Stable carbon-80 fullerene (C79B) would be an electron short, instead of having an extra electron. There would be the components of a molecular semiconductor. C79N (carbon 80 with one carbon changed to a nitrogen) would have an extra electron.
"No one has done anything like this," said Harry Dorn of Virginia Tech. "Since the article was published, we now know that we can take the electron back out of the fullerene cage."
He says the discovery could be important to the new fields of spintronics, molecular electronics, and micro to nanoscale electronics, as well as the new field of quantum computing.
"The single electron bonded-diatomic yttrium has unique spin properties that can be altered. Increasing the polarization of this spin, could be important for improving the sensitivity of MRI and NMR, he said.
Blacksburg, Va. – Virginia Tech chemistry Professor Harry Dorn has developed a new area of fullerene chemistry that may be the backbone for development of molecular semiconductors and quantum computing applications.
Dorn plays with the hollow carbon molecules known as fullerenes as if they are tinker toys. First, in 1999, he figured out how to put atoms inside the 80-atom molecule, then how to do it reliably, how to change the number of atoms forming the carbon cage, and how to change the number and kinds of atoms inside the cage, resulting in a new, more sensitive MRI material and a vehicle to deliver radioactive atoms for applications in nuclear medicine.
As part of the research to place gadolinium atoms inside the carbon cage for MRI applications, Dorn created 80-atom carbon molecule with two yttrium ions inside. Then he began to fool with the materials of the cage itself. He replaced one of the 80 atoms of carbon with an atom of nitrogen (providing Y2@C79N). This change leaves the nitrogen atom with an extra electron. Dorn discovered that the extra electron, instead of being on the nitrogen atom on the fullerene cage surface, ducks inside between the yttrium ions, forming a one-electron bond. "Basically, a very unusual one electron bond between two yttrium atoms," he said.
Discovery of this new class of stable molecules (M2@C79N ) was supported by computational studies by Daniel Crawford, associate professor of chemistry at Virginia Tech, and the structure was confirmed by x-ray crystallographic studies by Alan Balch , professor of chemistry at the University of California, Davis.
This research is reported in the September 6, 2008, online issue of the Journal of the American Chemical Society (JACS), in an article by Dorn and his colleagues at Virginia Tech and UC Davis.
FURTHER READING
The JACS article is "M2@C79N (M ) Y, Tb): Isolation and Characterization of Stable Endohedral Metallofullerenes Exhibiting M-M Bonding Interactions inside Aza[80]fullerene Cages," by Tianming Zuo, Liaosa Xu, Christine M. Beavers, Marilyn M. Olmstead, Wujun Fu, Crawford, Balch, and Dorn
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In a major step forward for computational protein design, University of Washington scientists have built from scratch a handful of enzymes that successfully catalyze a specific chemical reaction. These proteins have no naturally occurring counterparts, and the reaction--which breaks down a man-made chemical--has no natural catalyst.
David Baker and his colleagues at the University of Washington focused on a reaction that would break certain bonds between carbon atoms. The ability to design enzymes that can break and make carbon-carbon bonds could potentially enable scientists to break down environmental toxins, manufacture drugs, and create new fuels.
As they report in the journal Science, Baker and his group first designed what an ideal active site would look like for the reaction. An active site is a pocket within an enzyme where the catalyzed reaction takes place. In order to do its job, an active site must have precise geometry and chemical makeup, tailored to the reaction it catalyzes. Some components hold the reacting molecules in place, while others participate in the reaction's chemical mechanisms.
Once the researchers computed the active site, they used a newly developed set of algorithms to model proteins that have such a site. Each designed protein was ranked according to its ability to bind the reacting chemicals and hold them in the proper position.
The next step was to actually synthesize the selected proteins. The researchers derived gene sequences for 72 of the designed enzymes, ordered snippets of DNA containing those genes, and used bacteria to turn the genes into proteins. Each protein was then tested for its ability to catalyze the carbon-carbon bond breaking reaction.
Of the 72 proteins selected, 32 successfully helped along the reaction. The most efficient proteins sped up the reaction to 10,000 times the rate without an enzyme.
While that's an impressive feat compared with earlier enzyme design attempts, the synthesized enzymes pale in comparison to naturally occurring ones. "It's not very good at all," says Baker. "Naturally occurring enzymes can increase the rate of reactions by much, much greater amounts"--as much as a quadrillion-fold.
"One of our research problems is to figure out what's missing from our designs that naturally occurring enzymes have figured out," says Baker. In follow-up studies, his group has taken two approaches to this problem: refining its computer algorithms, and asking nature to step in where the researchers left off. By using their minimally functional enzymes as evolutionary starting points, the researchers can use directed evolution to create more efficient catalysts.
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The transcript of an email interview Robert Freitas is up at lifeboat.com
What I found to be the highlights of the interview:
1. Culminating 5 years of intermittent effort Robert Freitas has finished his latest theoretical scaling study of a new diamondoid medical nanorobot called the "chromallocyte". This is the first full technical description of a cell repair nanorobot ever published.
One conceptually simple form of basic cell repair is chromosome replacement therapy (CRT), in which the entire chromatin content of the nucleus in a living cell is extracted and promptly replaced with a new set of prefabricated chromosomes which have been artificially manufactured as defect-free copies of the originals. The chromallocyte is a hypothetical mobile cell-repair nanorobot capable of limited vascular surface travel into the capillary bed of the targeted tissue or organ, followed by extravasation, histonatation, cytopenetration, and complete chromatin replacement in the nucleus of one target cell, and ending with a return to the bloodstream and subsequent extraction of the device from the body, completing the CRT mission....
2. In February, 2007, Robert Freitas and Ralph Merkle completed the core of a major three-year project to computationally analyze a comprehensive set of DMS reactions and tooltips that could be used to build diamond, graphene (e.g., carbon nanotubes), and all of the tools themselves including all necessary tool recharging reactions.
So far they have defined a total of 53 reaction sequences incorporating 252 reaction steps with 1,192 individual DFT-based reaction energies reported. (These reaction sequences range in length from 1-13 reaction steps (typically 4) with 0-10 possible pathological side reactions or rearrangements (typically 3) reported per reaction.) The reactions have been laid out in tables and systematized.
These reactions will form the core of our roadmap to develop diamond mechanosynthesis along a direct path that leads, ultimately, to the design and construction of the first diamondoid nanofactory.
3. Based on the computational chemistry work, their latest estimates suggest that an ideal research effort paced to make optimum use of available computational, experimental, and human resources would probably run at a $1-5M/yr level for the first 5 years of the program, ramp up to $20-50M/yr for the next 6 years, then finish off at a ~$100M/yr rate culminating in a simple working desktop nanofactory appliance in year 16 of a ~$900M effort.
4. Robert Freitas believes that early nanofactories necessarily will be extremely primitive. They will be very limited in the composition and complexity of products they can build and in the types of chemical elements and feedstocks they can handle. They will be fairly unreliable and will require significant supervision and maintenance. They will be relatively expensive to own and operate. Over a period of perhaps 10-20 years, nanofactory costs and capabilities will slowly improve and product costs will gradually drift downward toward the likely $1/kg regulatory floor, giving society some time to adjust to new threats as nanofactories become increasingly ubiquitous in our environment and economy.
5. The interview also discusses details about feedstock choices for nanofactories, ecophages and nanoshields.
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