UV-vis spectra as an alternative to the Lowry method for quantify hair damage induced by surfactants.

It is well known that long term use of shampoo causes damage to human hair. Although the Lowry method has been widely used to quantify hair damage, it is unsuitable to determine this in the presence of some surfactants and there is no other method proposed in literature. In this work, a different method is used to investigate and compare the hair damage induced by four types of surfactants (including three commercial-grade surfactants) and water. Hair samples were immersed in aqueous solution of surfactants under conditions that resemble a shower (38 °C, constant shaking). These solutions become colored with time of contact with hair and its UV-vis spectra were recorded. For comparison, the amount of extracted proteins from hair by sodium dodecyl sulfate (SDS) and by water were estimated by the Lowry method. Additionally, non-pigmented vs. pigmented hair and also sepia melanin were used to understand the washing solution color and their spectra. The results presented herein show that hair degradation is mostly caused by the extraction of proteins, cuticle fragments and melanin granules from hair fiber. It was found that the intensity of solution color varies with the charge density of the surfactants. Furthermore, the intensity of solution color can be correlated to the amount of proteins quantified by the Lowry method as well as to the degree of hair damage. UV-vis spectrum of hair washing solutions is a simple and straightforward method to quantify and compare hair damages induced by different commercial surfactants.

Entropy and volume change of dissociation in tobacco mosaic virus probed by high pressure.

Virus dissociation and inactivation by high pressure have been extensively studied in recent decades. Pressure-induced dissociation of viral particles involves a reduction in the Gibbs free energy of dissociation and a negative change in volume. In this work, we investigated the combined effect of high pressure and temperature on the dissociation of tobacco mosaic virus (TMV). We assumed the presence of two states of TMV with different tendencies to dissociate. Thus one form presents a low tendency (L) and the other a high tendency (H) to dissociate. Based on the model described here, the L-H transition was favored by an increase in pressure and a decrease in temperature. The volume change of dissociation was pressure- and temperature-dependent, with a highly negative value of -80 mL/mol being recorded at 0 °C and atmospheric pressure. The entropy and enthalpy of dissociation were very temperature- and pressure-dependent, with values of entropy of 450 to -1300 kJ/mol and values of enthalpy of 5.5 × 10(4) to 2.4 × 10(4) kJ/mol. The dissociation of TMV was enthalpy-driven at all temperatures and pressures investigated. Based on these findings, we conclude that the model presented allows accurate predictions of viral dissociation behavior in different experimental conditions.

Different urea stoichiometries between the dissociation and denaturation of tobacco mosaic virus as probed by hydrostatic pressure.

Viruses are very efficient self-assembly structures, but little is understood about the thermodynamics governing their directed assembly. At higher levels of pressure or when pressure is combined with urea, denaturation occurs. For a better understanding of such processes, we investigated the apparent thermodynamic parameters of dissociation and denaturation by assuming a steady-state condition. These processes can be measured considering the decrease of light scattering of a viral solution due to the dissociation process, and the red shift of the fluorescence emission spectra, that occurs with the denaturation process. We determined the apparent urea stoichiometry considering the equilibrium reaction of TMV dissociation and subunit denaturation, which furnished, respectively, 1.53 and 11.1 mol of urea/mol of TMV subunit. The denaturation and dissociation conditions were arrived in a near reversible pathway, allowing the determination of thermodynamic parameters. Gel filtration HPLC, electron microscopy and circular dichroism confirmed the dissociation and denaturation processes. Based on spectroscopic results from earlier papers, the calculation of the apparent urea stoichiometry of dissociation and denaturation of several other viruses resulted in similar values, suggesting a similar virus-urea interaction among these systems.

Hair medulla morphology and mechanical properties.

The morphology of human hair was extensively discussed in the last century, except for hair medulla, mainly because it was believed to have little or no influence on any useful hair property. Early SEM results showed that medulla is formed by unorganized fibrilar material that could be macrofibrils randomly located in the fiber center. The present paper aims to correlate the fibrilar structures with the macrofibrils using transmission electron microscopy (TEM) and to evaluate the influence of medulla on the mechanical properties of hair. TEM micrographs show that the interface between cortex and medulla is surrounded by a CMC layer and that there is less electronically dense material between cortical cells. Cortical cells in medulla give the usual microfibril crystalline arrangement. The cells become scarce and less organized in the center of the medulla, which also shows air filled granules. Average values of the mechanical properties are similar for unmedullated and medullated fibers. However higher dispersion in data for medullated fibers is observed. Unmedulated fibers are more uniform and show smaller diameters. These data indicate that the air cavities in medulla do not interfere with the mechanical properties, but leave hair strength less uniform.

Hair melanin content and photodamage.

The aim of this study was to compare the susceptibility of hair with different melanin content (virgin white, blond and dark-brown) to photodegradation, evaluating changes on hair color and mechanical properties. Light exposure was carried out with a mercury-vapor lamp for up to 1800h. It was observed that color changes are different for each hair type and dependent on the wavelength range. Breaking elongation and breaking strength were affected in all hair types, mainly by UVB radiation. Results show that the melanin type and content of each hair is not the only parameter related to hair damages caused by sun exposure.

Electron microscopic observations of human hair medulla.

In the study of human hair, medulla is the less studied structure because it is believed that it has no influence on the fibre properties. The aim of this paper is to contribute to the better understanding of medulla morphology. Using reproducible methods for hair samples preparations allowed observing the inner fibre by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Three medulla subunits were observed in cryofractured samples. In addition, the application of plasma etching on samples allowed accessing chemical differences between them. Two kinds of medulla were identified using stereomicroscopy: thin and thick medulla. They were morphologically differentiated using TEM. These methods can be used to study systematically the effects of medulla on hair properties and to evaluate the efficiency of cosmetic products.

Yeast cells long-term interaction with asbestos fibers.

Saccharomyces cerevisiae was supported on chrysotile, crocidolite and lixiviated chrysotile. Samples of the supported cells and free cells were observed by confocal laser scanning microscopy. After 30 days, the free cells showed no viability when stored at 30 degrees C, and a viability of 40% when stored at 4 degrees C. Supported cells stored at 30 degrees C were more viable than the free cells at early times, but showed no viability after 30 days. Samples stored at 4 degrees C showed that the adhered cells are more viable than the free cells, up to 30 days. Cells supported on chrysotile and lixiviated chrysotile had 80% viability, and on crocidolite 70% viability. Scanning electron microscopy showed that cells supported on lixiviated chrysotile are fully covered by the support, but crocidolite fibers adhere less, since they are stiffer. Fermentation experiments performed after 3 years storage showed that four from the five lixiviated chrysotile samples and one of the three crocidolite samples were active. In all cases, a delay time for the onset of fermentation was observed indicating a state of latency.

Hair protein removal by sodium dodecyl sulfate.

The effect of sodium dodecyl sulfate (SDS) on protein loss was studied. Three kinds of human hair were tested by rubbing or immersion in water or immersion in SDS solution, at 25, 40 and 70 degrees C. Under friction, hair treated with SDS solution loses seven times more protein than in water, while by immersion, protein loss is roughly two times higher in SDS than in water. Protein loss increases at higher temperatures. Estimated activation energy values for protein loss by immersion are 69+/-22 kJ mol(-1) for blended brown hair; 40+/-12 kJ mol(-1) for blond hair (tip-end region) and 61+/-4 kJ mol(-1) for blond hair (root-end region) for samples treated in water, while 53+/-8, 7+/-5 and 32+/-8 kJ mol(-1) were the corresponding activation energy values for samples treated in 5% SDS solution. These values indicate that protein loss is mainly a diffusion-controlled process. The more damaged the hair, the lower the activation energy and the higher the protein loss. From these data, it can be estimated that daily care shampooing at room temperature will cause opacity and combing difficulties in 1 year and split ends after 3 years by removal of all cuticle layers.

Hair color changes caused by dyeing and thermal treatments.

The aim of this study was to show the effect of heat exposure, dyeing, and shampooing on hair color as measured by diffuse reflectance spectrophotometry. Successive dyeing of virgin hair with six permanent commercial formulations showed that color saturation was obtained after the first dyeing cycle. An unexpectedly high difference in hair color saturation, measured as DE* values, was obtained for virgin hair samples that differed only in cleansing history. After six sequential washings of the dyed hair samples, no difference was observed in color durability, indicating that the adhesion strength is similar to long-lasting and tone-up dyeing formulations. Exposure to a hot plate at 172 degrees C showed a significant darkening of the virgin hair samples after 2 min. On the other hand, virgin hair samples exposed to the gentler heat of a hand dryer (approximately 60 degrees C) showed partial disappearance of the hair medulla after 60 min. However, values of total color difference were near the error limit.

Extractable substances from human hair: a discussion about the origin of the holes.

The existence of holes in the endocuticle, in the inter-macrofibrilar matrix and in the cell membrane complex of hair fibers is described. In this paper, we show that these holes are absent in the hair follicle. However, cell remnants found in young hair inside the follicle are located in the same regions and are of the same dimensions as the holes observed in mature fibers. Since holes in the endocuticle have been described to appear as a result of daily care actions, it is probable that the development of holes in the inter-macrofibrilar matrix and in the cell membrane complex is related to the removal of extractable substances. We discuss hole formation in terms of the nature of the extractable substances and the presence of cell remnants in the young fibers.

Hair color changes and protein damage caused by ultraviolet radiation.

Ultraviolet and visible radiations are known to damage hair. However, quantitative data relating damage to hair type, proteins and color to the radiation wavelength are missing. We studied the effect of UV plus visible, UVA plus visible, visible mercury-vapor lamp radiation and sunlight on (blended) virgin dark-brown, blond and red hair and (one head) virgin black and curly dark-brown hair. All hair types showed a substantial increase in protein loss in water after lamp and sun irradiation. The damaging effect of UVB was about 2-5 times higher than that of UVA plus visible radiation, depending on the hair type. Significant color changes were also observed in every hair type, after lamp and sun irradiation, being more pronounced for the light colored hairs. The luminosity difference parameter was the major contributor to the hair color changes, but significant changes in the red-green and yellow-blue parameters of every hair were observed. In this case, the damaging effect is ascribable mainly to UVA radiation. No significant changes in the mechanical properties or topography were observed in any case. We discuss these results in terms of hair type and composition and melanin types.