Irina D. Kosenko

Nuclear spin hyperpolarization boosts NMR sensitivity but typically requires complex infrastructure. Signal Amplification by Reversible Exchange (SABRE), a parahydrogen-based hyperpolarization technique, can be conducted using a remarkably low-cost polarizer (<$100) comprising only magnetic coils and a standard PC sound card, avoiding magnetic shielding. However, under these conditions SABRE requires direct spin-coupling between parahydrogen and the target nucleus, limiting its application to distant heteronuclear spins such as ⁷⁷Se in biologically relevant selenium-nitrogen heterocycles (e.g. antioxidant, antiviral, and anticancer agents). Here, we overcome the distance restrictions by developing the ¹⁵N-mediated polarization transfer driven by optimized oscillating magnetic fields of the audio frequency. This enables a significant ⁷⁷Se NMR signal enhancement of 11,600-fold at 9.4 T in a shielding-free setup within several seconds, corresponding to over 6% of net 77Se polarization. Thus, our approach makes hyperpolarized ⁷⁷Se NMR widely accessible for biomolecular investigations.

A series of novel conjugates of cobalt bis(dicarbollide) and closo-dodecaborate with curcumin were synthesized by copper(I)-catalyzed azide-alkyne cycloaddition. These conjugates were tested for antibacterial activity. It was shown that all derivatives are active when exposed to Bacillus cereus ATCC 10702 and are not active against Gram-negative microorganisms and Candida albicans at the maximum studied concentration of 1000 mg/L. The conjugate of alkynyl-curcumin with azide synthesized from the tetrahydropyran derivative of cobalt bis(dicarbollide) exhibited activity against Gram-positive microorganisms: Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212 and the clinical isolate MRSA 17, that surpassed curcumin by 2–4 times.

New radical-cation salts based on tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenefulvalene (TMsTSF) with metallacarborane anions (TMTTF)[3,3′-Cr(1,2-C₂B₉H₁₁)₂], (TMTTF)[3,3′-Fe(1,2-C₂B₉H₁₁)₂], and (TMTSF)₂[3,3′-Cr(1,2-C₂B₉H₁₁)₂] were synthesized by electrocrystallization. Their crystal structures were determined by single crystal X-ray diffraction, and their electrophysical properties in a wide temperature range were studied. The first two salts are dielectrics, while the third one is a narrow-gap semiconductor: σ_RT = 5 × 10⁻³ Ohm⁻¹cm⁻¹; E_a ≈ 0.04 eV (aprox. 320 cm⁻¹).

Novel zwitter-ionic nido-carboranyl azide 9-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ was prepared by the reaction of 9-Cl(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ with NaN₃. The solid-state molecular structure of nido-carboranyl azide was determined by single-crystal X-ray diffraction. 9-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ was used for the copper(I)-catalyzed azide-alkyne cycloaddition with phenylacetylene, alkynyl-3β-cholesterol and cobalt/iron bis(dicarbollide) terminal alkynes to form the target 1,2,3-triazoles. The nido-carborane-cholesterol conjugate 9-3β-Chol-O(CH₂)C-CH-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ with charge-compensated group in a linker can be used as a precursor for preparation of liposomes for Boron Neutron Capture Therapy (BNCT). A series of novel zwitter-ionic boron-enriched cluster compounds bearing a 1,2,3-triazol-metallacarborane-carborane conjugated system was synthesized. Prepared conjugates contain a large amount of boron atom in the biomolecule and potentially can be used for BNCT.

9-Dimethyloxonium, 10-dimethyloxonium, 9-methoxy and 10-methoxy derivatives of nido-carborane (9-Me₂O-7,8-C₂B₉H₁₁, 10-Me₂O-7,8-C₂B₉H₁₁, [9-MeO-7,8-C₂B₉H₁₁]⁻, and [10-MeO-7,8-C₂B₉H₁₁]⁻, respectively) were prepared by the reaction of the parent nido-carborane [7,8-C₂B₉H₁₂]⁻ with mercury(II) chloride in a mixture of benzene and dimethoxymethane. Reactions of the 9 and 10-dimethyloxonium derivatives with triethylamine, pyridine, and 3-methyl-6-nitro-1H-indazole result in their N-methylation with the formation of the corresponding salts with 9 and 10-methoxy-nido-carborane anions. The reaction of the symmetrical methoxy derivative [10-MeO-7,8-C₂B₉H₁₁]⁻ with anhydrous FeCl₂ in tetrahydrofuran in the presence of t-BuOK results in the corresponding paramagnetic iron bis(dicarbollide) complex [8,8′-(MeO)₂-3,3′-Fe(1,2-C₂B₉H₁₀)₂]⁻, whereas the similar reactions of the asymmetrical methoxy derivative [9-MeO-7,8-C₂B₉H₁₁]⁻ with FeCl₂ and CoCl₂ presumably produce the 4,7′-isomers [4,7′-(MeO)₂-3,3′-M(1,2-C₂B₉H₁₀)₂]⁻ (M = Fe, Co) rather than a mixture of rac-4,7′- and meso-4,4′-isomers.