Illumination Of Complexes Research Articles

Mutation of a metal ligand stabilizes the high-spin form of the S2 state in the O2-producing Mn4CaO5 cluster of photosystem II.

The residue D1-D170 bridges Mn4 with the Ca ion in the O2-evolving Mn4CaO5 cluster of Photosystem II. Recently, the D1-D170E mutation was shown to substantially alter the Sn+1-minus-Sn FTIR difference spectra [Debus RJ (2021) Biochemistry 60:3841-3855]. The mutation was proposed to alter the equilibrium between different Jahn-Teller conformers of the S1 state such that (i) a different S1 state conformer is stabilized in D1-D170E than in wild-type and (ii) the S1 to S2 transition in D1-D170E produces a high-spin form of the S2 state rather than the low-spin form that is produced in wild-type. In this study, we employed EPR spectroscopy to test if a high-spin form of the S2 state is formed preferentially in D1-D170E PSII. Our data show that illumination of dark-adapted D1-D170E PSII core complexes does indeed produce a high-spin form of the S2 state rather than the low-spin multiline form that is produced in wild-type. This observation provides further experimental support for a change in the equilibrium between S state conformers in both the S1 and S2 states in a site-directed mutant that retains substantial O2 evolving activity.

ВИКОРИСТАННЯ ОПТОВОЛОКНА ЯК СКЛАДОВОЇ ЗАГАЛЬНОГО ЗОВНІШНЬОГО ОСВІТЛЕННЯДЛЯ СТВОРЕННЯ МАКСИМАЛЬНОГО РІВНЯ ЕНЕРГОЕФЕКТИВНОСТІ

Purpose. To develop a new lighting system for children's sports complexes. The introduction of the developed technology will improve the state of illumination of outdoor sports grounds without creating light pollution and increasing additional energy-efficient costs.Methodology. The combined technique of the technology of using two types of light sources, namely: low-power LED floodlights and optical fiber with a single light source, allows you to create an energy-efficient field illumination system. The proposed solution can be used for full illumination of street children's complexes. The selection of the parameters of the lighting system was carried out on the example of a real sports and children's complex.Findings. The performed measurements of the real parameters of the existing sports ground and taking into account its geometry allowed us to calculate the light parameters of light sources, select the appropriate materials and create a complete lighting model. A new lighting technology for sports and children's complexes has been developed, the level of lighting of sports facilities has been improved without creating light pollution.Originality. For the first time, a combined technology of illumination of sports and children's playgrounds was proposed using optical fiber and LED floodlights. The introduction of the developed technology will improve the state of illumination of such structures without creating an unnecessary light load on residents who are near the site. Moreover, such lighting will not lead to an increase in additional energy costs.Practical value. Today, most outdoor sports and entertainment venues are devoid of any lighting. The proposed complex solution can be used in any existing field lighting system. It is the most efficient and electrically safe because the optical fiber does not conduct electricity, but light. The light source itself can be located remotely and protected from vandals.

Artificial Illumination of Memorial Complexes Reconstruction and Creation of a New One

Memorial architecture is one of the most important resources for self-identification of society and the state. Recently, there has been a renewed interest of the population and tourists in memorial and museum complexes, and their attendance has increased. Old objects are being actively reconstructed, new ones are being built. The paper provides positive and negative examples of architectural illumination of memorial complexes. The techniques and means of lighting design are considered by the example of a number of reconstructed and newly created lighting installations.

Temperature Dependence of Light-Induced Absorbance Changes Associated with Chlorophyll Photooxidation in Manganese-Depleted Core Complexes of Photosystem II.

Mid-infrared (4500-1150 cm(-1)) absorbance changes induced by continuous illumination of Mn-depleted core complexes of photosystem II (PSII) from spinach in the presence of exogenous electron acceptors (potassium ferricyanide and silicomolybdate) were studied by FTIR difference spectroscopy in the temperature range 100-265 K. The FTIR difference spectrum for photooxidation of the chlorophyll dimer P680 was determined from the set of signals associated with oxidation of secondary electron donors (β-carotene, chlorophyll) and reduction of the primary quinone QA. On the basis of analysis of the temperature dependence of the P680(+)/P680 FTIR spectrum, it was concluded that frequencies of 13(1)-keto-C=O stretching modes of neutral chlorophyll molecules PD1 and PD2, which constitute P680, are similar to each other, being located at ~1700 cm(-1). This together with considerable difference between the stretching mode frequencies of keto groups of PD1(+) and PD2(+) cations (1724 and 1709 cm(-1), respectively) is in agreement with a literature model (Okubo et al. (2007) Biochemistry, 46, 4390-4397) suggesting that the positive charge in the P680(+) dimer is mainly localized on one of the two chlorophyll molecules. A partial delocalization of the charge between the PD1 and PD2 molecules in P680(+) is supported by the presence of a characteristic electronic intervalence band at ~3000 cm(-1). It is shown that a bleaching band at 1680 cm(-1) in the P680(+)/P680 FTIR spectrum does not belong to P680. A possible origin of this band is discussed, taking into account the temperature dependence (100-265 K) of light-induced absorbance changes of PSII core complexes in the visible spectral region from 620 to 720 nm.

Proteo-lipobeads for the oriented encapsulation of membrane proteins.

As a surrogate of live cells, proteo-lipobeads are presented, encapsulating functional membrane proteins in a strict orientation into a lipid bilayer. Assays can be performed just as on live cells, for example using fluorescence measurements. As a proof of concept, we have demonstrated proton transport through cytochrome c oxidase.

Quantum yield of P700+ photodestruction in isolated photosystem I complexes of the cyanobacteriumArthrospira platensis

The photostability of P700 cation radical (P700+) was studied by evaluating the quantum yields of P700(+) photodestruction in photosystem I (PSI) complexes of the cyanobacterium Arthrospira platensis. The time courses of P700+ photodestruction in PSI trimers and monomers have been measured in aerobic conditions under selective excitation of far-red absorption band of P700+ by intense light of laser diodes. Long-term exposure of PSI complexes to 808 or 870 nm laser light caused destruction of P700+ and antenna chlorophylls. The true integral quantum yield of P700+ photodestruction calculated from these data was less than 0.7-1.4 x 10(-8). Illumination of PSI complexes by 650 nm light caused destruction of antenna chlorophylls with true quantum yield of about 6-7 x 10(-6) and damage of P700 with apparent quantum yield 2-3 x 10(-8). Preferential photodestruction of the long-wavelength antenna chlorophyll absorbing at 710 nm as compared with bulk chlorophylls was observed. About three orders of difference in magnitude between quantum yields of P700+ and bulk chlorophyll photodestruction indicates that P700+ is extremely photostable for functioning as an efficient quencher of singlet excitation energy in PSI.

Peptide-Assembled Optically Responsive Nanoparticle Complexes

The design of active nanostructures whose form and properties can be modulated by remote means is an important challenge in nanoscience. Here we report two types of active nanoparticle complexes, with properties controlled by near-infrared illumination, resulting from the assembly of photothermally responsive plasmonic nanoparticles with thermally labile biomolecular linkers. Au nanoshells (NS) and quantum dots (QD) are assembled using coiled-coil peptides into NS-NS and NS-QD complexes. Illumination of the NS-NS complexes results in reversible disassembly reassembly, while illumination of NS-QD complexes results in a large, reproducible modulation of the quantum dot fluorescence without disassembly of the nanoparticle-peptide complex.

Charge separation in photosystem II core complexes induced by 690–730 nm excitation at 1.7 K

The illumination of oxygen-evolving PSII core complexes at very low temperatures in spectral regions not expected to excite P680 leads to charge separation in a majority of centers. The fraction of centers photoconverted as a function of the number of absorbed photons per PSII core is determined by quantification of electrochromic shifts on Pheo D1. These shifts arise from the formation of metastable plastoquinone anion (Q A −) configurations. Spectra of concentrated samples identify absorption in the 700–730 nm range. This is well beyond absorption attributable to CP47. Spectra in the 690–730 nm region can be described by the ‘trap’ CP47 absorption at 689 nm, with dipole strength of ∼1 chlorophyll a (chl a) , partially overlapping a broader feature near 705 nm with a dipole strength of ∼0.15 chl a. This absorption strength in the 700–730 nm region falls by 40% in the photoconverted configuration. Quantum efficiencies of photoconversion following illumination in the 690–700 nm region are similar to those obtained with green illumination but fall significantly in the 700–730 nm range. Two possible assignments of the long-wavelength absorption are considered. Firstly, as a low intensity component of strongly exciton-coupled reaction center chlorin excitations and secondly as a nominally ‘dark’ charge-transfer excitation of the ‘special pair’ P D1–P D2. The opportunities offered by these observations towards the understanding of the nature of P680 and PSII fluorescence are discussed.

Oxygen-evolving Photosystem II core complexes: a new paradigm based on the spectral identification of the charge-separating state, the primary acceptor and assignment of low-temperature fluorescence

We review our recent low-temperature absorption, circular dichroism (CD), magnetic CD (MCD), fluorescence and laser-selective measurements of oxygen-evolving Photosystem II (PSII) core complexes and their constituent CP 4 3, CP 47 and D1/D2/cytb(559) sub-assemblies. Quantitative comparisons reveal that neither absorption nor fluorescence spectra of core complexes are simple additive combinations of the spectra of the sub-assemblies. The absorption spectrum of the D1/D2/cytb(559) component embedded within the core complex appears significantly better structured and red-shifted compared to that of the isolated sub-assembly. A characteristic MCD reduction or 'deficit' is a useful signature for the central chlorins in the reaction centre. We note a congruence of the MCD deficit spectra of the isolated D1/D2/cytb(559) sub-assemblies to their laser-induced transient bleaches associated with P 680. A comparison of spectra of core complexes prepared from different organisms helps distinguish features due to inner light-harvesting assemblies and the central reaction-centre chlorins. Electrochromic spectral shifts in core complexes that occur following low-temperature illumination of active core complexes arise from efficient charge separation and subsequent plastoquinone anion (Q(A)(-)) formation. Such measurements allow determinations of both charge-separation efficiencies and spectral characteristics of the primary acceptor, Pheo(D1). Efficient charge separation occurs with excitation wavelengths as long as 700 nm despite the illuminations being performed at 1.7 K and with an extremely low level of incident power density. A weak, homogeneously broadened, charge-separating state of PSII lies obscured beneath the CP 47 state centered at 690 nm. We present new data in the 690-760 nm region, clearly identifying a band extending to 730 nm. Active core complexes show remarkably strong persistent spectral hole-burning activity in spectral regions attributable to CP 43 and CP 47. Measurements of homogeneous hole-widths have established that, at low temperatures, excitation transfer from these inner light-harvesting assemblies to the reaction centre occurs with approximately 70-270 ps(-1) rates, when the quinone acceptor is reduced. The rate is slower for lower-energy sub-populations of an inhomogeneously broadened antenna (trap) pigment. The complex low-temperature fluorescence behaviour seen in PSII is explicable in terms of slow excitation transfer from traps to the weak low-energy charge-separating state and transfer to the more intense reaction-centre excitations near 685 nm. The nature and origin of the charge-separating state in oxygen-evolving PSII preparations is briefly discussed.

Excited state properties of bis-tetraazaphenanthrene-Ru (II) diad complexes with a ferrocenyl unit

The excited state properties of the diad complexes Ru(tap) 2(ppFe) 2+ and Ru(bpy) 2(ppFc) 2+ (tap, 1,4,5,8-tetraazaphenanthrene; bpy, 2,2′-bipyridine), bearing a reducing ferrocenyl (Fe) centre on a derivatized (pyridine)pyrazole (pp) ligand, were compared with those of the corresponding complexes without an Fc unit. For these latter complexes, the existence of intermolecular photoelectron transfer with added ferrocene was clearly demonstrated. However, direct evidence for intramolecular photoelectron transfer in Ru(bpy) 2(ppFc) 2+ and Ru(tap) 2(ppFc) 2+ could not be obtained unambigously. Although the absence of luminescence in these diad complexes indicated the existence of this intramolecular process, laser flash photolysis did not allow the detection of a reduced complex entity in most experimental conditions. Only flash photolysis of Ru(bpy) 2(ppFc) 2+ in water generated a long-lived intermediate with the characteristics spectral features of the radical anion bpy −. Indirect arguments, such as the formation of a product on illumination of both diad complexes, were in favour of a photoreaction induced by intramolecular electron transfer.

Investigation of the differences in the local protein environments surrounding tyrosine radicals YZ. and YD. in photosystem II using wild-type and the D2-Tyr160Phe mutant of Synechocystis 6803.

The reaction center of photosystem II (PSII) of the oxygenic photosynthetic electron transport chain contains two redox-active tyrosines, Tyr160 (YD) of the D2 polypeptide and Tyr161 (YZ) of the D1 polypeptide, each of which may be oxidized by the primary electron donor, P680+. Spectroscopic characterization of YZ. has been hampered by the simultaneous presence of the much more stable YD., the short lifetime of YZ., and the difficulty in trapping the YZ. radical at low temperature. We present here a method for obtaining an uncontaminated YZ. radical, trapped by freezing under illumination of PSII core complexes isolated from YD-less mutants of Synechocystis 6803. Specific labeling with deuterium of the beta-methylene-3,3- or of the ring 3,5-protons of the PSII reaction center tyrosines in the YD-less D2-Tyr160Phe mutant results in a change in the hyperfine structure of the YZ. EPR signal, further confirming that this signal indeed arises from tyrosine. The trapped YZ. radical is also stable for several months at liquid nitrogen temperature. Due to both the absence of contaminating paramagnetic species and the stability at low temperature of YZ., this mutant core complex constitutes an excellent experimental system for the spectroscopic analysis of YZ.. We have compared the environments of YZ. and YD. by EPR, 1H ENDOR, and TRIPLE spectroscopies using both mutant and wild-type core complexes, with the following observations: (1) the EPR spectra of YZ. and YD. differ in line shape and line width. (2) Both YZ. and YD. exhibit D2O-exchangeable 1H hyperfine coupling near 3 MHz, consistent with the presence of a hydrogen bond from a proton donor to the phenolic oxygen atom of a neutral tyrosyl radical. This hyperfine coupling is sharp in the case of YD., indicating the hydrogen bond to be well-defined. In the case of YZ. it is broad, suggestive of a distribution of hydrogen-bonding distances. (3) YD. possesses three additional weak couplings that disappear in D2O, arising from three or fewer protons (protein or solvent) located within a shell between 4.5 and 8.5 A. (4) All of the 1H couplings of YD. are sharp, which is indicative of a well-ordered protein environment. (5) All of the 1H couplings in the YZ. spectrum are broad. The environment surrounding YZ. appears to be more disordered and solvent-accessible.

Efficient energy transfer from the long-wavelength antenna chlorophylls to P700 in photosystem I complexes from Spirulina platensis

To study the role of the long-wavelength chlorophylls (Chl) in photosystem I (PSI), the action spectra of P700 photooxidation at 293 and 77 K have been measured for PSI trimeric and monomeric complexes isolated from Spirulina platensis. The long-wavelength Chls which absorb in the region 710dash740 nm transfer excitation energy to the reduced P700 with the same efficiency as bulk antenna Chls, causing the oxidation of P700. The relative quantum yield of P700 photooxidation is about unity (293-77 K) even under the direct excitation of Chl absorbing at 735 nm (Chl735). At 77 K Chl735 exhibits a fluorescence band at 760 nm (F760) whose intensity is quenched under illumination of the PSI trimeric complexes from Spirulina. The relative quantum yield of F760 quenching is not dependent on the wavelength of excitation in the region 620–750 nm. Since the value of the overlap integral between the band of F760 and the absorption band of the cation radical of P700 (P700 +) is higher than that of the P700 band, it is suggested that Chl735 transfers energy to P700 + more efficiently than to reduced P700; energy transfer to P700 + causes the quenching of F760. A linear relationship between the photooxidation rate of P700 and the fraction of P700 + at 293 K indicates that the energy exchange between PSI subunits of the trimer is negligible. Thus, the antenna of PSI trimers of Spirulina is organized in separate photosynthetic units.

Investigation of the neighbour relationships between photosystem II polypeptides in the two types of isolated reaction centres (D1/D2/cyt b559 and CP47/D1/D2/cyt b559 complexes)

The nearest neighbour relationships within the D1/D2/cyt b 559 complex (PSIIRC) and the CP47/D1/D2/cyt b 559 complex (RC-CP47) were investgated by using different length bifunctional crosslinking agents. The crosslinking products were identified by immunoblotting with polyclonal antibodies and by two-dimensional gel electrophoresis. Seven products (CP47/D2, D1/D2/α, D1/D2, D2/α, D1/α, α/αa, α/β) have been revealed in both complexes. The crosslinking of both complexes does not increase their photostability. The photocrosslinking products (D1/α and D2/α) appeared under illumination of complexes with light of high intensity.

Time resolved studies of the photoinduced electron transfer in aqueous solutions of chloro- and cyanocuprate(I) complexes

Laser flash and continuous photolysis studies of equilibrated solutions of CuCl − 2CuCl −3 2, Cu(CN) − 2Cu(CN) 3 2− and Cu(CN) − 2Cu(CN) 2Cl 2− systems were carried out in the UV region. Neutral aqueous solutions of the complexes produce hydrated electrons when they absorb pulses of laser light at 266 nm. The electrons are scavenged by the ground-state copper(I) species itself. The second-order rate constants of these reactions are determined at various ionic strengths and concentrations. Illumination of chlorocuprate complexes in strong acidic media leads to formation of hydrogen (H 2) via electron scavenging by H +. In solutions of cyanocuprates, methylviologen (MV 2+) was added to scavenge the electron in a reaction resulting in a reducing intermediate MV .+. The formation of an oxidizing intermediate is demonstrated using NO 3 − and N 2O as electron scavengers. Continuous photolysis of the complexes reveals the dependence of quantum yield on concentration of Cl − ligand in CuCl 2 −CuCl 3 2− and Cu(CN) 2 −Cu(CN) 2Cl 2− systems, and the action spectra of Cu(CN) 2 − and Cu(CN) 2Cl 2− indicate an efficient excitation band at 265 nm for both complexes (the quantum yields are 0.37 and 0.21 respectively).

Interaction of rabbit hemopexin with rose bengal and photooxidation of the rose bengal-hemopexin complex

Rabbit hemopexin associates with rose bengal producing a hypochromic shift in the absorption spectrum of the dye; the extinction coefficient of the dye bound to heme-saturated hemopexin is approximately 20% lower than that of the dye bound to the apoprotein. The interaction of apo- and heme-saturated hemopexin with rose bengal was studied in detail by difference spectroscopy. Apo-hemopexin has one tight binding site for the dye with a dissociation constant in the micromolar range and a set of several weaker binding sites. In contrast, heme-saturated hemopexin has a very low affinity for the dye. Evidence that histidine residues of hemopexin participate in the binding of heme was obtained by photooxidation of hemopexin sensitized by rose bengal. Progressive modification of the 16 histidine residues of hemopexin is effected by illumination of the dye-hemopexin complexes. The midpoint of this pH-dependent reaction is at pH 6.8 +/- 0.1. In 15 min of irradiation, apo-hemopexin loses 50% of its ability to form a low spin hemichrome complex with deuteroheme while only 10% of the ligand coordination to heme iron of the deuteroheme-hemopexin is lost. At that time, approximately 2 more histidine residues are modified in apo-hemopexin than in deuteroheme-hemopexin, and no change is found in other potentially photolabile amino acid residues. The characteristic circular dichroism positive extremum at 231 nm of hemopexin also was decreased by photooxidation, and the loss was slower in the deuteroheme-hemopexin complex than in the apoprotein. When deuteroporphyrin IX was used as the photosensitizing agent, similar results were obtained.