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  • 1
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,4,7,10-Tetraazacyclododecane having β-ethylphosphoryl pendant groups on the nitrogen atoms can form a complementary ligand for the Cu cation. It gives rise to a square pyramidal complex of [CuL]2+ compositions, the ligand entering this complex with a slight energy strain. © 1996 John Wiley & Sons, Inc.
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved cube method has been developed for calculating the intensity of diffuse x-ray scattering of macromolecules in solution using a certain set of their atomic coordinates. The technique is based on the ideas of B. Lee and F. M. Richards [(1971) J. Mol. Biol. 55, 374-400] and Richards [(1977) Annu. Rev. Biophys. Bioeng. 6, 151-176] on the possibility of estimating the molecular and accessible surface of a particle by “rolling” a sphere, simulating a water molecule, on its molecular surface. It is shown that this technique is more advantageous than earlier versions of the cube methods. The improved technique for calculating scattering curves was utilized for several globular proteins, and for the first time, reliable scattering curves were obtained for protein-“bound” water complexes. In the case of globular proteins and tRNA, this technique has permitted a strict evaluation of their accessible surfaces, their volumes, and, apparently for the first time, their complete molecular surfaces.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1855-1857 
    ISSN: 1434-1948
    Keywords: Fullerenes ; Titanium ; Complexes ; X-ray analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first fullerene complex of titanium Cp2Ti(η2-C60) has been synthesized by reaction of the bis(trimethylsilyl)-acetylene complex of titanocene Cp2Ti(η2-Me3SiC2SiMe3) with an equimolar amount of fullerene-60 in toluene at room temperature under argon. An X-ray diffraction study of the complex has shown that it has the structure of a titanacyclopropane derivative.
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  • 4
    ISSN: 0749-1581
    Keywords: non-empirical calculations ; NQR parameters ; Townes and Dailey theory ; three-membered rings ; LMO approach ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nuclear and electronic contributions to the EFG tensor components eqii at 14N, 17O, 33S and 35Cl nuclei in aziridine, methylaziridine, chloroaziridine, oxirane and thiirane were determined. The nuclear contributions were calculated within classical representations, while electronic contributions were calculated non-empirically using a 6-31G* basis set within the framework of the LMO approach. On the basis of the analysis of the contributions to the EFG tensor components from definite bond and lone-pair orbitals, the main concepts of the Townes and Dailey approach were tested.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 52 (1961), S. 169-177 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The method of telomerization has been employed in the synthesis of the telomer homologs of polyacrylate esters with successively increasing degrees of polymerization (n) and of telomers differing in the nature of the polyester chain. Compounds have been synthesized of the general formula where R and R1are alkyl or aryl radicals and n = 2, 4, 8, and 20. With changes in (n) from 2 to 20 the structural viscosity of the polyacrylate esters increased from 150 to 8000 centistokes (at 20°), the specific gravity from 1.213 to 1.308, and nD20 from 1.515 to 1.5479. The presence of double bonds in the molecules of the polyacrylate esters synthesixed made it possible to carry out their polymerization (hardening) in the presence of radical chain initiators with the formation of glassy or elastic, insoluble, nonmelting polymers of sufficient thermal stability and endowed with a number of valuable properties so as to be of considerable practical potentiality. The changes in physical properties of the reaction system (gelation, gradual increase in density and finally the formation of a glass structure) in the course of the polymerization beginning from the very early stages (the gelation point is reached at 5-10% conversion) are responsible for a number of specificities in the kinetics of the hardening of polyacrylate esters. Owing to this we undertook a detailed investigation of the polymerization kinetics under widely varying conditions. Polymerization in bulk takes place autocatalytically, since with increasing degree of structuration in the course of polymerization the rate of diffusion of free radical diminished, leading to a decrease in rate of chain termination. The rate of reaction begins to diminish markedly only at large extents of polymerization. A study has been made of the effect of diluting the reaction mixture with an inert solvent, of the initiation rate, nature of the initiating agent, temperature, chemical structure of the initial polyacrylate ester, as well as of the addition of inhibiting agents on the polymerization kinetics. The results obtained have been discussed from the standpoint of the capacity of the system for structuration under the various conditions of reaction. The heats of hardening of the polyacrylate esters with successively increasing distance between their values have been discussed with respect to the reaction mechanism.
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  • 6
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Tumor adaptation to chronic energy starvation in vivo was studied on Ehrlich ascites carcinoma (EAC) cells. EAC cells were isolated from mice and incubated in a glucose-free medium containing blocators of mitochondrial ATP generation (rotenone, 2,4-dinitrophenol, or oligomycin). ATP level in the treated cells decreased to 3-4% of the initial during 30 min of the incubation. The aggregation of cytoskeletal proteins, blebbing, and necrotic death within 2-3 h were observed in ATP-depleted EAC which were isolated and treated in the exponential phase of growth (5 days after inoculation), whereas stationary EAC (8 days after inoculation) were considerably more resistant to ATP depletion, and actin aggregation as well as bleb formation were suppressed in these cells despite the ATP loss. In contrast to the exponentially growing cells, thermotolerance and unexpected expression of inducible HSP68 and HSP27 as well as an elevated level of HSP90 were found in stationary EAC. Since the stationary cells had decreased content of ATP, ATP/ADP ratio, and energy charge, we suggest that this energy dysbalance may be conducive to HSP induction within the ascites tumor in vivo, and, at the same time, EAC cells with elevated content of HSPs acquire resistance to chronic energy starvation occurring in late stages of the tumor growth. © 1995 Wiley-Liss Inc.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 18 (1997), S. 360-364 
    ISSN: 0197-8462
    Keywords: extremely-low-frequency (ELF) ; thymic lymphoma/leukemia ; dimethylbenz-(α)anthracene (DMBA) ; tumor promotion ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Several epidemiological investigations have suggested an increased incidence of lymphoma, leukemia, and brain tumor in residents living near power transmission lines. However, some observers failed to confirm such a positive correlation. To evaluate the effects of extremely low frequency (ELF) magnetic fields on leukemogenesis, an experimental animal model was used, in which thymic lymphoma/leukemia was induced by dimethylbenz(α)anthracene (DMBA) injected subcutaneously into the interscapular region of newborn mice within 24 h after birth. Beginning at the second week of age, 165 mice were exposed to 50 Hz magnetic field at 1 mT, 3 h/day, 6 days/week for 16 weeks, and 155 animals exposed to sham conditions. All surviving animals were killed by cervical dislocation at the age of 32 weeks and were examined pathologically. The results showed that the incidences of advanced thymic lymphoma, complicated with lymphomatous leukemia, were 21.8 and 23.9% in the two groups, respectively, without statistically significant differences. But dense metastatic infiltration by lymphoma cells into liver in the field exposure group greater (50%) than that in the sham-exposure group (16.2%) was observed (χ2 = 9.847, P 〈 0.01). To determine whether ELF acts as a tumor promoter, further experiments are required. Bioelectromagnetics 18:360-364, 1997. © 1997 Wiley-Liss, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 559 (1988), S. 171-181 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Über die Umsetzung der Di- und Tetrafluoride des Xenons mit Fluoriden der AlkalimetalleDie Umsetzung von XeF2 und XeF4 mit Verbindungen des Typs MF (M = Na, K, Rb, Cs) wird untersucht. Es bilden sich dabei Hexafluoroxenate(IV) mit der Summenformel M2XeF6, die das oktaedrische Anion XeF62- enthalten. Cs2XeF6 und Rb2XeF6 bilden monokline Kristalle (a0 = 853,7(5); b0 = 669,6(2); c0 = 843,6(5) pm; β = 121,7(1)° für Cs2XeF6 und a0 = 812,6(4); b0 = 631,9(2); c0 = 795,6(4) pm; β = 121,5(1)° für Rb2XeF6). K2XeF6: tetragonal mit a0 = 868,8(2); c0 = 747,8(2) pm; Na2XeF6: hexagonal mit a0 = 642,1(3); c0 = 844,8(5) pm. Es wird gezeigt, daß sich die Verbindungen M2XeF6 inkongruent in wasserfreiem HF lösen, wobei sich unter anderem das Solvolyseprodukt XeF4 bildet. Es wird nachgewiesen, daß die Thermolyse von M2XeIVF6 und M2XeVIF8 unter ähnlichen Bedingungen abläuft.
    Notes: Interaction of XeF2 or XeF4 with MF (M = Na, K, Rb, Cs) has been studied. Hexafluoroxenates(IV) M2XeF6 containing the octahedral XeF62- anion (in accordance with spectroscopy data) were formed in the reaction. Cs2XeF6 and Rb2XeF6 form monoclynic crystals (a0 = 853.7(5); b0 = 669.6(2); c0 = 843.6(5) pm; β = 121.7(1)° and a0 = 812.6(4); b0 = 631.9(2); c0 = 795.6(4) pm; β = 121.5(1)°, respectively). K2XeF6 has a tetragonal lattice (a0 = 868.8(2); c0 = 747.8(2) pm), while Na2XeF6 has a hexagonal one (a0 = 642.1(3); c0 = 844.8(5) pm). M2XeF6 is shown to dissolve in unhydrous HF incongruently, one of the solvolitic products being XeF4. Thermolysis of M2XeIVF6 and M2XeVIF8 were shown to proceed under similar temperatures.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 559 (1988), S. 182-190 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Über die Säure-Base-Eigenschaften des Di- und Tetrafluorxenons in Reaktionen bei erhöhten TemperaturenEs wurde die Reaktion von Xenondifluorid und Xenontetrafluorid mit Fluorkomplex-Verbindungen verschiedener Übergangsmetalle bei erhöhter Temperatur untersucht. Unter diesen Bedingungen wurde die Bildung von Anionenkomplexen M2XeIVF6 festgestellt. Es wurde gezeigt, daß XeF4 unabhängig davon, ob es direkt in die Reaktion eingeführt wird oder dort aus XeF2 entsteht, zwei typische Eigenschaften aufweist: die eines Oxydationsmittels (〉 300°C) und einer Säure (zwischen 150°C und 300°C). Das Reaktionsverhalten des XeF4 hängt ferner von den Eigenschaften des Reaktionspartners ab. Die Eigenschaften der Xenonfluoride als Lewis-Säuren folgen der Reihe: XeF6 ≈ XeF4 ≫ XeF2.
    Notes: Reaction of xenon di- and tetrafluoride with different transition element fluorocomplexes at high temperatures has been studied. The formation of XeIV anionic complexes M2XeF6 has been found. XeF4 is shown to reveal two kinds of properties: oxidative (higher than 300°C) and acidic (between 150-300°C), independently whether it was initially introduced into the system or arised in it from XeF2. The reaction path of xenon tetrafluoride is shown to depend upon the other reagent properties. The conclusion is made that Lewis acidic properties of xenon fluorides decrease as follows: XeF6 ≈ XeF4 ≫ XeF2.
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  • 10
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on equilibrium binding studies, as well as on kinetic investigations, two types of interactions of Cu2+ ions with native DNA at low ionic strength could be characterized, namely, a nondenaturing and a denaturing complex formation. During a fast nondenaturing complex formation at low relative ligand concentrations and at low temperatures, different binding sites at the DNA bases become occupied by the metal ions. This type of interaction includes chelate formation of Cu2+ ions with atoms N(7) of purine bases and the oxygens of the corresponding phosphate groups, chelation between atoms N(7) and O of C(6) of the guanine bases, as well as the formation of specific intestrand crosslink complexes at adjacent G°C pairs of the sequence dGpC. CD spectra of the resulting nondenatured complex (DNA-Cu2+)nat may be interpreted in terms of a conformational change of DNA from the B-form to a C-like form on ligand binding. A slow cooperative denaturing complex formation occurs at increased copper concentrations and/or at increased temperatures. The uv absorption and CD spectra of the resulting complex, (DNA-Cu2+)denat, indicate DNA denaturation during this type of interaction. Such a conclusion is confirmed by microcalorimetric measurements, which show that the reaction consumes nearly the same amount of heat as acid denaturation of DNA.From these and the kinetic results, the following mechanism for the denaturing action of the ligands is suggested: binding of Cu2+ ions to atoms N(3) of the cytosine bases takes place when the cytosines come to the outside of the double helix as a result of statistical fluctuations. After the completion of the binding process, the bases cannot return to their initial positions, and thus local denaturation at the G·C pairs is brought about. The probability of the necessary fluctuations occurring is increased by chelation of Cu2+ ions between atoms N(7) and O of C(6) of the guanine bases during nondenaturing complex formation, which loosens one of the hydrogen bonds within the G·C pairs, as well as by raising the temperature. The implications of the new binding model, which comprises both the sequence-specific interstand crosslinks and the described mechanism of denaturing complex formation, are discussed and some predictions are made. The model is also used to explain the different renaturation properties of the denatured complexes of Cu2+, Cd2+, and Zn2+ ions with DNA.In temperature-jump experiments with the nondenatured complex (DNA-Cu2+)nat, a specific kinetic effect is observed, namely, the appearance of a lag in the response to the perturbation. The resulting sigmoidal shape of the kinetic curves is considered to be a consequence of the necessity of disrupting a certain number of the crosslinks existing in the nondenatured complex before the local unwinding of the binding regions (a main step of denaturing complex formation) may proceed.
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