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Encyclopedia of Physical Science and Technology EN010b-481 July 14, 2001 18:45

Noble Metals (Chemistry) 489

In the biological, as opposed to medical, related uses the fects. OsO 4 is a useful biological fixative and specific stain
platinum–protein interaction is capitalized on to provide for lipid-containing structures. Because the compound re-
a heavy metal center to assist in X-ray diffraction studies acts selectively with olefinic bonds, Os 2 O 6 py 4 will react
and as a model to understand how platinum interacts with with the 2- and 3-hydroxyl groups in nucleosides, and os-
various biological systems in antitumor medication. Many mium amine complexes are used as a specific stain for
derivatives display bacteriostatic and bacteriocidal prop- polysaccharides.
erties (e.g., (NH 4 ) 2 [PtCl 4 ] and the corresponding iridium,
osmium, and palladium derivatives and (NH 4 ) 2 [PtCl 6 ] and
8. Ruthenium
its corresponding ruthenium derivative). PtCl 2 acts as a
lipid stain because of its ability to interact with the olefinic Ruthenium(III) complexes involving chloro, ammine,
group. and carboxylato ligands have shown antitumor activity
on initial screening. Ruthenium(II) 1,10-phenanthroline
4. Palladium derivatives have been investigated for their antibacte-
rial activities mainly against gram-positive microorgan-
Palladium alloys are used as replacements for damaged isms. Ruthenium Red, prepared by the air oxidation of
arthritic bones and joints in which there is a load-bearing [Ru(NH 3 ) 6 ]Cl 3 , is used to stain polysaccharides and elas-
requirement. Palladium(II) complexes have shown some tic tissue fibers. Of more theoretical interest to biological
antitumor activity on initial screening, and Pd(OH) 2 was systems is the work on electron exchange being done with
tested in treating obesity. Ru /Ru complex systems. This system is important be-
III
II
cause it is resistant to substitution in both oxidation states,
5. Iridium making it easy to study. [Ru(NH 3 ) 5 H 2 O] 2+ is hydrophilic
and remains solvated even though it is bound tightly to a
As discussed with platinum, iridium is a component in al- protein and the oxidation–reduction potentials of the sys-
loys used in pacemakers. The isotope 191m Ir, derived from
191 Os, is useful in radioangiography because it has a short tems studied are in the range of those found in biological
systems.
half-life, 4.9 sec, and it decays to a nontoxic product.
Because the exposure is minimal, it is well suited for
serial radiological studies. This has been applied to the K. Jewelry
study of heart defects in children. The human-made iso- In general, the noble metals, because of their attractive
tope 192 Ir can be placed in a platinum container, which
appearance, stability, and perceived value, have been trea-
allows gamma rays to pass while absorbing potentially
sured in jewelry, art, and decoration.
damaging beta ray emission. The container is then im-
planted into the tumor for treatment. Breast cancer has
been treated by this method. 1. Gold
Thepopularityofgoldisduetoitssocialacceptance,color,
6. Rhodium lack of allergenic properties in the metallic form, as well
The major medical use of rhodium is in radiotherapy. as for the properties discussed for the precious metals in
The isotopes 106 Ru/ 106 Rh have been shaped into cups that general. Gold is used predominately in jewelry and is rated
are coated with silver and then used to treat retinoblas- on a karatage or a fineness system. The karatage system is
toma. Rhodium(II) carboxylates may be antitumor agents the one in predominant use in the U.S. and Great Britain.
based on initial screening and RhCl 3 (DMSO) has been In the jewelry industry in the U.S. gold must be a minimum
1
shown to have activity against leukemia in mice. Sev- of 10 karat. Jewelry is commonly labeled gold filled or
2
eral rhodium(II) pyrimidine derivatives show bacterio- rolled gold plate, with the rolled gold plate having a lower
static and bacteriocidal properties. gold content. Bonding of the gold to a base is done by
soldering, brazing, welding, or mechanical methods. The
soldering or brazing alloy is usually Au–Ag–Cu with the
7. Osmium
Ag–Cu ratio varied to adjust the melting point. The most
Surprisingly, OsO 4 has been found to be an effective treat- common alloys are Au–Ag–Cu, yellow gold; Au–Ni–Cu–
ment for inflammatory arthritis of the knee. This applica- Zn, white gold; and Au–Pd, a more expensive but more
tion of osmic acid was approved in Sweden and Norway in corrosion resistant white gold. White golds that are rich in
1978, but its use is controversial. The potential of damage silver can tarnish. Depending on the application, the two
from the OsO 4 to healthy tissue has prompted a search white gold alloys may be interchangeable. The color of the
for other osmium derivatives. Work is being done on os- gold can be changed by varying its composition (e.g., red
miumcarbohydratepolymerstoavoidthepotentialsideef- gold is high in copper, and green gold is high in gold and