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  • 1
    Electronic Resource
    Electronic Resource
    The use of partially restricted molecular orbitals to investigate transmission mechanisms of spin-spin coupling constants. I. Theσ andπ contributions within the FPT INDO method (1981)
    Springer
    Theoretical chemistry accounts 59 (1981), S. 17-24 
    Details
    ISSN: 1432-2234
    Keywords: Coupling constants ; Transmission mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Partially restricted INDO MO Calculations have been carried out to separate the π-electron contributions to spin-spin coupling constants in ethylene, butadiene, benzene and toluene. Results reproduce very well known trends such as the pathway invariance, the alternation in sign and the methyl group replacement rule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00574433
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  • 2
    Electronic Resource
    Electronic Resource
    Quantum mechanical calculations and experimental measurement of N-terminal charge effects on 1HN and 1HCα chemical shifts in peptides (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 573-581 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nuclear magnetic resonance spectroscopists are increasingly utilizing chemical shifts to characterize the secondary structure of proteins. The present study addresses the effects that the positively charged amino group at the N-terminus of a peptide has on 1HN and 1HCα chemical shifts along the chain. This information is necessary for interpreting chemical shift data for proteins and/or for peptides that are used as models for protein structure. The chemical shifts for the 1H resonances of four peptides that differ only in the location of their N-terminii are assigned using two-dimensional nmr spectroscopy. The peptides have sequences derived from the β subunit of the glycoprotein hormone human chorionic gonadotropin (hCG-β). Comparison of the 1HN and the 1HCα chemical shifts for residues common to all four peptides reveals downfield shifts for 1HN and the 1HCα resonances within three residues of the N-terminus compared with chemical shifts in the interior of the peptide. The magnitude of the downfield shift is larger for resonances nearer the N-terminus. Quantum mechanical calculations of the 1HN and 1HCα chemical shifts in peptides constructed with six alanine units also predict a significant terminus effect. The calculations agree both qualitatively and quantitatively with the experimental data. The inductive nature of the end effect is confirmed in the calculations by Mulliken population analysis. End effects should be taken into account in determining protein secondary structures from chemical shifts. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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