Chemistry Reference
In-Depth Information
Chapter 1
Silicon in a Biological Environment
Paul M. Zelisko
1.1
Silicon-Based Life: Science-Fiction?
Given that the periodic table groups atoms with similar properties and reactivities
should silicon-based life not be possible? Since the late 1800s science fiction writers
such as H.G. Wells [
1
] and Stanley Weinbaum [
2
] have imagined silicon-based forms
of life.
1
More recently the original
Star Trek
series, in an episode entitled “Devil in the
Dark” depicted an organism called a Horta that terrorized a colony of miners. Howev-
er, in most instances the silicon-based organisms were simply rocks with a personality.
As much as it is intriguing to imagine organisms based on silicon, this does not
seem to be possible, given our understanding for the requirements for life at the very
least. Although both are members of Group IV, at a very fundamental level carbon
and silicon are two different types of elements; carbon is a non-metal while silicon
is classed as a metalloid. The true limitation for silicon in serving as the basis for
life as we understand it is the inherent reactivity of the bonds that silicon makes
with heteroatoms such as nitrogen and sulfur, bonds that tend to be relatively stable
in carbon-based systems; these bonds are essential for many of the aspects of the
biomachinary on Earth. A notable exception to this observation is the strength of the
Si-O bond compared to the C-O bond (Table
1.1
).
As can be seen from Tab.
1.1
C-C bonds are shorter and stronger than Si-Si
bonds. Couple this with the fact that unlike carbon, silicon is incapable of making
double and triple bonds with heteroatoms such as nitrogen and oxygen that are
