X-ray diffraction, and Raman scattering study of nanostructured ZrO2-TiO2 oxides prepared by sol-gel.

In the present work, we study the phase composition of ZrO2-TiO2 system by means of XRD and Raman spectroscopy, using also TG-ATD, and N2 adsorption isotherms as complementary characterization techniques. TiO2-ZrO2 samples of selected compositions (0, 10, 90, 50 and 100% in weight of TiO2) were prepared by sol-gel method and annealed at three different temperatures (400, 600 and 800 degrees C). Structural characterization reveals that only the pure oxides are crystalline at 400 degrees C: TiO2 as anatasa with a minor brookite component, and ZrO2 as a mixture of tetragonal (majority) and monoclinic phases. Following the 600 degrees C calcination, the TiO2-ZrO2 50-50% sample forms the ZrTiO4 mixed oxide, although this materials remains partly amorphous. In contrast, samples with higher and lower TiO2 content form solid solutions with, respectively, anatasa and tetragonal ZrO2 structures. Zirconium incorporation into the TiO2 lattice leads to the expansion of the unit cell parameters, and it stabilizes the anatase phase, hindering its transformation into rutile. Similarly, dissolving titanium atoms into the ZrO2 structure delays the transformation from the tetragonal to the monoclinic polymorph.

Membrane-damaging action of ricin on DPPC and DPPC-cerebrosides assemblies. A Raman and FTIR analysis.

Perturbations induced by a toxic lectin (ricin) on lipid organisation of model membranes prepared with DPPC and DPPC-cerebrosides mixtures have been analysed by Raman and infrared spectroscopy, two powerful and non-invasive methods. Our approach involves the observation of changes in the vibrational spectra of liquid multilayers in the PO2-, C = O and CH2 spectral regions for two lipid:ricin molar ratios (225:1, 75:1). The interfacial and polar regions of the multilayers, analysed by FTIR, appear to be perturbed by the protein. With both kinds of membranes, ricin mainly perturbs the C = O ester groups of the sn-2 acylchain of DPPC. In the PO2- stretching region, the frequency shifts are correlated with changes in polar group hydration. In the hydrophobic core of the multilayer membrane studied by Raman spectroscopy, the interaction of ricin is associated with changes in lipid packing. These perturbations depend upon the lipid composition of the membrane. With DPPC membranes, an affect is detected at temperatures lower than Tm. It corresponds to a decrease of the lipid ordering. With DPPC-cer membranes, the protein increases the acyl-chain packing order regardless of the temperature of the experiments (10 degrees C less than T less than 75 degrees C). No perturbation of Tm is observed after addition of ricin to either DPPC or DPPC-cer membranes. The different perturbations detected by Raman and FTIR suggest that ricin mainly interacts with the interfacial domains of the membranes.

Conformational changes of Robinia pseudoacacia lectin related to modifications of the environment: FTIR investigation.

The secondary structural characteristics of one of the Robinia pseudoacacia lectins (RPA3) have been investigated by FTIR spectroscopy and have been established from absorption measurements in the amide I,I' frequency range and from the quantitative estimation of the rate of NH----N2H exchange. In an anhydrous state the protein structure consists mainly of antiparallel and parallel beta-structures, which represent 60% of the overall secondary structure of RPA3. Data obtained in different polar media (KBr, 2-chloroethanol, 2H2O, NaCl-2H2O and/or DPPC) reveal that RPA3 is a highly flexible protein. In pure 2H2O a rapid solvation of free peptide units and weak peripheral hydrogen bonds occurs, followed by the solvation of more internal parts of the lectin. The protein precipitates before total unfolding is reached. Increasing the ionic strength modifies the rate of NH----N2H exchange. NaCl concentrations of less than or equal to 0.15 M stabilize RPA3 in a structure close to that of the lyophilized lectin and diminish the rate of exchange, whereas higher NaCl concentrations partially disrupt the original secondary structure and increase the rate of exchange. Furthermore RPA3 was shown to interact with DPPC through polar interactions between the polar heads of the phospholipid and specific peptide units. These interactions appear to favor the NH----N2H exchange.

Vibrational spectroscopic study of glutathione complexation in aqueous solutions.

A spectroscopic study of glutathione (GSH) and glutathione disulfide (GSSG) has been performed using Fourier-transformed infrared absorption and Raman scattering in order to pinpoint the sites of complexation of these two species with water and particularly with H2O2. Molecules of GSH and GSSG were studied in KBr pellets, and in aqueous solutions of H2O, D2O, and H2O with H2O2 (1 mol L(-1)) to characterize the specific influence of the solvent molecules. A time-resolved Raman study was performed for GSH/H2O2, in aqueous solution at 1:1 molar ratio in order to observe the formation of GSSG and to discuss the mechanism of this redox reaction.

Low frequency vibrations and structural characterization of a murine IgG2a monoclonal antibody studied by raman and IR spectroscopies.

The Raman and ir spectra of a murine IgG2a monoclonal antibody molecule are reported. In accordance with previous studies on immunoglobulins, the secondary structure is predominantly of the beta-sheet type. The low frequency region of the Raman spectrum was also analyzed in detail. A structured band with two maxima near 43 and 94 cm(-1) was observed. This band has been attributed to vibrations of elastic body. The results are interpreted using a simple elastic model.