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  • Articles: DFG German National Licenses  (45)
  • Electronic Resource  (45)
  • Chemistry  (45)
  • 11
    Electronic Resource
    Electronic Resource
    A nonhelical, multiple β-turn conformation in a glycine-rich heptapeptide fragment of trichogin A IV containing a single central α-aminoisobutyric acid residue (1995)
    New York : Wiley-Blackwell
    Biopolymers 35 (1995), S. 21-29 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational properties of the protected seven-residue C-terminal fragment the lipopeptaibol antibiotic Trichogin A IV (Boc-Gly-Gly-Leu-Aib-Gly-Ile-Leu-OMe) has been examined in CDCl3 and (CD3)2SO by 1H-nmr. Evidence for a multiple β-turn conformation [type I′ at Gly(1)-Gly(2), type II at Leu(3)-Aib(4), and a type I′ at Aib(4)-Gly(5)] suggests that Leu(3) has preferred an extended or semiextended conformation over a helical conformation in CDCl3. This structure is thus in contrast to earlier observations of seven-residue peptides containing a single central Aib preferring helical conformations in both solution and crystalline slates. A structural transition to a frayed right-handed helix is absented in (CD3)2SO. These results suggest that nonhelical conformations may be important in Gly-rich peptides containing Aib. Further, the presence of amino acids with contradictory influences on backbone conformational freedom can lead to well-defined conformational transitions even in small peptides. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360350104
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  • 12
    Electronic Resource
    Electronic Resource
    Solid state and solution conformations of a helical peptide with a central gly-gly segment (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 515-526 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of amino acids with contrasting conformational tendencies on the stereochemistry of oligopeptides has been investigated using an octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-OMe, which contains two helix-promoting Aib residues and a central helix-destabilizing Gly-Gly segment. Single crystal x-ray diffraction studies reveal that a 3 10-helix is formed up to the penultimate Aib residue, at which point there is a helix reversal in the backbone, reminiscent of a C-terminal 6 → I hydrogen bond. The curious feature in the crystal is the solvation of the possible 6 → 1 bond by a CH3OH molecule, where the OH is inserted between O(3) and N(8) and participates in hydrogen bonds with both. The cell parameters are as follows: space group P212121, a = 10.649(4) Å, b = 15.694(5) Å, c = 30.181(8) Å, R = 6.7% for 3427 data (| F0| 〉 3σF) observed to 0.9 Å. Nuclear magnetic resonance studies in CDCl3 using NH group solvent accessibility and nuclear Overhauser effects as probes are consistent with a 3 10-helical conformation. In contrast, in (CD3)2SO, unfolding of the central segment results in a multiple β-turn structure, with β-turn conformations populated at residues 1-2, 3-4, and 6-7. CD studies in methanol-2,2,2-trifluoroethanol (TFE) mixtures also provide evidence for a solvent-dependent structural transition. Helical conformations are populated in TFE, while type II β-turn structures are favored in methanol. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Infrared spectroscopic study of C7 intramolecular hydrogen bonds in peptidesContribution No. 156 from the Solid State and Structural Chemistry Unit. (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 2091-2104 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ir-spectra in the N—H stretching region of Piv-Pro-NHMe and Boc-Pro-NHMe have been studied in carbon tetrachloride and chloroform solutions over a wide range of concentrations. Based on the concentration dependence of the N—H stretching bands, it has been shown that the characteristic N—H stretching band due to the C7 intramolecular hydrogen bond is around 3335 cm-1. Intermolecular hydrogen bonding also occurs to a small extent in these peptides, giving rise to a slight concentration dependence of the N—H stretching bands. The band around 3335 cm-1 need not necessarily be due to C7 hydrogen bonds alone as proposed by Tsuboi et al. or to intermolecular hydrogen bonding alone as proposed by Maxfield et al.; this conclusion is supported by studies on Boc-Leu-NHMe, which undergoes only intermolecular hydrogen bonding. We have shown that Z-Aib-Aib-OMe and Z-Aib-Ala-OMe form C7 intramolecular hydrogen bonds in addition to C5 intramolecular hydrogen bonds. The present studies also show that all the peptides studied exist in more than one conformation in solution.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360220908
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  • 14
    Electronic Resource
    Electronic Resource
    Helix aggregation in peptide crystals: Occurrence of either all parallel or antiparallel packing motifs for α-helices in polymorphs of Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1835-1845 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three crystalline polymorphs of the helical decapeptide, Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe, have been obtained. Antiparallel helix aggregation is observed in crystals grown from methanol (A), while completely parallel packing is observed in crystals from isopropanol (B) or an ethylene glycol-ethanol mixture (C). Crystals B and C are very similar in molecular conformation and packing. The packing motifs in crystals A and B consist of rows of parallel molecules, with an almost identical arrangement in both crystals. In crystal A, adjacent rows assemble with helix axes pointed in oppsite directions, whereas in crystal B all rows assemble with helix axes pointed in the same direction. Electrostatic interactions between helix dipoles do not appear to be a major determinant of packing modes. The structures also do not provide a ready rationalization of packing preferences in terms of side-chain interactions or solvation. The α-helix of the peptide in crystal A has seven 5 → 1 hydrogen bonds; the helix in crystal B is a mixed 310/α-helix. The crystal parameters are as follows. Crystal A: C51H92N10O13·CH3OH, space group P21 with a = 10.498(1) Å, b = 18.189(3) Å, c = 16.475(3) Å, β = 99.28(1)°, Z = 2, R = 9.6% for 1860 data. Crystal B: C51H92N10O13·C3H7OH, space group P21 with a = 10.534(1) Å, b = 28.571(4) Å, c = 11.055(2) Å, β = 95.74(1)°, Z = 2, R = 6.5% for 3251 data. Crystal C: C51H92N10O13·C2H5OH, space group P21, with a = 10.450(1) Å, b = 28.442(5) Å, c = 11.020(2) Å, β = 95.44(1)°, Z = 2, R = 14.8% (isotropic) for 1948 data.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291414
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  • 15
    Electronic Resource
    Electronic Resource
    Synthetic peptide helices in crystals: Structure and antiparallel and skewed packing motifs for α-helices in two isomeric decapeptides (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 719-731 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomeric decapeptides Boc-Aib-Ala-Leu-Ala-Aib-Aib-Leu-Ala-Leu-Aib-OMe (II) and Boc-Aib-Ala-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Aib-OMe (III), are predominantly a-helical with little effect on the conformation with interchange of Aib/Ala residues or Aib/Leu residues. The packing motif of helices in crystal II is antiparallel, whereas the helices pack in a skewed fashion in crystal III, with a 40° angle between neighboring helix axes. Crystal III contains a water molecule in a hydrophobic hole that forms hydrogen bonds with two carbonyl oxygens that also participate in 5 → 1 type hydrogen bonds. Values for helical torsional angles φ and ψ assume a much wider range than anticipated. Crystal II: C49H88N10O13, space group P21 with a = 16.625(2) Å, b = 9.811(5) Å, c = 18.412(3) Å, β = 99.79(1)°, Z = 2, R = 5.7% for 4338 data with |F0 | 〉 3σ(F). Crystal III: C49H88N10O13. 1/2H2O, space group P21, with a = 11.072(2) Å, b = 34.663(5) Å, c = 16.446(3) Å, β = 107.85(1) °, Z = 4, R = 8.3% for 6087 data with |F0| 〉 3σ(F).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300707
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  • 16
    Electronic Resource
    Electronic Resource
    Contrasting solution conformations of peptides containing α,α-dialkylated residues with linear and cyclic side chains (1995)
    New York : Wiley-Blackwell
    Biopolymers 35 (1995), S. 11-20 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational properties of α,α-dialkylated amino acid residues possessing acyclic (diethylglycine, Deg: di-n-propylglycine, Dpg; di-n-butylglycine, Dbg) and cyclic (1-amino-cycloalkane-1-carboxylic acid, Acnc) side chains have been compared in solution. The five peptides studied by nmr and CD spectroscopy are Boc-Ala-Xxx-Ala-OMe, where Xxx = Deg(I). Dpg (II), Dbg (III), Ac6c (IV), and Ac7c (V). Delineation of solvent-shielded NH groups have been achieved by solvent and temperature dependence of NH chemical shifts in CDCl3 and (CD3)2SO and by paramagnetic radical induced line broadening in pepiide III. In the Dxg peptides the order of solvent exposure of NH groups is Ala(1) 〉 Ala(3) 〉 Dxg(2), whereas in the Acnc peptides the order of solvent exposure of NH groups is Ala(1) 〉 Acnc(2) 〉 Ala(3). The nmr results suggest that Acnc peptides adopt folded β-turn conformations with Ala(1) and Acnc(2) occupying i + 1 and i + 2 positions. In contrast, the Dxg peptides favor extended C5 conformations. The conformational differences in the two series are clearly borne out in CD studies. The solution conformations of peptides I-III are distinctly different from the β-turn structure observed in crystals. Low temperature nmr spectra recorded immediately after dissolution of crystals of peptide II provide evidence for a structural transition. Introduction of an additional hydrogen-bonding function in Boc-Ala-Dpg-Ala-NHMe (VI) results in a stabilization of a consecutive β-turn or incipient 310-helix in solution. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360350103
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  • 17
    Electronic Resource
    Electronic Resource
    Omega amino acids in peptide design: incorporation into helices (1996)
    New York : Wiley-Blackwell
    Biopolymers 39 (1996), S. 769-777 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Incorporation of easily available achiral ω-amino acid residues into an oligopeptide results in substitution of amide bonds by polymethylene units of an aliphatic chain, thereby providing a convenient strategy for constructing a peptidomimetic. The central Gly-Gly segment of the helical octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-Ome(1) has been replaced by δ-amino-valeric acid (δ-Ava) residue in the newly designed peptide Boc-Leu-Aib-Val-δ-Ava-Leu-Aib-Val-OMe(2). 1H-nmr results clearly suggest that in the apolar solvent CDCl3, the δ-Ava residue is accommodated into a folded helical conformation, stabilized by successive hydrogen bonds involving the NH groups of Val(3), δ-Ava(4), and Leu(5). The δ-Ava residue must adopt a gauche-gauche-trans-gauche-gauche conformation along the central polymethylene unit of the aliphatic segment, a feature seen in an energy-minimized model conformation based on nmr parameters. The absence of hydrogen bonding functionalities, however, limits the elongation of the helix. In fact, in CDCl3, the folded conformation consists of an N-terminal helix spanning residues 1-4, followed by a Type II β-turn at residues 5 and 6, whereas in strongly solvating media like (CD3)2SO, the unfolding of the N-terminal helix results in β-turn conformations at Leu(1)-Aib(2). The Type II β-turn at the Leu(5)-Aib(6) segment remains intact even in (CD3)2SO. CD comparisons of peptides 1 and 2 reveal a “nonhelical” spectrum for 2 in 2,2,2-trifluoroethanol. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    “Teflon-coated peptides”: Hexafluoroacetone trihydrate as a structure stabilizer for peptides (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 125-128 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Helix packing of leucine-rich peptides: A parallel leucine ladder in the structure of Boc-Aib-Leu-Aib-Aib-Leu-Leu-Leu-Aib-Leu-Aib-OMe (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 324-330 
    Details
    ISSN: 0887-3585
    Keywords: X-ray diffraction analysis ; hydrogen bonds ; peptide conformation ; 310/α-helix transition ; antiparallel helix packing ; leucyl-leucyl interaction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The packing of peptide helices in crystals of the leucine-rich decapeptide Boc-Aib-Leu-Aib-Aib-Leu-Leu-Leu-Aib-Leu-Aib-OMe provides an example of ladder-like leucylleucyl interactions between neighboring molecules. The peptide molecule forms a helix with five 5→1 hydrogen bonds and two 4→1 hydrogen bonds near the C terminus. Three head-to-tail NH ċ O = C hydrogen bonds between helices form continuous columns of helices in the crystal. The helicial columns associate in an antiparallel fashion, except for the association of Leu ċ Leu side chains, which occurs along the diagonal of the cell where the peptide helices are parallel. The peptide, with formula C56H102N10O13, crystallizes in space group P212121 with Z = 4 and cell parameters a = 16.774(3) Å, b = 20.032(3) Å and c = 20.117(3) Å; overall agreement factor R = 10.7% for 2014 data with |Fobs| 〈 3σ(F); resolution 1.0 Å.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340120404
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  • 20
    Electronic Resource
    Electronic Resource
    Effects of organic solvents on protein structures: Observation of a structured helical core in hen egg-white lysozyme in aqueous dimethylsulfoxide (1997)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 29 (1997), S. 492-507 
    Details
    ISSN: 0887-3585
    Keywords: folding intermediates ; NMR ; protein folding ; dimethylsulfoxide ; near-UV circular dichroism ; lysozyme ; molten globules ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A partly folded state of hen egg-white lysozyme has been characterized in 50% DMSO. Low concentrations of DMSO (〈10%) have little effect on the overall folded conformation of lysozyme as seen from 1H NMR chemical shift dispersion. At increasing DMSO concentrations (〉10%) a cooperative transition of the structure to a new, partially folded state is observed. This transition is essentially complete by ∼50% DMSO. NMR studies show an overall decrease in chemical shift dispersion with marked broadening of many resonances. A substantial number of backbone and side chain-side chain NOEs suggests the presence of secondary and tertiary interactions in the intermediate state. Tertiary organization of the aromatic residues is also demonstrated by enhanced near-UV circular dichroism and limited exposure of tryptophans as monitored by iodide quenching of fluorescence. The intermediate state exhibits enhanced binding to hydrophobic dyes. Further, the structural transition from this state to a largely unfolded conformation is cooperative. H/D exchange rates of several amide protons and four indole protons of tryptophans (W28, W108, W111, and W123), measured by refolding from 50% DMSO at different time intervals reveal that protection factors are high for the helical domain, whereas NH groups in the triple stranded antiparallel β-sheet domain are largely solvent-exposed. An ordered hydrophobic core in the intermediate state comprising of helix A, helix B, and helix D is consistent with the high protection factors observed. The structured intermediate in 50% DMSO resembles the early kinetic intermediate observed in the refolding of hen egg white lysozyme, as well as a molten globule state of equine lysozyme at low pH. The results demonstrate the potential use of nonaqueous structure perturbing solvents like DMSO to stabilize partially folded conformations of proteins. Proteins 29:492-507, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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