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1. Using δ¹⁸O and δ²H to Detect Hydraulic Connection Between a Sinkhole Lake and a First‐Magnitude Spring

   https://doi.org/10.1111/gwat.13105  

   Ahmed, Nur; Ye, Ming; Wang, Yang; Greenhalgh, Tom; Fowler, Karlee (April 2021, Groundwater)

   Abstract Oxygen and hydrogen isotopes were used in this study to detect a hydraulic connection between a sinkhole lake and a karst spring. In karst areas, surface water that flows to a lake can drain through sinkholes in the lakebed to the underlying aquifer, and then flows in karst conduits and through aquifer matrix. At the study site located in northwest Florida, USA, Lake Miccosukee immediately drains into two sinkholes. Results from a dye tracing experiment indicate that lake water discharges at Natural Bridge Spring, a first‐magnitude spring 32 km downgradient from the lake. By collecting weekly water samples from the lake, the spring, and a groundwater well 10 m away from the lake during the dry period between October 2019 and January 2020, it was found that, when rainfall effects on isotopic signature in spring water are removed, increased isotope ratios of spring water can be explained by mixing of heavy‐isotope‐enriched lake water into groundwater, indicating hydraulic connection between the lake and the spring. Such a detection of hydraulic connection at the scale of tens of kilometers and for a first‐magnitude spring has not been previously reported in the literature. Based on the isotope ratio data, it was estimated that, during the study period, about 8.5% the spring discharge was the lake water that drained into the lake sinkholes. 

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2. Phosphatidylinositol 3, 5‐bisphosphate regulates Ca ²⁺ transport during yeast vacuolar fusion through the Ca ²⁺ ATPase Pmc1

   https://doi.org/10.1111/tra.12736  

   Miner, Gregory E.; Sullivan, Katherine D.; Zhang, Chi; Rivera‐Kohr, David; Guo, Annie; Hurst, Logan R.; Ellis, Ez C.; Starr, Matthew L.; Jones, Brandon C.; Fratti, Rutilio A. (June 2020, Traffic)

   Abstract The transport of Ca²⁺across membranes precedes the fusion and fission of various lipid bilayers. Yeast vacuoles under hyperosmotic stress become fragmented through fission events that requires the release of Ca²⁺stores through the TRP channel Yvc1. This requires the phosphorylation of phosphatidylinositol‐3‐phosphate (PI3P) by the PI3P‐5‐kinase Fab1 to produce transient PI(3,5)P₂pools. Ca²⁺is also released during vacuole fusion upontrans‐SNARE complex assembly, however, its role remains unclear. The effect of PI(3,5)P₂on Ca²⁺flux during fusion was independent of Yvc1. Here, we show that while low levels of PI(3,5)P₂were required for Ca²⁺uptake into the vacuole, increased concentrations abolished Ca²⁺efflux. This was as shown by the addition of exogenous dioctanoyl PI(3,5)P₂or increased endogenous production of by the hyperactivefab1^T2250Amutant. In contrast, the lack of PI(3,5)P₂on vacuoles from the kinase deadfab1^EEEmutant showed delayed and decreased Ca²⁺uptake. The effects of PI(3,5)P₂were linked to the Ca²⁺pump Pmc1, as its deletion rendered vacuoles resistant to the effects of excess PI(3,5)P₂. Experiments with Verapamil inhibited Ca²⁺uptake when added at the start of the assay, while adding it after Ca²⁺had been taken up resulted in the rapid expulsion of Ca²⁺. Vacuoles lacking both Pmc1 and the H⁺/Ca²⁺exchanger Vcx1 lacked the ability to take up Ca²⁺and instead expelled it upon the addition of ATP. Together these data suggest that a balance of efflux and uptake compete during the fusion pathway and that the levels of PI(3,5)P₂can modulate which path predominates. 

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3. Computational protocol for predicting ¹⁹F NMR chemical shifts for PFAS and connection to PFAS structure

   https://doi.org/10.1002/jcc.26939  

   Mifkovic, Maleigh; Pauling, Jessica; Vyas, Shubham (June 2022, Journal of Computational Chemistry)

   Abstract Per‐ and polyfluoroalkyl substances (PFAS) are robust “forever” chemicals that have become global environmental contaminants due to their inability to degrade using traditional techniques. In addition to the persistent nature of PFAS, the structural and functional diversity in PFAS creates a unique challenge in identification and remediation. Their identification is further complicated by the absence of standards for many PFAS. This work is aimed at developing a protocol for computing and establishing accurate¹⁹F NMR chemical shifts for PFAS using density functional theory (DFT), which can aid in the identification of PFAS. The impact of solvation and basis sets was evaluated by comparing the computed data with the experimental measurements. Results showed the addition of dispersion corrections in the methodology improve the accuracy of calculated NMR parameters within 4 ppm of the experimental values. Adding a second diffuse function and additional polarization did not improve the accuracy, likely because of the electronegativity of fluorine which does not allow the electron density of fluorine atoms to be polarized. The inclusion of various implicit solvation (DMSO, chloroform, and water) yielded negligible differences in accuracy, and were overall less accurate than the gas phase calculations. The most accurate methodology was then applied to more environmentally relevant PFAS, and the impact of helical nature on the NMR signatures was evaluated. The implication of this work is to be able to improve the identification of structurally diverse PFAS using the¹⁹F NMR. 

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4. Formation of monomeric Sn( ii ) and Sn( iv ) perfluoropinacolate complexes and their characterization by ¹¹⁹ Sn Mössbauer and ¹¹⁹ Sn NMR spectroscopies

   https://doi.org/10.1039/d0dt02837a  

   Elinburg, Jessica K.; Hyre, Ariel S.; McNeely, James; Alam, Todd M.; Klenner, Steffen; Pöttgen, Rainer; Rheingold, Arnold L.; Doerrer, Linda H. (October 2020, Dalton Transactions)

   null (Ed.)

   The synthesis and characterization of a series of Sn( ii ) and Sn( iv ) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pin F ) ligand are reported herein. Three analogs of [Sn IV (pin F ) 3 ] 2− with NEt 3 H + ( 1 ), K + ( 2 ), and {K(18C6)} + ( 3 ) counter cations and two analogs of [Sn II (pin F ) 2 ] 2− with K + ( 4 ) and {K(15C5) 2 } + ( 5 ) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119 Sn Mössbauer and NMR spectroscopies. The six-coordinate Sn IV (pin F ) complexes display 119 Sn NMR resonances and 119 Sn Mössbauer spectra similar to SnO 2 (cassiterite). In contrast, the four-coordinate Sn II (pin F ) complexes, featuring a stereochemically-active lone pair, possess low 119 Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn( ii ) complexes are unreactive towards both Lewis bases (pyridine, NEt 3 ) and acids (BX 3 , Et 3 NH + ). Calculations confirm that the Sn( ii ) lone pair is localized within the 5s orbital and reveal that the Sn 5p x LUMO is energetically inaccessible, which effectively abates reactivity. 

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5. Total Synthesis of UCS1025A via Tandem Carbonylative Stille Cross Coupling and Diels‐Alder Reaction ^†

   https://doi.org/10.1002/cjoc.202300331  

   Cui, Chengsen; Dai, Mingji (August 2023, Chinese Journal of Chemistry)

   Comprehensive Summary We report an efficient and convergent strategy for the total synthesis of UCS1025A and its diastereomer tetra‐epi‐UCS1025A. UCS1025A is a representative member of the naturally occurring pyrrolizidinone polyketides, from which members with potent antibacterial, antifungal, and anticancer activities have been identified. Our approach features a tandem carbonylative Stille cross coupling and Diels‐Alder reaction to forge a key C—C bond and build thetrans‐decalin system. This tandem process utilizes carbon monoxide as a one‐carbon linchpin to stitch a vinyl triflate and a vinylstannane together and form the desired enone moiety for the subsequent intramolecular Diels‐Alder cyclization. Our synthesis also provides a versatile approach for the synthesis of other related pyrrolizidinone‐containing polyketides. 

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