However, if impurity atoms were present, they could donate an electron to the conduction band,
or remove one from the valance band, leading to mobile conduction electrons or mobile "holes" in the
valance band (4, 5). Szent-Gyorgyi postulated that these electronic processes within the energy bands-
electron mobility in the conduction band and charge transfer in the valance band-could give rise to
biological phenomena and, indeed, to life itself (6, 7). Figures 4.1 and 4.2. depict his theory as applied
to the bioelectrical role of ascorbate.
Fig. 4.1. A. A large protein molecule contains many electron pairs. In this state, a pair of electrons is
very stable and unreactive; thus the molecule as a whole is very stable and unreactive. B. A pair of
electrons with a negative charge. C. A methylglyoxal molecule with an uncoupled electron pair; i.e. an
electron is missing from one of the orbital rings. In this state, the methylglyoxal molecule is a free
radical and is highly reactive. It can now accept electrons from another molecule to fill its empty
orbital ring. (Reproduced, by permission from Nutrition Today, P. O. Box 1829, Annapolis, Maryland
21404, September/October, 1979.)
For ordinary materials the question of their band structure could be resolved by a coordinated
series of X-ray, chemical, and electrondynamics studies. But biological tissue is inhomogeneous and
impure, and suitable techniques for carrying out many of the necessary studies on such materials have
not yet been developed. Perhaps the most significant problem for the experimentalist is that posed by
the universal presence of water in tissue. It is well established that the electrical conductivity of tissue
increases sharply with water content (8,9). However, the nature of electrical conduction in tissue under
physiological conditions of temperature and moisture-the relative contribution of electronic, protonic,
and ionic processes-has not been established despite more than 30 years of study (10). Thus, no clear
picture of the band structure in tissue has emerged. Other important solid-state techniques that have
been used to study the electronic property of biological tissue include electron paramagnetic resonance
(11-13), and photoconductivity (14-16). Again, although the results are consistent with a common-
energy-band model proposed by Szent-Gyorgyi, they do not establish it as correct.
Piezoelectricity
The piezoelectric effect is the production of electrical polarization in a material by the
application of mechanical stress. Piezoelectric materials also display the converse piezoelectric effect-
mechanical deformation upon application of electrical charge. Polarization and stress are vector and
tensor properties respectively, and in general, arbitrary components of each can be related via the
piezoelectric effect. For this reason, piezoelectricity is a complicated property and up to 18 constants
may be required to specify it (17).
ELECTROMAGNETISM & LIFE - 59