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 fluorescence quantum yield of berberine in aqueous solution is significantly smaller than those of organic solution. The time profile of fluorescence intensity of berberine was analyzed by a bi-exponential function, showing that two kinds of states of berberine exist in the solutions. The observed fluorescence lifetime of shorter lifetime species of berberine in water (0.08 ns) was markedly smaller than those of organic solvents and the relative amplitude of the shorter lifetime was dominated in the aqueous solution. Thus, this shorter lifetime can be explained by the deactivation via intramolecular electron transfer. These two states of berberine were independent of pH. The enthalpy and entropy changes between these two states were - 23.2 kJ mol-1 and - 90 J K-1 mol-1, supporting the aggregation of berberine. In the aggregation state, an electrostatic interaction between cationic berberine and chloride ion decreases the electron accepting ability of the isoquinoline moiety of berberine, resulting in the suppression of intramolecular electron transfer. Furthermore, in the presence of clay, the interaction between berberine and clay increased the fluorescence intensity of berberine and its lifetime, showing that the negative charge of clay suppresses the intramolecular electron transfer. Since the electron transfer quenching of the photo-excited berberine is advantageous for suppressing the phototoxic effect of berberine, the inhibition of berberine aggregation is an important process for the phototoxicity prevention.
This paper investigates the evolution of changes in surface ultraviolet (UV) radiation globally, emphasizing the significant impacts of key factors influencing its variability, i.e., total column ozone, aerosols, clouds, and surface reflectivity. Simulations of UV radiation were performed by the UVSPEC radiative transfer model and span from the mid-twentieth century to the end of the twenty-first century. Input data were derived from eleven Earth System Models that participated in the 6th Phase of the Coupled Model Intercomparison Project (CMIP6). The UV Index (UVI) simulations for the late twentieth century indicate an increase in UVI levels relative to the 1950s in the Southern Hemisphere's mid and high latitudes, attributed to ozone depletion, and decreases in southeastern Asia due to increases in aerosols. Projections of changes in UVI for the last decade of the twenty-first century were derived for three Shared Socioeconomic Pathways (SSPs): SSP1-2.6, SSP3-7.0, and SSP5-8.5. Under SSP1-2.6, the scenario with the lowest greenhouse gas (GHG) and aerosol emissions, UVI is projected to increase relative to the 1950s by up to 20% in Europe and North America and to decrease by as much as - 10% over tropical and polar regions. Under SSP3-7.0 and SSP5-8.5, scenarios with higher GHG and aerosol emissions, UVI changes are generally negative globally due to ozone recovery and increases in aerosol optical depth, while localized positive changes are found over Central and South America, Europe, Africa, and the Pacific and Indian Oceans. The changes in the biologically effective solar irradiance for plant growth exhibit similar geographical patterns to UVI with slight differences, due to weaker sensitivity to changes in ozone.
The present work focuses on the photophysical behavior of meso-N-butylcarbazole-substituted BODIPY (CBZ-BDP) in different organized media towards exploring the possible use of the dye as a molecular sensor and imaging agent. The molecule shows an appreciable change in absorption and emission spectra at 75% water-acetonitrile mixture compared to pure acetonitrile. In water-acetonitrile mixture, it displays aggregate-induced emission (AIE) bands. New emission peaks are observed at 560 nm and 630 nm, corresponding to LE (locally excited) and ICT (intramolecular charge transfer) states of CBZ-BDP aggregates. The fluorescence anisotropy studies of CBZ-BDP in glycerol medium show its better sensitivity towards the microenvironment. CBZ-BDP was used to probe various microheterogeneous systems like bile salts, pluronics, and lipid bilayer systems in aqueous medium. The dye displays sensitive variation in emission intensity and fluorescence anisotropy in sodium cholate (NaC) bile salt in aqueous medium as a function of the bile salt concentration. The molecule detects the temperature-induced phase transitions in pluronic P123 and F127, as well as 1,2-dimyristoylphosphatidylcholine (DMPC) and 1,2-dipalmitoylphosphatidylcholine (DPPC) lipid bilayer systems in aqueous medium. These studies strongly suggest that CBZ-BDP can be used as an efficient fluorescent probe in sensing the micro-environmental changes in bile salts, pluronics, and lipid bilayers in aqueous medium. The imaging studies of CBZ-BDP-embedded Giant Unilamellar Vesicles (GUVs) were carried out. The molecule stains the lipid bilayers and displays bright-green fluorescent images, suggesting its potential in lipid bilayer imaging.
A new ratiometric and colorimetric fluorescent probe HTD was synthesized based on the reaction of 4-aminophenyl boronic acid pinacol ester and 4-(3-formyl-4-hydroxyphenyl) benzonitrile. The probe exhibited a unique fluorescence response to hypochlorous acid and had good anti-interference performance in the presence of other interference. When HTD met the NaClO, the light orange fluorescence was changed to green with the blue-shifted emission wavelength from 550 to 500 nm. Moreover, the absorbance of HTD's UV-vis at 300 nm and 375 nm decreased in the presence of NaClO. The limit of detection was 1.83 × 10-7 M and 2.96 × 10-6 M based on the fluorescence and UV-vis titration data. NMR, HRMS, and IR spectra suggested that the possible sensing mechanism of HTD to NaClO was the formation of initial compound 4-(3-formyl-4-hydroxyphenyl) benzonitrile due to the oxidation of hypochlorous acid in aqueous solution. The portable test strips were obtained, and the real water sample test reached good results with spiking recoveries among 92.00% ~ 103.25%. Finally, endogenous hypochlorous acid produced by LPS and PMA was successfully detected by HTD in living mice using in situ fluorescence bioimaging.
Numerous anthropogenic ultraviolet filters (UVF) have been detected in aquatic environments and concerns have arisen regarding their potential impacts on aquatic organisms. This manuscript reviews the environmental concentrations and potential toxicity of various UVF. The highest concentrations of UVF are typically observed near frequently visited recreational areas and during peak water-activity periods, which suggests that sunscreen application correlates with noticeable alterations in UVF concentrations. Aquatic concentrations of certain filters have sporadically exceeded 10 μg/L, although most measurements remain below 1 µg/L, which is below commonly reported toxicity levels. UVF have also been detected in aquatic organisms, typically ranging from nondetectable levels to a few hundred ng/g, depending on the species. The toxic effects from UVF, such as coral bleaching and diminished growth, have been observed in laboratory settings, however, toxicity tends to manifest only at significantly higher levels than what is typically detected in aquatic environments. Further research is imperative to provide consumers with improved guidance on selecting sunscreen containing UVF that poses the least environmental risk.
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).
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-, SO32-, 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.
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.
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