Chemistry Reference
In-Depth Information
Chapter 13
Iron: Essential for Almost All Life
GOLD is for the mistress
e
silver for the maid
e
Copper for the craftsman cunning at his trade.
“Good!” said the Baron, sitting in his hall,
“But Iron
e
Cold Iron
e
is master of them all.”
Rudyard Kipling 'Cold Iron'.
Introduction
247
Iron Chemistry
248
Iron and Oxygen
248
The Biological Importance of Iron
250
Biological Functions of Iron-Containing Proteins
250
Haemoproteins
251
Other Iron-Containing Proteins
267
Dinuclear Nonhaem Iron Enzymes
272
INTRODUCTION
Human prehistory is conveniently divided into three consecutive periods, the Stone Age,theBronze Age, and the
Iron Age, each defined by the materials out of which tools and weapons were manufactured. The Stone Age
began about 2.5 million years ago, with the evolution of humans in sub-Saharan Africa who made tools and
weapons out of stone. As the climate gradually grew warmer, the nomadic hunter-gatherer way of life of the
Paleolithic Age made its transition to the settled agricultural life of the Neolithic Age. The Stone Age was
superseded by the Bronze Age, during which metals, initially copper, began to be used to make metal tools and
weapons. The use of copper spread from Anatolia through Mesopotamia and the Middle East from 4000 to 3000
BC. True bronze (an alloy of copper and tin) was used only rarely initially, but during the second millenium BC
the use of true bronze increased greatly. The Bronze Age was also marked by important inventions, such as the
wheel and the ox-drawn plough. However, by around 1200 BC the ability to heat and forge another metal, iron,
brought the Bronze Age to an end. Thus began the Iron Age, when iron replaced bronze in implements and
weapons. This shift occurred because iron, when alloyed with a small amount of carbon (0.2
0.8%, absorbed
from the charcoal used in its extraction from iron ores), is harder, more durable, and maintains a sharper edge than
bronze. For over three thousand years, until its replacement by steel in the middle of the 19th century, iron formed
the material basis of human civilisation in Europe, Asia, and Africa. However, while we have many relics from
both the Stone and the Bronze Ages, little remains of the Iron Age on account of the poor stability of iron in the
face of oxygen and water (rust is not a very practical way of preserving historical relics!).
In this chapter we describe selected aspects of the biological chemistry of iron, with particular reference to
iron-containing enzymes. It would be difficult to underestimate the biological importance of iron for almost all
e
