Singlet oxygen photosensitizing properties of bithiophene and terthiophene derivatives

In vitro profiling of pesticides within the Tox21 10K compound library for bioactivity and potential toxicity

Pesticides include a diverse class of toxic chemicals, often having numerous modes of actions when used in agriculture against targeted organisms to control insect infestation, halt unwanted vegetation, and prevent the spread of disease. In this study, the in vitro assay activity of pesticides within the Tox21 10K compound library were examined. The assays in which pesticides showed significantly more activities than non-pesticide chemicals revealed potential targets and mechanisms of action for pesticides. Furthermore, pesticides that showed promiscuous activity against many targets and cytotoxicity were identified, which warrant further toxicological evaluation. Several pesticides were shown to require metabolic activation, demonstrating the importance of introducing metabolic capacity to in vitro assays. Overall, the activity profiles of pesticides highlighted in this study can contribute to the knowledge gaps surrounding pesticide mechanisms and to the better understanding of the on- and off-target organismal effects of pesticides.

Electron-Rich EDOT Linkers in Tetracationic bis-Triarylborane Chromophores: Influence on Water Stability, Biomacromolecule Sensing, and Photoinduced Cytotoxicity

Three novel tetracationic bis-triarylboranes with 3,4-ethylenedioxythiophene (EDOT) linkers, and their neutral precursors, showed significant red-shifted absorption and emission compared to their thiophene-containing analogues, with one of the EDOT-derivatives emitting in the NIR region. Only the EDOT-linked trixylylborane tetracation was stable in aqueous solution, indicating that direct attachment of a thiophene or even 3-methylthiophene to the boron atom is insufficient to provide hydrolytic stability in aqueous solution. Further comparative analysis of the EDOT-linked trixylylborane tetracation and its bis-thiophene analogue revealed efficient photo-induced singlet oxygen production, with the consequent biological implications. Thus, both analogues bind strongly to ds-DNA and BSA, very efficiently enter living human cells, accumulate in several different cytoplasmic organelles with no toxic effect but, under intense visible light irradiation, they exhibit almost instantaneous and very strong cytotoxic effects, presumably attributed to singlet oxygen production. Thus, both compounds are intriguing theranostic agents, whose intracellular and probably intra-tissue location can be monitored by strong fluorescence, allowing switching on of the strong bioactivity by well-focused visible light.

Recognition of antioxidants and photosensitizers in Dyssodia pinnata by EPR spectroscopy

INTRODUCTION

Previous studies report the isolation mainly of terthiophene derivatives and flavonoids from Dyssodia species. Terthiophenes are known as photosensitizers by their capacity to generate singlet oxygen (¹ O₂ ), and flavonoid antioxidant activity is recognized. These opposite properties could represent interesting options in photodynamic therapy.

OBJECTIVE

To determine the antioxidant and photosensitizer activities of extracts and isolates of Dyssodia pinnata by electron paramagnetic resonance (EPR).

METHODOLOGY

Extracts and isolates were evaluated as antioxidants by the interactions with copper ion (Cu²⁺ ) observed in EPR, and by the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and the thiobarbituric reactive substances (TBARS) methods. Their abilities as ¹ O₂ producers were also estimated by EPR.

RESULTS

Terthiophenes were obtained from hexane (DPH) and acetone (DPA) extracts, and flavonoids from DPA and methanol (DPM) extracts. The interaction with Cu²⁺ of extracts and isolated compounds of Dyssodia pinnata showed two effects in EPR: reduction and chelation; flavonoids exhibited both effects, while terthiophenes showed only reduction. DPA, DPM, and flavonoids were active in DPPH and TBARS assays. Quercetagetin-7-O-β-glucoside showed the highest antioxidant and chelating activities, 3-glycosidated flavonoids were less active. Upon irradiation extracts and terthiophenes induced ¹ O₂ formation.

CONCLUSION

Flavonoid reducing activity on Cu²⁺ and free radical scavenging capacity were related to the number of hydroxy groups and to the conjugation between the B and C rings. All tested flavonols showed a major complex with Cu²⁺ , with the most probable site of chelation between the 5-hydroxy and 4-oxo groups. Extracts and terthiophene derivatives showed photosensitizer activity. Thus, EPR is useful to evaluate free radical scavenging and pro-oxidant properties.

Luminescent lanthanide complexes with a pyridine-bis(carboxamide)-bithiophene sensitizer showing wavelength-dependent singlet oxygen generation

A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized.

The photoactivity of natural products - An overlooked potential of phytomedicines?

BACKGROUND

Photoactivity, though known for centuries, is only recently shifting back into focus as a treatment option against cancer and microbial infections. The external factor light is the ingenious key-component of this therapy: Since light activates the drug locally, a high level of selectivity is reached and side effects are avoided. The first reported photoactive medicines were plant extracts. Synthetic entities (so-called photosensitizers PSs), however, paved the route towards the clinical approval of the so-called photodynamic therapy (PDT), and thus natural PSs took a backseat in the past.

HYPOTHESIS

Many isolated bioactive phytochemicals hold a hidden photoactive potential, which is overlooked due to the reduced common awareness of photoactivity.

METHODS

A systematic review of reported natural PSs and their supposed medicinal application was conducted by employing PubMed, Scifinder, and Web of Science. The identified photoactive natural products were compiled including information about their natural sources, their photoyield, and their pharmacological application. Furthermore, the common chemical scaffolds of natural PS are shown to enable the reader to recognize potentially overlooked natural PSs.

RESULTS

The literature review revealed over 100 natural PS, excluding porphyrins. The PSs were classified according to their scaffold. Thereby it was shown that some PS-scaffolds were analyzed in a detailed way, while other classes were only scarcely investigated, which leaves space for future discoveries. In addition, the literature revealed that many PSs are phytoalexins, thus the selection of the starting material significantly matters in order to find new PSs.

CONCLUSION

Photoactive principles are ubiquitous and can be found in various plant extracts. With the increasing availability of light-irradiation setups for the identification of photoactive natural products, we anticipate the discovery of many new natural PSs in the near future. With the accumulation of chemically diverse PSs, PDT itself might finally reach its clinical breakthrough as a promising alternative treatment against multi-resistant microbes and cancer types.

Thiophenes, polyacetylenes and terpenes from the aerial parts of Eclipata prostrate

One new bithiophenes, 5-(but-3-yne-1,2-diol)-50-hydroxy-methyl-2,20-bithiophene (2), two new polyacetylenic glucosides, 3-O-b-D-glucopyranosyloxy-1-hydroxy-4E,6E-tetradecene-8,10,12-triyne (8), (5E)-trideca-1,5-dien-7,9,11-triyne-3,4-diol-4-O-b-D-glucopyranoside (9), six new terpenoid glycosides, rel-(1S,2S,3S,4R,6R)-1,6-epoxy-menthane-2,3-diol-3-O-b-D-glucopyranoside (10), rel-(1S,2S,3S,4R,6R)-3-O-(6-O-caffeoyl-b-D-glucopyranosyl)-1,6-epoxy menthane-2,3-diol (11), (2E,6E)-2,6,10-trimethyl-2,6,11-dodecatriene-1,10-diol-1-O-b-D-glucopyranoside (12), 3b,16b,29-trihydroxy oleanane-12-ene-3-O-b-D-glucopyranoside (13), 3,28-di-O-b-D-glucopyranosyl-3b,16b-dihydroxy oleanane-12-ene-28-oleanlic acid (14), 3-O-b-D-glucopyranosyl-(1?2)-b-D-glucopyranosyl oleanlic-18-ene acid-28-O-b-D-glucopyranoside (15), along with fifteen known compounds (1, 3–7, and 16–24), were isolated from the aerial parts of Eclipta prostrata. Their structures were established by analysis of the spectroscopic data. The isolated compounds 1–9 were tested for activities against dipeptidyl peptidase IV (DPP-IV), compound 7 showed significant antihyperglycemic activities by inhibitory effects on DPP-IV in human plasma in vitro, with IC50 value of 0.51 lM. Compounds 10–24 were tested in vitro against NF-jB-luc 293 cell line induced by LPS. Compounds 12, 15, 16, 19, 21, and 23 exhibited moderate anti-inflammatory activities.

Photophysics and light-activated biocidal activity of visible-light-absorbing conjugated oligomers

The photophysical properties of three cationic π-conjugated oligomers were correlated with their visible light activated biocidal activity vs S. aureus. The oligomers contain three arylene units (terthiophene, 4a; thiophene-benzotriazole-thiophene, 4b; thiophene-benzothiadiazole-thiophene, 4c) capped on each end by cationic -(CH2)3NMe3(+) groups. The oligomers absorb in the visible region due to their donor-acceptor-donor electronic structure. Oligomers 4a and 4b have high intersystem crossing and singlet oxygen sensitization efficiency, but 4c has a very low intersystem crossing efficiency and it does not sensitize singlet oxygen. The biocidal activity of the oligomers under visible light varies in the order 4a > 4b ≈ 4c.

Removal of sulfur compounds from diesel using ArF laser and oxygen

A laser-based technique for deep desulfurization of diesel and other hydrocarbon fuels by removal of dimethyldibenzothiophene (DMDBT), a persistent sulfur contaminant in fuel oils has been developed. We report a selective laser excitation of DMDBT in diesel and model compounds such as n-hexane in a reaction chamber under oxygen environment where oxidative reactions can take place. ArF laser emitting at 193 nm was employed for excitation of oxygen and DMDBT, while for process optimization, the laser energy was varied from 50 to 200 mJ/cm(2). The laser-irradiated DMDBT solution under continuous oxygen flow was analyzed by UV absorption spectrometer to determine the photochemical oxidative degradation of DMDBT. In just 5 min of laser irradiation time, almost 95% DMDBT was depleted in a diesel containing 200 ppm of DMDBT. This article provides a new method for the removal of sulfur compounds from diesel by laser based photochemical process.

Laser photo-oxidative degradation of 4,6-dimethyldibenzothiophene

Degradation of 4,6-dimethyldibenzothiophene (DMDBT), persistent sulfur contaminant in fuel oils has been achieved in non-polar phase by laser-irradiating DMDBT alone and in the presence of hydrogen peroxide and molecular oxygen. The most efficient degradation in the presence of molecular oxygen is judged to be the first example of self-sensitized photo-oxygenation of thiophenes, in which DMDBT sequentially acts as 1O2 sensitizer and reactant.

The synthesis and photolarvicidal activity of 2,5-diarylethynylthiophenes

The photoactivatable insecticides have photoactive features and broad applications. The derivatives of the alpha-terthienyl analogues were synthesized for evaluating their photolarvicidal activities and 13 2,5-diarylethynylthiophenes were investigated to determine their effect on the second-instar larvae of Plutella xylostella L. Based on their photolarvicidal activities, the 2,5-Dithienylethynylthiophene, 2,5-Diphenylethynylthiophene, 2,5-Di-4-Methoxylphenylethynylthiophene and 2,5-Di-3,4-Methylenedioxyphenylethynylthiophene were found to be the most potent compounds, and their LC(50) values were 34.1 mg l(-1), 48.4 mg l(-1), 60.8 mg l(-1) and 42.7 mg l(-1), respectively. The relationship analysis between structure and activity showed that the middle thiophene ring played an important role on the activities. The electron donor substituents increased the photolarvicidal activities and the length of the alkyl chain had negative influence on the activities.

Phototoxic process after rapid photosensitive membrane damage of 5,5"-bis(aminomethyl)-2,2':5',2"-terthiophene dihydrochloride

We report a new aspect of rapid (<30 s) light-induced cell membrane damage photosensitized by 5,5"-bis(aminomethyl)-2,2':5',2"-terthiophene dihydrochloride (BAT), which is a water-soluble alpha-terthienyl analogue, using a high-power laser (light intensity 1.6 W cm(-2)). In this paper, we will discuss the relationship between the exposure time of the cells to the photosensitizer and the phototoxic process. Three toxic processes can be identified: first, a non-light-mediated toxicity dependent on BAT-cell incubation; second, a phototoxicity independent of BAT exposure time when the BAT concentration is in the 2-10-microM range; third, a phototoxicity dependent on BAT exposure time when BAT concentration becomes 20 microM. The cytotoxicity decreases when alpha-tocopherol, an antioxidant, is added to a cell membrane. This pattern of phototoxicity is the typical of a phospholipid peroxidation chain reaction and oxidative damage of membrane proteins triggered by a reactive oxygen species generated by a triplet state of BAT. The BAT exposure time is clearly correlated with the partition of the photosensitizer in the cell membrane and inside the cell.

Study of photoinduced energy and electron transfer in alpha-terthienyl-bovine serum albumin conjugates: a laser flash photolysis study

The photochemistry of alpha-terthienyl (alpha-T) has been examined in bovine serum albumin (BSA). Freely associated and covalently conjugated alpha-T chromophores show similar behavior toward nonpolar quenchers such as oxygen and benzoquinone but show significant differences in the case of quenching by methyl viologen, a watersoluble cationic electron acceptor; in this case, triplet quenching reveals two distinct alpha-T populations, attributed to chromophores in sites showing very different accessibility from the aqueous phase. Rate constants for triplet quenching in BSA are generally slower than those observed in homogeneous solution for free alpha-T. For example, in the case of oxygen, the rate constant is about one order of magnitude smaller when alpha-T is associated or conjugated with the protein compared with alpha-T in solution. While triplet yields for alpha-T are essentially the same in solution and in the protein environment, the yield of detectable singlet oxygen is substantially reduced in the protein. This is attributed to a geminate reaction within the protein involving singlet oxygen trapping in the vicinity of the generation site.