Preparation, Testing and Characterization of Doped TiO2 Active in the Peroxidation of Biomolecules under Visible Light

Doped TiO2 samples using different preparative procedures were synthesized using either urea or thiourea leading to N- or S-doped TiO2. Photocatalytic peroxidation and oxidation (mineralization) of phosphatidylethanolamine (PE) lipid with doped TiO2 were carried out under light irradiation λ > 410 nm. The formation of conjugated double bonds in PE molecules was followed to detect the formation of peroxy radicals (peroxidation index) under light excitation (λ > 410 nm) when doped TiO2 was used. The kinetics of CO2 production was monitored during the mineralization of PE. Colored TiO2 powders were studied in detail by different and complementary physicochemical techniques. The band gap energies of colored TiO2 were determined by diffuse reflectance spectroscopy (DRS). The visible absorption shoulder of TiO2 was observed to follow Urbach\u27s law. The variation of the transient decay after 354 nm laser pulse excitation does not correlate with the different N− and S−TiO2 doping levels introduced by the addition of urea or thiourea. This suggests that the states (recombination centers or traps) introduced by the doping are not effective in varying the decay kinetics within the nanosecond and microsecond time scale. Elemental analysis shows comparable amounts of S- and N-doping of TiO2 when thiourea is used as dopant. X-ray diffraction reveals no rutile in S−TiO2 samples heated to 600 °C, suggesting that the addition of sulfur precludes rutilization during sample crystallization. X-ray photoelectron spectroscopy (XPS) of the S−TiO2 samples confirms the preferential localization of S on the 20 topmost layers of S−TiO2 upon calcination at 500 °C for 2 h

Effect of Dehydrated Trehalose Matrix on the Kinetics of Forward Electron Transfer Reactions in Photosystem I

The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pump–probe laser spectroscopy with 20-fs low-energy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of A∙−1A/A∙−1B→FX by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary P∙+700A∙−0 and the secondary P∙+700A∙−1 ion radical pairs were not affected by dehydration in the trehalose matrix, while the yield of the P∙+700A∙−1 was decreased by ~20%. Forward ET from the phylloquinone molecules in the A∙−1A and A∙−1B sites to the iron–sulfur cluster FX slowed from ~220 ns and ~20 ns in solution to ~13 μs and ~80 ns, respectively. However, as shown by EPR spectroscopy, the ~15 μs kinetic phase also contains a small contribution from the recombination between A∙−1B and P∙+700. These data reveal that the initial ET reactions from P700 to secondary phylloquinone acceptors in the A- and B-branches of cofactors (A1A and A1B) remain unaffected whereas ET beyond A1A and A1B is slowed or prevented by constrained protein dynamics due to the dry trehalose glass matrix

Femtosecond primary charge separation in Synechocystis sp. PCC 6803 photosystem I

AbstractThe ultrafast (<100fs) conversion of delocalized exciton into charge-separated state between the primary donor P700 (bleaching at 705nm) and the primary acceptor A0 (bleaching at 690nm) in photosystem I (PS I) complexes from Synechocystis sp. PCC 6803 was observed. The data were obtained by application of pump–probe technique with 20-fs low-energy pump pulses centered at 720nm. The earliest absorbance changes (close to zero delay) with a bleaching at 690nm are similar to the product of the absorption spectrum of PS I complex and the laser pulse spectrum, which represents the efficiency spectrum of the light absorption by PS I upon femtosecond excitation centered at 720nm. During the first ∼60fs the energy transfer from the chlorophyll (Chl) species bleaching at 690nm to the Chl bleaching at 705nm occurs, resulting in almost equal bleaching of the two forms with the formation of delocalized exciton between 690-nm and 705-nm Chls. Within the next ∼40fs the formation of a new broad band centered at ∼660nm (attributed to the appearance of Chl anion radical) is observed. This band decays with time constant simultaneously with an electron transfer to A1 (phylloquinone). The subtraction of kinetic difference absorption spectra of the closed (state P700+A0A1) PS I reaction center (RC) from that of the open (state P700A0A1) RC reveals the pure spectrum of the P700+A0− ion–radical pair. The experimental data were analyzed using a simple kinetic scheme: An* →k1 [(PA0)*A1→<100fs P+A0−A1] →k2P+A0A1−, and a global fitting procedure based on the singular value decomposition analysis. The calculated kinetics of transitions between intermediate states and their spectra were similar to the kinetics recorded at 694 and 705nm and the experimental spectra obtained by subtraction of the spectra of closed RCs from the spectra of open RCs. As a result, we found that the main events in RCs of PS I under our experimental conditions include very fast (<100fs) charge separation with the formation of the P700+A0−A1 state in approximately one half of the RCs, the ∼5-ps energy transfer from antenna Chl* to P700A0A1 in the remaining RCs, and ∼25-ps formation of the secondary radical pair P700+A0A1−

Evidence for differentiated ionic and surface contact effects driving bacterial inactivation by way of genetically modified bacteria

New evidence is presented for the bacterial inactivation of E. coli presenting normal porins on sputtered Ag-Cu surfaces compared with similar E. coli porinless bacteria. Inactivation at a reduced rate was observed on the genetically modified porinless bacteria interacting via surface contact with metal/oxides without the intervention of metal-ions

Effects of Surface Chemical Modification by Ethoxysilanes on the Evolution of 3D Structure and Composition of Porous Monoliths Consisting of Alumina Hydroxide Nanofibrils in the Temperature Range 25&ndash;1700 &deg;C

Bulk nanomaterials with an open porosity offer exciting prospects for creating new functional materials for various applications in photonics, IR-THz optics, metamaterials, heterogeneous photocatalysis, monitoring and cleaning toxic impurities in the environment. However, their availability is limited by the complexity of controlling the process of synthesis of bulk 3D nanostructures with desired physicochemical and functional properties. In this paper, we performed a detailed analysis of influence of a silica monolayer chemically deposited on the surface of a monolithic ultraporous nanostructure, consisting of a 3D nanofibril network of aluminum oxyhydroxide, on the evolution of structure and morphology, chemical composition and phase transformations after heat treatment in the temperature range of 20&minus;1700 &deg;C. The experimental results are interpreted in the framework of a physical model taking into account surface and volume mass transport and sintering kinetics of nanofibrils, which made it possible to estimate activation energies of the surface diffusion and sintering processes. It is shown that the presence of a surface silica monolayer on the surface affects the kinetics of aluminum oxyhydroxide dehydration and inhibits diffusion mass transfer and structural phase transformations. As a result, the overall evolution of the 3D nanostructure significantly differs from that of nanomaterials without surface chemical modification

Monitoring the energy of the metal ion-content plasma-assisted deposition and its implication for bacterial inactivation

Cu-polyester (Cu-PES) was sputtered by high power impulse magnetron sputtering (HIPIMS) and by low energy direct current magnetron sputtering (DCMS). The total amount and distribution of the Ar+, Cu+ and Cu2+ ions were determined as well as the bacterial inactivation kinetics mediated by DCMS and HIPIMS samples. The separation of extracellular and intracellular processes leading to bacterial inactivation was assessed on normal and genetically modified E. coli