Precision Bonding Makes Tiny High Performance Actuators Possible

For the first time, a team of investigators at Carnegie Mellon University has shown that the binding of metal ions can mediate the formation of peptide nucleic acid (PNA) duplexes from single strands of PNA that are only partly complementary. This result opens new opportunities to create functional, three-dimensional nanosize structures such as molecular-scale electronic circuits, which could reduce by thousands of times the size of today's common electronic devices.

Cartoon representation of a PNA duplex that contains both complementary Watson Crick AT and GC basepairs and metal-ligand alternative basepairs and of a metal-containing PNA duplex formed from partly complementary PNA strands. X = ligand; Gray ball = metal ion; A-T = Watson Crick base pair; G-C = Watson Crick base pair; A- = non-complementary parts of the PNA duplexes that could be used to construct larger structures

Normally, DNA occurs as the well-known double helix first proposed by James Watson and Francis Crick 50 years ago. Each strand of the helix consists of a backbone linked to nucleobases, which occupy the inside of the helix. Nucleobases of one strand bind only to specific nucleobases of a complementary strand, and the two strands wind around one another like a twisted ladder. Artificially manufactured PNAs incorporate nucleobases that are bound to a backbone chain of pseudo-amino acids, rather than the sugar-phosphate groups of DNA.

Researchers have synthesized PNAs with a variety of ligands and metal ions to broaden the range of thermal stability and electronic properties. By replacing a nucleobase of a PNA with the molecule 8-hydroxyquinoline, which readily binds to copper ions, the research team constructed PNAs whose nucleic acid strands are only partly complementary and found that these duplexes are held together by standard Watson-Crick nucleobase pairs, but also by bonds between copper ions and the 8-hydroxyquinolines projecting from each of the two strands.

Visit www.cmu.edu/mcs.