Reinvestigation on primary processes of PSII-dimer from Thermosynechococcus vulcanus by femtosecond pump-probe spectroscopy.

Cyanobacterial photosynthetic apparatus efficiently capture sunlight, and the energy is subsequently transferred to photosystem I (PSI) and II (PSII), to produce electrochemical potentials. PSII is a unique membrane protein complex that photo-catalyzes oxidation of water and majorly contains photosynthetic pigments of chlorophyll a and carotenoids. In the present study, the ultrafast energy transfer and charge separation dynamics of PSII from a thermophilic cyanobacterium Thermosynechococcus vulcanus were reinvestigated by femtosecond pump-probe spectroscopic measurements under low temperature and weak intensity excitation condition. The results imply the two possible models of the energy transfers and subsequent charge separation in PSII. One is the previously suggested "transfer-to-trapped limit" model. Another model suggests that the energy transfers from core CP43 and CP47 antennas to the primary electron donor ChlD1 with time-constants of 0.71 ps and 3.28 ps at 140 K (0.17 and 1.33 ps at 296 K), respectively and that the pheophytin anion (PheoD1-) is generated with the time-constant of 43.0 ps at 140 K (14.8 ps at 296 K) upon excitation into the Qy band of chlorophyll a at 670 nm. The secondary electron transfer to quinone QA: PheoD1-QA → PheoD1QA- is observed with the time-constant of 650 ps only at 296 K. On the other hand, an inefficient ß-carotene → chlorophyll a energy transfer (33%) occurred after excitation to the S2 state of ß-carotene at 500 nm. Instead, the carotenoid triplet state appeared in an ultrafast timescale after excitation at 500 nm.

Tunable chiral reaction media based on two-component liquid crystals: regio-, diastereo-, and enantiocontrolled photodimerization of anthracenecarboxylic acids.

Three kinds of enantiopure amphiphilic amino alcohols (1a-c) were newly synthesized, of which the stereochemistry of the stereogenic carbons adjacent to the amino (C2) and hydroxy (C1) groups was systematically varied. By using these amino alcohols and four photoreactive carboxylic acids, 12 kinds of salts were prepared. The structure and thermal behavior of the salts were thoroughly investigated by various techniques, which revealed that the stereochemistry of the amino alcohol unit has significant effects on the properties of the salts; the salts of 1a with (1R,2S)-configuration did not exhibit any liquid crystal (LC) phase but showed high crystallinity, whereas 1b and 1c with (1S,2S)- and (1S)-configurations, respectively, generally afforded stable LC salts with smectic structure(s). Within the matrix of these amphiphilic salts, the in situ photodimerizations of 2-anthracenecarboxylic acid (2c) and 1-anthracenecarboxylic acid (2d) were conducted by the irradiation with UV/vis light (500 W, a high-pressure mercury arc lamp, >380 nm). Concerning reactivity and regio-/diastereo-/enantioselectivities, the LC phases were found to be superior to isotropic and crystalline phases. For the two substrates 2c and 2d, every LC phase promoted the photodimerization with unprecedentedly high head-to-head selectivity. Particularly in the case of 2c, diastereoselecitivity (syn(HH) vs anti(HH)) could be rationally controlled by the choice of the amino alcohol unit and mesophase (syn(HH):anti(HH) = 61:37 to 26:72). Moreover, one of the LC phases exhibited by 1b·2c afforded the anti(HH)-dimer of 2c with excellent enantioselectivity (up to 86% ee). On the basis of the hypothesis that the present photochemical outcome arises from the preorientation of the substrates, a preliminary structural model of these LCs was proposed.