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  • Analytical Chemistry and Spectroscopy  (12)
  • Atomic, Molecular and Optical Physics  (6)
  • 1
    Digitale Medien
    Digitale Medien
    Ab-initio molecular orbital study of the cis/trans conformations of the peptide bond (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 117-127 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ab-initio molecular orbital (MO) calculations on the model peptide, N-methylacetamide (NMA), protonated N-methylacetamide (p-NMA), and two natural dipeptides, glyclyglycine (Gly-Gly) and alanylalanine (Ala-Ala), are reported. Calculations at the STO-3G. 3-21G. and 4-31 G levels account for the predominance of the trans conformation in globular proteins. By use of p-NMA as a model precursor, the formation of the peptide bond is studied by the methods of molecular quantum mechanics. These calculations lead to the conclusion that the trans conformation should predominate, in agreement with the crystal structural data on globular proteins. In order to reduce the amount of computer time required for what are evidently the first ab-initio MO calculations on natural dipeptides, force-field calculations have been employed to obtain the conformational potential energy maps.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560200710
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  • 2
    Digitale Medien
    Digitale Medien
    Angular aspects of exchange correlation and the fermi hole (1985)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 27 (1985), S. 439-449 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The complete (nonreduced) αα probability density functions evaluated from the Hartree-Fock and simple Hartree product wavefunctions have been used to elucidate the angular features of spin correlation and the Fermi hole in the 23S state of helium and the ground state of beryllium. This approach shows that the local Fermi holes in these two cases are very similar and that the Fermi hole is essentially spherically symmetric when the reference electron is close to the nucleus. As the reference electron is removed to larger radial distances, appreciable polarization of the Fermi hole is observed. The polarization is greater in the direction of the nucleus than away from the nucleus, contrary to the situation in the Coulomb hole of the helium ground state where the polarization is greater away from the nucleus than toward the nucleus. Several other differences between the He 23S Fermi hole and the He 11S Coulomb hole are noted.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560270408
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  • 3
    Digitale Medien
    Digitale Medien
    On the relationship between the electron-pair distribution function and the correlation energy of an atom (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1-9 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The pair distribution function h(r12;r1, γ) and the virial theorem are used to derive a general expression for the local contributions to the total correlation energy of an atom. A direct link between correlation effects and the correlation energy is obtained by use of G(r1, γ) and Γ(r1, y). The former is the probability associated with a given choice of r1 and γ, while the latter describes the local contribution to the correlation energy. Explicit calculations for the ground state of helium indicate that the angular dependence of the local contribution to the correlation energy is essentially independent of r1, whereas the local correlation energy shows a strong r1 dependence. The maximum contribution to the correlation energy occurs at intermediate values of γ where there is close agreement between the Hartree-Fock and exact densities.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560290102
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  • 4
    Digitale Medien
    Digitale Medien
    Statistical electron correlation coefficients for 29 states of the heliumlike ions (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 33-42 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Statistical electron correlation coefficients provide overall measures of the difference between the electron pair density and the product of one-electron densities. Explicitly correlated wave functions are used to compute radial and angular correlation coefficients for 29 low-lying states (n1S, n3S, n1P, n3P, n1D, and n3D with n 〈 7) of the two-electron ions from helium through Ne8+. This data base of 1566 correlation coefficients permits a systematic study of trends with respect to variation of nuclear charge, degree of excitation, angular momentum, and spin multiplicity. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560480807
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  • 5
    Digitale Medien
    Digitale Medien
    Collision-induced dissociations of deprotonated peptides. Dipeptides containing methionine or cysteine (1993)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 623-625 
    Details
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The collisional activation mass spectra of the [M - H]- ions of dipeptides containing Met or Cys show the usual backbone fragmentation allowing the sequence of the peptide to be determined. A methionine residue may be identified by the presence of a pronounced peak resulting from loss of MeSH, while a cysteine residue may be identified by the presence of a peak corresponding to loss of either H2S or (H2S + CO2).
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/rcm.1290070714
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  • 6
    Digitale Medien
    Digitale Medien
    A simple method for differentiating Leu and Ile in peptides. The negative-ion mass spectra of [M — h]- ions of phenylthiohydantoin Leu and Ile (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1241-1243 
    Details
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Phenylthiohydantoin (PTH) amino acid derivatives are formed during sequential Edman degradation of peptides and proteins. Isomeric Leu and Ile (which differ only in respectively having iso-butyl and sec-butyl chains, and are often difficult to distinguish by conventional mass spectrometric techniques) may be readily identified by the characteristic decompositions of the [M — H]- ions of their PTH derivatives. The Leu spectrum shows major loss of propane, while that of the Ile derivative shows elimination of both methane and ethane. This method may be used routinely with 10 μg quantities of peptide material.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/rcm.1290091305
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  • 7
    Digitale Medien
    Digitale Medien
    A review of the collision-induced dissociations of deprotonated dipeptides and tripeptides. An aid to structure determination (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 169-173 
    Details
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The structures of underivatized di- and tripeptides may be determined from a consideration of the collision-induced dissociations of their [M - H]- ions. There are three types of fragmentation, viz. (i) the backbone cleavage which provides sequencing information, (ii) α side-chain cleavage irrespective of the position of the amino acid residue, and (iii) cleavages which are characteristic of amino acid residues in specific positions, in particular the N- or C-terminal positions.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/rcm.1290080209
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  • 8
    Digitale Medien
    Digitale Medien
    Characterization of underivatized tetrapeptides by negative-ion fast-atom bombardment mass spectrometry (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 677-685 
    Details
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The [M — H]- ions derived from tetrapeptides generally show two different collision-induced backbone cleavages which allow the determination of the amino acid sequence of the peptide. The first of these involves the formation of the carboxylate anions of either constituent amino acids or fragment peptides. In the second, amino acids or fragment peptides are eliminated as neutrals. There are a number of residues which undergo characteristic sidechain fragmentations irrespective of their position in the tetrapeptide, e.g. Ser, Thr, Cys, Met, Phe and Tyr. However, there are also some residues which, when situated at the C-terminal end of the peptide, promote pronounced fragmentation at the C-terminal position which occurs to the exclusion of the normal backbone cleavages. We conclude that the data obtained from these negative-ion cleavages are analytically useful, and complement those provided by the cognate positive-ion technique.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/rcm.1290090810
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  • 9
    Digitale Medien
    Digitale Medien
    The oxyisocyanate [ONCO]- and amidoisocyanate [HNNCO]- negative ions (1989)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 3 (1989), S. 151-152 
    Details
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: Ab initio calculations indicate that the ion [ONCO]- is linear, whereas [HNNCO]- is effectively coplanar. The ions may be formed by collisional activation of deprotonated hydroxy and aminocarbamates. The characteristic fragmentations of [ONCO]- and [HNNOO]- are losses of O and NH respectively.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/rcm.1290030509
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  • 10
    Digitale Medien
    Digitale Medien
    Ion chemistry of the methylcarbonate anion (1989)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 3 (1989), S. 338-339 
    Details
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The ion MeOCO2- fragments upon collisional activation by competitive losses of Me, CH2 and CO2. The loss of formaldehyde involves hydride-ion transfer to form HCO2-. MeOCO2- reacts as a methoxyl-ion donor in a characteristic reaction with sulphur dioxide, i.e. MeOCO2- + SO2→ MeOSO2-+ CO2.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/rcm.1290031004
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