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1. Stereoisomer-dependent unimolecular kinetics of 2,4- dimethyloxetanyl peroxy radicals

   https://doi.org/10.1039/D2FD00029F  

   Doner, Anna C.; Zádor, Judit; Rotavera, Brandon (October 2022, Faraday Discussions)

   2,4,dimethyloxetane is an important cyclic ether intermediate that is produced from hydroperoxyalkyl (QOOH) radicals in the low-temperature combustion of n -pentane. However, the reaction mechanisms and rates of consumption pathways remain unclear. In the present work, the pressure- and temperature-dependent kinetics of seven cyclic ether peroxy radicals, which stem from 2,4,dimethyloxetane via H-abstraction and O 2 addition, were determined. The automated kinetic workflow code, KinBot, was used to model the complexity of the chemistry in a stereochemically resolved manner and solve the resulting master equations from 300–1000 K and from 0.01–100 atm. The main conclusions from the calculations include (i) diastereomeric cyclic ether peroxy radicals show significantly different reactivities, (ii) the stereochemistry of the peroxy radical determines which QOOH isomerization steps are possible, (iii) conventional QOOH decomposition pathways, such as cyclic ether formation and HO 2 elimination, compete with ring-opening reactions, which primarily produce OH radicals, the outcome of which is sensitive to stereochemistry. Ring-opening reactions lead to unique products, such as unsaturated, acyclic peroxy radicals, that form direct connections with species present in other chemical kinetics mechanisms through "cross-over" reactions that may complicate the interpretation of experimental results from combustion of n-pentane and, by extension, other alkanes. For example, one cross-over reaction involving 1-hydroperoxy-4-pentanone-2-yl produces 2-(hydroperoxymethyl)-3-butanone-1-yl, which is an iso-pentane-derived ketohydroperoxide (KHP). At atmospheric pressure, the rate of chemical reactions of all seven peroxy radicals compete with that of collisional stabilization, resulting in well-skipping reactions. However, at 100 atm, only one out of seven peroxy radicals undergoes significant well-skipping reactions. The rates produced from the master equation calculations provide the first foundation for the development of detailed sub-mechanisms for cyclic ether intermediates. In addition, analysis of the complex reaction mechanisms of 2,4-dimethyloxetane-derived peroxy radicals provides insights into the effects of stereoisomers on reaction pathways and product yields. 

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2. Visible-light induced degradation of diphenyl urea and polyethylene using polythiophene decorated CuFe2O4 nanohybrids

   https://doi.org/10.1038/s41598-023-30669-x  

   Riaz, Ufana; Gaffar, Shayista; Hauser, Kristen; Yan, Fei (December 2023, Scientific Reports)

   Abstract The present work reports facile synthesis of CuFe 2 O 4 nanoparticles via co-precipitation method and formulation of its nanohybrids with polythiophene (PTh). The structural and morphological properties were investigated using fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectra (SEM-EDS) and UV–Vis spectroscopy. The band gap was found to decrease with increase in the loading of PTh and was found to be 2.52 eV for 1-PTh/CuFe 2 O 4 , 2.15 eV for 3-PTh/CuFe 2 O 4 and 1.89 eV for 5-PTh/CuFe 2 O 4 . The nanohybrids were utilized as photocatalysts for visible light induced degradation of diphenyl urea. Diphenyl urea showed 65% degradation using 150 mg catalyst within 120 min. Polyethylene (PE) was also degraded using these nanohybrids under visible light as well as microwave irradiation to compare its catalytic efficiency under both conditions. Almost 50% of PE was degraded under microwave and 22% under visible light irradiation using 5-PTh/CuFe 2 O 4 . The degraded diphenyl urea fragments were analyzed using LCMS and a tentative mechanism of degradation was proposed. 

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3. Dual-site occupancy induced broadband cyan emission in Ba ₂ CaB ₂ Si ₄ O ₁₄ :Ce ³⁺

   https://doi.org/10.1039/D0TC02625E  

   You, Shihai; Zhuo, Ya; Chen, Qiulin; Brgoch, Jakoah; Xie, Rong-Jun (November 2020, Journal of Materials Chemistry C)

   null (Ed.)

   There is a significant need to identify cyan-emitting phosphors capable of filling the “cyan-gap” (480–520 nm) in full-visible-spectrum phosphor-converted white light-emitting diodes (pc-wLEDs). Here, a new broadband cyan-emitting phosphor that enables addressing of this challenge is reported. The compound, Ba 2 CaB 2 Si 4 O 14 :Ce 3+ , presents a bright cyan emission peaking at 478 nm with a large full width at half maximum of 142 nm (6053 cm −1 ), and minimal thermal quenching. The photoluminescence properties originate from Ce 3+ residing at two different crystallographic sites, a [BaO 9 ] distorted elongated square pyramid and a [CaO 6 ] trigonal prism. This combination results in an efficient, broad emission covering the blue to green region of the visible spectrum. Fabricating a simple dichromatic ultraviolet ( λ ex = 370 nm) pumped pc-wLED using Ba 2 CaB 2 Si 4 O 14 :Ce 3+ along with a commercially available red phosphor demonstrates full-visible-spectrum white light with high color rendering index ( R a > 90) and tunable correlated color temperature, showing the potential of this material for achieving high-quality LED-based lighting. 

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4. Molecular design of a novel thiophene-derived o-nitrobenzyl photolabile protecting group with visible light-absorption for the synthesis of hydroxamic acids

   Adjei-Sah, Ophelia A; Campbell, Albert D; Saint-Louis, Carl J (March 2024, American Chemical Society)

   Chemoselectivity is a significant barrier that synthetic chemists face while synthe sizing organic mols. As a remedy, protective groups (P Gs) are used during chem. reactions to prevent highly reactive functional groups from interf ering with other functional groups within the same mol. However, as the number of comparable PGs within a mol. increases, it becomes more difficult to remove individual P Gs using typical methods such as acidic and basic conditions. PGs have also been used in the synthesis of hydroxamic acids (H As), a class of organic compounds known for their potential use as precursors for anticancer drugs such as Trichostatin A, a powerful tumor cell inhibitor. Despite their widespread use, HAs are challenging to synthesize and purify due to their high reactivity and the formation of numerous polysubstituted byproducts during the synthetic process. In this study, we use ortho- nitrobenzyl (o-NB) photolabile protecting groups (PPGs) derived from thiophene to solve the problem of H A synthesis and purification This is a preferable method because it requires only visible light to deprotect these PPGs. However, most o-NB PPGs absorb in the UV region of the electromagnetic spectrum, making them unsuitable for use in biol. systems. Herein, we designed and synthesized a visible light-absorbing thiophenebased o-NB PPG that absorbs in the visible region of the spectrum while avoiding the challenges associated with H A synthesis and purification To demonstrate the stability of our o-NB PPG, we will selectively deprotect classic PGs using traditional methods without cleaving the HA moiety. With this method, visible light will be used to cleave and generate H A in high yields, with a diagnostic fluore scent byproduct used to quantify the amount of H A formed. 

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5. Pressure-dependent kinetics of peroxy radicals formed in isobutanol combustion

   https://doi.org/10.1039/d0cp02872j  

   Goldman, Mark Jacob; Yee, Nathan W.; Kroll, Jesse H.; Green, William H. (September 2020, Physical Chemistry Chemical Physics)

   null (Ed.)

   Bio-derived isobutanol has been approved as a gasoline additive in the US, but our understanding of its combustion chemistry still has significant uncertainties. Detailed quantum calculations could improve model accuracy leading to better estimation of isobutanol's combustion properties and its environmental impacts. This work examines 47 molecules and 38 reactions involved in the first oxygen addition to isobutanol's three alkyl radicals located α, β, and γ to the hydroxide. Quantum calculations are mostly done at CCSD(T)-F12/cc-pVTZ-F12//B3LYP/CBSB7, with 1-D hindered rotor corrections obtained at B3LYP/6-31G(d). The resulting potential energy surfaces are the most comprehensive isobutanol peroxy networks published to date. Canonical transition state theory and a 1-D microcanonical master equation are used to derive high-pressure-limit and pressure-dependent rate coefficients, respectively. At all conditions studied, the recombination of γ-isobutanol radical with O 2 forms HO 2 + isobutanal. The recombination of β-isobutanol radical with O 2 forms a stabilized hydroperoxy alkyl radical below 400 K, water + an alkoxy radical at higher temperatures, and HO 2 + an alkene above 1200 K. The recombination of β-isobutanol radical with O 2 results in a mixture of products between 700–1100 K, forming acetone + formaldehyde + OH at lower temperatures and forming HO 2 + alkenes at higher temperatures. The barrier heights, high-pressure-limit rates, and pressure-dependent kinetics generally agree with the results from previous quantum chemistry calculations. Six reaction rates in this work deviate by over three orders of magnitude from kinetics in detailed models of isobutanol combustion, suggesting the rates calculated here can help improve modeling of isobutanol combustion and its environmental fate. 

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