The photophysics of 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT) were investigated for assessing its limitations for use as a universal fluorophore and as a viable sensor for both polymeric ...and solution studies. This is of importance given the limitations of currently used materials. BBT’s steady-state and time-resolved fluorescence were additionally investigated to correlate its solid-state features, observed by fluorescence spectroscopy when mixed in poly(1,4-butylene succinate) (PBS) films, with its single crystal characteristics. The conjugated fluorophore was found to be highly fluorescent, with absolute quantum yields of (Φfl) ≥ 0.60. The Φfl values were high, regardless of solvent polarity and proticity and whether alone or in polymeric films. The major competitive fluorescence quenching pathway was found to occur by intersystem crossing to the triplet state. This was confirmed by laser flash photolysis in which the BBT triplet absorbed at 500 nm. The triplet transient was confirmed by quenching studies with 1,3-cyclohexadiene. Meanwhile, nonradiative deactivation of BBT’s singlet excited state by internal conversion was found to be negligible. In solution and especially when distributed in semicrystalline PBS, BBT exhibits spectral changes and a bathochromic shift as a function of concentration due to aggregation of ground state molecules, which is present even at low BBT concentrations. Consistent monoexponential lifetimes on the order of ∼2 ns were observed regardless of solvent and independent of both the excitation wavelength and concentration. The constant excited state kinetics confirm the absence of a singlet excited state deactivation by excimer formation. The electrochemistry of BBT demonstrated that it is irreversibly oxidized and the resulting radical cation is unstable. Conversely, the cathodic process, resulting in the radical anion, is reversible, confirming its n-doping character. Crystallographic studies revealed that the planes described by the benzoxazolyl moieties are twisted from the plane described by the central thiophene. Several weak C–H···π and π–π intermolecular interactions were also observed. BBT’s high solubility in common solvents combined with its measured enhanced optoelectronic properties make it a candidate as a universal fluorophore reference and smart material for both polymeric and solution studies.
In solution, 4,4′-bis(2-benzoxazolyl)stilbene (BBS) was found to exhibit consistently high absolute fluorescence quantum yields (Φfl ≥ 0.88) and a monoexponential lifetime, both independent of BBS ...concentration. The BBS steady-state and time-resolved photophysics were investigated by different techniques to understand the various deactivation pathways. Nonradiative deactivation of BBS singlet excited state by intersystem crossing was found to be negligible. Other than fluorescence, the excited state of BBS was found to be deactivated by trans– cis photoisomerization. At low concentrations (≈5 μg/mL), UV spectroscopy and laser flash photolysis showed concordant results that the photoinduced cis isomer gradually replaced the original absorption spectrum of the pure trans isomer. However, at high concentrations (≈0.2 mg/mL), 1H NMR and DOSY measurements confirmed that irradiating BBS at 350 nm induced a conversion from the trans-BBS into its cis isomer by photoisomerization. It was further found that the stilbene moiety of both isomers was photocleaved. The resulting photoproduct was an aldehyde that was oxidized under ambient conditions to its corresponding carboxylic acid, i.e., 4-(1,3-benzoxazol-2-yl)benzoic acid. The structure of the photoproduct was unequivocally confirmed by X-ray diffraction. Spectroscopic investigation of BBS showed a limited photoisomerization after irradiation at 350 nm of a trans solution. The BBS electrochemistry showed irreversible oxidation, resulting in an unstable and highly reactive radical cation. Similarly, the cathodic process was also found to be irreversible, giving rise to a radical anion and showing its n-doping character.
Forearm fractures are common injuries in childhood. Median nerve entrapment is a rare complication of forearm fractures, but several cases have been reported in the literature. This case report ...discusses the diagnosis and management of median nerve entrapment in a 13-year-old male who presented acutely with a both-bone forearm fracture and numbness in the median nerve distribution. Following the delayed diagnosis, surgical exploration revealed complete nerve entrapment and a nerve graft was performed.
The simultaneous orientation of poly(1,4-butylene)succinate (PBS) and 4,4′-bis(2-benzoxazolyl)stilbene (BBS) or 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT) in PBS–BBS and PBS–BBT films was ...investigated during stretching at 80 °C, about 33 °C below the PBS melting temperature. The PBS orientation was first investigated using the 3430 cm−1 infrared band and its order parameter goes from 0.36 at a local strain of 359% for pure PBS to 0.66 in blends containing 6 wt % of BBT at a local draw ratio of ≈350% (or 0.56 with 5 wt % of BBS). At the same time, BBT shows in the same films an orientation parameter reaching a maximum of 0.31 at a local strain of ≈350%, using the 1580 cm−1 band. Since polarized FT-IR was unable to provide the orientation of BBS due to overlapping bands with PBS, polarized fluorescence spectroscopy was then used and reveals an apparent order parameter of 0.32 for BBS monomers (or 0.34 for BBT monomers), but to no orientation of BBT aggregates and BBS excimers. In other words, the two small molecules behave similarly in terms of orientation independently of their molecular shape and packing. BBS and PBS both exhibit a sharp increase of S and when reaching a BBS concentration of ≈0.08 wt %, whereas BBT and PBS show a smooth increase of S and , respectively, in films containing BBT. The sharp increase, or transition in orientation, is accompanied by a conversion of BBS from monomers to excimers, whereas BBT-containing films show a regular increase of the number/size of BBT aggregates. These results indicate that the dye (BBS or BBT) has a profound influence on the orientation of the semi-crystalline polymer (PBS) since its almost doubles at dye concentrations above 0.08 wt %. The results also suggest that the use of a fluorescent probe to follow the polymer chain orientation is not applicable for such systems.
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This work aims to develop a new mineral porous tubular membrane based on mineral coal fly ash. Finely ground mineral coal powder was calcinated at 700
°C for about 3
h. The elaboration of the ...mesoporous layer was performed by the slip-casting method using a suspension made of the mixture of fly-ash powder, water and polyvinyl alcohol (PVA). The obtained membrane was submitted to a thermal treatment which consists in drying at room temperature for 24
h then a sintering at 800
°C. SEM photographs indicated that the membrane surface was homogeneous and did not present any macrodefects (cracks, etc…). The average pore diameter of the active layer was 0.25
μm and the thickness was around 20
μm. The membrane permeability was 475
l/h
m
2
bar.
This membrane was applied to the treatment of the dying effluents generated by the washing baths in the textile industry. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100
l
h
−1
m
−2). The quality of permeate was almost the same with the two membranes: the COD and color removal was 75% and 90% respectively.
The production of phosphoric acid from natural phosphate rock leads to an industrial waste called phosphogypsum (PG). About 5 tons of PG are generated per ton of phosphoric acid produced. This acidic ...waste (pH 2.2) is mostly disposed of by dumping into large stockpiles close to fertilizer production units, where they occupy large land areas that can cause serious environmental damages. Several attempts were made to test PG valorization via soil amendment because of its phosphate, sulphate and calcium content. The aim of the this study was to evaluate the potential use of PG as phosphate amendment in soil using two wild-type Arabidopsis thaliana ecotypes (Wassilewskija and Colombia) as model plants. Plants were grown in a greenhouse for 30 days, on substrates containing various PG concentrations (0%, 15%, 25%, 40% and 50%). The growth rate and physiological parameters (fresh weight, phosphate and chlorophyll content) were determined. The data revealed that 15% PG did not alter plant survival and leaf's dry weight, and the inorganic phosphate (Pi) uptake by plant seemed to be efficient. However, some alterations in Chlorophyll a/Chlorophyll b ratio were noticed. Higher PG concentrations (40 and 50% PG) exhibited an enhanced negative effect on plant growth, survival and Pi uptake. These inhibitory effects of the substrates may be related to the acidity of the medium in addition to its Cd content.
L’expansion cutanée chez le brûlé est réputée grevée d’un taux de complications élevé. Nous avons réalisé une étude rétrospective sur une période de 8 ans (2008 - 2015) dans le but d’identifier les ...facteurs de risque de survenue de complications. Quarante-cinq expandeurs ont été mis en place chez 31 patients présentant des séquelles de brûlures. Nous avons noté la survenue de complications (mineures et majeures) dans 33,4% des cas. L’expansion au niveau des membres augmente d’une façon statistiquement significative la survenue de complications. Les complications semblent plus fréquentes après le 2ème temps opératoire (reconstruction). Les facteurs qui n’influencent pas le taux de survenue de complications sont l’âge, le volume de l’expandeur et l’indication esthétique ou fonctionnelle de la réparation.
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