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The impact of the polymeric matrix on the photophysical characteristics of monomeric dyes responsive to excited-state intramolecular proton transfer (ESIPT) was investigated through UV-Vis absorption as well as steady-state and time-resolved emission spectroscopies. For this purpose, two benzoxazole monomers (M1 and M2) with acryloyl groups at different positions in their molecular structures were employed to facilitate covalent bonding within a styrene chain. Our findings reveal significant variations in their excited-state properties due to the proximity of the acryloyl groups, which affects the energy barrier of the ESIPT reaction, the emission wavelength, and the balance between the normal and tautomeric forms. The experimental results were corroborated through theoretical investigations at the DFT/TDDFT level, specifically using the B3LYP-D3/def2-TZVP methodology. Three notable observations emerged: donor/acceptor groups at the meta/para positions induced electron distribution changes, causing red-shifted emission for M2; in the polymer film, particularly in PM1, intramolecular hydrogen bond deactivation favored N* emission over T* emission; and the zwitterionic character of the T* species. This study underscores the advantages of functionalization in polymers, which can lead to colorless films and prevalent N* or T* emission, and contributes valuable insights into molecular design strategies for tailoring the photophysical properties of polymeric materials.

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Myricetin is a flavonol with high antioxidant properties. In this research, the fluorescence emission of myricetin powder and its solutions in different solvents were measured and analyzed by comparing with the results of calculations. Comparison of the calculated and measured characteristic wavelengths allowed the identification of all the spectral features in the fluorescence spectra of myricetin powder and solutions with different concentrations. The computation was based on modeling the process of the excited state intermolecular proton transfer, which predicts the formation of tautomeric forms of the flavonol molecule. Characteristic emission wavelengths were obtained using TDDFT/M06-2X/6-31++G(d,p). To understand the influence of the hydroxyl groups in the B-ring of the flavonol molecule on the emission spectrum, we also compared the fluorescence spectra of myricetin with those of kaempferol and quercetin. Moreover, based on the analysis of the changes in the shape of the FL spectra with the concentration of the solution, a criterion for the complete dissolution of the flavonol powders was established, which is important for bioavailability of flavonoids.

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Kaempferol (KMP) is one of the most common flavonoids, currently being extensively studied for its numerous beneficial health effects. Here we study the fluorescence (FL) emission of KMP powder and of its solutions prepared using different types of solvents (polar and non-polar). In the spectra of KMP powder and KMP solutions with high concentration, the same FL peak with maximum at 1.9 eV is observed. Another FL peak, at higher energy of 2.45 eV, emerges in solutions, its relative intensity increases with decreasing solution concentration. The FL emission of solutions with lowest concentration displays only that peak. To calculate characteristic energies of absorption and emission of KMP molecule in vacuum and in solutions we use time-dependent density functional theory. Comparing the results of computations with measured FL spectra, we associate the FL band at 1.9 eV with the emission due to excited state intramolecular transfer of the proton of -OH5 hydroxyl group. The FL emission at 2.45 eV is related to the -OH3 proton transfer. We measure the FL spectra of KMP powder using two different excitation energies, 3.06 eV and 2.33 eV, and find that its FL spectrum depends on the excitation energy. To understand that dependence, we compare the FL spectra of KMP and Q monohydrate powders. We consider the excited state intermolecular transfer of the proton from -OH3' hydroxyl group to a neighboring molecule in Q crystal and calculate the energy corresponding to the emission of the resulted anion of Q molecule. The spectral feature at 1.69 eV observed only in the FL spectrum of Q hydrate is attributed to the Q anion FL emission.

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This research provides new evidence regarding the different kinds of air quality episodes, and their underlying mechanisms, that frequently impact the urban area of Quintero Bay in Central Chile, which is located along complex coastal terrain and is surrounded by industries. The monitoring campaign was carried out in January 2022 and encompassed two distinctive meteorological regimes. The first part of the month was dominated by a coastal low centered to the south of Quintero, which resulted in prevailing northerly flow (or weak southerlies) and a deep cloud-topped marine boundary layer. After a 2-3-day transition, the latter collapsed, and a clear-sky regime ensued, which was characterized by a shallow boundary layer and strong southerly winds during the daytime that lasted until the end of the campaign. By using proton transfer reaction time of flight mass spectrometry (PTR-TOF-MS) at a high temporal resolution (1 s), we measured high levels of volatile organic compounds (VOCs) during air quality episodes in real time. The episodes detected were associated with different prevailing meteorological regimes, suggesting that different point sources were involved. In the first episode, propene/cyclopropane, butenes, benzene, toluene and ethylbenzene/xylenes were associated with north and northwesterly weak winds. Complaints associated with hydrocarbon odor were reported. The pollution originated from industrial and petrochemical units located to the north of Quintero, which transport and store natural gas, liquified petroleum gas and oil. The second episode was linked to an oil refinery located south of our measurement site. In this case, high levels of phenol, furan and cresols occurred under strong southwesterly winds. During this event, headaches and dizziness were reported. By contrast, the levels of other aromatic compounds (benzene, toluene, ethylbenzene/xylenes) were lower than in the first air pollution episode.

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Sulfamethazine [N1-(4,6-dimethylpyrimidin-2-yl)sulfanilamide] is an antimicrobial drug that possesses functional groups capable of acting as hydrogen-bond donors and acceptors, which make it a suitable supramolecular building block for the formation of cocrystals and salts. We report here the crystal structure and solid-state characterization of the 1:1 salt piperidinium sulfamethazinate (PPD+·SUL-, C5H12N+·C12H13N4O2S-) (I). The salt was obtained by the solvent-assisted grinding method and was characterized by IR spectroscopy, powder X-ray diffraction, solid-state 13C NMR spectroscopy and thermal analysis [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)]. Salt I crystallized in the monoclinic space group P21/n and showed a 1:1 stoichiometry revealing proton transfer from SUL to PPD to form salt I. The PPD+ and SUL- ions are connected by N-H+...O and N-H+...N interactions. The self-assembly of SUL- anions displays the amine-sulfa C(8) motif. The supramolecular architecture of salt I revealed the formation of interconnected supramolecular sheets.

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In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue-green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (Kq~1012 L·mol-1·s-1). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.

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The development of non-invasive screening techniques for early cancer detection is one of the greatest scientific challenges of the 21st century. One promising emerging method is the analysis of volatile organic compounds (VOCs). VOCs are low molecular weight substances generated as final products of cellular metabolism and emitted through a variety of biological matrices, such as breath, blood, saliva and urine. Urine stands out for its non-invasive nature, availability in large volumes, and the high concentration of VOCs in the kidneys. This review provides an overview of the available data on urinary VOCs that have been investigated in cancer-focused clinical studies using mass spectrometric (MS) techniques. A literature search was conducted in ScienceDirect, Pubmed and Web of Science, using the keywords "Urinary VOCs", "VOCs biomarkers" and "Volatile cancer biomarkers" in combination with the term "Mass spectrometry". Only studies in English published between January 2011 and May 2020 were selected. The three most evaluated types of cancers in the reviewed studies were lung, breast and prostate, and the most frequently identified urinary VOC biomarkers were hexanal, dimethyl disulfide and phenol; with the latter seeming to be closely related to breast cancer. Additionally, the challenges of analyzing urinary VOCs using MS-based techniques and translation to clinical utility are discussed. The outcome of this review may provide valuable information to future studies regarding cancer urinary VOCs.

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Excited-state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica-coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.

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We show by quantum mechanical/molecular mechanical (QM/MM) simulations that phenylbenzothiazoles undergoing an excited-state proton transfer (ESPT) can be used to probe protein binding sites. For 2-(2'-hydroxy-4'-aminophenyl)benzothiazole (HABT) bound to a tyrosine kinase, the absolute and relative intensities of the fluorescence bands arising from the enol and keto forms are found to be strongly dependent on the active-site conformation. The emission properties are tuned by hydrogen-bonding interactions of HABT with the neighboring amino acid T766 and with active-site water. The use of ESPT tuners opens the possibility of creating two-color fluorescent markers for protein binding sites, with potential applications in the detection of mutations in cancer cell lines.

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The structure of the 1:2 co-crystalline adduct C8H16N4·2C6H5BrO, (I), from the solid-state reaction of 1,3,6,8-tetra-aza-tri-cyclo-[4.4.1.1(3,8)]dodecane (TATD) and 4-bromo-phenol, has been determined. The asymmetric unit of the title co-crystalline adduct comprises a half mol-ecule of aminal cage polyamine plus a 4-bromo-phenol mol-ecule. A twofold rotation axis generates the other half of the adduct. The primary inter-species association in the title compound is through two inter-molecular O-H⋯N hydrogen bonds. In the crystal, the adducts are linked by weak non-conventional C-H⋯O and C-H⋯Br hydrogen bonds, giving a two-dimensional supra-molecular structure parallel to the bc plane.

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We studied the bis-allylic proton transfer reaction from 1,4-pentadiene to superoxide radical anion (O2.-). Minima and transition state geometries, as well as thermochemical parameters were computed at the B3LYP/6-311+G(3df,2p) level of theory. The electronic wave functions of reactants, intermediates, and products were analyzed within the framework of the Quantum Theory of Atoms in Molecules. The results show the formation of strongly hydrogen bonded complexes between the 1,4-pentadien- 3-yl anion and the hydroperoxyl radical as the reaction products. These product complexes (PCs) are more stable than the isolated reactants and much more stable than the isolated products. This reaction occurs via pre-reactive complexes which are more stable than the PCs and the transition states. This is in agreement with the fact that the net proton transfer reaction that leads to free products is an endothermic and nonspontaneous process.

Nosotros estudiamos la reacción de transferencia de protón bis-alílico del 1,4-pentadieno al radical anión superóxido (O2.--). Las geometrías de los mínimos y de los estados de transición, así como también los parámetros termoquímicos se calcularon usando el nivel de teoría B3LYP/6-311+G(3df,2p). Las funciones de onda electrónicas de los reactantes, intermedios y productos se analizaron dentro del marco de la teoría cuántica de átomos en moléculas. Nuestros resultados muestran la formación de complejos estabilizados por enlaces de hidrógeno entre el anión 1,4pentadien-3-ilo y el radical hidroperoxilo como productos de reacción. Estos complejos producto (PCs) son más estables que los reactantes aislados y mucho más estables que los productos aislados. Esta reacción ocurre vía la formación de complejos pre-reactivos, los cuales son más estables que los PCs y los estados de transición. Estos resultados están de acuerdo con el hecho de que la reacción global de transferencia de protón que conduce a la formación de los productos libres es un proceso endotérmico y no espontáneo.

Estudou-se a reação de transferência do próton bis-alílico do 1,4-pentadieno ao radical ânion superóxido (O2.-). As geometrias dos mínimos e dos estados de transição, bem como os parâmetros termoquímicos foram calculadas utilizando o nível de teoria B3LYP/6-311+G(3df, 2p). As funçÃμes de onda eletrònica dos reagentes, intermediários e produtos foram analisadas no âmbito da teoria quântica de átomos em moléculas. Os resultados obtidos demonstram a formação de complexos estabilizados por ligaçÃμes de hidrogênio entre o ânion 1,4-pentadieno- 3-ilo e o radical hidroperoxilo como produtos de reação. Estes complexos formados como produtos (PCs) são mais estáveis do que os reagentes isolados e muito mais estáveis do que os produtos isolados. Esta reação ocorre por meio de complexos pré-reativos mais estáveis do que os PCs e os estados de transição. Estes resultados estão de acordo com o fato da reação global de transferência de próton que conduz à formação dos produtos livres, é um processo endotérmico e não espontâneo.