21 October 2013

Super nano-anti-oxidant

Rice University scientists have created a superantioxidant

NanoNewsNet based on Rice University materials: Rice scientists create a super antioxidantA group of chemists from Rice University, led by Dr. Vicki Colvin, has developed biocompatible cerium oxide nanospheres with superantioxidant properties.

The researchers hope that their development will help in the treatment of traumatic brain injuries, cardiac arrest and patients with Alzheimer's disease, as well as protect against the side effects of radiotherapy in the treatment of cancer. In addition, their nanoparticles are likely able to protect astronauts from prolonged exposure to cosmic radiation and, perhaps, even slow down the aging process.

Cerium oxide nanocrystals have the ability to receive and release oxygen ions, a process known in chemistry as a redox reaction. This is the same process that allows catalytic converters to absorb and eliminate pollutants in cars.

The particles developed by scientists are small enough to be injected into the blood if it is necessary to protect organs from oxidation, especially after injuries, when the amount of reactive oxygen species (ROS) increases sharply.

Cerium particles start working immediately, absorbing free radicals, and continue to work for a long time as they return to their original state – a process that remains a mystery, according to Dr. Colvin. The oxygen forms formed during this process lose their oxidative activity and are no longer "super-reactive".

The layers of oleylamine (red dots) and oleic acid (blue) serve to protect the cerium oxide nanosphere, which absorbs reactive oxygen species and turns them into less harmful molecules. This development can help in the treatment of injuries, protection from the side effects of radiation in the treatment of cancer and the protection of astronauts from cosmic radiation.
(Photo: Colvin Group/Rice University)

During its transition from oxide III to oxide IV and back, the rare earth metal cerium remains relatively stable. In the first state, nanoparticles have zones on their surface that absorb oxygen ions like a sponge. When cerium III oxide is mixed with free radicals, it catalyzes a reaction that effectively weakens ROS by capturing oxygen atoms and converting to cerium IV oxide. Cerium IV oxide particles slowly release the oxygen captured by them, again becoming cerium III oxide, and can destroy free radicals again and again.

Nanoparticles and their smallest size make effective oxygen absorbers.

"The smaller the particles, the larger the surface area available for free radical capture," explains Dr. Colvin. "One gram of such nanoparticles can have a surface area equal to the area of a football field, and this gives a huge surface for oxygen absorption."

None of the cerium oxide particles developed earlier to solve this problem were stable enough to be used in biological conditions.

"We have created homogeneous particles, the surface of which is really clearly structured, and have found an anhydrous production method that allows us to maximize the surface areas that absorb oxygen," the scientist continues.

According to her, it was quite simple to add a polymer coating to the 3.8-nanometer spheres. This thin coating allows oxygen to pass to the particle and simultaneously protects it during multiple ROS absorption cycles.

In tests with such a strong oxidizer as hydrogen peroxide, cerium III oxide nanoparticles demonstrated nine times higher activity than the common antioxidant Trolox, and successfully withstood 20 redox cycles.

"The logical continuation of our research will be the development of passive targeting," says Colvin. "To do this, we plan to bind antibodies to the surface of nanoparticles so that they can interact with certain types of cells. We are going to evaluate the effectiveness of these modified particles in conditions closer to biological realities."

Most of all, Dr. Colvin is happy to be able to help cancer patients undergoing radiation therapy.

"Existing radioprotectors need to be given in incredibly high doses," she explains. "They also have their side effects, and their choice is not so great."

Self-healing antioxidants that can linger and protect organs where necessary will have clear advantages over toxic radioprotectors that must be eliminated from the body before they can harm healthy tissues.

"Probably the most interesting thing about all this is that so many nanomedical methods use the magnetic and optical properties of nanomaterials, and we have excellent examples of this at Rice," says Colvin. But these special properties of nanoparticles are rarely used for medical purposes. What I like about this work is that it opens up to the medical world a part of nanochemistry, in particular, catalysis. If we manage to make this chemistry work in biological conditions, cerium III and IV oxides – electronic "shuttles" – will have a wide scope of application."

The results of the study are published in the journal ACS Nano:
Antioxidant Properties of Cerium Oxide Nanocrystals as a Function of Nanocrystal Diameter and Surface CoatingPortal "Eternal youth" http://vechnayamolodost.ru


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