Photochemical & Photobiological Sciences最新文献

Colorimetric chemosensors L₁ and L₂, based on isoniazid hydrazones, have been designed for the highly sensitive and selective recognition of CN^- ion. Competing experiments were conducted with various other anions such as F^-, Cl^-, Br^-, I^-, SCN^-, ClO₃^-, ClO₄^-, NO₃^-, H₂PO₄^-, SO₃^2-, and HSO₄^- in an acetonitrile solution. In the UV-Vis spectra, a bathochromic shift in the absorption bands of both hydrazones was observed following the addition of cyanide. These spectral changes were accompanied by a color transition from transparent to orange for L₁ and from pale yellow to peach for L₂, which is attributed to the deprotonation of the chemosensors. The detection limits for cyanide ions were determined to be 0.36 µM for L₁ and 2.79 µM for L₂ using the 3σ rule. Quantum chemical calculations were employed to optimize the structure of the chemosensors, compute their UV-Vis spectra, and confirm the proposed detection mechanism for CN⁻ ions.

Flavin-dependent halogenases (FDHs) are promising candidates for the sustainable production of halogenated organic molecules by biocatalysis. FDHs require only oxygen, halide and a fully reduced flavin adenine dinucleotide (FADH^-) cofactor to generate the reactive HOX that diffuses 10 Å to the substrate binding pocket and enables regioselective oxidative halogenation. A key challenge for the application of FDHs is the regeneration of the FADH^-. In vitro, FADH^- can be regenerated by photoreduction of the oxidized FAD inside the protein using blue light, turning the halogenase into an inefficient artificial photoenzyme. We aimed to improve the photochemical properties of the tryptophan 5-halogenase PyrH from Streptomyces rugosporus by structure-guided mutagenesis. W279 and W281 of the conserved WxWxIP-motif close to FAD were exchanged against phenylalanine. Time-resolved UV-vis spectroscopy showed that the W281F exchange indeed increased the quantum yield of the one- and two-electron reduction, respectively. The cofactor binding affinity decreased slightly with dissociation constants rising from 31 to 74 μM, as examined by fluorescence anisotropy. FTIR difference spectroscopy demonstrated that the allosteric coupling between the FAD and substrate binding sites was mostly preserved. In contrast, the double mutant did not improve the yield further, while negatively affecting binding affinity and structural coupling. The distal W279F exchange was less effective in all parameters. Photoreductions were additionally delayed by a reversible inactive conformation. We conclude that there is a delicate balance to be considered for screening of FDHs for biocatalysis. Variant PyrH-W281F was found to be the most promising candidate for the application as artificial photoenzyme.

The chirality and chiroptical response of materials have attracted significant attention for their potential to introduce the new science of light-matter interactions. We demonstrate that collective mode formation under modal coupling between localized surface plasmon resonances (LSPRs) with a chiral arrangement and Fabry-Pérot (FP) nanocavity modes can induce chiroptical responses. We fabricated a cluster of isotropic gold nanodisks with a chiral arrangement (gold nano-windmills, Au-NWs) on the FP nanocavities of TiO₂ and Au film. The differential absorption of the Au-NWs coupled with the FP nanocavities under left- and right-handed circularly polarized light irradiations in the far field was significantly enhanced compared with the differential absorption without the FP nanocavities. Far- and near-field analyses by numerical simulation revealed that the Au-NWs coupled with the FP nanocavities formed a collective mode in the near field, and the collective mode represented the chiroptical response in the far field. The light field with the large helicity, can be used in chiral light-matter interactions. The concept of collective mode formation using isotropic metal nanodisks coupled with FP nanocavities provides a platform for controlling complex light fields.

Photodynamic Therapy (PDT) offers a minimally invasive approach for treating various health conditions, employing a photosensitizer (PS) and specific light. Recent enhancements make PDT outpatient-friendly and less discomforting. Effectiveness hinges on selecting the appropriate PS. This article delves into natural and synthetic PSs, emphasizing the rising interest in natural alternatives for their safety. It explores their mechanisms, characteristics, and applications, offering insights into their potential contributions to advancing PDT. This extensive review delves into the preclinical and clinical landscape of natural PSs for PDT, shedding light on their diverse applications and promising outcomes. Compounds like curcumin, piperine, riboflavin, psoralen, hypericin, and others show significant potential in preclinical in vitro studies across various cell lines. In vivo, these photosensitizers prove effective against skin tumors, carcinomas, and sarcomas, inducing apoptosis, autophagy, and ROS generation for therapeutic efficacy. The review underscores the critical role of proper dosing and monitoring in balancing therapeutic benefits and risks. It highlights the advantages and limitations of natural PSs, emphasizing their specific targeting, bioavailability, and limited side effects. The future of PDT holds promising breakthroughs, taking from some evidence like Bergamot oil in nanostructured lipid carriers for dermatological conditions. Second-generation photosensitizer Tookad shows potential in prostate cancer treatment, while Tripterygium wilfordii Hook. F. emerges as an antimicrobial PDT source etc. Thus, environmental concerns in PDT prompt a shift to plant extracts for PS purification. The evidence-supported focus on natural PSs establishes this article as a key resource for advancing natural compounds in PDT and their therapeutic applications.

Photophysical and photochemical studies were carried out to examine the photoreactivity of etheno adducts, 1,N⁶-ethenoadenine (εdA) and 1,N²-ethenoguanine (εdG), in the presence of two well-known photosensitizers acting by Type I and/or Type II mechanisms such as 4-carboxybenzophenone (CBP) and rose Bengal (RB), respectively. Steady-state photolysis experiments combined with HPLC and mass spectroscopy measurements lead to photoproducts that correspond to the repaired nucleosides. To determine the mechanism of this photooxidation processes, phosphorescence spectroscopy, direct detection of singlet oxygen luminescence and laser flash photolysis were carried out. This work establishes that εdG and εdA are sensitive to both types of processes (Type I and II).

The efficacy of photodynamic treatment (PDT) against deep-seated tumor is hindered by low penetration depth of light as well as hypoxic conditions which prevails in tumor. To overcome this limitation, Near-infrared (NIR) absorbing photosensitizers have been investigated actively. In the present study we evaluated the PDT efficacy of an NIR absorbing chlorophyll derivative 'Cycloimide Purpurin-18 (CIPp-18)' in Human Breast carcinoma (MCF-7) and cervical adenocarcinoma (Hela) cells under normoxic and hypoxic conditions. PDT with CIPp-18 (2.0 µM, 3 h) and NIR light (700 ± 25 nm, 0.36-1.4 J /cm²) induced potent phototoxicity in both the cell lines. Under hypoxic conditions, PDT induced ~ 32% and 42% phototoxicity at LD₅₀ and LD₇₀ light dose, respectively, which corresponds to phototoxic dose under normoxia. CIPp-18 in neat buffer (pH 7.4) showed generation of singlet oxygen (¹O₂) as well as superoxide (O₂^·-) radicals. Studies on ROS generation in cells using fluorescence probes and the effect of mechanistic probes of ¹O₂ (Sodium Azide, Histidine, D₂O) and free radicals (DMSO, Mannitol, Cyanocobalamin, SOD-PEG) on phototoxicity show that ¹O₂ plays major role in phototoxicity under normoxia. Whereas, under hypoxic conditions, PDT led to no significant generation of ROS and phototoxicity remained unaffected by cyanocobalamin, a quencher of O₂^·-. Moreover, CIPp-18 showed localization in cell membrane and PDT led to more pronounced loss of membrane permeability in cells under hypoxia than for normoxia. These results demonstrate that CIPp-18 is suitable for PDT of cancer cells under hypoxia and also suggest that phototoxicity under hypoxia is mediated via ROS-independent contact-dependent mechanism.

New photocatalytic materials based on complex oxides and a widely used and cheap polymer (PMMA) have been prepared. Among complex oxides previously investigated, the following have been used-RbTe_1.5W_0.5O₆, CsTeMoO₆, CsV_0.625Te_1.375O₆, NaVMoO₆, KVMoO₆. For comparison, the binary oxides TiO₂ and WO₃ were used. The form of PMMA matrix was used as sponge and glass. The amount of powder in PMMA was selected based on retaining the polymer properties and getting the photocatalytic activity, which corresponds to 1% powder in sponge and 0.5% in glass. The "photocatalyst/PMMA" composites decompose the methylene blue under visible and UV light as well as possess antibacterial properties. The high electron-hole recombination was found out for composites photocatalysts, which significantly influences only on organic compounds decomposition in solutions. However, there is no direct dependence between effective photodegradation of simple organic molecules and antimicrobial properties. Inactivation of bacteria is determined by many factors such as active generated radicals, adsorption properties of the surface and the photocatalyst form, which can change the main active radicals. The comparison of photocatalytic action on organic solutions and bacteria of initial powders and PMMA composites allow choosing the most effective combination for further application. The most promising antimicrobial properties for composites have been obtained using compounds with β-pyrochlore structure.

Zinc methyl 13²,13²-disubstituted 3-hydroxymethyl-pyropheophorbides-a were prepared as models of bacteriochlorophyll-d, which self-aggregated in the main light-harvesting antenna (chlorosome) of photosynthetic green bacteria. The synthetic zinc 3¹-hydroxy-13¹-oxo-chlorins possessing methyl and methoxycarbonyl groups at the 13²-position could not self-aggregate in an aqueous Triton X-100 solution. However, another model compound bearing an ethane-1,2-diyl group at the 13²-position did self-aggregate under the same conditions to give red-shifted and broadened Qy and Soret absorption bands. The spiro-cyclopropane condensation slightly suppressed the chlorosome-like self-aggregation due to an increase in the steric hindrance around the 13-carbonyl group. The red-shifted and broadened values of these bands by the self-aggregation were dependent on the 13²-substituents. The 13²-substitution substantially controlled the aqueous J-aggregation.

This review aims to provide the readership with an overview of the applications of the time-resolved spectroscopic techniques (often combined with steady-state measurements) in the elucidation of the mechanism of the photochemical behaviour of diaryl- and triarylamines. Such derivatives undergo cyclization to the carbazoles or ionization to the corresponding amine radical cations depending on both the nature of the starting substrates and the reaction conditions. In this context, time-resolved spectroscopy techniques allowed for the detection and the full characterization of all the excited states and the transients involved in these processes. The main characteristics of such species, including lifetime, time-resolved absorption spectra, quantum yield values and rate constants of formation and decay in both homogeneous and micro-heterogeneous environment (e.g. aqueous surfactant solutions) are thus summarized in the presented paper.