S. A. Tomás

Kinetic study of δ-Ala induced porphyrins in mice using photoacoustic and fluorescence spectroscopies

The production of delta-aminolevulinic acid (ALA)-induced porphyrins in mice skin and blood was studied by photoacoustic and fluorescence spectroscopies. Mice were intraperitoneally administered with 30 mg/kg of ALA. The abdominal skin was subsequently excised at specific times within an 8-h interval and its absorption spectrum obtained by photoacoustics. The highest porphyrins concentration in skin, determined from the optical absorption of the Soret band at 410 nm, was found to occur nearly 2 h after ALA administration, but a first peak was also observed at approximately 15 min. Our hypothesis that the first peak represents the porphyrins content in blood vessels within the skin, whereas the second peak corresponds to porphyrins production in skin tissue, was confirmed by analysing the evolution of protoporphyrin IX content in plasma extracted intracardiacally. By finally applying phase resolved photoacoustic spectroscopy, we were able to evaluate the mean depth at which porphyrins are generated.

Determination of aminolevulinic-acid-induced protoporphyrin IX in mice skin

The kinetics of Protoporphyrin IX (PpIX) production in mice skin was studied by photoacoustic spectroscopy. PpIX was induced in mice by intraperitoneal administration of δ-aminolevulinic acid (δ-ALA) in doses of 10, 20, and 30 mg/kg. Mice were sacrificed at specific times within an 8 h interval following δ-ALA administration, and their abdominal skin was excised for the optical measurements. The PpIX content was determined from the photoacoustic amplitude at 410 nm, where PpIX presents its Soret band. For each dose, maximum PpIX was observed at two points. The first maximum occurred at around 15–45 min, depending on the ALA dose, and the second one took place approximately 2 h after δ-ALA administration. These peaks are associated with PpIX production in blood vessels and tissue, respectively. Fluorescence measurements of the PpIX content in plasma extracted intracardiacally confirmed the previous statement. Finally, phase resolved photoacoustic spectroscopy was applied to evaluate the mean depth at which PpIX is generated within the mice skin. This evaluation confirms that the ALA-induced porphyrins in skin are rather produced in the epidermis than in the dermis.

Atmospheric pollution profiles in Mexico City in two different seasons

A CO2-laser-based photoacoustic spectrometer was used to determine the temporal concentration profile of atmospheric ethene in Mexico City. Ethene measurements were conducted at the facilities of our institute, which is located in the north of the city and next to an avenue with heavy traffic density. Ambient air from outside our laboratory was continuously pumped into the spectrometer. This campaign was performed for 24 h a day, from November 24–30, 2001. The maximum ethene levels ranged between 26 and 81 ppbV. As expected, the lowest concentrations were monitored on weekends. These data were analyzed in combination with ozone and nitrogen oxides profiles, which were permanently monitored by an air-pollution-monitoring government network. Information on the seasonal variability of ethene was obtained by comparing the results of this campaign with data obtained in the winter of 2001. In general, the ethene concentration in November was about 30% higher than in February. On weekdays, the mean dose of human...

Photothermal configuration applied to the study of water vapor permeability in biodegradable films under several water activities

A photothermal configuration was used to determine the water vapor permeability of biodegradable films (nixtamalized corn pericarps). The films were obtained from corn grains boiled in an alkaline solution containing water and Ca(OH)2. Samples were exposed to saturated salt solutions with relative humidity in the range 7%–97%. The water vapor diffusion coefficient was determined as a function of relative humidity. The obtained coefficients agreed with data available in the literature. It was also found that the photoacoustic amplitude shows a linear dependence on the water activity, in agreement with our theoretical model.

Photoinduced charge transfer in molecular materials studied by optical absorption using photoacoustic spectroscopy

Photoacoustic spectra of molecular materials based on the assembling of the [Fe(CN)6] molecular block were recorded and evaluated. Those compositions where the valence of the involved metals allows a charge transfer (an inner photoinduced redox reaction) through the CN ligand shown an intense photoacoustic signal around 600 nm; when this transition is unable only the signal corresponding to metal-to-ligand and d-d transitions within the metal were observed. This suggests that this technique provides a fast and reliable method to explore the existence of tunable photoinduced charge transfer in molecular materials.

CO2 laser photoacoustic spectroscopy applied to environmental analysis in the metropolitan area of Mexico city

Abstract Measurements of atmospheric ethene were performed in the Metropolitan Area of Mexico City by means of a 12C16O2 laser‐based photoacoustic spectrometer. Two types of experimental campaigns were conducted. In the first type, performed in November 1999 and March 2000, air samples were simultaneously collected in canisters during the morning (06:00 to 09:00 h) in Xalostoc (industrial site), La Merced (commercial site), and Pedregal (residential site). The highest ethene levels were usually detected in Xalostoc, followed by those in La Merced and Pedregal. In the second type of campaign, carried out in March 2002, real‐time ethene measurements were performed at the facilities of our institute (CINVESTAV) by continuously drawing ambient air to the photoacoustic spectrometer. Typically, the ethene concentration exhibited two broad bands daily, reaching up to 104 ppbV at around 07:10 h. Ethene levels were also studied as a function of nitrogen oxide data obtained from a government network for atmospheric monitoring, and a linear correlation between ethene and NOx concentrations was found. Finally, the ethene levels in Mexico City were compared with those measured in other cities worldwide.

Ricinus communis-based biopolymer and epidermal growth factor regulations on bone defect repair: A rat tibia model

We report the effect of the addition of an epidermal growth factor to a Ricinus communis-based biopolymer in the healing of a rat tibia model. Bone repair and osteointegration after a period of three weeks were evaluated employing photoacoustic spectroscopy and x-ray diffraction. A parallel study was performed at 1, 2, 3, 4, 5, 6, 7, and 8 weeks with energy dispersive x-ray spectroscopy. We conclude that the use of an epidermal growth factor (group EGF) in vivo accelerates the process of bony repair in comparison with other groups, and that the employment of the Ricinus communis-based biopolymer as a bone substitute decreases bone production.