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1. Solvent Effects in Hyperpolarization of ¹⁵ N Nuclei in [ ¹⁵ N ₃ ]Metronidazole and [ ¹⁵ N ₃ ]Nimorazole Antibiotics via SABRE‐SHEATH**

   https://doi.org/10.1002/anse.202400045  

   Yi, Anna_P; Salnikov, Oleg_G; Burueva, Dudari_B; Chukanov, Nikita_V; Chekmenev, Eduard_Y; Koptyug, Igor_V (August 2024, Analysis & Sensing)

   Abstract Metronidazole and nimorazole are antibiotics of a nitroimidazole group which also may be potentially utilized as hypoxia radiosensitizers for the treatment of cancerous tumors. Hyperpolarization of¹⁵N nuclei in these compounds using SABRE‐SHEATH (Signal Amplification By Reversible Exchange in SHield Enables Alignment Transfer to Heteronuclei) approach provides dramatic enhancement of detection sensitivity of these analytes using magnetic resonance spectroscopy and imaging. Methanol‐d₄is conventionally employed as a solvent in SABRE hyperpolarization process. Herein, we investigate SABRE‐SHEATH hyperpolarization of isotopically labeled [¹⁵N₃]metronidazole and [¹⁵N₃]nimorazole in nondeuterated methanol and ethanol solvents. Optimization of such hyperpolarization parameters as polarization transfer magnetic field, temperature, parahydrogen flow rate and pressure allowed us to obtain an average¹⁵N polarization of up to 7.2–7.4 % for both substrates. The highest¹⁵N polarizations were observed in methanol‐d₄for [¹⁵N₃]metronidazole and in ethanol for [¹⁵N₃]nimorazole. At a clinically relevant magnetic field of 1.4 T the¹⁵N nuclei of these substrates possess long characteristic hyperpolarization lifetimes (T₁) of ca. 1 to ca. 7 min. This study represents a major step toward SABRE in more biocompatible solvents, such as ethanol, and also paves the way for future utilization of these hyperpolarized nitroimidazoles as molecular contrast agents for MRI visualization of tumors. 

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2. In Situ Quantification of Biological N ₂ Production Using Naturally Occurring ¹⁵ N ¹⁵ N

   https://doi.org/10.1021/acs.est.9b00812  

   Yeung, Laurence Y.; Haslun, Joshua A.; Ostrom, Nathaniel E.; Sun, Tao; Young, Edward D.; van Kessel, Maartje A. H. J.; Lücker, Sebastian; Jetten, Mike S. M. (April 2019, Environmental Science & Technology)
3. Extreme enrichment in atmospheric ¹⁵ N ¹⁵ N

   https://doi.org/10.1126/sciadv.aao6741  

   Yeung, Laurence Y.; Li, Shuning; Kohl, Issaku E.; Haslun, Joshua A.; Ostrom, Nathaniel E.; Hu, Huanting; Fischer, Tobias P.; Schauble, Edwin A.; Young, Edward D. (November 2017, Science Advances)
4. Terminal Diazirines Enable Reverse Polarization Transfer from ¹⁵ N ₂ Singlets

   https://doi.org/10.1002/anie.201904026  

   Zhang, Guannan; Colell, Johannes F. P.; Glachet, Thomas; Lindale, Jacob R.; Reboul, Vincent; Theis, Thomas; Warren, Warren S. (July 2019, Angewandte Chemie International Edition)

   Abstract Diazirine moieties are chemically stable and have been incorporated into biomolecules without impediment of biological activity. The¹⁵N₂labeled diazirines are appealing motifs for hyperpolarization supporting relaxation protected states with long‐lived lifetimes. The (‐CH¹⁵N₂) diazirine groups investigated here are analogues to methyl groups, which provides the opportunity to transfer polarization stored on a relaxation protected (‐CH¹⁵N₂) moiety to¹H, thus combining the advantages of long lifetimes of¹⁵N polarization with superior sensitivity of¹H detection. Despite the proximity of¹H to¹⁵N nuclei in the diazirine moiety,¹⁵NT₁times of up to (4.6±0.4) min and singlet lifetimesT_sof up to (17.5±3.8) min are observed. Furthermore, we found terminal diazirines to support hyperpolarized¹H₂singlet states in CH₂groups of chiral molecules. The singlet lifetime of¹H singlets is up to (9.2±1.8) min, thus exceeding¹HT₁relaxation time (at 8.45 T) by a factor of ≈100. 

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5. Lanthanide Identity Governs Guest‐Induced Dimerization in Ln ^III [15‐MC _N(L‐pheHA) ‐5]) ³⁺ Metallacrowns

   https://doi.org/10.1002/chem.202103263  

   Sgarlata, Carmelo; Schneider, Bernadette_L; Zito, Valeria; Migliore, Rossella; Tegoni, Matteo; Pecoraro, Vincent_L; Arena, Giuseppe (November 2021, Chemistry – A European Journal)

   Abstract Series of lanthanide‐containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (Ln^III[15‐MC_N(L‐pheHA)‐5])³⁺metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host‐guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host‐guest‐host compartments. The driving force for the dimerization event across the series is thought to be a competition between formation of highly stable MCs (larger lanthanides) and optimally linked bridging guests (smaller lanthanides). 

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