Structural changes in lipid mesophases due to intercalation of dendritic polymer nanoparticles: Swollen lamellae, suppressed curvature, and augmented structural disorder

Abstract

Understanding interactions between nanoparticles and model membranes is relevant to functional nano-composites and the fundamentals of nanotoxicity. In this study, the effect of polyamidoamine (PAMAM) dendrimers as model nanoparticles (NP) on the mesophase behaviour of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) has been investigated using high-pressure small-angle X-ray scattering (HP-SAXS). The pressuretemperature () diagrams for POPE mesophases in excess water were obtained in the absence and presence of G2 and G4 polyamidoamine (PAMAM) dendrimers (29 Å and 45 Å in diameter, respectively) at varying NP-lipid number ratio 0.0002-0.02) over the pressure range p = 1-3000 bar and temperature range T = 20-80 °C. The phase diagram of POPE exhibited the L β , L α and H II phases. Complete analysis of the phase diagrams, including the relative area pervaded by different phases, phase transition temperatures (T t ) and pressures (p t ), the lattice parameters (d-spacing), the pressure-dependence of d-spacing (d/p), and the structural ordering in the mesophase as gauged by the Scherrer coherence length (L) permitted insights into the size-and concentration-dependent interactions between the dendrimers and the model membrane system. The addition of dendrimers changed the phase transition pressure and temperature and resulted in the emergence of highly swollen lamellar phases, dubbed L β-den and L α-den . G4 PAMAM dendrimers at the highest concentration  = 0.02 suppressed the formation of the H II phase within the temperature range studied, whereas the addition of G2 PAMAM dendrimers at the same concentration promoted an extended mixed lamellar region in which L α and L β phases coexisted.

I22: SAXS/WAXS beamline at Diamond Light Source – an overview of 10 years operation

“…Due to the collaborative development of the cell its functionality has been fully embedded into the beamline control system which has enabled an integrated approach to data collection from the outset. The cell has been in successful operation since 2011 delivering across a range of scientific areas (Bots et al, 2012;Carriero et al, 2014;Balmer et al, 2011;McCarthy et al, 2017;Lehmkü hler et al, 2019;Fox et al, 2020) covered by the beamline. We believe that the millisecond pressure jump capability of the cell is unique.…”

Interactions between PAMAM dendrimers and DOPC lipid multilayers: Membrane thinning and structural disorder

“…This corroborates with the hypothesis discussed above that the G2-NH 2 dendrimer NPs could have caused 'pinch points' in the lipid bilayers upon their insertion. It is interesting to note here that for hydrated POPE lipid mesophases [30] the presence of G2-NH 2 and G4-NH 2 resulted in substantial bilayer swelling, in contrast to the thinning effect of these dendrimers on dried lipid multilayers.…”

“…Model membrane systems, such as small and large unilamellar (SUVs/LUVs) [18] or multilamellar vesicles (MLVs) [19][20][21], Langmuir-Blodgett (LB) monolayers [22,23], supported lipid bilayers (SLBs) [18,[24][25][26][27], mesophases [28][29][30], purple membrane multilayers [31,32], and computational models [33][34][35] have also been used to study membrane interactions. The interactions between dendrimers and model membranes have been probed using different methods, such as atomic force microscopy (AFM) [36], cryogenic transmission electron microscopy (cryo-TEM) [37], differential scanning calorimetry (DSC) [38], LB-trough [39], quartz crystal microbalance with dissipation monitoring (QCM-D) [40], neutron reflectivity (NR) [40], dye release assays [19], and molecular dynamics (MD) simulations [33,41], as reviewed elsewhere [42,43].…”

Unexpected observation of an intermediate hexagonal phase upon fluid-to-gel transition: SDS self-assembly in glycerol

“…The coherence length L c , indicative of the structural order in the mesophase, was calculated using the Scherrer equation [38][39][40][41][42][43][44][45]…”