Benzazole-Based ESIPT Fluorophores: Proton Transfer from the Chalcogen Perspective. A Combined Theoretical and Experimental Study.

In this study, we present a comprehensive photophysical investigation of ESIPT-reactive benzazole derivatives in both solution and the solid state. These derivatives incorporate different chalcogen atoms (O, S, and Se) into their structures, and we explore how these variations impact their electronic properties in both ground and excited states. Changes in the UV-Vis absorption and fluorescence emission spectra were analyzed and correlated with the chalcogen atom and solvent polarity. In general, the spectral band of the benzazole derivative containing selenium was redshifted in both the ground and excited states compared to that of its oxygen and sulfur counterparts. Furthermore, we observed that the solvent played a distinctive role in influencing the ESIPT process within these compounds, underscoring once again the significant influence of the chalcogen atom on their photophysical behavior. Theoretical calculations provided a deeper understanding of the molecular dynamics, electronic structures, and photophysical properties of these compounds. These calculations highlighted the effect of chalcogen atoms on the molecular geometry, absorption and emission characteristics, and intramolecular hydrogen bonding, revealing intricate details of the ESIPT mechanism. The integration of experimental and computational data offers a detailed view of the structural and electronic factors governing the photophysical behavior of benzazole derivatives.

Organocatalytic Synthesis and DNA Interactive Studies of New 1,2,3-triazolyl-thiazolidines Hybrids.

An organocatalytic [3+2] cycloaddition reaction between thiazolidine-containing ß-ketoester 1 and aryl azides 2 was employed to synthesize new 1,2,3-triazolyl-thiazolidine hybrids 3. In this metal-free approach, twelve compounds were isolated in yields ranging from 23 % to 96 % by using diethylamine (10 mol%) and DMSO at 75 °C for 24 hours. DNA-binding assays were conducted through absorption, emission spectroscopy and viscosimetry analysis, to evaluate the interaction capacity of the studied derivatives with nucleic acids. All the synthesized compounds were evaluated for their interactions with a specific group of compounds containing the pharmacophoric groups triazole and thiazolidine through a molecular docking speculative study, aimed at identifying the interaction profile of these compounds with DNA. The obtained results suggest that 1,2,3-triazolyl-thiazolidine hybrids could be a promising approach in the development of novel therapeutic agents targeting DNA-related processes.

Organosulfur and Organoselenium Functionalized Benzimidazo[1,2-a]quinolines: From Experimental and Theoretical Photophysics to All-Solution-Processed OLEDs.

In this study, we present the synthesis of benzimidazo[1,2-a] quinoline-based heterocycles bearing organosulfur and organoselenium moieties through transition-metal-free cascade reactions involving a sequential intermolecular aromatic nucleophilic substitution (SNAr). Both sulfur and selenium derivatives presented absorption maxima located around 355 nm related to spin and symmetry allowing electronic 1π-π* transitions, and fluorescence emission at the violet-blue region (~440 nm) with relatively large Stokes shift. The fluorescence quantum yields were slightly influenced by the chalcogen, with the sulfur derivatives presenting higher values than the selenium analogs. In this sense, the quantum yields for selenium derivatives can probably be affected by the intersystem crossing or even the photoinduced electron transfer process (PET). The compounds were successfully applied in all-solution-processed organic light-emitting diodes (OLEDs), where poly(9-vinylcarbazole) was employed as a dispersive matrix generating single-layer device cells. The obtained electroluminescence spectra are a sum of benzimidazo[1,2-a]quinolines and PVK singlet and/or triplet emissive states, according to their respective energy band gaps. The best diode rendered a luminance of 25.4 cd⋅m-2 with CIE (0.17, 0.14) and current efficiency of 20.2 mcd⋅A-1, a fivefold improvement in comparison to the PVK device that was explained by a 50-fold increase of charge-carriers electrical mobility.

Evidence of a Photoinduced Electron-Transfer Mechanism in the Fluorescence Self-quenching of 2,5-Substituted Selenophenes Prepared through In Situ Reduction of Elemental Selenium in Superbasic Media.

A series of new 2,5-disubstituted selenophene derivatives are described from elemental selenium and 1,3-diynes in superbasic media. The activation of elemental selenium in a KOH/DMSO system allows cyclization with conjugated diynes at room temperature. The cyclization reaction is extended to a broad range of functional groups, for which photophysics were experimentally and theoretically investigated. The selenophene derivatives present absorption maxima in the UV-A region and fluorescence emission in the violet-to-blue region. Fluorescence decay profiles were obtained showing a monoexponential decay with fast fluorescence lifetimes (∼0.118 ns), as predicted by the Strickler-Berg relations. In general, in both investigations, no dependence on the solvent polarity on the absorption and emission maxima location was observed. On the other hand, solvents and substituents are shown to play a role in the fluorescence quantum yield values. In addition, a fluorescence self-quenching behavior could be observed, related to a photoinduced electron-transfer mechanism. Theoretical calculations performed at the MP2/ADC(2)/cc-pVDZ level of theory were performed in order to investigate the photophysical features of this series of selenophene derivatives.

Transition metal catalysed direct selanylation of arenes and heteroarenes.

Transition metal catalysed C-H functionalization has reached an exciting level of sophistication, and, today, it represents a paradigm shift from the standard logic of synthetic chemistry. The direct conversion of C-H bonds into C-heteroatoms remains, however, a critical challenge. Nowadays, there is a great demand in general synthetic chemistry in, for example, the materials science for the development of straightforward C-Se bond formation, in order to fulfil the practical requirements. In this sense, this review summarizes recent outstanding advances in the C-Se bond formation through transition metal-catalysed direct selanylation, providing new insights into their mechanistic aspects and disclosing effective synthetic routes with high atom economy. In addition, this review intends to show the growing opportunities to construct complex chemical scaffolds containing selenium atoms.

A bioanalytical HPLC method for coumestrol quantification in skin permeation tests followed by UPLC-QTOF/HDMS stability-indicating method for identification of degradation products.

Coumestrol is present in several species of the Fabaceae family widely distributed in plants. The estrogenic and antioxidant activities of this molecule show its potential as skin anti-aging agent. These characteristics reveal the interest in developing analytical methodology for permeation studies, as well as to know the stability of coumestrol identifying the major degradation products. Thus, the present study was designed, first, to develop and validate a versatile liquid chromatography (HPLC) method to quantify coumestrol in a hydrogel formulation in different porcine skin layers (stratum corneum, epidermis, and dermis) in permeation tests. In the stability-indicating test coumestrol samples were exposed to stress conditions: temperature, UVC light, oxidative, acid and alkaline media. The degradation products, as well as the constituents extracted from the hydrogel, adhesive tape or skin were not eluted in the retention time of the coumestrol. Hence, the HPLC method showed to be versatile, specific, accurate, precise and robust showing excellent performance for quantifying coumestrol in complex matrices involving skin permeation studies. Coumestrol recovery from porcine ear skin was found to be in the range of 97.07-107.28 µg/mL; the intra-day precision (repeatability) and intermediate precision (inter-day precision), respectively lower than 4.71% and 2.09%. The analysis using ultra-performance liquid chromatography coupled to a quadrupole time-of-flight high definition mass spectrometry detector (UPLC-QTOF/HDMS) suggest the MS fragmentation patterns and the chemical structure of the main degradation products. These results represent new and relevant findings for the development of coumestrol pharmaceutical and cosmetic products.

Anxiolytic effects of diphenyl diselenide on adult zebrafish in a novelty paradigm.

Anxiety-related disorders are frequently observed in the population. Because the available pharmacotherapies for anxiety can cause side effects, new anxiolytic compounds have been screened using behavioral tasks. For example, diphenyl diselenide (PhSe)2, a simple organoselenium compound with neuroprotective effects, has demonstrated anxiolytic effects in rodents. However, this compound has not yet been tested in a novelty-based paradigm in non-mammalian animal models. In this study, we assessed the potential anxiolytic effects of (PhSe)2 on the behavior of adult zebrafish under novelty-induced stress. The animals were pretreated with 0.1, 0.25, 0.5, and 1µM (PhSe)2 in the aquarium water for 30min. The fish were then exposed to a novel tank, and their behavior was quantified during a 6-min trial. (PhSe)2 treatment altered fish behavior in a concentration-dependent manner. At 0.01 and 0.25µM, (PhSe)2 did not elicit effects on fish behavior. At 0.5µM, moderate behavioral side effects (e.g., lethargy and short episodic immobility) were noted. At the highest concentration tested (1µM), dramatic side effects were observed, such as burst behavior and longer periods of immobility. The results were confirmed by spatiotemporal analysis of each group. Occupancy plot data showed dispersed homebase formation in the 0.25µM (PhSe)2-treated group compared with the control group (treated with 0.04% DMSO). Furthermore, animals treated with 0.25µM (PhSe)2 showed a reduction in latency to enter the top and spent more time in the upper area of the tank. These data suggest that (PhSe)2 may induce an anxiolytic-like effect in situations of anxiety evoked by novelty.

Antinociceptive and anti-hypernociceptive effects of Se-phenyl thiazolidine-4-carboselenoate in mice.

In this study, the antinociceptive, anti-hypernociceptive and toxic effects of orally administered (R)-Se-phenyl thiazolidine-4-carboselenoate (Se-PTC, 1-50 mg/kg) were evaluated in mice. Se-PTC did not change plasma aspartate (AST) and alanine aminotransferase (ALT) activities or urea and creatinine levels. Furthermore, in an open field test, Se-PTC did not alter the number of crossings and rearing. Se-PTC significantly reduced the amount of writhing when assessed by acetic acid-induced visceral nociception and attenuated the licking time of the injected paw in the early and late phases of a formalin test. In addition, Se-PTC reduced nociception produced by intra-plantar (i.pl.) injection of glutamate, capsaicin, cinnalmaldehyde, bradykinin, phorbol myristate acetate and 8-Bromo-cAMP. Se-PTC caused a significant increase in hot plate and tail-immersion response latencies, but the antinociceptive effect of Se-PTC in the tail immersion was not abolished by pretreatment with the non-selective opioid receptor antagonist, naloxone. Se-PTC (25 mg/kg) significantly inhibited nociceptive behavior induced by intrathecal (i.t.) injection of glutamate, N-methyl-D-aspartate (NMDA) and (±)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD), but failed to affect nociception induced by kainate and α-amino-3-hydroxy-5-mehtyl-4-isoxazolepropionic acid (AMPA). Mechanical hypernociception induced by carrageenan and Complete Freund's Adjuvant was attenuated by Se-PTC administration. These results indicate that Se-PTC produces antinociception in several models of nociception.