Cross‐correlated and conventional dipolar carbon‐13 relaxation in methylene groups in small, symmetric molecules

Abstract

A theory for dipolar cross-correlated relaxation processes in AMX or AX 2 spin system, with special reference to 13 C-methylene groups, is reviewed briefly. Simple experiments and protocols for measuring the transfer rates between the carbon-13 Zeeman order and the three-spin order, and for their analogues in the transverse plane, are discussed using a concentrated solution of the disaccharide trehalose as a model system. Experimental data sets consisting of conventional carbon-13 relaxation parameters (T 1 , T 2 , and NOE), along with the cross-correlated relaxation rates, are also presented for some small, rigid, polycyclic molecules. These data are interpreted using spectral density functions appropriate to spherical or symmetric tops reorienting according to small-step rotational diffusion model. The analysis results in a consistent picture of the auto-and cross-correlated spin relaxation processes.

NMR relaxation interference effects and internal dynamics in γ-cyclodextrin

“…The expanded form of Eq. (1) and a similar equation of motion related to transverse relaxation were provided in our previous article [21]. Under certain conditions, the relaxation equations can be simplified.…”

“…In a recent communication, we described a simple experimental methodology for studies of cross-correlated relaxation, suitable for methylene groups in smaller molecules and possible to use at natural abundance [21]. We have also applied these methods on some reasonably rigid molecules and investigated the consistency of the cross-correlated relaxation data with conventional heteronuclear relaxation properties (spin-lattice and spin-spin relaxation rates, nuclear Overhauser enhancement) for different molecules.…”

“…The task of interpreting relaxation data is reasonably simple for molecules which can be considered as rigid bodies undergoing rotational diffusion in small steps [21]. The presence of large-amplitude internal motions complicates the situation very significantly.…”

Beyond excitation NMR relaxation

“…Nevertheless, the weak interactions can play a significant role in the stabilization of conformational molecular states, especially when cooperativity is involved (119). Intramolecular contacts of the type C-H Recently, a strategy to measure the transfer rates within the 13 C Zeeman order was proposed; this approach considers the cross-correlated relaxation rates (CCRRs), the longitudinal and transversal relaxations, and the nOe in highly symmetric compounds (121).…”

Theoretical Study of the Effective Chemical Shielding Anisotropy (CSA) in Peptide Backbone, Rating the Impact of CSAs on the Cross-Correlated Relaxations in l-Alanyl-l-alanine

“…[34][35][36][37] The applicability of the CCRs exceeds the limited range of biomolecular studies. 38,39 Measurement of the CSA-DD cross-correlated relaxation rates probes both the dynamics (specific fluctuations of molecular motions) and the σ-tensor (see Theory). While reliable prediction of the CCR dynamic component might be a challenging task, 40,41 the structural dependence of the σ-tensor and its orientation with respect to the dipolar vector can be obtained with many calculation methods.…”