Collision-induced dissociation of sodiated α-glucose, β-glucose, α-galactose, β-galactose, α-mannose, and β-mannose was studied using electronic structure calculations and resonance excitation in a low-pressure linear ion trap. We made an extensive search of conformers and transition states in calculations to ensure the transition state with the lowest barrier height for each dissociation channel could be located. The major dissociation channels, in addition to desodiation, are cross-ring dissociation and dehydration. Cross-ring dissociation starts with H atom transfer from the O1 atom to the O0 atom, followed by the cleavage of the C1-O0 bond. Dehydration of the anomer with O1 and O2 atoms in the cis configuration involves the transfer of an H atom from the O2 atom to the O1 atom, followed by the cleavage of the C1-O1 bond. In contrast, dehydration of the anomer with O1 and O2 atoms in the trans configuration mainly occurs through H atom transfer from the O3 or O2 atom to the O1 atom for glucose, from the O3 or O4 atom to the O1 atom for galactose, and from the O4 or O2 atom to the O1 atom for mannose, followed by the cleavage of the C1-O1 bond. The dehydration barrier heights are lower than those of cross-ring dissociation for cis anomers, but higher than those of cross-ring dissociation for trans anomers. The relative barrier heights from calculations are consistent with the experimental measurements of branching ratios. Both computational and experimental results show that the branching ratio of dehydration can be generalized as a simple rule for rapidly identifying the anomeric configurations of these monosaccharides.

Collision-induced dissociation (CID) of sodiated glucose was investigated using electronic structure calculations and resonance excitation in a low-pressure linear ion trap. The major dissociation channels in addition to desodiation are dehydration and CHO elimination reactions which the barrier heights are near to or lower than the sodiation energy of glucose. Dehydration reaction involves the transfer of the H atom from the O2 atom to the O1 atom, followed by the cleavage of the C1-O1 bond. Notably, α-glucose has a dehydration barrier lower than that of β-glucose. This difference results in the larger branching ratio of dehydration reactions involving α-glucose, which provides a simple and fast method for identifying the anomeric configurations of glucose. The CHO elimination starts from the H atom transfer from the O1 atom to the O0 atom, followed by the cleavage of the C1-O0 bond. These results were further confirmed by experimental study using O-isotope-labeled compounds. Both the experimental data and theoretical calculations suggest that the dehydration reaction and cross-ring dissociation of sodiated carbohydrates mainly occur at the reducing end during low-energy CID.

The infrared spectra of the C-H stretching vibrations of pyridine, its dimer and trimer, and the N-H stretching vibrations of (pyridine)m-(NH3)n complexes were investigated with infrared (IR) - vacuum ultraviolet...

We report an optimization algorithm for studying bimetallic nanoclusters. The algorithm combines two state-of-the-art methods, the genetic algorithm and the basin hopping approach, widely employed in the literature for predicting structures of pure metallic and nonmetallic clusters. To critically test the present algorithm and its use in determining the lowest-energy structures of bimetallic nanoclusters, we apply it to study the bimetallic clusters Cu(n)Au(38-n) (0< or =n< or =38). It is predicted that the Au atoms, being larger in size than the Cu atoms, prefer to occupy surface sites showing thus the segregating behavior. As the atom fraction of Cu increases, the bimetallic cluster Cu(n)Au(38-n), as a whole, first takes on an amorphous structure and is followed by dramatic changes in structure with the Cu atoms revealing hexagonal, then assuming pentagonal, and finally shifting to octahedral symmetry in the Cu-rich range.