1H NMR studies of Cr(III)–imidazole complexes: can 1H NMR be used as a probe of Cr–guanine DNA adducts?

Aminopyridine complexes of Cr(III) basic carboxylates as potential polymer precursors: Synthesis, characterization, and crystal structure of [Cr3O(propionate)6(X-aminopyridine)3]+ (X = 3 or 4)

“…The chromium centers in these trinuclear assemblies are antiferromagnetically coupled, resulting in a reduction of the magnetic moment per Cr(III) ion; thus, the paramagnetic shifts and broadening of the resonances should be slightly reduced in comparison to NMR spectra of mononuclear Cr(III) complexes. Additionally, as the unpaired electrons of the chromic centers are in the t 2g orbitals, directed at the pi system so of the ligands and not along the sigma bonds, only pbased pathways for delocalization of the unpaired spin density from the metal ion to the ligands is expected to be significant, as observed previously for basic chromic carboxylates [13,[49][50][51].…”

“…Thus, NMR spectra of Cr(III) complexes display greatly broadened and shifted resonances, particularly for the atoms of aromatic ligands where the half-occupied t 2g orbitals are oriented at the pi clouds of the ligands, such that knowledge of the structure of the complex is often required to interpret the spectra, rather than the reverse. Yet, paramagnetic 1 H, 2 H, and 13 C NMR have been demonstrated to be of utility in characterizing Cr(III) carboxylate assemblies [13,[49][50][51].…”

Paramagnetic 19F NMR and electrospray ionization mass spectrometric studies of substituted pyridine complexes of chromium(III): Models for potential use of 19F NMR to probe Cr(III)–nucleotide interaction

“…The Cr–O(oxo) bond is short and strong such that bonds from ligands trans to the oxo groups are unusually labile for chromium(III) complexes. The terminal ligands are usually water molecules, but the water can readily be substituted with pyridine, imidazole, or other nitrogen heterocyclic molecules, for example [15–19]. Notably, imidazole and benzimidazole complexes, [Cr 3 O(O 2 CR) 6 L 3 ] + where L=imidazole or benzimidazole and R is an alkyl group, can readily be prepared in this manner in good yield; however, they have limited solubility in common NMR solvents [19].…”

“…For example, pyridine and imidazole derivatives can readily be prepared by exchange for terminal aqua ligands. Yet, 1 H and 2 H NMR studies of the imidazole derivatives revealed that these NMR techniques were unlikely to serve as useful probes of Cr-binding to DNA [19]. The only non-exchangeable hydrogen of guanine is bound to C-8, located between the nitrogens of the imidazole ring.…”

“…Using imidazole derivatives as models, this hydrogen corresponds to the 2-position hydrogen of imidazole. The NMR studies of Cr(III) assemblies with imidazole terminal ligands revealed that the NMR resonance of this hydrogen resides in a region unlikely to be separated from other NMR rersonances and that is signal was extremely broad (~1.4 × 10 3 Hz) [19]. Thus, the signal is unlikely to be detected at any reasonable concentration of DNA.…”