The effect of chemical variations on the structural polarity of relaxor ferroelectrics studied by resonance Raman spectroscopy.

Resonance Raman spectroscopy was applied to doped PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3 relaxor ferroelectrics, to better understand the effect of composition disorder on the mesoscopic-scale polar order in complex perovskite-type (ABO3) ferroelectrics. The excitation photon energy used was 3.8 eV, which is slightly above the energy gap and corresponds to the maximum of the optical dielectric permittivity. Group-theory analysis reveals that the resonance Raman scattering (RRS) observed under these conditions is allowed only in polar crystal classes. Therefore, RRS is dominated by the atomic dynamics of nanoregions with coherent polar distortions, which considerably facilitates the comparison of polar order in various compounds. The results show that A-site doping (Ba(2+), Sr(2+), La(3+), Bi(3+)) has significantly stronger effect on the structural polarity than the introduction of a third element at the B site (Nb(5+) or Sn(4+) doped in PbSc0.5Ta0.5O3). The A-site substitution by cations that in contrast to Pb(2+) have isotropic outermost electron shells disturbs the system of lone-pair electrons, thus reducing the correlation length of coupled polar distortions and the strength of the electric field associated with the mean polarization of polar nanoregions. A-site doping with larger cations (Ba(2+)) augments the polar deformation of the individual BO6 octahedra due to local elastic fields. As a result, such A-site doping intensifies the initial structural polarity at high temperatures and prevails the enlargement of the polar fraction at low temperatures. A-site doping with smaller cations (Sr(2+), La(3+)), regardless if they are isovalent or aliovalent to Pb(2+), increases the correlation length of antiferrodistortive order (BO6 tilts), which in turn assists the development of double-perovskite structure with coherent local polar distortions. A-site doping with aliovalent cations (Bi(3+)) having the same outermost electron shell and ionic radius as the host A-site Pb(2+) cations leads to stronger coupling along the -B-O-B- bond linkages due to enhanced random local electric fields.

The proteasome inhibitor bortezomib acts differently in combination with p53 gene transfer or cytotoxic chemotherapy on NSCLC cells.

In this report, the effects of a combined treatment with the proteasome inhibitor bortezomib and either a recombinant adeno-associated virus type 2 (rAAV-2)-mediated p53 gene transfer or chemotherapeutic agents, docetaxel and pemetrexed, were tested on p53 positive and p53negative non-small cell lung cancer (NSCLC) cell lines. The combination of bortezomib and rAAV-p53 led to a significant synergistic inhibition of cell growth between 62-82% depending on the p53 status of the cell line and drug concentration. Surviving cells of the combined treatment showed a significant reduced ability to form colonies. Enhanced cell toxicity was associated with a 5.3-14.4-fold increase of the apoptotic rate and intracellular p53 level up to 50.4% following vector-mediated p53 restoration and bortezomib treatment. In contrast, an antagonistic effect on tumor cell growth and colony formation was observed for the combination of bortezomib and docetaxel or pemetrexed as a reduction of cell growth between 31 and 48% was found in comparison to 50% using the single agents. Lower cytotoxic effects were associated with significantly reduced apoptosis and an increase of clonogenic growth. The observed antagonistic effects between bortezomib and docetaxel or pemetrexed might influence clinical trials using these compounds. Conversely, p53 restoration and bortezomib treatment led to enhanced, synergistic tumor cell toxicity.