Self-Recognition Between Two Almost Identical Macroions During Their Assembly: The Effects of pH and Temperature

Two Keplerate-type macroions, [Mo(VI) 72 Fe(III) 30 O252 - (CH3 COO)12 {Mo2 O7 (H2 O)}2 {H2 Mo2 O8 (H2 O)}(H2 O)91 ]⋅ca. 150 H2 O= {Mo72 Fe30 } and [{Na(H2 O)12 }⊂{Mo(VI) 72 Cr(III) 30 O252 (CH3 COO)19 - (H2 O)94 }]⋅ca. 120 H2 O={Mo72 Cr30 }, with identical size and shape but different charge density, can self-assemble into spherical "blackberry"-like structures in aqueous solution by means of electrostatic interactions. These two macroanions can self-recognize each other and self-assemble into two separate types of homogeneous blackberries in their mixed dilute aqueous solution, in which they carry -7 and -5 net charges, respectively. Either adjusting the solution pH or raising temperature is expected to make the self-recognition more difficult, by making the charge densities of the two clusters closer, or by decreasing the activation energy barrier for the blackberry formation, respectively. Amazingly, the self-recognition behavior remains, as confirmed by dynamic and static light scattering, TEM, and energy dispersive spectroscopy techniques. The results prove that the self-recognition behavior of the macroions due to the long-range electrostatic interaction is universal and can be achieved when only minimum differences exist between two types of macroanions.