Structural Characterization of Ionic Gelator Studied by Dynamic Light Scattering and Small-Angle Neutron Scattering

Antimicrobial activity of poly(3,4-ethylenedioxythiophene) n-doped with a pyridinium-containing polyelectrolyte

In spite of p-doped conducting polymers having been widely studied in the last decades and many applications having been developed, studies based on n-doped conducting polymers are extremely scarce. This fact is even more evident when it comes to conducting polymers n-doped with polycations, even though polyanions, such as poly(styrenesulfonate), are often used to obtain p-doped conducting polymers. In this work poly(pyridinium-1,4-diyliminocarbonyl-1,4-phenylene-methylene chloride), abbreviated as P(Py-1,4-P), has been used to prepare n-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes by applying a reduction potential to a de-doped PEDOT film in a P(Py-1,4-P) water solution. The utilization of this cationic polyelectrolyte as an n-dopant agent results in drastic superficial changes, as is observed by comparing the morphology, topography and wettability of p-doped, de-doped and n-doped PEDOT. Cytotoxicity, cell adhesion and cell proliferation assays, which have been conducted using epithelial and fibroblast cell lines, show that the amount of P(Py-1,4-P) in the re-doped PEDOT films is below that required to observe a cytotoxic harmful response and that n-doped PEDOT:P(Py-1,4-P) films are biocompatible. The non-specific bacteriostatic properties of n-doped PEDOT:P(Py-1,4-P) films have been demonstrated against E. coli and S. aureus bacteria (Gram-negative and Gram-positive, respectively) using bacterial growth curves and adhesion assays. Although the bacteriostatic effect is in part due to the conducting polymer, as is proved by results for p-doped and de-doped PEDOT, the incorporation of P(Py-1,4-P) through the re-doping process greatly enhances this antimicrobial behaviour. Thus, only a small concentration of this cationic polyelectrolyte (∼0.1 mM) is needed to inhibit bacterial growth.

A closure relation to molecular theory of solvation for macromolecules

We propose a closure to the integral equations of molecular theory of solvation, particularly suitable for polar and charged macromolecules in electrolyte solution. This includes such systems as oligomeric polyelectrolytes at a finite concentration in aqueous and various non-aqueous solutions, as well as drug-like compounds in solution. The new closure by Kobryn, Gusarov, and Kovalenko (KGK closure) imposes the mean spherical approximation (MSA) almost everywhere in the solvation shell but levels out the density distribution function to zero (with the continuity at joint boundaries) inside the repulsive core and in the spatial regions of strong density depletion emerging due to molecular associative interactions. Similarly to MSA, the KGK closure reduces the problem to a linear equation for the direct correlation function which is predefined analytically on most of the solvation shells and has to be determined numerically on a relatively small (three-dimensional) domain of strong depletion, typically within the repulsive core. The KGK closure leads to the solvation free energy in the form of the Gaussian fluctuation (GF) functional. We first test the performance of the KGK closure coupled to the reference interaction site model (RISM) integral equations on the examples of Lennard-Jones liquids, polar and nonpolar molecular solvents, including water, and aqueous solutions of simple ions. The solvation structure, solvation chemical potential, and compressibility obtained from RISM with the KGK closure favorably compare to the results of the hypernetted chain (HNC) and Kovalenko-Hirata (KH) closures, including their combination with the GF solvation free energy. We then use the KGK closure coupled to RISM to obtain the solvation structure and thermodynamics of oligomeric polyelectrolytes and drug-like compounds at a finite concentration in electrolyte solution, for which no convergence is obtained with other closures. For comparison, we calculate their solvation structure from molecular dynamics (MD) simulations. We further couple the 3D-RISM integral equation with the 3D-version of the KGK closure, and solve it for molecular mixtures as well as oligomeric polyelectrolytes and drug-like molecules in electrolyte solutions.

Alkoxy tail length dependence of gelation ability and supramolecular chirality of sugar-appended organogelators

A series of sugar-appended organogelators, 4-(4'-alkoxyphenyl)phenyl-β-O-D-glucoside (GBCn, where n = 1-12 denotes the number of carbon atom in the tail), are synthesized to elucidate the effect of terminal chain length on their gelation and chiral expression abilities in gels. In the mixture of H(2)O/dioxane (60/40 v/v), GBCn undergoes a phasic evolution of precipitation-solution-gel-precipitation-gel as its tail length increases from n = 1, 2, 3-6, and 7-10 to 11-12, respectively. Helical ribbons are observed in gels, but platelet-like structures are the dominant morphologies in the systems that precipitation happens. Combinatory analyses of microscopic, spectroscopic, and diffraction results reveal that the self-assembly into interdigitated bilayer structures of GBCn is driven by hydrogen bondings of sugar heads, π-π interactions of biphenyl rods, and hydrophobic interactions of alkoxy tails. The helical-morphology formation is caused by the significant steric repulsion between chiral moieties on the condition of the disordering or the size of alkoxy chains reaching the threshold of helical twisting and bending.

Effect of salt content on the rheological properties of hydrogel based on oligomeric electrolyte

Dynamic light scattering and oscillatory rheology experiments were performed to study the effects of various salts on the hydrogel consisting of an oligomeric electrolyte gelator, poly(pyridinium-1,4-diyliminocarbonyl-1,4-phenylenemethylene chloride) (1-Cl). Sol-gel transition temperature increased with increasing salt concentration that suggested the salt-in behavior. The concentration dependence of the dynamic shear moduli showed power-law scaling behavior and was compared with the predictions made by the fractal gel model. The brittleness was increased by increasing salt concentration, indicating that 1-Cl hydrogel became better packed into stronger networks in ionic solutions. After certain salt concentrations, 1-Cl hydrogel started precipitation that might be due to the excessive network formation resulting in collapse of the network structure. The recovery of the mechanical properties of 1-Cl hydrogel was completely reduced in the presence of salts.

Tuning the helicity of self-assembled structure of a sugar-based organogelator by the proper choice of cooling rate

A novel sugar-appended low-molecular-mass gelator, 4''-butoxy-4-hydroxy-p-terphenyl-beta-D-glucoside (BHTG), was synthesized. It formed thermally reversible gels in a variety of aqueous and organic solvents. Three-dimensional networks made up of helical ribbons were observed in the mixture of H(2)O/1,4-dioxane (40/60 v/v). The handedness of the ribbons depended on the rate of gel formation. Fast-cooling process led to right-handed ribbons, while slow-cooling process led to left-handed ones. A combinatory analyses of microscopic, spectroscopic, and diffraction techniques revealed that BHTG formed a twisted interdigitated bilayer structure with a d spacing of 3.1 nm in gels through a kinetically controlled nucleation-growth process. There were two kinds of molecular orientations of BHTG in the nuclei, clockwise and anticlockwise, which dictated the growth of ribbons. One was metastable and formed first during the cooling process of gel formation. It was able to gradually transform into the more stable latter one with further decreasing temperature. Fast-cooling process did not leave enough time for the nuclei to evolve from metastable to stable state and the ribbons grown from them exhibited right-handedness. However, the metastable nuclei transformed into the stable one when cooled slowly and directed the molecules of BHTG to grow into left-handed aggregates.