Ultrathin films of poly[N-(2-cyanoethyl)pyrrole] and poly(N-methylpyrrole) and their composites with Au nanoparticles were used for the electrochemical detection of small concentrations (10 mM-100 μM) of dopamine, a neurotransmitter related with neurological disorders. Results indicated that Au nanoparticles improve the sensing abilities of the two polymers, even though they are not essential to obtain effective and fast responses toward the presence of dopamine. Furthermore, although both polymers have been found to be highly sensitive to low concentrations of dopamine, the response of poly[N-(2-cyanoethyl)pyrrole] is better and more effective than the response of poly(N-methylpyrrole). Experimental results were corroborated with quantum mechanical calculations on model systems, which also indicated that the interaction of oxidized dopamine with poly[N-(2-cyanoethyl)pyrrole] is stronger than that with poly(N-methylpyrrole). This behavior has been attributed to two different factors: (i) the flexibility of the cyanoethyl groups, which allows maximize the number of attractive van der Waals interactions, and (ii) the dipole of the cyano group, which interacts favorably with the dipole of the CO bonds of oxidized dopamine. Finally, theoretical results were used to propose an atomistic model that explains the interaction behavior between the oxidized dopamine and the conducting polymers.
International audienceAtomistic molecular dynamics simulations in chloroform and solvent-free environments are used to build and study a homologous series of neutral dendronized linear polymers (DPs), whose repeat units are regularly branched dendrons of generations g = 1-7, excluding g = 5. We find that a DP with g ≤ 4 displays an elongated conformation, while a DP with g = 6 exhibits a helical backbone. The conformations essentially differ in their alternating (elongated) or regular (helical) twist with respect to the macromolecular axis, at similar average distance between repeat units (2.1-2.3 Å). With increasing g the dendrons tend to induce an increasing strain, stiffness and overall cylindrical shape onto the DP; the existence of DPs with g ≥ 7 is excluded. The fractal dimensionality of the backbone appears similar for DPs with g ≤ 4, while a discontinuous fractal behavior found for g = 6 is consistent with its helical backbone. Profiles describing the variation of the density as a function of the distance to the molecular backbone are extracted to analyze conformational effects of both backbone and sidegroups. For the solvent-free case the average density grows from 0.97 to 1.11 g cm−3 upon increasing g, while the radial density profile is basically constant at 1.1-1.2 g cm−3 and insensitive to g at intermediate distances, where dendrons are able to interpenetrate. The variation of obtained DP thicknesses is successfully compared with experimental estimates deduced from transmission electron microscopy measurements of polymers deposited onto attractive mica surfaces. Finally, we examine and discuss the distribution of solvent molecules inside elongated structures
We investigate the linear rheology of welldefined dendronized polymers (DPs). They consist of polymethacrylate backbones with tree-like branches (dendrons) of different generations, from zeroth to fourth, grafted at each monomer and a methyleneoxycarbonyl spacer between the polymerizable group and the dendritic substituent. The degrees of polymerization for the different generation polymers are almost constant, allowing for systematic studies as a function of generation. Because of the synthetic approach, these macromolecules possess tert-butoxycarbonyl (Boc) groups which promote hydrogen bonding, whereas the benzene groups allow for weaker bonding (π-stacking) as well. The master curves of frequency-dependent storage and loss moduli of these macromolecular structures were obtained via time− temperature superposition of dynamic frequency sweeps at various temperatures. To access slow relaxations, creep measurements were performed at long times and converted to frequency-dependent moduli. For the first generation, it was possible to detect relaxation processes suggesting an approach to the terminal regime (flow). On the other hand, the zeroth and second to fourth generation polymers exhibited a solid-like behavior throughout a wide range of frequencies. The fast relaxations reflect the coupling of segmental friction and hydrogen bonding and render the WLF-type analysis nontrivial. On the basis of the molecular structure of these unique materials as revealed by molecular dynamics simulations and complementary studies with their linear analogues poly(methyl methacrylate) and poly(tert-butyl)methacrylate, we propose that DPs resemble weakly interpenetrating elongated core−shell systems. As generation increases, their enhanced rigidity and intermolecular hydrogen bonding, which occurs primarily toward the outer surface of the DPs, appear to dominate the dynamics. PG0 is not a DP and has an open structure that promotes intermolecular bonding. These results provide design guidelines for ultrahigh-molecular-weight responsive polymers with possibilities for multifunctional substitution and tailoring Frheological response from liquid-like to solid-like.
Encapsulation of DNA into hydroxyapatite (HAp) has been investigated using a rational approach that involves computer simulation and experimental techniques. The temporal evolution of the radial distribution functions derived from atomistic molecular dynamics simulations of Ca
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.