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  • 1
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In dimethylformamide the ESR spectra of the radical anions of dibenzo[f,h]quinoxaline and dibenzo[a,c]phenazine both exhibit line broadening due to slow molecular tumbling over a wide temperature range. Similar effects are also observed in the spectra of the radical anions of quinoxaline and phenazine. The ESR spectra of the radical anions of dibenzo[f,h]quinoxaline and dibenzo[a,c]phenazine have been interpreted by computer reconstruction and the hyperfine splitting constants assigned with the aid of Hückel unpaired electron density calculations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomeric prostaglandins, A and B, can be readily distinguished by differences in the mass spectra of their derivatives. The mass spectra of the PGA1- or PGA2-methyl ester (ME)-trimethyl silyl (TMS) ether derivatives have a prominent ion at [M - 71]+ or [M - C5H11]+ while those of the PGB1- or PGB2-ME-TMS derivatives have a predominant ion at [M - 99]+ or [M - C6H11O]+ in addition to that at [M - 71]+. Ions of similar origin characterize the spectra of the PGA1- or PGA2-TMS ether-TMS ester and PGB1- or PGB1-TMS-TMS derivatives, respectively. The fragmentation of other derivatives of PGA1, PGA2, PGB1 and PGB2 such as the ME-t-Bu-DMS (t-butyl-dimethylsilyl ether); ME-MO (methoxime)-TMS; ME-MO-Ac (acetate), and ME-Ac are also described comparatively. The composition of important ions was confirmed by deuterium labeling and/or high resolution mass spectroscopy, where appropriate. The potential advantages and limitations of the derivatives for quantitative analysis of prostaglandins by the specialized technique of multiple ion detection (MID) are described.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0749-1581
    Keywords: ESR ; Cation migration ; Line-width variation ; 2-Pivaloyl-1,4-benzoquinone ; Radical anion ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2-pivaloyl-1,4-benzoquinone radical anion has been prepared by alkali metal reduction in tetrahydrofuran in the presence of dibenzo-18-crown-6, 15-crown-5, or 12-crown-4, and its ESR spectrum in each system has been recorded over a range of temperatures. Line-width variation in the ESR spectrum is observed in some systems. This line-width variation has been attributed to cation migration between sites adjacent to the non-equivalent carbonyl groups rather than to restricted rotation of the pivaloyl group. In some systems, however, the rate of migration is too fast and in others too slow, compared with the time-scale of the ESR experiment, for line-width variation to be observed. The influence of each crown ether upon the rate of cation migration has been found to depend upon the size of the crown ether ‘cavity’ compared with the size of the alkali metal counter-ion.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5001
    Keywords: Structural biology ; Isotopic enrichment ; Protein folding ; Protein degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Human ubiquitin is a 76-residue protein that serves as a protein degradation signal when conjugated to another protein. Ubiquitin has been shown to exist in at least three states: native (N-state), unfolded (U-state), and, when dissolved in 60% methanol:40% water at pH 2.0, partially folded (A-state). If the A-state represents an intermediate in the folding pathway of ubiquitin, comparison of the known structure of the N-state with that of the A-state may lead to an understanding of the folding pathway. Insights into the structural basis for ubiquitin's role in protein degradation may also be obtained. To this end we determined the secondary structure of the A-state using heteronuclear three-dimensional NMR spectroscopy of uniformly 15N-enriched ubiquitin. Sequence-specific 1H and 15N resonance assignments were made for more than 90% of the residues in the A-state. The assignments were made by concerted analysis of three-dimensional 1H-15N NOESY-HMQC and TOCSY-HMQC data sets. Because of 1H chemical shift degeneracies, the increased resolution provided by the 15N dimension was critical. Analysis of short- and long-range NOEs indicated that only the first two strands of β-sheet, comprising residues 2–17, remain in the A-state, compared to five strands in the N-state. NOEs indicative of an α-helix, comprising residues 25–33, were also identified. These residues were also helical in the N-state. In the N-state, residues in this helix were in contact with residues from the first two strands of β-sheet. It is likely, therefore, that residues 1–33 comprise a folded domain in the A-state of ubiquitin. On the basis of 1Hα chemical shifts and weak short-range NOEs, residues 34–76 do not adopt a rigid secondary structure but favor a helical conformation. This observation may be related to the helix-inducing effects of the methanol present. The secondary structure presented here differs from and is more thorough than that determined previously by two-dimensional 1H methods [Harding et al. (1991) Biochemistry, 30, 3120–3128].
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  • 5
    ISSN: 1573-5001
    Keywords: Structural biology ; Isotopic enrichment ; Protein-ligand interactions ; Cofactor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Sequence-specific 1H and 15N resonance assignments have been made for all 145 non-prolyl residues and for the flavin cofactor in oxidized Desulfovibrio vulgaris flavodoxin. Assignments were obtained by recording and analyzing 1H−15N heteronuclear three-dimensional NMR experiments on uniformly 15N-enriched protein, pH 6.5, at 300 K. Many of the side-chain resonances have also been assigned. Observed medium-and long-range NOEs, in combination with 3JNHα coupling constants and 1HN exchange data, indicate that the secondary structure consists of a five-stranded parallel β-sheet and four α-helices, with a topology identical to that determined previously by X-ray crystallographic methods. One helix, which is distorted in the X-ray structure, is non-regular in solution as well. Several protein-flavin NOEs, which serve to dock the flavin ligand to its binding site, have also been identified. Based on fast-exchange into 2H2O, the 1HN3 proton of the isoalloxazine ring is solvent accessible and not strongly hydrogen-bonded in the flavin binding site, in contrast to what has been observed in several other flavodoxins. The resonance assignments presented here can form the basis for assigning single-site mutant flavodoxins and for correlating structural differences between wild-type and mutant flavodoxins with altered redox potentials.
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  • 6
    ISSN: 1573-5001
    Keywords: Chemical shift index ; Flavodoxin ; Isotopic enrichment ; Nitrogen-15 ; Protein ; Secondary structure ; 3D NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Sequence-specific 1H and 15N resonance assignments have been made for 137 of the 146 nonprolyl residues in oxidized Desulfovibrio desulfuricans [Essex 6] flavodoxin. Assignments were obtained by a concerted analysis of the heteronuclear three-dimensional 1H-15N NOESY-HMQC and TOCSY-HMQC data sets, recorded on uniformly 15N-enriched protein at 300 K. Numerous side-chain resonances have been partially or fully assigned. Residues with overlapping 1HN chemical shifts were resolved by a three-dimensional 1H-15N HMQC-NOESY-HMQC spectrum. Medium-and long-range NOEs, 3JNH α coupling constants, and 1HN exchange data indicate a secondary structure consisting of five parallel β-strands and four α-helices with a topology similar to that of Desulfovibrio vulgaris [Hidenborough] flavodoxin. Prolines at positions 106 and 134, which are not conserved in D. vulgaris flavodoxin, contort the two C-terminal α-helices.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 7 (1973), S. 1011-1011 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 1 (1974), S. xi 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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