3 research outputs found
Undulating the Lamellar Interface of Polymer–Surfactant Complex by Dendrimer
Self-assembly
of the supramolecules formed by the complexation
between polyÂ(amidoamine) (PAMAM) generation four (G4) dendrimer and
the surfactant, dodecylbenzeneÂsulfonic acid (DBSA), generated
a hexagonal columnar phase and a typical flat lamellar phase at low
and high surfactant binding ratio, respectively, due to the dominance
of the dendrimer to attain its natural curvature and the surfactant
alkyl tails to reduce their hydrophobic interaction energy and packing
frustration. Most strikingly, the delicate balance between these two
free energy components at the intermediate binding ratios resulted
in an undulated lamellar structure characterized by the centered rectangular
unit cell. The finding demonstrates the power of dendrimer as a building
block for expanding the morphological window of polymeric assemblies
by modulating the interfacial curvature of microphase-separated structure
Spatial Distributions of Guest Molecule and Hydration Level in Dendrimer-Based Guest–Host Complex
Using the electrostatic complex of
G4 polyÂ(amidoamine) (PAMAM)
dendrimer with an amphiphilic surfactant as a model system, contrast
variation small angle neutron scattering (SANS) is implemented to
resolve the key structural characteristics of dendrimer-based guest–host
system. Quantifications of the radial distributions of the scattering
length density and the hydration level within the complex molecule
reveal that the surfactant is embedded in the peripheral region of
dendrimer and the steric crowding in this region increases the backfolding
of the dendritic segments, thereby reducing the hydration level throughout
the complex molecule. The insights into the spatial location of the
guest molecules as well as the perturbations of dendrimer conformation
and hydration level deduced here are crucial for the delicate design
of dendrimer-based guest–host system for biomedical applications
PEGylation Site-Dependent Structural Heterogeneity Study of MonoPEGylated Human Parathyroid Hormone Fragment hPTH(1–34)
The structures of C- and N-terminally
monoPEGylated human parathyroid
hormone fragment hPTH(1–34) as well as their unmodified counterparts,
polyÂ(ethylene glycol) (PEG) and hPTH(1–34), have been studied
by small-angle neutron scattering (SANS). The scattering results show
that free hPTH(1–34) in 100 mM phosphate buffer (pH 7.4) aggregates
into clusters. After conjugation with PEG, the PEG–peptide
conjugates self-assemble into a supramolecular core–shell structure
with a cylindrical shape. The PEG chains form a shell around the hPTHÂ(1–34)
core to shield hPTH(1–34) from the solvent. The detailed structural
information on the self-assembled structures is extracted from SANS
using a model of the cylindrical core with a shell of Gaussian chains
attached to the core surface. On the basis of the data, because of
the charge–dipole interactions between the conjugated PEG chain
and the peptide, the conjugated PEG chain forms a more collapsed conformation
compared to free PEG. Moreover, the size of the self-assembled structures
formed by the C-terminally monoPEGylated hPTHÂ(1–34) is about
3 times larger than that of the N-terminally monoPEGylated hPTH(1–34).
The different aggregation numbers of the self-assembled structures,
triggered by different PEGylation sites, are reported. These size
discrepancies because of different PEGylation sites could potentially
affect the pharmacokinetics of the hPTH(1–34) drug