CORVALLIS, Ore., Jan. 13 -- Biochemists have "rediscovered" and characterized an important type of chemical bond -- the "halogen bond" -- that once formed the basis for a Nobel Prize but has been largely ignored for decades and never explored for its potential value in medical or pharmaceutical research. They could open the door for new, more effective approaches to drug development, advances in nanotechnology or understanding the possible biological effects of some chemicals to which humans are commonly exposed.
The research at Oregon State University (OSU) explains the formation of an unusual structure of DNA called a "Holliday junction," which was found to incorporate a halogen bond instead of the more typical hydrogen bond that holds most biological molecules together. As an arcane aspect of chemistry that is currently known only to a few researchers working in the field of material science, these halogen bonds may actually play powerful roles in biology and could be a key to advances in pharmacology or nanotechnology, researchers now believe.
OSU alumnus and two-time Nobel laureate Linus Pauling first became famous in the early 1900s for explaining the nature of the chemical "bond," or forces which hold molecules together. And in the 1940s and 1950s, material scientists learned about the "halogen" bond, a special type of bond that uses the halogen elements of chlorine, bromine and iodine, rather than hydrogen. Some of those studies led to the Nobel Prize for chemistry in 1969 for Norwegian chemist Odd Hassel. At that point, the limited knowledge of halogen bonds was largely shelved and almost completely ignored by biologists for more than 30 years, said Pui Shing Ho, an OSU professor and chair of the Department of Biochemistry and Biophysics.
Most atoms have "spheres" of electrons, Ho said, but the electron clouds of the atoms that form halogen bonds are somewhat misshaped, sort of like a donut with a hole in the middle. In their research, the OSU scientists explained the role of such forces in very large molecules, which will help biochemists better understand how halogen bonds affect the structure of biologically important molecules, for good or ill. The findings are outlined in the Proceedings of the National Academy of Sciences, a professional journal.
"One of the more interesting current fields in nanotechnology is to build molecular structures using these DNA Holliday junctions, stitching them together into sheets or fabrics of DNA that other things can bind to, and you might use for a certain purpose, such as electronics or biological computing," Ho said. But a challenge, he said, is to control the shape of the DNA, which in turn depends on a solid understanding of basic molecular structure. The new study could help in that regard, say the OSU researchers.
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