Molecular orbital considerations in probing the stereoselective dissociations of cobalt-coordinated hexosamine monosaccharides.

The mechanisms for the stereoselective dissociation pathways of isomeric [CoIII(diaminopropane)2(hexosamine-2H)]+ complexes are studied by ion trap and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The exact masses of product ions were measured in order to determine the composition of each loss, and isotopic labeling experiments were used to determine which atoms were lost during dissociation. MS3 studies were used to probe the structures of the product ions from MS2 experiments. Based on the experimental evidence obtained, mechanisms explaining the dissociations are postulated. In deciphering the mechanisms, careful attention was paid to the molecular orbital alignment of the reacting bonds, and based on the molecular orbitals, transition state conformations were postulated. These transition states suggest how the observed stereoselectivity occurs. In each case, the carbohydrate/metal interaction was crucial in the dissociation processes.