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

• Lactose in aqueous solution was characterised by IR, HATR and Raman spectroscopies.
• The vibrational assignment of lactose in aqueous solution was performed.
• The presence of four lactose forms in an aqueous solution is proposed.
• The stabilities of three lactose species were studied by NBO and AIM analyses.
• The presence of four lactose forms is evidenced by HATR and Raman bands.

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.

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