RESOLV chemist Guido Clever has just synthesized two nano objects showing unprecedented structures and properties in specific solvents. One object has two cavities, resembling the shell of a peanut. Another object has a complex chain-like structure and can bind to DNA. The interaction with biomolecules like DNA suggests that these compounds may be used as potential diagnostic or therapeutic tools. The results have been reported as a VIP paper in the renowned journal ‘Angewandte Chemie International Edition’.
Follow the recipe
Guido Clever knows the recipe: Take organic molecules, put them into a solvent, add a metal (palladium preferred), heat and stir. Then prepare for the surprise, usually a nano object with spectacular shape and promising functions.
This time was not different. Clever and his colleagues from TU Dortmund University induced the reaction of m-shaped organic ligands with palladium. They obtained nanostructures with two cavities that resemble the shell of a peanut. In a domino-like synthesis, two peanut-like cages can join in acetonitrile and form a chain-like structure. The latter contains five consecutive pockets – a structure never reported before, belonging to the class of catenanes. “It is remarkable how many bonds break and form between the organic parts and the metals to make that highly entangled chain structure”, says Clever.
Solvent nudges molecular puzzle to assemble
The underlying mechanism leading to these fascinating structures is called ‘self-assembly’. “It can be compared to a pile of puzzle pieces that assemble into the final picture, just by shaking the box. Something impossible on the macroscopic scale is achievable with molecules, provided that the design is perfect”, adds Clever. The role of the solvent in the process is significant: Acetonitrile is able to interact with the palladium atoms; it takes the role of a sewing needle that mediates the reaction between the organic components and the metal cations. Besides, the polarity of the solvent also induces the chain-like objects to aggregate into 14 nanometer wide discs. The latter observation was achieved by irradiating the solution with a dense ray of neutrons produced by research reactor BER II in Berlin, using a technique called small angle neutron scattering.
Finally came the surprising function. In water, DNA can break the discs apart and bind to the constituent chain structures. The new objects have a high positive charge and elongated silhouette that favor an interaction with the negatively charged DNA strands. “Similar large molecules, carrying multiple positive charges, are known to facilitate cell uptake and localization of DNA, therefore these new molecules may lead to applications in the fields of bio imaging and gene therapy”, says Clever. Further studies within RESOLV will elaborate on solubility tuning effects as a function of molecular structure and charge.
R. Zhu, I. Regeni, J. J. Holstein, B. Dittrich, M. Simon, S. Prévost, M. Gradzielski, G. H. Clever: "Catenation and Aggregation of Multy-Cavity Coordination Cages", in: Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201806047