A Numerical Study on the Dynamics of Distant Dipolar Field in Solution NMR: Understanding Spatial Aspect of Magnetizations

摘要

Over the past few decades, the distant dipolar field (DDF) induced by bulk magnetization and its quantum mechanical origin (intermolecular dipolar couplings between distant nuclear spins) have attracted the attention of many researchers since they could produce anomalous cross peaks or additional resonances in 2D-NMR experiments. For example, the CRAZED sequence (π/2-t1-[gradient, length T]-π/2-[gradient, length nT]-t2) generates unexpected cross peaks in the indirectly detected dimension at n-times of the resonance frequencies (e.g., [nΔω, Δω]), which have the characteristic properties of intermolecular multiple quantum coherences created by intermolecular dipolar couplings. These signals were quite unexpected in conventional NMR frameworks, but have been analyzed either classically using the modified Bloch equations including the DDF, and quantum mechanically using a full density matrix picture including dipolar coupling between intermolecular spins. Despite differences in calculation models, both the classical and quantum pictures generally allow the same predictions.