Photochemical & Photobiological Sciences

Một quy trình một bước rất hiệu quả để oxi hóa trực tiếp aldehyde thành este dưới sự trung gian của ánh sáng nhìn thấy đã được trình bày. Sử dụng sự kết hợp giữa indium triflate và N-bromosuccinimide (NBS), cùng với ortho-este hoặc rượu, đã cung cấp cách tiếp cận nhanh chóng đến nhiều loại este. Một số cơ chất hoàn toàn biến đổi trong vài giây, trong khi các este tert-butyl khó điều chế hơn có thể được hình thành với năng suất tốt sau không quá 4 giờ.

A series of dinuclear Ru(ii) polypyridine complexes have been prepared and their absorption spectra and luminescence properties (both at room temperature in acetonitrile fluid solution and at 77 K in butyronitrile rigid matrix) have been investigated. The species studied are [(bpy)2Ru(L1)Ru(bpy)2]4+ (1; bpy = 2,2′-bipyridine), [(tpy)Ru(Ln)Ru(tpy)]4+ (2, Ln = L2; 3, Ln = L3; 4, Ln = L4; tpy = 2,2′:6′,2″-terpyridine; for L1–L4 bridging ligands, see Fig. 1). All the compounds exhibit intense absorption bands in the UV region, assigned to spin-allowed ligand-centered (LC) transitions, and moderately intense spin-allowed metal-to-ligand charge-transfer (MLCT) absorption bands in the visible. The compounds also exhibit relatively intense emissions, originating from triplet MLCT levels, both at 77 K and at room temperature. All the new compounds contain a free chelating bipyridine site within their bridging ligand structure, and this confers to the new species interesting properties as far as the effect of perturbation (e.g., addition of acid or zinc salts) on the absorption and luminescence properties is concerned. Indeed, the luminescence intensity of each species is strongly affected by the presence of protons or cations. In particular, upon acid or zinc salts addition the luminescence intensity of 1 decreases, while the luminescence intensity of 2–4 increases. This different behaviour is related to the different dominating pathways for MLCT excited-state decay in Ru(ii) chromophores containing tridentate or bidentate polypyridine ligands. The redox behavior of 1 and 2 has also been investigated in acetonitrile solution in the absence and presence of zinc salts. It has been found that the electronic interaction between the peripheral chromophores is enhanced by zinc coordination.

The photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one was studied in different solvents and in SDS micelles. This compound presents characteristics which include an S0 → S11(π,π*) transition with a 1(n,π*) perturbative component, due to the electronic coupling between the diethylamino group and the coumarin ring, considerable solvatochromism, dual fluorescence and high fluorescence quantum yields in almost all solvents studied. The electronic structure of the S1 and S2 excited states permits vibronic coupling between them, making configurational changes of the S2 excited state possible, leading to the formation of an S2(TICT) state. Analysis of the TCSPC data indicates an equilibrium between the S2(TICT) and S1(LE) states in favour of the former. In protic solvents, the hydrogen bonding between the solvent and the diethylamino moiety results in the formation of an S2(HICT) state, making internal conversion an important deactivation process. Quantum mechanical calculations for the isolated molecule show that the diethylamino group in the S2(TICT) state is twisted at least 56° from the plane of the coumarin ring, with partial electronic decoupling between—NEt2 and the coumarin ring. This twisting angle must be positively influenced by solute-solvent interactions. ΦST is found to be small, but not negligible. However, ΦΔ can be considered negligible, an indication that T1 is a short-lived state. Based on the experimental data and theoretical calculations, the most probable sequence for the first excited states, including the TICT state, is T1(n,π*) < S2(TICT) < S1(π,π*) ≈ S2(n,π*).

Firefly luciferases are widely used as bioluminescent reporter genes for bioimaging and biosensors. Aiming at simultaneous analyses of different gene expression and cellular events, luciferases and GFPs that exhibit distinct bioluminescence and fluorescence colors have been coupled with each promoter, making dual and multicolor reporter systems. Despite their wide use, firefly luciferase bioluminescence spectra are pH-sensitive, resulting in a typical large red shift at acidic pH, a side-effect that may affect some bioanalytical purposes. Although some intracellular pH-indicators employ dual color and fluorescent dyes, none has been considered to benefit from the characteristic spectral pH-sensitivity of firefly luciferases to monitor intracellular pH-associated stress, an important indicator of cell homeostasis. Here we demonstrate a linear relationship between the ratio of intensities in the green and red regions of the bioluminescence spectra and pH using firefly luciferases cloned in our laboratory (Macrolampis sp2 and Cratomorphus distinctus), allowing estimation of E. coli intracellular pH, thus providing a new analytical method for ratiometric intracellular pH-sensing. This is the first dual reporter system that employs a single luciferase gene to simultaneously monitor intracellular pH using spectral changes, and gene expression and/or ATP concentration using the bioluminescence intensity, showing great potential for real time bioanalysis of intracellular processes associated with metabolic changes such as apoptosis, cell death, inflammation and tissue acidification, among the other physiological changes.

Cyanobacterial phycobilisomes funnel the harvested light energy to the reaction centers via two terminal emitters, allophycocyanin B and the core–membrane linker. ApcD is the a-subunit of allophycocyanin B responsible for its red-shifted absorbance (?max 665 nm). Far-red photo-acclimated cyanobacteria contain certain allophycocyanins that show even further red-shifted absorbances (?max > 700 nm). We studied the chromophorylation of the three far-red induced ApcD subunits ApcD2, ApcD3 and ApcD4 from Chroococcidiopsis thermalis sp. PCC7203 during the expression in E. coli. The complex behavior emphasizes that a variety of factors contribute to the spectral red-shift. Only ApcD2 bound phycocyanobilin covalently at the canonical position C81, while ApcD3 and ApcD4 gave only traces of stable products. The product of ApcD2 was, however, heterogeneous. The major fraction had a broad absorption around 560 nm and double-peaked fluorescence at 615 and 670 nm. A minor fraction was similar to the product of conventional ApcD, with maximal absorbance around 610 nm and fluorescence around 640 nm. The heterogeneity was lost in C65 and C132 variants; in these variants only the conventional product was formed. With ApcD4, a red-shifted product carrying non-covalently bound phycocyanobilin could be detected in the supernatant after cell lysis. While this chromophore was lost during purification, it could be stabilized by co-assembly with a far-red light-induced ß-subunit, ApcB3.

The photophysics of fac-[Re(R)(CO)3(CO2Et-dppz)]+ (R = py (1), 4-Me2N-py (2); CO2Et-dppz = dipyrido[3,2a:2′,3′c]phenazine-11-carboxylic ethyl ester) was studied with luminescence spectroscopy and time-resolved infrared (TRIR) spectroscopy in the metal carbonyl (2100–1800 cm−1) and organic ester (1800–1600 cm−1) regions. For 1, the picosecond TRIR spectra in the metal carbonyl region provided evidence for the formation of an intra-ligand IL (π–π*) excited state, which partially decays to an equilibrium with the metal-to-ligand charge transfer (MLCT) excited state. For 2 it is evident that both IL (π–π*) and MLCT excited states are formed within 2 ps of excitation. The magnitude of the ν(CO) shift in the metal carbonyl region following excitation allows the MLCT excited states to be described more precisely as a dπ(Re) → π*(phenazine) 3MLCT state for 1 and as a dπ(Re) → π*(phenanthroline) 3MLCT state for 2.

A combination of spectroscopic methods and density functional theory (DFT) computations was used to study the excited state proton transfer (ESPT) processes of (8-bromo-7-hydroxyquinolin-2-yl)methyl-protected phenol (BHQ-OPh). Characterization of the prototropic forms of BHQ-OPh in different solvent environments revealed that the neutral form predominates in acetonitrile and in 1:1 acetonitrile/water (pH 5.0), whereas the anionic form predominates in 1:1 acetonitrile/PBS (pH 7.4). Both the neutral and anionic forms were significantly populated in 1:1 acetonitrile/water. Upon irradiation in acetonitrile the triplet neutral form was observed, whereas the triplet anionic form was detected in 1:1 acetonitrile/PBS (pH 7.4). The existence of the triplet tautomeric form of BHQ-OPh in both 1:1 acetonitrile/water and 1:1 acetonitrile/water (pH 5.0), and the ESPT processes from the neutral to the anionic to the tautomeric forms in the excited state were observed using time-resolved spectroscopy. A reaction mechanism in 1:1 acetonitrile/water and 1:1 acetonitrile/water (pH 5.0) was proposed based on the spectroscopic and DFT computational results. A comparison of the results for BHQ-OPh with those of BHQ-OAc reveals that the initial prototropic states and photochemical processes are similar. The understanding gained of the initial photo-induced processes of BHQ-based photoremovable protecting groups (PPGs) is useful for the design of new quinolinyl-based PPGs for specialized applications.

The XeCl excimer 308 nm radiation system is described as a powerful tool for synthetic organic photochemistry involving carbonyl and carbonyl-type chromophores. Scaleable photochemical reactions which have been tested and optimized for this system were photodecarboxylation, [2 + 2]-photocycloaddition, and Type III (electron transfer) photooxygenation reactions.

Động lực học trạng thái kích thích siêu nhanh của protein huỳnh quang Kaede đã được nghiên cứu thông qua việc sử dụng huỳnh quang thời gian phân giải và hấp thụ tạm thời. Khi chiếu sáng trạng thái trung tính của nó, protein trải qua sự chuyển đổi hiệu quả sang một trạng thái phát huỳnh quang ở bước sóng dài hơn. Cơ sở phân tử của quá trình quang chuyển liên quan đến sự mở rộng của sự đồng phân π của chromophore thông qua việc loại bỏ β chính thức, nhưng chi tiết về con đường phản ứng vẫn còn đang tranh cãi. Dựa trên động lực học quan sát được trong các thí nghiệm trên mẫu protein trong hai dung dịch đệm H2O và D2O, chúng tôi cho rằng một cơ chế cắt liên kết do ánh sáng khởi đầu (20 ps) có thể xảy ra, tạo ra trạng thái trung tính màu đỏ mà chromophore đỏ tồn tại. Sự kích thích của dạng trung tính màu đỏ dẫn đến sự hình thành các loài anion màu đỏ thông qua hai kênh truyền năng lượng cộng hưởng Förster (FRET). FRET giữa các dạng trung tính đỏ và anion đỏ xảy ra trong tetramer với các hằng số thời gian là 13.4 ps và 210 ps. Ngược lại với các đề xuất trong tài liệu, không có hiện tượng ESPT nào được quan sát.