Distribution Coefficient and Log D
The distribution coefficient is the ratio of the sum of the concentrations of all forms of the compound (ionized plus un-ionized) in each of the two phases. For measurements of distribution coefficient, the pH of the aqueous phase is buffered to a specific value such that the pH is not significantly perturbed by the introduction of the compound. The logarithm of the ratio of the sum of concentrations of the solute's various forms in one solvent, to the sum of the concentrations of its forms in the other solvent is called Log D:
In addition, log D is pH dependent, hence one must specify the pH at which the log D was measured. Of particular interest is the log D at pH = 7.4 (the physiological pH of blood serum).
For un-ionizable compounds, log P = log D at any pH.
Read more about this topic: Partition Coefficient
Famous quotes containing the words distribution and/or log:
“The man who pretends that the distribution of income in this country reflects the distribution of ability or character is an ignoramus. The man who says that it could by any possible political device be made to do so is an unpractical visionary. But the man who says that it ought to do so is something worse than an ignoramous and more disastrous than a visionary: he is, in the profoundest Scriptural sense of the word, a fool.”
—George Bernard Shaw (1856–1950)
“There was now no road further, the river being the only highway, and but half a dozen log huts, confined to its banks, to be met with for thirty miles. On either hand, and beyond, was a wholly uninhabited wilderness, stretching to Canada.”
—Henry David Thoreau (1817–1862)