Theoretical Study of Dipolar Relaxation of Coupled Nuclear Spins at Variable Magnetic Field

Pravdivtsev, Andrey N.; Ivanov, Konstantin L.; Kaptein, Robert; Yurkovskaya, Alexandra V.

doi:10.1007/s00723-012-0404-z

Cited by 12 publications

(12 citation statements)

References 43 publications

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“…However, since the splitting is relatively small, both LACs together work in almost the same way as a single LAC. In general, LACs are supposed to result in pronounced features in the field dependence of spin relaxation 29,41,42,57 and polarization transfer. [39][40][41][45][46][47] Here, we will study the polarization transfer at the LAC in the three-spin 1/2 system in detail and support the experimental results with theoretical calculations.…”

Section: Resultsmentioning

confidence: 99%

“…Our method gives an alternative way of observing ZQCs formed at low fields as compared to that proposed by Pileio et al 80 who excited coherence between the singlet and T 0 states by pumping "forbidden" spin transitions with "extremely low-frequency" irradiation. Last but not least, the high precision of our theoretical approach, which can be straightforwardly extended 29 to consider dipolar relaxation, enables such studies on a quantitative level.…”

Section: Discussionmentioning

confidence: 99%

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Coherent transfer of nuclear spin polarization in field-cycling NMR experiments

Pravdivtsev

Yurkovskaya

Vieth

et al. 2013

The Journal of Chemical Physics

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Coherent polarization transfer effects in a coupled spin network have been studied over a wide field range. The transfer mechanism is based on exciting zero-quantum coherences between the nuclear spin states by means of non-adiabatic field jump from high to low magnetic field. Subsequent evolution of these coherences enables conversion of spin order in the system, which is monitored after field jump back to high field. Such processes are most efficient when the spin system passes through an avoided level crossing during the field variation. The polarization transfer effects have been demonstrated for N-acetyl histidine, which has five scalar coupled protons; the initial spin order has been prepared by applying RF-pulses at high magnetic field. The observed oscillatory transfer kinetics is taken as a clear indication of a coherent mechanism; level crossing effects have also been demonstrated. The experimental data are in very good agreement with the theoretical model of coherent polarization transfer. The method suggested is also valid for other types of initial polarization in the spin system, most notably, for spin hyperpolarization.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Coherent transfer of nuclear spin polarization in field-cycling NMR experiments

Pravdivtsev

Yurkovskaya

Vieth

et al. 2013

The Journal of Chemical Physics

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“…As has been found earlier, the calculation method described gives accurate predictions not only for the high-field T 1 -relaxation times but also for the whole T 1 (B) dependence. 4 As was discussed before the long-lived singlet spin state in the two-spin system of the b-CH 2 protons corresponds to the difference in populations of the singlet and triplet states, which is given by the spin order (Î b1 ÁÎ b2 ). Previously it was shown 4,43 that in the case of adiabatic field cycling such spin order at low magnetic field is correlated with the (Î b1 z À Î b2 z ) spin order at high magnetic field.…”

Section: Simulation Methodsmentioning

confidence: 95%

“…For simulating the experiment we used the same theory as before. 4,35,37 It takes into account every stage of the experimental protocol. For modelling the generation of HP by means of photo-CIDNP we used a Green function approach 38,39 for calculating the spin evolution in radical pairs.…”

Section: Simulation Methodsmentioning

confidence: 99%

Magnetic field dependent long-lived spin states in amino acids and dipeptides

Pravdivtsev

Yurkovskaya

Zimmermann

et al. 2014

Phys. Chem. Chem. Phys.

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Magnetic field dependence of long-lived spin states (LLSs) of the β-CH2 protons of aromatic amino acids was studied. LLSs are spin states, which are immune to dipolar relaxation, thus having lifetimes far exceeding the longitudinal relaxation times; the simplest example of an LLS is given by the singlet state of two coupled spins. LLSs were created by means of the photo-chemically induced dynamic nuclear polarization technique. The systems studied were amino acids, histidine and tyrosine, with different isotopomers. For labeled amino acids with the α-CH and aromatic protons substituted by deuterium at low fields the LLS lifetime, TLLS, for the β-CH2 protons was more than 40 times longer than the T1-relaxation time. Upon increasing the number of protons the ratio TLLS/T1 was reduced; however, even in the fully protonated amino acids it was about 10; that is, the long-lived mode was still preserved in the system. In addition, the effect of paramagnetic impurities on spin relaxation was studied; field dependencies of T1 and TLLS were measured. LLSs were also formed in tyrosine-containing dyads; a TLLS/T1 ratio of ∼7 was found, usable for extending the spin polarization lifetime in such systems.

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“…A homonuclear spin pair would then be strongly coupled at low field and weakly coupled at high field. 26,27 In the two-spin EMOR model, a homonuclear spin pair is always strongly coupled due to the large dipole coupling.…”

Section: A Spin Hamiltonianmentioning

confidence: 99%

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for a dipole-coupled spin-1/2 pair

Chang

Halle

2013

The Journal of Chemical Physics

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In complex biological or colloidal samples, magnetic relaxation dispersion (MRD) experiments using the field-cycling technique can characterize molecular motions on time scales ranging from nanoseconds to microseconds, provided that a rigorous theory of nuclear spin relaxation is available. In gels, cross-linked proteins, and biological tissues, where an immobilized macromolecular component coexists with a mobile solvent phase, nuclear spins residing in solvent (or cosolvent) species relax predominantly via exchange-mediated orientational randomization (EMOR) of anisotropic nuclear (electric quadrupole or magnetic dipole) couplings. The physical or chemical exchange processes that dominate the MRD typically occur on a time scale of microseconds or longer, where the conventional perturbation theory of spin relaxation breaks down. There is thus a need for a more general relaxation theory. Such a theory, based on the stochastic Liouville equation (SLE) for the EMOR mechanism, is available for a single quadrupolar spin I = 1. Here, we present the corresponding theory for a dipole-coupled spin-1/2 pair. To our knowledge, this is the first treatment of dipolar MRD outside the motional-narrowing regime. Based on an analytical solution of the spatial part of the SLE, we show how the integral longitudinal relaxation rate can be computed efficiently. Both like and unlike spins, with selective or non-selective excitation, are treated. For the experimentally important dilute regime, where only a small fraction of the spin pairs are immobilized, we obtain simple analytical expressions for the auto-relaxation and cross-relaxation rates which generalize the well-known Solomon equations. These generalized results will be useful in biophysical studies, e.g

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Theoretical Study of Dipolar Relaxation of Coupled Nuclear Spins at Variable Magnetic Field

Cited by 12 publications

References 43 publications

Coherent transfer of nuclear spin polarization in field-cycling NMR experiments

Coherent transfer of nuclear spin polarization in field-cycling NMR experiments

Magnetic field dependent long-lived spin states in amino acids and dipeptides

Nuclear magnetic relaxation induced by exchange-mediated orientational randomization: Longitudinal relaxation dispersion for a dipole-coupled spin-1/2 pair

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