Search results for "PHOTOS"

Ultrafast electron transfer in photosynthesis: reduced pheophytin and quinone interaction mediated by conical intersections.

2006

The mechanism of electron transfer (ET) from reduced pheophytin (Pheo(-)) to the primary stable photosynthetic acceptor, a quinone (Q) molecule, is addressed by using high-level ab initio computations and realistic molecular models. The results reveal that the ET process involving the (Pheo(-) + Q) and (Pheo + Q(-)) oxidation states can be essentially seen as an ultrafast radiationless transition between the two hypersurfaces taking place via conical intersections (CIs). According to the present findings, an efficient ultrafast ET implies that the Pheo- and Q move toward each other in a given preferential parallel orientation, reaching the most effective arrangement for ET at intermolecular…

Toward an Understanding of Ultrafast Electron Transfer in Photosynthesis

2008

The mechanism of electron transfer (ET) from reduced pheophytin (Pheo−) to the primary stable photosynthetic acceptor, a quinone (Q) molecule, is addressed by using high-level ab initio computations and realistic molecular models. The results reveal that the ET process involving the (Pheo−+Q) and (Pheo+Q−) oxidation states can be seen essentially as an ultrafast radiationless transition between the two hypersurfaces taking place via conical intersections (CIs) and is favoured when the topology of the interacting moieties makes possible some overlap between the lowest occupied molecular orbitals (LUMO) of the two systems. Thus, it is anticipated that large scale motions, which are difficult …

PHOSPHOROUS SEED COATING AFFECT TO GERMINATION, PHOTOSYNTHETIC PIGMENTS AND YIELD OF RAPE

2005

Rape (Brassica napus L. var. napus) is long ago-known vegetable of Brassicaceae in agriculture. It is important and valuable oil, forage, green-fertiliser and nectar plant. The experience of last years shows that rape is suitable for growing in conditions of Latvia, but investigations about its cultivars and growing technologies are not wide enough.The phosporus-fertilizer adding in the rape plantations is of great importance for increasing of its productivity. With the aim to reduce the expenses the phosphorus treated rape seeds are made use.In our investigations the velocity of seeds germination, germinating viability, germinating vigour, green pigments” quantity in seed-lobes and seeds” …

Photochemical and Photobiological Studies of a Furonaphthopyranone as a Benzo-spaced Psoralen Analog in Cell-free and Cellular DNA

1997

Photobiological activities of the benzo-spaced psoralen analog furonaphthopyranone 3 have been investigated in cell-free and cellular DNA. The molecular geometry parameters of 3 suggest that it should not form interstrand crosslinks with DNA. With cell-free DNA no evidence for crosslinking but also not for monoadduct formation was obtained; rather, the unnatural furocoumarin 3 induces oxidative DNA modifications under near-UVA irradiation. The enzymatic assay of the photosensitized damage in cell-free PM2 DNA revealed the significant formation of lesions sensitive to formamidopyrimidine DNA glycosylase (Fpg protein). In the photooxidation of calf thymus DNA by the furonaphthopyranone 3, 0.2…

PV and magnetic field effects in poly(3-hexylthiophene)-fullerene cells doped with phthalocyanine soluble derivative

2007

An attempt was made to widen the photosensitivity spectral range of poly(3-hexylthiophene)-fullerene blend by adding an extra electron donor — a newly synthesized soluble phthalocyanine derivative (SnClPc) having the electron absorption band at 708 nm. As the electron acceptor, home-synthesised di(ethoxycarbonyl) methano-fullerene carboxylate (C 61 (CO 2 Et) 2 ) was used, and as the hole transporter — the regioregular poly 3-hexylthiophene (P3HT). The sandwich-type samples were prepared on an ITO glass substrate by coating it with a 30–50 nm thick PEDOT:PSS layer followed by a ~100 nm thick P3HT:C 61 (CO 2 Et) 2 :SnClPc blend. For the top electrodes In or Au were used. Spectral dependences …

FUSED NITROGEN HETEROCYCLES AS PROMISING SMALL MOLECULES FOR THE TREATMENT OF CANCER

2020

Photosynthesis of the red alga Gracilaria chilensis under natural solar radiation in an estuary in southern Chile

2005

The photosynthetic performance and pigment content of Gracilaria chilensis Bird, McLachlan, and Oliveira were measured under natural solar radiation in the Quempillen river estuary (southern Chile) in order to assess the short-term acclimation of this species to the current levels of ultraviolet (UV) radiation during midsummer. The effect of the tidal fluctuation was evaluated in algae exposed for 3 days to two light climates in cages suspended at two depths (0.5 and 1.5 m from the bottom). Responses to high solar radiation at noon were also assessed to gain insights into rapid photochemical kinetics and the degree of photoinhibition. Results indicated that G. chilensis is a shade-adapted s…

Studies on the mechanism of photosystem II photoinhibition I. A two-step degradation of D1-protein

1990

The role of D1-protein in photoinhibition was examined. Photoinhibition of spinach thylakoids at 20°C caused considerable degradation of D1-protein and a parallel loss of variable fluorescence, QB-independent electron flow and QB-dependent electron flow. The breakdown of D1-protein as well as the loss of variable fluorescence and QB-independent electron flow were largely prevented when thylakoids were photoinhibited at 0°C. The QB-dependent electron flow markedly decreased under the same conditions. This inactivation may represent the primary event in photoinhibition and could be the result of some modification at the QB-site of D1-protein. Evidence for this comes from fluorescence relaxati…

Studies on the mechanism of photosystem II photoinhibition II. The involvement of toxic oxygen species.

1990

In a previous paper it was shown that photoinhibition of reaction centre II of spinach thylakoids was predominantly caused by the degradation of D1-protein. An initial inactivation step at the QB-site was distinguished from its breakdown. The present paper deals with the question as to whether this loss of QB-function is caused by oxygen radical attack. For this purpose the photoinhibition of thylakoids was induced at 20°C in the presence of either superoxide dismutase and catalase or the antioxidants glutathione and ascorbic acid. This resulted in comparable though not total protection of D1-protein, photochemistry and fluorescence from photoinhibition. The combined action of both the enzy…

Changes of the Quantum Yield of Oxygen Evolution and the Electron Transport Capacity of Isolated Spinach Thylakoids during Photoinhibition

1992

Summary Isolated spinach thylakoids can be protected from photoinhibitory loss of electron transport capacity by the radical defense system composed of the enzymes SOD and catalase, as well as the antioxidants glutathione and ascorbate. With these compounds present at saturating concentrations, thylakoids not only retain a high photochemical capacity but also do not suffer D1-protein degradation during photoinhibition. However, a strong decrease in the quantum yield of oxygen evolution, Φ O 2 , occurs with the same thylakoids. These results support the view that the photochemical capacity and the quantum yield of oxygen evolution decline due to different mechanisms during photoinhibition. T…