Platinum, a neat bit of photochemistry, nanospheres and where drugs act in the cell...

John Shelnut and colleagues at Sandia National Laboratories and the University of New Mexico in Albuquerque as well as the University of Georgia in Athens have developed a novel system for developing , hollow, porous platinum nanospheres which might enable researchers to identify where drugs react within cell structures.

Liposomes are familiar biological structures, that are effectively balls of fat that enable the contents to be carried in the body, isolating and insulating the contents until they are released to act. For example liposomes have an ability to target cancer because typically less than 400nm, they can rapidly enter tumour sites from the blood, but are kept in the bloodstream by the endothelial cell walls which they cannot permeate. Currently available anti- Cancer drugs such as Doxorubicin (Doxil a liposomal injenction for ovarian cancers)) and Daunorubicin (Daunoxome - a liposomal injection for treating AIS related Karposi's sarcoma) utilise this "liposome delivery".

Shelnut and his colleagues utilised a manufactured liposome containing a light activated porphyrin catalyst (the active part of photosynthetic proteins) containing tin - placed in a platinum salt solution and irradiated with light - this precipitates or stimulates the photocatalyst to transfer electrons to the platinum ions and as the atoms build up sheets or dendrites of the metal are formed as hollow metal spheres. Dissolving the liposomes reveals the structures (see pic) which have the shape of the liposomes of up to 200 nm aggregates of foam like structures. The trick to developing the structures depends upon the initial levels of tin so that sufficient platinum is deposited. The size of the nanostructures can be altered by changing the porphyrin concentration, the concentration of platinum in solution, the amount of light illuminating the reaction and the length of time the light was on.

One application is "nanotagging" of biological structures such as drug molecules.

"This would involve labeling the drug by attaching a porphyrin molecule and, after allowing the drug to bind to a cell, using light to grow a nanometer-sized particle. The nanoparticles can then be imaged with electron microscopy to reveal the location of the drug receptor molecules on the cell," Shelnut says. "This type of nanotagging technique might be used in non-biological applications as well - such as finding flaws in semiconductor surfaces."

Tantalisingly they suggest that "Further, nanocages composed of other metals and alloys can be made."

Sandia Labs are of course part of Lockheed Martin and see that can manipulate the nanoscale structure of platinum to have control over the size, porosity, composition, surface species, solubility, stability and other functional properties, they can redesigned nanometric platinum structures for use other applications, including catalysis, sensors and optoelectronic and magnetic devices. Find out more about this fascinating use of photochemistry at the Shelnut team website (http://jasheln.unm.edu/)

Platinum mining in the US

Stillwater Mining Company (NYSE:SMC) is a company controlled by Norimet Limited and Russian state owned, MMC Norilsk Nickel under NYSE Rule 303A.00 and is is the only U.S. producer of palladium and platinum. It is the largest primary producer of platinum group metals outside South Africa and Russia. Mining commenced in 1987, west of Nye, Montana. Platinum Group Metals (pgm) are extracted from the J-M Reef, which contains very high grades of pgm - about 20 g per tonne. Palladium accounts for about three-quarters of the pgm extracted, with the remainder largely platinum.

MMC Norilsk Nickel is the world's leading producer of nickel (19% share of world mined production) and palladium (52% share of world mined production) and is Russia's leading gold producer Ranked 4th for Platinum (12% share of world mined production)and among top 10 copper producers.

They signed agreements for mining in Western Siberia with bhp Billiton on June 12th, 2006 and with Rio Tinto Zinc on January 27th, 2006 for mining in Eastern and Far Eastern Siberia - More here.

References
Synthesis of Platinum Nanocages by Using Liposomes Containing Photocatalyst Molecules
Yujiang Song, Robert M. Garcia, Rachel M. Dorin, Haorong Wang, Yan Qiu, John A. Shelnutt
Angewandte Chemie Volume 118, Issue 48, 2006. Pages 8306-8310

Also here in pre-publication form from the Shelnut Group.