A theoretical study on proton transfer in the mutarotation of sugars

Abstract

The epimerisation process of the model sugar 2-tetrahydropyranol was studied by means of ab initio calculations. The results suggest that the rate limiting step of sugar ring opening involves a high-energy intramolecular proton transfer reaction or a low-energy process in which the proton transfer is mediated by a catalyst molecule, formic acid in the case investigated. The catalysed process is an asynchronous concerted double proton transfer reaction, where both protons are transferred within the same elementary step but one of them is transferred much earlier than the other one along the reaction coordinate. The motion of both protons in the transition state of the catalysed process is strongly coupled with the breaking of the C-O bond of the sugar ring. Geometry optimisation at the B3LYP/6-31G* level, with additional p polarisation functions located on the hydrogen atoms involved in proton transfer, appears to be suitable for further MP2/6-31G** single point energy calculations, as it provides hydrogen bond and activation energies in good agreement with those obtained from geometry optimisation at the full MP2 level of theory

Gas‐phase basicities of polyfunctional molecules. Part 1: Theory and methods

“…A systematic study shows that if X has a proton affinity between that of O and C of CO the barrier for rearrangement completely disappears (Chalk & Radom, 1997). Other examples of rearrangements of protonated or cationized species involving assisted proton (or even alkyl cation) transport have been reported so far, from small species HNNO + /NNOH + (Ferguson, 1989), CH 3 CO + /CH 3 OC + (Cunje et al, 1998) to 2‐tetrahydropyranol, a model for the study of sugar epimerization (Morpurgo et al, 2000).…”

Products of sugar beet processing as raw materials for chemicals and biodegradable polymers

“…66 The mutarotation process has also been the subject of theoretical research using quantum mechanical methods. 67,68 Theoretical calculations have shown that mutarotation is assisted by solvents and that the rst molecule acts as a catalyst, playing a crucial role in the reaction. 69 Monosaccharides can be obtained from various waste products of the sugar, agricultural and food industries.…”

Anomerization reaction of bare and microhydrated d‐erythrose via explicitly correlated coupled cluster approach. Two water molecules are optimal

“…[4] Numerous related investigations have been reported on the cyclic and open-chain tautomers' equilibria of simple sugars, mostly involving hexoses. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Spectroscopic studies of mutarotation of monosaccharides in the aqueous solution, [8][9][10] pure anhydrous [25][26][27][28][29][30][31] and crystalline [32,33] states have been an active research field. In the gas phase, an initial step of the anomerization reaction is thought to entail both migrating of the hydrogen atom from the hydroxyl group linked to the anomeric carbon (C1) to the ring oxygen and bond breaking between the ring oxygen and the anomeric carbon to form an open-chain intermediate (for the aldose case, this step is illustrated in Scheme 1).…”

“…Interconversion of this type called mutarotation or anomerization, was first observed for d ‐glucose in the aqueous solution . Numerous related investigations have been reported on the cyclic and open‐chain tautomers' equilibria of simple sugars, mostly involving hexoses …”