Light-induced EPR spectra of reaction centers fromRhodobacter sphaeroides at 80 K: Evidence for reduction of QB by B branch electron transfer in native reaction centers

Photosynthetic reaction centers (RCs) fromRhodobacter sphaeroides capture solar energy by electron transfer from primary donor D to quinone acceptor Q_B through the active A branch of electron acceptors. The light-induced electron paramagnetic resonance (EPR) spectrum from native RCs that had Fe²⁺ replaced by Zn²⁺ was investigated at cryogenic temperature (80 K, 35 GHz). In addition to the light-induced signal due to the formation of D^+.Q _A ^?. observed previously, a small fraction (ca. 5%) of the signal displayed very different characteristics. The signal was absent in RCs in which the Q_B was displaced by the inhibitor stigmatellin. Its decay time (τ=6 s) was the same as observed for D^+.Q _B ^?. in mutant RCs lacking Q_A, which is significantly slower than for D^+.Q _A ^?. (τ=30 ms). Its EPR spectrum was identical to that of D^+.Q _B ^?. . The quantum efficiency for forming the major component of the signal was the same as that found for mutant RCs lacking Q_A (?=0.2%) and was temperature independent. These results are explained by direct photochemical reduction of Q_B via B branch electron transfer in a small fraction of native RCs.     

Synthesis,Characterization, and Antibacterial Activity of RE(III) Complexes with L-Isoleucine and 1,10-Phenanthroline

Six new ternary rare-earth (La, Eu, Sm, Nd, Y, Yb) complexes with L-isoleucine and 1,10-phenanthroline have been synthesized. Their compositions were characterized as RE(Ile)₃PhenCl₃ · 4H₂O (RE = La, Eu, Sm, Nd, Y, Yb; Ile = L-isoleucine; phen = 1,10-phenanthroline) by elemental analysis, EDTA titration, molar conductance measurement, UV spectra, FT-IR spectra, and TG-DTA. The average diameters of growth inhibition area and the minimal inhibitory concentration (MIC) of the complexes were studied by disc diffusion method and dilution method in nutrient broth. The results showed that the ternary rare-earth complexes strongly exhibited the antibacterial activity against Escherichia coli and Staphylococcus aureus and that their antibacterial effects were better than those of rare-earth chlorides, L-isoleucine, and 1,10-phenanthroline.     

A Model of spin catalysis in bacterial photosynthetic reaction centres

A model of influence of non-heme Fe²⁺ ion on kinetics of electron transfer between quinone anion-radicals Q_A⁻ and Q_B⁻ in bacterial reaction centres is proposed and investigated. Physical mechanism of the influence is associated with singlet-triplet transitions in Q_A⁻Q_B⁻ Pair caused by interactions with paramagnetic Fe²⁺. The model incorporates exchange couplings between the particles and zero-field splittings in high-spin Fe²⁺. These interactions are shown to catalyze electron transfer in triplet pairs and alter the reaction yield significantly.     

Photoluminescence of fluoroacrylate polymers impregnated with Eu(bta)<Subscript>3</Subscript> using supercritical CO<Subscript>2</Subscript>

Optical properties (photoluminescence and absorption) of Eu(bta)₃(B) _n (B = H₂O or 1,10-phenanthroline) polycrystalline powders and fluoroacrylate polymers (FAPs) impregnated with these compounds using supercritical CO₂ (SC CO₂) were investigated. It was established that impregnation of Eu(bta)₃phen into the FAPs using an SC CO₂ solution was difficult to achieve. The type of B (ancillary ligand) and the polymer matrix were shown to influence the temperature quenching of photoluminescence of Eu³⁺ ions in the range 25–100°C. A comparative analysis of quantum yields (λ_ex = 300 and 380 nm) and photoluminescence decay times (λ_ex = 337.1 nm) for Eu(bta)₃B _n and for Eu(bta)₃B _n -doped FAPs was performed.     

Photolysis of light-transforming polymer materials on the basis of europium(III) nitrate with 1,10-phenanthroline and anthranilic acid

Light-transforming polymer materials on the basis of europium(III) nitrate with 1,10-phenanthroline and anthranilic acid, having an intense luminescence in the 400–650 nm spectral range, were obtained. It is shown that the photostability of the polymer materials on the basis of the obtained compositions is higher than of polymer materials activated by europium(III) compounds. Luminescent and photochemical characteristics of the obtained polymer compositions are determined by the molar ratio of the dopants: the maximum luminescence intensity and photostability is characteristic for the polymeric material containing europium(III) nitrate with 1,10-phenanthroline and anthranilic acid at a molar ratio of 1: 2.     

Studies on the Fluorescence Fiber-Optic DNA Biosensor Using <Emphasis Type="Italic">p</Emphasis>-Hydroxyphenylimidazo[f]1,10-phenanthroline Ferrum(III) as Indicator

A complex Fe(phen)₂·PHPIP·3ClO₄·2H₂O, where phen = 1,10-phenanthroline and PHPIP = p-hydroxyphenylimidazo[f]1,10-phenanthroline, was synthesized and acted as a good fluorescence indicator based on its interaction with double-duplex DNA. Then a fiber-optic DNA biosensor of fluorimetric detection was developed based on the recognition of target DNA in DNA hybridization assays. A probe ssDNA was covalently immobilized onto the surface of quartz optical fibers and then the probe ssDNA hybridized with complementary ssDNA introduced into the local environment of the sensor. The hybridization with complementary strands was monitored in real time by fluorimetric detection. Several factors affecting the probe immobilization, target DNA hybridization, and indicator binding reactions were optimized to maximize the sensitivity and shorten the assay time. Using this method, a sequence of the 16-mer oligonucleotides could be quantified over the range from 4.98 × 10⁻⁷ to 4.88 × 10⁻⁶ M and a detection limit of 1.08 × 10⁻⁷ M. And the designed optic-fiber biosensor could be conveniently regenerated by thermal denature. The utility of the novel hybridization indicator could provide a simple, rapid, low toxicity and reusable detection.     

采用选择激发研究光系统Ⅱ反应中心β-Car的物理特性

光系统Ⅱ反应中心包含有2个去镁叶绿素分子(Pheo),2个β胡萝卜素分子(β-Car)和6个叶绿素a分子(Chla).对反应中心的时间分辨荧光光谱表明,两个β-Car具有不同的吸收光谱,吸收峰分别为489 nm(Car489)和507 nm(Car507),Car489靠近吸收峰为667 nm和675 nm的叶绿素a(Chl a),它的主要功能是保护反应中心免受单态氧的破坏,而不能将激发能传递给光化学反应活性的色素分子P680;Car507靠近吸收峰为669 nm的Chl a分子;能够将激发能传递给P680,进行电荷分离.采用全局优化拟合的方法对荧光光谱进行处理,Car489在61 ps时间内将能量传递给Chl a672, 随后传给Chl a677,处于激发态的Chl a677在3 ns衰减到基态;Car507在274 ps时间内将能量传递给P680,P680＋Pheo-的电荷重组发生在3.8 ns和16 ns.     

Spectral,luminescent, and electrochemical properties of cyclometalated complexes of Rh(III) based on 1-phenylpyrazole with ethylenediamine and heterocyclic diimines

A series of [Rh(ppz)₂(N^N)]⁺ complexes (ppz^? is the deprotonated form of 1-phenylpyrazole and (N^N) is ethylenediamine, 2,2′-bipyridyl, 1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, and 2,2′-biquinoline) is obtained and characterized by ¹H NMR spectroscopy, electronic absorption and emission spectroscopy, and cyclic voltamperometry. A 0.75-V anodic shift of the ligand-centered reduction potentials of complexes compared to free heterocyclic (N^N) ligands is observed. The vibrationally structured luminescence spectra of complexes are attributed to intraligand spin-forbidden optical transitions localized on the {Rh(N^N)} metal-complex fragments.     

Effect of mean-square amplitude of atomic vibrations on the creep behaviour of cubic crystals

Correlation between the activation energyQ of high-temperature creep and the Debye-Waller thermal parameterB, which is proportional to the mean-square amplitude of atomic vibrations, has been examined in the case of 17 faced-centred cubic, body-centred cubic and diamond-structure cubic elements. It is observed thatQ is a function ofB, irrespective of the crystal structure;Q decreases asB increases. The correlation is governed by the power-lawQ=Q ₀(B/B ₀) ^M0 , whereQ ₀=0.095eV andM ₀=−0.62 are numerical constants determined by least-squares fit method, and the constantB ₀=1 nm².     

Electrospinning fabrication and oxygen sensing properties of Cu(I) complex-polystyrene composite microfibrous membranes

In this paper, a phosphorescent Cu(I) complex of [Cu(POP)(ECI-Phen)]BF₄, where POP=bis[2-(diphenylphosphino)phenyl]ether, and ECI-Phen=1-ethyl-2-(N-ethyl-carbazole-yl-4-)imidazo[4,5-f]1,10-phenanthroline, is incorporated into a polystyrene matrix of polystyrene (PS) to form microfibers membranes. The possibility of using the resulted composite microfibrous membranes as an optical oxygen sensor is explored. Good linearity and short response time are obtained with a sensitivity of 9.8. These results suggest that phosphorescent [Cu(POP)(ECI-Phen)]BF₄ is a promising candidate for oxygen-sensors and PS is an excellent matrix for oxygen sensing material because it owns a large surface-area-to-volume ratio and can supply a homogeneous matrix for probe molecules. Further analysis suggests that the molecular structure of diamine ligand in Cu(I) complexes is critical for sensitivity due to the characteristic electronic structure of excited state Cu(I) complexes.