Ultraviolet photodegradation of folic acid

The vitamin folate is vital for all living creatures. Scientists have suggested that ultraviolet degradation of folate in vivo played a role in the evolution of mankind. In order to better understand the photodegradation of folate, we have provided a spectroscopic study of the ultraviolet photodegradation of aqueous folic acid under aerobic conditions. We found strong indications that the folic acid molecule is cleaved into p-aminobenzoyl-L-glutamic acid and 6-formyl pterin when exposed to ultraviolet radiation. When the irradiation continues, 6-formyl pterin is degraded to pterin-6-carboxylic acid. The photodegradation of folic acid is divided into three phases. In the first phase, the formation of photoproducts follows a zero order rate law. In the second phase the presence of photoproducts sensitizes the degradation of folic acid and the degradation process is accelerated. In the third phase the degradation of 6-formyl pterin to pterin-6-carboxylic acid is the dominating process. This reaction follows a first order rate law. We show that both 6-formyl pterin and pterin-6-carboxylic acid sensitize the photodegradation of folic acid. However, experiments performed in heavy water indicate that generation of singlet oxygen is probably not the explanation for the photosensitizing of folic acid.     

Recombination luminescence and decay of trapped electrons in UV-irradiated solution of tryptophan in ethylene glycol/water glass

The luminescence resulting from electron-ion recombination in a UV-irradiated rigid solution of tryptophan in ethylene glycol/water has been investigated as well as the decay of trapped electrons (e^-_t) in the same matrix. The activation energy associated with the thermoluminescence in the temperature region 77°K is about 0.27 eV while the photodetachment threshold of e^-_t in the matrix is about 2.2 eV. Hence a recombination model is proposed which considers e^-_t moving as an entity through the viscous medium in the field of its mother ion without being detrapped. The tunnelling model of recombination is rejected because of the temperature dependence of the afterglow decay rate.On warming, e^-_t mainly disappears by a viscosity dependent reaction with the solvent. However, below 123°K the reaction of e^-_t with the solvent may probably be interpreted in terms of electron tunnelling.     

Photobleaching of hypericin bound to human serum albumin,cultured adenocarcinoma cells and nude mice skin

Hypericin is a promising photosensitizer for photodynamic therapy (PDT) characterized by a high yield of singlet oxygen. Photobleaching of hypericin has been studied by means of absorption and fluorescence spectroscopy in different biological systems: in human serum albumin solution, in cultured human adenocarcinoma WiDr cells and in the skin of nude mice. Prolonged exposure to light (up to 95 min, 100 mW/cm2) of wavelength around 596 nm induced fluence-dependent photobleaching of hypericin in all studied systems. The photobleaching was not oxygen dependent, and singlet oxygen probably played no significant role. Emission bands in the spectral regions 420-560 nm and above 600 nm characterize the photoproducts formed. An emission band at 615-635 nm was observed after irradiation of cells incubated with hypericin or of mouse skin in vivo but not in albumin solution. The excitation spectrum of these products resembled that of hypericin. Hypericin appears to be more photostable than most sensitizers used in PDT, including mTHPC and Photofrin.     

Frequency-domain analysis of non-linear wave effects on offshore platform responses

In this study, the effects of second-order non-linear random waves on the structural response of slender fixed offshore platforms are investigated based on frequency-domain Volterra-series approach and previously proposed correlation function/FFT-based cumulant spectral method. The cumulants of non-Gaussian water particle kinematics are derived and, Morison force is approximated in cubic functional transformations of Gaussian processes. Volterra series is applied to evaluate the power spectra of wave force and induced structural displacement. The more convenient and more efficient power spectral and tri-spectral analyses by cumulant spectral method are presented as well. The thereby estimated variance, skewness and kurtosis excess agree well with time-domain simulation results. It is found that non-linear wave effects result in stronger non-Gaussian behavior of wave force and structural response, especially in seas of finite water depth.     

Sun beds and cod liver oil as vitamin D sources

The objective of this study was to (1) to determine the contribution of moderate sun bed exposure to serum 25(OH)D(3) levels; (2) to estimate the decay time of a high 25(OH)D(3) level obtained by sun bed exposure; and (3) to evaluate if the recommended ingestion of vitamin D is sufficient to maintain the 25(OH)D(3) concentration obtained by sun bed exposure. Ten volunteers (20-35 y.o.), skin type I and II, living in Olso, Norway were whole body exposed twice per week to the radiation of a commercial and approved sun bed (Life Sun S 100 W, Wolff System), starting with 0.5 MED (minimal erythema dose) and escalating to up to 1 MED per exposure for 4 weeks. After that, half of the volunteers were given a daily supplement of 200 IU vitamin D in the form of cod liver oil capsules, while the other half of the persons received no supplements. Erythema did not occur at any time and a slight pigmentation was seen in most of the volunteers after the sun bed exposures. Serum level of 25(OH)D(3) increased by about 40% on the average. The initial serum 25(OH)D(3) level was different among the volunteers (40-100 nmol/L). Within eight weeks after the last exposure the 25(OH)D(3) level decreased to the initial value in all volunteers irrespective of vitamin D supplementation or not.     

Microneedle arrays permit enhanced intradermal delivery of a preformed photosensitizer

Silicon microneedle (MN) arrays were used to puncture excised murine and porcine skin in vitro and transdermal and intradermal delivery of meso-tetra ( N -methyl-4-pyridyl) porphine tetra tosylate (TMP) investigated using topical application of a bioadhesive patch containing 19 mg TMP cm⁻². Animal studies, using nude mice, were then conducted to investigate the in vivo performance of the bioadhesive patch following MN puncture of skin. MN puncture significantly enhanced both intradermal and transdermal delivery of TMP in vitro , though the total amounts of drug delivered (25.22% into porcine skin and 0.07% across murine skin) were still quite small in each case. Notwithstanding this, in vivo experiments showed that MN puncture was capable of permitting a prolonged increase in TMP fluorescence at the site of application. Importantly, fluorescence was negligible at distant sites, meaning systemic delivery of the drug was not sufficient to induce TMP accumulation other than at the application site. In this study we have conclusively demonstrated proof of principle; MN puncture allows true intradermal delivery of a preformed photosensitizer in animal skin models in vitro and in vivo . Importantly, transdermal delivery was much reduced in each case. Increasing MN density would allow increased amounts of photosensitizer to be delivered. However, as MNs create aqueous pores in the stratum corneum, a preformed photosensitizer must possess at least some degree of water solubility in order to permit enhanced intradermal delivery in this way. We believe that use of MN array technology in this way has the potential to significantly improve topical photodynamic therapy of skin tumors.     

Rheological properties and percolation in suspensions of multiwalled carbon nanotubes in polycarbonate

This paper is concerned with several issues related to the rheological behavior of polycarbonate/multiwalled carbon nanotube nanocomposites. The composites were prepared by diluting a masterbatch of 15 wt.% nanotubes using melt-mixing method, and the dispersion was analyzed by SEM, TEM, and AFM techniques. To understand the percolated structure, the nanocomposites were characterized via a set of rheological, electrical, and thermal conductivity measurements. The rheological measurements revealed that the structure and properties were temperature dependent; the percolation threshold was significantly lower at higher temperature suggesting stronger nanotube interactions. The nanotube networks were also sensitive to the steady shear deformation particularly at high temperature. Following preshearing, the elastic modulus decreased markedly suggesting that the nanotubes became more rigid. These results were analyzed using simple models for suspensions of rod-like particles. Finally, the rheological, electrical, and thermal conductivity percolation thresholds were compared. As expected, the rheological threshold was smaller than the thermal and electrical threshold.