Structural Analysis of Unimer Nanoparticles Composed
of Hydrophobized Poly(amino acid)s
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Abstract
Amphiphilic
random copolymers of poly(γ-glutamic acid)-<i>graft</i>-l-phenylalanine (γ-PGA-Phe), with various lengths
of γ-PGA main chains (molecular weight of 70, 140, and 220 kDa)
plus hydrophobic moieties of Phe groups (grafting degree 12–60%),
self-assembled in aqueous media to form nanoparticles (NPs). The aggregation
number (<i>N</i><sub>agg</sub>) could be adjusted according
to their molecular structures as well as the preparative methods/conditions.
The γ-PGA-Phe NPs were further characterized by means of dynamic
and static light scattering, small-angle neutron scattering, as well
as steady-state fluorescence measurements/quenching techniques. The
single chain state had hydrophobic domains, and formed spherical structures,
herein called unimer NPs, and were obtained using molecular weights
of γ-PGA higher than 140 kDa conjugated with Phe at 27–42%
due to the balance of hydrophobicity/hydrophilicity along the single
polymer chain. The number of hydrophobic domains in one NP (<i>N</i><sub>domain</sub>), estimated by means of fluorescence
quenching techniques and the rigidity of the inner particles detected
by dipyrene fluorescence demonstrated that the <i>N</i><sub>domain</sub> and the rigidity were affected by the particle size
and preparative methods. In addition, the effect of pH on the stability
of the unimer NPs indicated a reduction of the <i>N</i><sub>domain</sub> upon the pH, supporting a loose packing due to hydrophobic
association under alkaline conditions
