Chemistry Reference
In-Depth Information
9
Complexes and Commerce
It would be inappropriate, before concluding, to leave the subject without some mention of
the roles that coordination complexes play in the working world. Otherwise, one could be
left with the impression that the field is little more than an academic plaything. Of course,
we have seen in Chapter 8 how Nature has made fine use of coordination complexes, but
this goes on essentially without human intervention. What is important to appreciate is
that coordination chemistry and coordination complexes lie at the core of an array of
important applications in industry, medicine and other fields. Given the inventiveness of
humans, it should come as no real surprise to find that development of new compounds
often leads to an analysis of their potential applications, and these can be surprisingly
diverse. Here, we shall touch on a few areas and examples, to give but a flavour for the
field; a full serving can be pursued in specialist texts and reviews, if desired.
9.1
Kill or Cure? - Complexes as Drugs
Medicine is an area of high activity and interest, partly because health issues are of strong
interest to us, as we seek to achieve and retain the best possible quality of life. Recovery
from and/or control of disease often involves the use of drugs, which may be natural
products, synthetic organic compounds and, though less often met, synthetic coordination
complexes. To distinguish the latter from the more common organic drugs, those containing
metal complexes are sometimes defined as
metallodrugs
. The use of metals in medicine has
a history thousands of years old, at least back to the ancient Egyptians (who used copper
compounds in potions) and Chinese (who used gold compounds), and perhaps beyond. In
the distant past, some treatments may have caused more damage than provided a cure, but
to be useful in modern medicine a compound must provide a measured beneficial effect
while displaying low toxicity. The Therapeutic Index defines relative benefit versus toxicity,
expressed as LD
50
/ED
50
, or the ratio of the dose required to kill 50% of a host versus the
dose needed to produce an effective therapeutic response in 50% of the host. Before any new
drug can be introduced, it must go through a series of clinical trials covering, for human use,
four phases; needless to say, given the expense and time involved in this process, a new drug
has to be markedly better than any others already on the market to succeed commercially.
Pharmaceutical companies have appeared somewhat resistant to the development of met-
allodrugs in the past, perhaps concerned about toxicity, specificity and metal accumulation
in patients over extended periods of use, but also reflecting relative unfamiliarity with the
background chemistry. They have also benefited from serendipity as regards discovery of
some current metallodrugs, allowing them to put aside rational design in approaches to spe-
cific targets. Changes are afoot, however, with growing recognition in recent decades that
