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Atomic Polarizability Dominates the Electronic Properties of Peptide Bonds upon Thioxo or Selenoxo Substitution
Author(s) -
Huang Yun,
Jahreis Günther,
Fischer Gunter,
Lücke Christian
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200863
Subject(s) - chalcogen , polarizability , chemistry , amide , electronegativity , crystallography , peptide bond , computational chemistry , bond dissociation energy , natural bond orbital , peptide , density functional theory , dissociation (chemistry) , organic chemistry , molecule , biochemistry
The amide bond as peptide linkage plays an important role in protein structure and function. A large number of theoretical and experimental studies have focused on the specific nature of the peptide bond. Little attention, however, has been paid to their chalcogen‐substituted congeners, although experimental data on thioamides revealed inconsistencies with the conventional view of amide resonance theory. Here, we employed thioxo and selenoxo substitution to determine experimentally how heavier chalcogens affect the properties of the peptide bond and adjacent atoms. NMR data revealed pronounced deshielding of heteronuclei within a three‐bond distance to the chalcogen atom; this indicates an enhanced electron‐withdrawing potential of the heavier chalcogens despite their lower electronegativities compared to oxygen. Interestingly, linear correlations were observed between chalcogen atomic polarizability and the chemical shift values of those neighboring heteronuclei as well as several physicochemical properties, such as electronic excitation energy, CN rotation barrier, dipole moment and amide proton dissociation. We conclude that the chalcogen polarizability, which relates to the charge capacity, is the dominant factor that determines the electronic properties of peptide bonds substituted with heavier chalcogens.