Chemistry Reference
In-Depth Information
Chapter 1
An Overview of Metals and Selected
Nonmetals in Biology
Introduction
1
Why do We Need Anything Other Than C, H, N, and O (together with some P and S)?
2
What are the Essential Elements and the Essential Metal Ions?
3
An Idiosyncratic View of the Periodic Table
7
INTRODUCTION
The extraordinarily important role of metals in biology, the environment, and medicine has become increasingly
evident over the last twenty to thirty years. Iron- and copper-containing proteins (cytochromes, iron-sulfur
proteins, and plastocyanins) are key players in electron transfer, both in the electron-transfer pathways of
photosynthetic organisms and in the respiratory chain of mitochondria. Coupling electron transfer with proton
pumping across membranes to establish proton gradients is a universal way of generating the currency of cellular
free energy, ATP: this constitutes the process which we call oxidative phosphorylation. Photosystem II, which
produces oxygen, protons, and electrons from water, which our renewable energy enthusiasts would dearly love to
mimic, utilises sophisticated manganese chemistry. Metals like cadmium, manganese, and lead in our environ-
ment represent a serious toxic hazard. Even relatively unheard-of elements like polonium can seize the front pages
of our national newspapers when their alpha radiation is used to poison a Soviet dissident in London. While many
metals are toxic, some metals are used as drugs
cisplatin and related metal-based drugs are used to treat cancer,
while lithium, in the form of lithium carbonate, is used in the treatment of manic depression. Modern medicine has
increasingly developed noninvasive techniques, both for diagnosis and for therapy. Magnetic resonance imaging
depends heavily on the use of paramagnetic metal complexes as contrast agents. A number of metals such as
isotopes of cobalt, gallium, and technetium are used as radiopharmaceuticals to deliver sterilizing radiation to
targets within the body. A small number of trace elements, like selenium, and the halogens, chlorine and iodine,
are also required to ensure human health. While metal deficiencies are well known (for example, inadequate
dietary iron causes anemia), it is evident that excessive levels, even of essential metals, can also be toxic
e
as we
e
will see, this is the case for iron in excess.
It has been clear from the outset that the study of metals in biological systems can only be approached by
a multidisciplinary approach, involving many branches of the physical and biological sciences. The study of the
roles of metal ions in biological systems represents the exciting and rapidly growing interface between inorganic
chemistry and the living world. It has been defined by chemists as bioinorganic chemistry, and by biochemists as
inorganic biochemistry. As explained in the Preface, I prefer to use the definition 'biological inorganic chemistry'
in this topic, but would like to indicate to the prospective reader that this text will deal to a much greater extent
with the biochemical aspects of metals and other inorganic elements in living systems rather than with their
inorganic chemistry.
