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  • Analytical Chemistry and Spectroscopy  (3)
  • Polymer and Materials Science  (3)
  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Values for the thermodynamic quantities, ΔH° = 11.8 ± 2.0 Kcal/mole and ΔS° = 43.6 ± 6.0 e.u., of the 3-13 helix-coil equilibrium of isolated S-peptide (19 residue N-terminal fragment of ribonuclease A) in aqueous solution (3 m M, 1M NaCl, pD 5.4) have been determined from a joint analysis of the Thr 3γ, Ala 6β, Phe 8meta, and Phe 8para 1H chemical shift vs temperature curves (-7 to 80°C) in several aqueous-trifluorethanol mixtures. Chemical shifts in the coil and in the helix have been determined for up to 16 protons belonging to the 3-13 fragment. Thermodynamic parameters have also been determined for C-peptide (13 residue fragment) and a number of S-peptide derivatives. From the variation of the values of the thermodynamic parameters at pD 2.5, 5.4, and 8.0, a quantitation of the two helix-stabilizing side-chain interactions can be made: (1) Δ(ΔH°) ≃ 5 Kcal/mole and Δ(ΔS°) ≃ 18 e.u. for the salt bridge Glu 2- … Arg 10+ and (2) Δ(ΔH°) ≃ 3 Kcal/mole and Δ(ΔS°) = 9 e.u. for the one in which the His 12+ imidazolium group is involved, presumably a partial stacking with the Phe 8 side chain.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 36 (1995), S. 751-763 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new thionin from barley, ω-hordothionin, has been shown to exist in aqueous solution as a mixture of two different isoforms in a 3:2 ratio, as revealed by a complete analysis of its two-dimensional 1H-nmr spectra. The conformational heterogeneity arises frtm cis-trans isomerism ahout the Phe 12-Pro 13 peptide bond, where the major, form corresponds to the cis conformation. The complete assignment of chemical shifts and nuclear Overhaiiser effects (NOES) of the two isoforms allow a detailed comparative analysis of their conformational properties, even though a complete calculation of their solution structures is not possible because of a somewhat limited number of NOE constraints. Structures for the two isomers could be modeled, however, on the basis of the high structural homology between ω-hordothionin and related γ-thionins, and under the conditions of satisfying all observed experimental data. The two isoforms adopt practically identical global folds and the structural changes imposed by cis-trans isomerization are confined to the region proximal to Pro 13. The cis-trans isomerism occurs in a conserved loop connecting the first β-strand of the triple-stranded antiparallel β-sheet and the α-helix. A comparative analysis of the sequences of this loop in the different thionins suggests that the cis-trans equilibrium about the X-Pro peptide bond depends on the size of the side chain of X (X = Gly in γ-thionins and Phe in ω-thionin). The structural homology of this new thionin with γ-thionins as well as with some scorpion toxins and insect defensins suggests that these proteins may share a common mode of functional activity. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 23 (1985), S. 2283-2289 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The microstructure of tetrahydrofuran (A)-3,3 dimethyloxetane (B) copolymers was studied by 13C-{1H}-NMR spectroscopy. Only the methyl carbons corresponding to the 3,3 dimethyloxetane unit appear as a singlet, whereas the other carbons present a more complicated spectral pattern than it would be expected if ∊ effects were negligible. The assignment of the resonance signals allowed the determination of the values of the probabilities of the different triads, which were in good agreement with those obtained from the reactivity ratios.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 21 (1983), S. 555-563 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H NMR chemical shifts and the spin-spin coupling constants of the non-exchangeable protons of the N-terminal 13-residue C-peptide of ribonuclease A, obtained by cleavage of the enzyme with cyanogen bromide, have been measured in a 5 mM solution in D2O (pH 3.0, 24°C) at 360 MHz. The titration parameters for end groups (Lys-1 and homo-Ser-13) and side chains (Lys-1, Glu-2, Lys-7, Glu-9 and His-12) have been determined. The chemical shifts, their temperature coefficients and the vicinal coupling constants, 3J(HNCH-α), for the exchangeable NH protons have been measured in a 5 mM solution in D2O/H2O (1:9 v/v) at pH 3.0. An assignment of observed signals to individual residue protons based on characteristic shifts, standard double resonance experiments, spectral simulations and titration shifts is proposed. All experimental evidence indicates that under the conditions studied the C-peptide is in a random coil form.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 8 (1976), S. 49-55 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complete analysis of the 1H NMR spectra of the six acetylated glycals as well as that of tetra-O-acetyl-2-hydroxy-D-glucal has been carried out. The conformation of these compounds, as determined from the proton couplings (±0.05Hz) obtained, has been interpreted in terms of a rapid interconversion equilibrium between the two possible dihydropyran half-chair conformations. A computer treatment of all observed couplings has been carried out to obtain optimized values for the populations and couplings characteristic of the two alternative half-chair conformations. The rotamer populations of the acetoxy-methyl group are discussed on the basis of the measured 5J16 and 5J36 couplings.
    Additional Material: 4 Ill.
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  • 6
    ISSN: 0749-1581
    Keywords: 13C NMR ; Diterpenes ; ent-Beyeranes ; ent-Beyer-15-enes ; Bicyclo[3.2.1]octanes ; Substituent effects ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed analysis of the 13C NMR spectra of 39 isomeric ent-beyer-15-enes and ent-beyeranes functionalized at C-7, C-14, C-15 and C-16 has been performed. This diterpenic skeleton is a good example of a semirigid bicyclo[3.2.1]octane system. The sensitivity of 13C shielding to the stereochemical environment, particularly in polyfunctional compounds, has been confirmed. In some cases the ent-beyer-15-enes and ent-beyeranes show similar behaviour to that of similarly functionalized bicyclo[3.2.1]octane derivatives, but in other cases the shielding effects are very different. The compounds studied are a good model for the evaluation of shielding effects in exo/endo isomers of strained and rigid carbocyclic compounds.
    Additional Material: 12 Tab.
    Type of Medium: Electronic Resource
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