Residual Dipolar Couplings Between Nuclear Spins

5 Residual Dipolar Couplings Between Nuclear Spins 

The influence of anisotropic indirect nuclear spin-spin coupling tensors on residual dipolar couphng constants (RDCs) has been investigated for many small molecules dissolved in Uquid crystalline solvents. ° The total nuclear spin-spin coupling Hamiltonian for two nuclear spins Tm and In may be written in Cartesian form as  

is the orientational order parameter (relative to the external magnetic field) of the vector mn, and indicates averaging over internal vibrations. The coefficients sfp in eq. (4.26) are Saupe orientational order tensor elements relative to the external magnetic field in a molecular-fixed frame. Consequently, it is necessary to know the tensor in order to be able to determine experimentally the direct dipolar contribution from 

Jokisaari and Autschbach calculated the isotropic average and anisotropy of the Se) and J( Se, Se) spin-spin coupling tensors in carbon diselenide 

The measurement and interpretation of RDCs between spatially proximate spin-pairs in biopolymers such as proteins, nucleic acids, and oligosaccharides in partially oriented environments has become a popular method for structure determination. All observed RDCs, D s contain an unknown contribution from the anisotropic part of coupling tensor, J in addition to the direct dipolar contribution, Bryce and Wasylishen evaluated the influence of J on RDCs 

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