Kinetic study of heavy crude oils by thermal analysis

The present work investigates the thermal behavior and kinetic of four types of petroleum samples: a medium crude oil—P1, one heavy oil—P2, and two extra heavy oils—P3 and P4 by TG, DTG, and DSC methods. Thus, this study may contribute to the characterization of petroleum with different °API values.     

Influence of secondary preparative parameters and aging effects on PLGA particle size distribution: a sedimentation field flow fractionation investigation

Poly(lactic-co-glycolic acid) particles in the 200–400-nm size range were formulated through nanoprecipitation and solvent evaporation methods. Different concentrations of the polymer and stabilizer (Pluronic® F 68) were tested in order to identify the best conditions for making poly(lactic-co-glycolic acid) particles of suitable size, stable in time, and to be used as carriers for brain-targeting drugs. The particles with the best characteristics for delivery system design were those formulated by nanoprecipitation with an organic/water phase ratio of 2:30, a polymer concentration of 25 mg/mL, and a surfactant concentration of 0.83 mg/mL; their surface charge was reasonably negative (approximately -27 mV) and the average size of the almost monodisperse population was roughly 250 nm. Particle characterization was obtained through ζ-potential measurements, scanning electron microscope observations, and particle size distribution determinations; the latter achieved by both photon-correlation spectroscopy and sedimentation field flow fractionation. Sedimentation field flow fractionation, which is considered more reliable than photon-correlation spectroscopy in describing the possible particle size distribution modifications, was used to investigate the effects of 3 months of storage at 4 °C had on the lyophilized particles.

Increased Antioxidant Activity and Changes in Phenolic Profile of Kalanchoe pinnata (Lamarck) Persoon (Crassulaceae) Specimens Grown Under Supplemental Blue Light

Antioxidant compounds protect plants against oxidative stress caused by environmental conditions. Different light qualities, such as UV‐A radiation and blue light, have shown positive effects on the production of phenols in plants. Kalanchoe pinnata (Lamarck) Persoon (Crassulaceae) is used for treating wounds and inflammations. Some of these beneficial effects are attributed to the antioxidant activity of plant components. We investigated the effects of blue light and UV‐A radiation supplementation on the total phenol content, antioxidant activity and chromatographic profile of aqueous extracts from leaves of K. pinnata. Monoclonal plants were grown under white light, white plus blue light and white plus UV‐A radiation. Supplemental blue light improved the antioxidant activity and changed the phenolic profile of the extracts. Analysis by HPLC of supplemental blue‐light plant extracts revealed a higher proportion of the major flavonoid quercetin 3‐O‐α‐l ‐arabinopyranosyl (1→2) α‐l ‐rhamnopyranoside, as well as the presence of a wide variety of other phenolic substances. These findings may explain the higher antioxidant activity observed for this extract. Blue light is proposed as a supplemental light source in the cultivation of K. pinnata, to improve its antioxidant activity.     

Electrochemical Evaluation of Pollutants in the Environment: Interaction Between the Metal Ions Zn(II) and Cu(II) with the Fungicide Thiram in Billings Dam

Pesticides are organic molecules used in the control of various pests in different crops. These molecules show functional groups that can interact with metal ions, forming new species with different properties. These new compounds have been attracting attention because they can become a new environmental problem. In this work the interaction of copper and zinc metal ions with Thiram pesticide was studied using electrochemical techniques. Studies in ultrapure water showed the formation of Zn?Thiram complex with reduction potential at ?1.330 V; Cu?Thiram complex showed a cathodic peak at 0.020 V. Thiram causes a different effect on the two metal ions studied. It was observed that the ligand stabilizes more the Cu(II) than Zn(II). Both systems proved to be quasi‐reversible, controlled by the adsorption of the species on the electrode surface. The formation constants of the complexes were calculated to be 2.1×10⁵ for Zn?Thiram and 1.5×10¹⁹ for Cu?Thiram. In the samples from Billings dam, the Zn‐complex showed reduction potential at ?1.403 V; Cu‐complex exhibited a reduction peak at 0.012 V. Although there are interferers in river waters, the interaction of these metals with the pesticide showed high affinity, being possible to detect them in natural samples. The Cu(II) complex showed to be more stable in natural matrices when compared to the Zn(II) complex. The sensitivity for thiram electroanalytical determination decreases in the presence of Zn(II) and Cu(II).     

Multi-walled carbon nanotubes as the gas chromatographic stationary phase: role of their functionalization in the analysis of aliphatic alcohols and esters

Presented hereafter is the novel application of differently functionalized multi-walled carbon nanotubes (f-MWCNTs) as stationary phases for the GC separation of C(1)-C(5) alcohols and esters. Low-cost packed columns, easily prepared in laboratory, were used with satisfactory results. Depending on the functional groups introduced on the pristine MWCNTs, remarkably different behaviours have been observed, thus indicating that derivatization is a key factor to achieve optimal resolution. The best performance was shown by the 2,2'-(ethylenedioxy)diethylamine derivatized MWCNTs, allowing the separation of alcohol isomers, for this reason chosen for the investigation of fermentation by-products in distilled spirits. The degree of derivatization has been assessed for each packing material by thermogravimetric analysis (TGA). A computational study has been performed to correlate the physico-chemical properties of alcohol probes with the retention behaviour.     

New basic catalysts obtained from layered double hydroxides nanocomposites

A new route for the preparation of basic mixed oxides using nanocomposite precursors obtained from layered double hydroxides (LDH) was investigated. These nanocomposites have been prepared by intercalation of negatively charged guest entities containing Ca²⁺, Sr²⁺, Ba²⁺ or La³⁺ cations in the interlayer space of host Mg/Al LDH by anionic exchange. The guest entities have been previously prepared by complexation of the required cations in the presence of edta or citrate chelating anions. Intercalation of [Mⁿ⁺(edta)]^(4?n)? or [La(cit)OH]^? complexes is proved by elemental analysis, XRD analysis and FT-IR spectroscopy. However, in order to satisfy the charge equilibrium in the materials, (edta)^4? and (citrate)^3? species are also co-intercalated in the nanocomposites. The basic properties of the mixed oxides obtained after thermal decomposition of the nanocomposites precursors were evaluated in the disproportionation of 2-methyl-3-butyn-2-ol (MBOH) and the transesterification of 1-phenylethanol with diethylcarbonate (DEC). The Sr- and Ba-containing mixed oxides exhibit basicity close to the one of MgO and Mg(La)O mixed oxides. A comparative study of the reactivity of La-containing mixed oxides obtained following different preparation routes, i.e. coprecipitation or anionic exchange, allows to conclude that the nanocomposite route led to the most active samples.     

Chalcones in bioactive Argentine propolis collected in arid environments

The aim of this study was to assess the chemical and biological profile of propolis samples collected in arid environments of north-western Argentina. The samples were from two phytogeographical regions (Prepuna and Monte de Catamarca Province). Propolis ethanolic extracts (PEE) and chloroform (CHL), hexane (HEX) and aqueous (AQ) sub-extracts of samples from three regions (CAT-I; CAT-II and CAT-III) were obtained. All PEE exhibited antioxidant activity in the DPPH radical scavenging assay (SC50 values between 28 and 43 microg DW/mL). The CHL extract was the most active (SC50 values between 10 and 37 microg DW/mL). The antioxidant activity in the beta-carotene bleaching assays was more effective for PEE and CHL (IC50 values between 2 and 9 microg DW/mL, respectively). A similar pattern was observed for antibacterial activity. The highest inhibitory effect on the growth of human Gram-positive bacteria was observed for CHL-III and CHL-I (Monte region) with minimal inhibitory concentration values (MIC100) of 50 to 100 microg DW/mL. Nine compounds were identified by HPLC-PAD. Two of them (2', 4'- dihydroxychalcone and 2',4'- dihydroxy 3'-methoxychalcone) were found only in propolis samples from the Monte phytogeographical region. We consider that the Argentine arid region is appropriate to place hives in order to obtain propolis of excellent quality because the dominant life forms in that environment are shrubby species that produce resinous exudates with a high content of chalcones, flavones and flavonols.     

Rheological Analysis of Biopolymer Produced by Aureobasidium Pullulans in Different Sources of Nitrogen

Summary: In this study, the rheological behaviors of media fermented by two Aureobasidium pullulans strains (IOC 3467 and IOC 3011) were evaluated in different nutritional conditions. The media consisted of crystal sugar (sucrose), as the main carbon source, and different nitrogen sources (ammonium sulfate, sodium nitrate, ammonium nitrate, urea or residual brewery yeast - RBY). Viscosity measurements were performed on cell-free supernatants, from 48-hour fermentation assays, at 25 ^°C. Shear rates ranged between 0.1000 and 500 s⁻¹. All samples showed pseudoplastic behavior. Nevertheless, the viscosimetric profile of each one varied according to the nitrogen source, its concentration and the strain used. The maximum viscosity of 0.06 Pa.s. was achieved at 15.6 s⁻¹ for IOC 3011 strain grown on RBY as nitrogen source.     

Designing Novel Contrast Agents for Magnetic Resonance Imaging. Synthesis and Relaxometric Characterization of three Gadolinium(III) Complexes Based on Functionalized Pyridine‐Containing Macrocyclic Ligands

The three novel pyridine‐containing 12‐membered macrocyclic ligands 1 – 3 were synthesized. The coordinating arms are represented by three acetate moieties in 1 and 3 and by one acetate and two phosphonate moieties in 2 . In all three ligands, the acetate arm in the distal position is substituted, with a benzyl group in 1 and 2 and with an arylmethyl moiety in 3 . The relaxivities r_1p (20 MHz, 25°) of Gd^III complexes are: GD?1 , r_1p=8.3 mM ^?1 s^?1; GD?2 , r_1p8.1 mM ^?1 s^?1; Gd?3 , r_1p10.5 mM ^?1 s^?1. ¹H‐NMRD and ¹⁷O‐NMR T₂ data show that Gd?1 and Gd?3 contain two H₂O molecules in the inner sphere, whereas the presence of two phosphonate arms allows the coordination of only one H₂O molecule in Gd?2 . Interestingly, the exchange lifetime of coordinated H₂O in the three complexes is similar in spite of the difference in the coordination number of the Gd^III ion (i.e., 9 in Gd?1 and Gd?3 , and 8 in Gd?2 ). ¹H‐Relaxometric measurements at different pH and in the presence of lactate and oxalate were carried out to get some insight into the formation of ternary complexes from Gd?1 and Gd?3 . Finally, it was found that binding to human‐serum albumin (HSA) of Gd?1 and Gd?2 , though weak, yields limited relaxivity enhancements, likely as a consequence of effects on the hydration sphere caused by donor atoms on the surface of the protein.     

Loading of praziquantel in the crystal lattice of solid lipid nanoparticles

Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans. Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this article, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential (ZP) were 500 nm and −34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography, were 99.06 ± 0.3 and 17.48 ± 0.05, respectively. Effective incorporation of PZQ into the particles was confirmed by small angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room temperature (25 °C) and at 4 °C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days. Results showed a relatively long-term physical stability after storage at 4 °C, without drug expulsion.