Electron-Equivalent Valency through Molecularly Well-Defined Multivalent DNA

Oligonucleotide-functionalized nanoparticles (NPs), also known as programmable atom equivalents (PAEs), have emerged as a class of versatile building blocks for generating colloidal crystals with tailorable structures and properties. Recent studies have shown that, at small size and low DNA grafting density, PAEs can also behave as electron equivalents (EEs), roaming through and stabilizing a complementary PAE sublattice. However, it has been challenging to obtain a detailed understanding of EEPAE interactions and the underlying colloidal metallicity because there is inherent polydispersity in the number of DNA strands on the surfaces of these NPs; thus, the structural uniformity and tailorability of NP-based EEs are somewhat limited. Herein, we report a strategy for synthesizing colloidal crystals where the EEs are templated by small molecules, instead of NPs, and functionalized with a precise number of DNA strands. When these molecularly precise EEs are assembled with complementary NP-based PAEs, X-ray scattering and electron microscopy reveal the formation of three distinct metallic phases. Importantly, we show that the thermal stability of these crystals is dependent on the number of sticky ends per EE, while lattice symmetry is controlled by the number and orientation of EE sticky ends on the PAEs. Taken together, this work introduces the notion that, unlike conventional electrons, EEs that are molecular in origin can have a defined valency that can be used to influence and guide specific phase formation.

Automated summary

Recent studies have shown that PAEs can behave as electron equivalents at small size and low DNA grafting density, however, the polydispersity in the number of DNA strands on the surfaces of these NPs limits the structural uniformity and tailorability of NP-based EEs. By assembling molecularly precise EEs with complementary NP-based PAEs, three distinct metallic phases can be formed, demonstrating that molecular-based EEs can influence specific phase formation.