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Introduction to Bioinorganic Chemistry

University of Lund, May/June 2008
Lecture notes

Dieter Rehder

1. Scope and Introduction

“Bioinorganic Chemistry“ is at the gate-way of inorganic chemistry and biochemistry, i.e. it
describes the mutual relationship between these two sub-disciplines, with focus upon the
function of inorganic “substances“ in living systems, including the transport, speciation and,
eventually, mineralisation of inorganic materials, and including the use of inorganics in
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medicinal therapy and diagnosis. These “substances” can be metal ions (such as K , ferrous
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and ferric), composite ions (e.g. molybdate), coordination compounds (like cisplatin and
carbonyltechnetium), or inorganic molecules such as CO, NO, O 3. Medicinal inorganic
chemistry on the one hand, and biomineralisation on the other hand, are important integral
parts.

Inorganic reactions have possibly played an important role in the formation and development
of organic “life molecules” in the prebiotic area (terrestrial and/or extraterrestrial), and from
the very beginning of life on Earth. Inorganic chemistry is involved in structure and function of
all life forms present nowadays on Earth, belonging to one of the three main branches, viz.
bacteria, archaea and eucarya (Fig. 1). Life started ca 3.5 billion years ago with LUCA, the first
uniform (and unknown) common ancestor. At that time, our planet was already covered by
oceans. The overall situation was, however, completely different from that of today: The
primordial atmosphere (also referred to as “primordial broth”) contained CO 2, N 2 and H 2O as
the main components, and trace amounts of gases like H 2, CO, COS, H 2S, NH 3 and CH 4 from
volcanic exhalations, and trace amounts of oxygen from the decomposition of water by electric
discharges, cosmic rays and radioactivity. The Earth’s crust was essentially unstable due to
wide-spread volcanism and bombardment by debris (meteorites), remainders from the
constitution of the solar system some 4.5 billion years ago.
A key reaction at that time was the conversion of ferrous sulfide to ferrous disulfide
(pyrite, FeS 2) (eqn. 1), accompanied by a reduction potential of -620 mV, enough to enable
reductive carbon fixation, including reductive C-C coupling, and thus to allow entrance into the
world of organic compounds. Eqns. (2) (formation of thiomethanol as a key compound) and (3)
(formation of thioacetic acid) are examples. Of particular interest is the formation of “active
acetic acid methylester“ (eqn. 3b), which is an essential constituent of acetyl-coenzyme-A, a
focal product in biological carbon cycling, the synthesis of which is catalysed by an
acetylcoenzyme-M synthase, a iron-nickel-sulphur enzyme.
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FeS + HS → FeS 2 + 2[H] , ∆E = - 620 mV (1)
COS + 6[H] → CH 3SH + H 2O (2)
CH 3SH + CO → CH 3COSH (3a)
2CH 3SH + CO 2 + FeS → CH 3CO(SCH 3) + H 2O + FeS 2 (3b)

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For the definition and further aspects of coordination compounds see insets on pp. 5 and 7.