PITTSBURGH - -For the first time, a team of investigators at CarnegieMellon University has shown that the binding of metal ions can mediatethe formation of peptide nucleic acid (PNA) duplexes from singlestrands of PNA that are only partly complementary. This result opensnew opportunities to create functional, three-dimensional nanosizestructures such as molecular-scale electronic circuits, which couldreduce by thousands of times the size of today's common electronicdevices. The research results will appear in the October 26 issue ofthe Journal of the American Chemical Society.
"DNA nanotechnology has led to the construction of sophisticatedthree-dimensional nano-architectures composed exclusively from nucleicacid strands. These structures can acquire a completely new set ofmagnetic and electrical properties if metal ions are incorporated inthe nucleic acids at specific locations because the metal ions haveunpaired electrons," said Catalina Achim, assistant professor ofchemistry at the Mellon College of Science. "Our goal is to harness theinformation storage ability of metal-containing PNAs to buildmolecular-scale devices -- tiny replicas of today's electronic circuitcomponents, such as wires, diodes and transistors."
Normally, DNA occurs as the well-known double helix firstproposed by James Watson and Francis Crick 50 years ago. Each strand ofthe helix consists of a backbone linked to nucleobases, which occupythe inside of the helix. Nucleobases of one strand bind only tospecific nucleobases of a complementary strand, and the two strandswind around one another like a twisted ladder. Artificiallymanufactured PNAs incorporate nucleobases that are bound to a backbonechain of pseudo-amino acids, rather than the sugar-phosphate groups ofDNA.
"In modifying our PNAs so that they are significantly morestable, we have discovered that the PNA strands don't have to be fullycomplementary for a metal-containing PNA duplex to form. This is animportant finding because it should permit us to use non-complementaryparts of the PNA duplexes to construct larger structures, which areuseful for material science applications," said Achim.
Two years ago, Achim was the first scientist to report theconstruction of PNA duplexes that contained metal ions (nickel ions,specifically) and ligands inserted in place of a central nucleobasespair. Since then, the researchers, including graduate students andpostdocs Richard Watson, Yury Skorik and Goutam Patra, have synthesizedPNAs with a variety of ligands and metal ions to broaden the range ofthermal stability and electronic properties. By replacing a nucleobaseof a PNA with the molecule 8-hydroxyquinoline, which readily binds tocopper ions, the research team constructed PNAs whose nucleic acidstrands are only partly complementary and found that these duplexes areheld together by standard Watson-Crick nucleobase pairs, but also bybonds between copper ions and the 8-hydroxyquinolines projecting fromeach of the two strands.
The research was supported by the National Science Foundation and the Camille and Henry Dreyfus Foundation.
The Mellon College of Science at Carnegie Mellon maintainsinnovative research and educational programs in biological sciences,chemistry, physics, mathematics and several interdisciplinary areas.For more information, visit www.cmu.edu/mcs.
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