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 ß 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.

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 Pulay's 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.

A complete characterization of the vibrational spectra of sucrose.

We combined experimental vibrational spectroscopy (FTIR-Raman) and ab-initio calculations based on density functional theory (DFT) to predict the structural and vibrational properties of sucrose in solid phase. The structural properties of sucrose, such as the bond order, possible charge-transfer, and the topological properties of the glucopyran and glucofuran rings were studied by means of the Natural Bond Orbital (NBO) and Atoms in Molecules theory (AIM) investigation. For a complete assignment of the infrared and Raman spectra, the density functional theory (DFT) calculations were combined with Pulay's Scaled Quantum Mechanics Force Field (SQMFF) methodology in order to fit the theoretical frequency values to the experimental ones. An agreement between theoretical and available experimental results was found. A complete assignment of the 129 normal vibration modes for sucrose was performed. Five very intense characteristic bands in the infrared spectrum of sucrose at 3391, 3339, 1069, 1053, and 991 cm(-1) were assigned, the first two to the OH stretching modes while the other ones to C-O stretching modes.