Photochemical & Photobiological Sciences

The primary or acquired cancer chemoresistance is a major problem in the treatment of cancer patients. It could be overcome by non-overlapping treatment regimens such as photodynamic therapy (PDT). PDT is based on the oxidation of cellular components which occurs when a light-excited photosensitizer generates reactive oxygen species (ROS). In this study the effect of mTHPC mediated PDT (mTHPC-PDT) on 5-FU resistant colorectal cancer (CRC) cells HCT116 was investigated. The results show that mTHPC-PDT overcomes 5-FU resistance and is effective against chemoresistant colorectal carcinoma cells.

In this paper we discuss how to push the temporal resolution limits of transient absorption spectroscopy in order to detect very fast processes (energy relaxation, energy or charge transfer, vibrational coherence) taking place in molecules of biological relevance. After reviewing the main principles of femtosecond pump–probe spectroscopy, we describe an experimental setup based on two synchronized non-collinear optical parametric amplifiers (NOPAs). Each NOPA can be independently configured to generate ultra-broadband sub-10 fs visible pulses, tunable 10–15 fs visible pulses, tunable 15–40 fs near-infrared pulses (900–1500 nm). This system enables to perform pump–probe experiments over nearly two octaves of spectrum with sub-20 fs temporal resolution. We then present an application example highlighting the capability of this instrument to track excited state dynamics in biomolecules on the sub-100 fs timescale: the study of carotenoid–bacteriochlorophyll energy transfer processes in peripheral light-harvesting complexes (LH2) from purple bacteria. We show that, by comparing excited-state dynamics of the carotenoids in organic solvents and inside the LH2 complexes, it is possible to visualize in the time domain the primary events in photosynthesis.

Two Chromophore-Quencher Conjugates (CQCs) have been synthesized by covalent attachment of the anti-oxidant dibutylated-hydroxytoluene (BHT) to a pyrrole-BF2 chromophore (BOPHY) in an effort to protect the latter against photofading. In fluid solution, light-induced intramolecular charge transfer is favoured in polar solvents and helps to inhibit photo-bleaching of the chromophore. The rate of photo-fading, which scales with the number of BHT residues, is zero-order in polar solvents but shows a linear dependence on the number of absorbed photons. The zero-order rate constant shows an inverse correlation with the fluorescence quantum yield measured in the same solvent. Photo-bleaching in benzonitrile involves autocatalysis while reaction in cyclohexane shows an unexpected stoichiometry. NMR spectroscopy indicates initial damage takes place at the BHT unit and allows identification of a reactive hydroperoxide as being the primary product. In the presence of an adventitious substrate, this hydroperoxide is a photocatalyst for amide formation under mild conditions.

The structural origin and evolution of bioluminescent activity of beetle luciferases from AMP/CoA ligases remains a mystery. Previously we cloned the luciferase-like enzyme from Zophobas morio mealworm, a reasonable protoluciferase model that could shine light on this mystery. Kinetic characterization and studies with D- and L-luciferin and their adenylates showed that stereoselectivity constitutes a critical feature for the origin of luciferase activity in AMP/CoA ligases. Comparison of the primary structures and modeling studies of this protoluciferase and the three main families of beetle luciferases showed that the carboxylic acid substrate binding site of this enzyme is smaller and more hydrophobic than the luciferin binding site of beetle luciferases, showing several substitutions of otherwise conserved residues. Thus, here we performed a site-directed mutagenesis survey of the carboxylic binding site motifs of the protoluciferase by replacing their residues by the respective conserved ones found in beetle luciferases in order to identify the structural determinants of luciferase/oxygenase activity. Although most of the substitutions had negative impact on the luminescence activity of the protoluciferase, only the substitution I327T improved the luminescence activity, resulting in a broad and 15 nm blue-shifted luminescence spectrum. Such substitution indicates the importance of the loop motif 322YGMSEI327 (341YGLTETT347 in Photinus pyralis luciferase) for luciferase activity, and indicates a possible route for the evolution of bioluminescence function of beetle luciferases.

Organic–metal complexes are promising molecules for use in photodynamic therapy (PDT). The aim of this study was to investigate in vitro effects of novel Ru(II) and Ir(III) BODIPY complexes for PDT. These hybrid organic–metal molecules (Ru-BD and Ir-BD) have been synthesized via reactions of a BODIPY precursor (BD) with a phenanthroline unit bearing Ru(II) (3) and novel Ir(III) (4) compounds. The crystal structures of the new distyryl BODIPY (BD) and Ru(II) complex (3) are also reported. The photophysical and singlet oxygen generation properties of Ru-BD and Ir-BD were investigated in comparison with unsubstituted BODIPY (BD). Moreover, Ru-BD and Ir-BD have been biologically evaluated in vitro in chronic myeloid leukemia and cervical cancer cell lines in terms of photodynamic therapy efficacy in the presence of BD control. These complexes were not toxic in the dark but red light was needed to induce cell death. These data support the fact that Ru-BD could be accepted as a valuable photosensitizer-drug for further PDT treatment.

Correction for ‘Patients with polymorphic light eruption have decreased serum levels of 25-hydroxyvitamin-D(3) that increase upon 311 nm UVB photohardening’ by Peter Wolf et al., Photochem. Photobiol. Sci., 2012, 11, 1831–1836.

Antivenom therapy has been ineffective in neutralizing the tissue damage caused by snakebites. Among therapeutic strategies to minimize effects after envenoming, it was hypothesized that a low level laser would reduce complications and reduce the severity of local snake venom effects. In the current study, the effect of a low-level semiconductor gallium arsenide (GaAs) laser on the local pathological alterations induced by B. moojeni snake venom was investigated. The experimental groups consisted of five male mice, each administered either B. moojeni venom (VB), B. moojeni venom + antivenom (VAV), B. moojeni venom + laser (VL), B. moojeni venom + antivenom + laser (VAVL), or sterile saline solution (SSS) alone. Paw oedema was induced by intradermal administration of 0.05 mg kg−1 of B. moojeni venom and was expressed in mm of directly induced oedema. Mice received by subcutaneous route 0.20 mg kg−1 of venom for evaluating nociceptive activity and the time (in seconds) spent in licking and biting the injected paw was taken as an indicator of pain response. Inflammatory infiltration was determined by counting the number of leukocytes present in the gastrocnemius muscle after venom injection (0.10 mg kg−1). For histological examination of myonecrosis, venom (0.10 mg kg−1) was administered intramuscularly. The site of venom injection was irradiated by the GaAs laser and some animals received antivenom intraperitoneally. The results indicated that GaAs laser irradiation can help in reducing some local effects produced by the B. moojeni venom in mice, stimulating phagocytosis, proliferation of myoblasts and the regeneration of muscle fibers.

A sensitive and simple flow injection chemiluminescence (CL) system was constructed for the determination of meropenem, in which the CL intensity of the KMnO4-rhodamine B (Rh B) reaction was enhanced in the presence of CdS quantum dots (QDs). A CL resonance energy transfer (CRET) occurs between CdS QDs as a donor and Rh B as an energy acceptor. Based on the strong specific quenching effect of meropenem on the CL intensity, a novel chemosensor for meropenem sensing was developed. Under the optimized conditions, the quenched CL emission intensity was proportional to the concentration of meropenem in the range of 0.002-10.0 mg L−1 with a detection limit (3s) of 0.8 µg L−1 Moreover, the feasibility of the induced CL system was studied via the meropenem determination in environmental water samples.