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  • 1
    Electronic Resource
    Electronic Resource
    Pressure-induced reversible changes in secondary structure of poly(L-lysine): An ir spectroscopic study (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 837-844 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of elevated hydrostatic pressure on the secondary structure of poly(L-lysine) was studied using Fourier transform ir spectroscopy. According to changes observed in the amide I band, both the β-sheet and the unordered polypeptide undergo a reversible, pressure-induced conformational change to α-helix. The conversion occurs at a much higher pressure from the unordered conformer (∼ 9 kbar) than from the β-sheets (∼ 2 kbar). The structural changes were found to be slower at pH 〉 11, especially at the highest concentration investigated (10 wt%), reflecting the fact that extensive hydrogen-bond networks have to reorganize. This study shows that alterations of polypeptidic conformations induced by elevated hydrostatic pressure are reversible, but that an apparent irreversibility can result from kinetic factors in the case of conformational changes involving extensive rearrangements. The present results also show that the strength of the hydrogen bonds between the backbone amide groups is not the only factor that determines the closest packing of the polypeptide molecules.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290417
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  • 2
    Electronic Resource
    Electronic Resource
    Valinomycin and its interaction with ions in organic solvents, detergents, and lipids studied by Fourier transform IR spectroscopy (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1205-1212 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of valinomycin in a range of organic solvents of varying polarity and in detergent and lipid dispersions has been studied by Fourier transform ir Spectroscopy. In solvents of low polarity such as chloroform, ir spectra of valinomycin are fully consistent with the bracelet structure proposed on the basis of nmr Spectroscopy, showing a single narrow amide I component attributable to the presence of β-turns and a single band arising from nonhydrogen-bonded ester C=O groups. K+ complexation results in a downward shift in the amide I band frequency, indicating an increase in the strength of the amide hydrogen bonds, along with a shift to lower frequencies of the ester C=O absorption due to a reduction in electron density in these bonds upon complexation. Identical results were obtained with NH4+, a finding not previously reported.In solvents of both medium (CHCl3/DMSO 3 : 1) and high (pure DMSO) polarity, we find evidence of significant disruption of the internal hydrogen-bonding network of the peptide and the appearance of a band suggesting the presence of free amide C=O groups. In such solvents, complexation with K+ and NH4+ was not observed.The structure of valinomycin in detergent micelles resembles that in nonpolar organic solvents. However, changes were found in the amide I and ester carbonyl maxima as 2H2O penetrated the micelle which suggest significant interaction between the solvent and peptide. Complexation with K+ was reduced in cationic detergent micelles as a result of a decrease in the effective K+ concentration due to charge repulsion at the micelle surface.In lipid bilayers the structure again appears identical to that found in chloroform. As in detergent micelles, the amide I and ester carbonyl bands exhibit shifts that indicate interactions with solvent. Complexation with both K+ and NH4+ is efficient, producing spectral changes similar to those seen in organic solvents.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311008
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  • 3
    Electronic Resource
    Electronic Resource
    Infrared spectroscopic determination of hepatic nuclei oxidation (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 2 (1996), S. 39-45 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Infrared spectroscopy was applied to the investigation of normal and oxidatively modified hepatic nuclei. The hepatic nuclei were oxidized by two different free-radical-generating systems. Infrared spectra of oxidized nuclei were remarkably different from those of normal nuclei; the major alteration found in the spectra of oxidized nuclei was the emergence of a new population of nucleic acids with a hydrogen-bonding pattern different from that of the normal phosphodiester groups, and a redistribution of the hydrogen bonding of the protein amide groups of the histones, indicative of protein-structural rearrangements. The spectral changes in the phosphate bands of the nucleic acid resemble those previously observed in different types of malignant tissue, and suggest that there could be a link between nuclei oxidation and carcinogenesis which may involve a free-radical-mediated process. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Two-dimensional mid-IR and near-IR correlation spectra of ribonuclease A: Using overtones and combination modes to monitor changes in secondary structure (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 4 (1998), S. S19 
    Details
    ISSN: 1075-4261
    Keywords: near-IR ; protein folding ; denaturation ; ribonuclease A ; overtone and combination bands ; 2-dimensional correlation analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: We introduce near-IR spectroscopy as an ancillary tool for monitoring structural changes of proteins in aqueous solution using ribonuclease A (RNase A) as a model protein. The thermal unfolding of RNase A results in clear spectral changes in the near-IR and the mid-IR regions. In the near-IR the most pronounced changes are observed in the spectral region between 4820 and 4940 cm-1. The strong N—H combination band found at 4867 cm-1 in the spectrum of native RNase A shifts to 4878 cm-1 upon thermal unfolding. Hydrogen-deuterium exchange experiments that validate the N—H character of this mode can also be used to estimate the number of unexchanged amide protons after exposure to D2O. The transition profiles and temperatures derived from the temperature dependence of the N—H combination mode were found to be practically identical with those derived from the temperature dependence of the C=O amide I band in the mid-IR region, demonstrating that the near-IR region can be used as a conformation-sensitive monitor for the thermally induced unfolding of proteins in H2O solution. A 2-dimensional correlation analysis was applied to the mid-IR and near-IR spectra of RNase A to establish correlations between IR bands in both regions. The correlation analysis demonstrates that the thermal unfolding of RNase A is not a completely cooperative process; rather it begins with some changes in β-sheet structure, followed by the loss of α-helical structures, and then ending with the unfolding of the remaining β-sheets. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: S19-S29, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Salt bridge induced changes in the secondary structure of ionic polypeptides (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1181-1186 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The carboxylate-containing homopolypeptides poly(L-glutamate) [poly(Glu)] and poly(L-aspartate) [poly(Asp)] were found to form different types of ordered structures in the presence of poly(L-lysine) [poly(Lys)]. Mixing poly(Glu) with poly(Lys) in aqueous solution at neutral pH results in the instantaneous formation of a gel-like precipitate. The secondary structure of the gel precipitate can be best described as intermolecular antiparallel β-strands, involving the backbone amide groups, as evidenced by the presence of characteristic amide I bands in the ir spectrum at 1684 and 1612 cm-1. Mixing poly (Asp) with poly(Lys) under identical conditions results in the formation of a fine precipitate with a different morphology. Examination of the ir spectrum of the precipitate revealed that unlike poly(Glu), poly (Asp) did not yield any discrete secondary structure upon precipitation with poly(Lys). Addition of solutions containing Ca2+ or Mg2+ to the poly (Glu)/poly (Lys) aggregates resulted in complete dissolution of the gel, with the disappearance of the ir bands characteristic of the intermolecular hydrogen-bonded network. The results demonstrate the importance of salt bridges in establishing strong hydrogen bonds between the backbone amide groups. Reaggregation occurred upon heating the poly (Glu)/poly (Lys) mixture in the presence of Ca2+, but not in the presence of Mg2+ ions. In the presence of Ca2+ ions, aggregation and formation of an extended hydrogen-bonded network occurred upon heating. The aggregates formed upon heating poly (Glu)/poly (Lys) in the presence of Ca2+ were attributed solely to complexation of Ca2+ to the carboxylate groups of poly (Glu) with poly (Lys) remaining free in solution. Dissolution of the aggregate could be accomplished through addition of Mg2+ at room temperature. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320907
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  • 6
    Electronic Resource
    Electronic Resource
    A comparative infrared spectroscopic study of human breast tumors and breast tumor cell xenografts (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 1 (1995), S. 37-45 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Fourier transform infrared spectroscopy has been applied to the study of human breast tumors, human breast tumor cell lines and xenografted human tumor cells. The results presented indicate that substantial differences exist on a macroscopic level between human tumors, xenografted tumors and human tumor cell lines, which are related to the presence of a significant connective tissue matrix in the tumors. On a macroscopic level tumor cell xenografts appear, in spectroscopic terms, to be relatively homogeneous with a relatively weak signature characteristic of connective tissue. Differences on a microscopic level between adjacent small (30 μm2) areas of the same xenografted tumor could be detected, which were due to local variations in collagen content. In addition to variations in collagen content, variation in the deposition of microscopic fat droplets throughout both human and xenografted tumors could be detected. These results indicate the care with which infrared spectroscopic studies of tissues must be carried out to avoid incorrect interpretation of results due to an incomplete understanding of tissue pathology. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bspy.350010106
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of hydrostatic pressure on the phase state and molecular structure of aqueous lysolecithins: A Raman spectroscopic studyIssued as NRCC publication No. 24548. (1986)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 17 (1986), S. 335-340 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman spectrum of aqueous palmitoyl lysolecithin was monitored as a function of pressure between 1 bar and 26.1 kbar. The changes observed in these Raman spectra are discussed in terms of the effect of hydrostatic pressure on the phase state and the molecular structure of lysolecithins. At pressures between 1 and 1900 bar aqueous palmitoyl lysolecithin exists in a micellar state and at pressures above 1.9 kbar it converts into a series of three coagel phases. The critical pressures at 28°C are 1.9 kbar for the micellar to coagel I transition, 4 kbar for the coagel I to coagel II transition and 15 kbar for the coagel II to coagel III transition. The transition from the micellar phase to the coagel I phase has a high pressure hysteresis of 1.1 kbar, while the transitions between the three coagel phases show only negligible pressure hysteresis. The major change in structure occurs at 1.9 kbar where the cylindrical micellar phase converts to an interdigitated lamellar coagel phase; the structural changes at 4 kbar (coagel I/II transition) and at 15 kbar (coagel II/III transition) involve only a modification of the interchain packing.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250170408
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