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1. Heterogeneous ¹ H and ¹³ C Parahydrogen‐Induced Polarization of Acetate and Pyruvate Esters

   https://doi.org/10.1002/cphc.202100156  

   Salnikov, Oleg_G; Chukanov, Nikita_V; Kovtunova, Larisa_M; Bukhtiyarov, Valerii_I; Kovtunov, Kirill_V; Shchepin, Roman_V; Koptyug, Igor_V; Chekmenev, Eduard_Y (May 2021, ChemPhysChem)

   Abstract Magnetic resonance imaging of [1‐¹³C]hyperpolarized carboxylates (most notably, [1‐¹³C]pyruvate) allows one to visualize abnormal metabolism in tumors and other pathologies. Herein, we investigate the efficiency of¹H and¹³C hyperpolarization of acetate and pyruvate esters with ethyl, propyl and allyl alcoholic moieties using heterogeneous hydrogenation of corresponding vinyl, allyl and propargyl precursors in isotopically unlabeled and 1‐¹³C‐enriched forms with parahydrogen over Rh/TiO₂catalysts in methanol‐d₄and in D₂O. The maximum obtained¹H polarization was 0.6±0.2 % (for propyl acetate in CD₃OD), while the highest¹³C polarization was 0.10±0.03 % (for ethyl acetate in CD₃OD). Hyperpolarization of acetate esters surpassed that of pyruvates, while esters with a triple carbon‐carbon bond in unsaturated alcoholic moiety were less efficient as parahydrogen‐induced polarization precursors than esters with a double bond. Among the compounds studied, the maximum¹H and¹³C NMR signal intensities were observed for propyl acetate. Ethyl acetate yielded slightly less intense NMR signals which were dramatically greater than those of other esters under study. 

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2. Gd ^III ‐ ¹⁹ F Distance Measurements for Proteins in Cells by Electron‐Nuclear Double Resonance

   https://doi.org/10.1002/anie.202218780  

   Seal, Manas; Zhu, Wenkai; Dalaloyan, Arina; Feintuch, Akiva; Bogdanov, Alexey; Frydman, Veronica; Su, Xun‐Cheng; Gronenborn, Angela M.; Goldfarb, Daniella (April 2023, Angewandte Chemie International Edition)

   Abstract Studies of protein structure and dynamics are usually carried out in dilute buffer solutions, conditions that differ significantly from the crowded environment in the cell. The double electron‐electron resonance (DEER) technique can track proteins’ conformations in the cell by providing distance distributions between two attached spin labels. This technique, however, cannot access distances below 1.8 nm. Here, we show that Gd^III‐¹⁹F Mims electron‐nuclear double resonance (ENDOR) measurements can cover part of this short range. Low temperature solution and in‐cell ENDOR measurements, complemented with room temperature solution and in‐cell Gd^III‐¹⁹F PRE (paramagnetic relaxation enhancement) NMR measurements, were performed on fluorinated GB1 and ubiquitin (Ub), spin‐labeled with rigid Gd^IIItags. The proteins were delivered into human cells via electroporation. The solution and in‐cell derived Gd^III‐¹⁹F distances were essentially identical and lie in the 1–1.5 nm range revealing that both, GB1 and Ub, retained their overall structure in the Gd^IIIand¹⁹F regions in the cell. 

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3. Mosaic Cu ^I −Cu ^II −In ^III 2D Perovskites: Pressure‐Dependence of the Intervalence Charge Transfer and a Mechanochemical Alloying Method

   https://doi.org/10.1002/anie.202300957  

   Li, Jiayi; Matheu, Roc; Ke, Feng; Liu, Zhenxian; Lin, Yu; Karunadasa, Hemamala I. (April 2023, Angewandte Chemie International Edition)

   Abstract The perovskite (BA)₄[Cu^II(Cu^IIn^III)_0.5]Cl₈(1_BA; BA⁺=butylammonium) allows us to study the high‐pressure structural, optical, and transport properties of a mixed‐valence 2D perovskite. Compressing1_BAreduces the onset energy of Cu^I/IIintervalence charge transfer from 1.2 eV at ambient pressure to 0.2 eV at 21 GPa. The electronic conductivity of1_BAincreases by 4 orders of magnitude upon compression to 20 GPa, when the activation energy for conduction decreases to 0.16 eV. In contrast, Cu^IIperovskites achieve similar conductivity at ≈50 GPa. The solution‐state synthesis of these perovskites is complicated, with more undesirable side products likely from the precursor mixtures containing three different metal ions. To circumvent this problem, we demonstrate an efficient mechanochemical synthesis to expand this family of halide perovskites with complex composition by simply pulverizing together powders of 2D Cu^IIsingle perovskites and Cu^IIn^IIIdouble perovskites. 

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4. Thiophene‐Based Double Helices: Radical Cations with SOMO–HOMO Energy Level Inversion ^†

   https://doi.org/10.1111/php.13475  

   Rajca, Andrzej; Shu, Chan; Zhang, Hui; Zhang, Sheng; Wang, Hua; Rajca, Suchada (July 2021, Photochemistry and Photobiology)

   Abstract We report relatively persistent, open‐shell thiophene‐based double helices, radical cations 1^•+‐TMS₁₂and 2^•+‐TMS₈. Closed‐shell neutral double helices, 1‐TMS₁₂and 2‐TMS₈, have nearly identical first oxidation potentials,E^+/0 ≈ +1.33 V, corresponding to reversible oxidation to their radical cations. The radical cations are generated, using tungsten hexachloride in dichloromethane (DCM) as an oxidant,E^+/0 ≈ +1.56 V. EPR spectra consist of a relatively sharp singlet peak with an unusually lowg‐value of 2.001–2.002, thus suggesting exclusive delocalization of spin density over π‐conjugated system consisting of carbon atoms only. DFT computations confirm these findings, as only negligible fraction of spin density is found on sulfur and silicon atoms and the spin density is delocalized over a single tetrathiophene moiety. For radical cation, 1^•+‐TMS₁₂, energy level of the singly occupied molecular orbital (SOMO) lies below the four highest occupied molecular orbitals (HOMOs), thus indicating the SOMO–HOMO inversion (SHI) and therefore, violating the Aufbau principle. 1^•+‐TMS₁₂has a half‐life of the order of only 5 min at room temperature. EPR peak intensity of 2^•+‐TMS₈, which does not show SHI, is practically unchanged over at least 2 h. 

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5. NMR Crystallography: Evaluation of Hydrogen Positions in Hydromagnesite by ¹³ C{ ¹ H} REDOR Solid‐State NMR and Density Functional Theory Calculation of Chemical Shielding Tensors

   https://doi.org/10.1002/anie.201813306  

   Cui, Jinlei; Olmsted, David L.; Mehta, Anil K.; Asta, Mark; Hayes, Sophia E. (February 2019, Angewandte Chemie International Edition)

   Abstract Solid‐state NMR measurements coupled with density functional theory (DFT) calculations demonstrate how hydrogen positions can be refined in a crystalline system. The precision afforded by rotational‐echo double‐resonance (REDOR) NMR to interrogate¹³C–¹H distances is exploited along with DFT determinations of the¹³C tensor of carbonates (CO₃²⁻). Nearby¹H nuclei perturb the axial symmetry of the carbonate sites in the hydrated carbonate mineral, hydromagnesite [4 MgCO₃⋅Mg(OH)₂⋅4 H₂O]. A match between the calculated structure and solid‐state NMR was found by testing multiple semi‐local and dispersion‐corrected DFT functionals and applying them to optimize atom positions, starting from X‐ray diffraction (XRD)‐determined atomic coordinates. This was validated by comparing calculated to experimental¹³C{¹H} REDOR and¹³C chemical shift anisotropy (CSA) tensor values. The results show that the combination of solid‐state NMR, XRD, and DFT can improve structure refinement for hydrated materials. 

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