Display Settings:

Items per page

Results: 8

2.
Figure 3

Figure 3. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

CEST spectra of Eu(4) (red) and Eu(5) (blue) recorded at 9.4 T and 298 K in CH3CN at B1 = 10.8 µT (459Hz) and 10.0 µT (426 Hz), respectively. (Inset: B1= 2.5 µT for both spectra.)

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.
3.
Figure 2

Figure 2. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

Comparison of chemical shifts of the Eu-OH2 resonances vs. the H4 ligand proton resonances in each complex (measured in CD3CN). The two dashed lines correspond to 66 % and 50 % of the δH4 / δEu-OH2 ratios, respectively.

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.
4.
Figure 4

Figure 4. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

The CEST spectra of Eu(7) (red, 17 mM), Eu(8) (green, 30 mM total, 12 mM SAP), Eu(9) (yellow, 18 mM) and Eu(10) (blue, 3.6 mM) recorded at 400 MHz and 298K in H2O:CH3CN (1:1) for Eu(7) and Eu(8) and water for Eu(9) and Eu(10) using applied B1 field of 10.4 µT.

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.
5.
Figure 1

Figure 1. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

Expected resonance contributions in europium (III) chelate bonds in ligands containing a carboxylate oxygen, an amide oxygen, enol oxygen or a ketone oxygen donor and the anticipated trends in the metal-bound water oxygen bond lengths and bound water residence lifetimes. The calculated Mulliken charges on the oxygen donor atom in each type of complex is also shown.

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.
6.
Chart 2

Chart 2. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

Gas phase DFT calculations were performed using a hybrid functional (B3LYP) as implemented in Gaussian 03. For ligands 46 (see ) all atoms were optimized using the 6–311G(d,p) basis set, while 3–21G was used for the corresponding metal ion-based calculations. A frequency calculation of each showed the there were no imaginary frequencies, supporting a stable ground state. The .chk files of the optimized geometries were used to produce the Electrostatic Potential Plots and HOMO/LUMO orbital overlays in GaussView.–

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.
7.
Chart 3

Chart 3. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

The NMR spectrum of 2 provided evidence for keto-enol tautomerism of the side arms, a well-understood phenomenon for β-diketones. Prototropic rearrangements between the keto and the enol forms are acid-base catalyzed and occurs readily in the presence of water. In general, simple ketones exist in the more stable keto form but such compounds can exist in the enol form when stabilized by hydrogen bonding or steric factors. A classic example is acetylacetone, a β-dicarbonyl compound in which the enol form is favored due to intramolecular hydrogen bonding. The 13C NMR of 2 showed that the β-dicarbonyl side chains exist predominantly in the enol form as evidenced by the upfield shift of the -carbonyl carbon to about 118 ppm (). In contrast, the absence of peaks around 120 ppm in the 13C NMR of ligand 1 () suggests that this γ-dicarbonyl derivative exists primarily in the keto form, consistent with the fact that intramolecular stabilization of the enol form by H-bonding does not occur in γ-dicarbonyl compounds (). Ligand 11, shown in , was designed to prevent keto-enol tautomerization via gem-dimethyl substitution on the carbon to the ketone carbonyl. As expected, enol species were not observed in the 13C spectrum of 11 (). NMR spectra of the remaining diketone ligands in (4, 5 & 6) showed no evidence for enol formation.

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.
8.
Chart 1

Chart 1. From: Europium(III) DOTA-derivatives having ketone donor pendant arms display dramatically slower water exchange.

Lanthanide ions other than Eu(III) have also shown promise but Eu(III) remains an area of piqued interest since these complexes typically display the longest bound water lifetimes. Intrinsically, the bound water lifetime τm is directly dependent on the electron deficiency at the lanthanide ion. Qualitatively, the greater the positive character remaining on the Ln3+, the stronger the resulting Ln3+-OH2 interaction will be. A negatively charged carboxylate group is electron rich and interacts more strongly with Ln3+ ions than an oxygen donor atom in the electron deficient amide. A comparison of resident water lifetime for the two Gd3+ complexes in clearly illustrates this effect: GdDOTAm = 208 ns) vs. GdDOTA(GlyOEt)43+m = 190 µs),– about 3 orders of magnitude different. Therefore, poor donors that leave the central lanthanide ion electron deficient are likely to produce slower water exchange systems (longer τm). There are many other factors that affect τm including the coordination geometry of the complex (the SAP/TSAP ratio), steric constraints (bulkiness of side-chains) and hydrophobic/hydrophilic effects that alter second coordination sphere water molecules. In a recent paper, we have shown that Eu(III) complexes of DOTA tetraamide ligands with different amino acid extended side-chains produce remarkably different CEST effects. Preliminary DFT studies corroborated the relationship between weaker donors and longer τm. Morrow and co-workers extended this theory to pendent alcohols, known to remain protonated upon binding to a lanthanide ion. Unfortunately, these systems display small Δω values and have been limited to CH3CN for observable PARACEST due to shorter than optimal metal bound water lifetime.

Kayla N. Green, et al. Inorg Chem. ;50(5):1648-1655.

Display Settings:

Items per page

Supplemental Content

Recent activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...
Write to the Help Desk