Chemistry Reference
In-Depth Information
Ni, like Co, seems to be much more extensively utilised by anaerobic bacteria, in reactions involving chemicals
like CH
4
, CO, and H
2
, the metabolism of which was important before the appearance of dioxygen. In higher
organisms, notably plants, the only Ni-containing enzyme is urease. Since humans, in common with most
terrestrial vertebrates, excrete excess nitrogen from the metabolism of their proteins and constituent amino acids
in the form of urea
they do not produce this urea-hydrolysing enzyme. Over half of the
supply of palladium and its congener platinum goes into catalytic converters. Palladium is also found in many
electronic devices and in fuel cell technology. A large number of carbon
they are ureotelic
e
e
carbon bond forming reactions in
organic chemistry (such as the Heck and Suzuki coupling) are facilitated by catalysis with palladium compounds,
and in 2010, palladium-catalysed organic reactions were recognised by the Nobel Prize in chemistry. Pt, initially
in the form of the cis isomer of Pt(NH
3
)
2
Cl
2
, used under the name of cisplatin, has been hugely successful in the
treatment of testicular and ovarian cancers. Since the appearance of cis-platin resistant tumours, new Pt anti-
tumour drugs have been developed. The precise mode of action of cis-platin is discussed in detail in Chapter 20,
together with a number of other striking examples of metals as drugs.
One direct consequence of the appearance of dioxygen was that new redox systems and enzymes were required
which could operate at much higher redox potentials than previously. As we will see in Chapter 14, copper proved
to be particularly suited to this role, and, like Fe, is frequently encountered in reactions involving dioxygen.
Ag and Au are known as precious metals, although, unlike Au, Ag forms a black tarnish of silver sulfide in contact
with air. Its bromides and iodides are used in photographic film. Over the last six millennia, Ag has been used to
prevent microbial infections, which is particularly important in the treatment of burn wounds, making it the most
important antimicrobial agent available before the introduction of antibiotics. However, the last few years have
seen the emergence of silver nanoparticles which are being heralded as an excellent candidate for therapeutic
purposes. Gold might seem to be a surprising (and at first sight costly) therapeutic agent. Nonetheless, gold
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The orally active anti-rheumatoid arthritis drug Auranofin
.
FIGURE 1.9
administered at doses of 3
6 mg/day without necessitating regular visits to the doctor, represents a 'second-
generation' drug in the treatment of this painful condition.
As we will see in Chapter 12, zinc shares with the alkaline earths the property of belonging to one block of the
periodic table while having many of the properties characteristic of another. In the case of zinc and the other two
elements in its block, cadmium and mercury, they resemble the three heavy elements of the boron group. Zn, in
addition to its use as a Lewis acid in enzyme catalysis, plays a structural role stabilizing protein molecules. It is
also involved in a characteristic motif, termed a Zn finger, in a number of eukaryotic DNA-binding proteins, which
regulate the transcription of DNA into RNA. The other two elements in group 12, cadmium and mercury, are both
extremely toxic, as will be discussed in Chapter 23. Cd is the cause of Itai-itai disease, while Hg is the cause of
“hatter's shakes.” Mercurous nitrate was employed in hat-making to render the felt used in the production of 'top
e
