Freezing-Induced Loading of TiO2 into Porous Vaterite Microparticles: Preparation of CaCO3/TiO2 Composites as Templates To Assemble UV-Responsive Microcapsules for Wastewater Treatment.

The photocatalytic degradation of organic molecules is one of the effective ways for water purification. At this point, photocatalytic microreactor systems seem to be promising to enhance the versatility of the photoassisted degradation approach. Herein, we propose photoresponsive microcapsules prepared via layer-by-layer assembly of polyelectrolytes on the novel CaCO3/TiO2 composite template cores. The preparation of CaCO3/TiO2 composite particles is challenging because of the poor compatibility of TiO2 and CaCO3 in an aqueous medium. To prepare stable CaCO3/TiO2 composites, TiO2 nanoparticles were loaded into mesoporous CaCO3 microparticles with a freezing-induced loading technique. The inclusion of TiO2 nanoparticles into CaCO3 templates was evaluated with scanning electron microscopy and elemental analysis with respect to their type, concentration, and number of loading iterations. Upon polyelectrolyte shell assembly, the CaCO3 matrix was dissolved, resulting in microreactor capsules loaded with TiO2 nanoparticles. The photoresponsive properties of the resulted capsules were tested by photoinduced degradation of the low-molecule dye rhodamine B in aqueous solution and fluorescently labeled polymer molecules absorbed on the capsule surface under UV light. The exposure of the capsules to UV light resulted in a pronounced degradation of rhodamine B in capsule microvolume and fluorescent molecules on the capsule surface. Finally, the versatility of preparation of multifunctional photocatalytic and magnetically responsive capsules was demonstrated by iterative freezing-induced loading of TiO2 and magnetite Fe3O4 nanoparticles into CaCO3 templates.

Octamer formation in lysozyme solutions at the initial crystallization stage detected by small-angle neutron scattering.

Solutions of lysozyme in heavy water were studied by small-angle neutron scattering (SANS) at concentrations of 40, 20 and 10 mg ml-1 with and without the addition of precipitant, and at temperatures of 10, 20 and 30°C. In addition to the expected protein monomers, dimeric and octameric species were identified in solutions at the maximum concentration and close to the optimal conditions for crystallization. An optimal temperature for octamer formation was identified and both deviation from this temperature and a reduction in protein concentration led to a significant decrease in the volume fractions of octamers detected. In the absence of precipitant, only monomers and a minor fraction of dimers are present in solution.

Synthesis and comparative photoswitching studies of unsymmetrical 2,3-diarylcyclopent-2-en-1-ones.

Photochromic diarylethenes (DAEs) based on the unsymmetrical ethene "bridge" bearing heterocycles of the different nature (oxazole and thiophene) as aromatic moieties have been designed and the photoswitching properties have been studied. The comparative studies of the photochromic characteristics of unsymmetrical isomeric 2,3-diarylcyclopent-2-en-1-ones have shown that the isomers have different thermal stability, absorption maxima, and quantum yields. It was found that the unsymmetrical diarylcyclopentenone bearing at second position of the cyclopentenone ring the thiophene unit displays high thermally stability, hypsochromic shift of absorption maxima wavelengths of initial and cyclic forms, and high quantum yields of cyclization and cycloreversion reactions. The replacement of the carbonyl group with oxime leads to a reduction of the difference in the photochromic properties of these isomers and just as the reduction of the carbonyl group to the hydroxy-group negates this difference to zero. The intramolecular hydrogen bond formation in the oxime and hydroxy derivatives was confirmed by IR and (1)H NMR spectral analysis, but the increase of the quantum yields of the cyclization reaction in a nonpolar hexane is observed only in the case of hydroxy derivatives that can be explained by the formation of more rigid six-membered heterocycle in hydrogen bonding.

Coumarinyl(thienyl)thiazoles: novel photochromes with modulated fluorescence.

Novel photochromic 5-(3'-coumarinyl)-4-(3''-thienyl)thiazoles have been synthesized. These compounds display intensive fluorescence emission in the open form A, which is modulated by light. Fluorescence intensity decreases significantly upon irradiation of A with UV-light (lambda<400 nm) due to formation of the cyclic form B. Irradiation of B with visible light (lambda>470 nm) promotes its opening and the recovering of fluorescence. Novel dihetarylethenes undergo photochromic modulation of fluorescence both in solution and in polymeric matrices.