Chemistry

Nanoparticles with optical and magnetic responses are of great applicability in different fields. In this work, zero valent iron nanoparticles were prepared by laser ablation and stabilized in a surfactant solution to keep particles dispersed and protected in the solution. Optical and magnetic properties of nanoparticles were measured, by UV and Mössbauer spectroscopy. The results show the formation of nanoparticles of a-Fe (ferromagnetic). Our method of preparation, which uses a high H + concentration in the medium, diminishes the zero valent iron oxidation, producing iron nanoparticle with a core of a-Fe and a small shell probably composed of iron oxides.

Nanoparticles with optical and magnetic responses are of great applicability in different fields. In this work, zero valent iron nanoparticles were prepared by laser ablation and stabilized in a surfactant solution to keep particles dispersed and protected in the solution. Optical and magnetic properties of nanoparticles were measured, by UV and Mössbauer spectroscopy. The results show the formation of nanoparticles of α-Fe (ferromagnetic). Our method of preparation, which uses a high H + concentration in the medium, diminishes the zero valent iron oxidation, producing iron nanoparticle with a core of α-Fe and a small shell probably composed of iron oxides.

We compare thermal lensing and absorbance spectra of a fluorescent dye solution. When the dye solution shows a strong fluorescence, the thermal lensing spectrum is blue-shifted and broadened when comparing to the absorbance spectrum. No such differences between both types of spectra are reported when the fluorescence is quenched.

Resonant molecular optical second harmonic generation (SHG) was obtained from(2, 3, 7, 8, 12, 13, 17, 18-Octaethyl- porphinato)M, with M equals none, vanadyl and Ni(II), adsorbed onto fused silica substrates. The polarization dependence of the SHG signals at 1064 nm allowed the determination of average molecular orientations. For the vanadium porphyrin the average angle between the long axis molecules and the surface normal was 38 degrees, while, for the Nickel porphyrin, and the non-metal porphyrin the angle was close to 0 degrees. These results can be understood in terms of the different symmetries of the molecules.

Ultraviolet pulses (266 nm) delivered by a quadrupled Nd:YAG laser were used to analyze organic samples with laser-induced breakdown spectroscopy (LIBS). We present characteristics of the spectra obtained from organic samples with special attentions on the emissions of organic elements, O and N, and molecular bonds CN. The choice of these atomic or molecular species is justified on one hand, by the importance of these species to specify organic or biological materials; and on the other hand by the possible interferences with ambient air when laser ablation takes place in the atmosphere. Time-resolved LIBS was used to determine the time-evolution of line intensity emitted from these species. We demonstrate different kinetic behaviors corresponding to different origins of emitters: native atomic or molecular species directly vaporized from the sample or those generated through dissociation or recombination due to interaction between laser-induced plasma and air molecules. Our results show the ability of time-resolved UV-LIBS for detection and identification of native atomic or molecular species from an organic sample.

The proposition of the hypothesis-relating structure with properties of asphaltenes is a very important endeavor. In view of their complexity, being an intricate mixture of high-molecular-mass compounds, experimental and theoretical procedures must be designed to check whether the structures proposed are consistent with expected and found behavior. During recent years, a structural characteristic of asphaltene, whereby the several polycyclic systems present in them are joined by flexible aliphatic chains, has been proposed by several authors. For simplicity, we will refer to this as the rosary-type structure. In this paper, using both reported as well as new experimental and theoretical results, an attempt is made to show how asphaltene properties, such as molecularmass distribution, molecular fragmentation, solubility, adsorption, trapping of molecules, solvent swelling, and aging, could be accounted for in terms of the above rosary-type structures.

The coherent Raman emission from primary alcohols [CH3(CH2)nOH, n = 0–10], 2-propyl alcohol and tert-butyl alcohol was studied using a frequency-doubled Nd:YAG pump laser (532 nm). We show that increases in the chain length (CH2 groups) and the number of CH3 groups in the alcohols (CH3 > CH2) enhance the Raman emission efficiency. Theoretical density functional theory (DFT) calculations and frequency scaling allow one to associate the vibrational wavenumbers with the molecular fragment responsible for the vibration. We obtained good agreement between the observed phenomena and the predictions of the theory. Copyright © 2005 John Wiley & Sons, Ltd.

In this work, we report the thermo-optical properties of nanoparticles in colloidal suspensions. Spherical gold nanoparticles obtained by laser ablation in condensed media were characterized using thermal lens spectroscopy pumping at 532 nm with a 10 ns pulse laser-Nd-YAG system. The obtained nanoparticles were stabilized in the time by surfactants (sodium dodecyl sulfate or SDS) in water with different molar concentrations. The morphology and size of the gold nanoparticles were determined by transmission electron microscopy (TEM) and UV-visible techniques. The plasmonic resonance bands in gold nanoparticles are responsible for the light optical absorption, and the positions of the absorption maximum and bandwidth in the UV-visible spectra are given by the morphological characteristics of these systems. The thermo-optical constants such as thermal diffusion, thermal diffusivity, and (dn/dT ) are functions of the nanoparticle sizes and the dielectric function of the media. For these reasons, the thermal lens (TL) signal is also dependent on nanoparticle sizes. An analysis of the TL signal of the nanoparticles reveals the existence of an inverse dependence between the thermo-optical functions and the size. This methodology can be used in order to evaluate these systems and characterize nanoparticles in different media. These results are expected to have an impact in bioimaging, biosensors, and other technological applications such as cooling systems.

Nanoparticles with optical and magnetic responses are of great applicability in different fields. In this work, zero valent iron nanoparticles were prepared by laser ablation and stabilized in a surfactant solution to keep particles dispersed and protected in the solution. Optical and magnetic properties of nanoparticles were measured, by UV and Mössbauer spectroscopy. The results show the formation of nanoparticles of a-Fe (ferromagnetic). Our method of preparation, which uses a high H + concentration in the medium, diminishes the zero valent iron oxidation, producing iron nanoparticle with a core of a-Fe and a small shell probably composed of iron oxides.

The adsorption of asphaltenes and other natural surfactants at the water/toluene interface has been studied here, using both the ring and pendant drop method to measure the interfacial tension (γ). The dependence of γ on the logarithm of the sample concentration (ln C) (represented as the γ(ln C) isotherm) leads to a stepwise isotherm similar to that corresponding to the adsorption of asphaltenes at the toluene/silica interface. As is the case for the toluene/silica interface, the stepwise γ(ln C) isotherm seems to be the result of adsorption at the toluene/water interface of molecules, as well as aggregates formed in solution. Once adsorbed, these aggregates flocculate at the interface, leading to the well-known three-dimensional asphaltene films. In agreement with previous evidence from thermal lens experiments, the onset of asphaltene aggregation was observed near a sample concentration of C ) 60 mg/L. Although the presence of aliphatic (acid fraction soluble in heptane, AFSH) and other types of acidic components in the asphaltene mixture increases the interfacial activity of asphaltenes, the removal of these components does not prevent the adsorption and leads to a film with an interfacial tension of γ ) 26 mJ/m 2 . This shows that such asphaltene films are less hydrophobic than what might be expected. As suggested by the detailed description of the results given in this paper, the asphaltene interfacial film is a mixed film formed by both AFSH and asphaltenes, where the role of AFSH is to reduce the value of γ and the role of asphaltenes is to reduce hydrophobic effects by forming a film that effectively separates oil from water. Figure 2.

RESUMEN La técnica de espectroscopia de plasma inducida por láser, ha demostrado ser una herramienta efectiva para el análisis químico cualitativo y cuantitativo de sólidos. En este trabajo estudiamos la influencia de la longitud de onda del haz incidente sobre la señal de emisión del plasma y sobre el tamaño y volumen del cráter generado en la superficie de la muestra. Para esto cráteres de 7 y 50 m de diámetro fueron generados empleando un microscopio de ablación láser acoplado a un espectrofotómetro provisto de una cámara ICCD, en dos distintas condiciones de energía y para dos distintas longitudes de onda del haz incidente (266 y 1064 nm). Encontrando que existe una mayor eficiencia en la remoción del material cuando se trabaja con longitudes de ondas menores (UV). Por otro lado cuando se trabaja con una longitud de onda mayor en nuestro caso 1064 nm, se encuentra que existe una mayor eficiencia de excitación de las especies en el plasma. También se estudio la influencia del tamaño del cráter sobre la intensidad de emisión del plasma y se relaciono esta con los límites de detección de las especies de interés.

Considerando que dentro del campo de la medicina, los polímeros biodegradables han encontrado una gran aplicación como agentes liberadores de fármacos, particularmente como sistemas de implantes subcutáneos de microcápsulas. En este trabajo se presenta la síntesis de homopolímeros ó copolímeros de glicolida y lactida, que han demostrado ser no tóxicos y biocompatibles y la preparación de microcápsulas conteniendo perclorato de rodamina 640. Se ha realizado el estudio, por microscopia electrónica de barrido, de la morfología y la estructura interna de las microcápsulas, observándose que eran lisas con una estructura interna tipo reservorio. Empleando microscopia c onfocal, fue posible seguir los cambios morfológicos ocurridos en las microcápsulas incubadas en un tampón fosfato de pH 7, y así simular, el comportamiento que tendrían en un medio fisiológico.

h i g h l i g h t s • Asphaltene adsorption measured on the surface using white light interferometry. • Experiments show the aggregate formation in a good solvent a low concentration. • The existence of asphaltene nanoagregates in good solvent is cleaver demonstrated. • The role of A1 and A2 subfractions in the aggregation process is clearly showed.

In this work we present the preparation and functionalization of gold nanoparticles (AuNPs) for the detection of presence of gp63 glycoprotein in the surface of Leishmania genus parasites. AuNPs were prepared by induced laser ablation in a clean and biologically suitable media. The nanoparticles were functionalized with anti-gp63 lgG antibody in order to study the interaction with the glycoprotein component gp63 (63 kDa) present on the membrane surface of Leishmania genus parasites. The functionalized AuNPs showed potential as a spectrometric indicator of the parasite existence, both by the detection of the presence of the gp63 in solution and through the specific interaction with the parasites in vitro. The specificity of the study opens a new line of research on the use of modified nanoparticles in the development of a fast and easy assay for Leishmaniosis diagnostics.

In this work, we present a methodology of production for iron nanoparticles (iron Np) in organic solvents, by laser ablation.Using an inert gas stream the particles are blowing into solvent (LAiGS). The nanoparticles produced by this methodwere compared with nanoparticles produced by direct laser ablation in metal plate immersed in solvent (LAiS). Theablation procedure was performed in 10 minutes steps by triplicate with cooling periods of 5 minutes between ablations.Comparatively particles were obtained under continuous ablation iron plate at different ablation times, 10, 20 and 30 min.The same procedure was utilized in both cases, LAiS and LAiGS. Nps of size ranging between 8 -10 nm were obtainedby both methods. The particles exhibited a Resonance Plasmon Surface (RPS) band between 300 and 380 nm, typical ofFe NP in acid medium. In LAiS, an increment of particle size and in consequence a lower absorbance was observed whenan irradiation wavelength of 532 nm was used. In LAiGS no de...

Thermal lens microscopy is a very sensitive photothermal technique with many applications in environment, organic chemistry, biochemistry and biomedicine. This paper shows the development of a thermal lens microscope for asphaltene analysis. Two coaxial laser beams were pumped through the microscope objective to the sample. The wavelength of the excitation beam was selected to coincide with an absorption band of the analyte, and the wavelength of the probe beam was chosen so that the sample solution has no absorption. When the analyte molecules absorb the excitation beam, they emitted heat increasing the temperature in the confocal region that decreases the refractive index generating a lens-like object. This instrument was used to measure the response of thermal lens in different Venezuelan asphaltene solutions, finding variations in the signal with the concentration of asphaltene and the degree of aggregation or flocculation of the sample in the solvent.

Lead (Pb) emission intensity (atomic line 405.78 nm) dependence on the sample matrix (metal alloy) was studied by means of collinear double pulse (DP)-laser induced breakdown spectroscopy (LIBS). The measurement of the emission intensity produced by three different wavelength combinations (i.e. I:532 nm-II:1064 nm, I:532 nm-II:532 nm, and I:532 nm-II:355 nm) from three series of standard reference materials showed that the lead atomic line 405.78 nm emission intensity was dependent on the sample matrix for all the combination of wavelengths, however reduced dependency was found for the wavelength combination I:532 nm-II:355 nm. Two series of standard reference materials from the National Institute of Standards and Technology (NIST) and one series from the British Chemical Standards (BCS) were used for these experiments. Calibration curves for lead ablated from NIST 626-630 ("Zn 95 Al 4 Cu 1 ") provided higher sensitivity (slope) than those calibration curves produced from NIST 1737-1741 ("Zn 99.5 Al 0.5 ") and with the series BCS 551-556 ("Cu 87 Sn 11 "). Similar trends between lead emission intensity (calibration curve sensitivities) and reported variations in plasma temperatures caused by the differing ionization potentials of the major and minor elements in these samples were established.

RESUMEN La técnica de espectroscopia de plasma inducida por láser, ha demostrado ser una herramienta efectiva para el análisis químico cualitativo y cuantitativo de sólidos. En este trabajo estudiamos la influencia de la longitud de onda del haz incidente sobre la señal de emisión del plasma y sobre el tamaño y volumen del cráter generado en la superficie de la muestra. Para esto cráteres de 7 y 50 m de diámetro fueron generados empleando un microscopio de ablación láser acoplado a un espectrofotómetro provisto de una cámara ICCD, en dos distintas condiciones de energía y para dos distintas longitudes de onda del haz incidente (266 y 1064 nm). Encontrando que existe una mayor eficiencia en la remoción del material cuando se trabaja con longitudes de ondas menores (UV). Por otro lado cuando se trabaja con una longitud de onda mayor en nuestro caso 1064 nm, se encuentra que existe una mayor eficiencia de excitación de las especies en el plasma. También se estudio la influencia del tamaño del cráter sobre la intensidad de emisión del plasma y se relaciono esta con los límites de detección de las especies de interés.

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