Spectroscopic and calorimetric studies on the protonation of polymeric aminoacids

The protonation of some poly(amido amines) has been studied in aqueous solution by FTIR spectrophotometry and by calorimetry. On the basis of the stretching bands of both the ionized and the un-ionized carboxyl groups, the structures of all four polymeric amino acids in their different protonation states are determined. Calorimetric studies show that the enthalpies of protonation do not change with pH and follow a trend similar to that observed in simple amino acids of comparable structure. An anomalously high value of |ΔH2°| observed for the polymer obtained by the polyaddition of ß-alanine to diacryloylpiperazine has been found and attributed to the formation of a very highly symmetrical structure when the carboxyl groups are in the un-ionized form. © 1986, American Chemical Society. All rights reserved.