Effect of aggregation state, temperature and phospholipids on photobleaching of photosynthetic pigments in spinach Photosystem II core complexes

Photosystem II (PSII) complex activity is known to decrease under strong white light illumination, and this photoinhibition phenomenon is connected to the photobleaching of the PSII photosynthetic pigments. In this work the pigment photobleaching has been studied on PSII core complexes, by observing the effects of different factors such as the aggregation state (PSII monomers and dimers were used), temperature (20 degrees C and 10 degrees C temperatures were tested) and the presence of the exogenous phospholipids (cardiolipin and phosphatidylglycerol). In particular, PSII resistance against white light stress was studied by means of UV/VIS Absorption and Fluorescence Emission measurements. It was found that PSII dimers resulted more resistant against photobleaching and that lower temperature reduces the pigment photodestruction. Moreover, the presence of phosphatidylglycerol or cardiolipin enhanced the PSII resistance to the photobleaching phenomenon, mainly at lower temperatures.     

Photobleaching, Mobility, and Compartmentalisation: Inferences in Fluorescence Correlation Spectroscopy

In living cells the transport and diffusion of molecules is constrained by compartments of various sizes. This paper is an attempt to show that the size of these compartments can in principle be estimated experimentally from Fluorescence Correlation Spectroscopy (FCS) combined with the measurement of the photobleaching rate. In this work, confocal fluorescence microscopy experiments have been carried out on giant unilamellar vesicles, a system that mimics cellular compartmentalisation. We have developed numerical and analytical models to describe the fluorescence decay due to photobleaching in this geometry, which has enabled us to point out two regimes depending on the value of the parameter P(B) = sigma(B)P/D (where sigma(B) is the photobleaching cross section of the dye, D its diffusion constant, and P the laser power (in photon/s)). In particular, when P(B) < 1 (i.e. in the fast diffusion regime), the photobleaching rate is independent of the diffusion constant and scales like sigma(B)P/R2, in agreement with the experimental results. On the other hand, the standard diffusion models used to analyse the FCS data do not take into account the effects of the fluorescence decay on the autocorrelation curve. We show here how to correct the raw data for these drawbacks.     

An Alternate Solution of the Fluorescence Recovery Kinetics after Spot-Bleaching for Measuring Diffusion Coefficients. 1. Theory and Numerical Analysis

The classical three-point method for obtaining a diffusion coefficient of probes from the fluorescence recovery function in the Fluorescence Recovery After Photobleaching (FRAP) technique, when Gaussian or uniform spot-photobleaching profiles are used, leads to an expression that is not suitable for linear fittings. Therefore, determination of the diffusion coefficient is complex and very dependent on the recovery time. In this work we propose a new solution for the fluorescence recovery function after spot-bleaching using a Gaussian beam, which is a better alternative method than the three-point method for the data analysis of the FRAP kinetics. The new method can be applied for shorter recovery times thereby minimizing errors due to convective effects. It leads to a linear relationship between the recovery function and the diffusion coefficient and, as shown in the analysis of a model case, allows a more accurate determination of the diffusion coefficient of fluorescent probes.     

Solvent effects on the photochemical and fluorescence properties of zinc phthalocyanine derivatives

The effects of solvents on the singlet oxygen, photobleaching and fluorescence quantum yields for zinc phthalocyanine (ZnPc) and its derivatives; (pyridino)zinc phthalocyanine ((py)ZnPc), zinc octaphenoxyphthalocyanine (ZnOPPc) and zinc octaestronephthalocyanine (ZnOEPc), is presented. The effects of the solvents on the ground state spectra are also discussed. The largest red shift of the Q band was observed in aromatic solvents, the highest shift being observed for 1-chloronaphthalene. Higher singlet fluorescence quantum yields were observed in THF for ZnPc and ZnOPPC. Also in the same solvent phototransformation rather than photobleaching was observed for ZnOPPc. Split Q band in the emission and excitation spectra of ZnOPPc was observed in some solvents and this is explained in terms of the lowering of symmetry following excitation.     

Photochemical studies of tetra-2,3-pyridinoporphyrazines

Tetra-2,3-pyridinoporphyrazines and the corresponding water-soluble N,N′,N′′,N′′′-tetramethyl-tetra-2,3-pyridinoporphyrazine complexes, containing central metal atoms; M=Ge, Sn, Si and Zn, were synthesized and their photochemical properties were investigated. The reductive quenching of pyridinoporphyrazines excited states, enhanced relative to phthalocyanines, was considered as the first photochemical step of dyes phototransformation in dimethylformamide (DMF) and dimethylsulfoxide (DMSO) solutions under irradiation with visible light. Efficiency of singlet oxygen photosensitization decreases significantly in the row phthalocyanines, unquaternized, quaternized tetra-2,3-pyridinoporphyrazine metallocomplexes.     

Distribution of single molecules in polymer thin films

Distribution of fluorescent dye molecules in polymer thin (100 nm) films was investigated using far-field single-molecule video microscopy, by varying concentrations of dye molecules mixed in the polymer. Histograms of fluorescence photocounts of individual fluorescent spots showed wide distribution, varying in the number of fluorescent spots composed of one, two, three or group of molecules. The number of the molecules present in the fluorescent spots was also ascertained by fluorescence photobleaching experiments. Photocounts associated with maxima of the histograms were found to be independent of the concentrations; however, the number of occurrences associated with more than one molecule decreased with decreasing concentration. By reducing concentration as well as by mixing dye molecules into a polymer solution, fluorescent spots grouping more than one molecule were separated considerably into fluorescent spots including a single-molecule.     

肿瘤细胞中表达的GFP蛋白的荧光漂白特性的研究

GFP作为生物源性荧光探针具有其他荧光标记物所无法比拟的优势，目前已广泛应用于生物学研究的各个领域。利用常规转染方法将带有EGFP基因的质粒载体导入人肺腺癌肿瘤细胞(ASTC-a-1)，并得到GFP稳定表达的细胞株。研究中发现，肿瘤细胞中表达的GFP长时间暴露于强激发光中会发生非常强列的荧光漂白作用，并且这种漂白作用是不可恢复的。对不同强度的激发光(饱和光源、阻断片ND4／ND8／ND16)对GFP的漂白作用进行了研究，并对冷冻保存样品的光漂白作用进行了初步的探讨。     

沢吨染料的光化漂白动力学及全息特性研究

研究了以三乙醇胺作为引发剂,五种沢吨染料的光化漂白过程.实验结果表明五种染料的光化漂白速率大小顺序是藻红B(ErB)＞曙红Y(EY)＞孟加拉玫瑰红B(RsB)＞罗丹明B(RoB)＞荧光素(F).并研究了曝光强度及染料浓度对漂白过程的影响,以及这五种染料的全息记录性能.     

PHOTOCHROMIC PROPERTIES OF (E)-DICYCLOPROPYLMETHYLENE-(2,5-DIMETHYL-3-FURYLETHYLIDENE)-SUCCINIC ANHYDRIDE DOPED IN POLYSTYRENE THIN FILMS

Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures.Upon irradiation with UV light(366 nm),fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C.The later color was switched back to the original color when the films were irradiated with white light.The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at itsλ_(max) of 525 nm.The fir...     

碳化聚合物点发光主体的探究

以聚丙烯酸和乙二胺为原料, 通过水热法合成了碳化聚合物点(CPDs), 利用荧光光谱、 X射线光电子能谱和时间相关单光子计数等手段对3种不同碳化温度下形成的CPDs进行表征; 采用375 nm的紫外光对200 ℃下合成的CPDs进行光漂白, 分析了CPDs漂白前后的荧光寿命以及基团的变化, 探究了该CPDs的发光机理, 确定该CPDs具有碳核态和分子态共同控制的双发光中心.