Morphology of crystals of alpha-lactose hydrate grown from aqueous solution

When dissolved in aqueous solution, alpha -lactose, whether originally in t he anhydrous or the monohydrated form, readily undergoes mutarotation to yi eld the beta isomer. At equilibrium, which is reached in 6.5 h at 292 K and more rapidly with increasing temperatures, the latter is present to the ex tent of ca. 60% w/w. At saturation, alpha -lactose hydrate precipitates fro m this solution being considerably less soluble than the beta form. The res ulting crystals have a highly asymmetric, tomahawk shaped morphology charac terized by large {0(1) over bar 1} in the {0(1) over bar 1} sectors of the crystals coupled with a characteristic lack of growth in the [0(1) over bar 0] direction;. Growth under conditions that restrict the formation of the beta isomer yields more symmetrically shaped, needlelike crystals. These sh ow a gradual transition to the tomahawk shape as the concentration of the b eta isomer in solution and hence in the crystal is increased. An assessment is made of the degree of incorporation of the beta isomer into the crystal , its distribution and its influence on the defect structure of the materia l.