Physical and chemical properties of molecular compounds of lactose

The physical and chemical properties of the molecular compounds of lactose 5 alpha-/3 beta- and 3 alpha-/2 beta-lactose were studied. The melting point and the heat of combustion were determined. The specific optical rotation of aqueous and organic solutions of these compounds was measured and was in agreement with their stoichiometric formula. Weak differences were observed in the chromatographic mobility of the lactose molecular compounds provided that nonaqueous solvents were used. The analysis by infrared spectroscopy showed that these compounds were due to association of alpha-lactose and beta-lactose crystals by a specific lattice of hydrogen bonding. The latter could be destroyed under controlled water vapor uptake. These physical and chemical properties led us to hypothesize on the means of association of these molecular compounds by comparison with the known structures of the other crystalline lactose forms.