Electron in a cage
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| Fred Hawthorne - creating centrally charged cages |
US chemists have created a spectacular blue cage compound in which they have trapped a single unpaired electron. The blue cage is far more stable than would expected and may offer new possibilities in the design of boron reagents for treating cancer and in materials science.
Frederick Hawthorne's team at the University of California at Los Angeles has worked for many years developing a way to deliver a radiation dose straight to the site of a cancer so as to reduce or even eliminate the side-effects of radiotherapy. The technique they are developing is known as boron neutron capture therapy and the basic idea is to use molecules containing clusters of 10B to get at the cancer cells and then to fire a beam of neutrons at the site. The result is nuclear fission of the boron isotope, which releases lethal helium and lithium nuclei to kill the cancer cells.
Hawthorne describes his boron compounds as molecular "landmines" where nothing happens until a neutron steps on one. One of the main areas in which the approach will be very important is in treating brain tumours where damage to peripheral cells is even more undesirable than in other tissues.
The team including Toralf Peymann and Carolyn Knobler has created a {[closoB12(CH3)12].}- a paramagnetic cage by the one-electron oxidation of the non-radical cage using ceric(IV) ammonium nitrate (CAN) in acetonitrile. The lone electron is trapped within the hydrocarbon sheath of the borane cage.
Hawthorne described the organoboron radical as a camouflaged species which means it might be used in the development of new materials whereas the 'naked' versions are usually too reactive to be useful synthetically.
The team reports its latest discoveries in Chemical Communications, 1999, 2039*.
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