Analytical Ultracentrifugation as a Tool in Supramolecular Chemistry: A Feasibility Study using a Metal Coordination Array

Schubert, Dieter; van den Broek, Jacomina A.; Sell, Bernd; Durchschlag, Helmut; Mächtle, Walter; Schubert, Ulrich S.; Lehn, Jean-Marie
Self-assembling systems composed of org. mols. and metal ions represent one of the topics in modern supramol. chem. Up to now, their phys. characterization was essentially limited to crystals or to surface layers. Studies on solubilized systems, e.g., on their mol. mass distribution or assocn. behavior, are rare. We have explored whether sedimentation equil. anal. in the Beckman Optima XL-A anal. ultracentrifuge can be successfully applied. A grid-like Co coordination array (2 2-Co(II)-grid) was used as a model compd. The tech. problem involved, concerning the chem. resistance of the cell components against org. solvents, was solved by Ti centerpieces and polyethylene gaskets. Another potential problem, the high UV absorbance of the solvents, could be circumvented by measuring the absorbance vs. radius profiles in the visible wavelength range, where "grids" and most other related compds. show absorption bands. Special efforts were made to solve the remaining problems: (i) the suppression of nonidealities in sedimentation behavior, which could prevent or greatly complicate a successful anal. of self-assocg. systems, and (ii) the detn. of the partial sp. vol. .hivin.v of the complexes, in particular considering compds. either not available in sufficient quantities for d. measurements or exhibiting low soly. With respect to problem (i), solvent/salt systems were found in which the model compd. apparently shows ideal sedimentation behavior. Procedures are suggested to overcome problem (ii).
Type of Publication:
Progress in Colloid and Polymer Science
166 – 177