nanotehnoloogia, nanoteknologia, nanotechnologija, nanotehnologijas, nanoteknologija,
nanotechnologii, nanotecnologia, nanotehnologijo,
Tenn. – Soccer-ball-shaped “buckyballs” are the most
famous players on the nanoscale field, presenting
tantalizing prospects of revolutionizing medicine
and the computer industry. Since their discovery
in 1985, engineers and scientists have been exploring
the properties of these molecules for a wide range
of applications and innovations.
But could these microscopic spheres represent a potential environmental hazard?
A new study published in December 2005 in Biophysical Journal raises a red flag
regarding the safety of buckyballs when dissolved in water. It reports the results
of a detailed computer simulation that finds buckyballs bind to the spirals in
DNA molecules in an aqueous environment, causing the DNA to deform, potentially
interfering with its biological functions and possibly causing long-term negative
side effects in people and other living organisms.
The research, conducted at Vanderbilt by chemical engineers Peter T. Cummings
and Alberto Striolo (now a faculty member at the University of Oklahoma), along
with Oak Ridge National Laboratory scientist Xiongce Zhao, employed molecular
dynamics simulations to investigate the question of whether buckyballs would
bind to DNA and, if so, might inflict any lasting damage.
“Safe is a difficult word to define, since few substances that can be ingested
into the human body are completely safe,” points out Cummings, who is the John
R. Hall Professor of Chemical Engineering and director of the Nanomaterials Theory
Institute at Oak Ridge National Laboratory.
“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,” he says.
Despite the caveat, Cummings suggests that his research reveals a potentially
serious problem: “Buckyballs have a potentially adverse effect on the structure,
stability and biological functions of DNA molecules.”
The findings came as something of a surprise, despite earlier studies that have
shown buckyballs to be toxic to cells unless coated and to be able to find their
way into the brains of fish. Before these cautionary discoveries, researchers
thought that the combination of buckyballs' dislike of water and their affinity
for each other would cause them to clump together and sink to the bottom of a
pool, lake, stream or other aqueous environment. As a result, researchers thought
they should not cause a significant environmental problem.
Cummings' team found that, depending on the form the DNA takes, the 60-carbon-atom
(C60) buckyball molecule can lodge in the end of a DNA molecule and break apart
important hydrogen bonds within the double helix. They can also stick to the
minor grooves on the outside of DNA, causing the DNA molecule to bend significantly
to one side. Damage to the DNA molecule is even more pronounced when the molecule
is split into two helices, as it does when cells are dividing or when the genes
are being accessed to produce proteins needed by the cell.
“The binding energy between DNA and buckyballs is quite strong,” Cummings says. “We
found that the energies were comparable to the binding energies of a drug to
receptors in cells.”
It turns out that buckyballs have a stronger affinity for DNA than they do for
themselves. “This research shows that if buckyballs can get into the nucleus,
they can bind to DNA,” Cummings says. “If the DNA is damaged, it can be inhibited
The computer simulations showed that buckyballs make first contact with the DNA
molecule after one to two nanoseconds. Once the C60 molecules bind with the DNA,
they remained stable for the duration of the simulation.
Researchers tested the most common forms of DNA, the “A” and “B” forms. The “B” form
is the most common form. In a stronger saline solution, or when alcohol is added,
the DNA structure can change to the “A” form. A third, rarer form, “Z,” occurs
in high concentrations of alcohol or salt and was not tested.
The researchers found that buckyballs docked on the minor groove of “A” DNA,
bending the molecule and deforming the stacking angles of the base pairs in contact
with it. The simulations also showed that buckyballs can penetrate the free end
of “A” form DNA and permanently break the hydrogen bonds between the end base
pair of nucleotides.
As expected, the buckyballs bound most strongly to single helix DNA, causing
the most deformation and damage. While buckyballs did bind to “B” form double-strand
DNA, the binding did not affect the overall shape of the DNA molecule.
More research needed
What the researchers don't know is whether these worrisome binding events will
take place in the body. “Earlier studies have shown both that buckyballs can
migrate into bodily tissues and can penetrate cell membranes,” Cummings says. “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. What are needed now are experimental and theoretical
studies to demonstrate whether they can actually get there. Because the toxicity
of nanomaterials like buckyballs is not well known at this point, they are regarded
in the laboratory as potentially very hazardous, and treated accordingly.”
Media contacts: Vivian F. Cooper, (615) 322-2762
David F. Salisbury, (615) 343-6803