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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 13 (1980), S. 396-402 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rotational barriers and 15N chemical shifts have been measured in a number of ureas and thioureas. As anticipated on the basis of the 15N shifts, several previously unobserved rotational barriers could be detected by using lanthanide reagents or a high field spectrometer. Nearly constant effects on both the rotational activation energy and the 15N shift are produced on going from ureas to the corresponding thioureas, and correlations are found between the ΔG
    Additional Material: 3 Tab.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 462 (1980), S. 231-240 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Darstellung, IR- und VIS-Spektren von Sulfatkomplexen des Uran(IV)Es wird über die Darstellung, die IR- und VIS-Spektren von neuen hydratisierten Sulfatkomplexen des Uran(IV) berichtet. Die bei der Hydrolyse entstehenden Hydroxo-sulfate werden ebenfalls charakterisiert. Alle Verbindungen wurden durch photochemische Reduktion von alkoholischen Lösungen gewonnen, die durch Zugabe von schwefelsauren Lösungen von Uranyl-sulfat zu den entsprechenden Sulfaten hergestellt worden waren. Die IR-Spektren erlauben, zwischen neutralen und basischen Sulfaten zu unterscheiden, deren Banden diskutiert werden. Die Sauerstoffumgebung des Uran(IV) in den Sulfatlösungen ruft dem UCL4 ähnliche VIS-Spektren hervor, so daß angenommen werden kann, daß die Ligandenfelder in diesen Fällen wenig Einfluß auf die Absorptionsspektren haben.
    Notes: This paper reports the preparation and the i. r. and visible spectra of new hydrated sulfate complexes of uranium(IV). The hydroxy-sulfates originated from hydrolyses are also characterized. All the compounds were isolated by photochemical reduction from alcoholic solutions which were obtained by the addition of sulfuric acidified solution of uranyl sulfate to the appropriate sulfate. The i. r. spectra allow to distinguish between neutral and basic sulfates the bands of which are discussed. The oxygen environment for uranium(IV) in the sulfate solutions originates visible spectra similar to those of the uranium(IV) chloride so that it might be supposed that ligand fields have little effects on the absorption spectra in these cases.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 19 (1980), S. 1329-1344 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complex of CH3Hg(II) with the accessible cysteines of glyceraldehyde-3-phosphate dehydrogenase (GAPD, EC 1.2.1.12) from rabbit muscle has been studied by phosphorescence and optically detected magnetic resonance (ODMR) spectroscopy. The wavelength dependence of the phosphorescence decay kinetics has also been measured. Comparison of CH3Hg(II)-GAPD with GAPD by these methods shows that a specific optically resolved tryptophan site of GAPD is perturbed by the interaction with a nearby mercury atom. The perturbation on the luminescence and ODMR properties is typical of an external heavy-atom effect. Based on the x-ray diffraction structure of the lobster enzyme, it is proposed that the heavy-atom effect results from the interaction of tryptophan-310 with CH3Hg(II) bound to cysteine-281 in the rabbit muscle enzyme.
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 1657-1666 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ionization constants of the tyrosyl groups of chymotrypsinogen and of nitrated-chymotrypsinogen (two tyrosyl residues nitrated) have been determined by difference spectrophotometry. In chymotrypsinogen, two of the four tyrosyl groups ionize without any time dependence. Above pH greater than ca. 12.5, time-dependent spectral changes are seen for 0.7 group equivalent. The data can be fitted to the values of pK′1 9.75 ± 0.07, pK′2 11.55 ± 0.05, pK′3 13.30 ± 0.05. In nitrated-chymotrypsinogen, the two nitrated tyrosyl residues have pK′1 6.44 and pK′2 8.30. For both proteins, these pK′ values are in agreement with those evaluated from potentiometric titration and calorimetric data using computer-assisted curve-fitting analysis.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 87-91 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Near- and far-uv CD spectra of microtubule protein preparations have been examined to study the possible role of protein conformation in relation to the kinetics of the self-assembly of these proteins into microtubules in vitro. Although tubulin can form conformations with high helical content under apolar solution conditions, this transformation is apparently not involved in self-assembly. There is no major perturbation of tubulin near-uv CD by reagents and solution conditions favoring assembly. Thus, in these preparations, tubulin, as dimer and as oligomer with MAPs, is effectively in the conformation in which it undergoes self-assembly. This conclusion is consistent with a hybrid model of assembly of microtubule protein involving direct incorporation of oligomeric species as an alternative to the condensation polymerization of tubulin dimer as the exclusive assembly mechanism.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 471-491 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical modes of DNA that displace one strand against the other are modeled by the motion of an oscillator in an asymmetric quartic double-well potential whose minima represent the A- and B-conformations. Assuming that the variation of the polarizability during vibration derives mainly from the tilting of the base rings relative to the helix axis, the total polarizability tensor is shown to possess approximately ellipsoidal symmetry and to depend nonlinearly on the instantaneous displacement of the two strands. The Raman spectrum of a collection of randomly oriented molecules is calculated. It consists of one or more peaks with characteristic shape. The depolarization ratio is 3/4, independent of molecular conformation and frequency. The results are discussed in the light of existing experimental and theoretical information.
    Additional Material: 8 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 19 (1980), S. 899-911 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The heats of ionization of protons, ΔHi, of oxidized and reduced horse heart cytochrome c in 0.15M KCl at 20°C were determined using a titration calorimeter which simultaneously afforded the potentiometric titration curve. Reproducibility of the thermal titrations is within 2%, and evaluation of the heats observed after the heat loss corrections is estimated to be within 5%. A single titration of oxidized cytochrome c from pH 11 to 3 is in excellent agreement with the thermal titration of this protein obtained with flow calorimetry. The thermal titration, however, is not reversible, due in part to the loss of titratable group(s) in this pH region and to the heat contribution of the acid and alkaline conformational changes which occur. Although of lesser magnitude, the reduced form also indicates similar thermal transitions. These differences are due solely to conformational contributions to the thermal process, since the potentiometric curves are reversible. The nature of the irreversibility for oxidized cytochrome c appears to involve the loss of a group with pK′ 8.9 and the shift of two groups from pK′ 5.6 to 4.8. Thermal difference curves for this process indicate that heats of -7.8 and -24.1 kcal/mol are liberated which are centered at pH 9.3 and 3.9, respectively.
    Additional Material: 10 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 629-632 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 9
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simultaneous curve fitting for the ionization parameters of oxidized and reduced horse heart cytochrome c in 0.15M KCl and 20°C yields values for the ionization constants (as pK′) and the heats of ionization (ΔHi) which can reconstruct either the potentiometric or thermal titration curves. Reduced cytochrome c requires 8 sets of groups, whereas oxidized cytochrome c requires 10 sets of groups. The additional groups in the oxidized preparation appear to involve the ferriheme (pK′, 9.25; ΔHi, 13.7 kcal/mol) and a tyrosine (pK′ ≃ 10.24) that is not present in the reduced form. The potentiometric and thermal difference curves (reduced - oxidized) involve the appearance of 17 kcal/mol centered at pH 9.7 and 5.8 kcal/mol centered at pH 4.9. The carboxyl groups in both species appear to be normal for the hydrogen-bonded form. Only one histidine has normal ionization properties (pK′, 6.7; ΔHi, 7.5 kcal/mol), as do 17 of the lysine residues (pK′, 10.8; ΔHi, 11.5 kcal/mol).
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2509-2531 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermodynamic parameters for the double-strand formation of the molecules rCAmG + rCUnG, m,n = 5-7, and dCAmG + dCTnG, m,n = 5,6, were measured from optical melting curves. Normal helices are formed when m = n. The deoxyoligomers are more stable than the ribo-oligomers, due to a more favorable enthalpy. Double helices with mismatched bases can be formed by mixing oligomers with m ≠ n. Such helices may form several possible structures. A structure with a dangling base is favored over a structure with a bulged base. The destabilization of the double strands by the formation of a bulged base was determined to be greater than 1.6 kcal/mol at 10°C. The extent of aggregation in the oligomer double strand rCA7G·rCU7G was determined using ultracentrifugation equilibrium. The possible effects of aggregation on the determination of the thermodynamic parameters for double-strand formation are discussed.
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