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Phycobilisome (PBS) structures are elaborate antennae in cyanobacteria and red algae 1,2 . These large protein complexes capture incident sunlight and transfer the energy through a network of embedded pigment molecules called bilins to the photosynthetic reaction centres. However, light harvesting must also be balanced against the risks of photodamage. A known mode of photoprotection is mediated by orange carotenoid protein (OCP), which binds to PBS when light intensities are high to mediate photoprotective, non-photochemical quenching 3-6 . Here we use cryogenic electron microscopy to solve four structures of the 6.2 MDa PBS, with and without OCP bound, from the model cyanobacterium Synechocystis sp. PCC 6803. The structures contain a previously undescribed linker protein that binds to the membrane-facing side of PBS. For the unquenched PBS, the structures also reveal three different conformational states of the antenna, two previously unknown. The conformational states result from positional switching of two of the rods and may constitute a new mode of regulation of light harvesting. Only one of the three PBS conformations can bind to OCP, which suggests that not every PBS is equally susceptible to non-photochemical quenching. In the OCP-PBS complex, quenching is achieved through the binding of four 34 kDa OCPs organized as two dimers. The complex reveals the structure of the active form of OCP, in which an approximately 60 Å displacement of its regulatory carboxy terminal domain occurs. Finally, by combining our structure with spectroscopic properties 7 , we elucidate energy transfer pathways within PBS in both the quenched and light-harvesting states. Collectively, our results provide detailed insights into the biophysical underpinnings of the control of cyanobacterial light harvesting. The data also have implications for bioengineering PBS regulation in natural and artificial light-harvesting systems., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Oximes are valuable synthetic intermediates for the preparation of a variety of functional groups. To date, the stereoselective synthesis of oximes remains a major challenge, as most current synthetic methods either provide mixtures of E and Z isomers or furnish the thermodynamically preferred E isomer. Herein we report a mild and general method to achieve Z isomers of aryl oximes by photoisomerization of oximes via visible-light-mediated energy transfer (EnT) catalysis. Facile access to ( Z )-oximes provides opportunities to achieve regio- and chemoselectivity complementary to those of widely used transformations employing oxime starting materials. We show an enhanced one-pot protocol for photocatalyzed oxime isomerization and subsequent Beckmann rearrangement that enables novel reactivity with alkyl groups migrating preferentially over aryl groups, reversing the regioselectivity of the traditional Beckmann reaction. Chemodivergent N - or O - cyclizations of alkenyl oximes are also demonstrated, leading to nitrones or cyclic oxime ethers, respectively.

Photosystem I (PS I) is a transmembrane protein that assembles perpendicular to the membrane, and performs light harvesting, energy transfer, and electron transfer to a final, water-soluble electron acceptor. We present here a supramolecular model of it formed by a bicationic oligofluorene 1 2+ bound to the bisanionic photoredox catalyst eosin Y (EY 2- ) in phospholipid bilayers. According to confocal microscopy, molecular modeling, and time dependent density functional theory calculations, 1 2+ prefers to align perpendicularly to the lipid bilayer. In presence of EY 2- , a strong complex is formed (K a =2.1±0.1×10 6  m -1 ), which upon excitation of 1 2+ leads to efficient energy transfer to EY 2- . Follow-up electron transfer from the excited state of EY 2- to the water-soluble electron donor EDTA was shown via UV-Vis absorption spectroscopy. Overall, controlled self-assembly and photochemistry within the membrane provides an unprecedented yet simple synthetic functional mimic of PS I., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Photosynthesis and respiration rates, pigment contents, CO 2 compensation point, and carbonic anhydrase activity in Cyanidioschizon merolae cultivated in blue, red, and white light were measured. At the same light quality as during the growth, the photosynthesis of cells in blue light was significantly lowered, while under red light only slightly decreased as compared with white control. In white light, the quality of light during growth had no effect on the rate of photosynthesis at low O 2 and high CO 2 concentration, whereas their atmospheric level caused only slight decrease. Blue light reduced markedly photosynthesis rate of cells grown in white and red light, whereas the effect of red light was not so great. Only cells grown in the blue light showed increased respiration rate following the period of both the darkness and illumination. Cells grown in red light had the greatest amount of chlorophyll a, zeaxanthin, and β-carotene, while those in blue light had more phycocyanin. The dependence on O 2 concentration of the CO 2 compensation point and the rate of photosynthesis indicate that this alga possessed photorespiration. Differences in the rate of photosynthesis at different light qualities are discussed in relation to the content of pigments and transferred light energy together with the possible influence of related processes. Our data showed that blue and red light regulate photosynthesis in C. merolae for adjusting its metabolism to unfavorable for photosynthesis light conditions.

The importance of green light for driving natural photosynthesis has long been underappreciated, however, under the presence of strong illumination, green light actually drives photosynthesis more efficiently than red light. This green light is absorbed by mixed vibronic Q y -Q x states, arising from chlorophyll (Chl)-Chl interactions, although almost nothing is known about these states. Here, we employ polarization-dependent two-dimensional electronic-vibrational spectroscopy to study the origin and dynamics of the mixed vibronic Q y -Q x states of light-harvesting complex II. We show the states in this region dominantly arise from Chl b and demonstrate how it is possible to distinguish between the degree of vibronic Q y versus Q x character. We find that the dynamics for states of predominately Chl b Q y versus Chl b Q x character are markedly different, as excitation persists for significantly longer in the Q x states and there is an oscillatory component to the Q x dynamics, which is discussed. Our findings demonstrate the central role of electronic-nuclear mixing in efficient light-harvesting and the different functionalities of Chl a and Chl b.

Some cyanobacteria remodel their photosynthetic apparatus by a process known as Far-Red Light Photoacclimation (FaRLiP). Specific subunits of the phycobilisome (PBS), photosystem I (PSI), and photosystem II (PSII) complexes produced in visible light are replaced by paralogous subunits encoded within a conserved FaRLiP gene cluster when cells are grown in far-red light (FRL; λ = 700-800 nm). FRL-PSII complexes from the FaRLiP cyanobacterium, Synechococcus sp. PCC 7335, were purified and shown to contain Chl a, Chl d, Chl f, and pheophytin a, while FRL-PSI complexes contained only Chl a and Chl f. The spectroscopic properties of purified photosynthetic complexes from Synechococcus sp. PCC 7335 were determined individually, and energy transfer kinetics among PBS, PSII, and PSI were analyzed by time-resolved fluorescence (TRF) spectroscopy. Direct energy transfer from PSII to PSI was observed in cells (and thylakoids) grown in red light (RL), and possible routes of energy transfer in both RL- and FRL-grown cells were inferred. Three structural arrangements for RL-PSI were observed by atomic force microscopy of thylakoid membranes, but only arrays of trimeric FRL-PSI were observed in thylakoids from FRL-grown cells. Cells grown in FRL synthesized the FRL-specific complexes but also continued to synthesize some PBS and PSII complexes identical to those produced in RL. Although the light-harvesting efficiency of photosynthetic complexes produced in FRL might be lower in white light than the complexes produced in cells acclimated to white light, the FRL-complexes provide cells with the flexibility to utilize both visible and FRL to support oxygenic photosynthesis. This article is part of a Special Issue entitled Light harvesting, edited by Dr. Roberta Croce., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Changes in the light energy distribution between the photosystems 1 and 2 (PS1 and PS2, respectively) due to the reversible migration of a part of the light-harvesting complex (LHC2) between the photosystems (state transitions, ST) have been studied in leaves of barley (Hordeum vulgare) and Arabidopsis thaliana plants upon short-term illumination with light of various intensity that excited predominantly PS2. Changes in the ratio of fluorescence maxima at 745 and 685 nm in the low-temperature (77 K) fluorescence spectrum of chlorophyll a (Chl a) characterizing energy absorption by the PS1 and PS2, respectively, were insufficient for revealing the differences in the STs in barley and Arabidopsis plants at various light intensities, because they were not associated with STs at high-intensity illumination. Light-induced accumulation of the LHC2 phosphorylated proteins Lhcb1 and Lhcb2 involved in the relocation of a part of the LHC2 from PS2 to PS1 in the leaves of both plants decreased with the increase in the light intensity and was more pronounced in barley than in Arabidopsis at the same light intensity. Relaxation of the non-photochemical quenching (NPQ) of Chl a fluorescence after illumination corresponding to the return of the part of LHC2 from PS1 to PS2 was observed in barley leaves in a wider range of increasing light intensities than in Arabidopsis leaves. The differences in the accumulation of phosphorylated Lhcb1 and Lhcb2, as well as in the parameters of NPQ relaxation after illumination, revealed that STs in barley leaves could occur not only at low-but also at high-intensity light, when it is absent in Arabidopsis leaves.

Under a 980-nm excitation, the up-conversion (UC) spectra of LuNbO 4 :Yb 3+ ,Tm 3+ powders exhibited predominantly near-infrared bands (~805 nm) of Tm 3+ through an energy transfer process from Yb 3+ to Tm 3+ . Regarding the down-conversion (DC) luminescence of the powders, the photoluminescence excitation spectra consisted of a broad charge transfer band (270 nm) due to [NbO 4 ] 3- and sharp band (360 nm) of Tm 3+ , while the corresponding emission spectra exhibited a blue emission at 458 nm. Upon substitution of Ga 3+ and Ta 5+ for Lu 3+ and Nb 5+ , respectively, both UC and DC luminescence properties were significantly enhanced. For the Ga 3+ substitution, the increased emission intensity could be explained by the crystal field asymmetry surrounding the Tm 3+ ions induced by the large difference in ionic radius between Ga 3+ and Lu 3+ . For the Ta 5+ substitution, we believe that an M'-LuTaO 4 substructure was formed in the host, which led to the formation of a TaO 6 octahedral coordination instead of a NbO 4 tetrahedral coordination. Consequently, the crystal symmetry of the local structure was modified, and thus the UC and DC luminescence properties were enhanced. The dual-mode (UC and DC) luminescence demonstrates that LuNbO 4 :Yb 3+ ,Tm 3+ has a great potential in the fields of temperature sensing probes, anti-counterfeiting, and bioapplications., (© 2019 John Wiley & Sons, Ltd.)

Dual-emissive systems showing color-specific photoswitching are promising in bioimaging and super-resolution microscopy. However, their switching efficiency has been limited because a delicate manipulation of all the energy transfer crosstalks in the systems is unfeasible. Here, we report a perfect color-specific photoswitching, which is rationally designed by combining the complete off-to-on fluorescence switching capability of a fluorescent photochromic diarylethene and the frustrated energy transfer to the other fluorescent dye based on the excited-state intramolecular proton transfer (ESIPT) process. Upon alternation of UV and visible light irradiations, the system achieves 100% switching on/off of blue emission from the diarylethene while orange emission from the ESIPT dye is unchanged in the polymer film. By fabricating this system into biocompatible polymer nanoparticles, we demonstrate microscopic imaging of RAW264.7 macrophage cells with reversible blue-color specific fluorescence switching that enables super-resolution imaging with a resolution of 70 nm.

Design and engineering of highly efficient light-harvesting nanomaterial systems to emulate natural photosynthesis for maximizing energy conversion have stimulated extensive efforts. Here we present a new class of photoactive semiconductor nanocrystals that exhibit high-efficiency energy transfer for enhanced photocatalytic hydrogen production under visible light. These nanocrystals are formed through noncovalent self-assembly of In(III) meso-tetraphenylporphine chloride (InTPP) during microemulsion assisted nucleation and growth process. Through kinetic control, a series of uniform nanorods with controlled aspect ratio and high crystallinity have been fabricated. Self-assembly of InTPP porphyrins results in extensive optical coupling and broader coverage of the visible spectrum for efficient light harvesting. As a result, these nanocrystals display excellent photocatalytic hydrogen production and photostability under the visible light in comparison with the commercial InTPP porphyrin powders.

Oxygenic photosynthetic organisms perform photosynthesis efficiently by distributing captured light energy to photosystems (PSs) at an appropriate balance. Maintaining photosynthetic efficiency under changing light conditions requires modification of light-harvesting and energy-transfer processes. In the current study, we examined how green algae regulate their light-harvesting functions in response to different light qualities. We measured low-temperature time-resolved fluorescence spectra of unicellular green algae Chlamydomonas reinhardtii and Chlorella variabilis cells grown under different light qualities. By observing the delayed fluorescence spectra, we demonstrated that both types of green algae primarily modified the associations between light-harvesting chlorophyll protein complexes (LHCs) and PSs (PSII and PSI). Under blue light, Chlamydomonas transferred more energy from LHC to chlorophyll (Chl) located far from the PSII reaction center, while energy was transferred from LHC to PSI via different energy-transfer pathways in Chlorella. Under green light, both green algae exhibited enhanced energy transfer from LHCs to both PSs. Red light induced fluorescence quenching within PSs in Chlamydomonas and LHCs in Chlorella. In Chlorella, energy transfer from PSII to PSI appears to play an important role in balancing excitation between PSII and PSI.

The ordered structure of UV chromophores in DNA resembles photosynthetic light-harvesting complexes in which quantum coherence effects play a major role in highly efficient directional energy transfer. The possible role of coherent excitons in energy transport in DNA remains debated. Meanwhile, energy transport properties are greatly important for understanding the mechanisms of photochemical reactions in cellular DNA and for DNA-based artificial nanostructures. Here, we studied energy transfer in DNA complexes formed with silver nanoclusters and with intercalating dye (acridine orange). Steady-state fluorescence measurements with two DNA templates (15-mer DNA duplex and calf thymus DNA) showed that excitation energy can be transferred to the clusters from 21 and 28 nucleobases, respectively. This differed from the DNA-acridine orange complex for which energy transfer took place from four neighboring bases only. Fluorescence up-conversion measurements showed that the energy transfer took place within 100 fs. The efficient energy transport in the Ag-DNA complexes suggests an excitonic mechanism for the transfer, such that the excitation is delocalized over at least four and seven stacked bases, respectively, in one strand of the duplexes stabilizing the clusters. This result demonstrates that the exciton delocalization length in some DNA structures may not be limited to just two bases.

Applicability of phototherapeutic CO-releasing molecules (photoCORMs) is limited because they are activated by harmful and poorly tissue-penetrating near-ultraviolet light. Here, a strategy is demonstrated to activate classical photoCORM Mn 2 (CO) 10 using red light (635 nm). By mixing in solution a triplet photosensitizer (PS) with the photoCORM and shining red light, energy transfer occurs from triplet excited-state 3 PS* to a photolabile triplet state of Mn 2 (CO) 10 , which, like under near-UV irradiation, led to complete release of carbonyls. Crucially, such "triplet-sensitized CO-release" occurred in solid-state materials: when PS and Mn 2 (CO) 10 were embedded in electrospun nonwoven fabrics, CO was liberated upon irradiation with low-intensity red light (≤36 mW 635 nm).

Herein, we present the intramolecular [2+2] cycloadditions of dienones promoted through sensitization, using a polypyridyl iridium(III) catalyst, to form bridged cyclobutanes. In contrast to previous examples of straight [2+2] cycloadditions, these efficient crossed additions were achieved under irradiation with visible light. The reactions delivered desired bridged benzobicycloheptanone products with excellent regioselectivity in high yields (up to 96%). This process is superior to previous syntheses of benzobicyclo[3.1.1]heptanones, which are readily converted to B-norbenzomorphan analogues of biological significance. Electrochemical, computational, and spectroscopic studies substantiated the mechanism of triplet energy transfer and explained the unusual regiocontrol.

Purpose: To simulate the deceleration processes of secondary electrons produced by a high-energy Auger electron in water, and particularly to focus on the spatial and temporal distributions of the secondary electron and the collision events (e.g. ionization, electronic excitation, and dissociative electron attachment) that are involved in the multiplication of lesions at sites of DNA damage., Materials and Methods: We developed a dynamic Monte Carlo code that considers the Coulombic force between an ejected electron and its parent cation produced by the Auger electron in water. Thus our code can simulate some return electrons to the parent cations. Using the code, we calculated to within the order of femtoseconds the temporal evolution of collision events, the mean energy, and the mean traveling distance (including its spatial probability distribution) of the electron at an ejected energy of 20 eV., Results: Some of the decelerating electrons in water in the Coulombic field were attracted to the ionized atoms (cations) by the Coulombic force within hundreds of femtoseconds, although the force did not significantly enhance the number of ionization, electronic excitation, and dissociative electron attachment collision events leading to water radiolysis., Conclusions: The secondary electrons are decelerated in water by the Coulombic force and recombined to the ionized atoms (cations). Furthermore, the some return electrons might be prehydrated in water layer near the parent cation in DNA if the electrons might be emitted from the DNA. The prehydrated electron originated from the return electron might play a significant role in inducing DNA damage.

Purpose: To compare some biological materials in respect to the water and tissue equivalence properties for photon, electron, proton and alpha particle interactions as means of the effective atomic number (Zeff) and electron density (Ne)., Methods: A Z-wise interpolation procedure has been adopted for calculation of Zeff using the mass attenuation coefficients for photons and the mass stopping powers for charged particles., Results: At relatively low energies (100 keV-3 MeV), Zeff and Ne for photons and electrons were found to be constant while they vary much more for protons and alpha particles. In contrast, Zeff and Ne for protons and alpha particles were found to be constant after 3 MeV whereas for photons and electrons they were found to increase with the increasing energy. Also, muscle eq. liquid (with sucrose) have Zeff and Ne values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) within low relative differences below 9%. Muscle eq. liquid (without sucrose) have Zeff and Ne values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) with difference below 10%., Conclusions: The reported data should be useful in determining best water as well as tissue equivalent materials for photon, electron, proton and alpha particle interactions.

Purpose: Recently, there has been an increase in interest into research into radioprotective agents. Radioprotectors are compounds that protect against radiation injury when given orally (through drinking water) prior to radiation exposure. The purpose is to achieve preferred protection of normal tissues against injury inflicted by ionizing radiation used to treat tumors. The main aim of this work is to investigate energy absorption (EABF) and exposure buildup factors (EBF) of commonly used some radioprotective agents., Materials and Methods: We have used the Geometric Progression (G-P) fitting method for calculating the equivalent atomic number (Zeq), for EABF and EBF buildup factors of the radioprotective agents in the energy range 0.015-15 MeV for penetration depths up to 40 mean free path., Results: Significant variations in both EABF and EBF values were observed for several agents at the moderate energy region. At energies below 0.1 MeV, EABF and EBF values increased with decreasing equivalent atomic number Zeq of the samples. At energies >0.15 MeV, EABF and EBF values were found to decrease with decreasing Zeq of all agents. In addition, EABF and EBF were the largest for carnosin, tempol, melatonin, interferon gamma and orientine at 0.05 and 0.06 MeV, respectively, and the minimum values of buildup factors were at 0.1 MeV for cysteine, amifostine, penicillamine and glutathione., Conclusions: Cysteine and amifostine are good compounds for gamma rays absorption applications among the selected compounds. The presented results in this study are expected to be helpful in radiation dosimetry.

In the purple phototrophic bacterium Rhodobacter sphaeroides, light harvesting LH2 complexes transfer absorbed solar energy to RC-LH1-PufX core complexes, which are mainly found in the dimeric state. Many other purple phototrophs have monomeric core complexes and the basis for requiring dimeric cores is not fully established, so we analysed strains of Rba. sphaeroides that contain either native dimeric core complexes or altered monomeric cores harbouring a deletion of the first 12 residues from the N-terminus of PufX, which retains the PufX polypeptide but removes the major determinant of core complex dimerization. Membranes were purified from strains with dimeric or monomeric cores, and with either high or low levels of the LH2 complex. Samples were interrogated with absorption, steady-state fluorescence, and picosecond time-resolved fluorescence kinetic spectroscopies to reveal their light-harvesting and energy trapping properties. We find that under saturating excitation light intensity the photosynthetic membranes containing LH2 and monomeric core complexes have fluorescence lifetimes nearly twice that of membranes with LH2 plus dimeric core complexes. This trend of increased lifetime is maintained with RCs in the open state as well, and for two different levels of LH2 content. Thus, energy trapping is more efficient when photosynthetic membranes of Rba. sphaeroides consist of RC-LH1-PufX dimers and LH2 complexes., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The efficient use of excitation energy in photosynthetic membranes is achieved by a dense network of pigment-protein complexes. These complexes fulfill specific functions and interact dynamically with each other in response to rapidly changing environmental conditions. Here, we studied how in the intact cells of Chlamydomonas reinhardtii (C.r.) the lack of the photosystem I (PSI) core or the photosystem II (PSII) core affects these interactions. To that end the mutants F15 and M18 (both PSI-deficient) and FUD7 (PSII-deficient) were incubated under conditions known to promote state transitions in wild-type. The intact cells were then instantly frozen to 77K and the full-spectrum time-resolved fluorescence emission of the cells was measured by means of streak camera. In the PSI-deficient mutants excitation energy transfer (EET) towards light-harvesting complexes of PSI (Lhca) occurs in less than 0.5 ns, and fluorescence from Lhca decays in 3.1 ns. Decreased trapping by PSII and increased fluorescence of Lhca upon state 1 (S1)→state 2 (S2) transition appears in the F15 and less in the M18 mutant. In the PSII-deficient mutant FUD7, quenched (0.5 ns) and unquenched (2 ns) light-harvesting complexes of PSII (LHCII) are present in both states, with the quenched form more abundant in S2 than in S1. Moreover, EET of 0.4 ns from the remaining LHCII to PSI increases upon S1→S2 transition. We relate the excitation energy kinetics observed in F15, M18 and FUD7 to the remodeling of the photosynthetic apparatus in these mutants under S1 and S2 conditions., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Bi(3+)/Tb(3+), Eu(3+) co-doped Li6Gd(BO3)3 (LGBO) phosphors were synthesized via a traditional solid-state method. Phase purity was investigated using X-ray diffraction, absorption strength of the phosphors were investigated by UV-vis absorption spectra, and the photoluminescence properties of the phosphors were studied systematically. Results showed that the emission intensity of Bi(3+), Eu(3+) co-doped LBOG was 2.76 times higher than that of Eu(3+)-doped LGBO irradiated at 275 nm, thereby implying the possibility of energy transfer from Bi(3+) to Eu(3+). The excitation spectra of Tb(3+), Eu(3+) co-doped LGBO phosphors are broader in comparison with single-doped phosphors and show tunable colors from green to yellow to orange-red when the ratio of Tb(3+) to Eu(3+) is adjusted These results demonstrate that LGBO:Tb(3+), Eu(3+) phosphors have potential use in light-emitting diodes., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Though the Er:YAG laser (ErL) has been used in periodontal therapy, the irradiated tip damage has not been studied in detail. In this study, the change in the energy output, surface morphology, and temperature of quartz tips was evaluated following contact irradiation. Soft tissue, calculus on extracted human teeth, and porcine bone were irradiated by ErL for 60 min at 14.2 or 28.3 J/cm(2)/pulse and 20 Hz with or without water spray. The energy output ratio declined the most in the calculus group, followed by the bone and soft tissue groups with and/or without water spray. Carbon contamination was detected in all groups, and contamination by P, Ca, and/or other inorganic elements was observed in the calculus and bone groups. The rate of energy output reduction and the degree of surface alteration/contamination is variously influenced by the targeting tissue, temperature elevation of the tip and water spray.

Photosynthesis relies on energy transfer from light-harvesting complexes to reaction centers. Phycobilisomes, the light-harvesting antennas in cyanobacteria and red algae, attach to the membrane via the multidomain core-membrane linker, L(CM). The chromophore domain of L(CM) forms a bottleneck for funneling the harvested energy either productively to reaction centers or, in case of light overload, to quenchers like orange carotenoid protein (OCP) that prevent photodamage. The crystal structure of the solubly modified chromophore domain from Nostoc sp. PCC7120 was resolved at 2.2 Å. Although its protein fold is similar to the protein folds of phycobiliproteins, the phycocyanobilin (PCB) chromophore adopts ZZZssa geometry, which is unknown among phycobiliproteins but characteristic for sensory photoreceptors (phytochromes and cyanobacteriochromes). However, chromophore photoisomerization is inhibited in L(CM) by tight packing. The ZZZssa geometry of the chromophore and π-π stacking with a neighboring Trp account for the functionally relevant extreme spectral red shift of L(CM). Exciton coupling is excluded by the large distance between two PCBs in a homodimer and by preservation of the spectral features in monomers. The structure also indicates a distinct flexibility that could be involved in quenching. The conclusions from the crystal structure are supported by femtosecond transient absorption spectra in solution.

The effects of fission gas pressure, uranium swelling and thermal contact conductance on the thermal-mechanical behavior of an annular target containing a low-enriched uranium foil (LEU) encapsulated in a nickel foil have been presented in this paper. The draw-plug assembly method is simulated to obtain the residual stresses, which are applied to the irradiation model as initial inputs, and the integrated assembly-irradiation process is simulated as an axisymmetric problem using the commercial finite element code Abaqus FEA. Parametric studies were performed on the LEU heat generation rate and the results indicate satisfactory irradiation performance of the annular target. The temperature and stress margins have been provided along with a discussion of the results., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

UV-vis absorption, steady state and time resolved spectroscopic investigations in pico and nanosecond time domain were made in the different environments on a novel synthesized dyad, 3-(2-methoxynaphthalen-1-yl)-1-(4-methoxyphenyl)prop-2-en-1-one (MNTMA) in its pristine form and when combined with gold (Au) nanoparticles i.e., in its nanocomposite structure. Both steady state and time resolved measurements coupled with the DFT calculations performed by using Gaussian 03 suit of software operated in the linux operating system show that though the dyad exhibits mainly the folded conformation in the ground state but on photoexcitation the nanocomposite form of dyad prefers to be in elongated structure in the excited state indicating its photoswitchable nature. Due to the predominancy of elongated isomeric form of the dyad in the excited state in presence of Au Nps, it appears that the dyad MNTMA may behave as a good light energy converter specially in its nanocomposite form. As larger charge separation rate (kcs ~ 4 x 10(8) s-1) is found relative to the rate associated with the energy wasting charge recombination processes (kcR ~ 3 x 10(5) s-1) in the nanocomposite form of the dyad, it demonstrates the suitability of constructing the efficient light energy conversion devices with Au-dyad hybrid nanomaterials.

Dye-sensitized solar cells (DSSCs) were assembled using natural dyes extracted from red cabbage as a sensitizer. In this work, we investigated the adsorption characteristics and the electrochemical behavior for harvesting sunlight and electron transfer in red cabbage DSSCs under different solvents and pH. For the red cabbage dye-sensitized electrode adsorbed at pH 3.5, the solar cell yields a short-circuit current density (Jsc) of 1.60 mA/cm2, a photovoltage (Vcc) of 0.46 V, and a fill factor of 0.55, corresponding to an energy conversion efficiency (η) of 0.41%.

Ultrasonic vibration-assisted (UV-A) pelleting can increase cellulosic biomass density and reduce biomass handling and transportation costs in cellulosic biofuel manufacturing. Effects of input variables on pellet density in UV-A pelleting have been studied experimentally. However, there are no reports on modeling of pellet density in UV-A pelleting. Furthermore, in the literature, most reported density models in other pelleting methods of biomass are empirical. This paper presents a constitutive model to predict pellet density in UV-A pelleting. With the predictive model, relations between input variables (ultrasonic power and pelleting pressure) and pellet density are predicted. The predicted relations are compared with those determined experimentally in the literature. Model predictions agree well with reported experimental results., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Light-harvesting pigment-protein complexes (PPC) represent the fundamental units through which the photosynthetic organisms absorb sunlight and funnel the energy to the reaction centre for carrying out the primary energy conversion reactions of photosynthesis. Here we apply a multiscale computational strategy to a specific PPC present in the photosystem II of plants and algae (CP29) to investigate in what detail should the environment effects due to protein and membrane/solvent be included for an accurate description of optical spectra. We find that a refinement of the crystal structure is needed before any meaningful quantum chemical calculations of pigment transition energies can be performed. For this purpose we apply classical molecular dynamics simulations of the PPC within its natural environment and we perform ab initio computations of the exciton Hamiltonian of the complex, including the environment either implicitly by the polarizable continuum model (PCM) or explicitly using the polarizable QM/MM methodology (MMPol). However, PCM essentially leads to an unspecific redshift of all transition energies, and MMPol is able to reveal site-specific changes in the optical properties of the pigments. Based on the latter and the excitonic couplings obtained within a polarizable QM/MM methodology, optical spectra are calculated, which are in good qualitative agreement with experimental data. A weakness of the approach is however found in the overestimation of the fluctuations of the excitonic parameters of the pigments along the MD trajectory. An explanation for such a finding in terms of the limits of the force fields commonly used for protein cofactors is presented and discussed.

Cholecalciferol, vitamin D3, was found to isomerize to 5,6-trans-vitamin-D3 with a quantum yield of 0.15 ± 0.01 in air-saturated 7/3 tert-butyl alcohol/water (v/v) at 25 °C, increasing to 0.32 ± 0.02 in the absence of oxygen, through quenching of triplet excited state flavin mononucleotide, FMN, rather than becoming oxidized. The quenching was found by laser flash photolysis to have a rate constant of 1.4 × 10(8) L mol(-1) s(-1) in 7/3 tert-butyl alcohol/water (v/v) at 25 °C, assigned to energy transfer from (3)FMN* to form a reactive vit.D3 diradical. vit.D3 forms a 1/1 precomplex with FMN by hydrophobic stacking with ΔH° = -36 ± 7 kJ mol(-1) and ΔS° = -4 ± 3 J mol(-1) K(-1), as shown by single photon counting fluorescence spectroscopy and steady-state fluorescence spectroscopy. Both ground-state precomplex formation and excited-state energy transfer seem important for vit.D3 protection against flavin-sensitized photooxidation of nutrients in food and biological systems.

Photoactive reaction centers (RCs) are protein complexes in bacteria able to convert sunlight into other forms of energy with a high quantum yield. The photostimulation of immobilized RCs on inorganic electrodes result in the generation of photocurrent that is of interest for biosolar cell applications. This paper reports on the use of novel electrodes based on functional conductive nanocrystalline diamond onto which bacterial RCs are immobilized. A three-dimensional conductive polymer scaffold grafted to the diamond electrodes enables efficient entrapment of photoreactive proteins. The electron transfer in these functional diamond electrodes is optimized through the use of a ferrocene-based electron mediator, which provides significant advantages such as a rapid electron transfer as well as high generated photocurrent. A detailed discussion of the generated photocurrent as a function of time, bias voltage, and mediators in solution unveils the mechanisms limiting the electron transfer in these functional electrodes. This work featuring diamond-based electrodes in biophotovoltaics offers general guidelines that can serve to improve the performance of similar devices based on different materials and geometries.

Scintillating nanoparticles (NPs) in combination with X-ray or γ-radiation have a great potential for deep-tissue cancer therapy because they can be used to locally activate photosensitizers and generate singlet oxygen in tumours by means of the photodynamic effect. To understand the complex spatial distribution of energy deposition in a macroscopic volume of water loaded with nanoscintillators, we have developed a GEANT4-based Monte Carlo program. We thus obtain estimates of the maximum expected efficiency of singlet oxygen production for various materials coupled to PS, X-ray energies, NP concentrations and NP sizes. A new parameter, ηnano, is introduced to quantify the fraction of energy that is deposited in the NPs themselves, which is crucial for the efficiency of singlet oxygen production but has not been taken into account adequately so far. We furthermore emphasise the substantial contribution of primary interactions taking place in water, particularly under irradiation with high energy photons. The interplay of all these contributions to the photodynamic effect has to be taken into account in order to optimize nanoscintillators for therapeutic applications.

Guanine rich DNA strands, such as those encountered at the extremities of human chromosomes, have the ability to form four-stranded structures (G-quadruplexes) whose building blocks are guanine tetrads. G-quadruplex structures are intensively studied in respect of their biological role, as targets for anticancer therapy and, more recently, of their potential applications in the field of molecular electronics. Here we focus on their electronic excited states which are compared to those of non-interacting mono-nucleotides and those of single and double stranded structures. Particular emphasis is given to excited state relaxation processes studied by time-resolved fluorescence spectroscopy from femtosecond to nanosecond time scales. They include ultrafast energy transfer and trapping of ππ* excitations by charge transfer states. The effect of various structural parameters, such as the nature of the metal cations located in the central cavity of G-quadruplexes, the number of tetrads or the conformation of the constitutive single strands, are examined.

A modified dye-sensitized solar cell consisting of a thin TiO2 barrier layer sensitized with natural trimeric light-harvesting complex II (LHCII) from spinach was used as a biomimetic model to study the effects of LHCII aggregation on the photovoltaic properties. The aggregation of individual trimers induced molecular reorganization, which dramatically increased the photocurrent. The morphology of small- and large-size LHCII aggregates deposited on a surface was confirmed by atomic force microscopy. Enhanced LHCII immobilization was accomplished via electrostatic interaction with amine-functionalized photoanodes. The photocurrent responses of the assembled solar cells under illumination at three characteristic wavelength bands in the UV-Vis absorption spectra of LHCII solutions confirmed that a significant photocurrent was generated by LHCII photosensitizers. The enhanced photocurrent by large aggregated LHCII is shown to correlate with the quenching in the far-red fluorescence deriving from chlorophyll-chlorophyll charge transfer states that are effectively coupled with the TiO2 surface and thus inject electrons into the TiO2 conduction band. The large aggregated LHCII with more chlorophyll-chlorophyll charge transfer states is a much better sensitizer since it injects electrons more efficiently into the conduction band of TiO2 than the small aggregated LHCII mostly consisting of unquenched chlorophyll excited state. The assembled solar cells demonstrated remarkable stability in both aqueous buffer and acetonitrile electrolytes over 30 days.

We describe a method to measure ultrafast protein structural changes using time-resolved wide-angle X-ray scattering at an X-ray free-electron laser. We demonstrated this approach using multiphoton excitation of the Blastochloris viridis photosynthetic reaction center, observing an ultrafast global conformational change that arises within picoseconds and precedes the propagation of heat through the protein. This provides direct structural evidence for a 'protein quake': the hypothesis that proteins rapidly dissipate energy through quake-like structural motions.

Although the actuation mechanisms that drive plant movement have been investigated from a biomimetic perspective, few studies have looked at the wider sensing and control systems that regulate this motion. This paper examines photo-actuation-actuation induced by, and controlled with light-through a review of the sun-tracking functions of the Cornish Mallow. The sun-tracking movement of the Cornish Mallow leaf results from an extraordinarily complex-yet extremely elegant-process of signal perception, generation, filtering and control. Inspired by this process, a concept for a simplified biomimetic analogue of this leaf is proposed: a multifunctional structure employing chemical sensing, signal transmission, and control of composite hydrogel actuators. We present this multifunctional structure, and show that the success of the concept will require improved selection of materials and structural design. This device has application in the solar-tracking of photovoltaic panels for increased energy yield. More broadly it is envisaged that the concept of chemical sensing and control can be expanded beyond photo-actuation to many other stimuli, resulting in new classes of robust solid-state devices.

The large multiprotein complex, photosystem I (PSI), which is at the heart of light-dependent reactions in photosynthesis, is integrated as the active component in a solid-state organic photovoltaic cell. These experiments demonstrate that photoactive megadalton protein complexes are compatible with solution processing of organic-semiconductor materials and operate in a dry non-natural environment that is very different from the biological membrane., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A numerical study of optimal bandgaps of light absorbers in tandem solar cell configurations is presented with the main focus on dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). The limits in efficiency and the expected improvements of tandem structures are investigated as a function of total loss-in-potential (V(L)), incident photon to current efficiency (IPCE) and fill factor (FF) of individual components. It is shown that the optimal absorption onsets are significantly smaller than those derived for multi-junction devices. For example, for double-cell devices the onsets are at around 660 nm and 930 nm for DSSCs with iodide based electrolytes and at around 720 nm and 1100 nm for both DSSCs with cobalt based electrolytes and PSCs. Such configurations can increase the total sunlight conversion efficiency by about 35% in comparison to single-cell devices of the same VL, IPCE and FF. The relevance of such studies for tandem n-p DSSCs and for a proposed new configuration for PSCs is discussed. In particular, it is shown that maximum total losses of 1.7 V for DSSCs and 1.4 V for tandem PSCs are necessary to give any efficiency improvement with respect to the single bandgap device. This means, for example, a tandem n-p DSSC with TiO2 and NiO porous electrodes will hardly work better than the champion single DSSC. A source code of the program used for calculations is also provided.

Oligo(phenylenevinylene)s (OPVs) are extensively investigated π-conjugated molecules that exhibit absorption and fluorescence in the UV-Vis spectral region, which can be widely tuned by chemical functionalisation and external control (e.g. solvent, temperature, pH). Further modulation of the optoelectronic properties of OPVs is possible by supramolecular aggregation, primarily driven by hydrogen bonding or π-stacking interactions. In recent years, extensive research work has been accomplished in exploiting the unique combination of the structural and electronic properties of OPVs, most of which has been targeted at the preparation of molecules and materials featuring photoinduced energy transfer. This review intends to offer an overview of the multicomponent arrays and self-assembled materials based on OPV which have been designed to undergo energy transfer by means of a thorough choice of excitation donor-acceptor partners. We present a few selected examples of photoactive dyads and triads containing organic moieties (e.g. fullerene, phenanthroline) as well as coordination compounds (Cu(I) complexes). We then focus more extensively on self-assembled materials containing suitably functionalised OPVs that lead to hydrogen bonded aggregates, helical structures, gels, nanoparticles, vesicles, mesostructured organic-inorganic hybrid films, functionalised nanoparticles and quantum dots. In most cases, these materials exhibit luminescence whose colour and intensity is related to the efficiency and direction of the energy transfer processes.

Nanoparticles with photoresponsive character can be assembled from amphiphilic macromolecular components and hydrophobic chromophores. In aqueous solutions, the hydrophobic domains of these species associate to produce spontaneously nanosized hosts with multiple photoresponsive guests in their interior. The modularity of this supramolecular approach to nanostructured assemblies permits the co-encapsulation of distinct subsets of guests within the very same host. In turn, the entrapped guests can be designed to interact upon light excitation and exchange electrons, energy or protons. Such photoinduced processes permit the engineering of properties into these supramolecular constructs that would otherwise be impossible to replicate with the separate components. Alternatively, noninteracting guests with distinct functions can be entrapped in these supramolecular containers to ensure multifunctional character. In fact, biocompatible luminescent probes with unique photochemical and photophysical signatures have already emerged from these fascinating investigations. Thus, polymer nanocarriers can become invaluable supramolecular scaffolds for the realization of multifunctional and photoresponsive tools for a diversity of biomedical applications.

The development of multicomponent (supramolecular) systems that can perform predetermined functions under external control - i.e., molecular devices - is a challenging task in chemistry and a fascinating objective in the frame of a bottom-up approach to nanostructures. In this context light signals can be conveniently used both for supplying energy to the system and for probing its states and transformations. The aim of this tutorial review is to recall a few basic aspects of light-induced processes that can be used to "write" and "read" onto molecular and supramolecular systems. These principles are illustrated through some examples of artificial molecular devices and machines taken from our work, which provide a flavour of current research. They are molecular and supramolecular systems that operate and/or perform valuable functions by exploiting photoinduced energy- or electron-transfer processes, photoisomerization reactions, or photoinduced proton transfer. The choice of these examples was based on both their intrinsic importance for the referred topic and their educational value. In the last section of the review potential applications, limitations and future directions of the research in the field of artificial molecular devices and machines are also discussed.

A theoretical model of plasmon and molecular luminescence induced by scanning tunneling microscopy using a molecule-covered tip on clean metal surfaces is developed. The effects of coupling between molecular exciton and interface plasmon on the luminescence spectra are investigated for variable energy of plasmon modes by means of the nonequilibrium Green's function method. It is found that spectral features arising from interference between the processes of energy absorption by the molecule and interface plasmons appear near the energy of the excitonic mode. For the energy of plasmon above (below) the energy of excitonic mode, an additional peak structure appears in the energy range slightly below (above) the energy of the excitonic mode. Prominent peak and dip structures observed in recent luminescence experiments are interpreted by the developed theory whereby its utility in the fields of plasmonics and nanophotonics is demonstrated.

To assess the roles of the cyclic electron flow around PSI (CEF-PSI) and O₂-dependent alternative pathways including the water-water cycle in fluctuating light, we grew the wild type and pgr5 mutant of Arabidopsis thaliana in constant light, and measured Chl fluorescence and P700 parameters in their leaves in the fluctuating light alternating between 240 (HL) and 30 µmol photons m⁻² s⁻² (LL) every 2 min. At 20% O₂, the photochemical quantum yield of PSII decreased, in particular in the pgr5 plants, soon after the start of the fluctuating light treatment. PSI of the pgr5 plants was markedly photoinhibited by this treatment for 42 min. Slight PSI photoinhibition was also observed in the wild type. We measured energy sharing between PSII and PSI and estimated the PSI and PSII electron transport rates (ETRs). pgr5 showed larger energy allocation to PSI. In contrast to the wild type, the ratio of the PSI to the PSII ETR in pgr5 was higher in LL but lower in HL at 20% O₂ due to PSI acceptor-side limitation. At 2.7% or 0% O₂, the CEF-PSI of the pgr5 plants was enhanced, the acceptor-side limitation of PSI electron flow was released and PSI photoinhibition was not observed. The results suggest that the light fluctuation is a potent stress to PSI and that the CEF-PSI is essential to protect PSI from this stress.

In "imaging the biomechanical properties of tissues," a number of approaches analyze shear wave propagation initiated by a short radiation force push. Unfortunately, it has been experimentally observed that the displacement-versus-time curves for lossy tissues are rapidly damped and distorted in ways that can confound simple tracking approaches. This article addresses the propagation, decay and distortion of pulses in lossy and dispersive media, to derive closed-form analytic expressions for the propagating pulses. The theory identifies key terms that drive the distortion and broadening of the pulse. Furthermore, the approach taken is not dependent on any particular viscoelastic model of tissue, but instead takes a general first-order approach to dispersion. Examples with a Gaussian beam pattern and realistic dispersion parameters are given along with general guidelines for identifying the features of the distorting wave that are the most compact., (Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

The effect of radiation on laminar and turbulent mixed convection heat transfer of a semitransparent medium in a square enclosure was studied numerically using the Finite Volume Method. A structured mesh and the SIMPLE algorithm were utilized to model the governing equations. Turbulence and radiation were modeled with the RNG k-ε model and Discrete Ordinates (DO) model, respectively. For Richardson numbers ranging from 0.1 to 10, simulations were performed for Rayleigh numbers in laminar flow (10⁴) and turbulent flow (10⁸). The model predictions were validated against previous numerical studies and good agreement was observed. The simulated results indicate that for laminar and turbulent motion states, computing the radiation heat transfer significantly enhanced the Nusselt number (Nu) as well as the heat transfer coefficient. Higher Richardson numbers did not noticeably affect the average Nusselt number and corresponding heat transfer rate. Besides, as expected, the heat transfer rate for the turbulent flow regime surpassed that in the laminar regime. The simulations additionally demonstrated that for a constant Richardson number, computing the radiation heat transfer majorly affected the heat transfer structure in the enclosure; however, its impact on the fluid flow structure was negligible.

Accurate temperature measurements are essential to safe and effective thermal therapies for cancer and other diseases. However, conventional thermometry is challenging so using the heating agents themselves as probes allows for ideal local measurements. Here, we present a new noninvasive method for measuring the temperature of the microenvironment surrounding magnetic nanoparticles from the Brownian relaxation time of nanoparticles. Experimentally, the relaxation time can be determined from the nanoparticle magnetization induced by an alternating magnetic field at various applied frequencies. A previously described method for nanoparticle temperature estimation used a low frequency Langevin function description of magnetic dipoles and varied the excitation field amplitude to estimate the energy state distribution and the corresponding temperature. We show that the new method is more accurate than the previous method at higher applied field frequencies that push the system farther from equilibrium.

We give a new explanation for why some biological systems can stay quantum coherent for a long time at room temperature, one of the fundamental puzzles of quantum biology. We show that systems with the right level of complexity between chaos and regularity can increase their coherence time by orders of magnitude. Systems near Critical Quantum Chaos or Metal-Insulator Transition (MIT) can have long coherence times and coherent transport at the same time. The new theory tested in a realistic light harvesting system model can reproduce the scaling of critical fluctuations reported in recent experiments. Scaling of return probability in the FMO light harvesting complex shows the signs of universal return probability decay observed at critical MIT. The results may open up new possibilities to design low loss energy and information transport systems in this Poised Realm hovering reversibly between quantum coherence and classicality.

We propose a hierarchical reduction scheme to cope with coupled rate equations that describe the dynamics of multi-time-scale photosynthetic reactions. To numerically solve nonlinear dynamical equations containing a wide temporal range of rate constants, we first study a prototypical three-variable model. Using a separation of the time scale of rate constants combined with identified slow variables as (quasi-)conserved quantities in the fast process, we achieve a coarse-graining of the dynamical equations reduced to those at a slower time scale. By iteratively employing this reduction method, the coarse-graining of broadly multi-scale dynamical equations can be performed in a hierarchical manner. We then apply this scheme to the reaction dynamics analysis of a simplified model for an illuminated photosystem II, which involves many processes of electron and excitation-energy transfers with a wide range of rate constants. We thus confirm a good agreement between the coarse-grained and fully (finely) integrated results for the population dynamics., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

In this review, the concept of utilization of solar spectrum in order to increase the solar cell efficiency is discussed. Among the three mechanisms, down-shifting effect is investigated in detail. Organic dye, rare-earth minerals and quantum dots are three most popular down-shift materials. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. A multiple layer structure, including PDMS as the isolation layer, is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved and the optimized concentration can be found.

Cellulosic biomass can be used as a feedstock for biofuel manufacturing. Pelleting of cellulosic biomass can increase its bulk density and thus improve its storability and reduce the feedstock transportation costs. Ultrasonic vibration-assisted (UV-A) pelleting can produce biomass pellets whose density is comparable to that processed by traditional pelleting methods (e.g. extruding, briquetting, and rolling). This study applied response surface methodology to the development of a predictive model for the energy consumption in UV-A pelleting of wheat straw. Effects of pelleting pressure, ultrasonic power, sieve size, and pellet weight were investigated. This study also optimized the process parameters to minimize the energy consumption in UV-A pelleting using response surface methodology. Optimal conditions to minimize the energy consumption were the following: ultrasonic power at 20%, sieve size at 4 mm, and pellet weight at 1g, and the minimum energy consumption was 2.54 Wh., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Modeling of thermal-induced mechanical behaviors of soft tissues is of great importance for thermal ablation. This paper presents a method by integrating the heating process with thermal-induced mechanical deformations of soft tissues for simulation and analysis of the thermal ablation process. This method combines bio-heat transfer theories, constitutive elastic material law under thermal loads as well as non-rigid motion dynamics to predict and analyze thermal-mechanical deformations of soft tissues. The 3D governing equations of thermal-mechanical soft tissue deformation are discretized by using the finite difference scheme and are subsequently solved by numerical algorithms. Experimental results show that the proposed method can effectively predict the thermal-induced mechanical behaviors of soft tissues, and can be used for the thermal ablation therapy to effectively control the delivered heat energy for cancer treatment.