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  • 1
    ISSN: 1573-4943
    Keywords: Secondary structure ; circular dichroism spectroscopy ; Raman spectroscopy ; neurotoxin ; nemertine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The secondary structure ofCerebratulus lacteus toxin B-IV, a neurotoxic polypeptide containing 55 amino acid residues and four disulfide bonds, was experimentally estimated by computer analyses of toxin circular dichroism (CD) and laser Raman spectra. The CD spectrum of the toxin displayed typical α-helical peaks at 191, 208, and 222 nm. At neutralpH, the α-helix estimates from CD varied between 49 and 55%, when nonrepresentative spectrum analytical methods were used. Analysis of the laser Raman spectrum obtained at a much higher toxin concentration yielded a 78% α-helix estimate. Both CD and Raman spectroscopic methods failed to detect any β-sheet structure. The spectroscopic analyses revealed significantly more α-helix and less β-sheet for toxin B-IV than was predicted from its sequence. To account for the difference between the 49–55% helix estimate from CD spectra and the 78% helix estimate from the Raman spectrum, we postulate that some terminal residues are unfolded at the low toxin concentrations used for CD measurements but form helix at the high toxin concentration used for Raman measurements. Our CD observations showing thatCerebatulus toxin B-IV helix content increases about 15% in trifluoroethanol or at highpH are consistent with this interpretation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 94 (1972), S. 3343-3345 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 98 (1976), S. 4296-4301 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 100 (1978), S. 2939-2944 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The circular dichroism (CD) spectrum of poly[(R)-oxypropylene] in a number of solvents has been measured in the vacuum ultraviolet region. Two CD bands were measured for cyclohexane, acetonitrile, and trifluoroethanol solutions. The CD spectrum was extended to 140 nm and three bands were measured in a 1,1,1,3,3,3-hexafluoro-2-propanol solution. The similarity of these four CD spectra in sign, shape, and intensity confirm that poly[(R)-oxypropylene] has similar conformations in all solvents studied, even though the optical rotatory dispersion (ORD) in the visible region is positive for the cyclohexane solution but negative for the alcohol solutions. A Kronig-Kramers transform of the two CD bands observed for the cyclohexane solution accounts for the observed positive ORD spectrum. In contrast, a third large and negative CD band centered below 160 nm is necessary to account for the negative ORD spectra observed for the alcohol solutions. Apparently the anomalous sign variation of the ORD curves observed in the visible region is due to subtle changes in the interplay of a large number of CD bands. Solvent interaction, observed as a blue shift of the first two CD bands for the alcohol solutions, could produce the subtle changes necessary to change the sign of the ORD curve in the visible region. The first two CD bands of poly[(R)-oxypropylene] are tentatively assigned as n—σ* and the third as an n—3s.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 12 (1973), S. 975-992 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism and absorption for five alkyl amino acids as zwitterions has now been measured to 160 nm. Two bands are found, the nπ* at long wavelengths and ππ* at short wavelengths. In an effort to extract conformal information from the circular dichroism measurmenths, the circular dichroism spectra for these molecules is calculated using an independent systems apporach. It is found that the signs calculated using these methods are quite reliable, but that reliable magnitudes must await more accurate data to use in the calculations. Comparing the signs for both the measured and calculated circular dichriosm it if possible to determine the region inhabited by the carboxylate anion chromophore of these amino acid zwitterions. The greatest failure of the calculations is that thay are unable to explain the sigmoidal shape of the nπ* transition in proline. The problems facing workers trying to make calculations to relate circular dichroism measurements to conformation are discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Circular dichroism spectra for acid-soluble calfskin collagen, gelatin, and poly(proline) II in solution have been extended into the vacuum ultraviolet region. The extended spectrum of gelatin reveals that the circular dichroism of this unordered polymer is more closely related to the spectrum of charged polypeptides than might be evident from near ultraviolet work. A short-wavelength band is found at about 172 nm, which corresponds in position, magnitude, and sign to a band recorded earlier for poly(L-glutamic acid) at pH 8.0. This band is observed in a helical structure for the first time in the vacuum ultraviolet circular dichroism and absorption spectra of poly(proline) II. Both circular dichroism and absorption spectra point to the assignement of this band as the nσ*. Neither the nσ* nor the expected positive lobe of the ππ* helix band is observed in the extended circular dichroism spectrum of collagen. We postulate that these two bands cancel here in analogy to the case of α-helical poly(L-glutamic acid).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 321-329 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intensities of the CD bands at about 275 and 190 nm were monitored for DNAs with different G + C contents as a function of temperature. The 190-nm bands showed a nearly complete and cooperative collapse on melting of the DNA, demonstrating that the CD arises from base-base interactions. The small cooperative change on melting shown by the 275-nm bands indicates that base-base interactions do not contribute much CD intensity here. No significant difference in melting temperature was found between the two wavelengths, but the lack of premelting in the 190-nm bands contrasted with the significant premelting in the 275 nm bands. Since the 190-nm bands are particularly sensitive to base-base interactions, the relative positions of the bases must not change much during premelting. Still, changes in such interactions would be noticeable on top of the low intensity of the 275-nm bands. Premelting is discussed in the light of recent studies on DNA conformation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 1763-1780 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We demonstrate that the isotropic absorption and linear dichroism in an unknown flow field can be used to determine base tilt in polynucleotides if three transitions are measured and the directions of the corresponding dipoles are known. The method is applied here to reach conclusions about the base tilt in poly(rA), poly(rA)+·poly(rA), and poly(rC). The respective values are: 28° tilt about the axis + 50° toward C8 from the C1′ → N9, and 25° tilt about the axis + 118° toward C5 from C1′ → N1. The results for poly(rA)+·poly(rA) are consistent with the accepted model. Spectra were measured for poly(rC)+·poly(rC), but definite conclusions must await reliable directions for transition dipoles. The dipole direction for the 218-nm transition in rC is found to be +13° or +43° toward C5 from C1′ → N1. The CD spectra to about 168 nm are presented and discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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