Synthesis of DL-alanine hollow tubes and core-shell mesostructures

Three double hydrophilic block copolymers were used as crystalgrowth modifiers of DL-alanine to generate amorphous precursor nanoparticles that undergo subsequent mesoscopic transformation to core-shell mesostructures and hollow tubes with quadratic cross-sections. The growth sequence can be stopped at various stages so that a series of intermediates between amorphous core- and crystalline-shell particles and tubes can be obtained. Time-dependent conductivity, TEM, SEM, and environmental scanning electron microscopy (ESEM) measurements were used to obtain a better understanding of the crystallization process, and a formation mechanism for the generation of the tubes is proposed. Na₂SO₄, NaCl, and NaNO₃ as salts differ in their influence on the crystallization behavior of alanine by changing the solubility of alanine and by decreasing the stability of the intermediate particles. Core-shell mesostructures that formed in the dissolution- recrystallization process were captured as the transformation rate was decreased by the addition of copolymers or salts. Hollow tubes with quadratic cross-sections are the final product of the transformation process.