DOSE-RESPONSE OF CHRONIC ULTRAVIOLET EXPOSURE ON EPIDERMAL FORWARD SCATTERING-ABSORPTION IN SK-1 HAIRLESS MOUSE SKIN

This work provides a dose-response model of UV-induced epidermal-stratum corneum thickening induced by irradiation at wavelength lambda. This model assumes that photobiochemical reaction(s) can give rise to hyperplasia in a manner which is predictable from a simple photochemical kinetic scheme. In this work, we derive an equation which predicts an approximately linear relationship between the logarithm of the increase in optical skin thickening measured at 320 nm (delta OD320) and total cumulative dose (DT) seen by the target cells in or near the basal layer. For each excitation wavelength lambda, the slope R(lambda) of the log delta OD320 vs DT plot is proportional to epsilon(lambda) phi rx, where epsilon(lambda) is the extinction coefficient for the target chromophore at excitation wavelength, and phi rx is the quantum yield for the photochemical reaction(s) leading to hyperplasia. Our data previously obtained from irradiation of SK-1 hairless mice with "monochromatic" UV wavebands at 280, 290, 300, 307 and 313 nm (Menter et al., 1988, Photochem. Photobiol. 47, 225-260.) and data from Sterenborg and van der Leun at 254 and 313 nm (1988, Photodermatology 5, 71-82) are in good agreement with this model, except for 254 and 280 nm excitation, which are greatly attenuated by epidermis-stratum corneum. For excitation at the latter wavelengths, "dark" regressive processes successfully compete with the "light" reaction(s) which lead to (pre)cancerous lesion. This difficulty notwithstanding, the "intrinsic" action spectrum for hyperplasia derived from these measurements indicates that the target chromophore preferentially absorbs in the UV-C region.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microemulsion-based synthesis of CeO(2) powders with high surface area and high-temperature stabilities

Pure ceria powders, CeO(2), were synthesized in heptane-microemulsified aqueous solutions of CeCl(3) or Ce(NO(3))(3) stabilized by AOT (sodium bis(2-ethylhexyl) sulfosuccinate), DDAB (di-n-didodecyldimethylammonium bromide), or DDAB + Brij 35 surfactant mixtures. Micellar DTAB (n-dodecyltrimethylammonium bromide) and vesicular DDAB systems were also used as media for generating CeO(2). Characterization of the powders by X-ray powder diffractometry, laser-Raman spectroscopy, and Fourier transform infrared spectroscopy revealed that in the presence of surfactants almost-agglomerate-free nanosized crystallites (6-13 nm) of anionic vacancy-free cubic CeO(2) were produced. In the absence of surfactants 21-nm-sized crystallites were formed, comparing with the 85-nm-sized crystallites when cubic CeO(2) was created via thermal decomposition of cerium oxalate. Surface characterization, by X-ray photoelectron spectroscopy, N(2) sorptiometry, and high-resolution electron microscopy showed AOT- or (DDAB + Brij 35)-stabilized microemulsions to assist in formation of crystallites exposing surfaces of large specific areas (up to ca. 250 m(2)/g) but of low stability to high-temperature calcination (28-13 m(2)/g at 800 degrees C). In contrast, the double-chained DDAB was found to generate cubic CeO(2) crystallites of lower initial surface areas (144 (microemulsion) to 125 (vesicles) m(2)/g)) but of higher thermal stability (55-45 m(2)/g at 800 degrees C). Hence, the latter cerias could be considered as appropriate components for total oxidation (combustion) catalysts.     

Impossibility of a Certain Cyclotomic Equation with Applicationsto Difference Sets

Under certain conditions, we show the nonexistence ofan element in the p-th cyclotomicfield over , that satisfies . As applications, we establish the nonexistence ofsome difference sets and affine difference sets.     

Palladium-catalyzed amination of aryl nonaflates

The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions.     

Hybrid fluorocarbon-hydrocarbon CO2-philic surfactants. 2. formation and properties of water-in-CO2 microemulsions

Hybrid fluorocarbon-hydrocarbon (F-H) sulfate surfactants are shown to be efficient stabilizers in water-in-CO2 (w/c) microemulsions. The chain structure and F-H ratio affect the regions of P-T phase stability and aggregation structure in these w/c phases. High-pressure near-infrared spectroscopy and small-angle neutron scattering measurements of microemulsified water provide evidence for the stabilization of w/c microemulsion droplets. The relative lengths of the two chains were found to influence the favored aggregation structure: for symmetric chain surfactants (F8H8, F7H7) spherical reverse micelles are present, but for asymmetric chain surfactants (F7H4, F8H4) extended cylinder aggregates form. These changes in aggregation are consistent with different surfactant packing parameters owing to the controlled variations in molecular structure. Furthermore, the general order of w/c phase transition pressures (F8H8 < F7H7 and F8H4 < F7H4) is in line with estimations of surfactant fractional free volume, as proposed by Johnston et al. (J. Phys. Chem. B 2004, 108, 1962-1966). Studies of adsorption at the poly(dimethylsiloxane)-water interface are shown to be valuable for assessing the CO2-philicity of new surfactants. All in all, the symmetric F8H8 and F7H7 analogues are seen to be the most efficient compounds from this class for applications in CO2.     

PHOTOCHEMISTRY OF TYPE I ACID-SOLUBLE CALF SKIN COLLAGEN: DEPENDENCE ON EXCITATION WAVELENGTH

Although previous studies have demonstrated that the predominant photochemistry of type I collagen under 254 nm irradiation may be attributed either to direct absorption by tyrosine/phenylalanine or to peptide bonds, direct collagen photochemistry via solar UV wavelengths is much more likely to involve several age- and tissue-related photolabile collagen fluorophores that absorb in the latter region. In this study, we compare and contrast results obtained from irradiation of a commercial preparation of acid-soluble calf skin type I collagen in solution with UVC (primarily 254 nm), UVA (335–400nm) and broad-band solar-simulating radiation (SSR; 290^1–00nm). Excitation spectroscopy and analysis of photochemically induced disappearance of fluorescence (fluorescence fading) indicates that this preparation has at least four photolabile fluorescent chromophores. In addition to tyrosine and L-3,4-dihydroxyphenylalanine, our sample contains two other fluorophores. Chromophore I, with emission maximum at 360 nm, appears to be derived from interacting aromatic moieties in close mutual proximity. Chromophore II, with broad emission at430–435 nm, may be composed of one or more age-related molecules. Collagen fluorescence fading kinetics are sensitive to excitation wavelength and to conformation. Under UVC, chromophore I fluorescence disappears with second-order kinetics, indicating a reaction between two proximal like molecules. Adherence to second-order kinetics is abrogated by prior denaturation of the collagen sample. A new broad, weak fluorescence band at400–420 nm, attributable to dityrosine, forms under UVC, but not under solar radiation. This band is photolabile to UVA and UVB wavelengths. Amino acid analysis indicates significant destruction of aromatic amino acids under UVC, but not under UVA or SSR. When properly understood, collagen fluorescence fading phenomena may act as a sensitive molecular probe of structure, conformation and reactivity.     

Two new terpyridine dimanganese complexes: a manganese(III,III) complex with a single unsupported oxo bridge and a manganese(III,IV) complex with a dioxo bridge. Synthesis, structure, and redox properties

Two new terpyridine dimanganese oxo complexes [Mn(2)(III,IV)(mu-O)(2)(terpy)(2)(CF(3)CO(2))(2)](+) (3) and [Mn(2)(III,III)(mu-O)(terpy)(2)(CF(3)CO(2))(4)] (4) (terpy = 2,2':6,2' '-terpyridine) have been synthesized and their X-ray structures determined. In contrast to the corresponding mixed-valent aqua complex [Mn(2)(III,IV)(mu-O)(2)(terpy)(2)(H(2)O)(2)](3+) (1), the two Mn atoms in 3 are not crystallographically equivalent. The neutral binuclear monooxo manganese(III,III) complex 4 exhibits two crystallographic forms having cis and trans configurations. In the cis complex, the two CF(3)CO(2)(-) ligands on each manganese adopt a cis geometry to each other; one CF(3)CO(2)(-) is trans to the oxygen of the oxo bridge while the second is cis. In the trans complex, the two coordinated CF(3)CO(2)(-) have a trans geometry to each other and are cis to the oxo bridge. The electrochemical behavior of 3 in organic medium (CH(3)CN) shows that this complex could be oxidized into its corresponding stable manganese(IV,IV) species while its reduced form manganese(III,III) is very unstable and leads by a disproportionation process to Mn(II) and Mn(IV) complexes. Complex 4 is only stable in the solid state, and it disproportionates spontaneously in CH(3)CN solution into the mixed-valent complex 3 and the mononuclear complex [Mn(II)(terpy)(2)](2+) (2), thereby preventing the observation of its electrochemical behavior.