Abstract:

Glutamic acid can crystallize in two polymorphic structures depending on the crystn. regime. The study demonstrates an efficient method to preferentially crystallize the nonstable polymorphic structure (the $\alpha$-form) in the presence of surface active agents. The rate of transformation depends on the rate of growth of $\beta$ and not on the rate of dissoln. of $\alpha$. The growth rate of $\beta$ was a function of the supersatn. of the solute in soln. The transformation could be inhibited by the addn. of surfactants. The surfactants are capable of adsorbing preferentially to the $\alpha$-growing crystals and soln. mediating (retarding) the transformation of the $\alpha$- to the $\beta$-form. Probably the surfactant nature and steric considerations were important for the inhibition of both nucleation and growth of the $\beta$-polymorph. A Langmuir approach indicated that the kinetic parameter was related to the vol. of surfactant adsorbed at the crystal surface. No changes in crystal morphol. were obsd., indicating that adsorption was not specific to any crystal face. Different mechanisms of surfactant adsorption were suggested: adsorption of single mols. at low concns. of surfactant and formation of hemimicelles at higher concns. [on SciFinder(R)]