Lineshape and relaxation of spins I=1/2 coupled to S=3. Application to selective detection of protons attached to boron-10

The rapid spin-lattice relaxation of quadrupolar nuclei is a dominant mechanism for the transverse relaxation of attached hydrogens. The effects of this scalar relaxation were calculated exactly for protons attached to nuclei with spin S = 3, assuming that the quadrupolar relaxation is in the isotropic extreme narrowing limit. The preferred technique for indirect detection of the spin-3 nuclei, via their attached hydrogens, depends on the ratio between the heteronuclear coupling constant and the quadrupolar relaxation rate. The theoretical analysis was found to be in good agreement with the results of spin-echo difference experiments conducted on borocaptate monomer (BSH) and dimer (BSSB) anions in aqueous solution. (C) 1995 Academic Press, Inc.