Comparative study of oxidative stability of sunflower and cotton biodiesel through P-DSC

Biodiesel can contain unsaturated fatty acids, which are susceptible to oxidation, being able to change into polymerized compounds. Oxidative stability is very important in the quality control of oils and biodiesel. In this study, biodiesel samples were produced through the methyl route, using a homogeneous catalyst. The determination of methyl esters was performed by gas chromatography in order to confirm the conversion of the carboxylic acids present in the raw material for the methyl esters. Also proved the presence of methyl linoleate and methyl oleate to the major constituent of biodiesel. The thermal and oxidative stability of sunflower and cotton oils and their biodiesel, using TG and P-DSC techniques were investigated. The use of P-DSC to measure the oxidative induction time was very important. These measurements were used to evaluate the cotton and sunflower oils, and their respective biodiesel. It was found that the thermal-oxidative stability of vegetable oils and their biodiesel were similar, due to the fact that both presented chemical composition and percentages of fatty acids similar.     

Nature of the binding of a c(2×2)-CO overlayer on Ag(001) and surface mediated intermolecular coupling

We present a first-principles study of the nature of the binding of a c(2×2)-CO overlayer on Ag(001) and of the origin of CO-CO interactions upon adsorption. Electronic structural changes induced by molecular adsorption provide an interpretation for earlier X-ray photoemission valence band spectra of CO/Ag(001). Our results establish that CO chemisorbs on clean Ag(001) and follows the Blyholder model of donation and back-donation between CO and metal orbitals. We analyze the origin of the dispersion of the C-O stretch mode and attest that it is caused by the metal-CO coupling. Specifically, the coupling of CO to Ag, although the weakest of those between it and transition and other noble metals, greatly enhances the intermolecular force constants. We also find that the response of the charge density around CO is much stronger and of longer range when the molecule stretches than when it rigidly vibrates against the surface. This difference explains why the C-O stretch mode disperses while the Ag-CO stretch mode does not.     

Electronic properties of Fibonacci and random Si-Ge chains

In this paper we address a theoretical calculation of the electronic spectra of an Si-Ge atomic chain that is arranged in a Fibonacci quasi-periodic sequence, by using a semi-empirical quantum method based on the Hückel extended model. We apply the Fibonacci substitutional sequences in the atomic building blocks A(Si) and B(Ge) through the inflation rule or a recursion relation. In our ab initio calculations we use only a single point, which is sufficient for considering all the orbitals and charge distribution across the entire system. Although the calculations presented here are more complete than the models adopted in the literature which take into account the electronic interaction only up to the second and third neighbors, an interesting property remains in their electronic spectra: the fractality (which is the main signature of this kind of system). We discuss this fractality of the spectra and we compare them with the random arrangement of the Si-Ge atomic chain, and with previous results based on the tight-binding approximation of the Schr?dinger equation considering up to the nearest neighbor.     

Synthesis of Styrene Monomers Hydroxyl Functionalized

Bifunctional monomers provide the possibility of preparing new polymeric and nano structures such as random or graft copolymers. These materials can potentially be used as surfactants or coupling agents in polymeric blends, especially where each functionality in the monomer has different chemical properties. This article describes the organic synthesis of bifunctional monomers derived from styrene through the Grignard reaction with aldehydes and ketones. The Grignard reagent was synthesized from 4-bromostyrene and magnesium in THF. At the end of the synthesis four different bifunctional monomers were obtained bearing two terminal substituents: a vinyl and a hydroxyl group. These monomers were obtained in high yield and purity. The reactivities of the monomers were probed via the random copolymerization of one of these monomers with styrene and acrylonitrile.     

Modelling spatial and temporal variations in the water quality of an artificial water reservoir in the semiarid midwest of Argentina

Temporal and spatial patterns of water quality of an important artificial water reservoir located in the semiarid Midwest of Argentina were investigated using chemometric techniques. Surface water samples were collected at 38 points of the water reservoir during eleven sampling campaigns between October 1998 and June 2000, covering the warm wet season and the cold dry season, and analyzed for dissolved oxygen (DO), conductivity, pH, ammonium, nitrate, nitrite, total dissolved solids (TDS), alkalinity, hardness, bicarbonate, chloride, sulfate, calcium, magnesium, fluoride, sodium, potassium, iron, aluminum, silica, phosphate, sulfide, arsenic, chromium, lead, cadmium, chemical oxygen demand (COD), biochemical oxygen demand (BOD), viable aerobic bacteria (VAB) and total coliform bacteria (TC). Concentrations of lead, ammonium, nitrite and coliforms were higher than the maximum allowable limits for drinking water in a large proportion of the water samples. To obtain a general representation of the spatial and temporal trends of the water quality parameters at the reservoir, the three-dimensional dataset (sampling sites×parameters×sampling campaigns) has been analyzed by matrix augmentation principal component analysis (MA-PCA) and N-way principal component analysis (N-PCA) using Tucker3 and PARAFAC (Parallel Factor Analysis) models. MA-PCA produced a component accounting for the general behavior of parameters associated with organic pollution. The Tucker3 models were not appropriate for modelling the water quality dataset. The two-factor PARAFAC model provided the best picture to understand the spatial and temporal variation of the water quality parameters of the reservoir. The first PARAFAC factor contains useful information regarding the relation of organic pollution with seasonality, whereas the second factor also encloses information concerning lead pollution. The most polluted areas in the reservoir and the polluting sources were identified by plotting PARAFAC loadings as a function of the UTM (Universal Transverse Mercator) coordinates.     

Experimental Studies on Low-Pressure Plane-Parallel Hollow Cathode Discharges

Hollow cathode discharge (HCD) is widely used in material processing and plasma emission spectroscopy due to several advantages over other plasma sources. Basically, the HCD consists of a cathode with a hollow structure (cavity, hole, or parallel faces) and an anode of arbitrary shape. In this investigation, experimental studies on low-pressure plane-parallel HCD operated at different process conditions are reported. Herein, we investigate the dependence of the discharge current on the product of the gas pressure and inter-cathode distance (pD). In addition, the electron temperature and density were inferred from the current-voltage characteristics of a single cylindrical Langmuir probe positioned between the cathodes, on the discharge axis. The measurements were carried out at different gas pressures, magnetic field intensities, working gases, inter-cathode distances, cathode materials, and discharge voltages. The results showed that, at different gas pressures, the maximum discharge current (I_d,max) is not only a function of the product pD, but also of the pressure itself. Application of a uniform longitudinal magnetic field improved plasma confinement between cathodes, leading to a substantial increase in I_d,max in most of the situations considered in this study. However, for oxygen discharge, a strong discharge current reduction after the application of the magnetic field was observed. In relation to the Langmuir probe studies, it was observed that the uniform longitudinal magnetic field reduced the electron temperature, but this behavior depends strictly on pD. The typical values of electron density and electron temperature in the case of the nitrogen discharge were n_e?=?10¹⁷ m^?3 and T_e?=?2.5 eV, respectively. Finally, our experiments showed that the pD range for hollow cathode effects was between 0.2–5 Pa m.     

The Sonogashira Coupling on Palladium Milling Balls—A new Reaction Pathway in Mechanochemistry

Utilizing direct mechanocatalytical conditions, the Sonogashira coupling was successfully performed on the surface of milling tools by using pure Pd and Pd coated steel balls. The optimization of co-catalyst forming additives led to a protocol, which generates quantitative yields under aerobic conditions for various substrates within as little as 90 minutes. Using state-of-the-art spectroscopic, diffractive, as well as in situ methods lead to the identification of a previously unknown and highly reactive complex of the co-catalyst copper. This new complex differs substantially from the known complexes in liquid phase Sonogashira couplings, proving that reaction pathways in mechanochemistry may differ from those in established synthetic procedures.     

Photocurable Nitric Oxide-Releasing Copolyester for the 3D Printing of Bioresorbable Vascular Stents

The design of bioresorbable vascular stents (BVS) capable of releasing nitric oxide (NO) at the implant site may enable BVS to mimic the antiplatelet, antiproliferative, and pro-endothelial actions of NO, overcoming complications of BVS such as late thrombosis and restenosis. In this study, the fabrication of BVS composed of methacrylated poly(dodecanediol citrate-co-dodecanediol S-nitroso-mercaptosuccinate) (mP(DC-co-DMSNO)), a novel elastomeric, bioabsorbable, and photocurable copolyester, containing covalently bound S-nitrosothiol groups in the carbon backbone of the polymer, is reported. The mP(DC-co-DMSNO) stents are manufactured via photoinduced 3D printing and allow deployment via a self-expansion process from a balloon catheter. After deployment, hydration of the stents triggers the release of NO, which is maintained during the slow hydrolysis of the polymer. Real-time NO release measurements show that by varying the copolyester composition and the strut geometry of the mP(DC-co-DMSNO) stents, it is possible to modulate their NO release rate in the range of 30–52 pmol min⁻¹ cm⁻². Preliminary biological assays in cell culture show that endothelial cells adhere to the surface of the stents and that NO release favors their endothelization. Thus, mP(DC-co-DMSNO) may emerge as a new platform for the fabrication of advanced BVS.