Javier Lara-Romero

Malfunctioning of the Iron-Sulfur Cluster Assembly Machinery in Saccharomyces cerevisiae Produces Oxidative Stress via an Iron-Dependent Mechanism, Causing Dysfunction in Respiratory Complexes

Biogenesis and recycling of iron–sulfur (Fe–S) clusters play important roles in the iron homeostasis mechanisms involved in mitochondrial function. In Saccharomyces cerevisiae, the Fe–S clusters are assembled into apoproteins by the iron–sulfur cluster machinery (ISC). The aim of the present study was to determine the effects of ISC gene deletion and consequent iron release under oxidative stress conditions on mitochondrial functionality in S. cerevisiae. Reactive oxygen species (ROS) generation, caused by H2O2, menadione, or ethanol, was associated with a loss of iron homeostasis and exacerbated by ISC system dysfunction. ISC mutants showed increased free Fe2+ content, exacerbated by ROS-inducers, causing an increase in ROS, which was decreased by the addition of an iron chelator. Our study suggests that the increment in free Fe2+ associated with ROS generation may have originated from mitochondria, probably Fe–S cluster proteins, under both normal and oxidative stress conditions, suggesting that Fe–S cluster anabolism is affected. Raman spectroscopy analysis and immunoblotting indicated that in mitochondria from SSQ1 and ISA1 mutants, the content of [Fe–S] centers was decreased, as was formation of Rieske protein-dependent supercomplex III2IV2, but this was not observed in the iron-deficient ATX1 and MRS4 mutants. In addition, the activity of complexes II and IV from the electron transport chain (ETC) was impaired or totally abolished in SSQ1 and ISA1 mutants. These results confirm that the ISC system plays important roles in iron homeostasis, ROS stress, and in assembly of supercomplexes III2IV2 and III2IV1, thus affecting the functionality of the respiratory chain.

Temperature optimisation of CNT synthesis by spray pyrolysis of alpha-pinene as the carbon source

Multi-wall carbon nanotubes (MWCNTs) were prepared by spray-pyrolysis of a botanical hydrocarbon, alpha-pinene and ferrocene as the catalyst at 700–1000°C. The MWCNTs were analysed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction. The microscopy studies show the formation of carbon nanotubes with diameters between 20 and 30 nm and length greater than 100 µm. Raman spectroscopy revealed that the alpha-pinene-grown carbon nanotubes were graphitised showing both the D and G bands at 1330 and 1590 cm−1, respectively, and that the corresponding intensity band ratio (I D/I G) varied with respect to temperature formation.

Temperature Effect on the Synthesis of Multi-Walled Carbon Nanotubes by Spray Pyrolysis of Botanical Carbon Feedstocks: Turpentine, α-pinene and β-pinene

The chemistry of the different components of turpentine and the effect of temperature on the synthesis of multi-walled carbon nanotubes (MWCNTs) by spray pyrolysis using ferrocene as catalyst in a temperature range of 700–1000°C at 100°C intervals was investigated. Turpentine with high α-pinene concentration (83.4%) and low β-pinene concentration (8.22%), as well as pure α-pinene and β-pinene, were used as carbon sources. The MWCNTs were analyzed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction and thermogravimetrical analysis. When using turpentine, the optimum temperature to produce high yields of crystalline MWCNTs was 800°C. A comparative analysis between pure α- and β-pinene reveals that α-pinene produces more crystalline MWCNTs than β-pinene at 800°C, indicating that α-pinene is the active component in turpentine for the production of crystalline MWCNTs.

Friction and Wear Performance of Tetraalkylammonium Thiomolybdates in Aqueous Solutions

Aqueous solutions of three tetraalkylammonium thiomolybdates (R 4 N) 2 MoS 4 (R = methyl, propyl, or hydrogen) were prepared and their tribological performance was tested using a pin-on-disc tribometer on a steel-aluminum contact. Tests were performed at the same conditions of load, entrainment speed, sliding distance, temperature, and concentration of the solution in order to compare the activity (lubrication effect) of the thiomolybdates. Although there is a friction reduction for the three salts compared to pure water, a significant difference in the friction coefficient is observed, depending on the alkyl group. SEM/EDAX and Raman analysis of the wear tracks reveal the formation of a solid film rich in molybdenum and sulfur, which indicates the in situ formation of a MoS 2 film.

A Mathematical Programming Approach for the Optimal Synthesis of Nanofibers through an Electrospinning Process

This paper presents a general mathematical programming formulation to determine the optimal operating conditions to synthesize nanofibers through an electrospinning process at minimum cost. Several relationships based on experimental data for different polymers to determine the nanofiber diameter and costs are proposed. Also, a general optimization approach is proposed to trade off the relationships between cost and nanofiber diameter. A case study including the specific relationships for three polymers and five operating conditions is presented. The proposed approach is general, and it can be applied to different cases.

In‐Situ Deposition of Nickel Nanoparticles on Carbon Nanotubes by Spray Pyrolysis

Nickel nanoparticles have been deposited on carbon nanotubes by spray pyrolysis of toluene as carbon source and nickelocene as catalyst at different temperatures. The optimum temperature to produce well‐grown Ni/carbon nanotubes was found to be 850°C. The carbon nanotubes were characterized by SEM, TEM, XRD, Raman spectroscopy and TGA‐DTA. The microscopy studies show that the produced carbon nanotubes have disorder morphologies with diameters between 60 and 100 nm and lengths of a few hundred microns. Ni particles of 40 nm are well dispersed along the carbon nanotubes. XRD patterns show the crystalline planes corresponding to graphite and metallic Ni. The TGA‐DTA results indicate a Ni loading of 20wt%. Raman spectroscopy reveals that the grown carbon nanotubes are graphitized, showing both the D and G bands at 1330 cm−1 and 1590 cm−1, respectively. The corresponding intensity ratio of these bands (ID/IG) varies with respect to synthesis temperature and catalyst concentration.

Tribology of Aqueous Thiomolybdate and Thiotungstate Additives in Low-Pressure Contacts

The wear reducing properties of aqueous solutions of ammonium thiomolybdate and ammonium thiotungstate were evaluated using a frontal cylinder-on-cylinder test tribometer on an AISI 304 steel–steel contact. The antiwear characteristics of the lubricating solutions of thiomolybdate and thiotungstate were evaluated at 24.5, 30, and 40 N keeping fixed the entrainment speed, sliding distance, temperature, and additive concentration. Although there was a reduction in wear for the two salts compared to fluid reference, it is worth mentioning that the thiotungstate additive was slightly more effective under tested lubricating contact conditions than thiomolybdate additive. Energy-dispersive X-ray spectroscopy (EDS) analysis of a wear track lubricated with thiomolybdate showed Mo and S elements and for the track lubricated with thiotungstate W and S were detected. Raman spectra of the wear track showed peaks at 373, 404 and 208, 253, 280, 353 cm−1 corresponding to 2H-MoS2 and FeS, respectively. Ammonium thiomolybdate releases sulfur atoms that also react with the freshly exposed surface, forming FeS, which takes part in reducing wear.

Improved hydrothermal synthesis of MoS2 sheathed carbon nanotubes

MoS2 sheathed carbon nanotubes have been successfully synthesized using a hydrothermal route under controlled conditions. The resultant material was studied by XRD, EDS, HRTEM, and Raman spectroscopy. Advantages of the preparation presented here compared to other methods are: a) lower reaction temperature, b) high yield of sheathed nanotubes including ends and full body, c) simple process with non-toxic materials, and d) no damage inflicted to nanotubes.

Synthesis of iron sulfide films through solid–gas reaction of iron with diethyl disulfide

Iron sulfide films were synthesized by the solid–gas reaction of diethyl disulfide on iron foils in the temperature range of 658–768 K using a microbalance, where the film growth kinetics followed Deal–Grove behavior. Analysis of the films by X-ray photoelectron and Raman spectroscopies as well as X-ray diffraction and scanning electron microscopy analysis revealed the formation of combined FeS/FeS2 (troilite/pyrite) films with a sheet-like morphology at low temperatures and only FeS (troilite) films with granular morphology at higher temperatures. GRAPHICAL ABSTRACT

Tribological Characteristics of Protected Silver Nanoparticles in Oil

In recent years, there has been considerable interest in employing dispersed solid particles in the nanoscale range to enhance the friction and wear characteristics of liquid lubricants. Previous studies have suggested that tiny colloidal particles, under tribochemical conditions, deposit on rubbing surfaces influencing tribological characteristics of the contact. This article presents a study of the tribological behavior of stabilized silver nanoparticles dispersed in n-hexadecane. Friction and wear measurements are combined to investigate the extent to which colloidal solid particles influence a lubricated contact. It is shown that the silver nanoparticles studied contribute to reduce friction and wear only in the thin film regime. Nanoparticles help to reduce friction and wear down to a certain concentration value. Higher concentrations of nanoparticles do not bring any further contribution to reduce friction or wear, suggesting the existence of an optimum concentration of nanoparticles.