THE EFFECT OF ORGANIC NITRATES IN PHYTOCHROME-CONTROLLED GERMINATION OF Paulownia tomentosa SEEDS

The long light irradiation requirement in Paulownia tomentosa (empress tree) seeds can be substituted by organic nitrates such as nitroglycerine, isosorbide di- and mononitrate, and pentaerythri-tyl tetranitrate and a pulse of red light (5 min). The most effective was nitroglycerine (0.1 mM). Its effect depended on the time of application, i.e. a simultaneous presence of P_fr and these compounds was required. The effect decreased with delayed time of application after red light pulse. In seeds imbibed in nitroglycerine, an escape from far-red light reversible action was similar to that obtained for seeds which can be induced to germinate by a brief exposure to red light. However, the application of nitroglycerine to seeds after a far-red light pulse was ineffective. The effectiveness of organic nitrates also depended on the number of nitro groups in the compound. Isosorbide mononitrate was less effective than isosorbide dinitrate. Substances with structures similar to nitroglycerine, such as glycerol and glyceryl triacetate, in combination with the pulse of red light, failed to reduce the long light requirement.     

ACOUSTIC DETECTION OF TRIPLET STATES FORMED BY RADICAL PAIR RECOMBINATION IN QUINONE-DEPLETED PHOTOSYNTHETIC REACTION CENTERS, BY MAGNETIC FIELD MODULATION (MAGNETOPHOTOACOUSTIC EFFECT)-A FEASIBILITY STUDY

Abstract: An acoustic method is outlined to detect triplet states formed by radical pair recombination in photosynthetic reaction centers. It is based on magnetic field effect on the probability of triplet state formation by recombination. Using a periodically modulated magnetic field in the presence of constant exciting light, a periodic modulation of the triplet state concentration is set in the sample, which is detected through the corresponding modulated heat emission, transduced to acoustic vibration of the gas phase around the sample. This effect is similar to the photoacoustic effect, except that here the light is not modulated. The feasibility of detecting such an effect was proven experimentally, by obtaining a signal from quinone-depleted reaction centers of Rhodobacter sphaeroides. The signal had twice the frequency of the magnetic field modulation; it was proportional to the light intensity and significantly stronger at the lower temperatures (in the investigated range 113–278 K). No signal was obtained from quinone-containing reaction centers, which do not produce triplets. A theoretical outline of the effect and the experimental set-up are described. The magnitude of the effect was calibrated against ordinary photoacoustic measurements, allowing numerical evaluation of certain parameters of the triplet state ( e.g. triplet energy or yield) with the aid of auxiliary information from the literature.     

ACOUSTIC DETECTION OF TRIPLET STATES FORMED BY RADICAL PAIR RECOMBINATION IN QUINONE-DEPLETED PHOTOSYNTHETIC REACTION CENTERS, BY MAGNETIC FIELD MODULATION (MAGNETOPHOTOACOUSTIC EFFECT)-A FEASIBILITY STUDY

Abstract –An acoustic method is outlined to detect triplet states formed by radical pair recombination in photosyn-thetic reaction centers. It is based on magnetic field effect on the probability of triplet state formation by recombination. Using a periodically modulated magnetic field in the presence of constant exciting light, a periodic modulation of the triplet state concentration is set in the sample, which is detected through the corresponding modulated heat emission, transduced to acoustic vibration of the gas phase around the sample. This effect is similar to the photoacoustic effect, except that here the light is not modulated. The feasibility of detecting such an effect was proven experimentally, by obtaining a signal from quinone-depleted reaction centers of Rhodobacter sphaeroides. The signal had twice the frequency of the magnetic field modulation; it was proportional to the light intensity and significantly stronger at the lower temperatures (in the investigated range 113–278 K). No signal was obtained from quinone-containing reaction centers, which do not produce triplets. A theoretical outline of the effect and the experimental set-up are described. The "magnitude of the effect was calibrated against ordinary photoacoustic measurements, allowing numerical evaluation of certain parameters of the triplet state ( e.g. triplet energy or yield) with the aid of auxiliary information from the literature.     

利用pⅧ展示系统改进噬菌体抗体芯片

将展示单链抗体的重组噬菌体与羧基终止的硅片偶联, 制成噬菌体抗体芯片, 可用于检测多类蛋白质和蛋白质组. 通常抗体被展示于噬菌体外壳蛋白pⅢ上, 由此制备的芯片灵敏度和信噪比较低. 我们选用凝血酶特异的单链抗体为代表, 比较了pⅢ展示系统和pⅧ展示系统制成芯片的检测效果. 由于pⅧ展示系统的融合蛋白拷贝数多, 所受空间位阻小, 大幅度提高了噬菌体抗体芯片的灵敏度和信噪比, 有望用于制备新型蛋白质芯片.     

THE INFLUENCE OF LIGHT UPON SEED GERMINATION. POSSIBLE INTERPRETATIONS OF DATA

Abstract— The response of seeds to irradiation by white light varies with the species: induction of germination, inhibition of germination or both according to the time-irradiation. The low energy reaction (LER) which acts via phytochrome can explain many cases of influence of light upon germination. It seems possible that a second reaction, the high energy reaction (HER), acts through another photoreceptor.     

Ultraweak Photon Emission from the Seed Coat in Response to Temperature and Humidity—A Potential Mechanism for Environmental Signal Transduction in the Soil Seed Bank

Seeds beneath the soil sense the changing environment to time germination and seedling emergence with the optimum time of year for survival. Environmental signals first impact with the seed at the seed coat. To investigate whether seed coats have a role in environmental sensing we investigated their ultraweak photon emission (UPE) under the variable temperature, relative humidity and oxygen conditions they could experience in the soil seed bank. Using a custom‐built luminometer we measured UPE intensity and spectra (300–700 nm) from Phaseolus vulgaris seeds, seed coats and cotyledons. UPE was greatest from the internal surface of the seed coat. Seed coat UPE increased concomitantly with both increasing temperature and decreasing relative humidity. Emission was oxygen dependent and it was abolished by treatment with dinitrophenylhydrazine, demonstrating the key role of seed coat carbonyls in the phenomenon. We hypothesize that beneath the soil surface the attenuation of light (virtual darkness: low background noise) enables seeds to exploit UPE for transducing key environmental variables in the soil (temperature, humidity and oxygen) to inform them of seasonal and local temperature patterns. Overall, seed coats were found to have potential as effective transducers of key fluctuating environmental variables in the soil.     

RED-LIGHT-INDUCED GERMINATION OF LETTUCE SEEDS: RELATIONSHIP BETWEEN ESCAPE FROM REVERSIBILITY AND FLUENCE*

Abstract— Dormant seeds of Lactuca saliva L. (cv. ‘May Queen’) germinate after a brief light treatment. The seeds escape from photoreversibility by far-red irradiation after a lag time. The duration of the lag decreases with increasing levels of the far-red absorbing form of phytochrome (P_fr). During the lag time the percentage of seeds germinating after the reversing far-red irradiation is slowly rising. This is not due to an escape reaction proper, but to an increase of sensitivity to P_fr.     

羟基卟啉化合物的电化学、顺磁共振及时间分辨光电压性质

通过循环伏安法、电子顺磁共振谱和时间分辨电压光谱研究了羟基取代基数目和位置的不同对羟基苯基卟啉化合物的电化学、电子顺磁共振和时间分辨光电压性质的影响. 研究结果表明, 所有氧化还原反应都是在卟啉环上进行的. 卟啉周边取代基数目的增加使得卟啉共轭体系平均电子云密度增大, 导致体系易氧化而难以还原. 对称性增强可能使卟啉化合物的半波电位值向正方向移动, 羟基取代基的给电子效应对于卟啉化合物电化学性质的影响起主导作用. 常态下卟啉分子没有EPR信号, 在光的激发下, 卟啉分子由原来的逆磁性分子变成顺磁性的激发三重态分子, 这种激发三重态分子在分子轨道上具有两个未成对电子, 这两个电子相距很近, 彼此之间发生很强的相互作用而产生电子, 它的g值随卟啉共轭体系平均电子云密度增大而变大. 时间分辨光电压是由分子中的自由光声载流子的存在而产生的, 光电压的衰减与分子结构密切相关, 它们的电荷分离速度基本上随卟啉周边羟基取代基数目的增加而减慢.     

SPECTRA OF FLUORESCENCE LIFETIME AND INTENSITY OF Rhodopseudomonas sphaeroides AT ROOM AND LOW TEMPERATURE. COMPARISON BETWEEN THE WILD TYPE, THE C 71 REACTION CENTER-LESS MUTANT AND THE B800–850 PIGMENT-PROTEIN COMPLEX

Abstract— Spectra of the fluorescence lifetime and intensity of chromatophores from the wild type Rhodopseudomonas sphaeroides , from the C 71 reaction center-less mutant and of the B800–850 light harvesting pigment-protein complex have been studied by phase fluorimetry techniques at different light modulation frequencies at room and low temperature.
As already known, closed reaction centers (saturating light) are still quenchers of antenna fluorescence although with a lower efficiency than when they are opened. The fluorescence yields and lifetimes of both the C 71 mutant strain and the B800–850complex are found to increase by about 30% between room and low temperature.
The fluorescence lifetimes obtained for the C 71 strain (0.65 ns at 20C; 0.85 ns at 77 K) and for the B850 complex (1 ns at 20C; 1.3 ns at 77 K) indicate that the non-radiative deactivation pathways, in the antenna, remain important in the absence of the reaction centers even at low temperature. We suggest that these data arise from the presence of special antenna molecules which act as intrinsic quenchers of the B875 antenna fluorescence. Between room and low temperature, the fluorescence yield and lifetime of the wild type are found roughly constant. This result suggests that the energy trapping by the reaction centers is independent of the temperature. The mechanism governing the energy transfer from the antenna to the reaction centers may differ from the mechanism leading to the energy transfer within the antenna. We suggest that a partially irreversible trapping of the excitation energy, on its way to the reaction center, takes place in the vicinity of the reaction center.     

VARIATION IN ELECTRON PARAMAGNETIC RESONANCE SIGNALS OF PHOTOSYNTHETIC SYSTEMS WTTH THE REDOX LEVEL OF THEIR ENVIRONMENT

Abstract— The redox dependence of the light-induced electron paramagnetic resonance signal at g=2 in R. rubrum, R. spheroides and Chromatium chromatophore particles and quantasonie particles from spinach chloroplasts has been determined qualitatively over the range —0.3 to +0.6 V and quantatively over the range +0.3 to ±0.6 V. A light-induced EPR signal has been titrated and demonstrated to have a midpoint potential of +0.44 v at pH 7 and 20°C. Concentration, ionic strength and pH dependence for this transition in R. rubrum chromatophores is reported. In addition to the dark signal which replaces the light signal, in chromatophore material another dark signal, occurring in the seine location as the light signal, has been demonstrated to occur at high potential.
Selective chemical oxidation with K₂lrCl₆ of chromatophore particles from the three bacteria resulted in the removal of some 95 per cent of the absorbance in the near infrared and left the photoactive pigments.
Two light-induced EPR signals were found in quantasome particles by their dependence upon the redox level. Of particular interest is a signal observed at quite high potential (e.g. + 0.60 V). It was demonstrated that oxygen evolution by these quantasonie particles in the presence of K³Fe(cN)₀ occurred at the same rate at +0.55 V as at +0.40 V.     

Electrochemical reactions of redox cofactors in Rhodobacter sphaeroides reaction center proteins in lipid films.

Cyclic voltammetry of thin films made from the lipid dimyristoylphosphatidyl choline and reaction centers from the purple bacterium Rhodobacter sphaeroides on pyrolytic graphite electrodes in bromide-free pH 8 buffers at 4 degrees C revealed an oxidation peak at 0.98 V and a reduction peak at -0.17 V vs. NHE. No reverse CV peaks were found, suggesting chemical irreversibility. The reduction peak disappeared for reaction centers depleted of quinones, suggesting that the peak represents reduction of this cofactor. The oxidation peak showed a catalytic current increase in the presence of small amounts of ferrous cytochrome c, and decreased by 85% when illuminated by visible light, suggesting assignment to the primary donor (P) cofactor. While oxidized primary donor P(+) is destroyed upon electrochemical formation in the film, reaction of ferrous cyt c with P(+) suggests its persistence in the films on the microsecond time scale.     

FLASH PHOTOLYSIS-ELECTRON SPIN RESONANCE STUDIES OF THE INTERACTION OF PHENAZINE METHOSULFATE WITH REACTION-CENTER PREPARATIONS FROM THE R-26 MUTANT OF RHODOPSEUDOMONAS SPHEROIDES*

Abstract— Using the technique of flash photolysis-electron spin resonance, we have shown, by means of a kinetic analysis, that phenazine methosulfate (PMS) interacts with reaction-center preparations from the blue-green mutant R26 of Rhodopseudomonas spheroides. At intermediate concentrations of PMS, biphasic decay kinetics of the P870⁺ ESR signal are observed demonstrating that the PMS radical interacts with reaction centers by a specific binding mechanism. With PMS bound to reaction centers, the P870⁺ ESR signal decays in ˜ 1 ms; whereas, in unbound reaction centers the decay is ˜ 120 ms. A model is proposed involving the interaction of PMS on the donor side of P870.     

纳米管钛酸的ESR特性及其可见光照的影响

本文报道了纳米管钛酸在真空-0.1MPa、温度100℃的条件下,经过不同时间处理后的ESR特性及其可见光照的影响.发现纳米管钛酸经一定处理后,不经光照即出现g=2.003ESR信号,该信号是由捕获一个电子的氧空位(V_o)产生的,此信号随着处理时间的延长而增强;在532nm的可见光照射下,随着光照时间的延长信号强度随之增加,达到一定强度值后,不再随光照时间的延长而增加;光源关闭后,信号强度又逐渐减小,但不能恢复到原来信号强度的水平.     

LIGHT QUENCHING OF FLUORESCENCE: A NEW METHOD TO CONTROL THE EXCITED STATE LIFETIME AND ORIENTATION OF FLUOROPHORES

Abstract Experimental studies have recently demonstrated that fluorescence emission can be quenched by laser light pulses from modem high-repetition rate lasers, a phenomenon we call “light quenching.” In this overview article, we describe the possible effects of light quenching on the steady-state and time-resolved intensity and anisotropy of fluorophores. One can imagine two classes of experiments. Light quenching can occur within the single excitation pulse, or light quenching can be accomplished with a second time-delayed quenching pulse. The extent of light quenching depends on the amplitude of the emission spectrum at the quenching wavelength. Different effects are expected for light quenching by a single laser beam (within a single laser pulse) or for a time-delayed quenching pulse. Depending upon the polarization of the light quenching beam, light quenching can decrease or increase the anisotropy. Remarkably, the light quenching can break the usual z-axis symmetry of the excited state population, and the measured anisotropy (or polarization) depends upon whether the observation axis is parallel or perpendicular to the propagation direction of the light quenching beam. The polarization can increase to unity under selected conditions. Quenching with time-delayed light pulses can result in step changes in the intensity or anisotropy, which is predicted to result in oscillations in the frequency-domain intensity and anisotropy decays. These predicted effects of light quenching, including oscillations in the frequency-domain data, were demonstrated to occur using selected fluorophores. The increasing availability and use of pulsed laser sources requires consideration of the possible effects of light quenching and offers the opportunity for a new class of two-pulse or multiple-pulse time-resolved experiments where the sample is prepared by the excitation pulse and subsequent quenching pulses to modify the excited state population, followed by time- or frequency-domain measurement of the optically prepared excited fluorophores.     

PHOTOREPAIR OF PYRIMIDINE DIMERS IN HUMAN SKIN IN VIVO

Abstract— The exposure of human skin in vivo to UV radiation emitted from a sunlamp induces the formation of pyrimidine dimers. The number of dimers, as detected by UV-endonuclease, decreases following exposure of the UV–irradiated skin to visible wavelengths of light. These results suggest that humans possess a mechanism by which pyrimidine dimers are photorepaired upon illumination of human skin in vivo with visible light.     

Pretreatment-induced redox processes in molybdena-alumina metathesis catalysts

The ESR investigation of MoO₃/Al₂O₃ metathesis catalysts was carried out and the results interpreted in relation to the previous XPS study [1]. The increase of the Mo(V) signal upon treatment with argon was attributed to the oxidation of ESR-silent Mo(IV) centers. The enhancement of Mo(V) signal upon exposure to propene at 303 K was assigned to the reduction of Mo(VI). This revised version was published online in June 2006 with corrections to the Cover Date.     

Origin of photoactivity of nitrogen-doped titanium dioxide under visible light

Nitrogen-doped titanium dioxide (N-TiO2), a photocatalytic material active in visible light, has been investigated by a combined experimental and theoretical approach. The material contains single-atom nitrogen impurities that form either diamagnetic (Nb-) or paramagnetic (Nb*) bulk centers. Both types of Nb centers give rise to localized states in the band gap of the oxide. The relative abundance of these species depends on the oxidation state of the solid, as, upon reduction, electron transfer from Ti3+ ions to Nb* results in the formation of Ti4+ and Nb-. EPR spectra measured under irradiation show that Nb centers are responsible for visible light absorption with promotion of electrons from the band gap localized states to the conduction band or to surface-adsorbed electron scavengers. These results provide a characterization of the electronic states associated with N impurities in TiO2 and, for the first time, a picture of the processes occurring in the solid under irradiation with visible light.     

An EPR study of two-electron sensitization by fragmentable electron donors

Fragmentable electron donors (FEDs) are molecules designed to undergo bond fragmentation after capturing the hole created by photoexposure of silver halide. By design, the radical remaining after fragmentation is a potent reductant expected to be capable of injecting an electron into the conduction band of the silver halide. Thus, the addition of a FED to the AgX surface should allow the creation of two electrons for each photon absorbed by the substrate. Photographic studies have confirmed that the addition of FEDs can increase the photosensitivity of AgX materials. In this work, EPR spectroscopy was employed to study the processes of hole capture, donor fragmentation, and secondary electron injection by FEDs in AgBr dispersions. To do so, we used AgBr microcrystals doped with diamagnetic transition metal complexes that act as deep electron traps. For samples exposed to actinic light at 15 K, secondary electron injection was detected as an increase in the EPR signal from electrons trapped at the dopant upon annealing the samples above 50 K. Organic radical intermediates and self-trapped hole centers were the other paramagnetic species monitored in this study. The results presented here confirm that the FED sensitization mechanisms originally proposed by Gould et al. take place at silver halide surfaces and result in additional electrons in the silver halide conduction band.     

Electron spin resonance studies on Ziegler-Natta type catalyst systems

Electron spin resonance spectra of Ziegler-Natta type catalyst systems (titanium trichloride and alkyl aluminums) have been studied. When triethylaluminum was added to titanium trichloride, an absorption with a g value of 1.96 was observed from the solid phase of the system. The number of spins of this signal is equal to that of the active centers for propylene polymerization. The solid phase from the mixture of titanium trichloride and diethylaluminum chloride also gives the same signal, which suggests the identity of the action of two alkyl aluminums on titanium trichloride surface. The signals obtained from the liquid phase of the both systems are all ascribed to the reaction products of the reaction of alkyl aluminum with titanium tetrachloride occluded in solid.     

EFFECT OF HUMIDITY ON PHOTOINDUCED ESR SIGNAL FROM HUMAN HAIR

Abstract— Human red hairs, equilibrated at 79.8%, 58.0%, 32.3% humidity and at dry conditions, were irradiated with UV-visible (Λ > 290 nm) light. ESR intensity of the photo-induced transient free radicals was measured, at room temperature, as a function of time during and after exposure to light. Photoenhancement was found to be most pronounced in 79.8%-humidity conditioned hair and least in dry hair. The lifetimes of the transient free radicals in these samples were measured as 360s (79.8%), 180s (58.0%), 140s (32.3%), and 50s (dry). The gradual increase in lifetime as a function of humidity conditions was attributed to an increasing number of decay rates of the centers varying from fast to slow, the slow ones being unable to decay unless the fast ones do. This process is best described by a stretched exponential time function, I ( t ) = I _oexp[-( t/t _o)^α].