Dendronized vesicles: formation, self-organization of dendron-grafted amphiphiles and stability

Fundamental bacterial functions like quorum sensing can be targeted to replace conventional antibiotic therapies. Nanoparticles or vesicles that bind interfacially to charged biomolecules could be used to block quorum sensing pathways in bacteria. Towards this goal, dendronized vesicles (DVs) encompassing polyamidoamine dendron-grafted amphiphiles (PDAs) and dipalmitoyl-sn-glycero-3-phosphocholine lipids are investigated using the molecular dynamics simulation technique in conjunction with an explicit solvent coarse-grained force field. The key physical factors determining the stability of DVs as a function of the dendron generation and relative concentration are identified. The threshold concentration of each dendron generation that yields stable DVs is determined. Dendrons with lower generations rupture the DVs at high relative concentrations due to the electrostatic repulsions between the terminally protonated amines. Whereas, dendrons with intermediate generations demonstrate a mushroom-to-brush transition. Conformational changes in the dendrons expand the outer DV surface, resulting in instability in the DV bilayer. DVs encompassing dendrons with higher generations incur stresses on the bilayer due to their high charge density and spontaneous curvature. The self-organization of PDAs on the DV surface are examined to understand how the asymmetric stresses are minimized across the bilayer. A set of conditions are determined to be conducive for the formation of a single cluster of PDAs that decorates the DV surface like a mesh. Results from this study can potentially guide the design and synthesis of nanoparticles which target quorum sensing pathways in bacteria towards the prevention and treatment of bacterial infections. Furthermore, these nanoparticles can be used in diverse applications in biomedicine, energy or electronics that require synthetic dendronized cells or the adsorption and transport of charged species.

High-χ alternating copolymers for accessing sub-5 nm domains via simulations

Based on molecular dynamics simulations, we designed novel high-χ alternating copolymers (ACPs) for fabricating sub-5 nm domains.

Mechanisms underlying interactions between PAMAM dendron-grafted surfaces with DPPC membranes

Biofouling is a pervasive problem which demands the creation of smart, antifouling surfaces. Towards this end, we examine the interactions between a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer and a polyamidoamine (PAMAM) dendron-grafted surface. In addition, we investigate the impact of dendron generation on the system behavior. To resolve the multiscale dynamical processes occurring over a large spatial scale, we employ Molecular Dynamics simulations with a coarse-grained implicit solvent force field. Our results demonstrate the transient and equilibrium system dynamics to be determined by the PAMAM dendron generation along with the underlying mechanisms. Higher generation dendrons are observed to favor penetration of the DPPC molecules into the dendron branches, thereby enabling sustained interactions between the membrane and the dendron-grafted surface. Under equilibrium, the membrane adopts a bowl-shaped morphology whose dimensions are determined by the dendron generation and density of interactions. The results from our study can be used to guide the design of novel surfaces with selective antifouling properties which can prevent the adsorption of microorganisms onto lipid membranes.

The interactions between a DPPC lipid membrane and a PAMAM dendron-grafted surface.

Carboxymethyl chitosan-modified magnetic-cored dendrimer as an amphoteric adsorbent

Carboxymethyl chitosan-modified magnetic-cored dendrimers (CCMDs) were successfully synthesized in a three step method. The synthesized samples were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, thermogravimetry analysis, zeta potential analyzer, X-ray photoelectron spectroscopy, surface area analysis, and Fourier transform infrared spectroscopy. The CCMD exhibited selective adsorption for anionic and cationic compounds at specific pH conditions. With the substitution of amino groups of MD with carboxymethyl chitosan moieties, the adsorption sites for cationic compounds were greatly increased. Since the adsorption onto CCMD was mainly electrostatic interaction, the adsorption of MB and MO was significantly affected by the pHs. The optimal adsorption pH values were 3 and 11 for MO and MB. The maximal adsorption of MO and MB on the CCMD at pH values of 3 and 11 were 20.85mgg(-1) and 96.31mgg(-1), respectively. Reuse of the CCMD as an adsorbent was experimentally tested through adsorption and desorption with simple pH control. More than 99% and 91% of the initial adsorption of MB and MO on the CCMD was maintained with five consecutive recycling.

Implicit solvent coarse-grained model of polyamidoamine dendrimers: Role of generation and pH

Highly branched polymers such as polyamidoamine (PAMAM) dendrimers are promising macromolecules in the realm of nanobiotechnology due to their high surface coverage of tunable functional groups. Modeling efforts of PAMAM can provide structural and morphological properties, but the inclusion of solvents and the exponential growth of atoms with generations make atomistic simulations computationally expensive. We apply an implicit solvent coarse-grained model, called the Dry Martini force field, to PAMAM dendrimers. The reduced number of particles and the absence of a solvent allow the capture of longer spatiotemporal scales. This study characterizes PAMAM dendrimers of generations one through seven in acidic, neutral, and basic pH environments. Comparison with existing literature, both experimental and theoretical, is done using measurements of the radius of gyration, moment of inertia, radial distributions, and scaling exponents. Additionally, ion coordination distributions are studied to provide insight into the effects of interior and exterior protonation on counter ions. This model serves as a starting point for future designs of larger functionalized dendrimers.