The binding of the protonated fourth generation poly(amido amine) dendrimer as a guest polyelectrolyte
(GPE) to the anionic homopolyelectrolyte poly(l-glutamic acid) sodium salt as a host polyelectrolyte (HPE)
has been investigated by potentiometric and turbidimetric titration in aqueous 0.25 M NaCl solutions. The
polyelectrolyte behaviors of interpolyelectrolyte complex (IPEC)-forming mixtures were compared with those
of hypothetically noninteracting individual polyelectrolytes (PEs) at different stoichiometric ratios, Φ, of
GPE to HPE. From the overall degree of protonation, β, at a given pH and Φ, the degree of conversion,
ϑ(pH), of oppositely charged groups to ion pairs with released counterions has been calculated, as well as
the thermodynamic dissociation constant, K
D, of an ion pair in the IPEC. A high cooperativity of the binding
of the ammonium groups of the GPE to the HPE is concluded from the strong linear increase in the pK
D with
ϑ. As soon as the GPE becomes partly charged below pH 11, both ϑ and the turbidity, which are proportional
to the molecular weight, increase linearly with the decreasing pH, showing that the initial increase in ϑ is
due to an increased number of bound GPEs. From the increase in ϑ to well above 0.5, it is likely that the
linear HPE penetrates partly into the interior shells of the dendrimer GPE.
The size and molecular mass of water-soluble interpolyelectrolyte complex (PEC) formed between poly(l-glutamate) and poly(amido amine) dendrimer in aqueous solution were estimated as a function of the decreasing
pH from the turbidities (τ) and their wavelength dependence, by comparison with numerical τ calculations
by applying the Rayleigh−Debye−Gans and Mie scattering theories. Close to the pK
a of the peripheral amino
groups of the dendrimer, PECs with densities comparable to that of fractal clusters from a reaction limited
colloid aggregation process collapsed to dense particles with ∼1 μm diameter. At a pH close to the pK
a of
the amino groups in the interior of the dendrimer, systems with carboxylate excess over amino/ammonium
groups formed compact particles, and ion pairing likely extended to the ammonium groups in the dendrimer
interior. PECs with the highest polymer density were formed at the stoichiometric ratio: They appeared to
be stable against dissociation at pH 3 in contrast to PECs formed with high dendrimer excess.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.