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 ( August 2023 , Photochemistry and Photobiology)

   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. Atmospheric Metallicity and C/O of HD 189733 b from High-resolution Spectroscopy

   https://doi.org/10.3847/1538-3881/ad1180  

   Finnerty, Luke ; Xuan, Jerry W. ; Xin, Yinzi ; Liberman, Joshua ; Schofield, Tobias ; Fitzgerald, Michael P. ; Agrawal, Shubh ; Baker, Ashley ; Bartos, Randall ; Blake, Geoffrey A. ; et al ( January 2024 , The Astronomical Journal)

   We present high-resolutionK-band emission spectra of the quintessential hot Jupiter HD 189733 b from the Keck Planet Imager and Characterizer. Using a Bayesian retrieval framework, we fit the dayside pressure–temperature profile, orbital kinematics, mass-mixing ratios of H₂O, CO, CH₄, NH₃, HCN, and H₂S, and the¹³CO/¹²CO ratio. We measure mass fractions of${\mathrm{logH}}_2\mathrm{O}=-{2.0}_{-0.4}^{+0.4}$and$\mathrm{logCO}=-{2.2}_{-0.5}^{+0.5}$, and place upper limits on the remaining species. Notably, we find logCH₄< −4.5 at 99% confidence, despite its anticipated presence at the equilibrium temperature of HD 189733 b assuming local thermal equilibrium. We make a tentative (∼3σ) detection of¹³CO, and the retrieved posteriors suggest a¹²C/¹³C ratio similar to or substantially less than the local interstellar value. The possible¹³C enrichment would be consistent with accretion of fractionated material in ices or in the protoplanetary disk midplane. The retrieved abundances correspond to a substantially substellar atmospheric C/O = 0.3 ± 0.1, while the carbon and oxygen abundances are stellar to slightly superstellar, consistent with core-accretion models which predict an inverse correlation between C/O and metallicity. The specific combination of low C/O and high metallicity suggests significant accretion of solid material may have occurred late in the formation process of HD 189733 b.

    

   more » « less
3. Synthesis and Characterization of Ru(II) Complexes with π‐Expansive Imidazophen Ligands for the Photokilling of Human Melanoma Cells

   https://doi.org/10.1111/php.13177  

   Ghosh, Goutam ; Yin, Huimin ; Monro, Susan M. A. ; Sainuddin, Tariq ; Lapoot, Lloyd ; Greer, Alexander ; McFarland, Sherri A. ( January 2020 , Photochemistry and Photobiology)

   Ru(II) complexes were synthesized with π‐expanding (phenyl, fluorenyl, phenanthrenyl, naphthalen‐1‐yl, naphthalene‐2‐yl, anthryl and pyrenyl groups) attached at a 1H‐imidazo[4,5‐f][1,10]phenanthroline ligand and 4,4′‐dimethyl‐2,2′‐bipyridine (4,4′‐dmb) coligands. These Ru(II) complexes were characterized by 1D and 2D NMR, and mass spectroscopy, and studied for visible light and dark toxicity to human malignant melanoma SK‐MEL‐28 cells. In the SK‐MEL‐28 cells, the Ru(II) complexes are highly phototoxic (EC₅₀ = 0.2–0.5 µm) and have low dark toxicity (EC₅₀ = 58–230 µm). The highest phototherapeutic index (PI) of the series was found with the Ru(II) complex bearing the 2‐(pyren‐1‐yl)‐1H‐imidazo[4,5‐f][1,10]phenanthroline ligand. This high PI is in part attributed to the π‐rich character added by the pyrenyl group, and a possible low‐lying and longer‐lived³IL state due to equilibration with the³MLCT state. While this pyrenyl Ru(II) complex possessed a relatively high quantum yield for singlet oxygen formation (Φ_∆ = 0.84), contributions from type‐I processes (oxygen radicals and radical ions) are competitive with the type‐II (¹O₂) process based on effects of added sodium azide and solvent deuteration.

    

   more » « less
4. Computational Discovery of Active and Selective Metal‐Nitrogen‐Graphene Catalysts for Electrooxidation of Water to H 2 O 2

   https://doi.org/10.1002/cctc.202300055  

   Chaudhary, Payal ; Evazzade, Iman ; Belosludov, Rodion ; Alexandrov, Vitaly ( April 2023 , ChemCatChem)

   A direct electrosynthesis of H₂O₂from either O₂or H₂O is an attractive strategy to replace the energy‐intensive industrial anthraquinone process. Two‐electron water oxidation reaction (2e‐WOR) offers several advantages over the oxygen reduction reaction such as better mass transfer due to the absence of gas‐phase reactants. However, 2e‐WOR is a more challenging and less studied process with only a handful of metal oxides exhibiting reasonable activity/selectivity properties. Herein, we employ density‐functional‐theory calculations to screen a variety of metal‐nitrogen‐graphene structures for 2e‐WOR. As a consequence of scaling between the adsorption energies of reaction intermediates, we determine a linear relation between selectivities for the first and second reaction steps of 2e‐WOR, viz. that if selectivity toward adsorbed OH is improved, then selectivity toward H₂O₂at the subsequent step is decreased. We also find that selectivity and activity are linearly scaled in such a way that a higher activity (i. e., a lower overpotential) leads to a lower selectivity for the H₂O₂formation step. Based on the obtained results several chemistries, e. g., containing NiN_x−C moieties, are predicted to rival the best‐performing metal oxides such as ZnO and CaSnO₃in terms of combination of their activity/selectivity characteristics for 2e‐WOR.

    

   more » « less
5. Elucidation of the Synergistic Effect of Dopants and Vacancies on Promoted Selectivity for CO 2 Electroreduction to Formate

   https://doi.org/10.1002/adma.202005113  

   Li, Zhongjian ; Cao, Ang ; Zheng, Qiang ; Fu, Yuanyuan ; Wang, Tingting ; Arul, K. Thanigal ; Chen, Jeng‐Lung ; Yang, Bin ; Adli, Nadia Mohd ; Lei, Lecheng ; et al ( November 2020 , Advanced Materials)

   Sn‐based materials are identified as promising catalysts for the CO₂electroreduction (CO2RR) to formate (HCOO⁻). However, their insufficient selectivity and activity remain grand challenges. A new type of SnO₂nanosheet with simultaneous N dopants and oxygen vacancies (V_O‐rich N‐SnO₂NS) for promoting CO₂conversion to HCOO⁻is reported. Due to the likely synergistic effect of N dopant andV_O, theV_O‐rich N‐SnO₂NS exhibits high catalytic selectivity featured by an HCOO⁻Faradaic efficiency (FE) of 83% at−0.9 V and an FE of>90% for all C1 products (HCOO⁻and CO) at a wide potential range from −0.9 to−1.2 V. Low coordination Sn–N moieties are the active sites with optimal electronic and geometric structures regulated byV_Oand N dopants. Theoretical calculations elucidate that the reaction free energy of HCOO* protonation is decreased on theV_O‐rich N‐SnO₂NS, thus enhancing HCOO⁻selectivity. The weakened H* adsorption energy also inhibits the hydrogen evolution reaction, a dominant side reaction during the CO2RR. Furthermore, using the catalyst as the cathode, a spontaneous Galvanic Zn‐CO₂cell and a solar‐powered electrolysis process successfully demonstrated the efficient HCOO⁻generation through CO₂conversion and storage.

    

   more » « less