FTIR, HATR and FT-Raman studies on the anhydrous and monohydrate species of maltose in aqueous solution

MAXIMILIANO ALBERTO. IRAMAIN; LILIAN DAVIES; SILVIA ANTONIA. BRANDÁN

CARBOHYDRATE RESEARCH

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2016 p. 41 - 56

0008-6215

The structures of α- and β-maltose anhydrous and their corresponding monohydrated species were studiedcombining the FT-IR, FT-Raman and HATR spectra with DFT calculations. The four structures were optimizedin gas and aqueous solution by using the hybrid B3LYP/6-31G* method. The self-consistent forcefield (SCRF) calculations together with the polarized continuum (PCM) model were used to study thesystems in solution while the solvation energies were computed using the solvation model (SM). Thecalculated structural and vibrational properties could explain the anomerization of maltose in solution,as was reported in the literature while the natural bond orbital (NBO) analyses for those species supportclearly the mutarotation equilibria between both forms in solution, evidencing the anhydrous forms theequilibrium: α (45%)⇔β (55%), similar to that experimentally reported at 20 °C. Bands of all the speciesobserved in the vibrational spectra support the presence of the anomeric species of maltose in solutionwhile the presence of dimeric species justify the intense IR bands observed in the higher wavenumbersregion. The similar gap values for maltose and lactose probably justify that these sugars are reducingsugars while the high values in sucrose could explain that it is a non-reducing sugar. On the other hand,the sweeteners cyclamate and saccharine are most reactive in solution than the sugars maltose, lactoseand sucrose, as expected due to their ionic characteristics. The predicted vibrational spectra for the fourspecies of maltose show reasonable concordances with the corresponding experimental ones. The f(δCO-C) force constants of the glycosidic bonds follow the tendency: maltose > lactose > sucrose.