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.
Typical
ring-opening copolymerization (ROCOP) of cyclic anhydrides
(A) and epoxides (B) catalyzed by most metal complexes underwent strict
alternating monomer insertions giving (AB)
n
polyesters. In this contribution, a novel polyester containing (ABB)
n
polymer sequences was prepared via the ROCOP of cyclic anhydrides and cyclohexene oxide (CHO) using
a tin(II) alkoxide complex. Quantum calculations revealed that the
preference for the (ABB)
n
sequence was
enhanced by the energetic preference of the second CHO insertion.
The copolymer with (ABB)
n
content as high
as 70% was obtained from the ROCOP of succinic anhydride and CHO with
an enhanced T
g of 65 °C (>20 °C
higher than the (AB)
n
analogue). The ROCOP
of maleic anhydride and CHO also gave a copolymer with high (ABB)
n
content at 48% and improved T
g of 89 °C (38 °C higher). The improved thermal
properties were a result of the more rigid (ABB)
n
polymer backbone compared with conventional alternating (AB)
n
copolymer analogues. In addition, terpolymerization
with ε-caprolactone (ε-CL) was achieved by sequential
addition of ε-CL affording the block copolymer with the (ABB)
n
backbone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.