"Few substances that can be ingested into the human body are completely safe," said Peter Cummings of Vanderbilt and Oak Ridge. "Even common table salt, if eaten in sufficient quantity, is lethal. What we are doing is looking at the mechanisms of interaction between buckyballs and DNA; we don't know yet what actually happens in the body."

The scientists used atomistic molecular dynamics simulations to model the interactions. They predicted that buckyballs would attach to nucleotides with binding energies of -27 to -42 kcal/mol. That compares to a binding energy between two buckyballs in aqueous solution of -7.5 kcal/mol. In other words, an association between a C60 and DNA molecule is more energetically favourable than one between two C60 molecules.

"The binding energy between DNA and buckyballs is quite strong," said Cummings. "We found that the energies were comparable to the binding energies of a drug to receptors in cells."

Where the buckyball attached depended on the form of DNA with which it was interacting. For "A" DNA, the buckyballs either attached to the minor groove on the structure, bending the molecule, or penetrated the molecule's free end, which broke hydrogen bonds between the end base pair. Attachment to "B" form DNA did not alter the shape of the DNA molecule, in contrast. The buckyballs bound most strongly to single strand DNA, meanwhile, causing relatively large amounts of deformation.

Modelling a double-stranded DNA molecule that had been deliberately damaged showed that a buckyball could occupy the site of the damage. The scientists believe this might "negatively impact the self-repairing process of the double-strand DNA".

"Earlier studies have shown both that buckyballs can migrate into bodily tissues and can penetrate cell membranes," said Cummings. "We don't know whether they can penetrate a cell nucleus and reach the DNA stored there. What this study shows is that if the buckyballs can get into the nucleus they could cause real problems."

The researchers say that experimental and theoretical studies are needed to demonstrate whether buckyballs can reach the nucleus.

The team reported its work in Biophysical Journal.