  Reanalysis of data (Bruice and York 1961) for the pH dependences of the
calculated apparent second-order rate constants (k2) for the reaction of
tris-(hydroxymethyl)-aminomethane (TRIS) with phenyl esters reveals that the pH
profiles are consistently much better represented as multiphasic, i.e. as a
series of straight lines separated by discontinuities in the form of sharp
breaks or noncontiguities (jumps), than by the continuous function used by the
authors. For p-nitrophenyl acetate, m-nitrophenyl acetate, p-chlorophenyl
acetate and phenyl acetate, the profiles are best represented as multiphasic in
plots of log k2 vs. pH, whereas the profile for p-methylphenyl acetate is only
multiphasic in a plot of k2 vs. pH. Data for the pseudo-first-order rate
constants (kobs) give multiphasic pH profiles with patterns identical or very
similar to those for k2. Extensive reanalyses of data for a wide variety of
enzymatic and non-enzymatic reactions show, similarly, that pH profiles are in
general better represented as multiphasic than as curvilinear.
