The +4 charged dye tetramethylpyridylporphyrin, TMPyP (≡H2TMPyP4+), and the metallo ZnTMPYP are water-soluble. The cationic TMPy groups are nearly perpendicular to the plane of the porphine. When the dyes were applied to the layered inflatable clay mineral Laponite a ∼30 nm red shift in the spectrum of both TMPyP−'s adsorbed on outer surfaces and a ∼60 nm shift in the dyes trapped in interlamellar galleries were found. The negatively charged clay surface may be very acidic. In previous works, the red shifts were interpreted in terms of diprotonation of TMPyP. In this work, several possible causes of the observed red shifts were rigorously examined. These included diprotonation, redox reactions, solvent effects, π-electron interaction with the oxygen plane, and electronic changes due to the flattening of TMPyP on the clay. To facilitate in a deductive manner a possible explanation for the observed metachromasy, the charged, flat Laponite was replaced with its neutral analogue:  talc and porous silica. The electronic structure of the porphine ring is classically treated by means of the 4-level model. In charged porphyrins, such as TMPyP, the modelization is much complicated. Here, semiempirical quantum chemical PM3 modeling in a vacuum confirmed the perpendicularity of the TMPy groups. The dihedral angles were constrained toward planarity and the resulting red shifts in the spectra were calculated, then a classical (four-level) adaptation was applied. It then appears that the ∼30° twists from the vertical would cause a ∼30 nm red shift in the Soret band with a ∼3 kcal/mol rise in ground-state energy. Then ∼46° twists would cause a ∼60 nm red shift in the Soret band with a ∼11 kcal/mol rise in ground-state energy. Hence, sterically induced hindrance in adsorbed TMPyP had a profound influence on the absorption spectra, confirming our conclusions from the experimental part.

In this work, an oxidation model for alpha-uranium is presented. It describes the internally lateral stress field built in the oxide scale during the reaction. The thickness of the elastic, stress-preserving oxide (UO(2+x)) scale is less than 0.5 microm. A lateral, 6.5 GPa stress field has been calculated from strains derived from line shifts (delta(2theta)) as measured by the X-ray diffraction of UO(2). It is shown that in the elastic growth domain, (110) is the main UO(2) growth plane for gas-solid oxidation. The diffusion-limited oxidation mechanism discussed here is based on the known "2:2:2" cluster theory which describes the mechanism of fluorite-based hyperstoichiometric oxides. In this study, it is adapted to describe oxygen-anion hopping. Anion hopping toward the oxide-metal interface proceeds at high rates in the [110] direction, hence making this pipeline route the principal growth direction in UO(2) formation. It is further argued that growth in the pure elastic domain of the oxide scale should be attributed entirely to anion hopping in 110. Anions, diffusing isotropically via grain boundaries and cracks, are shown to have a significant impact on the overall oxidation rate in relatively thick (>0.35 microm) oxide scales if followed by an avalanche break off in the postelastic regime. Stress affects oxidation in the elastic domain by controlling the hopping rate directly. In the postelastic regime, stress weakens hopping, indirectly, by enhancing isotropic diffusion. Surface roughness presents an additional hindering factor for the anion hopping. In comparison to anisotropic hopping, diffusion of isotropic hopping has a lower activation energy barrier. Therefore, a relatively stronger impact at lower temperatures due to isotropic diffusion is displayed.

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In this study, we analyzed the development of a compact oxide scale built in course of Uranium surface oxidation. The process was monitored by an in-situ acquisition of the reflectance interference peaks in the NIR-MIR. Dielectric properties of the growing oxide scale were derived in accord to the oscillator model. We used effective media approach to simulate heterogeneous dielectric content in the oxide-metal interface. Following dielectric parameterization, structural properties (e.g., scale thickness) of the proposed multi-scale scheme were calculated. As scale's growth process quantified, a valid kinetic model was proposed. Analysis showed that oxidation dynamics is governed by a multi-parabolic, true diffusion-limited mechanism of activation energy conveniently equaling the known anion diffusion enthalpy of 26 kcal/mol. The applied kinetic model suggested a setup of two consecutive oxide scales, characterized by differing anion diffusion rates. Though mathematical formalism presented a similar to the paralinear, time-dependent solution, here, in contrast to the classic paralinear assumption, both scales consisted of a compact, diffusion limited oxide barriers. As a result, the difference in anion flow across the outer and inner scale barriers assigned the overall, pseudo-linear rate constant-kl, of a negative (in contrast to the paralinear approach) value. Next, Uranium oxidation has been studied in the post-elastic domain. Markedly, upon breakaway of the compact oxide scale, classic paralinear behavior was reestablished for scale thickness of > or = 0.5 microm.

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