Target theory and the photoinactivation of Photosystem II

Application of target theory to the photoinactivation of Photosystem II in pea leaf discs (Park et al. 1995, 1996a,b) reveals that there is a critical light dosage below which there is complete photoprotection and above which there is photoinactivation (i.e a light-induced loss of oxygen flash yield). The critical dosage is about 3 mol photons m^–2 for medium and high light-grown leaves and 0.36 mol photons m^–2 for low light-grown leaves. Photoinactivation is a one-hit process with an effective cross-section of 0.045 m² mol^–1 photons which does not vary with growth irradiance, unlike the cross-section for oxygen evolution which increases with decreasing growth irradiance. The cross-section for oxygen evolution increased by about 20% following exposure to 6.8 mol photons m^–2 which may be due to energy transfer from photoinactivated units to functional Photosystem II units. We propose that the photoinactivation of PS II begins when a small group of PS II pigment molecules whose structure is uninfluenced by growth irradiance, becomes uncoupled energetically from the rest of the photosynthetic unit and thus no longer transfers excitions to P680. De-excitation of this group of pigment molecules provides the energy which leads to the damage of Photosystem II. Treatment of pea leaves with dithiothreitol, an inhibitor of the xanthophyll cycle, decreases the critical dosage i.e. decreases photoprotection but has no effect on the PS II photoinactivation cross-section. Treatment with 1 M nigericin increased the photoinactivation cross-section of PS II as did exposure to lincomycin which inhibits D1 protein synthesis and thus the repair of PS II reaction centres.Abbreviations DTT- dithiothreitol - PS II- Photosystem II - Fm- maximum fluorescence - Fv- variable fluorescence - LHCIIb- main light harvesting pigment-protein complex of PS II - D1 protein- psbA gene product - P680- reaction centre chlorophyll of Photosystem II - Qa- first quinone electron acceptor of Photosystem II - (o₂)- cross-section for oxygen evolution - (pi)- cross-section for photoinactivation     

竹红菌甲素对红细胞膜上几种酶光敏失活作用的研究

本文比较了竹红菌甲素对人红细胞膜AchE,GPDH,Na~ -K~ ATPase和Ca~(2 )-Mg~(2 )ATPase的光敏失活能力,结果表明甲素对Ca~(2 )-Mg~(2 )ATPase作用最强,Na~ -K~ ATPase次之,GPDH再次之,AchE最不敏感,甲素还引起膜蛋白巯基氧化,膜脂质过氧化。其中,巯基氧化可能是ATPase光敏失活的主要原因,而脂质过氧化对ATPase活力损伤作用不大。游离GPDH不如与膜结合的GPDH敏感。GSH,NAD分别对ATPase,GPDH有保护作用。膜蛋白的电泳及内源荧光证据表明:在GPDH活力受到严重损伤时,酶结构并未发生剧烈改变。     

Aerosol OT/Water System Coupled with Triiodide/Iodide (I3−/I−) Redox Electrolytes for Highly Efficient Dye‐Sensitized Solar Cells

Dye‐sensitized solar cells (DSCs) are considered to be a promising alternative to Si‐based photovoltaic cells. The electrolyte of the DSC primarily uses triiodide/iodide (I₃^?/I^?) as a redox couple. Therefore, it is essential to understand the regeneration and recombination kinetics of the I₃^?/I^? redox couples in the device. In this context, controlling the total and local concentrations of the I₃^?/I^? redox couples is an important parameter that can influence the DSC performance. Here, we propose that the introduction of a sodium bis (2‐ethylhexyl) sulfosuccinate (AOT)/water system to the I₃^?/I^? electrolyte enables the control of the concentration of the redox couples, which consequently achieves a high power conversion efficiency of ～11% for ～1000 h (under 1 sun illumination) owing to the enhanced dye‐regeneration efficiency and the reduced recombination rate. This novel concept assists in the comprehension of the regeneration and recombination kinetics and develops highly efficient DSCs.     

High Efficiency Up‐Converting Single Phase Elastomers for Photon Managing Applications

Optically active materials able to up‐convert the frequency of the incident radiation can be used to enhance the performance of photovoltaic and photocatalityc cells, recovering sub‐bandgap photons not directly absorbed by the devices. Actually, sensitized up‐conversion (SUC) based on multi‐component organic systems is the most promising approach for these photon energy managing processes, being efficient also at the solar irradiance. However, applications of SUC on real devices have not been yet accomplished because its conversion yield usually drops dramatically in the solid state where the low dye mobility inhibits the diffusion controlled mechanisms ruling SUC photophysics. To overcome this limit, we prepared a single‐phase elastomer (poly‐butylacrilate) doped with proper dyes (platinum (II) octaetyl‐porphyrin and 9,10‐diphenylanthracene) to fabricate an efficient photon up‐converting material. Thanks to the residual molecular diffusion provided by the soft host, and to the quenching reduction of involved metastable electronic excited‐states in a solid environment compared to a liquid one, we obtained a record SUC yield of 17% at the solid state. SUC efficiency has been studied as function of the excitation power and sample temperature, elucidating the photophysical processes at the base of the high observed yield and assessing the guidelines for the fabrication of technologically appealing low power up‐converting materials.     

High‐Surface‐Area Porous Platinum Electrodes for Enhanced Charge Transfer

Cobalt‐based electrolytes are highly tunable and have pushed the limits of dye‐sensitized solar cells, enabling higher open‐circuit voltages and new record efficiencies. However, the performance of these electrolytes and a range of other electrolytes suffer from slow electron transfer at platinum counter electrodes. High surface area platinum would enhance catalysis, but pure platinum structures are too expensive in practice. Here, a material‐efficient host‐guest architecture is developed that uses an ultrathin layer of platinum deposited upon an electrically conductive scaffold, niobium‐doped tin oxide (NTO). This nanostructured composite enhances the counter electrode performance of dye‐sensitized solar cells (DSCs) using a Co^(II/III)BPY₃ electrolyte with an increased fill factor and power conversion efficiency (11.26%), compared to analogous flat films. The modular strategy is elaborated by integrating a light scattering layer onto the counter electrode to reflect unabsorbed light back to the photoanode to improve the short‐circuit current density and power conversion efficiency.