RESUMEN
Yellowing is an undesirable phenomenon that is common in people with white and grey hair. Because white hair has no melanin, the pigment responsible for hair colour, the effects of photodegradation are more visible in this type of hair. The origin of yellowing and its relation to photodegradation processes are not properly established, and many questions remain open in this field. In this work, the photodegradation of grey hair was investigated as a function of the wavelength of incident radiation, and its ultrastructure was determined, always comparing the results obtained for the white and black fibres present in grey hair with the results of white wool. The results presented herein indicate that the photobehaviour of grey hair irradiated with a mercury lamp or with solar radiation is dependent on the wavelength range of the incident radiation and on the initial shade of yellow in the sample. Two types of grey hair were used: (1) blended grey hair (more yellow) and (2) grey hair from a single-donor (less yellow). After exposure to a full-spectrum mercury lamp for 200 h, the blended white hair turned less yellow (the yellow-blue difference, Db(*) becomes negative, Db(*)=-6), whereas the white hair from the single-donor turned slightly yellower (Db(*)=2). In contrast, VIS+IR irradiation resulted in bleaching in both types of hair, whereas a thermal treatment (at 81 °C) caused yellowing of both types of hair, resulting in a Db(*)=3 for blended white hair and Db(*)=9 for single-donor hair. The identity of the yellow chromophores was investigated by UV-Vis spectroscopy. The results obtained with this technique were contradictory, however, and it was not possible to obtain a simple correlation between the sample shade of yellow and the absorption spectra. In addition, the results are discussed in terms of the morphology differences between the pigmented and non-pigmented parts of grey hair, the yellowing and bleaching effects of grey hair, and the occurrence of dark-follow reactions.
Asunto(s)
Colorantes/química , Blanqueadores del Pelo/química , Cabello/efectos de la radiación , Luz , Humanos , Fotólisis , Factores de TiempoRESUMEN
It is known that Brazilian chrysotile is rapidly removed from the lungs, but quantitative studies about the influence of lung surfactants on chrysotile dissolution have not been investigated. In this work, the chemical behavior of chrysotile and its dissolution in the presence of dipalmitoylphosphatidylcholine (DPPC) were investigated in physiological conditions. The dissolution was investigated through quantification of magnesium and silicon released by chrysotile. At 37 degrees C, the magnesium concentration is similar to control (without DPPC), which is about 2.0x10(-4)molL(-1), meaning that the dissolution process is not affected by the presence of this surfactant. The same was observed for silicon. The silicon concentration released by chrysotile is similar in all media tested. It is known that the dissolution mechanisms of brucite and tridymite layers are different. From our results, we propose that under physiological conditions, the mechanism of brucite dissolution is based on its interaction with hydrogen ions and that the mechanism of tridymite dissolution is based on a hydrolysis process.
Asunto(s)
1,2-Dipalmitoilfosfatidilcolina/química , Asbestos Serpentinas/farmacocinética , Surfactantes Pulmonares/metabolismo , Asbestos Serpentinas/química , Magnesio/metabolismo , Silicio/metabolismoRESUMEN
In general, human hair is claimed to turn yellower after sun exposure. This is particularly affirmed for white hair. However, quantitative data relating yellowness to hair type and to the radiation wavelength are missing. This work shows results of the effect of full or UVB-filtered radiation of a mercury vapor or a xenon-arc lamp on the yellowness of virgin white, dark-brown, blond and red hair. All hair types showed a substantial change in yellowness after irradiation, which is dependent on the hair type and radiation wavelength. Surprisingly, white hair turns less yellow after both full and UVB-filtered radiation exposure. This effect is more pronounced when UVB is filtered from the radiation system. The only radiation that shows a photo-yellowing effect on white hair is infrared. As the yellowness of white hair is commonly related to tryptophan degradation, fluorescence experiments with hair solutions were performed to identify the natural degradation of tryptophan which occurs in hair after light irradiation. Pigmented hairs were also studied, as well as hair treated with a bleaching solution. Although we observe a decrease in tryptophan content of hair after lamp radiation, a direct correlation with hair yellowness was not achieved. Results are discussed in terms of hair type, composition and melanin content.
Asunto(s)
Filtración/métodos , Color del Cabello/efectos de la radiación , Cabello/efectos de la radiación , Mercurio , Rayos Ultravioleta , Xenón , Relación Dosis-Respuesta en la Radiación , Cabello/química , Cabello/metabolismo , Color del Cabello/fisiología , Humanos , Melaninas/análisis , Melaninas/química , Melaninas/metabolismo , Pigmentos Biológicos/análisis , Pigmentos Biológicos/metabolismo , Factores de Tiempo , Triptófano/química , Triptófano/metabolismoRESUMEN
This paper reviews the current knowledge about human hair photodamage and the photodegradation mechanisms proposed in the literature. It is shown that there are still a number of questions without answer regarding this issue. For example, a better understanding of the hair structural changes caused by different radiation wavelengths is still lacking. We also find controversies about the effects of sun exposure on different hair types. Explanations to these questions are frequently sustained on the amount and type of melanin of each hair, but factors such as the absence of knowledge of melanin structure and of established methodologies to use in human hair studies make it difficult to reach a general agreement on these issues.
Asunto(s)
Cabello/efectos de la radiación , Rayos Ultravioleta/efectos adversos , Cabello/química , Humanos , Melaninas/química , FotoquímicaRESUMEN
The aim of this work was to investigate the diffusion of Rhodamine B into bleached, photo bleached and abraded hair, treated or not with an emulsion of ceramide using two different techniques: spectrophotometry and fluorescence optical microscopy with image analysis. This comparison, combined with the Einstein-Smoluchowski equation, allowed validating a methodology that uses the apparent diffusion coefficient of a dye as an index for hair damage. Distinct behaviors of the dye were observed in the cuticle and in the cortex. For a bleached hair sample the apparent diffusion coefficient in the cuticle ranges from 8.2 x 10(-11) cm2 s(-1) to 10 x 10(-11)cm2 s(-1), while for the cortex this value drops to 4.0 x 10(-11) cm2 s(-1) to 4.2 x 10(-11) cm2 s(-1). The diffusion is always faster in the cuticle than in the cortex and the apparent diffusion coefficient shows up to a seven-fold decrease when the dye penetrates the cortex. The chemical, photochemical and physical treatments applied to hair significantly change the values of the apparent diffusion coefficients in the cuticle. The data also proved that the penetration of Rhodamine B into hair occurs via an intercellular path.
Asunto(s)
Cabello/metabolismo , Rodaminas/química , Materiales Biocompatibles , Cationes , Ceramidas/química , Difusión , Colorantes Fluorescentes/farmacología , Glicosilación , Cabello/química , Humanos , Procesamiento de Imagen Asistido por Computador , Cinética , Microscopía Fluorescente , Rodaminas/farmacología , Espectrofotometría , Temperatura , Factores de Tiempo , Rayos UltravioletaRESUMEN
The interaction between Saccharomyces cerevisiae and chrysotile fibers was studied by scanning electron microscopy. The yeast cells adhere preferentially to the fibrils. In the extreme case, all the adhered fibrils were broken, resulting in a complete coverage of the surface. The chrysotile covered cells showed less buds, but retained metabolic capacities, and were fully active in fermentation experiments after one year. The interaction degree was depending on contact time and adhesion medium. The longer the contact period, the stronger the interaction between the cells and the fibers. Cells adhered in water show poor entrapment after short contact time, but were highly entrapped after longer periods and did not show any agglomerates. Cells adhered in the presence of nutrients showed a lower entrapment and a higher degree of cellular growth.
RESUMEN
Several strains of Saccharomyces sp. and commercial Baker's yeast were immobilized by adhesion onto chrysotile, a fibrous magnesium silicate (Mg6Si4O10 (OH)8). The activity of the cells is higher when immobilized, mainly for fermentation of 30 to 50% w/v glucose solutions. In the medium containing 30% w/v glucose, the initial fermentation rate increased 1.2-2.5 times. Yields were in the range of 80.4 to 97.3% for the immobilized cells and 72.7 to 84.5% for the free cells. A packed bed reactor for continuous fermentation was set up using one of the tested strains immobilized onto chrysotile. An average productivity of 20 to 25 g.l(-1).h(-1) was obtained in the first 20 d, and an average of 16 g.l(-1).h(-1) was obtained after 50 d of operation.
RESUMEN
The introduction of microporous polypropylene hollow fibers in recent years has brought considerable advances to blood oxygenators. However, lifetime and assembly problems are still unresolved. In this work we tried to rate the oxygen permeation velocity by turning the fibers more hydrophobic through the sorption of a perfluorocarbon. Fomblin HC/25, a perfluoropolyether, is well known for its low surface tension and high affinity for oxygen. Celgard X10, X20, and X30 commercial hollow fibers were tested. The hollow fibers showed high affinity for the perfluoropolyether; swelling was clearly shown. A new system for the measurement of oxygen permeation velocity was developed. The oxygen transport velocity was not significantly changed after sorption. The Celgard microporous hollow fibers impregnated with perfluoropolyether showed no water permeation after 2 months of use, reducing one of the most serious problems in the lifetime of these types of fibers.