5 research outputs found

    Effect of Surface Modification on Water Adsorption and Interfacial Mechanics of Cellulose Nanocrystals

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    With increasing environmental concerns about petrochemical-based materials, the development of high-performance polymer nanocomposites with sustainable filler phases has attracted significant attention. Cellulose nanocrystals (CNCs) are promising nanocomposite reinforcing agents due to their exceptional mechanical properties, low weight, and bioavailability. However, there are still numerous obstacles that prevent these materials from achieving optimal performance, including high water adsorption, poor nanoparticle dispersion, and filler properties that vary in response to moisture. Surface modification is an effective method to mitigate these shortcomings. We use computational approaches to obtain direct insight into the water adsorption and interfacial mechanics of modified CNC surfaces. Atomistic grand-canonical Monte Carlo simulations demonstrate how surface modification of sulfated Na-CNCs impacts water adsorption. We find that methyl­(triphenyl)­phosphonium (MePh<sub>3</sub>P<sup>+</sup>)-exchanged CNCs have lower water uptake than Na-CNCs, supporting experimental dynamic vapor sorption measurements. The adsorbed water molecules show orientational ordering when distributed around the cations. Steered molecular dynamics simulations quantify traction–separation behavior of CNC–CNC interfaces. We find that exchanging sodium for MePh<sub>3</sub>P<sup>+</sup> effectively changes the surface hydrophilicity, which in turn directly impacts interfacial adhesion and traction–separation behavior. Our analysis provides guidelines for controlling moisture effects in cellulose nanocomposites and nanocellulose films through surface modifications

    The Role of Structural Enthalpy in Spherical Nucleic Acid Hybridization

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    DNA hybridization onto DNA-functionalized nanoparticle surfaces (e.g., in the form of a spherical nucleic acid (SNA)) is known to be enhanced relative to hybridization free in solution. Surprisingly, via isothermal titration calorimetry, we reveal that this enhancement is enthalpically, as opposed to entropically, dominated by ∌20 kcal/mol. Coarse-grained molecular dynamics simulations suggest that the observed enthalpic enhancement results from structurally confining the DNA on the nanoparticle surface and preventing it from adopting enthalpically unfavorable conformations like those observed in the solution case. The idea that structural confinement leads to the formation of energetically more stable duplexes is evaluated by decreasing the degree of confinement a duplex experiences on the nanoparticle surface. Both experiment and simulation confirm that when the surface-bound duplex is less confined, i.e., at lower DNA surface density or at greater distance from the nanoparticle surface, its enthalpy of formation approaches the less favorable enthalpy of duplex formation for the linear strand in solution. This work provides insight into one of the most important and enabling properties of SNAs and will inform the design of materials that rely on the thermodynamics of hybridization onto DNA-functionalized surfaces, including diagnostic probes and therapeutic agents

    Size-Selective Nanoparticle Assembly on Substrates by DNA Density Patterning

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    The vision of nanoscale self-assembly research is the programmable synthesis of macroscale structures with controlled long and short-range order that exhibit a desired set of properties and functionality. However, strategies to reliably isolate and manipulate the nanoscale building blocks based on their size, shape, or chemistry are still in their infancy. Among the promising candidates, DNA-mediated self-assembly has enabled the programmable assembly of nanoparticles into complex architectures. In particular, two-dimensional assembly on substrates has potential for the development of integrated functional devices and analytical systems. Here, we combine the high-resolution patterning capabilities afforded by electron-beam lithography with the DNA-mediated assembly process to enable direct-write grayscale DNA density patterning. This method allows modulation of the functionally active DNA surface density to control the thermodynamics of interactions between nanoparticles and the substrate. We demonstrate that size-selective directed assembly of nanoparticle films from solutions containing a bimodal distribution of particles can be realized by exploiting the cooperativity of DNA binding in this system. To support this result, we study the temperature-dependence of nanoparticle assembly, analyze the DNA damage by X-ray photoelectron spectroscopy and fluorescence microscopy, and employ molecular dynamics simulations to explore the size-selection behavior

    Simulation and Experimental Assembly of DNA–Graft Copolymer Micelles with Controlled Morphology

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    Nanoparticles formed through complexation of plasmid DNA and copolymers are promising gene-delivery vectors, offering a wide range of advantages over alternative delivery strategies. Notably, recent research has shown that the shape of these particles can be tuned, which makes it possible to gain understanding of their shape-dependent transfection properties. Whereas earlier methods achieved shape tuning through the use of block copolymers and variation of solvent polarity, here we demonstrate through a combined experimental and computational approach that the same degree of shape control can be achieved through the use of graft copolymers that are easier to synthesize and provide a wider range of parameters for shape control. Moreover, the approach presented here does not require the use of organic solvents. The simulation work provides insight into the mechanism governing the shape variation as well as an effective model to guide further design of nonviral gene-delivery vectors. Our experimental findings offer important opportunities for the facile and large-scale synthesis of biocompatible gene-delivery vectors with well-controlled shape and tunable transfection properties. The in vitro study shows that both micelle shape and transfection efficiency are strongly correlated with the key structural parameters of the graft copolymer carriers

    Interactions between Membranes and “Metaphilic” Polypeptide Architectures with Diverse Side-Chain Populations

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    At physiological conditions, most proteins or peptides can fold into relatively stable structures that present on their molecular surfaces specific chemical patterns partially smeared out by thermal fluctuations. These nanoscopically defined patterns of charge, hydrogen bonding, and/or hydrophobicity, along with their elasticity and shape stability (folded proteins have Young’s moduli of ∌1 × 10<sup>8</sup> Pa), largely determine and limit the interactions of these molecules, such as molecular recognition and allosteric regulation. In this work, we show that the membrane-permeating activity of antimicrobial peptides (AMPs) and cell-penetrating peptides (CPPs) can be significantly enhanced using prototypical peptides with “molten” surfaces: metaphilic peptides with quasi-liquid surfaces and adaptable shapes. These metaphilic peptides have a bottlebrush-like architecture consisting of a rigid helical core decorated with mobile side chains that are terminated by cationic or hydrophobic groups. Computer simulations show that these flexible side chains can undergo significant rearrangement in response to different environments, giving rise to adaptable surface chemistry of the peptide. This quality makes it possible to control their hydrophobicity over a broad range while maintaining water solubility, unlike many AMPs and CPPs. Thus, we are able to show how the activity of these peptides is amplified by hydrophobicity and cationic charge, and rationalize these results using a quantitative mean-field theory. Computer simulations show that the shape-changing properties of the peptides and the resultant adaptive presentation of chemistry play a key enabling role in their interactions with membranes
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