The current enthusiasm for photochemistry can be partially attributed to the booming interest of the synthetic community in photoredox catalysis. Photoredox catalysis has enabled nontraditional reaction
Authors:S. D’souza, N. Nathawat, J. Nair, P. Radha Krishna, N. Ramaswamy, G. Singh, and M. Sahu
Primary photochemical reactions and the activities of the antioxidant enzymes chloroplastic superoxide dismutase (SOD), glutathione reductase (GR) and glutathione-S-transferase (GST) were determined in water-stressed pearl millet (
L. cv. HHB-67) plants sprayed with the thiol compounds dithiothreitol (DTT), thioglycolic acid (TGA) and thiourea (TU) and the thiol modifiers 5,5′-dithio-bis-2-nitrobenzoic acid (DTNB) and N-ethylmaleimide (NEM) at the earhead emergence stage (47 days after sowing, DAS), together with a control. Sampling was done at 54 and 67 days after sowing. Photosystem I and II (PS I and II) activities (ferricyanide site) were found to increase in plants sprayed with TU, TGA and DTT at both stages (54 and 67 DAS), but a reduction in PS II activity (DCQ Site) compared with the control was caused by NEM (66.66%) and DTNB (27.77%) at 54 DAS. A similar decrease in the activity of PS II (ferricyanide site) was found at 67 DAS for DTNB (55.55%). The chloroplastic SOD activity increased in chloroplasts isolated from leaves sprayed with thiol compounds at both sampling stages, except for NEM at 54 and 67 DAS. The activities of GR and GST in the leaves were higher in thiol-treated plants than in the control at 54 and 67 DAS, while the lowest GR activity was seen for the sulphydryl modifiers (DTNB and NEM) in leaves at 54 DAS. The experimental data suggest an enhancement in the primary photochemistry and antioxidant enzyme activities of water-stressed pearl millet in response to foliar spraying with thiol compounds.
Authors:Zorana Katanić, Lejla Atić, Dž. Ferhatović, Vera Cesar, and H. Lepeduš
Vegetative buds represent developmental stage of Norway spruce (Picea abies L. Karst.) needles where chloroplast biogenesis and photosynthetic activity begin. We used the analyses of polyphasic chlorophyll a fluorescence rise (OJIP) to compare photosystem II (PSII) functioning in vegetative buds and fully photosynthetically active mature current-year needles. Considerably decreased performance index (PIABS) in vegetative buds compared to needles pointed to their low photosynthetic efficiency. Maximum quantum yield of PSII (Fv/Fm) in buds was slightly decreased but above limited value for functionality indicating that primary photochemistry of PSII is not holdback of vegetative buds photosynthetic activity. The most significant difference observed between investigated developmental stages was accumulation of reduced primary quinine acceptor of PSII (QA−) in vegetative buds, as a result of its limited re-oxidation by passing electrons to secondary quinone acceptor, QB. We suggest that reduced electron transfer from QA− to QB could be the major limiting factor of photosynthesis in vegetative buds.
Unstable novel species produced by photolysis of ferrocene (Cp2Fe) isolated in low-temperature matrix were studied by means of the57Fe Mössbauer spectroscopy. On the UV-irradiation of57Fe-enriched ferrocene co-condensed with CCl4 in low-temperature N2 matrix (20 K), unknown high spin ferrous species (I.S.=0.90±0.01 mm/s, Q.S=1.94±0.02 mm/s) were produced as well as ferricinium ion [Cp2Fe]+ (I.S.=0.52±0.01 mm/s, Q.S.=0.0 mm/s). On the annealing, these photoproducts disappeared to reform ferrocene by the reverse reaction in the matrix. The mechanisms of the photochemical reaction were discussed.
A well-known photolabile substance, nifedipine, was used as a sample material to test self-constructed irradiation cells and
demonstrate their usefulness in photostability studies. The devices were made as accessories for a commercial isothermal microcalorimeter.
Several powder samples containing various amounts of moisture were irradiated with monochromatic light as a scan measurement
from 700 to 280 nm, and the heat flow evolved in the photodegradation of nifedipine was determined. According to the results,
light does not affect the nifedipine molecule directly, but the photodegradation is a result of the combined effects of moisture
Authors:Han Yueh, Anastasia Voevodin, and Aaron B. Beeler
9-Hydroxymethylxanthene derivatives were optimized as a photolabile protecting group for amines in flow chemistry. 9-Methylxanthene and 2-methoxy-9-methylxanthene showed excellent deprotection yields in protic and aprotic solvents, respectively. The protecting group has good stability in acidic, basic, and thermal conditions and was successfully utilized for protection and deprotection of a variety of amines. A multistep continuous-flow synthesis of a piperazinylcarbonyl-piperidine derivative utilized the 2-methoxy-9-methylxanthene as the key protecting group utilized in an orthogonal manner.
Authors:Kimitada Terao, Yasuhiro Nishiyama, Hiroki Tanimoto, Tsumoru Morimoto, Michael Oelgemöller, and Tsumoru Morimoto
The diastereoselective [2+2] photocycloaddition of ethylene to a chiral cyclohexenone was studied in a continuous flow microcapillary reactor. In all cases examined, the microcapillary reactor gave higher conversions and selectivity than the batch system, even after shorter irradiation times. These findings were explained by the superior temperature control, favorable light penetration, and generation of a gas–liquid slug flow with improved mass transfer in the microreactor.
Authors:Oksana Shvydkiv, Carolin Limburg, Kieran Nolan, and Michael Oelgemöller
Photooxygenation of 1,5-dihydroxynaphthalene to Juglone was studied in a falling film microreactor. Moderate conversion rates of up to 31% were achieved after just 160 s of exposure to visible light. In contrast, batch reactions gave much lower conversions of up to 14% after a prolonged time period of 10 min. The difference in performance is explained by the superior light penetration in the microfilm and the large gas-liquid contact area.