Lilian Davies

A complete assignment of the vibrational spectra of sucrose in aqueous medium based on the SQM methodology and SCRF calculations.

In the present study, a complete assignment of the vibrational spectra of sucrose in aqueous medium was performed combining Pulays Scaled Quantum Mechanics Force Field (SQMFF) methodology with self-consistent reaction field (SCRF) calculations. Aqueous saturated solutions of sucrose and solutions at different molar concentrations of sucrose in water were completely characterized by infrared, HATR, and Raman spectroscopies. In accordance with reported data of the literature for sucrose, the theoretical structures of sucrose penta and sucrose dihydrate were also optimized in gas and aqueous solution phases by using the density functional theory (DFT) calculations. The solvent effects for the three studied species were analyzed using the solvation PCM/SMD model and, then, their corresponding solvation energies were predicted. The presence of pure water, sucrose penta-hydrate, and sucrose dihydrate was confirmed by using theoretical calculations based on the hybrid B3LYP/6-31G(∗) method and the experimental vibrational spectra. The existence of both sucrose hydrate complexes in aqueous solution is evidenced in the IR and HATR spectra by means of the characteristic bands at 3388, 3337, 3132, 1648, 1375, 1241, 1163, 1141, 1001, 870, 851, 732, and 668cm(-1) while in the Raman spectrum, the groups of bands in the regions 3159-3053cm(-1), 2980, 2954, and 1749-1496cm(-1) characterize the vibration modes of those complexes. The inter and intra-molecular H bond formations in aqueous solution were studied by Natural Bond Orbital (NBO) and Atoms in Molecules theory (AIM) investigation.

Spectroscopic and structural studies on lactose species in aqueous solution combining the HATR and Raman spectra with SCRF calculations.

In this work, the α and β isomers, the α-lactose monohydrate and dihydrate and the dimeric species of lactose were studied from the spectroscopic point of view in gas and aqueous solution phases combining the infrared, Horizontal Attenuated Total Reflectance (HATR) and Raman spectra with the density functional theory (DFT) calculations. Aqueous saturated solutions of α-lactose monohydrate and solutions at different molar concentrations of α-lactose monohydrate in water were completely characterized by infrared, HATR and Raman spectroscopies. For all the species in solution, the solvent effects were studied using the solvation polarizable continuum (PCM) and solvation (SM) models and, then, their corresponding solvation energies were predicted. The vibrational spectra of those species in aqueous solution were completely assigned by employing the Scaled Quantum Mechanics Force Field (SQMFF) methodology and the self-consistent reaction field (SCRF) calculations. The stabilities of all those species were studied by using the natural bond orbital (NBO), and atoms in molecules (AIM) calculations.

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

The structures of α- and β-maltose anhydrous and their corresponding monohydrated species were studied combining the FT-IR, FT-Raman and HATR spectra with DFT calculations. The four structures were optimized in gas and aqueous solution by using the hybrid B3LYP/6-31G* method. The self-consistent force field (SCRF) calculations together with the polarized continuum (PCM) model were used to study the systems in solution while the solvation energies were computed using the solvation model (SM). The calculated 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 support clearly the mutarotation equilibria between both forms in solution, evidencing the anhydrous forms the equilibrium: α (45%) ⇔ β (55%), similar to that experimentally reported at 20 °C. Bands of all the species observed in the vibrational spectra support the presence of the anomeric species of maltose in solution while the presence of dimeric species justify the intense IR bands observed in the higher wavenumbers region. The similar gap values for maltose and lactose probably justify that these sugars are reducing sugars 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, lactose and sucrose, as expected due to their ionic characteristics. The predicted vibrational spectra for the four species of maltose show reasonable concordances with the corresponding experimental ones. The f(δC-O-C) force constants of the glycosidic bonds follow the tendency: maltose > lactose > sucrose.