Premium
T 1 and T 2 relaxations of the 13 C nuclei of deuterium‐labeled nucleosides
Author(s) -
Maltseva T. V.,
Földesi A.,
Chattopadhyaya J.
Publication year - 1998
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199804)36:4<227::aid-omr266>3.0.co;2-9
Subject(s) - chemistry , deuterium , relaxation (psychology) , deuterium nmr , methylene , carbon 13 , carbon 13 nmr , geminal , kinetic isotope effect , dipole , protonation , nuclear magnetic resonance , computational chemistry , stereochemistry , organic chemistry , atomic physics , nuclear physics , physics , psychology , social psychology , ion
The effect of 2 H on 13 C longitudinal ( T 1 ) and transverse ( T 2 ) relaxation parameters was determined for the first time for diastereospecifically deuterium‐labeled nucleosides, which are used as the building blocks for non‐uniform isotope labeling for the solution NMR structure determination of the large biologically functional oligo‐DNA and ‐RNA (‘NMR window’ approach, ref. 7). It emerged that the T 1 and T 2 of the deuterated methine carbon in the diastereospecifically deuterium‐labeled nucleoside 9 could be used as the correction term to give the monoexponential decay of 13 C longitudinal and transverse magnetization of the constituent 1 H– 13 C– 2 H group. The correlation time derived from this corrected T 1 of the methylene carbon corresponds well with the correlation time obtained from deuterium relaxation study. The extreme narrowing limit (ωτ c ≪1) where dipole–dipole (DD) relaxation of 13 C and quadrupole (Q) relaxation of 2 H are related by T 1 DD / T 2 DD ≈1 and T 1 Q / T 2 Q ≈1 was used to demonstrate the above conclusion. The difference in the observable T 1 and T 2 in various methylene and methine‐type carbons with either fully protonated or diastereospecifically deuterated nucleosides 1 – 14 allowed the estimation of the contribution of the alternative relaxation pathways other than DD relaxation. It was found by comparison of the T 1 relaxation of the quaternary carbon with the methine carbon ( 13 C– 2 H) or ( 13 C– 1 H) in compound 2 that the contribution of the intermolecular and intramolecular relaxations of 13 C with protons that are two bonds away is larger than DD( 13 C– 2 H), and the sum of all these contributions define the T 1 of the methine carbon ( 13 C– 2 H). The observed difference between the experimental T 1 and T 2 of the methine carbon is attributed to the cross‐correlation between DD( 13 C– 2 H) and Q( 2 H) relaxation, which is consistent with recent theoretical predictions. For T 2 measurement, the decoupling of deuterium with 0.6–2.5 kHz power during the echo period by WALTZ does not effectively eliminate the DD( 13 C– 2 H)–Q( 2 H) cross‐correlation for the methine carbon. The suppression of this DD( 13 C– 2 H)–Q( 2 H) cross‐correlation was, however, more effective by applying a 180° deuterium pulse in the middle of the short (0.5 ms) echo period (compare T 2 of 3.91s and 0.3s, respectively, at 294 K using these two different decoupling procedures). The comparison of the observed T 1 and T 2 relaxations of the methylene carbon shows that they are indeed very close. The various contributions of the methine carbon relaxation such as DD( 13 C– 2 H), intermolecular and cross‐correlation, DD( 13 C– 1 H)–Q( 2 H), to the relaxation of the methylene carbon were ca. 15% in T 1 and ca . 25% in T 2 . © 1998 John Wiley & Sons, Ltd.