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Transverse Relaxation of Scalar‐Coupled Protons
Author(s) -
Segawa Takuya F.,
Baishya Bikash,
Bodenhausen Geoffrey
Publication year - 2010
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201000350
Subject(s) - homonuclear molecule , chemistry , proton , relaxation (psychology) , dipole , scalar (mathematics) , nuclear magnetic resonance , physics , crystallography , molecule , nuclear physics , psychology , social psychology , organic chemistry , geometry , mathematics
In a preliminary communication (B. Baishya, T. F. Segawa, G. Bodenhausen, J. Am. Chem. Soc. 2009 , 131 , 17538–17539), we recently demonstrated that it is possible to obtain clean echo decays of protons in biomolecules despite the presence of homonuclear scalar couplings. These unmodulated decays allow one to determine apparent transverse relaxation rates R 2 app of individual protons. Herein, we report the observation of R 2 app for three methyl protons, four amide H N protons, and all 11 backbone H α protons in cyclosporin A. If the proton resonances overlap, their R 2 app rates can be measured by transferring their magnetization to neighboring 13 C nuclei, which are less prone to overlap. The R 2 app rates of protons attached to 13 C are faster than those attached to 12 C because of 13 C– 1 H dipolar interactions. The differences of these rates allow the determination of local correlation functions. Backbone H N and H α protons that have fast decay rates R 2 app also feature fast longitudinal relaxation rates R 1 and intense NOESY cross peaks that are typical of crowded environments. Variations of R 2 app rates of backbone H α protons in similar amino acids reflect differences in local environments.