Role Of Charge Density Research Articles

Role of Charge Density and Surface Area of Tailored Ionic Porous Organic Polymers for Adsorption and Antibacterial Actions.

The development of high-performance adsorbents for environmental remediation is a current need, and ionic porous organic polymers (iPOPs), due to their high physicochemical stability, high surface area, added electrostatic interaction, and easy reusability, have already established themselves as a better adsorbent. However, research on the structural design of high-performance iPOP-based adsorbents is still nascent. This study explored the building blocks' role in optimizing the polymers' charge density and surface area to develop better polymeric adsorbents. Among the three synthesized polymers, iPOP-ZN1, owing to its high surface area and high charge density in its active sites, proved to be the best adsorbent for adsorbing inorganic and organic pollutants in an aqueous medium. The polymers were efficient enough to capture and store iodine vapor in the solid state. Further, this study tried to address using iodine-loaded polymers in antibacterial action. Iodine-loaded iPOPs show impressive antibacterial behavior against E. coli, B. subtilis, and H. pylori.

Simultaneous ε-Keggin Al13 chloride salt and anionic polyacrylamide coagulation-flocculation system for agglomeration of trimetallic Cr-Ni-Fe doped core-shell microspheres of graphitized coke

Core-shell microspheres of graphitized carbon consisting of a solid carbonaceous core surrounded by a porous Cr-Ni-Fe shell are produced in ultra-high temperature ethane steam crackers. Considerable volumes of these microspheres are suspended in quench water and are directed to oceans while they have not been detected as pollutants so far. The importance of this work is studying and development of an environmental remediation process for extraction of coke microspheres from aqueous solution by ε-Keggin Al13 chloride salt as coagulant and anionic polyacrylamide (PAM) as flocculant in a stirred tank reactor equipped with silt density index meter and particle size analyzer. The effect of dissolved ions of Hofmeister series on zeta potential and electrical double layer compression was investigated. The role of charge density and chain length of PAM were also examined in favor of patch mechanism. The results revealed that the surface charge of suspended coke microspheres is controlled by the solid carbonaceous core while the porous metallic shell is ineffective. The aggregation of coke:Al13 flocs follows a multiple mechanism including point of zero charge, electrical double layer compression, charge neutralization, hydrophobic interaction, sweep floc, inter-particle polymer bridging and electrostatic patch flocculation. Surface adsorption of ε-Keggin Al13 chloride salt coagulants on the coke microspheres is limited to the critical level of 8 ppm because of the steric effect of ε-Keggin Al13 chloride salt clusters and the restricted bare surface of carbonaceous core matrix under the porous metallic shell. The sphericity parameter determined by surface to volume ratio of coke:Al13 flocs and it was used to quantify the degree of polymer bridging between the flocs.

Predictions for structural stability and electronic evolution in pressure-induced overdoped YBa2Cu3O7

The electronic evolution in the entire overdoped region of cuprates has never been accessed, though the clarification of this evolution should help to refine the crucial physical arguments in producing the superconductivity. Motivated by uncovering this, we performed first-principles calculations and molecular dynamics simulations for the pressure-induced overdoped YBa2Cu3O7. The mechanical and dynamic stability of orthorhombic YBa2Cu3O7 lays the foundation of exploration for the electronic evolution. We found that no transition of semiconducting state was identified and similar Fermi surfaces still exist in the entire overdoped region. The role of charge density at CuO2 plane was also discussed. Moreover, based on the analysis of BCS picture, we recommended that the electron-phonon regime is not prominently responsible for the Tc, and the evolution of N(EF) or the position of Van Hove singularity (VHs), i.e., EF-EVHs, may direct an alternative way instead to uncover the superconductivity of YBa2Cu3O7 category if the BCS picture is taken.

Equilibration of Micelle-Polyelectrolyte Complexes: Mechanistic Differences between Static and Annealed Charge Distributions.

The role of charge density and charge annealing in polyelectrolyte complexation was investigated through systematic comparison of two micelle-polyelectrolyte systems. First, poly(dimethylaminoethyl methacrylate)-block-poly(styrene) (PDMAEMA-b-PS) micelles were complexed with poly(styrenesulfonate) (PSS) at pH values above and below the pKa of PDMAEMA to investigate the role of charge annealing in the complexation process. Second, complexes of poly(DMAEMA-stat-oligo(ethylene glycol) methyl ether methacrylate)-block-poly(styrene) (P(DMAEMA-stat-OEGMA)-b-PS) micelles with the same PSS at low pH were used to investigate how the complexation process differs when the charged sites are in fixed positions along the polymer chains. Characterization by turbidimetric titration, dynamic light scattering, and cryogenic transmission electron microscopy reveals that whether or not the charge distribution can rearrange during the complexation process significantly affects the structure and stability of the complexes. In complexes of PDMAEMA-b-PS micelles at elevated pH, in which the charge distributions can anneal, the charge sites redistribute along the corona chains upon complexation to favor more fully ion-paired configurations. This promotes rapid rearrangement to single-micelle species when the micelles are in excess but traps complexes formed with PSS in excess. In complexes with static charge distributions introduced by copolymerization of DMAEMA with neutral OEGMA monomers, on the other hand, the opposite is true: in this case, reducing the charge density promotes rearrangement to single-micelle complexes only when the polyanion is in excess. Molecular dynamics simulations show that disruption of the charge density in the corona brush reduces the barrier to rearrangement of individual ion pairs, suggesting that the inability of the brush to rearrange to form fully ion-paired complexes fundamentally alters the kinetics of complex formation and equilibration.

Assessing the in Vitro Cardiotoxicity of Superparamagnetic Ion Oxide Nanoparticles (SPIONs)

Understanding the mechanism of toxicity of nanoparticles (NPs) represents a major challenge for biomedical application. Since the cardiotoxicity of drugs is mainly due to blockade of the human ether-a-go-go related gene (hERG) protein, the inhibition of hERG channel is a first step in a non-clinical testing strategy. Superparamagnetic iron oxide nanoparticles (SPIONs) are composed of either a magnetite (Fe3O4) or maghemite (γ-Fe2O3) core coated with a biocompatible polymer. Both maghemite and magnetite are ferrimagnetic in nature, and when the size of the particles enters the nanometric scale (below ca. 80-120 nm) they assume a single domain magnetic structure and superparamagnetic feature. SPIONs are suitable for biological application for the following reasons: i) Fe is a naturally occurring metal in the human body; ii) they can be utilized by the body in subsequent metabolic processes; iii) their magnetic behavior allows them to be used in various biomedical applications, e.g. magnetic fluid hyperthermia.In this work we describe the interaction of SPIONs, coated with different ligands, with hERG channel. The NPs were synthesized by thermal decomposition and investigated by XRD, TEM and DLS analysis; the superparamagnetic behavior was confirmed by SQUID magnetometric analysis. We functionalized the NPs by a coating exchange reaction with several ligands and analyzed them by DLS and Z-Potential analysis. The interaction between SPIONs and hERG channel, expressed in HEK cells, was investigated by patch-clamp. We found that NPs coated with polyacrylic acid (PAA) or 2,3-dimercaptosuccinic acid (DMSA) blocked hERG channels. On the contrary, 3-aminopropyl phosphonic acid (APPA)-stabilized NPs or non-coated NPs had no effect on hERG channel, suggesting an important role of charge density of NPs in hERG binding interactions. A mode of action fitting the experimental evidence has been proposed for the observed hERG blocking activity.

The Role of Charge Density and Hydrophobicity on the Biocidal Properties of Self-Protonable Polymeric Materials.

Intrinsic antimicrobial thermoplastic A(BC)n copolymers (n = 1, 2, 4), where A was poly(ethylene glycol) (PEG), BC was a random chain of methylmethacrylate (MMA), and alkyl-aminoethyl methacrylate (AAEMA), were synthesized and the antimicrobial activity and hemolyticity were evaluated on plaques obtained by casting as a function of the architecture, the N-substituent groups of the AAEMAs (methyl, ethyl, isopropyl, and tert-butyl groups) and the hydrophobic/charge density balance. Antimicrobial effectiveness and efficiency is controlled by the surface charge density and by the influence of N-alkyl groups on the surface morphology. Also interestingly, it is the absence of hemolitytic activity in all copolymers. In presence of Escherichia coli, the A(BC)2 copolymer with 40% of N-methyl groups is the most efficient, killing 91% of the bacteria already after 1.5 h.

Drift and Diffusion in Disordered Organic Semiconductors: The Role of Charge Density and Charge Energy Transport

Using Monte Carlo simulations, we revisited charge transport in degenerate disordered organic semiconductors that are characterized by hopping transport. We found that, when a non-negligible fraction of the molecules is ionized (i.e., high charge density), charge transfer (transport) involves transfer of energy as well. Although Monte Carlo simulations confirm that, at low electric fields, the generalized Einstein relation describes the relation between drift and diffusion well, the use of the energy flux model provides a more intelligible and transparent description of the phenomenon at hand, enabling its generalization under the same premise as the thermoelectric effect and establishing a basis for the monitoring of charge-carrier energy trajectories within the traversed media.

Complex coacervation: A field theoretic simulation study of polyelectrolyte complexation

Using the complex Langevin sampling strategy, field theoretic simulations are performed to study the equilibrium phase behavior and structure of symmetric polycation-polyanion mixtures without salt in good solvents. Static structure factors for the segment density and charge density are calculated and used to study the role of fluctuations in the electrostatic and chemical potential fields beyond the random phase approximation. We specifically focus on the role of charge density and molecular weight on the structure and complexation behavior of polycation-polyanion solutions. A demixing phase transition to form a "complex coacervate" is observed in strongly charged systems, and the corresponding spinodal and binodal boundaries of the phase diagram are investigated.

Relation between the physicochemical characteristics of collagen and its interactions with chitosan: I

The interaction between bovine atelocollagen and a high molecular weight fully deacetylated chitosan has been studied. Considering the apparent mass of an anionic equivalent of collagen and the results of various techniques (potentiometry, conductometry and IR spectroscopy), a purely electrostatic mechanism is demonstrated. The role of charge density and chain length of collagen chains is discussed, and although the interaction is weak and hindered by gel formation in collagen solutions, a polyanion-polycation complex is obtained. Circular dichroism spectroscopy experiments show an organization in the solid state of the complex which is quite different to those of collagen and chitosan.