Toward modeling phosphate tellurate glasses: the devitrification and addition of gadolinium ions behavior

Glasses in the xGd2O3 x (100 - x)[7TeO2 x 3P2O5] system with 0 < or = x < or = 20 mol % have been prepared using the melt quenching method. The influence of gadolinium ions on structural behavior of the phosphate tellurate glass has been investigated using infrared spectroscopy and density functional theory (DFT) calculations. The addition of gadolinium ions into the host glass matrix leads to an increase of the glass network polymerization due to the replacement of P-O-P bonds by the more resistant P-O-Te bonds having as result the improvement of the chemical durability of the glass. The structural evolution of the studied glasses with the gradual increase of the gadolinium oxide content up to 20 mol % could be explained by considering that the excess of oxygen may be accommodated by the conversion of some orthophosphate structural units into metaphosphate or/and pyrophosphate units. X-ray diffraction and IR spectra revealed that heat treatment of the samples also causes an increase of the glass network polymerization for heat treatment times, t, up to 36 h, while for 36 h > t > or = 48 h showed a drastic structural modification which lead to the apparition of the Te4P2O13 crystalline phase. DFT calculations show that tellurium atoms occupy two different sites in the proposed model. In the first case the tellurium atom is coordinated with four oxygen atoms giving a trigonal bipyramide arrangement, while in the second case the tellurium atom is coordinated with three O atoms. The calculated IR absorption spectrum of the proposed model for phosphotellurite glasses is in good agreement with the experimental absorption data.     

SAXS investigation of a cubic to a sponge (L3) phase transition in self-assembled lipid nanocarriers

The encapsulation and release of peptides, proteins, nucleic acids, and drugs in nanostructured lipid carriers depend on the type of the self-assembled liquid-crystalline organization and the structural dimensions of the aqueous and membraneous compartments, which can be tuned by the multicomponent composition of the systems. In this work, small-angle X-ray scattering (SAXS) investigation is performed on the 'melting' transition of the bicontinuous double diamond cubic phase, formed by pure glycerol monooleate (MO), upon progressive inclusion of varying fractions of pharmaceutical-grade glycerol monooleate (GO) in the hydrated system. The self-assembled MO/GO mixtures are found to form diamond (Pn3m) inverted cubic, inverted hexagonal (H(II)), and sponge (L(3)) phases at ambient temperature in excess of aqueous medium without heat treatment. Mixing of the inverted-cubic-phase-forming MO and the sponge-phase-forming GO components, in equivalent proportions (50/50 w/w), yields an inverted hexagonal (H(II)) phase nanostructured carrier. Scattering models are applied for fitting of the experimental SAXS patterns and identification of the structural changes in the aqueous and lipid bilayer subcompartments. The possibility of transforming, at ambient temperature (20 °C), the bicontinuous cubic nanostructures into inverted hexagonal (H(II)) or sponge (L(3)) mesophases may facilitate novel biomedical applications of the investigated liquid crystalline self-assemblies.     

FTIR and UV–VIS spectroscopy investigations on the structure of the europium–lead–tellurate glasses

Glasses in the xEu₂O₃·(100-x)[4TeO₂·PbO₂] system where 0 ≤ x ≤ 50 mol% have been prepared using the melt quenching method. The influence of europium ions on the structure of lead–tellurate glasses has been investigated using density measurements, FTIR and UV–VIS spectroscopy. Structural changes produced by increasing the rare earth concentration were followed.The europium and lead ions show a preference towards [TeO₃] structural units causing a deformation of the TeOTe linkages. Structural changes inferred by analyzing the band shapes of IR spectra revealed that the increase of the Eu^+ 3 content causes the intercalation of [EuO_n] entities in the [TeO₄] chain network. The excess of oxygen can be supported into the glass network by the formation of [PbO_n] and [EuO_n] structural units.The UV–VIS spectroscopy data show that europium ions enter the glass matrix in the Eu²⁺ and Eu³⁺ valence states, the last being predominant in the studied glasses. The Pb^+ 2 ions produce strong absorption in the ultraviolet domain.     

Structural and optical properties in gadolinium-aluminum-lead-germanate quaternary glasses

Glasses in the quaternary system 0.05Al₂O₃·0.95[xGd₂O₃·(100-x)(7GeO₂·3PbO)] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. In this paper, we investigated structural and optical properties in gadolinium-alumino-lead-germanate glasses through investigations of FTIR (Fourier-Transform Infrared Spectroscopy) and UV-VIS (Ultra-Violet) spectroscopy.The observations presented in these mechanisms show that by increasing Gd₂O₃ content up to 40 mol%, the glass network modification has taken place mainly in the germanate part, while the excess of oxygen can be accommodated in the host network by the creation of shorter rings of [Ge₂O₇] structural units and the formation of [AlO₄] structural units. The affinity pronounced of the gadolinium cations towards germanate structural units produces the formation of the Gd₂Ge₂O₇ crystalline phase.The UV-VIS spectroscopy data show the charge transfer transitions of Pb^+ 2-O^− 2, Al^+ 3-O^− 2 and Gd^+ 3-O^− 2, respectively. The additional absorption in the range of 300 to 600 nm was attributed to other types of defects such as: non-bridging oxygen ions, change in valency of ions and other color centers.The values of the direct optical band gap of the glasses are determined from the optical absorption spectra. By increasing Gd₂O₃ content in the glass matrix, the optical band gap energy increases indicating changes of the lattice parameters by Gd₂O₃ incorporation.     

Retarded regular graphs are regular or semiregular

A graph G is said to be retarded regular if there is a positive integral number s such that the number of walks of length s starting at vertices of G is a constant function. Regular and semiregular graphs are retarded regular with s?=?1 and s\!≤ \!2, respectively. We prove that any retarded regular connected graph is either regular or semiregular.     

Polymerisation von Methylmethacrylat mit FeCI3 als Initiator in sauren wäßrigen Lösungen

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