Electron Transfer Fluorescence Quenching of Blepharisma japonicum Photoreceptor Pigments

Abstract

Abstract— The hypericin analogs blepharismin (BP), oxyblepharismin (OxyBP) and stentorin (ST), the photosensing chromophores responsible for photomotile reactions in the ciliates Blepharisma japonicum (red and blue cells) and Stentor coeruleus, represent a new class of photoreceptor pigments whose chemical structures have recently been determined. In the case of ST it has been shown that the first excited singlet state can be deactivated by donation of an electron to an appropriate acceptor molecule (e.g. a quinone molecule). This charge transfer can be considered a possible mechanism for the primary photoprocess for the photomotile responses in S. coeruleus. To determine whether an electron transfer process also occurs in the deactivation of excited blepharismin, we studied the fluorescence quenching of OxyBP in dimethyl‐sulfoxide (DMSO) and in ethanol using electron acceptors with different reduction potentials. Under our experimental conditions ground state and excited state complexes (like fluorescent exciplexes) are not formed between the fluorophore and the quenchers. In DMSO the bimolecular quenching constant values (kq) calculated on the basis of the best fitting procedures clearly show that the quenching efficiency decreases with the quencher negative reduction potential, E0. The kq (M‐1 s‐1) and E0 (V) values are, respectively, 7.8 times 109 and ‐0.134 for 1,4‐benzoquinone, 8.9 times 109 and ‐0.309 for 1,4‐naphthoquinone, 2.4 times 109 and ‐0.8 for nitrobenzene, 0.009 times 109 and ‐1.022 for azobenzene and 0 and ‐1.448 for benzophenone. These findings point to the conclusion that upon formation of the encounter complex between OxyBP and the quencher, an electron is released from excited OxyBP to the quencher, similar to what happens in ST. It is suggested that in the pigment granules such a light‐induced charge transfer from excited blepharismin to a suitable electron acceptor triggers sensory transduction processes in B. japonicum.

Fluorescence Dynamics of Organic Laser Dyes in Azobenzene Polymer

“…On the other hand, semiempirical molecular orbital calculations confirmed that the highest occupied molecular orbital (HOMO) of an azobenzene group is located at higher energy by 2-3 eV compared with the laser dyes. Thus, it is suggested that the photoexcitation of a dye molecule induced absorption saturation of pDR1M through oxidative electron transfer from azobenzene to the dye [3,4] in ca. 3 ps.…”

Ratiometric fluorescence nanosensors based on core‐shell structured carbon/CdTe quantum dots and surface molecularly imprinted polymers for the detection of sulfadiazine

“…The type of fluorescence quenching can be determined by bimolecular quenching constant ( K q ). When the fluorescent lifetime (τ 0 ) and K SV are known, bimolecular quenching constant is calculated by the following equation : …”

“…The type of fluorescence quenching can be determined by bimolecular quenching constant (K q ). When the fluorescent lifetime (τ 0 ) and K SV are known, bimolecular quenching constant is calculated by the following equation [34]: The fluorescence lifetime of TGA-CdTe QDs was typically in the range of 6-11 ns with the change of particle size. Therefore, K q was at 10 12 order of magnitude by formula of calculation K q =K SV /τ 0 , which far outweighed the maximum dynamic fluorescence collision quenching constant of (1.0-2.0) × 10 10 L/mol/s [35].…”

Analyses of Structure of Photoreceptor Organelle and Blepharismin-associated Protein in Unicellular Eukaryote Blepharisma¶

“…Previous study (15) has demonstrated that purified free cise, some of the light-excited OxyBL are able to decay through the deexcitation pathway other than radiative transition, such as an electron transfer, (17) which is possibly responsible for the photosignal transduction leading to the modification of photobehavior in Blepharisma. The pigments eluted in fraction I are not associated with the proteins, or are not specifically associated with the proteins if they are bound.…”