Experimental and theoretical investigation of the reactions between glucose and Cu+ in the gas phase

Tandem mass spectrometry was used in the analysis of Cu+-D-glucose complexes. The MIKE spectrum of these complexes generated by FAB shows that the loss of a water molecule is the most important spontaneous fragmentation, followed by a second dehydration or the loss of H-2, whereas the metal ion Cu+ is never eliminated. A theoretical survey of the potential energy surface, based on the use of density functional theory approaches, shows that the attachment of Cu+ to the different basic centers of glucose induces nonnegligible bond activation phenomena within the sugar moiety. As a consequence, the cleavage of the C-O linkages of the six-membered ring leads to open complexes which are systematically much more stable than those in which the cyclic structure of the sugar is preserved. These significant stability differences reflect the preference of Cup to yield bisligated complexes in which the metal forms almost linear arrangements with two oxygen atoms of the neutral through the participation of sd hybrids. The Cu+ cation has a catalytic effect on these ring-opening mechanisms. Several pathways for the successive loss of two molecules of water can be envisaged with the origin in the cyclic and the open glucose-Cu+ complexes. In general, the most stable product ions are those formed by a spontaneous fragmentation of the most stable open structures.