A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
Spectral spin diffusion and magnetic dipolar energy in the NMR of (CH3)-C-13 compounds
Tekijät: Ylinen EE, Kankaanpaa M, Punkkinen M
Kustantaja: ACADEMIC PRESS INC ELSEVIER SCIENCE
Julkaisuvuosi: 2006
Lehti:: Solid State Nuclear Magnetic Resonance
Tietokannassa oleva lehden nimi: SOLID STATE NUCLEAR MAGNETIC RESONANCE
Lehden akronyymi: SOLID STATE NUCL MAG
Vuosikerta: 29
Numero: 4
Aloitussivu: 330
Lopetussivu: 344
Sivujen määrä: 15
ISSN: 0926-2040
DOI: https://doi.org/10.1016/j.ssnmr.2005.11.004
Tiivistelmä
Spin diffusion between (CH3)-C-13 groups in solids is Studied both theoretically and experimentally. It is shown to be dominated by mutual spin flip-flops of protons belonging to neighbouring methyl groups. Also nonmethyl protons may contribute significantly if present in the sample. The spin-rotational around state of (CH3)-C-13 consists of 16 sublevels. When their populations are used to describe spin diffusion, eight population combinations are shown to be important, two of them corresponding to the C-13-proton and proton-proton intramethyl magnetic dipolar energies, D-c and D-p respectively. Spin-diffusion transitions modulate these combinations so that a further reduction to two sets of four combinations is possible, with no coupling between the sets. Coupled differential equations are derived to describe the time dependence of the combinations in each set. They are solved numerically and compared with experimental results on ia single crystal of aspirin with C-13-labelled methyl goups at the carbon resonance. The C-13 NMR induction signal was observed as a function of time after the preparation either at the carbon resonance (a two-pulse sequence) or at the proton resonance (proton saturation). Usually carbon spectra were Computed first and then three of the mentioned population combinations were obtained from the individual spectral components. Some results on the time dependence of D-c were also obtained directly from the amplitude oft he out-of-phase induction signal. Theoretical predictions are found to describe semiquantitatively the overall time dependence of these three combinations and especially their variation with different initial conditions, which are discussed in detail. Also the partial transfer of the magnetic dipolar energy between D-c and D-p is nicely explained. Reasons for discrepancies are discussed. (c) 2005 Elsevier Inc. All rights reserved.
Spin diffusion between (CH3)-C-13 groups in solids is Studied both theoretically and experimentally. It is shown to be dominated by mutual spin flip-flops of protons belonging to neighbouring methyl groups. Also nonmethyl protons may contribute significantly if present in the sample. The spin-rotational around state of (CH3)-C-13 consists of 16 sublevels. When their populations are used to describe spin diffusion, eight population combinations are shown to be important, two of them corresponding to the C-13-proton and proton-proton intramethyl magnetic dipolar energies, D-c and D-p respectively. Spin-diffusion transitions modulate these combinations so that a further reduction to two sets of four combinations is possible, with no coupling between the sets. Coupled differential equations are derived to describe the time dependence of the combinations in each set. They are solved numerically and compared with experimental results on ia single crystal of aspirin with C-13-labelled methyl goups at the carbon resonance. The C-13 NMR induction signal was observed as a function of time after the preparation either at the carbon resonance (a two-pulse sequence) or at the proton resonance (proton saturation). Usually carbon spectra were Computed first and then three of the mentioned population combinations were obtained from the individual spectral components. Some results on the time dependence of D-c were also obtained directly from the amplitude oft he out-of-phase induction signal. Theoretical predictions are found to describe semiquantitatively the overall time dependence of these three combinations and especially their variation with different initial conditions, which are discussed in detail. Also the partial transfer of the magnetic dipolar energy between D-c and D-p is nicely explained. Reasons for discrepancies are discussed. (c) 2005 Elsevier Inc. All rights reserved.
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