2 research outputs found
Formation of Unimer Nanoparticles by Controlling the Self-Association of Hydrophobically Modified Poly(amino acid)s
Amphiphilic block or graft copolymers have been demonstrated
to
form a variety of self-assembled nano/microstructures in selective
solvents. In this study, the self-association behavior of biodegradable
graft copolymers composed of polyÂ(γ-glutamic acid) (γ-PGA)
as the hydrophilic segment and l-phenylalanine (Phe) as the
hydrophobic segment in aqueous solution was investigated. The association
behavior and unimer nanoparticle formation of these γ-PGA-<i>graft</i>-Phe (γ-PGA-Phe) copolymers in aqueous solution
were characterized with a focus on the effect of the Phe grafting
degree on the intra- and interpolymer association of γ-PGA-Phe.
The particle size and number of polymer aggregates (<i>N</i><sub>agg</sub>) in one particle of the γ-PGA-Phe depended on
the Phe grafting degree. The size of γ-PGA-Phe with 12, 27,
35, or 42% Phe grafting (γ-PGA-Phe-12, -27, -35, or -42) was
about 8–14 nm and the <i>N</i><sub>agg</sub> was
about 1, supporting the presence of a unimolecular graft copolymer
in PBS. The pyrene fluorescence data indicated that γ-PGA-Phe-35
and -42 have hydrophobic domains formed by the intrapolymer association
of Phe attached to γ-PGA. These results suggest that the Phe
grafting degree is critical to the association behavior of γ-PGA-Phe
and that γ-PGA-Phe-35 and -42 could form unimer nanoparticles.
Moreover, when γ-PGA-Phe-42 dissolved in DMSO was added to various
concentrations of NaCl solution, the particle size and <i>N</i><sub>agg</sub> could be easily controlled by changing the NaCl concentration
during the formation of the particles. These results suggest that
biodegradable γ-PGA-Phe is useful for the fabrication of very
small nanoparticles. It is expected that γ-PGA-Phe nanoparticles,
including unimer particles, will have great potential as multifunctional
carriers for pharmaceutical and biomedical applications, such as drug
and vaccine delivery systems
Structural Analysis of Unimer Nanoparticles Composed of Hydrophobized Poly(amino acid)s
Amphiphilic
random copolymers of polyÂ(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