Characterization of Ethylene-propylene Composites Filled with Perlite and Vermiculite Minerals: Mechanical, Barrier, and Flammability Properties.

Perlite and vermiculite are naturally occurring minerals, commonly used by industry to obtain highly thermoisolative and/or non-flammable materials. However, there has been little research into the preparation and application of rubber compounds containing these inexpensive mineral fillers. Here, we show the benefits of perlite and vermiculite minerals as fillers for ethylene-propylene rubber (EPM) composites. To obtain more uniform dispersion and improved compatibility between the minerals and the elastomer matrix, 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (AMIMTFSI) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI) imidazolium ionic liquids (ILs) were added. The mineral fillers were found to be attractive semi-reinforcing fillers, which also act as flame retardants in the elastomer composites. Furthermore, a higher content of vermiculite mineral significantly reduced the air permeability of the composites. The incorporation of ionic liquids into the EPM-filled systems had a considerable effect on the torque increment, crosslink density, and more importantly the flammability of the studied compounds. The application of 2.5 parts per hundred parts of rubber (phr) BMIMTFSI, in particular, reduced the flammability of the EPM composite, as the maximum heat release rate (HRRmax) decreased from 189.7 kW/m2 to 170.2 kW/m2.

Characteristics of juglone (5-hydroxy-1,4,-naphthoquinone) using voltammetry and spectrophotometric methods.

The objective of this work was to analyse the antiradical capacity of juglone (5-hydroxy-1,4,-naphthoquinone). The influence of oxidation and reduction on juglone was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), as well as spectrophotometric based methods. The role of juglone in oxidation processes, as either an antioxidant in browning reactions, was examined. These processes are characterized by a high chemical reactivity in redox. Juglone is irreversibly oxidized in at least one electrode step and reduced quasi-reversibly in at least three electrode steps. These results demonstrate that walnut genotypes have different radical scavenging powers. In addition, on the basis of thermogravimetry, it was demonstrated that 5-hydroxy-1,4-naphthalenedione has high thermal stability above 500 °C. The generation of reactive oxygen species and activity in redox processes show the properties of naphthoquinones that render these compounds interesting leads for the development of novel biomolecules for potential use in various therapeutic settings.

Characterization and Structure⁻Property Relationships of Organic⁻Inorganic Hybrid Composites Based on Aluminum⁻Magnesium Hydroxycarbonate and Azo Chromophore.

In this study, novel organic⁻inorganic composites were prepared by the complexation of dicarboxylic azo dye (AD) with aluminum⁻magnesium hydroxycarbonate (AlMg⁻LH). This procedure provides an effective method for the stabilization of dicarboxylic organic chromophores on an AlMg-LH host. The structures of the hybrid composites were examined by X-ray diffraction (XRD), secondary ion mass spectrometry (TOF-SIMS), 27-Al solid-state nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA) and scanning transmission electron microscopy (STEM). The TOF-SIMS method was applied to investigate the metal⁻dye interactions and to monitor the thermal stability of the organic⁻inorganic complexes. Secondary ion mass spectrometry confirmed the presence of a characteristic peak for C18H10O5N2Mg22+, indicating that both carboxylic groups interacted with AlMg-LH by forming complexes with two Mg2+ ions. Modification with hybrid pigments affected the crystal structure of the AlMg-LH mineral, as shown by the appearance of new peaks on the X-ray diffraction patterns. Adsorption of the dicarboxylic chromophore not only led to significantly enhanced solvent resistance but also improved the thermal and photostability of the hybrid pigments. We propose a possible arrangement of the azo dye in the inorganic matrix, as well as the presumed mechanism of stabilization.

Carminic Acid Stabilized with Aluminum-Magnesium Hydroxycarbonate as New Colorant Reducing Flammability of Polymer Composites.

In this study, hybrid pigments based on carminic acid (CA) were synthesized and applied in polymer materials. Modification of aluminum-magnesium hydroxycarbonate (LH) with CA transformed the soluble chromophore into an organic-inorganic hybrid colorant. Secondary ion mass spectroscopy (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and UV-Vis spectroscopy were used to study the structure, composition, and morphology of the insoluble LH/CA colorant. Successful modification of the LH was confirmed by the presence of interactions between the LH matrix and molecules of CA. XPS analysis corroborated the presence of CA complexes with Mg2+ ions in the LH host. The batochromic shift in UV-Vis spectra of the organic-inorganic hybrid colorant was attributed to metal-dye interactions in the organic-inorganic hybrid colorants. Strong metal-dye interactions may also be responsible for the improved solvent resistance and chromostability of the modified LH. In comparison to uncolored ethylene-norbornene copolymer (EN), a modified EN sample containing LH/CA pigment showed lower heat release rate (HRR) and reduced total heat release (THR), providing the material with enhanced flame retardancy.

Characteristics of Hybrid Pigments Made from Alizarin Dye on a Mixed Oxide Host.

This paper describes the fabrication of a new hybrid pigment made from 1,2-dihydroxyanthraquinone (alizarin) on a mixed oxide host (aluminum-magnesium hydroxycarbonate, LH). Various tools were applied to better understand the interactions between the organic (alizarin) and inorganic (LH) components, including ion mass spectroscopy (TOF-SIMS), 27-Aluminm solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). TOF-SIMS showed that modification of the LH had been successful and revealed the presence of characteristic ions C14H7O4Mg⁺ and C14H6O5Al-, suggesting interactions between the organic chromophore and both metal ions present in the mixed oxide host. Interactions were also observed between Al3+ ions and Alizarin molecules in 27Al NMR spectra, with a chemical shift detected in the case of the modified LH matrix. Any changes in color following reactions with Mg2+ and Al3+ ions were observed. Some of the physicochemical properties of alizarin, such as resistance to dissolution and color stability at elevated temperatures, were improved in comparison to the pure dye. This effect can be attributed to strong dye-LH interactions and the effective transformation of alizarin into an insoluble form. Moreover, the pigments exhibited higher thermal resistance and greater color stability in comparison to commercially available alizarin lakes (Alizarin Crimson).

Aluminum-Magnesium Hydroxycarbonate/Azo Dye Hybrids as Novel Multifunctional Colorants for Elastomer Composites.

This study presents the preparation and characterization of new organic-inorganic pigments based on aluminum-magnesium hydroxycarbonate (LH) and azo dyes. Solvent resistance studies, XRD, SEM, and TGA confirmed the successful formation of hybrid pigments, which were characterized in terms of their physicochemical properties. The new hybrid pigments were applied in acrylonitrile-butadiene (NBR) and ethylene-propylene (EPM) rubber composites and cured with sulfur and peroxide curing systems, respectively. The mechanical properties, dispersion quality, and flame-retardant properties of the NBR/hybrid and EPM/hybrid pigment composites were determined by dynamic mechanical analysis (DMA), SEM, and microscale combustion calorimetry (MCC). Complex experimental investigations revealed that the layered nature of hybrid pigments could improve the barrier ability and flame retardancy of elastomer composites. In comparison to unmodified aluminum-magnesium hydroxycarbonate, the modified LH dye structures contributed to significantly decrease the heat release rate and the total heat release of the NBR and EPM composites, offering a new approach to imparting low flammability to elastomer materials.

Effect of Zinc Oxide Modified Silica Particles on the Molecular Dynamics of Carboxylated Acrylonitrile-Butadiene Rubber Composites.

This work examines the molecular dynamics of carboxylated acrylonitrile-butadiene rubber crosslinked with zinc oxide modified silica particles. ZnO/SiO2 with the wide range of ZnO concentrations were used as both a crosslinking agent and filler. A series of thermal measurements were applied to the characterization of the samples: differential scanning calorimetry, dynamical mechanical thermal analysis, and dielectric relaxation spectroscopy. A complementary experimental technique, which is equilibrium swelling in solvents, confirms the presence of ionic crosslinks, which are created between zinc ions and the functional carboxyl groups of the rubber, within the structure of the vulcanizates. These interactions influenced not only the affinity of the vulcanizates to solvents, but also their dynamic mechanical and dielectric properties. In these investigations, the influence of concentration of ZnO on the surface of the ZnO/SiO2 on the properties of the vulcanizates are described.

Influence of hydroxyl substitution on flavanone antioxidants properties.

The aim of our study was to determine the effect of the position of the hydroxyl group on the antioxidant properties of flavonoid derivatives. For this purpose, we performed electrochemical analysis and quantum-mechanical calculations to describe the mechanisms of electrochemical oxidation, and we selected the two methods of ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate), which allowed us to determine the ability to scavenge free radicals. On the basis of the research, we found that the derivatives of flavonoids, which have a hydroxyl group substituted at the R-3 position on the C ring, have outstanding antioxidant activity. Flavone, which had an OH group substituted at the R-6 and R-7 position on the ring A, showed similar antioxidant activity to flavone without -OH groups in the structure and slightly higher activity than the di-substituted flavone on the ring A.

Characteristics of compounds in hops using cyclic voltammetry, UV-VIS, FTIR and GC-MS analysis.

The article presents the antioxidant properties of the extracts of hop EI and EII, by the electrochemical methods on a platinum electrode and comparative analysis of the composition of the extracts of hops using UV-VIS, FTIR and GC-MS methods. The hops extract EI, was obtained from the waste of the hops cone. The hops extract EII, was obtained from the hops cone itself. Hops contain a wide range of polyphenolic compounds with antioxidant properties divided in various chemical classes. Flavonoids and other polyphenolic compounds contained in hops show antioxidant capacity because of the presence of hydroxyl groups in various configurations and numbers within their molecules. The electrochemical properties and antioxidant capacity of hop samples were determined to select the most effective antioxidant. Based on the cyclic and pulse voltammograms, it was observed that hop extract EI contains polyphenols that are oxidised at a less positive potential than extract EII, i.e., it shows better antioxidant capacity. From the analysis of the UV-VIS and FTIR spectra and the GC-MS analysis, it was observed that extract EI contains less phenyl compounds than EII. In addition to flavonoids, EII contains hop acids and chlorophyll. The solutions of hop extracts show very good antioxidant capacities; therefore, they can effectively inhibit or slow negative oxidation reactions and scavenge free radicals and reactive oxygen species (ROS).

Optimization of the heavy metal (Bi-W-Gd-Sb) concentrations in the elastomeric shields for computer tomography (CT).

Eight elastomeric composites (NRU, GR1-GR4, NRBG08-NRBG24) containing mixtures of different proportions of heavy metal additives (Bi, W, Gd and Sb) have been synthesized and examined as protective shields. The NRU sample was a pure rubber matrix and served as a reference sample for heavy metal modified composites. Experimental procedure used for evaluation of the composite shields and their attenuation properties was based on the utilization of HPGe spectrometry and analysis of X-ray fluorescence radiation intensity of the heavy metal additives in the following energy ranges for: Sb (20-35 keV), Gd (35-55 keV), W (55-70 keV) and Bi (70-90 keV). The main contributor to the induced X-ray fluorescence radiation within the shield is Bi additive and the intensity of the X-ray radiation generated within the energy range of 70-90 keV strongly depends on its concentration. It was found that decreasing concentration of the Bi fraction from 0.35 (GR samples) to 0.15 (NRBG samples) results in significant lowering Bi X-ray fluorescence radiation within the 70-90 keV energy range. Secondary effect of decreasing Bi concentration was efficient diminishing excitation processes for lower Z heavy metal additives (W, Gd and Sb, GR vs. NRBG samples). As the final quality parameter of the shielding properties for the examined elastomers, dose reduction factor (DRF) coefficients were calculated for each shield. It was found, that the best shielding properties are observed for composites with lower Bi concentration (0.15 vs. 0.35 Bi mass fraction) with only slight further improvement of their parameters (DRF) with increasing of Gd concentration (Gd mass fraction 0.08, 0.16 and 0.24). The most efficient dose reduction composite was found to be NRBG24 elastomer with DRF value 0.47 (53 % dose reduction) for ca. 2 mm and 0.44 g/cm2 layer thickness.

Electrooxidation of morin hydrate at a Pt electrode studied by cyclic voltammetry.

The process and the kinetics of the electrochemical oxidation of morin in an anhydrous electrolyte have been investigated using cyclic and differential pulse voltammetry. The oxidation mechanism proceeds in sequential steps related to the hydroxyl groups in the three aromatic rings. The oxidation of the 2',4'dihydroxy moiety at the B ring of morin occurs first, at very low positive potentials, and is a one-electron, one-proton irreversible reaction. The rate constant, electron transfer coefficient and diffusion coefficients involved in the electrochemical oxidation of morin were determined. The influence of the deprotonation of the ring B hydroxyl moiety is related to the electron/proton donating capacity of morin and to its radical scavenging antioxidant activity.

Surface properties of calcium and magnesium oxide nanopowders grafted with unsaturated carboxylic acids studied with inverse gas chromatography.

Inverse gas chromatography (IGC) was applied at infinite dilution to evaluate the surface properties of calcium and magnesium oxide nanoparticles and the effect of surface grafted unsaturated carboxylic acid on the nanopowder donor-acceptor characteristics. The dispersive components (γ(s)(D)) of the free energy of the nanopowders were determined by Gray's method, whereas their tendency to undergo specific interactions was estimated based on the electron donor-acceptor approach presented by Papirer. The calcium and magnesium oxide nanoparticles exhibited high surface energies (79 mJ/m² and 74 mJ/m², respectively). Modification of nanopowders with unsaturated carboxylic acids decreased their specific adsorption energy. The lowest value of γ(s)(D) was determined for nanopowders grafted with undecylenic acid, approximately 55 mJ/m². The specific interactions were characterised by the molar free energy (ΔG(A)(SP)) and molar enthalpy (ΔH(A)(SP)) of adsorption as well as the donor and acceptor interaction parameters (K(A), K(D)).

Carbosilane dendrimers are a non-viral delivery system for antisense oligonucleotides: characterization of dendriplexes.

The success of gene therapy depends on the development of suitable carriers, and because of their architecture dendrimers are promising tools for gene delivery. This research concerns the use of second generation carbosilane dendrimers as carriers for anti-HIV oligodeoxynucleotides (ODNs). The aim was to characterize complexes formed by positively charged dendrimers and negatively charged oligonucleotides using a fluorescence method, laser Doppler electrophoresis, dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy (TEM) and molecular modeling. The zeta-potential of ODNs increased from -25 mV to positive values after the addition of dendrimers. DLS and TEM revealed that the diameters of dendriplexes ranged from 75 to 240 nm and from 50 to 260 nm, respectively, and this was dependent on the type of dendrimer and the molar ratios of the complexes formed; complexes were stable for between 100 and 300 minutes. AFM measurements and molecular modeling studies were carried out to determine the structure and size of dendriplexes. The physicochemical properties of the dendriplexes studied and data from previous research suggest that carbosilane dendrimers are good candidates for nucleic acid delivery.

Characterization of complexes formed by polypropylene imine dendrimers and anti-HIV oligonucleotides.

Current anti-HIV therapies are capable of controlling viral infection but do not represent a definitive cure. They rely on the administration of antiretroviral nucleoside analogues, either alone or in combination with vectors. Dendrimers are branched, synthetic polymers with layered architectures, promising non-viral vectors in gene therapy. The aim of the paper was to study the interactions between three anti-HIV antisense oligonucleotides (ODNs): SREV, ANTI TAR, GEM91 and different generation polypropylene imine dendrimers (PPI) by monitoring changes in the fluorescence polarization of fluorescein attached to the ends of the ODNs when increasing concentrations of dendrimers were added. Laser Doppler electrophoresis, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to characterize, respectively, zeta potential, particle size and morphology of dendriplexes formed in different molar ratios. Antisense oligonucleotides interacted with polypropylene imine dendrimers in different molar ratios depending on generation. Zeta potential of dendriplexes varied from (-25 to -21) mV to -5 mV (for PPIG3 and PPIG4 complexes) and to zero (for PPIG2 complexes). The structures presented a polydisperse size from about 50 nm to even 700-800 nm by TEM and about 250 nm by DLS. It means that besides single dendriplexes, aggregates were also present.

Electrooxidation of flavonoids at platinum electrode studied by cyclic voltammetry.

Flavonoids are natural vegetable dyes synthesized from phenylalanine. They are responsible for colour of blooming plant portions. Moreover, they are very important for human health due to their activity as free radical acceptors. Cyclic and differential pulse voltammetry was used in the determination of kinetic parameters of flavonoids electrooxidation. Electrochemical measurements of the oxidation of organic compounds can be helpful in understanding how these compounds are metabolised by living organisms. Flavonoids electrochemical oxidation is an irreversible reaction at a platinum electrode. In the case of morin hydrate, rutin, dihydroxyflavone, trihydroxyflavone, hesperidin, quercetin, the first step of the electrooxidation includes an exchange of two electrons during the oxidation of hydroxyl groups in the ring B. Hydroxyl groups in the rings A and C are probably oxidised in subsequent steps. The heterogeneous rate constants (k(bh)) determined for the flavonoids electrooxidation are as follows: morin - 3.59×10(-4), rutin - 4.42×10(-4), dihydroxyflavone - 4.54×10(-4), trihydroxyflavone - 4.19×10(-4), hesperidin - 4.50×10(-4) and quercetin - 4.63×10(-4)cms(-1). Their anodic transition coefficient ranged from 0.63 to 0.48 (n=2). Xanthone and flavone were oxidised easiest and quickest among other substrates at the platinum electrode with the heterogeneous rate constants (k(bh)) of 7.08×10(-4) and 6.46×10(-4)cms(-1), respectively.

Carbosilane dendrimers NN8 and NN16 form a stable complex with siGAG1.

A new mechanism of gene expression inhibition has been discovered as RNA interference, in which the ability of double-stranded RNA to stimulate specific degradation of an mRNA target with a complementary sequence to one of the double-stranded RNA strands. Water-soluble carbosilane dendrimers containing ammonium or amine groups at their periphery are biocompatible molecules that may be good candidates as non-viral carriers of small interfering RNA. In studying the formation of complex between anti-HIV siRNA siGAG1 and carbosilane dendrimers NN8 and NN16 by circular dichroism, fluorescence, and zeta-potential, the size of nanoparticles formed has been estimated by dynamic light scattering. At a charge ratio of 1:3-4 (siGAG1:dendrimer), the dendriplexes formed were in the size range of 250-350 nm.

Surface properties of zinc oxide nanoparticles studied by inverse gas chromatography.

Inverse gas chromatography (IGC) was applied in infinite dilution to evaluate the surface properties of zinc oxide nanoparticles with respect to their specific surface area, particle size and morphology (spherical, whiskers, and snowflakes). The dispersive components (gamma(S)(D)) of the free energy of zinc oxides were determined by Gray's method, whereas their tendency to undergo specific interactions was estimated based on the electron donor-acceptor approach presented by Papirer. The zinc oxide nanoparticles exhibited high surface energies that were dependent on their morphology. The highest value of gamma(S)(D) was determined for spherical zinc oxide particles with high specific surface area, which had the most structure defects. The specific interactions were characterized by the energy (DeltaG(A)(SP)) and enthalpy (DeltaH(A)(SP)) of adsorption as well as the donor and acceptor interaction parameters (K(A), K(D)).

The interaction between PAMAM G3.5 dendrimer, Cd2+, dendrimer-Cd2+ complexes and human serum albumin.

The interactions between PAMAM G3.5 dendrimer, Cd2+, a complex of "PAMAM G3.5 dendrimer-Cd2+" and human serum albumin were studied by equilibrium dialysis, fluorescence quenching, fluorescence anisotropy and zeta-potential. It was found that in water one molecule of PAMAM 3.5 dendrimer can bind 38+/-9 cadmium ions with Kb=1.3+/-0.13 x 10(3). The calculated Stern-Volmer constants of albumin fluorescence quenching by Cd2+, G3.5 and the "PAMAM G3.5-Cd2+" complex were 2.2+/-0.2, 1.6+/-0.3 and 1.4+/-0.1(mmol/l)(-1), respectively. The data from the fluorescence and zeta-potential studies show that the "PAMAM G3.5-Cd2+" complex interacted much less strongly with human serum albumin than the pure dendrimer or Cd2+.

Impact of PAMAM G2 and G6 dendrimers on bovine serum albumin (fatty acids free and loaded with different fatty acids).

Dendrimers are a new class of nanotechnological polymers suitable for drug targeting, microarray systems or detoxication. The present study is devoted to a detailed analysis of binding between PAMAM dendrimers and bovine serum albumin (fatty acid free or loaded with oleic, linoleic, oleic+linoleic or oleic+linoleic+arachodonic acids) by measuring zeta-potential, fluorescence quenching, fluorescence anisotropy and electron paramagnetic resonance. Addition of PAMAM G2 and G6 dendrimers to protein solutions resulted in attachment to the protein molecule. The PAMAM dendrimers also competed with BSA for fatty acids if two or three fatty acids were loaded per protein. This can lead to the extraction of fatty acids from BSA to the PAMAM dendrimer.

Serum albumins have five sites for binding of cationic dendrimers.

The detailed analysis of the interaction between PAMAM G4 dendrimer and serum albumins was performed using circular dichroism, isothermal titration calorimetry, capillary electrophoresis, zeta-potential and fluorescence polarization. It was shown that serum albumins and PAMAM G4 dendrimer form the complex with stoichiometry of 4-6:1 for G4:HSA and 4-5:1 for G4:BSA molar ratio. The possible sites of PAMAM G4 dendrimers binding to protein surface were discussed. Also, it has been proposed that dendrimer does not significantly affect the protein secondary structure studied by circular dichroism.