More Like this

1. Role of curvature in acridone for ¹O₂ oxidation of a natural product homoallylic alcohol: A novel iso ‐hydroperoxide intermediate

   https://doi.org/10.1111/php.13843  

   Lapoot, Lloyd; Jabeen, Shakeela; Durantini, Andrés M; Greer, Alexander (March 2024, Photochemistry and Photobiology)

   Cadet, Jean (Ed.)

   Abstract A density functional theoretical (DFT) study is presented, implicating a¹O₂oxidation process to reach a dihydrobenzofuran from the reaction of the natural homoallylic alcohol, glycocitrine. Our results predict an interconversion between glycocitrine and aniso‐hydroperoxide intermediate [R(H)O⁺–O⁻] that provides a key path in the chemistry which then follows. Formations of allylic hydroperoxides are unlikely from a¹O₂‘ene’ reaction. Instead, the dihydrobenzofuran arises by¹O₂oxidation facilitated by a 16° curvature of the glycocitrine ring imposed by a pyramidalN‐methyl group. This curvature facilitates the formation of theiso‐hydroperoxide, which is analogous to theisospecies CH₂I⁺–I⁻and CHI₂⁺–I⁻formed by UV photolysis of CH₂I₂and CHI₃. Theiso‐hydroperoxide is also structurally reminiscent of carbonyl oxides (R₂C=O⁺–O⁻) formed in the reaction of carbenes and oxygen. Our DFT results point to intermolecular process, in which theiso‐hydroperoxide's fate relates to O‐transfer and H₂O dehydration reactions for new insight into the biosynthesis of dihydrobenzofuran natural products. 

   more » « less
2. Deep Search for Molecular Oxygen in TW Hya

   https://doi.org/10.3847/1538-4357/acf717  

   Williams, Becky J; Cleeves, L Ilsedore; Eistrup, Christian; Ramsey, Jon P (October 2023, The Astrophysical Journal)

   Abstract The dominant form of oxygen in cold molecular clouds is gas-phase carbon monoxide (CO) and ice-phase water (H₂O). Yet, in planet-forming disks around young stars, gas-phase CO and H₂O are less abundant relative to their interstellar medium values, and no other major oxygen-carrying molecules have been detected. Some astrochemical models predict that gas-phase molecular oxygen (O₂) should be a major carrier of volatile oxygen in disks. We report a deep search for emission from the isotopologue¹⁶O¹⁸O (N_J= 2₁− 0₁line at 233.946 GHz) in the nearby protoplanetary disk around TW Hya. We used imaging techniques and matched filtering to search for weak emission but do not detect¹⁶O¹⁸O. Based on our results, we calculate upper limits on the gas-phase O₂abundance in TW Hya of (6.4–70) × 10⁻⁷relative to H, which is 2–3 orders of magnitude below solar oxygen abundance. We conclude that gas-phase O₂is not a major oxygen carrier in TW Hya. Two other potential oxygen-carrying molecules, SO and SO₂, were covered in our observations, which we also do not detect. Additionally, we report a serendipitous detection of the C¹⁵NN_J= 2_5/2− 1_3/2hyperfine transitions,F= 3 − 2 andF= 2 − 1, at 219.9 GHz, which we found via matched filtering and confirm through imaging. 

   more » « less
3. Crystal structure of (1,4,7,10,13,16-hexaoxacyclooctadecane-κ ⁶ O )potassium-μ-oxalato-triphenylstannate(IV), the first reported 18-crown-6-stabilized potassium salt of triphenyloxalatostannate

   https://doi.org/10.1107/S2056989024007758  

   Song, Xueqing; Li, William; Torres, Yolanda; Greaves, Tazena (September 2024, Acta Crystallographica Section E Crystallographic Communications)

   The title complex, (1,4,7,10,13,16-hexaoxacyclooctadecane-1κ⁶O)(μ-oxalato-1κ²O¹,O²:2κ²O^1′,O^2′)triphenyl-2κ³C-potassium(I)tin(IV), [KSn(C₆H₅)₃(C₂O₄)(C₁₂H₂₄O₆)] or K[18-Crown-6][(C₆H₅)₃SnO₄C₂], was synthesized. The complex consists of a potassium cation coordinated to the six oxygen atoms of a crown ether molecule and the two oxygen atoms of the oxalatotriphenylstannate anion. It crystallizes in the monoclinic crystal system within the space groupP2₁. The tin atom is coordinated by one chelating oxalate ligand and three phenyl groups, forming acis-trigonal–bipyramidal geometry around the tin atom. The cations and anions form ion pairs, linked through carbonyl coordination to the potassium atoms. The crystal structure features C—H...O hydrogen bonds between the oxygen atoms of the oxalate group and the hydrogen atoms of the phenyl groups, resulting in an infinite chain structure extending alonga-axis direction. The primary inter-chain interactions are van der Waals forces. 

   more » « less
4. Amination of polypropylene‐ g ‐(maleic anhydride) using reactive extrusion

   https://doi.org/10.1002/app.56085  

   Kay, Ian P; Goddard, Julie M (November 2024, Journal of Applied Polymer Science)

   Abstract We report synthesis of a radical scavenging aminated thermoplastic polymer through reactive extrusion of polyethyleneimine (PEI) with a polypropylene and polypropylene‐graft‐maleic anhydride (PP‐g‐MA) meltblend. The reaction was confirmed using acid orange 7 (AO7) amine density assay, toluidine blue O (TBO) carboxylic acid density assay, Fourier transform infrared spectroscopy (FTIR), and a migration assay. FTIR spectra revealed a reduction of the asymmetric stretching of the maleic anhydride (MA) carbonyl group at 1777 cm⁻¹and the emergence of the maleimide carbonyl peak at 1702 cm⁻¹. AO7 supported surface orientation of grafted amine groups by introduction of 7.22 nmol cm⁻²primary amines, corresponding to the reduction of surface carboxylic acids quantified by TBO from 12.46 nmol cm⁻²to 0.43 nmol cm⁻². After incubation (40°C, 10 days) in ethanol, acetic acid, and water, < 0.1 mg cm⁻²PEI migrated from the materials, supporting the covalent nature of the grafting. Antioxidant activity was demonstrated exhibiting 5.90 and 4.31 nmol Trolox_eqcm⁻²in aqueous and organic environments, respectively. Results indicate a successful condensation reaction during reactive extrusion, producing an aminated thermoplastic polymer with antioxidant activity for target applications such as food packaging, wastewater treatment, carbon capture, and others. 

   more » « less
5. Reactions of Aluminum Oxide Cluster Cations with Ethane: A Mass‐Spectrometric and Vibrational Spectroscopy Study

   https://doi.org/10.1002/cphc.202400427  

   Phasuk, Apakorn; Metz, Ricardo B (December 2024, ChemPhysChem)

   Abstract The pathways for the reactions of aluminum oxide cluster ions with ethane have been measured. For selected ions (Al₂O⁺, Al₃O₂⁺, Al₃O₄⁺, Al₄O₇⁺) the structure of the collisionally‐stabilized reaction intermediates were explored by measuring the photodissociation vibrational spectra from 2600 cm⁻¹–3100 cm⁻¹. Density functional theory was used to calculate features of the potential energy surfaces for the reactions and the vibrational spectra of intermediates. Generally, more than one isomer contributes to the observed spectrum. The oxygen‐deficient clusters Al₂O⁺and Al₃O₂⁺have large C−H activation barriers, so only the entrance channel complexes in which intact C₂H₆binds to aluminum are observed. This interaction leads to a substantial (~200 cm⁻¹) red shift of the C−H symmetric stretch in ethane, indicating significant weakening of the proximal C−H bonds. In Al₃O₄⁺, the complex formed by interactions with three C₂H₆is investigated and, in addition to entrance channel complexes, the C−H activation intermediate Al₃O₄H⁺(C₂H₅)(C₂H₆)₂is observed. For oxygen‐rich Al₄O₇⁺, the C₂H₆is favored to bind at an aluminum site far from the reactive superoxide group, reducing the reactivity. As expected, oxygen‐rich species and open‐shell cluster ions have smaller barriers for C−H bond activation, except for Al₃O₄⁺which is predicted and observed to be reactive. 

   more » « less