Singlet oxygen generation in the reaction centers of Rhodobacter sphaeroides

Abstract

Singlet oxygen (1O2) generation in the reaction centers (RCs) of Rhodobacter sphaeroides wild type was characterized by luminescent emission in the near infrared region (time resolved transients and emission spectra) and quantified to have quantum yield of 0.03 +/- 0.005. 1O2 emission was measured as a function of temperature, ascorbate, urea and potassium ferricyanide concentrations and as a function of incubation time in H2O:D2O mixtures. 1O2 was shown to be affected by the RC dynamics and to originate from the reaction of molecular oxygen with two sources of triplets: photoactive dimer formed by singlet-triplet mixing and bacteriopheophytin formed by direct photoexcitation and intersystem crossing.

A Cluster of Four Homologous Small RNAs Modulates C 1 Metabolism and the Pyruvate Dehydrogenase Complex in Rhodobacter sphaeroides under Various Stress Conditions

“…In contrast, singlet oxygen ( 1 O 2 ) is generated upon excitement transfer from a photosensitizer to molecular oxygen. In R. sphaeroides, it was shown that 1 O 2 is generated in considerable amounts by bacteriochlorophylls of the reaction center (6,7). 1 O 2 can lead to the damage of various macromolecules within the cell and triggers a special set of sigma factors, which consequently leads to the activation of specific defense mechanisms (8).…”

Photodynamic antimicrobial chemotherapy (PACT) for the treatment of malaria, leishmaniasis and trypanosomiasis

“…Although photosynthesis has an excellent yield of light to chemical energy conversion, side processes compete with normal electron transfer reactions favouring the production of reactive oxygen species (ROS) and nitrogen oxygen species (RNS) (9,10). These species damage biomolecules, causing photoinhibition and photodestruction of the photosynthetic apparatus.…”

Singlet oxygen quantum yields (Φd) in water using beetroot extract and an array of LEDs

“…Data acquisition was performed by a MSA 300 MHz acquisition board (Becker&Hickl GmbH, Berlin). 16,25,26 The experiments were performed at room temperature, in air-saturated aqueous solution. [17][18][19][20][21] In the simplest one, which use monochromatic light sources, the solution absorbance at the irradiation wavelength of the standard and sample is set at the same value, in order to guarantee that the same number of photons is absorbed.…”

“…12,13 Usually, φ D is obtained by measuring the slope of emission versus energy plots and comparing them with standard compounds. [14][15][16] However, expensive lasers and detection schemes are required, specially if the detection is to be performed in aqueous solutions where the lifetime of 1 O 2 is only ca. 4 µs.…”

“…4 µs. [10][11][12][13][14][15][16] Perhaps the most commonly used method to quantify the production of 1 O 2 is based in chemical trapping, 12,13,[17][18][19] i.e., 1 O 2 reacts with compounds that absorb in the UV-Vis region, causing the decay of its absorption and/or emission bands and/or the rise of the absorption/emission bands associated with the oxidized species. Several compounds have been proposed and used as scavengers including, Rubrene, DPBF (1,3-diphenylisobenzofuran) or other water-soluble compounds.…”