Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 216
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Biochemistry (Mosc) ; 84(9): 1065-1073, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31693466

RESUMO

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.


Assuntos
Arabidopsis/efeitos da radiação , Hordeum/efeitos da radiação , Complexos de Proteínas Captadores de Luz/efeitos da radiação , Luz , Iluminação , Fotossíntese/efeitos da radiação , Arabidopsis/metabolismo , Transferência de Energia/efeitos da radiação , Hordeum/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo
2.
Nat Commun ; 10(1): 3089, 2019 07 12.
Artigo em Inglês | MEDLINE | ID: mdl-31300649

RESUMO

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.


Assuntos
Transferência de Energia/efeitos da radiação , Corantes Fluorescentes/química , Microscopia Intravital/métodos , Imagem Molecular/métodos , Nanopartículas/química , Animais , Materiais Biocompatíveis/química , Materiais Biocompatíveis/efeitos da radiação , Cor , Fluorescência , Corantes Fluorescentes/efeitos da radiação , Luz , Camundongos , Microscopia Eletrônica de Transmissão/métodos , Microscopia de Fluorescência/métodos , Nanopartículas/efeitos da radiação , Polímeros/química , Polímeros/efeitos da radiação , Células RAW 264.7
3.
Luminescence ; 34(5): 500-507, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30924274

RESUMO

Under a 980-nm excitation, the up-conversion (UC) spectra of LuNbO4 :Yb3+ ,Tm3+ powders exhibited predominantly near-infrared bands (~805 nm) of Tm3+ through an energy transfer process from Yb3+ to Tm3+ . Regarding the down-conversion (DC) luminescence of the powders, the photoluminescence excitation spectra consisted of a broad charge transfer band (270 nm) due to [NbO4 ]3- and sharp band (360 nm) of Tm3+ , while the corresponding emission spectra exhibited a blue emission at 458 nm. Upon substitution of Ga3+ and Ta5+ for Lu3+ and Nb5+ , respectively, both UC and DC luminescence properties were significantly enhanced. For the Ga3+ substitution, the increased emission intensity could be explained by the crystal field asymmetry surrounding the Tm3+ ions induced by the large difference in ionic radius between Ga3+ and Lu3+ . For the Ta5+ substitution, we believe that an M'-LuTaO4 substructure was formed in the host, which led to the formation of a TaO6 octahedral coordination instead of a NbO4 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 LuNbO4 :Yb3+ ,Tm3+ has a great potential in the fields of temperature sensing probes, anti-counterfeiting, and bioapplications.


Assuntos
Gálio/química , Tantálio/química , Túlio/química , Ítrio/química , Cor , Transferência de Energia/efeitos da radiação , Raios Infravermelhos , Luminescência
4.
Nano Lett ; 19(4): 2614-2619, 2019 04 10.
Artigo em Inglês | MEDLINE | ID: mdl-30848602

RESUMO

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.


Assuntos
Catálise , Hidrogênio/química , Nanopartículas/química , Porfirinas/química , Emulsões/efeitos da radiação , Transferência de Energia/efeitos da radiação , Luz , Nanopartículas/efeitos da radiação , Nanoestruturas/química , Fotossíntese/efeitos da radiação , Porfirinas/síntese química
5.
Photosynth Res ; 139(1-3): 145-154, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29808364

RESUMO

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.


Assuntos
Chlorella/metabolismo , Luz , Chlorella/efeitos da radiação , Transferência de Energia/efeitos da radiação , Fotossíntese/efeitos da radiação , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema I/efeitos da radiação , Complexo de Proteína do Fotossistema II/metabolismo , Complexo de Proteína do Fotossistema II/efeitos da radiação
7.
Nucleic Acids Res ; 46(7): 3543-3551, 2018 04 20.
Artigo em Inglês | MEDLINE | ID: mdl-29186575

RESUMO

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.


Assuntos
DNA/química , Transferência de Energia/efeitos da radiação , Conformação de Ácido Nucleico/efeitos da radiação , Laranja Acridina/química , Animais , Bovinos , DNA/genética , DNA/efeitos da radiação , Fluorescência , Nanoestruturas/química , Fotossíntese/genética , Fotossíntese/efeitos da radiação , Teoria Quântica , Prata/química , Raios Ultravioleta
8.
J Am Chem Soc ; 139(43): 15292-15295, 2017 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-28969423

RESUMO

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 Mn2(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 3PS* to a photolabile triplet state of Mn2(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 Mn2(CO)10 were embedded in electrospun nonwoven fabrics, CO was liberated upon irradiation with low-intensity red light (≤36 mW 635 nm).


Assuntos
Monóxido de Carbono/química , Cor , Luz , Compostos de Manganês/química , Compostos de Manganês/efeitos da radiação , Polímeros/química , Monóxido de Carbono/efeitos da radiação , Transferência de Energia/efeitos da radiação , Polímeros/efeitos da radiação , Raios Ultravioleta/efeitos adversos
9.
J Am Chem Soc ; 139(29): 9807-9810, 2017 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-28683547

RESUMO

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.


Assuntos
Reação de Cicloadição , Ciclobutanos/síntese química , Transferência de Energia/efeitos da radiação , Cetonas/química , Luz , Processos Fotoquímicos , Catálise , Ciclobutanos/química , Irídio/química , Estrutura Molecular
10.
Int J Radiat Biol ; 92(9): 508-20, 2016 09.
Artigo em Inglês | MEDLINE | ID: mdl-27419342

RESUMO

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.


Assuntos
Absorção de Radiação , Materiais Biomiméticos/química , Materiais Biomiméticos/efeitos da radiação , Transferência de Energia/efeitos da radiação , Água/química , Partículas alfa , Elétrons , Teste de Materiais , Peso Molecular , Fótons , Prótons , Doses de Radiação , Espalhamento de Radiação
11.
Int J Radiat Biol ; 92(11): 654-659, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-27332896

RESUMO

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.


Assuntos
DNA/química , DNA/efeitos da radiação , Elétrons , Transferência de Energia/efeitos da radiação , Modelos Químicos , Modelos Estatísticos , Simulação por Computador , Modelos Biológicos , Método de Monte Carlo , Doses de Radiação
12.
Int J Radiat Biol ; 92(7): 380-7, 2016 07.
Artigo em Inglês | MEDLINE | ID: mdl-27124103

RESUMO

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.


Assuntos
Absorção de Radiação , Algoritmos , Relação Dose-Resposta à Radiação , Modelos Químicos , Protetores contra Radiação/química , Protetores contra Radiação/efeitos da radiação , Simulação por Computador , Transferência de Energia/efeitos da radiação , Teste de Materiais , Doses de Radiação
13.
Biochim Biophys Acta ; 1857(6): 625-33, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-26946087

RESUMO

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.


Assuntos
Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/metabolismo , Transferência de Energia/fisiologia , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Proteínas de Algas/genética , Chlamydomonas reinhardtii/genética , Chlamydomonas reinhardtii/efeitos da radiação , Transferência de Energia/genética , Transferência de Energia/efeitos da radiação , Immunoblotting , Luz , Complexos de Proteínas Captadores de Luz/genética , Mutação , Fotossíntese/genética , Fotossíntese/fisiologia , Fotossíntese/efeitos da radiação , Complexo de Proteína do Fotossistema I/genética , Complexo de Proteína do Fotossistema II/genética , Espectrometria de Fluorescência , Tilacoides/genética , Tilacoides/metabolismo , Tilacoides/efeitos da radiação
14.
Biochim Biophys Acta ; 1857(6): 634-42, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-27013332

RESUMO

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.


Assuntos
Cromatóforos Bacterianos/metabolismo , Proteínas de Bactérias/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Rhodobacter sphaeroides/metabolismo , Algoritmos , Cromatóforos Bacterianos/efeitos da radiação , Proteínas de Bactérias/química , Transferência de Energia/efeitos da radiação , Cinética , Luz , Complexos de Proteínas Captadores de Luz/química , Modelos Biológicos , Fotossíntese/efeitos da radiação , Multimerização Proteica/efeitos da radiação , Rhodobacter sphaeroides/efeitos da radiação , Espectrofotometria
15.
Dent Mater J ; 35(1): 51-62, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26830823

RESUMO

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.


Assuntos
Processo Alveolar/efeitos da radiação , Cálculos Dentários/radioterapia , Instrumentos Odontológicos , Transferência de Energia/efeitos da radiação , Gengiva/efeitos da radiação , Terapia a Laser/instrumentação , Lasers de Estado Sólido , Quartzo/química , Quartzo/efeitos da radiação , Animais , Contaminação de Equipamentos , Humanos , Técnicas In Vitro , Microscopia Eletrônica de Varredura , Espectrometria por Raios X , Propriedades de Superfície/efeitos da radiação , Suínos , Temperatura Ambiente , Água
16.
Appl Radiat Isot ; 108: 148-153, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26720264

RESUMO

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.


Assuntos
Cor , Transferência de Energia/efeitos da radiação , Elementos da Série dos Lantanídeos/química , Iluminação/métodos , Medições Luminescentes/métodos , Colorimetria/métodos , Relação Dose-Resposta à Radiação , Teste de Materiais , Doses de Radiação
17.
Proc Natl Acad Sci U S A ; 112(52): 15880-5, 2015 Dec 29.
Artigo em Inglês | MEDLINE | ID: mdl-26669441

RESUMO

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.


Assuntos
Proteínas de Bactérias/metabolismo , Nostoc/metabolismo , Ficobiliproteínas/metabolismo , Ficobilissomas/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Cristalografia por Raios X , Transferência de Energia/efeitos da radiação , Cinética , Luz , Modelos Moleculares , Mutação , Nostoc/genética , Nostoc/efeitos da radiação , Fotossíntese/efeitos da radiação , Ficobiliproteínas/química , Ficobiliproteínas/genética , Dobramento de Proteína , Multimerização Proteica , Estrutura Terciária de Proteína , Espectrofotometria/métodos
18.
J Nanosci Nanotechnol ; 15(8): 5775-84, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26369151

RESUMO

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.


Assuntos
Fontes de Energia Elétrica , Ouro/química , Nanopartículas Metálicas/química , Modelos Químicos , Nanocompostos/química , Compostos Orgânicos/química , Simulação por Computador , Transferência de Energia/efeitos da radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Ouro/efeitos da radiação , Luz , Teste de Materiais , Nanopartículas Metálicas/efeitos da radiação , Nanocompostos/efeitos da radiação , Compostos Orgânicos/efeitos da radiação , Tamanho da Partícula , Doses de Radiação , Análise Espectral/métodos , Propriedades de Superfície , Transdutores
19.
J Nanosci Nanotechnol ; 15(8): 5840-4, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26369159

RESUMO

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%.


Assuntos
Brassica/química , Corantes/química , Fontes de Energia Elétrica , Extratos Vegetais/química , Energia Solar , Corantes/isolamento & purificação , Corantes/efeitos da radiação , Condutividade Elétrica , Eletrodos , Transferência de Energia/efeitos da radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Concentração de Íons de Hidrogênio , Luz , Teste de Materiais , Extratos Vegetais/efeitos da radiação
20.
Appl Radiat Isot ; 103: 1-8, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26036440

RESUMO

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.


Assuntos
Modelos Químicos , Condutividade Térmica , Urânio/química , Urânio/efeitos da radiação , Força Compressiva/efeitos da radiação , Simulação por Computador , Relação Dose-Resposta à Radiação , Módulo de Elasticidade/efeitos da radiação , Transferência de Energia/efeitos da radiação , Doses de Radiação , Resistência ao Cisalhamento/efeitos da radiação , Estresse Mecânico , Temperatura Ambiente , Resistência à Tração/efeitos da radiação
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA