Complexes of imidazole with dioxouranium(VI) nitrate and acetate

Interactions of 1-Methylimidazole with UO2(CH3CO2)2 and UO2(NO3)2: Structural, Spectroscopic, and Theoretical Evidence for Imidazole Binding to the Uranyl Ion

“…The IR spectrum (Table 1 and Supporting Information) shows an intense band at 916 cm -1 for the asymmetric uranyl stretch, close to the value of 928 cm -1 for UO 2 (Ac) 2 62 and 910 cm -1 reported by Marzotto for the complex of uranyl acetate with imidazolate and water. 18 The IR data indicate that acetate binds as a bidentate ligand (with the symmetric ν s (COO) and the antisymmetric ν a (COO) carboxylate stretching modes at 1468 and 1538 cm -1 , respectively) rather than a monodentate ligand, consistent with our previously calculated values for UO 2 (Ac) 2 . 23 The Raman measurements are also consistent (ν(CC) stretch at 955 cm -1 ) with bidentate acetate binding to uranyl.…”

“…2 A uranyl-polypeptide low-resolution X-ray structure shows an imidazole coordinated to U with a U-N distance of 2.57 Å. 3 Other experiments including NMR, 16 calorimetry, 17 conductivity, and infrared (IR) 18 of imidazole-containing ligands to uranium suggest that coordination through the nitrogen atom is likely to be an important binding mode under biological conditions. The binding stoichiometries and complexation modes of the uranyl cation depended on the type of uranyl salt.…”

“…Marzotto et al crystallized solid samples of imidazole-containing complexes of UO 2 (CH 3 CO 2 ) 2 and UO 2 (NO 3 ) 2 from ethyl acetate. 18 On the basis of IR assignments, they concluded that the nitrate complex consisted of two bound imidazole ligands (through the N atoms) and a bidentate and monodentate nitrate. The acetate complex contained a bidentate acetate, a bound water molecule, and a bound imidazolate anion, resulting in infinite chains, as in similar Co(II) and Zn(II) complexes.…”

“…16 The differing modes of complexation were similar to what was observed on the basis of IR measurements. 18 It was concluded that direct coordination of 1-methylimidazole would be likely to occur under physiological conditions where the low pH problem is not an issue and led to hypotheses for uranyl binding to histidine residues in proteins. 16 The NMR analysis was supported by a calorimetric study based on the higher heat for formation of the 1:2 UO 2 (NO 3 ) 2 :imidazole complex in solution versus the 1:1 UO 2 (CH 3 CO 2 ) 2 :imidazole complex.…”

“…The binding stoichiometries and complexation modes of the uranyl cation depended on the type of uranyl salt. Marzotto et al crystallized solid samples of imidazole-containing complexes of UO 2 (CH 3 CO 2 ) 2 and UO 2 (NO 3 ) 2 from ethyl acetate . On the basis of IR assignments, they concluded that the nitrate complex consisted of two bound imidazole ligands (through the N atoms) and a bidentate and monodentate nitrate.…”