Conformational and structural studies of N-methylacetohydroxamic acid and of its mono- and bis-chelated uranium(VI) complexes

Effects of preorganization in the chelation of UO22+by hydroxamate ligands: cyclic PIPO−vs.linear NMA−

“…Besides, PBAand IBPHAform isolated molecular species of [UO2(L)S] general formula, where S designates a monodentate organic solvent (MeOH, EtOH, DMF, or DMSO) unable to promote intermolecular association of the complexes unlike water. [34][35][36] Considering the uranyl bond metrics, the [UO2(PIPO)2(H2O)] structure shows U=O distances of 1.778(4) and 1.783(4) Å with O3 and O5, respectively (Table 1), which are very close to those reported for [UO2(NMA)2(H2O)] (1.785(3) Å on average) 15 and, more generally, fall into the typical range found for the other crystallographically characterized hydroxamato uranyl complexes (Table S3, see ESI †). As far as the O=U=O angle is concerned (179.2(2)°), the triatomic coordination center can be considered as essentially linear, in accordance with the angular values compiled in Table S3 for the related structures.…”

“…In addition, single crystals of the complex [UO2(PIPO)2(H2O)] were examined by X-ray diffraction, and the resulting structure is compared with those of related complexes described in the literature. Similarly to the related [UO2(NMA)2(H2O)] compound, 15 the crystal structure of [UO2(PIPO)2(H2O)] shows a butterfly-like arrangement of both PIPOligands which are chelated in such a way that both pairs of OC and ON oxygen atoms are facing each other. The bound water molecule (O4) is located in between the carbonyl oxygen atoms O1 and O1A, and interacts by a pair of hydrogen bonds with the hydroxamic O2 and O2A oxygen atoms belonging to the neighboring motif (Table S2, see ESI †), thus forming head-to-head linear chains along the a direction of the crystal lattice.…”

“…After a long lasting controversy in the literature, it was recently ascertained that the E rotamer of both NMAH and its conjugated base NMAprevail in aqueous solution and at room temperature in a nearly 3:1 and 9:1 ratio over a large concentration range, respectively. [15][16] In contrast, the E/Z concentration ratio was found to be strongly concentration dependent in less-polar media like chloroform, with predominance of the Z form in dilute solutions possibly stabilized through intramolecular C=OHO-N hydrogen bonding, while at higher concentrations the E isomer is favored, suggesting intermolecular chain-type aggregation. 17 The interconversion kinetics in water, which is slow on the NMR time scale, has been elucidated independently by two groups using either 2D exchange-correlated (EXSY) 15 or variabletemperature 1 H NMR spectroscopy 18 (G  ZE = 68.0 kJ mol -1 and G  EZ = 70.6 kJ mol -1 for NMAH, G  ZE = 73.6 kJ mol -1 and G  EZ = 79.2 kJ mol -1 for NMAat 300 K).…”

“…Recently, the crystal structure of two mono-and bischelated uranyl complexes of N-methylacetohydroxamate of [UO2(NMA)(NO3)(H2O)2] and [UO2(NMA)2(H2O)] composition have been described. 15 In both compounds, the uranium atom is surrounded by five equatorial and essentially planar oxygen atoms provided by the bidentate hydroxamate and the additional monodentate ligands (H2O and/or NO3 -). Interestingly, both environments give rise to distinct IR and Raman spectral signatures for the U=O stretches, allowing to easily distinguish them from the pentaaquo UO2 2+ cation.…”

Direct comparison of the in vitro and in vivo stability of DFO, DFO* and DFOcyclo* for 89Zr-immunoPET

“…The main difference between DFO* and DFOcyclo* is the cyclic structure of the additional hydroxamic acid group derived from 1,2-PIPOH. While open-chain hydroxamic acids, including DFO, are known to exist as a mixture of two E ( trans ) and Z ( cis ) isomers [28–30], the Z configuration of the hydroxamate group is imparted by the cyclic structure of PIPO - , and is obviously more favourable for Zr 4+ coordination and could therefore result in a more stable complex [31]. The crystal structure of a Zr 4+ complex in which the metal is coordinated by four 1,2-PIPO - chelates has been reported previously [32].…”