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

Abstract

BackgroundUnderstanding the structure of hybrid nanoparticle-lipid multilayers is of fundamental importance to their bioanalytical applications and nanotoxicity, where nanoparticlemembrane interactions play an important role. Poly(amidoamine) (PAMAM) dendrimers are branched polymeric nanoparticles with potential biomedical applications due to precise tunability of their physicochemical properties. Here, the effect of PAMAM dendrimers (2.9 -4.5 nm) with either a hydrophilic amine (NH 2 ) or a hydrophobic C 12 chain surface termination on the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) multilayers has been studied for the first time.Methods DOPC multilayers were created by the liposome-rupture method via drop-casting dendrimerliposome dispersions with the dendrimers added at different concentrations and at three different stages. The multilayer structure was evaluated via the analysis of the synchrotron Xray reflectivity (XRR) curves, obtaining the bilayer d-spacing, the coherence length from the Scherrer (L s ) analysis of the Bragg peaks, and the paracrystalline disorder parameter (g). ResultsDendrimer addition led to lipid bilayer thinning and more disordered multilayer structures. Larger hydrophobic dendrimers caused greater structural disruption to the multilayers compared to the smaller dendrimers. The smallest, positively charged dendrimers at its highest concentration caused the most pronounced bilayer thinning. The dendrimer-liposome mixing method also affected the multilayer structure due to different dendrimer aggregation involved. ConclusionsThese results show the complexity of the effect of dendrimer physicochemical properties and the addition method of dendrimers on the structure of mixed dendrimer-DOPC multilayers.General significance These insights are useful for fundamental understanding of nanotoxicity and future biomedical application of nanocomposite multilayer materials in which nanoparticles are added for enhanced properties and functionality.

Heads or tails: Nanostructure and molecular orientations in organised erucamide surface layers

“…lamellar d-spacing) could be ascertained as 𝑑 = 2𝑛𝜋 𝑄 𝑛 [37,38]. The coherence length La, defined as the lower limit of the crystalline domain size normal to the surface, could be analysed using Scherrer's equation [38][39][40][41][42][43][44][45][46], 𝐿 𝑎 = 2𝜋𝐾 ΔQ , where K is the Scherrer constant (i.e. a shape factor) of order unity depending on the actual shape of the crystalline (here K = 1).…”

Effects of Erucamide on Fiber “Softness”: Linking Single-Fiber Crystal Structure and Mechanical Properties

“…Analysis of Bragg peaks using the Scherrer equation (Section SI.08; Figure S8showing L a and m from different Bragg peaks) − yielded an estimate of the crystallite size L a ∼ 100–250 Å for both PP and PP + ER single fibers (cf. Table ; also Table S2), a value comparable to that typically reported for the thickness of the polymer microfibrils .…”

Structure, Nanomechanical Properties, and Wettability of Organized Erucamide Layers on a Polypropylene Surface

“…The characteristic layer thickness within the multilayer (i.e., lamellar d -spacing) could be ascertained as . The coherence length L a , defined as the lower limit of the crystalline domain size normal to the surface, could be analyzed using Scherrer’s equation − , where K is the Scherrer constant (i.e., a shape factor) of order unity depending on the actual shape of the crystalline (here K = 1). Lattice spacing fluctuations (paracrystalline disorder), evident from characteristic peak broadening were considered by plotting the peak broadening defined as (Δ Q ) 2 /(2π) 2 vs the fourth power of diffraction order ( h 4 ) for a plane of the Miller index ( h 00). ,, The degree of disorder ( g ) together with coherence length L a were obtained from the slope ( a ) and intercept ( y 0 ) of the linear fit ( y = y 0 + ah 4 ) as and L a = y 0 –1/2 .…”