Stability constants of ct series of metal
complexes derived from the series of α-amino acids, glycine, alanine,
leucine, valine, histidine, and 8-hydroxyquinoline 5-sulphonic acid have been
determined by an electrometric method.
The metals fall in the same order, as
regards stability of their complexes, as was found for the chelating molecules
studied in Part I of this series.
As the length of the a chain of the amino
acid increases, there is a small decrease in the stability of the amino acid
complexes of any one metal. The cobalt II complex of histidine is much more
stable than cobalt II complexes derived from any of the other α-amino
acids. It is suggested that this explains why histidine is able to nullify the
inhibiting action of cobalt on the growth and respiration of various aerobic
and anaerobic organisms.
Though there is no great difference in the
stability of corresponding metal complexes derived from 8-hydroxyquinoline and
8-hydroxyquinoline 5-sulphonic acid (when allowance is made for different
solvents used in making the measurements), there is a marked difference in the
bacteriostatic action of these two chelating molecules. A reason for this
difference is suggested.
The stability constants of any chelating
reaction involving the liberation of any number of hydrogen ions can be
evaluated by using the generalized mathematical treatment which has been set
out in this series of papers.
