Photodegradation of 5-methyltetrahydrofolate: biophysical aspects

5-methyltetrahydrofolate (5MTHF) absorbs UV radiation and has an absorption coefficient of 24250+/-1170 M(-1) cm(-1) at 290 nm. It has a weak fluorescence emission in the wavelength region around 360 nm. Our data demonstrated induction of 5-methyldihydrofolate by exposure to UVB and, after continues irradiation, p-aminobenzoyl-L-glutamic acid was found. The photodegradation of 5MTHF follows a first order kinetic with a degradation rate constant of 9.2 x 10(-3) min(-1) under our conditions (fluence rate of 2.15 mW cm(-2), exposure wavelengths from 280 to 350 nm). Our results indicate that a direct degradation of 5MTHF by UV exposure in humans in vivo is rather unlikely. 5MTHF mainly absorbs, and is degraded by, UVB and UVC, radiation that does not penetrate the earth's atmosphere and the human skin well.     

Thermokinetic study of CODA azoic liquid crystal and thin films deposition by matrix-assisted pulsed laser evaporation

Azoic dyes are compounds of interest from the point of view of their potential applications, such as the use of liquid crystals in optoelectronic and organic electroluminescent devices, or may be employed as template matrices for producing high-aspect ratio inorganic nanomaterials. Herein, 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene azoic dye, known as CODA, is selected as a choice compound among such materials due to its liquid crystalline properties and may be further used as nanostructured material in various applications. Thermokinetic study of CODA azoic dye thermal decomposition in air flow atmosphere was performed by employing thermogravimetric data; the kinetic parameters of the two decomposition steps were obtained under non-isothermal linear regimes, by means of multi-heating rates methods. Differential and integral “model-free” kinetic methods like Friedmann, Kissinger–Akahira–Sunose and Ortega, the invariant kinetic parameters method and the Perez-Maqueda et al. criterion (by Coats–Redfern and differential equations) were used. The kinetic study reveals very different behaviour related to the two decomposition steps of CODA, with complex processes composed of more than one kinetic mechanism for each of those, as indicated also by the Gotor et al. master plot method. Modern devices incorporating such materials tend to use them as thin films due to their specific properties; the CODA thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG laser working at the wavelength of 266 nm. The preservation of the CODA compound after the transfer on the substrates was confirmed by Fourier transform infrared spectroscopy, while the morphology and topography of the deposited materials and of the thin film surfaces were investigated by atomic force microscopy and optical microscopy.     

Azorubine: physical,thermal and bioactive properties of the widely employed food,pharmaceutical and cosmetic red azo dye material

Journal of Thermal Analysis and Calorimetry - Azorubine (E122), an azoic dye with the chemical formula C20H12N2Na2O7S2, has a wide range of applications in the food and cosmetic industries....     

Depth Profile of Protoporphyrin IX Fluorescence in an Amelanotic Mouse Melanoma Model

Protoporphyrin IX (PpIX) fluorescence was measured at different depths in a subcutaneous amelanotic melanoma model (LOX) in mice. PpIX was induced by topical application of 5‐aminolevulinic acid (ALA) and two of its derivatives, the methylester (MAL) and hexylester (HAL) onto the normal skin covering the tumor. The PpIX fluorescence intensity on the surface of the tumors was the highest for HAL, followed by ALA and MAL. Using equimolar concentrations (0.5 mmol g^?1), HAL induced nearly twice as much fluorescence as ALA did. The depth profile of PpIX fluorescence was measured at different layers of the tumor, which was carefully sliced and controlled in situ ex vivo. The PpIX fluorescence was mainly localized within the upper 2 mm of the tissue for ALA and within 1 mm for MAL and HAL. There were no significant differences in the shape of the fluorescence excitation spectra, but the long wavelength excitation peak (633 nm) was so weak that these results are unreliable for depth estimation. When considering the low fluorescence intensity (around 5% of the intensity at the tumor surface), the actual penetration depth of HAL was comparable to that of ALA. The fluorescence after topical application of ALA and HAL was significantly above the background level down to a depth of around 6 mm, and there were traces of PpIX fluorescence even at the tumor base (10 mm). The fluorescence after topical application of MAL was detectable down to 1 mm. In the depth of 2–6 mm, the fluorescence was slightly higher for HAL than for ALA. Using the estimated diffusion coefficients for topically applied ALA (0.16 ± 0.03 mm² h^?1), MAL (0.045 ± 0.005 mm² h^?1) and HAL (0.037 ± 0.003 mm² h^?1), the behavior of the drugs after different application times could be estimated in this tumor model.     

The stability of 5-aminolevulinic acid in solution

5-Aminolevulinic acid (ALA) is being assessed for photodynamic therapy of cancer and other diseases worldwide. However, its stability properties in solution are not well understood yet. The breakdown of ALA in pH-buffered solutions was examined in this work. Solutions of ALA in PBS buffered to physiological pH were found to be unstable, leading to a breakdown product that absorbs photons around 278 nm. The ability of the solution to stimulate porphyrin production in cells is gradually lost upon breakdown, though the kinetics for this are different from those for formation of the UV absorbing product. It is likely, therefore, that several chemical pathways contribute to the breakdown of dissolved ALA at physiological pH. Temperature studies of the formation kinetics of the UV absorbing product also indicate that a complex formation process is involved.     

Linear and non-linear rheological behaviour of cement and silica suspensions. Effect of polymer addition

Oil well cement pastes and model silica suspensions demonstrate similar rheology: in oscillatory shear, beyond a critical stress, a sharp transition is ob- served between gel and liquid behaviour. In creep tests, an apparent yield stress and shear-thinning are followed by the appearance of shear thickening. The minimum viscosity measured in steady shear is close in value to the complex viscosity obtained from oscillatory measurements. The observations can be explained by the formation of liquid trapping aggregates whose compactness may be estimated by fitting the Tsenoglou model, and whose cohesion is reflected in the rigidity of the gel and in the critical strain (or stress) of gel dissolution. Substituting cement or silica particles by polymer redispersible powder causes a decrease of the storage modulus in the gel state and a lower viscosity, while leaving the general features of the flow curve unchanged. Decrease in material rigidity may be due to a weaker inter-particle attraction generated by the polymer presence. The decrease in viscosity is explained by a lessening of water entrapped within the aggregates, which now contain polymer particles which are less hydrophilic than either cement or silica.     

The importance of the depth distribution of melanin in skin for DNA protection and other photobiological processes

Melanin pigments are important regulators for the evolution of essential functions of human skin. The concentration of melanin, as well as its depth distribution, is strongly affected by ultraviolet radiation. In un-tanned skin, melanin pigments are found only in the basal layer of the epidermis, while in tanned skin it is distributed throughout the epidermis. So far, mainly the amount of melanin, and not its distribution, has been considered in view of skin photobiology. With an advanced radiative transfer model we investigate, for the first time, how the depth distribution of melanin influences the amount of ultraviolet radiation that reaches living cells in the epidermis, and thus can damage the DNA in the cells. The simulations are performed for average pigmented skins (type III-IV). A surprisingly large factor, up to 12, is found between the ultraviolet protection of skin with melanin distributed throughout the epidermis, and skin with melanin only in the basal layer of the epidermis. We also show that the synthesis of previtamin D3, in skin, can vary with more than 100% if the depth distribution of melanin is changed, while the degradation of folate in dermal blood is almost un-affected by variations in the melanin depth distribution.     

Colon cancer: prognosis for different latitudes, age groups and seasons in Norway

The survival of colon cancer patients in Norway, as determined three years after diagnosis, is dependent on the season of diagnosis. This has been attributed to seasonal variations of the vitamin D status. Since solar radiation and food are the human sources of vitamin D, we divided Norway in three regions: The southeast region with a high annual dose of ultraviolet (UV) to the population, as evidenced by a high incidence rate of squamous cell carcinoma of the skin (SCC), the midwest region and the north region with low annual UV doses. The latter region is characterized by a high consumption of vitamin D, mainly through fish intake. Vacations to southern latitudes were equally frequent for all the three geographical regions. Two age groups were analyzed separately (< or =65 years and >65 years), since the photosynthesis of vitamin D(3) in skin decreases with age. In all three regions, and in both age groups, the survival was highest for summer and autumn diagnosis. The seasonal effect was slightly, but not significantly, better for the younger than for the older age group. The effect was similar for all three geographical regions, irrespective of SCC incidence.     

Wall effects in the flow of flexible polymer solutions through small pores

Effective viscosities of dilute and semidilute flexible solutions flowing through small cylindrical pores were determined in the Newtonian regime for various pore diameters. The low viscosities relative to the bulk were associated with a depletion phenomenon due to a steric exclusion of macromolecules from the pore wall. Using a two-fluid flow model, the depletion layer thickness was determined and discussed as a function of polymer concentration, ionic strength, and molecular weight. This thickness, which was constant and close to the macromolecule gyration radius in dilute regime, was found to decrease rapidly with polymer concentration in the semidilute regime.