Surface analysis of inhibitor films formed by imidazolines and amides on mild steel in an acidic environment

Imidazolines and amidic precursors were synthesized with good yields through an optimized process. These compounds were evaluated as corrosion inhibitors in an aqueous solution of 1.0 M HCl by gravimetric and polarization techniques. AISI 1018 carbon steel displayed a corrosion rate dependent on the molecular structure and concentration of inhibitor in the testing environment. Adsorption of inhibitors was found to follow the Langmuir's isotherm, this concept together with Gibbs’ free energy provided the basis to arrange corrosion inhibitors according to efficiency and stability. The surface analysis by AFM displayed that the damage on the metallic surface was considerably reduced in the presence of certain inhibitors. XPS determined the presence of a layer of inhibitor on the metal surface with protective properties.     

Multi-capillary column-ion mobility spectrometry: a potential screening system to differentiate virgin olive oils

The potential of a headspace device coupled to multi-capillary column-ion mobility spectrometry has been studied as a screening system to differentiate virgin olive oils (“lampante,” “virgin,” and “extra virgin” olive oil). The last two types are virgin olive oil samples of very similar characteristics, which were very difficult to distinguish with the existing analytical method. The procedure involves the direct introduction of the virgin olive oil sample into a vial, headspace generation, and automatic injection of the volatiles into a gas chromatograph-ion mobility spectrometer. The data obtained after the analysis by duplicate of 98 samples of three different categories of virgin olive oils, were preprocessed and submitted to a detailed chemometric treatment to classify the virgin olive oil samples according to their sensory quality. The same virgin olive oil samples were also analyzed by an expert’s panel to establish their category and use these data as reference values to check the potential of this new screening system. This comparison confirms the potential of the results presented here. The model was able to classify 97% of virgin olive oil samples in their corresponding group. Finally, the chemometric method was validated obtaining a percentage of prediction of 87%. These results provide promising perspectives for the use of ion mobility spectrometry to differentiate virgin olive oil samples according to their quality instead of using the classical analytical procedure.     

Electrodetermination of Gallic Acid Using Multi-walled Carbon Nanotube Paste Electrodes and N-Octylpyridinium Hexafluorophosphate

In this work, the determination of gallic acid was performed using surface-renewable carbon paste electrodes fabricated with multi-walled carbon nanotubes (MWCNT) and a mixture of N-octylpyridinium hexafluorophosphate (OPyPF₆) ionic liquid with mineral oil (MO) as binder. This system shows remarkable amperometric sensor characteristics and promotes a better electronic transfer. An electroanalytical study of gallic acid shows a linear range from 4.98±0.25 to 74.1±2.2 μmol L⁻¹, with R²=0.9958 and an experiment a limit of detection of 2.70±0.08 μmol L⁻¹ (S/N=3), and a sensitivity of 0.029 μA μmol⁻¹ L.     

Thermally controlled preferential molecular aggregation state in a thiacarbocyanine dye

Herein we report the experimental and theoretical study of the temperature dependence of a thiacarbocyanine dye in its monomer, H- and J-aggregates states. We demonstrate the ability to control the ratio of monomer, H- and/or J-aggregates with heat. We link such a control to the conformation dependence of the molecule. An alternative way to gain access to the dominating species without changing the concentration as a complete switching mechanism between all the present species is proposed. The results presented in this work lead to a better understanding of thiacarbocyanine dye's behavior.     

Modification of surface properties of a poly(dimethylsiloxane)-based elastomer, RTV11, upon exposure to seawater

Atomic force microscopy (AFM) was combined with surface analytical techniques to investigate the rarely addressed issue of the effect of seawater on the surface properties of a selected fouling-release coating, silicon elastomer RTV11 (trademark of General Electric). The exposure of the RTV11 surface to seawater resulted in a modification of its morphology and mechanical properties, as confirmed by AFM and scanning electron microscopy (SEM). Surface modification was dependent on sample preparation and curing process, namely, curing agent concentration and relative humidity during curing. The RTV11 surface remained largely unaltered for samples cured under 100% relative humidity. SEM and X-ray photoelectron spectroscopy studies confirmed that the modified surface of RTV11 had the same elemental composition as the unexposed surface of the elastomer and showed excess Ca. However, the modified surface deformed plastically under load and was stiffer than the original surface. No major change was found on surfaces exposed to nanopure water during similar times of exposure as in seawater, regardless of curing conditions. The rate of increase in the aggregate formation in seawater can be described by an exponential function, with a decay constant of approximately 4.99 x 10(-)(3) min(-)(1) and a pre-exponential factor of approximately 1.77 x 10(-)(2) microm/min.     

Assembly of multilayer films incorporating a viral protein cage architecture

Protein cage architectures such as viral capsids, heat shock proteins, ferritins, and DNA-binding proteins are nanoscale modular subunits that can be used to expand the structural and functional range of composite materials. Here, layer-by-layer (LbL) assembly was used to incorporate cowpea chlorotic mottle virus (CCMV) into multilayer films. Three types of multilayer films were prepared. In the first type, ionic interactions were employed to assemble CCMV into triple layers. In the second type, complementary biological interactions (streptavidin/biotin) were used for this purpose. In a third variation of LbL assembly, complementary biological interactions were employed to produce nanotextured films that exhibit in-plane order over a micron scale without the need to adsorb onto a prepatterned template.     

Value of high-performance liquid chromatographic analysis of amino acids in the determination of Panax ginseng radix extract effect in cultured neurons

The present research describes a reversed-phase high-performance liquid chromatographic (RP-HPLC) method that allows the determination of several amino acids in primary cultured cortical neurons of rats. The concentration of amino acids was determined by using pre-column derivatization with dansyl chloride and UV-diode array detection. Data show that Panax ginseng radix extract (GS) can modulate amino acid release in neurons. The levels of glutamate (Glu), aspartate (Asp), gamma-aminobutyric acid (GABA) and glycine (Gly) in the GS-treated groups were higher than in the non-treated groups dose-dependentwise. In this case, Glu and GABA were the most released amino acids (74.43% +/- 0.97 and 88.41% +/- 4.12 at ginseng dose 0.01 mg/ml after 1h from treatment, respectively). The values obtained in the determination of the analytical parameters (linearity, precision, limit of detection and accuracy) confirm the quality of the method. The average recoveries for intra and inter-day assay (n = 5) were 101.18 and 102.38 for Asp, 99.35 and 98.44 for Glu, 99.59 and 99.66 for Gly, and 100.06 and 100.37 for GABA. These data proved that the method yields accurate results, with RSD lower than 2.2%. The precision of the method was estimated on the basis of RSD of six injections at two different concentrations of amino acids. This technique is useful in studying the GS-mediated modulation of the dynamic equilibrium of amino acids and neurotransmission in neurons.     

Modeling of high-pressure vapor–liquid equilibrium in ionic liquids + gas systems using the PRSV equation of state

Ionic liquids are environmentally friendly solvents composed of large organic cations and relatively small inorganic anions, whose melting point is below T = 373.15 K. This is an arbitrary limit defined in order to organize the dramatically increasing number of possible applications in chemical processes. These compounds are regarded as potentially environmentally benign solvents due to their almost negligible vapor pressure, which essentially eliminates emission to the atmosphere; besides, they present a wide range of liquid existence. Ionic liquids are applicable in separation processes, such as recovery of valuable products and remotion of polluting agents in effluents 1, 2, 3 and 4 and are a new and exciting class of compounds that have the potential to overcome many of the problems associated with current CO₂-capture techniques. In this work, high-pressure vapor–liquid equilibrium (VLE) of 17 binary mixtures ionic liquid + gas has been modeled with the Peng–Robinson/Stryjek–Vera (PRSV) 5 and 6 equation of state (EoS) applying the Wong–Sandler (WS) [7] mixing rules, including the van Laar (VL) model for the excess Gibbs free energy [8] for the gamma–phi approach and the one-fluid van der Waals (VDW) mixing rules for the phi–phi approach. Critical properties and acentric factor of ionic liquids [pmim][Tf₂N] and [hmmim][Tf₂N] were determined using the extended group contribution method by Lydersen–Joback–Reid [9], while, for the other ionic liquids, these properties are available in the literature 10 and 11. Experimental data were obtained from literature 12, 13, 14, 15, 16, 17 and 18 and the adjustable parameters were fitted by minimizing the errors between predicted and experimental bubble pressure. van Laar and binary interaction parameters were regarded as temperature-dependent. The results, in terms of main deviations between experimental and calculated pressures for the 17 binary systems, are reasonably satisfactory (3.62% and 2.59% for the gamma–phi and phi–phi approaches, respectively).     

INTERMEDIATES IN THE ROOM TEMPERATURE FLASH PHOTOLYSIS OF ADENINE AND SOME OF ITS DERIVATIVES

The transient absorption spectra of aqueous solutions of adenine, 2′-deoxyadenosine, 2′-deoxyadenosine-5′-phosphate and 2′-deoxyadenylyl-(3′-5′)-2′-deoxyadenosine have been determinated at different pH values using conventional flash photolysis. Reactives intermediates produced in the flash photolysis of these adenine derivatives present similar absorption regions: two higher intensity bands in the UV and 560–720 nm wavelength region and a third weaker band at 420–560 nm. On the basis of the effects produced by triplet quenchers and/or electron scavengers the bands have been assigned to hydrated electrons, radical cations, radical anions and/or neutral radicals resulting from neutralization reactions of the charged radicals. The results indicate that the bases photoionize via a triplet state under these conditions.     

Formamidopyrimidines as major products in the low- and high-intensity UV irradiation of guanine derivatives

Two major UV-induced transformation products of guanosine (Guo) in oxygen-free aqueous solution were isolated and characterized using reverse-phase HPLC-ESI-MS and UV absorption spectrophotometric techniques. These products were identified as two different sugar isomers of 2,6-diamino-4-hydroxy-5-formamidopyrimidine ribonucleosides, FapyGuo. A formation quantum yield of the order of 10(-3) for these products was obtained at a 75 microM concentration of Guo, while an increase in the ground state concentration of Guo from 10(-5) to 10(-4) M decreased their formation yield by a factor of ten. The formation of FapydGuo was also observed in the 254 nm photolysis of 2'-deoxyguanosine. In addition, the formation FapyGua was identified in the UV photolysis of all the guanine derivatives investigated. A formation quantum yield of the order of 10(-4) was obtained for the latter product, except in the photolysis of Gua in which a higher formation yield (10(-3)) was determined. These results suggest that hydration of the radical cation of guanine, followed by opening of the imidazole ring to form Fapy products, is one of the main low-intensity UV radiation-induced photo-transformation pathway of the guanine derivatives in oxygen-free aqueous solutions. Furthermore, the formation of the Fapy products and base release occurs through a similar photo-transformation pathways using a high-intensity UV radiation source.