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Paramagnetic Relaxation of Long‐Lived Coherences in Solution NMR
Author(s) -
Singh Maninder,
Srinivas Chinthalapalli,
Deb Mayukh,
Kurur Narayanan D.
Publication year - 2013
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.201300718
Subject(s) - paramagnetism , relaxation (psychology) , chemistry , proton , ion , zeeman effect , magnetization , spin–lattice relaxation , nuclear magnetic resonance , condensed matter physics , magnetic field , physics , psychology , social psychology , organic chemistry , quantum mechanics
Long‐lived coherences (LLCs) are known to have lifetimes much longer than transverse magnetization or single quantum coherences (SQCs). The effect of paramagnetic ions on the relaxation of LLCs is not known. This is particularly important, as LLCs have potential applications in various fields like analytical NMR, in vivo NMR and MR imaging methods. We study here the behaviour of LLCs in the presence of paramagnetic relaxation agents. The stepwise increase in the concentration of the metal ion is followed by measuring various relaxation rates. The effect of paramagnetic ions is analysed in terms of the external random field’s contribution to the relaxation of two coupled protons in 2,3,6‐trichlorobenzaldehyde. The LLCs relax faster than ordinary SQCs in the presence of paramagnetic ions of varying character. This is explained on the basis of an increase in the contribution of the external random field to relaxation due to a paramagnetic relaxation mechanism. Comparison is also made with ordinary Zeeman relaxation rates like R 1 , R 2 , R 1ρ and also with rate of relaxation of long‐lived states R LLS which are known to be less sensitive to paramagnetically induced relaxation. Also, the extent of correlation of random fields at two proton sites is studied and is found to be strongly correlated with each other. The obtained correlation constant is found to be independent of the nature of added paramagnetic impurities.