The first page of this article is displayed as the abstract.

Neither the thermodynamically determined probability isotherm nor its kinetically manifest rate isotherm can be applied to photo-absorptive reactions such that the participants, including photons, may be treated as if they were chemical reactants. Photons and chemical reactants differ from each other fundamentally: firstly, a photon's energy is absolute and, in all instances of practical relevance to the present paper, independent of its surrounding electrochemical field, while the energy of a chemical reactant is relative and defined by its surrounding field; secondly, while both photons and chemical reactants can and do engage in entropy creation, only chemical reactants can engage in entropy exchange. Clarification of these differences requires identification and abandonment of fundamental historical errors in photochemical thought deriving from inappropriate overreach of analogies drawn between light and ideal gases, and including: treatment of photo-absorption as a reversible chemical reaction; attribution to light of thermal potential, or temperature (as distinct from the idealised abstraction of a ‘temperature signature’); attribution to light of exchangeable entropy content. We begin by addressing widespread misapprehensions concerning the perennially misunderstood concept of entropy and the frequently overlooked distinction between entropy creation and entropy exchange. Armed with these clarifications, we arrive at a useful perspective for understanding energy absorption and transfer in photosynthetic processes which, through the chemical ‘kidnapping’ of metastable excited states within structured metabolic pathways, achieves outcomes which the Second Law denies to thermal chemical reactions.

Oxygen vacancies (OVs) defects in metal oxide-based photocatalysts play a crucial role in improving the charge carrier separation efficiencies to enhance the photocatalytic performances. In this work, OVs were introduced in 3D Bi2MoO6 microspheres through a facile and fast microwave-assisted method via the modulation of tetramethylethylenediamine (TMEDA). EPR, Raman and XPS results demonstrated that large amounts of oxygen vacancies were formed on the surface of BMO microspheres. The photocatalytic properties of the samples were studied by degradation of tetracycline (TC) under visible light. The optimal Bi2MoO6 with OVs exhibited optimum photocatalytic activity, and the degradation rate was 7.0 times higher than that of pristine Bi2MoO6. This enhancement can be attributed to the 3D structure furnishing more surface active sites and suitable OVs defects favoring the electron–hole separation. Moreover, the defective Bi2MoO6 microspheres exhibit high stability because the photocatalytic activity remains almost unchanged after 5 cycles, making them favorable for practical applications. Finally, a possible visible light photocatalysis mechanism for the degradation of TC was tentatively proposed.

A 2,5-bis(4-phenylquinazolin-2-yl)thiophene (BQT) probe is designed, synthesized and explored for selective ratiometric fluorescence and visual detection of Fe3+ and as a turn-off fluorescence probe for I− anion. BQT is colorless and has blue emission in CH3CN solution. BQT selectively complexes with Fe3+, turns its solution from colorless to greenish yellow and enables the ratiometric sensing of Fe3+ with limit of detection (LOD) and limit of quantitation (LOQ) of 2 × 10−8 M and 6.1 × 10−8 M, respectively. Binding constant of BQT with Fe3+ is found to be 4.1 × 10−4 M−1. BQT is also able to sense I− anion present in aqueous solution by selectively turning colorless to yellow and fluorescence quenching with a LOD of 1.7 × 10−7 M and LOQ of 5.2 × 10−7 M. BQT sensing ability is not influenced by the presence of other metal ions and anions in the vicinity. The BQT–Fe3+ complex is thoroughly characterized using MALDI-TOF, NMR and Job's plot. A reversibility experiment with EDTA suggests BQT is a reversible fluorescent chemosensor for Fe3+ ions. The spectroscopic data of BQT and its complexes are employed to construct a field test kit for qualitative analysis and INHIBIT logic gate.

Mitochondria damaged by ultraviolet-B radiation (UV-B, 280–315 nm) are removed by mitophagy, a selective autophagic process. Recently, we demonstrated that autophagy-deficient Arabidopsis thaliana mutants exhibit a UV-B-sensitive phenotype like that of cyclobutane pyrimidine dimer (CPD)-specific photolyase (PHR1)-deficient mutants. To explore the relationship between UV-B sensitivity and autophagy in UV-B-damaged plants, we monitored mitochondrial dynamics and autophagy in wild-type Arabidopsis (ecotype Columbia); an autophagy-deficient mutant, atg5; a PHR1-deficient mutant, phr1; an atg5 phr1 double mutant; and AtPHR1-overexpressing (AtPHR1ox) plants following high-dose UV-B exposure (1.5 W m−2 for 1 h). At 10 h after exposure, the number of mitochondria per mesophyll leaf cell was increased and the volumes of individual mitochondria were decreased independently of UV-B-induced CPD accumulation in all genotypes. At 24 h after exposure, the mitochondrial number had recovered or almost recovered to pre-exposure levels in plants with functional autophagy (WT, phr1, and AtPHR1ox), but had increased even further in atg5. This suggested that the high dose of UV-B led to the inactivation and fragmentation of mitochondria, which were removed by mitophagy activated by UV-B. The UV-B-sensitive phenotype of the atg5 phr1 double mutant was more severe than that of atg5 or phr1. In wild-type, phr1, and AtPHR1ox plants, autophagy-related genes were strongly expressed following UV-B exposure independently of UV-B-induced CPD accumulation. Therefore, mitophagy might be one of the important repair mechanisms for UV-B-induced damage. The severe UV-B-sensitive phenotype of atg5 phr1 is likely an additive effect of deficiencies in independent machineries for UV-B protection, autophagy, and CPD photorepair.

Correction for ‘A library of action spectra for erythema and pigmentation’ by Alois W. Schmalwieser et al., Photochem. Photobiol. Sci., 2012, 11, 251–268, DOI: 10.1039/c1pp05271c.

A graphical abstract is available for this content

The first page of this article is displayed as the abstract.

Phytochromes are ubiquitous photosensor proteins, which control the growth, reproduction and movement in plants, fungi and bacteria. Phytochromes switch between two photophysical states depending on the light conditions. In analogy to molecular machines, light absorption induces a series of structural changes that are transduced from the bilin chromophore, through the protein, and to the output domains. Recent progress towards understanding this structural mechanism of signal transduction has been manifold. We describe this progress with a focus on bacteriophytochromes. We describe the mechanism along three structural tiers, which are the chromophore-binding pocket, the photosensory module, and the output domains. We discuss possible interconnections between the tiers and conclude by presenting future directions and open questions. We hope that this review may serve as a compendium to guide future structural and spectroscopic studies designed to understand structural signaling in phytochromes.

Given the prevalence of fluorescence spectroscopy in biological systems, and the prevalence of pterin derivatives throughout biological systems, presented here is an assessment of the two-photon absorption spectroscopy as it applies to a range of the most commonly studied pterin derivatives. QR-CAMB3LYP//ccpVTZ calculations suggest that the use of two-photon spectroscopic methods would enable a more capable differentiation between closely related derivatives in comparison to the one-photon spectra, which show minimal qualitative deviation. Study of short tail derivatives shows that, in most cases, two-photon accessible states solely involve the π* LUMO as the particle orbital, with biopterin, neopterin, and 6-(hydroxymethyl)pterin presenting exceptional potential for targetting. Investigation of derivatives in which the tail contains an aromatic ring resulted in the observation of a series of two-photon accessible states involving charge transfer from the tail to the pterin moiety, the cross sections of which are highly dependent on the adoption of a planar geometry. The observation of these states presents a novel method for tracking the substitution of biologically important molecules such as folic acid and 5-methenyltetrahydrofolylpolyglutamate.

Firefly luciferases display a typical change in bioluminescence color to red at acidic pH, high temperatures and in the presence of heavy metals. Recently, the proton and metal sensing site responsible for the pH-sensitivity of firefly luciferases, which involves the salt bridges between E311-R337 and H310-E354, was identified. However, it is unclear what other residues contribute to the distinct degrees of pH-sensitivity observed in other firefly luciferases. A multialignment of primary structures of a large set of pH-sensitive and pH-insensitive beetle luciferases showed that the conserved E270 among adult firefly luciferases is substituted by Gly (railroad worms)/Gln (click-beetles) in pH-insensitive ones. Site-directed mutagenesis studies using Macrolampis sp2 and Amydetes vivianii firefly luciferases indeed showed that E270 is important for the pH-dependent activity and spectral profiles: the substitution E270A/G drastically decreases the spectral pH-sensitivity, and extends the activity profile above pH 9.0. These mutations also decrease the sensitivity to metals such as zinc, mercury and cadmium. Modelling studies showed that the residue E270 is located in a three-glutamate motif (269EEE271) at the N-terminal of α-helix-10. The results suggest that at acidic pH, the protonation of E270 carboxylate may extend a turn of the helix at the N-terminal, misaligning the pH-sensor and luciferin phenolate binding site residues: S286, I288 and E311. In contrast, the substitution of E270A/G may unwind a turn of the α-helix-10, indirectly increasing the interaction of the pH-sensor and other residues at the bottom of the luciferin binding site, stabilizing the green light emitting conformation.

Studies have previously shown that anthracene and naphthalene derivatives serve as compounds for trapping and chemically generating singlet molecular oxygen [O2(1Δg)], respectively. Simple and efficient synthetic routes to anthracene and naphthalene derivatives are needed, for improved capture and release of O2(1Δg) in cellular environments. Because of this need, we have synthesized a dihydroxypropyl amide naphthlene endoperoxide as a O2(1Δg) donor, as well as five anthracene derivatives as O2(1Δg) acceptor. The anthracene derivatives bear dihydroxypropyl amide, ester, and sulfonate ion end groups connected to 9,10-positions by way of unsaturated (vinyl) and saturated (ethyl) bridging groups. Heck reactions were found to yield these six compounds in easy-to-carry out 3-step reactions in yields of 50–76%. Preliminary results point to the potential of the anthracene compounds to serve as O2(1Δg) acceptors and would be amenable for future use in biological systems to expand the understanding of O2(1Δg) in biochemistry.

A graphical abstract is available for this content

Cryptochromes (CRYs) are blue-light receptors involved in photomorphogenesis in plants. Flavin adenine dinucleotide (FAD) is one of the chromophores of cryptochromes; its resting state oxidized form is converted into a signalling state neutral semiquionod radical (FADH˙) form. Studies have shown that cryptochrome 1 from Arabidopsis thaliana (AtCRY1) can bind ATP at its photolyase homology region (PHR), resulting in accumulation of FADH˙ form. This study used light-induced difference Fourier transform infrared spectroscopy to investigate how ATP influences structural changes in AtCRY1-PHR during the photoreaction. In the presence of ATP, there were large changes in the signals from the protein backbone compared with in the absence of ATP. The deprotonation of a carboxylic acid was observed only in the presence of ATP; this was assigned as aspartic acid (Asp) 396 through measurement of Asp to glutamic acid mutants. This corresponds to the protonation state of Asp396 estimated from the reported pKa values of Asp396; that is, the side chain of Asp396 is deprotonated and protonated for the ATP-free and -bound forms, respectively, in our experimental condition at pH8. Therefore, Asp396 acts a proton donor to FAD when it is ptotonated. It was indicated that the protonation/deprotination process of Asp396 is correlated with the accunumulation of FADH˙ and protein conformational changes.

Extending the applications of Photoremovable Protecting Groups (PPGs) to “cage” phenols has generally met with unusually complex PPG byproducts. In this study, we demonstrate that the p–hydroxyphenacyl (pHP) cage for both simple and complex phenolics, including tyrosine, dispenses free phenols. With the simpler unsubstituted phenols, the reaction is governed by their Brønsted Leaving Group ability. On the other hand, the byproducts of the cage vary with these phenols. For the more acidic phenols the cage byproduct follows the Favorskii rearrangement to form p-hydroxyphenylacetic acid whereas for the weaker phenols other reactions such as reduction and hydrolysis begin to emerge. When the photolysis is conducted in octa acid (OA) containers, non-Favorskii, unrearranged fragments of the cage and other byproducts arise.

Photobiomodulation therapy (PBMT) is an effective therapeutic strategy and a noninvasive method to improve the regulation of inflammation and pain. Our aim was to examine the effects of different doses of PBMT on improvement of edematogenic and nociceptive responses in a myositis model in rats. We administered complete Freund's adjuvant (CFA) into the gastrocnemius muscle (GS) of rats to induce myositis and observe the effect of PBMT using different doses of energy and two types of light sources, a low-level laser (LLL) and light emitting diodes (LED). For this, we evaluated the effects of these different energies to improve nociceptive and edematogenic responses using behavioural tests. In addition, we analysed histological images in animals with myositis induced by CFA. The administration of CFA to the GS induced increased cellular infiltrates, edema and a nociceptive response when compared to animals without myositis. When we treated the CFA-induced myositis animals with PBMT (LLLT or LEDT), we observed a decrease in nociception and edema formation. Our results demonstrated that only the major energy for both the LED and LLL was able to remain in a homogeneous form throughout the period analyzed. Based on our results, we suggest that both LLLT and LEDT using the highest dose (3 J) could be an alternative treatment for myositis in rats.

The remarkable properties of deuterium have led to many exciting and favourable results in enhancing material properties, for applications in the physical, medical, and biological sciences. Deuterated isotopologues of avobenzone, a sunscreen active ingredient, were synthesised to examine for any changes to the equilibrium between the diketone and enol isomers, as well as their UV photostability and photoprotective properties. Prior to UV irradiation, deuteration of the diketone methylene/enol moiety (i.e. avobenzone-d2) led to an increase in the % diketone compared to non-deuterated, determined by 1H NMR experiments in CDCl3 and C6D12. This can be rationalised from two angles; mechanistically by a deuterium kinetic isotope effect for the CH vs. CD abstraction step during tautomerisation from the diketone to the enol, and a weaker chelating hydrogen bond for the enol when deuterated allowing increased equilibration to the diketone. Avobenzone-d2 was further examined by solid state 13C NMR. The higher % diketone for avobenzone-d2 was postulated to favour increased photodegradation by a non-reversible pathway. This was investigated by UV irradiation of the avobenzone isotopologues in C6D12, both in real time in situ within the NMR by fibre optic cable as well as ex situ using sunlight. An increase in the relative amount of photoproducts for avobenzone-d2 compared to non-deuterated was observed by 1H NMR upon UV irradiation ex situ. Overall, the study demonstrates that deuteration can be applied to alter complex equilibria, and has potential to be manifested as changes to the properties and behaviour of materials.

A series of water soluble 8-alcoxypyrene-1,3,6-trisulfonic sodium salts bearing different alcoxy lateral chains and functional end groups was synthesized and the molecular structure was corroborated by nuclear magnetic resonance spectroscopy. The photophysical properties in water analyzed by UV-Vis and static and dynamic fluorescence revealed that all of the pigments emit in the blue region at a maximal wavelength of 436 nm and with fluorescence lifetimes in the range of ns. Among them, sodium 8-((10-carboxydecyl) oxy) pyrene-1,3,6-trisulfonate M1 exhibits a high fluorescence quantum yield (ϕ = 80%) and a good interaction with B. subtilis LPM1 rhizobacteria; this has been demonstrated through in vitro staining assays. Tomato plants (Solanum lycopersicon cv. Micro-Tom) increased the release of root exudates, mainly malic and fumaric acids, after 12 h of treatment with benzothiadiazole (BTH) as a foliar elicitor. However, the chemotaxis analysis demonstrated that malic acid is the most powerful chemoattractant of the rhizobacteria Bacillus subtilis LPM1: in agar plates, a major growth (60 mm) was found for a concentration of 100 mM, while in capillary tubes, the earliest response was at 30 min with 3.3 × 108 CFU mL−1. The confocal microscopic analysis carried out on the tomato roots of the pyrene stained B. subtilis LPM1 revealed that this bacterium mainly colonizes the epidermal zones, i.e. the junctions to primary roots, lateral roots and root hairs, meaning that these root hair sections are the highest colonisable sites involved in the biosynthesis of exudates. This fluorescent pyrene marker M1 represents a valuable tool to evaluate B. subtilis–plant interactions in an easy and quick test in both in vitro and in vivo tomato crops.

Conventional photodynamic therapy (PDT) has proved effective in the management of primary tumors and individual metastases. However, most cancer mortality arises from wide-spread multiple metastases. The latter has thus become the principal target in oncology, and X-ray induced photodynamic therapy (XPDT or PDTX) offers a great solution for adapting the PDT principle to deep tumors and scattered metastases. Developing agents capable of being excited by X-rays and emitting visible light to excite photosensitizers is based on challenging physical and chemical technologies, but there are fundamental biological limitations that are to be accounted for as well. In the present review, we have established eight major groups of safety determinants of NPs encompassing 22 parameters of clinical applicability of XPDT nanoparticulate formulations. Most, if not all, of these parameters can be accounted for and optimized during the design and development of novel XPDT nanoparticles.

Escherichia coli bacteria were determined by in flow cytometry with laser excitation and fluorescence detection applying ultraluminescent core–shell nanoparticles based on Metal Enhanced Fluorescence (MEF). Core–shell nanoparticles consisted of a 40 nm core modified with a silica spacer grafted with Rhodamine B (RhB). The electromagnetic field in the near field of the core surface enhanced the fluorescence of RhB by plasmonic and fluorophore coupling. The hydrophilic silica spacer allowed the non-covalent interaction with the polar E. coli surface and thus ultraluminescent bacteria biolabelling was developed. Clearly, well defined and bright bacteria imaging was recorded by Laser Fluorescence Microscopy based on the non-covalent deposition of the ultraluminescent nano-emitters. Using these nano-labellers, it was possible to detect labelled E. coli by in flow cytometry. Higher values of Side-scattered light (SSC) and Forward-scattered light (FSC), and number of fluorescent event detections, were observed for labelled bacteria compared to those non-labelled. The sensitivity of the methodology was evaluated by varying bacteria concentration and acceptable analytical figures of merit were determined. Applying this methodology we could quantify E. coli from a synthetic real sample of fortified water. Similar results were obtained by bacteria counting with Laser Fluorescence Microscopy and with a cell-bacteria counter.