Chemical oxidative polymerization of safranines

Phenosafranine and safranine have been oxidized with ammonium peroxydisulfate in acidic aqueous solution. The oxidative coupling of both safranines was proved by gel permeation chromatography demonstrating the presence of oligomeric chains of mass-average molar masses 6500 and 4500 g mol-1 for polyphenosafranine and polysafranine, respectively. A theoretical study of the mechanism of safranine and phenosafranine polymerization was based on the MNDO-PM3 semiempirical quantum chemical computations of the heat of formation of dimeric reaction intermediates, taking into account solvation effects. The study of the redox properties of the hydrated safranines and their reactive species shows that nitrenium cations are the main reactive species generated by the oxidation of the parent safranines with a two-electron oxidant, peroxydisulfate, in the initiation phase. The dominant dimers of safranines are formed by N-C coupling reactions between nitrenium cations and the parent safranines. The main coupling reactions of phenosafranine are N-C2 (C8) and N-C4 (C6); N-C4 (C6) is the dominant coupling mode for safranine. The molecular structure of oligosafranines has been studied by FTIR, Raman, and UV-vis spectroscopies. Besides prevalent unoxidized monomeric units, polymerization products of safranines contain also the iminoquinonoid and newly formed fused phenazine units.     

Cooperative hydrogen bonds of macromolecules. 3. A model study of the proximity effect

Experimental and theoretical evidence for the proximity effect as a basic mechanism of the hydrogen bond cooperativity was obtained in a model system. Hydrogen bond (HB) interaction between poly(4-vinylpyridine) (PVP) and selected acids as HB donors was studied using PFG NMR self-diffusion measurements, 1H NMR longitudinal relaxation and quantum-mechanical DFT calculations. Bivalent HB donors, such as glutaric (GA) and adipic acid (AA), were compared to univalent donors 4-chlorobutyric acid, 4-acetylbutyric acid and 5-chlorovaleric acid. PFG NMR established substantially larger HB equilibrium constants for AA and, in particular, GA than for univalent donors, thus indicating cooperativity of COOH groups in bivalent donors. According to the values of these constants, the fraction of the transiently bound GA and AA molecules, which are bound by two hydrogen bonds, is 0.70 and 0.63, respectively. This result, which means substantial cooperativity in particular in GA, was then independently verified by a relaxation study comparing longitudinal relaxation rates of univalent and bivalent donors. Analysis of relaxation led to the same probabilities that HB of one COOH group of a bivalent donor will be accompanied by HB of another COOH group of the same molecule, namely 0.70 for GA and 0.63 for AA. Such cooperativity must be due to the proximity effect, i.e., the lowering of the entropy demand of the next binding by the motional restriction imposed by the already existing bonds. This conclusion is in excellent agreement with DFT calculations on the interaction of GA with a model vinylpyridine dimer, which predict preference of double binding of the same GA molecule over that of two GA molecules and show that this preference is due to a substantially lower entropy demand.     

Nanostructures in a binary mixture confined in slit-like pores with walls decorated with tethered polymer brushes in the form of stripes: dissipative particle dynamics study

Using dissipative particle dynamics, we investigate the behavior of a binary mixture, exhibiting demixing in a bulk phase, confined in slit-like pores with walls modified by the stripes of tethered brush of chains. Our main interest is to determine possible morphologies that can be formed inside the pore, depending on the geometrical parameters characterizing the system (the size of the pore and the width of the stripes). In order to describe the observed morphologies we calculate several characteristics, as the density and local temperature profiles, the radii of gyration for the attached polymers, and the minimum polymer-polymer distances in the direction parallel and perpendicular to the pore walls. The summary of our findings is presented as a sketch of the diagram of morphologies.     

Equivalent chain lengths of all C4-C23 saturated monomethyl branched fatty acid methyl esters on methylsilicone OV-1 stationary phase

Isomer mixtures of monomethyl branched saturated C7-C23 fatty acid methyl esters (FAME) were prepared by performing a methylene insertion reaction to the straight chain FAME and this study model was completed by using commercially available standards of C4-C7 FAME. The equivalent chain lengths (ECL) of all 220 C4-C23 monomethyl branched FAME on OV-1 stationary phase were measured, achieving an average repeatability of ±0.0004 ECL units. The monomethyl branched FAME was identified by GC on the basis of regularity of the fractional chain lengths (FCL) dependence on the number of carbon atoms (C(z)) of individual homologous series of methyl 2-, 3-, …, 21-FAME. The prediction of retention of the first homologues, having the new position of methyl group beginning at higher carbon atoms number, and analogously for the second, third, fourth, and other members of the homologous series, allowed the dependence FCL=f(C(z)) for the first and subsequent members of beginning homologous of monomethyl derivatives of FAME. The identification was confirmed by mass spectrometry. All of the methyl isomers of FAME, which could not be completely separated by gas chromatography due to having a methyl group in surroundings of the middle of the carbon chain, were resolved by mass spectrometry using deconvolution in a SIM-mode. Measured gas chromatographic and mass spectrometric data were applied for identification of the monomethyl branched saturated FAME in tongue coating.     

Exploring a reaction mechanism for acetato ligand replacement in paddlewheel tetrakisacetatodirhodium (II,II) complex by ammonia: computational density functional theory study

This study focuses on the first step of interaction between DNA and the paddle-wheel dirhodium complex. The ammonia molecule was used to model the oligonucleotide sequence. The reaction was considered in neutral and acidic conditions, in gas phase, and in solvent, using the COSMO model. Molecular structures of the complexes were optimized in both models at the B3PW91/6-31G(d) level. The B3LYP functional and aug-cc-pvdz basis set were employed for single-point energy determination and electron distribution analyses. It was shown that in neutral solution the replacement of axial aqua ligand is mildly exoergic. The reaction is characterized by a relatively low activation barrier (10-12 kcal/mol), and, according to Eyring transition state theory, it proceeds very quickly. The breaking of the Rh-O(ac) bond in neutral solution is mildly endoergic (less than 1 kcal/mol) with an activation barrier of about 21 kcal/mol. However, this process can occur much more spontaneously (ΔG of -14 kcal/mol) when the dirhodium complex is protonated at the acetyl oxygen in remote position.     

Structure changes of electrorheological fluids based on polyaniline particles with various hydrophilicities and time dependence of shear stress and conductivity during flow

Particles of polyaniline protonated with perfluorooctanesulfonic acid provided a material with hydrophobic surface. This property enabled its perfect dispersion in silicone oil due to its good compatibility with the hydrophobic medium. In contrast, in a suspension of hydrophilic polyaniline particles doped with sulfamic acid, strong interactions of particles prevailed, which led to the formation of entangled chains of aggregated particles in suspension. The difference in structural properties of suspensions exists already in the absence of electric field and significantly influences their electrorheological behavior after application of electric field. The formation of electrorheological structure has been monitored by recording time dependences of the shear stress and the electric current passing through the flowing suspensions.     

Wall effects on terminal falling velocity of spherical particles moving in a Carreau model fluid

Experimental verification of our previous numerical simulation of wall effects on the terminal falling velocity of spherical particles moving slowly along the axis of a cylindrical vessel filled with a Carreau model fluid is presented. Dependences of the wall correction factor F _W on the sphere to tube ratio d/D and on the dimensionless Carreau model parameters m, Λ, and η _r were obtained using a finite element method. Calculated data of the wall correction factor were compared with the results of our new falling sphere experiments. The experiments were carried out in six types of cylindrical Perspex columns (16 mm, 21 mm, 26 mm, 34 mm, 40 mm, and 90 mm in diameter) filled with aqueous solutions of polymers exhibiting different degrees of shear thinning and elasticity. Seventeen types of spherical particles (1–8 mm in diameter) made of glass, ceramics, steel, lead, and tungsten carbide were used for the drop tests. Measurements of the liquid flow curves, primary normal stress differences, oscillatory, creep and recovery, stress relaxation, and stress growth tests were carried out on the rheometer Haake MARS (Thermo Scientific). A good agreement between numerically and experimentally obtained F _W data was found.     

Mathematical modeling and simulation of flow in domains separated by leaky semipermeable membrane including osmotic effect

In this paper, we propose a mathematical model for flow and transport processes of diluted solutions in domains separated by a leaky semipermeable membrane. We formulate transmission conditions for the flow and the solute concentration across the membrane which take into account the property of the membrane to partly reject the solute, the accumulation of rejected solute at the membrane, and the influence of the solute concentration on the volume flow, known as osmotic effect.     

Multi-wall carbon nanotubes with nitrogen-containing carbon coating

Polyaniline coating was deposited on the surface of multi-wall carbon nanotubes of Russian and Taiwanese origin in situ during the polymerization of aniline. The deposited polyaniline film was subsequently carbonized under an inert atmosphere at various temperatures to produce coaxial coating of the carbon nanotubes with nitrogen-containing carbon. The new materials were investigated by infrared and Raman spectroscopies, which demonstrated the conversion of the polyaniline coating to a carbonized structure. X-ray photoelectron spectroscopy proved that the carbonized overlayer contains nitrogen atoms in various covalent bonding states. Transmission electron microscopy confirmed the coaxial structure of the composites. The Brunauer-Emmett-Teller method was used to estimate the specific surface area, the highest being 272 m² g^?1. The conductivity of 0.9–16 S cm^?1 was measured by the four-point method, and it was only a little affected by the carbonization of the polyaniline coating.     

Electrical transport properties of poly(aniline-co-p-phenylenediamine) and its composites with incorporated silver particles

Statistical copolymers of aniline and p-phenylenediamine, poly(aniline-co-p-phenylenediamine)s, were synthesised by oxidative polymerisation using various oxidants, ammonium peroxydisulphate or silver nitrate. Depending on the choice of oxidant, copolymers or composites with silver particles were obtained. Different molar concentrations of p-phenylenediamine in the reaction mixture provided materials of different conductivities. The influence of both the copolymer composition and the presence of discrete silver particles on the electric and dielectric properties of the system was studied. The results showed a decrease in the conductivity of copolymers and their composites with the silver content compared with the content of standard polyaniline salt. The reduction in conductivity was described in terms of the decreased density of hopping centres due to defects in the copolymer structure. The dielectric relaxations observed were described in terms of their activation energies and were linked to the corresponding conduction mechanism.