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  • 1
    Electronic Resource
    Electronic Resource
    Evaluation of errors of interproton distances and correlation time determined from NMR cross-relaxation rates (1992)
    Springer
    Journal of biomolecular NMR 2 (1992), S. 573-582 
    Details
    ISSN: 1573-5001
    Keywords: Amaninamide ; Correlation time ; Evaluation of errors ; Interproton distances ; NOESY ; ROESY ; 2D NMR ; Peptides ; Cross-relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have analyzed a combined use of the two-dimensional nuclear Overhauser effect in the laboratory frame (NOESY) and in the rotating frame (ROESY) to determine interproton distances and correlation time in medium-sized rigid molecules (Davis, 1987). This method can be applied in the intermediate motional regime, 0.2 〈 ωoτc, 〈 5, (τc, correlation time, (ωo resonance frequency). Error limits depend on the motional regime and are smallest near ωoτc=1.14. The method was tested on six geminal proton pairs in the bicyclic octapeptide (S-deoxo-γ-[R]-OH-Ile3 amaninamide, Mw =870) for which at 297 K in DMSO, a correlation time of 1.0 ns, with a standard deviation of 0.12 ns, and an interproton distance of 1.87 Å, with standard deviation of 0.04 Å, are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02192846
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  • 2
    Electronic Resource
    Electronic Resource
    Hemoprotein Models Based on a Covalent Helix-Heme-Helix Sandwich: 2. Structural Characterization of CoIII Mimochrome I δ and δ Isomers (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 350-362 
    Details
    ISSN: 0947-6539
    Keywords: cobalt ; helical structures ; heme proteins ; NMR spectroscopy ; por-phyrinoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: FeIII mimochrome I is the prototype of a new class of hemoprotein models characterized by a covalent helix-heme-helix sandwich. It contains deuterohemin bound through two propionyl groups to two identical N- and C-terminal protected α-helical nonapeptides, each of which bears a His residue (a potential axial lig-and of the iron ion) in the central position. In order to understand better the three-dimensional structure of FeIII mimochrome I and its correlation with spectral properties, we have characterized the fully diamagnetic parent compound CoIII mimochrome I by UV/visible, CD, and NMR spectroscopy, coupled with conformational energy calculations. CoIII mimochrome I is a highly water-soluble compound present in solution as two isomers, which slowly interconvert only at very low pH values. These isomers were isolated and separately characterized. Their UV/visible spectral properties are very similar, while their CD spectral properties differ markedly in both the far UV and Soret regions. The isomers were identified by 1H NMR spectroscopy as diastereomers of the δ and δ type. This is the first example of an accurate three-dimensional structure determination in solution of a hemoprotein mimetic that allows a straightforward correlation between structure and spectral properties.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030306
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  • 3
    Electronic Resource
    Electronic Resource
    Radical polymerization of poly(butyl acrylate) in the presence of poly(L-lactic acid), 1. Synthesis, characterization and properties of blends (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 49-63 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Poly(L-milchsäure) ist ein biokompatibler, semikristalliner, thermoplastischer Polyester mit ungünstigen mechanischen Eigenschaften. Daher wurde in einem “reactive blending”-Prozeß ein Acrylkautschuk, n-Butylacrylat, mittels einer Suspensionspolymerisation in Wasser auf in einem organischen Lösungsmittel gelöste Poly(L-milchsäure) gepfropft. Die gebildeten Copolymeren konnten isoliert und durch NMR-Spektroskopie und DSC-Messungen charakterisiert werden. Die Untersuchung der mechanischen Eigenschaften ergab keine befriedigenden Ergebnisse, weil die Kautschukphase wahrscheinlich aus viskosen linearen Makromolekülen besteht und daher keine elastischen Eigenschaften besitzt. In weiteren Arbeiten soll der Syntheseweg so modifiziert werden, daß durch den Einbau von Diacrylaten eine zumindest partielle Vernetzung der Kautschukphase erreicht wird.
    Notes: Poly(L-lactic acid) is a biocompatible polyester, semicrystalline, thermoplastic, with low versatility in mechanical properties. To overcome this problem, a reactive blending procedure was performed by grafting an acrylic rubber, n-butyl acrylate, via water suspension polymerization onto poly(L-lactic acid) dissolved in an organic solvent. It was possible to isolate the copolymeric phase formed from the two polymers and characterize it by using NMR and DSC techniques. Mechanical tests on blends gave no satisfactory response, probably because the rubbery phase is composed essentially of viscous linear macromolecules, not able to perform elastic properties. Work is in progress to modify the synthetic pathway to incorporate diacrylates in order to realize a rubbery phase at least partially cross-linked.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052460104
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  • 4
    Electronic Resource
    Electronic Resource
    Conformational behaviour of A cyclolinopeptide a analogue: Two-dimensional NMR study of cyclo(Pro1-Pro-Phe-Phe-Ac6c-IIe-ala-Val8) (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 1 (1995), S. 330-340 
    Details
    ISSN: 1075-2617
    Keywords: Cyclolinopeptide A ; cyclooctapeptides ; NMR ; conformational studies ; restrained molecular dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclic octapeptide cyclo[-Pro1-Pro-Phe-Phe-Ac6c-Ile-ala-Val8-] [C8-Ac6c], containing the Pro1-Pro-Phe-Phe sequence, followed by a bulky helicogenic Cα,α-dialkylated glycine residue Ac6c (1-aminocyclohexane-1-carboxylic acid), and a D-Ala residue at position 7 has been synthesized. This cyclic peptide is a deletion analogue of the naturally occurring cyclic nonapeptide cyclolinopeptide A (CLA). It has been designed with the aim of studying the role that the Ac6c and D-Ala residues play on the conformational behaviour of the whole molecule and their influence on the conformation of the Pro1-Pro-Phe-Phe sequence when compared with cyclolinopeptide A.C8Ac6c has been investigated in chloroform and acetonitrile solutions by 2D NMR techniques. Only one set of sharp signals is observed in both solvents. This evidence strongly supports the hypothesis that only one conformational state exists in the chosen solvents. The interpretation of the experimental data points to the existence for C8-Ac6c of a very rigid structure stabilized by intramolecular hydrogen bonds. The measured NOE effects allow the calculation of internuclear distances, which have been used as restraints in molecular dynamic calculations. The proposed conformation of the molecule shows that the Pro-Pro-Phe segment retains the conformation observed in natural CLA both in solution and in the solid state and that the Ac6c residue indeed reinforces the ring rigidity not permitting the formation of any appropriate cavity in which inorganic cations could be complexed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/psc.310010508
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  • 5
    Electronic Resource
    Electronic Resource
    Elucidation of the structure of constrained bicyclopeptides in solution by two-dimensional cross-relaxation spectroscopy: Amatoxin analogues (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 2 (1996), S. 3-13 
    Details
    ISSN: 1075-2617
    Keywords: Structure of amatoxin analogues ; constrained bicyclopeptides ; NMR ; molecular dynamics ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The evaluation of peptide structures in solution is made feasible by the combined use of two-dimensional NMR in the laboratory (NOESY) and rotating frames (ROESY), and by the use of molecular dynamics calculations. The present paper describes how both the NMR method and molecular dynamics calculations were applied to very rigid synthetic bicyclic peptides that are analogues of natural amatoxins. The NMR theory, which allows the estimate of interatomic distances between interacting nuclei, is briefly discussed. The experimental data were compared with those of known solid-state structures. Three amatoxin analogues have been examined. Of these, one is biologically active (S-deoxo γ[R] OH-Ile3-amaninamide) and its structure in the solid state has recently been worked out. The second and third analogues (S-deoxo-Ile3 -Ala5-amaninamide and S-deoxo-D-Ile3 -amaninamide, respectively) are inactive and their solid-state structures are unknown. The data presented confirm the authors' previous hypothesis that lack of biological activity of S-deoxo-Ile3-Ala5- amaninamide is due to the masking of the tryptophan ring by the methyl group of L-Ala and not to massive conformational changes of the analogue.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/psc.44
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  • 6
    Electronic Resource
    Electronic Resource
    A conformational study in solution of pro-somatostatin fragments by NMR and computational methods (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 305-318 
    Details
    ISSN: 1075-2617
    Keywords: pro-somatostatin ; β-turn ; NMR ; computational methods ; conformational analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of a conformational study by nuclear magnetic spectroscopy and computational methods on a series of point-mutated synthetic peptides, containing 14 amino acid residues and mimicking the region containing the Arg-Lys dibasic cleavage site of pro-somatostatin, have confirmed the possible role of a well defined secondary structure in the recognition phenomenon by processing enzymes.The importance of the residues located near the Arg-Lys dibasic site in the C-terminal region of the pro-hormone for the cleavage of the precursor into somatostatin-14 has been confirmed. The present structural analysis indicates the occurrence of two β-turns in the 4-7 and 11-14 regions, flanking the cleavage site, for all the peptides recognized as substrates by the processing enzyme.Interestingly, in the point-mutated analogue not processed by the enzyme and containing the replacement of proline by alanine in position 5 the first β-turn is displaced by one residue and involves the Ala5-Arg8 segment. This observation may explain the lack of recognition by the maturation enzyme. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Conformational studies on synthetic peptides reproducing the dibasic processing site of pro-ocytocin-neurophysin (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 1 (1995), S. 251-265 
    Details
    ISSN: 1075-2617
    Keywords: Hormone biosynthesis ; ocytocin ; prohormone ; proteolytic processing ; β-turn ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic peptides reproducing the proteolytic processing site of pro-ocytocin were studied by different spectroscopic techniques, including circular dichroism, Fourier tranform infrared absorption, and mono and bidimensional nuclear magnetic resonance, in order to ascertain the possible role of three-dimensional structure in the recognition process by maturation enzymes. Experimental results were compared with energy minimization calculations and suggest that: (i) the region situated on the N-terminus of the Lys-Arg doublet may form a β-turn; (ii) the sequential organization of the residues participating in the β-turn determines the privileged relative orientation of the basic amino acid sidechains and the subtype of turn; and (iii) the peptide segment situated on the C-terminal side of the dibasic doublet may assume a helix arrangement. These findings, in spite of the limitations connected to the flexibility of linear peptides, seem to substantiate the hypothesis that structural motifs around the cleavage site could be important for recognition and processing. However, a straightforward correlation between details of the secondary structure and the in vitro reactivity toward a putative convertase is not yet possible.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/psc.310010406
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis, Characterization and Conformational Analysis of gp120-derived Synthetic Peptides That Specifically Enhance HIV-1 Infectivity (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 15-30 
    Details
    ISSN: 1075-2617
    Keywords: gp120/CD4 interactions ; HIV-1 PND ; conformation by CD and NMR ; solid-phase peptide synthesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of peptides patterned on the principal neutralizing domain of the HIV-1 envelope glycoprotein gp120 have been synthesized by solid-phase techniques. Interestingly, in vitro experiments have shown that some of these peptides specifically interact with CD4 and, in particular, that the peptide corresponding to the sequence 307-330 of the HIV-1 MN isolate was able to enhance infection in a dose- specific and not a strain-restricted way. To bypass problems observed in preliminary runs, several peptides were synthesized by both Fmoc and Boc chemistry. Comparison of the two strategies has allowed the set up of convenient protocols for the preparation of the target peptides in good yield, and with the high-purity grade needed for biological and physicochemical studies. Since the biological effects were present in the carboxyl-free C-terminal linear peptide but not in the amidated C-terminal analogue, preliminary conformational studies by circular dichroism and nuclear magnetic resonance techniques were also performed in an attempt to correlate these effects with possible contributions of structured conformations as predicted by theoretical calculations. The possibility of a β-turn structure for the crucial Gly-Pro-Gly-Arg sequence has been confirmed by 2D NMR experiments. Ongoing studies suggest the exploitation of the activating properties of the MN-derived peptides to design a more sensitive and innovative serological test based on the virus itself and not on anti-HIV antibodies, as is the case for the large majority of tests currently in use. © 1997 European Peptide Society and John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Solvent-mediated conformational transition in β-alanine containing cyclic peptides. VIIIprevious parts of this series are in Refs 1-7. (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 693-703 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present paper we describe the solution nmr structural analysis and restrained molecular dynamic simulation of the cyclic pentapeptide cyclo-(Pro-Phe-Phe-β-Ala-β-Ala). The conformational analysis carried out in CD3CN and dimethylsulfoxide (DMSO) solutions by nmr spectroscopy was based on interproton distances derived from rotating frame nuclear Overhauser effect spectroscopy spectra and homonuclear coupling constants. A restrained molecular dynamic simulation in vacuo was also performed to build refined molecular models. The molecule is present in both solvent systems as two slowly interconverting conformers, characterized by a cis-trans isomerism around the β-Ala5-Pro1 peptide bond. In CD3CN solution, the conformer with a cis peptide bond is quite similar to that observed in the solid state, while the conformer containing all trans peptide bonds is characterized by an intramolecular hydrogen bond stabilizing a C10- and a C13-ring structure. In DMSO solution, the trans isomer is partly similar to that observed in CD3CN solution while the cis isomer is different from that observed in the solid state. The effect of the solvent in stabilizing different conformations was also investigated in DMSO-CD3CN solvent mixtures. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Bicyclic peptides: Solution conformation and Ca2+ binding of the heterodetic bicyclic decapeptide cyclo(Glu1-Leu2-Pro3-Gly4-Ser5-Ile6-Pro7-Ala8)-cyclo(1γ → 5β) Phe9-Gly10 (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 305-317 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational behavior of a heterodetic bicyclic decapeptide (BCPLT) in the absence and in the presence of calcium ions has been studied by means of mono and two-dimensional nmr techniques. Free BCPLT possesses a quite compact structure stabilized by intramolecular bonds and turns. In the structure a cluster of carbonyls is located in a cavity that is supposed to be the cation binding site.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280131
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