14 N nuclear quadrupolar relaxation and 1 H line shapes in nitrogen-containing heterocycles

On the effects of quadrupolar relaxation in Earth's field NMR spectra

There is growing interest in using low-field magnetic resonance experiments for routine chemical characterization. Earth's field NMR is one such technique that can garner structural information and enable sample differentiation with low cost and highly portable designs. The resulting NMR spectra are primarily influenced by J-couplings, resulting in so-called J-coupled spectra (JCS). Many small molecules include atoms with NMR-active nuclei that are quadrupolar either at natural abundance or are often isotopically enriched (e.g.,2H, 6Li, 11B, 14N, 17O, etc.) where the effects of quadrupolar J-couplings and relaxation on JCS of strongly- and weakly-coupled spin systems have not been explored to date. Herein, using a set of seven fluoropyridine samples with unique substitution and J-couplings, we demonstrate that the 14N relaxation rates can induce drastic line-broadening in the JCS. This includes a previously unexplored unique line broadening mechanism enabled by strongly coupled spins at low-field. Numerical simulations are used to model and refine the magnitudes and signs of J-couplings, as well as indirectly determine the 14N relaxation rates in a single 1D experiment that has a higher fidelity than observed in high-field NMR experiments.

Gallium and indium complexes with isoniazid-derived ligands: Interaction with biomolecules and biological activity against cancer cells and Mycobacterium tuberculosis

Gallium and indium octahedral complexes with isoniazid derivative ligands were successfully prepared. The ligands, isonicotinoyl benzoylacetone (H₂L¹) and 4-chlorobenzoylacetone isonicotinoyl hydrazone (H₂L²), and their respective coordination compounds with gallium and indium [GaL¹(HL¹)] (GaL¹), [GaL²(HL²)] (GaL²), [InL¹(HL¹)] (InL¹) and [InL²(HL²)] (InL²) were investigated by NMR, ESI-MS, UV-Vis, IR, single-crystal X-ray diffraction and elemental analysis. In vitro interaction studies with human serum albumin (HSA) evidenced a moderate affinity of all complexes with HSA through spontaneous hydrophobic interactions. The greatest suppression of HSA fluorescence was caused by GaL² and InL², which was associated to the higher lipophilicity of H₂L². In vitro interaction studies with CT-DNA indicated weak interactions of the biomolecule with all complexes. Cytotoxicity assays with MCF-7 (breast carcinoma), PC-3 (prostate carcinoma) and RWPE-1 (healthy human prostate epithelial) cell lines showed that complexes with H₂L² are more active and selective against MCF-7, with the greatest cytotoxicity observed for InL² (IC₅₀ = 10.34 ± 1.69 μM). H₂L¹ and H₂L² were labelled with gallium-67, and it was verified that ⁶⁷GaL² has a greater lipophilicity than ⁶⁷GaL¹, as well as higher stability in human serum or in the presence of apo-transferrin. Cellular uptake assays with ⁶⁷GaL¹ and ⁶⁷GaL² evidenced that the H₂L²-containing radiocomplex has a higher accumulation in MCF-7 and PC-3 cells than the non-halogenated congener ⁶⁷GaL¹. The anti-Mycobacterium tuberculosis assays revealed that both ligands and metal complexes are potent growth inhibitors, with MIC₉₀ (μg mL^-1) values observed from 0.419 ± 0.05 to 1.378 ± 0.21.

Intramolecular cooperativity in frustrated Lewis pairs

The doubly Lewis-acid functionalised aniline PhN[(CH₂)₃B(C₆F₅)₂]₂ features two competing boron functions in fast exchange for binding to the central Lewis base. In contrast to the mono acid-functionalised PhMeN[(CH₂)₃B(C₆F₅)₂], it is an active frustrated Lewis pair.