and DNA repair are performed by the same enzyme system.
Synthetic Precious Stones
Authors: Liebertz Josef 
Published: December 2003

AbstractThe first industrially feasible process for the synthesis of rubies was developed by Verneuil around the turn of the century. Progress in growing single crystals led in time to numerous other processes, some of which can be applied to the production of precious stones. In this way it became possible to synthesize the most important precious stones. Even crystals that do not occur in nature, but were originally of interest in other connections, have acquired importance for jewelry in recent years.
Direct Quantitative Photometry on Thin Layer Chromatograms
Authors: Hezel Ute 
Published: December 2003

AbstractThe principal methods for the direct photometric evaluation of thin layer chromatograms are discussed with the aid of examples. Since light is strongly scattered by TLC adsorbents, absorption measurements in reflection are preferable to transmission measurements. In the reflection measurements, an approximation method for the Kubelka‐Munk function leads to satisfactory straight calibration lines. The working range for quantitative reflection measurements is in the μg range, and the detection limit is of the order of 10−8g. The standard deviation for spots of equal concentration is less than ±1%. The signal‐to‐background ratio is improved by simultaneous measurement of reflection and transmission. The measurement of diminution in fluorescence (“fluorescence quenching”) is found to be less sensitive than the reflection at the absorption maximum. However, combined measurement of the reflection and the diminution of fluorescence gives an increase in sensitivity as compared to pure reflection measurements. As in solution photometry, fluorescence measurements are generally much more sensitive than absorption measurements. The working range is normally in the ng region, and the detection limit is around 10−11g. All the investigations described in this paper were carried out on the Zeiss chromatogram spectrophotometer.
The Cytochalasans: A New Class of Biologically Active Microbial Metabolites
Authors: Binder Michael , Tamm Christoph 
Published: December 2003

AbstractA series of cytostatically active metabolites have been isolated from microorganisms in recent years. These compounds, which are chemically closely related, are of a new structural type. A highly substituted hydrogenated isoindolone unit is fused to an 11‐ to 14‐membered macrocycle. The large ring may be carbocyclic or heterocyclic (lactone or carbonic diester). The absolute configurations of two cytochalasans (phomin and a cytochalasin D derivative) have been established by X‐ray analysis. The biogenesis of phomin (cytochalasin B) is broadly known, and it is probable that all cytochalasans have a common biogenetic scheme. All the compounds of this class have a more or less pronounced specifically cytostatic action.
Iron‐Sulfur Proteins: Structural Chemistry of Their Chromophores and Related Systems
Authors: Mason Ronald , Zubieta J. A. 
Published: December 2003

AbstractIntensive studies of iron‐sulfur proteins were begun only a decade or so ago but many biological and physicochemical data have since been accumulated and summarized[1–5]. As a result of the very recent X‐ray analyses of the structures of rubredoxin[6], ferredoxin (Peptococcus aerogenes)[7] and the Chromatium vinosum high potential iron protein (Hipip)[8], it has become possible to review our understanding of the nature and function of the inorganic chromophores in these proteins; to relate these findings to ‘model’ systems of varying relevance; but of more general interest, to comment on redox processes in biological systems particularly with respect to what might be termed electron transfer—allosteric effects in metalloenzymes.
Light Guide Systems for the Ultraviolet Region of the Spectrum
Authors: Dislich Helmut , Jacobsen Alfred 
Published: December 2003

AbstractWhereas diverse and highly refined fiber optics have long been in technical use for the conduction of visible light, traditional but expensive silica glass lenses and prisms have had to be utilized until quite recently for the transmission of ultraviolet light. The reason for this was the lack of suitable materials. UV light cannot be transported to any technically useful extent either with pure glass‐glass (core and sheath materials) light guides or with plastic‐plastic light guides. UV light guides for wavelengths down to 200 nm can be produced by combination of a silica glass as the core material with a tetrafluoroethylene‐hexafluoropro pylene copolymer or methylpolysiloxane as the sheath material. Fiber optics of this type constitute a new aid for medical technology, medicine, and many technical and scientific fields, whose range of applications cannot yet be fully envisaged.
Extrachromosomal DNA in Bacteria
Authors: Goebel Werner 
Published: December 2003

AbstractIn addition to chromosomal DNA carrying the genetic information of the cell, many bacterial cells contain smaller circular DNA factors known as plasmids or episomes. These genetic elements endow the cell with additional biochemical capabilities. The fertility factors (F and F′), the antibiotic resistance factors (R), the colicinogenic factors (Col), the hemolytic factors (Hly), and other extrachromosomal DNA systems are described. These small DNA molecules can be isolated, and are therefore particularly suitable for the investigation of DNA replication and the stable establishment of genetic material in the bacterial cell.
Structural Information from the Habit of Crystals
Authors: Follner Heinz 
Published: December 2003

AbstractThe question whether information about the internal structure of crystals can be deduced from their external form, i.e. from their habit, has often been discussed. A rule formulated by Donnay and Harker attempts to establish the relationship on the basis of structural geometry. Deviations from this rule make it clear that purely geometric correspondence criteria are only of limited applilcation. Physical factors are also taken into account in the PBC vector method. A combination of the two methods can be of practical use in some cases for the determination of the crystal structures of organic compounds.
The Bacterial Flagella and the Flagellar Protein Flagellin
Authors: Bode Wolfram 
Published: December 2003

AbstractIn comparison with the relatively complicated flagella of all nucleated organisms, most of the actively motile bacteria have very much simpler locomotion organelles. These flagella are long thin filaments with a helical superstructure, anchored at one end in the cell membrane. Helical waves pass along the flagella in the distal direction during locomotion. In the flagella, identical structural units of a single protein species, flagellin, are linked to one another by non‐covalent bonds. The flagellin subunits can be separated from one another by mild methods, and their biochemistry as well as their structure and morphology can be investigated in the isolated state. Under certain conditions they can reaggregate in vitro to form polymorphous helical filaments, which are practically indistinguishable from intact flagella. In the flagellum, the elongated flagellin molecules have a layered arrangement in about ten parallel strands, which in turn form a hollow cylinder. Since this cylinder is deformed into a large helix, the individual chemically identical flagellin protomers and the protomer strands in the helical flagella are only quasi‐equivalent. The conformation and bonding pattern of the individual longitudinal flagellin lines can presumably be controlled in vitro by the basal structures, so that movement within the flagellum could conceivably occur as follows. A cyclically induced change in the length of the individual strands could result in an apparent rotation of the helical flagellum. According to hydrodynamic calculations, the resulting forward thrust is sufficient to propel the bacteria at the observed speeds of up to 50 μm/s.
Nuclear Medicine and Radiochemistry
Authors: Götte Hans , Kloss Gerhard 
Published: December 2003

AbstractNuclear‐medical diagnostic methods are widely used at present, examples being localization diagnosis e.g. of the thyroid, the kidney, and the spleen and function tests, e.g. on the thyroid and on the liver. For these tests it is essential to have organ‐specific vehicle substances that can be labeled with suitable radionuclides. For in‐vivo investigations, the exposure of the patient to radiation should be kept as small as possible, but the radiation must nevertheless be sufficient to allow the detection of the nuclide. Today, the therapeutic use of radionuclides is only small in comparison with their use in diagnosis.
Asymmetric Syntheses with the Aid of Homogeneous Transition Metal Catalysts
Authors: Bogdanović Borislav , Henc Biserka , Lösler Arnold , Meister Burkhard , Pauling Horst , Wilke Günther 
Published: December 2003

AbstractThe progress made in the field of homogeneous catalysis during the last five to six years has led, inter alia, to the development of highly selective catalysts for asymmetric syntheses. Homogeneous asymmetric hydrogenation, using well defined transition metal catalysts, may be achieved with optical yields of 85 to 90% or more. Catalytic reactions, in which the chiral centers are generated by CC bond formation, can result in optical yields of 70 to 80%. The hydrogenation catalysts consist primarily of rhodium(I) complexes containing “Homer phosphanes”, phosphanes with chiral C atoms, or optically active amides. Catalysts which induce optical activity through the formation of CC bonds have been developed from π‐allylnickel halides, Lewis acids, and phosphanes containing chiral C atoms. The results obtained signify a breakthrough in an area of catalysis previously restricted to syntheses involving enzymes.
Cyclooligomerization with Transition Metal Catalysts
Authors: Heimbach Paul 
Published: December 2003

AbstractThis report is concerned not only with the syntheses of new ring systems and the preparation of derivatives of known rings but also with new types of catalysts based upon, e. g., nickel, iron, molybdenum, manganese, and palladium. The broad applicability of the methylene insertion reaction as a method for identifying mono‐ and di‐methyl‐substituted eight‐, ten‐, and twelve‐membered rings is also demonstrated. A further section is concerned with the possible mechanism of CC bond formation in transition metal complexes; several earlier suggestions have been revised in the light of new experimental data. In addition, experimental results are discussed which indicate that the reactivity and selectivity of the complexes formed by the nickel‐ligand catalyst and olefins or alkynes depend upon the structure of the ligands.
The Variety of Thermal Pericyclic Reactions
Authors: Hendrickson James B. 
Published: December 2003

AbstractThe six‐electron thermal pericyclic reactions are examined systematically as to the number and kind which are possible by varying both the σ shell and the combinations of different atoms in all orientations, on both a six‐atom and a five‐atom framework. A simple unifying nomenclature is offered for these reactions, which number in the thousands. Further, in order to comprehend this very large number of possible reactions, they are also organized systematically in terms of their value for basic synthesis operations: construction, elimination, refunctionalization, etc. The methodology is aimed at providing a basis of selection for the invention of useful new reactions. A discussion of reaction energetics leads also to an analysis of molecular features which can facilitate reaction.
Polymers in Medicine
Authors: Lyman Donald J. 
Published: December 2003

AbstractThe problems encountered in the use of artificial materials in the body are discussed, using as example the artificial heart. In the quest for suitable materials, numerous investigations have been carried out, including, inter alia, studies on the adsorption of proteins on polymer surfaces and on the passivation of such surfaces by coating with proteins or by the growth of cell cultures. The development of passive artificial substances is also discussed.