NMR Relaxation in Multipolar AX Systems under Spin Locking Conditions

Abstract

A relaxation matrix has been calculated for a multipolar AX spin system under the on-resonance spin-locking condition. Auto- and cross-correlation terms between dipolar, quadrupolar, and CSA interactions are considered. It is shown that the spin-lock leads to many relaxation pathways being blocked, resulting in a considerably simplified relaxation network. The presence of spectral densities at zero frequency, associated with locked nuclei, allows efficient relaxation also in the absence of fast molecular motions.

NMR Relaxation in Multipolar AMX Systems under Spin-Locking Conditions

“…Auto-and cross-correlation terms between dipolar, quadrupolar, and CSA interactions have been taken into account. We have previously performed similar calculations for the case of multipolar AX systems (10). The AX spin system does not have dipolar-dipolar cross correlations, which under certain spin locking condition, may compete with strong quadrupolar relaxation mechanism in AMX spin system as will be shown later.…”

13C NMR Relaxation Analysis of Protein GB3 for the Assessment of Side Chain Dynamics Predictions by Current AMBER and CHARMM Force Fields

“…Interference due to the 2 H− 13 C interactions can be suppressed by the application of spin lock fields. 53,54 In part, the selection of the GB3 protein for the experimental substantiation of the proposed analysis was based on the fact that near room temperature the NMR spectra of GB3 do not exhibit evidence of slow conformational transitions that would give rise to either resonance doubling or conformational exchange line broadening. It may be noted that NMR relaxation measurements in supercooled solution do indicate conformational exchange line broadening in the first β-turn of GB3 (Gly 9 to Lys 13) that when extrapolated to 25 °C predicts a transition time of ∼1 μs which is too rapid to alter the observed R 2 rates via this line broadening mechanism.…”

“…That observation is consistent with the relaxation interference effects that occur between the 2 H quadrupole and the 2 H− 13 C dipole interactions 69,70 having been efficiently suppressed by the simultaneous application of 2 H and 13 C spin lock fields during the transverse relaxation pulse experiments. 53,54 Optimization of NMR relaxation predictions at methylene positions was carried out in two steps. Initially for each methylene bond vector, the geminal 1 H− 13 C and 2 H− 13 C relaxation effects were modeled using a single set of (S f ) values and the bond vector-specific rotational diffusion decay constant for the 1 H− 13 C vector.…”

Nuclear magnetic relaxation of spinI=1/2 scalar coupled to a quadrupolar nucleus in the presence of cross-correlation effects

“…It is interesting to compare these equations with those obtained by other authors. If we substitute S = 1 and use the identity relation for spin S = 1 we can see that the equations for the longitudinal magnetization modes (I~), (/.S~), and (IzS~ z) agree with the equations for the AX spin system with the use of the Redfield method in ref 31. which were used for the study of the spin system behavior in spin-locking.Equations for/~, ZeS z, IeS~, IeS~, and S~, S i, S i can be useful to get the equations describing the evolution of each longitudinal component of the spectrum of the nucleus I = 1/2 scalar coupled with any quadrupolar nucleus S > 1/2.…”

“…The study of the differential line broadening in scalar-coupled dipo!ar-quadrupolar spin systems with the unusual multiplet structure effects induced by the cross-correlation dipolar-quadrupolar interaction and the chemical-shift anisotropy-quadrupolar interaction was carried out by a number of scientists, who used the Redfield mat¡ [7,8,10,[17][18][19][24][25][26][27][28]. Other works treat the relaxation behavior of the spin system with the quadrupolar nucleus in the presence of radio-frequency (RF) fields combining the Redfield method with the magnetization-mode conception [29][30][31][32][33]. Such treatment of relaxation problems required the calculation of matrix elements of the relaxation matrix for each spin system.…”