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.     

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.     

Luminescence-Based Oxygen Sensors: ReL(CO)3Cl and ReL(CO)3CN Complexes on Copolymer Supports

A new class of luminescent rhenium complexes has been tested as oxygen sensors based on luminescent quenching. ReL(CO)₃Cl and ReL(CO)₃CN (L = 2,2-bipyridine or 1,10-phenanthroline and substituted analogues) have several features that seem to indicate suitability as oxygen sensors. These include simple synthesis, long excited-state lifetimes, and high luminescence quantum yields. Intensity and lifetime oxygen quenching measurements were used to study the complexes in various polymer supports including homopolymers of PDMS (polydimethylsiloxane), a methacryloxy containing PDMS (Gp-163), and trimethylsilylmethylmethacrylate (T3642), and copolymers containing Gp-163 and T3642. In contrast to previous studies utilizing [Ru(4,7-diphenyl-1,10-phenanthroline)₃]²⁺ as an oxygen sensor, quenching of the Re complexes proved much more sensitive to the polymer support. With suitable supports, the rhenium chloro complexes demonstrated significant quenching; but the cyano complexes, in spite of being robust in solution, exhibited severe photochemical instability in polymers. The potential of this class of complexes as oxygen sensors and as molecular probes as well as the ramifications in the design of new and different types of sensors is discussed.     

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.     

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.     

Some structural features of MoO3-1,10-phenanthroline intercalation compounds

Three MoO₃-1,10-phenanthroline intercalation compounds were synthesized at room temperature, by suspending α-MoO₃ in a water-ethanol solution of 1,10-phenanthroline. The obtained hybrid matrices were characterized by elemental analysis, infrared spectroscopy, thermogravimetry, X-ray diffractometry and scanning electron microscopy. Based on X-ray diffraction data, can be verified that ate two possible orientations of 1,10-phenanthroline into MoO₃ interlayer space: an orientation to allow the interaction of the nitrogen atoms with the acidic Lewis sites on the oxide surface and another orientation to allow the interaction of the π electrons with such sites The SEM micrographs show that as the 1,10-phenanthroline total amount is increased, there is a progressive exfoliation of the oxide grains, resulting in the total disruption of the initial platy morphology.     

ESEEM study of the location of spin-polarized chlorophyll-quinone radical pair in membrane-oriented spinach photosystems I and II complexes

Light-induced spin-polarized radical pairs, P700⁺A₁ ^? in spinach photosystem (PS) I particles and P680⁺Q_A ^? in Zn-substituted PS II core complexes, in oriented membranes were studied by pulsed electron paramagnetic resonance (EPR). Based on the determined distance of 25.2 ± 0.2 Å between P700 and A₁, the angular dependence of the spin-polarized electron spin echo envelope modulation (ESEEM) spectra on the magnetic field suggests that the angle between $R_{P700 - {\rm A}_1 } $ , the radius-vector connecting P700 and A₁, and the membrane normaln was 24 ± 4° in PS I particles. Obtained angle and distance of P700-A₁ axis suggested Q_K side in the molecular geometry of cofactors presented in a recent X-ray crystallography of cyanobacterial PS I reaction center to be an active branch of electron transfer. The distance between P680 and Q_A was determined to be 27.4 ± 0.3 Å for a nonoriented PS II. The angle between $R_{P680 - Q_{\rm A} } $ , the radius-vector connecting P680 and Q_A, andn was determined to be 21 ± 5°. The angle of P680-Q_A axis was close to that of 20° of P870-Q_A axis reported in X-ray analysis of the purple bacterial reaction center crystal.     

Photosynthetic electron transport in the cyanobacteriumSynechocystis sp. PCC 6803: High-Field W-band and X-band EPR study of electron flow through photosystem I

In this work, by using the respective advantages of W- and X-band electron paramagnetic resonance (EPR) spectroscopy techniques to investigate electron transport processes, we have studied the light-induced redox transients of the primary electron donor P₇₀₀ and the secondary acceptor A₁ in photosystem (PS) I complexes of intact cyanobacterial cellsSynechocystis sp. PCC 6803. We found that the kinetic behavior of the cation radical P₇₀₀ ^·+ generated by illumination with continuous light, and the EPR intensity of the radical pair P₇₀₀ ^·+A ₁ ^·? generated upon laser pulse illumination strongly depend on the illumination prehistory (either the sample was frozen in the dark or during illumination). Both these processes were sensitive to the presence of electron transport inhibitors which block electron flow between the two photosystems. In line with our X-band EPR data on the kinetics of light-induced redox transients of P₇₀₀, our high-field W-band EPR study of the radical-pair state P₇₀₀ ^·+A ₁ ^·? shows that photosynthetic electron flow through the PS I reaction center is controlled both on the donor and on the acceptor side of PS I.     

Singlet Oxygen Quantum Yield Determination for a Fluorene-Based Two-Photon Photosensitizer

The quantum yield, Φ_Δ, of singlet oxygen generation under two-photon excitation has been determined for a fluorene derivative. A photochemical method was developed using 1,3-diphenylisobenzofuran (DPBF), a chemical quencher of ¹O₂, and 2-(9,9-didecyl-7-nitrofluoren-2-yl)benzothiazole (1) as a two-photon photosensitizer (PS). The photochemical kinetics of the quencher was measured by two different fluorescence methods. Fluorene 1 exhibited relatively high singlet oxygen quantum yield, Φ_Δ ≈ 0.4 ± 0.1, and had a two-photon absorption cross-section of 28 ± 5 GM. Thus, 1 may have potential for use as a two-photon PS in the near-IR spectral region for biomedical applications.     

Optical and electrochemical properties of cyclometalated Rh(III) complexes based on 4,6-diphenylpyrimidine with ethylenediamine, 2,2′-bipyridyl,and 1,10-phenanthroline

The [Rh(Hdp)₂(N∧N)]ClO₄ complexes (Hdp⁻ is the monodeprotonated form of 4,6-diphenylpyrimidine and (N∧N) is ethylenediamine, 2,2′-bipyridyl, and 1,10-phenanthroline) are synthesized and characterized by ¹H and ¹³C NMR, IR, electronic absorption, and emission spectroscopy, as well as by cyclic voltammetry. The magnetic equivalence of two cyclometalated 4,6-diphenylpyrimidine ligands in the composition of complexes points to the cis position of metalated phenyl rings in the inner sphere. Quasi-reversible one-electron reduction waves are attributed to the ligand-centered electron transfer to the π* antibonding orbital of heterocyclic ligands, while irreversible oxidation waves are associated with electron detachment from the Rh-C σ bonding orbital of the {Rh(Hdp)₂} metal-complex fragment. The characteristic long-wave-length absorption bands and the vibrationally structured phosphorescence bands of complexes are assigned to the spin-allowed and spin-forbidden charge-transfer optical transitions between the σ_Rh-C and π_Hdp* orbitals localized on the {Rh(Hdp)₂} fragment of the complex.     

A simple 1,10-phenanthroline-based fluorescent receptor in solution and 1,10-phenanthroline in solid state for urea recognition

1,10-phenanthroline-based fluorescent chemosensor has been designed and synthesized for the recognition of urea and 1,3-dimethyl urea in CH₃CN. Interactions of this compound with urea and 1,3-dimethyl urea are studied with UV-visible and fluorescence spectroscopic methods. 1,10-phenanthroline was found to be capable of distinguishing urea from 1,3-dimethyl urea. The formation of a highly stable hydrogen bonded complex between 1,10-phenanthroline and urea was confirmed by single crystal X-ray diffraction analysis.     

Calculations of derivatives of porphin and porphyrazine with an annulated five-membered heteroaromatic ring using a modified INDO method

Quantum-chemical calculations for series of porphin (H₂P) and porphyrazine (H₂PA) derivatives whose molecules contain a 3,4-annulated five-membered heteroaromatic ring of pyrrole, furan, and thiophene as well as 1,2,5-triazole, 1,2,5-oxadiazole, and 1,2,5-thiadiazole have been carried out by the AM1 and INDO/Sm methods (m means “modified parametrization”). As follows from the unrestricted Hartree-Fock AM1 calculations, the ground state energy of the a isomer is lower than that of the b isomers for all compounds, the a and b isomers being NH isomers with the additional five-membered ring fused to a pyrrolenine or pyrrole ring, respectively. Condensation of the five-membered ring for the b isomers of the H₂P derivatives is shown to extend the main conjugation path from 18-membered to 21-membered cyclopolyene. However, the 18-membered cyclopolyene for the a isomers of the H₂P derivatives and 16-membered cyclopolyene for both isomers of the H₂PA derivatives prove to be isolated from the five-membered ring carrying six π-electrons. Based on INDO/Sm computations of electronic absorption spectra of the H₂P and H₂PA derivatives, it is shown that the Q_x level of the a isomers is sensitive to the nature of the annulated ring whereas the Q_y level is practically not shifted. On the contrary, the Q_x level of the b isomers is relatively insensitive to the nature of the annulated ring while the Q_y level decreases monotonously in the H₂P and H₂PA series, being the first excited state level for the majority of the derivatives (X is along the NH-HN axis; Y, perpendicular to it). The electronic absorption spectra at the border of the visible and near-UV regions are determined mainly by two high-intensity G → B_x and G → B_y transitions for the H₂P derivatives. However, four intense G → B_x, G → B_y, G → N_x, and G → N_y transitions are characteristic of the spectra of the H₂PA derivatives. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 606–622, September–October, 2008.     

Ionic photoconductivity of RbAg4I5 superionic crystals

A new effect of illumination on ionic conductivity and activation energy of migration of mobile Ag⁺ cations in RbAg₄I₅ superionic crystals has been detected and studied. Reversible changes in the ionic conductivity due to illumination of superionic crystals are caused by reversible changes in the structure of electronic centers caused by elastic strain around these centers. The effect of elastic deformation on the process of ionic transport and activation energy for diffusion of mobile silver cations has been studied. Photostimulated recovery of the ionic conductivity after its change due to preliminary illumination of a RbAg₄I₅ superionic crystal with light of wavelength λ≃430 nm has been detected. This recovery of the ionic conductivity is due to excitation of centers in complexes generated by previous illumination of tested samples. Zh. éksp. Teor. Fiz. 112, 698–706 (August 1997)     

Does color confinement imply massive gluons?

Color confinement is one of the central issues in QCD, and there are various interpretations of this feature. In this paper we have adopted the interpretation that colored particles cannot be observed just because colored states are unphysical in the sense of Q_B|quark〉≠0, Q_B|gluon〉≠0. It is shown that there are two phases in QCD distinguished by different choices of the gauge parameter. In one phase, called the “confinement phase,” color confinement is realized and gluons are no longer massless. In the other phase, called the “deconfinement phase,” color confinement is not realized, but the gluons remain massless.