Photochemistry and Photobiology

Photoreceptor phytochromes switch photochromically between two states; a red- (Pr) and a far-red (Pfr) absorbing form. Here, we summarize recent solid-state MAS NMR work on this conversion. As demonstrated, the process is initiated by a double-bond photoisomerization of the chromophore at the methine bridge of rings C–D (left panel). Our NMR studies also revealed a soft chromophore and a less well-defined protein-binding pocket in the cyanobacterial Cph1 phytochrome in Pr relative to Pfr (overlay of ¹³C–¹³C dipolar-assisted rotational resonance spectra of the chromophore in both states, right panel). NMR measurement of the intermediates during the Pfr-to-Pr back-reaction achieved insight into a clockwork-like mechanics. The physical aspects of the photoactivation in phytochromes are discussed.

In the presence of RuCl₆²⁻, chloroform decomposes under near-UV irradiation to phosgene and hydrogen chloride. The photoactive species is suggested to be RuCl₅(CHCl₃) ⁻.

The photophysical properties of 7-(diethylamino)coumarin-3-carboxylic acid (7-DCCA) were studied in three cyclodextrins (α, β, γ-CDs) using steady state absorption, emission and time-resolved fluorescence spectroscopy. We have proposed that 7-DDCA form 1:1 capped complex with β-CD. In presence of urea, 7-DCCA form 1:1 inclusion complex with β-CD. With γ-CD it forms 1:1 and 1:2 (guest:host) inclusion complex. The photophysics of 7-DCCA was studied in neat solvents and solvent mixtures. It was found that the photophysics of 7-DCCA depended on the structural feature of the solvents and solvent mixtures.

The fluorescence lifetimes of estrone, 17β-estradiol, and 17α-ethinylestradiol are strongly solvent dependent. The ability of the solvent to accept hydrogen bonds has a significant effect on the excited state dynamics of these molecules.

Intracellular pH plays an important role in cellular events such as cell growth, endocytosis and cell adhesion and abnormal pH values will result in cellular dysfunction. A good pH Probe is an essential tool. The mechanisms of fluorescent pH probes can mainly be divided into two types; the Photoinduced Charge Transfer (PCT) mechanism and the Photoinduced Electron Transfer (PET) mechanism. The principles of these two typical two-photon pH fluorescent probes are specifically validated by theoretical methods and some improved probes on the basis of these molecules are designed. Molecules with larger Two-photon Absorption (TPA) cross sections will be designed and investigated.

Blood vessels growing toward the light: can light protect blood plasma from oxidative damage?

DHICA units enhance aggregation-dependent contributions to Eumelanin black color.

It is commonly believed that the emissive excited state in the bio-, chemiluminescence, and fluorescence phenomena is the same, although from a mechanistic viewpoint, these processes might differ. To solve this dilemma in the Firefly oxyluciferin, we study by means of ab initio quantum chemistry and hybrid quantum chemistry/molecular mechanics methods the emission process in the three luminescent phenomena.

Pyrazole meso-substituted heptamethine cyanine dye showed pH-dependent fluorescence lifetime change within physiological useful range. This novel fluorescent probe is a good candidate for in vivo diagnostics using fluorescence lifetime imaging method.

The self-organizing and scaffolding properties of DNA are often used to assemble complex structures. We describe duplex DNA oligomers that contain a pyrene chromophore linked by a trimethylene chain to N⁴ of cytosine. Intercalation of the pyrene group stabilizes the duplex and causes efficient quenching of pyrene's fluorescence.

Irradiation of butyrylcholinesterase (BChE) in the presence of methylene blue results in a variety of oxidations typical of phenothiazine photochemistry of proteins (hydroxylated methionine, hydroxylated tryptophan, kynurenine, N-formyl-kynurenine, hydroxylated and peroxidized-cysteine), but in addition there are novel oxidations (oxidation of serine, oxidation of histidine, 3-OH-kynurenine) and there is extensive protein degradation such that when the enzymatic activity is finally eliminated there is little to no intact protein remaining.

Three chimeras of PYP were constructed that have Rhodobacter capsulatus PYP regions exchanged in a Halorhodospira halophila PYP backbone. With more regions exchanged, we observed decreased overall protein stability and increased solvent exposure in the ground state, while the spectra showed increasing amounts of the intermediate spectral form (λ_max = 380 nm). Chimeras that have the β4–β5 loop exchange show at least 20 000 times slower recovery kinetics as compared to the prototypical H. halophila PYP.

Listeria monocytogenes is a food-borne bacterial pathogen responsible for listeriosis, an infectious disease in the human host. The pathogen has been identified to contain the Listeria Lmo0799 protein, a virulence factor activated by blue light. Genomic search has identified a LOV-domain protein coupled to a STAS domain, homologues to Bacillus subtilis YtvA, to be the only light sensor so far. We have cloned, expressed in E. coli and purified the full-length LM-LOV-STAS. Here, we report the photocycle and other spectroscopic features of the protein. Although it is a homolog of YtvA, LM-LOV-STAS has unique structural and spectroscopic features that are not reported for YtvA.

Readily available blue-diode based pulse amplitude modulation (PAM) fluorimeters can be used to measure photosynthetic electron transport (ETR) in nonsulfur purple photosynthetic bacteria. PAM machines can measure photosynthesis not only in oxygenic photorganisms and in those with a RC-2 photosystem. Figure shows a comparison of the electron transport rate (ETR) vs irradiance of acetate-grown Afifella cells with and without added acetate (5 mol m⁻³). ETR in both cases show a waiting-in-line saturation curve with inhibition at high irradiances (r > 0.9731). Added acetate increases ETR but increases optimum irradiance as well.

Damage of DNA and Photosystem-II are among the most significant primary effects of UV-B irradiation in photosynthetic organisms. Both damaged DNA and PSII can be repaired representing important defense mechanisms against detrimental UV-B effects. Correlation of Photosystem-II damage and repair with the concurrent DNA damage and repair was investigated in the cyanobacterium Synechocystis PCC6803 using its wild type and a photolyase deficient mutant. This contribution shows that repair capacity of Photosystem-II depends on the ability of cells to repair UV-B damaged DNA through maintaining the transcription of genes, which are essential for protein synthesis dependent repair of the Photosystem-II reaction center.

This study reports a potential use of blue light as a supplemental light source in cultivation of Kalanchoe pinnata, an important medicinal species. We investigated the effects of blue and UV-A light supplementation on the total phenol content, antioxidant activity and chromatographic profile of K. pinnata extracts. Supplemental blue light improved the antioxidant activity and changed the phenolic profile. Analysis by HPLC of supplemental blue-light plant extracts (A) revealed a higher proportion of the major flavonoid in K. pinnata, as well as the presence of quercitrin and a wide variety of other phenolic substances, when compared with control (B).

This study examined the effects of salinity and artificial UV radiation on accumulation of mycosporine-like amino acids (MAAs) in sexual and parthenogenetic Artemia from Lake Urmia. The results showed a significant increase in MAA concentrations in both Artemia populations by increment of water salinity. Also, the acquisition efficiency of MAAs in both Artemia populations increased under exposure to UVR-supplemented photosynthetically active radiation (PAR) compared to those raised under PAR. The presence of these compounds in these populations of Artemia may increase their adaptability for living in high-UV and high-salinity conditions prevailing in Lake Urmia.

Effects of PAR and UV-B radiation on herbal yield, secondary metabolites (essential oils, polyphenols) and their antioxidant capacity of lemon catmint, lemon balm and sage were tested under soilless greenhouse conditions. Intensive UV-B radiation (2.5 kJ m⁻² d⁻¹) influenced the herbal productivity and essential oil composition of all three species, while only essential oil content of lemon catmint and lemon balm was affected. Intensive UV-B radiation was favorable for strong antioxidant capacity of essential oils. Low-dose UV-B radiation (1 kJ m⁻² d⁻¹) resulted in high polyphenolic content with strong antioxidant capacity. Polyphenolic composition of herbs was also impacted by PAR and UV-B.

Cyanobacteria respond to ultraviolet radiation using several strategies. These can include an increase in the production of antioxidant and DNA damage repair enzymes, UV-absorbing pigments, a decrease in the production of photosynthesis and light-harvesting complexes, as well as physical motility away from the UV source. The sensing of UV in cyanobacteria is not well understood and could involve an unidentified photoreceptor or occur as a secondary response to other effects of UV, such as oxidative stress.

Deleterious effects of solar ultraviolet-B (UVB) radiation lead most plant-dwelling mites to inhabit the lower leaf surfaces. In contrast, Panonychus spider mites frequently occur also on upper leaf surfaces. P. citri is tolerant to UVB damage, and inhabiting the upper surfaces of shaded leaves is advantageous to this mite.

For the first time, photodynamic activity in vitro of natural Chlorophyll a (Chl a) has been investigated evidencing which types of ROS are formed. Chl a has been solubilized in aqueous solution by means of various cyclodextrins forming inclusion complexes. The ROS production has been carried out in the system using specific molecules, called primary acceptors, which react selectively with the reactive species.

Acyl-SG derivatives are capable of crossing plasma membrane thanks to their lipophilic acyl chain, which is attached via a thioester bond to the free sulfhydryl group of the GSH cysteine residue. Once internalized, acyl-SG derivatives are cleaved by cellular esterases, which release free reduced GSH, which acts as a scavenger and the parent fatty acid, which acts as a carrier and itself has inherent antioxidant properties. The protective effect of thioesters was dependent on the degree of acyl chain saturation, with more unsaturated linolenoyl-SG derivatives affording greater protection than palmitoyl-SG derivatives against UV-induced cell death, ROS production and lipid peroxidation.

The purpose of this study was to evaluate the cytoprotective activity of ethanol extract of peanut sprout (EPS) from ultraviolet B (UVB)-induced oxidative stress in human dermal fibroblasts (HDF). EPS suppressed UVB-induced ROS production in HDF, as it also inhibited UVB-induced apoptotic cell death. EPS induced up-regulation and nuclear translocation of Nrf2 in HDF. UVB irradiation up-regulated Nrf2-dependent enzymes of HO-1, NQO-1, and GSTpi, and they were further stimulated by EPS treatment. Taken together, EPS is an efficient cytoprotective agent against UVB-induced oxidative stress by activation of Nrf2 and up-regulation of Nrf2-relating antioxidant and detoxifying enzymes in HDF.

The long ethylene oxide (EO) chain of a nonylphenolpolyethoxylate(NPEO[70]) was broken near the benzene ring by UV, producing NPEOs with a short EO chain (around 10 units). NPEO(10) was further degraded and disappeared. The effect was dependent on the energy of UV. A genotoxic marker, phosphorylation of histone H2AX (γ-H2AX), was generated according to the degradation patterns; shortening of the EO chain changed NPEO(70) into an inducer for γ-H2AX, and degradation of NPEO(10) attenuated the genotoxicity. UV rays can make NPEOs harmless orgenotoxic according to the degradation of EO side-chains.

Effects of monochromatic and white LED lighting on human retinal pigment epithelial cells in vitro. HRPEpiC cells were exposed to LED lighting (irradiated cells) or maintained in darkness (control) for three light–darkness cycles (12 h/12 h). Apoptosis determined by the activation of caspases-3, -7 is observed as a pink coloration around DAPI-stained cells: (1) Representative images of effects of LED lighting on HRPEpiC cells and (2) Graphs displays mean fluorescence intensity radios of irradiated cells versus non irradiated controls. Bars represent mean ± SD from n = 3–5 experiments. The asterisk (*) indicates significant differences as compared to controls (P < 0.05, Student's t-test).

UVB irradiation of the cornea leads to the increase in corneal hydration and changes in corneal transparency, resulting in the increase in corneal light absorption and the decrease in the visual acuity. The reversibility of these changes is dependent on the UVB dose. The corneal disturbances evoked by the irradiation of the rabbit cornea with the daily UVB dose of 0.5 J cm⁻² during 4 days (equivalent approximately to 5 h exposure of solar UVB radiation to the human cornea for 4 consecutive days), restored within 2 months. Higher UVB doses are dangerous from residual corneal disorders, including changes in optics.

Characterisation of urine of normal subjects and cancer patients and discriminating them were carried out by native fluorescence spectroscopic techniques viz., Excitation emission matrix and Fluorescence emission spectroscopy (FES) at 405 nm excitation. The EEM and FES reveals that there is a considerable variation in the emission indicating that the emission characteristics of urine metabolites, flavin and its derivatives have altered photophysical characteristics.

Zinc(II) phthalocyanine-loaded polymeric micelles generated singlet molecular oxygen in high yields. Photocytotoxicity assays using human nasopharynx KB carcinoma cells confirmed that the encapsulation of zinc(II) phthalocyanine in the polymeric micelles T1107 and T1307, increases its photocytotoxicity by 10 times in comparison with the free form in water–DMSO. A lysosomal localization was observed.

We performed a single trauma in tibialis anterior muscle of rats. Animals were treated with sodium diclofenac (11.6 mg g⁻¹ of solution) or LLLT (810 nm; continuous mode; 100 mW; 3.57 W cm⁻²; 1, 3 or 9 J). Histological analysis and quantification of gene expression of COX-1, COX-2 and TNF-α were performed at 6, 12 and 24 h after trauma. LLLT improved morphological aspects of muscle tissue showing better results than injury and diclofenac groups. LLLT decreased COX-2 compared to injury group at all time points, and to diclofenac group at 24 h after trauma. In addition, LLLT decreased TNF-α compared to injury and diclofenac groups at all time points.

The aim of this study was to evaluate the effect of single and combined therapies (LLLT, topical application of diclofenac and intramuscular diclofenac) on functional and biochemical aspects in an experimental model of controlled muscle strain in rats. Injured groups received either no treatment, or a single treatment with topical or intramuscular diclofenac (TD and ID), or LLLT (3 J, 810 nm, 100 mW) 1 h after injury. All treatments significantly decreased COX-1 and COX-2 gene expression compared with injury group (P < 0.05). However, LLLT showed better effects than TD and ID regarding PGE₂ levels and walking track analysis (P < 0.05).