An international team of chemists have developed an environmentally-friendly coupling reaction for connecting together the molecular equivalent of Lego building blocks into large structures.

Janet Scott at Monash University, Clayton, Australia, and colleagues devised a widely applicable schema to prepare open-ended series of macromolecules, while remaining true to the environmentally aware philosophies of green chemistry. She designed various types of building blocks with different structural and chemical characteristics, which can be rationally connected together into specific sequences using aldol-type Claisen-Schmidt condensation reactions.

Scott explains that 'male' building blocks contain activated nucleophilic methylene groups, while 'female' blocks have non-enolisable aldehyde groups. Some blocks have just one of these active functional groups and are called terminal, while the connecting blocks that contain two are coined unions. There are also rigid and flexible blocks, allowing the properties of the molecular architectures built from them to be tailored closely to their intended use.

Outlining the benefits and green credentials of her strategy, Scott reports that couplings proceed 'catalytically and in high atom economy with good chemo, regio and stereoselectivity', adding that the reactions' major by-product is water.

Looking towards the future, Scott says she sees many possible applications for macromolecules engineered in this way, including as polymer and peptide linkers, chelating agents, molecular wires and switches.

David Parker