Stability constants of europium complexes with a nitrogen heterocycle substituted methane-1,1-diphosphonic acid Page: 4 of 17
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of 0.0025 M H4PMDPA with NaOH in 2.0 M NaCIO4 at 25.0 *C under N2. The constants for the
protonation of HPMDPA- and H4PMDPA were also determined from the "P NMR chemical shifts of 10%
D20 solutions containing 0.01 M H4PMDPA in 2.0 M H/NaCIO4 measured between p[H] 1.1 and 4.8.
Decoupled spectra were collected on a 300 MHz GE Omega spectrometer at 25 *C with 85% H3PO4 as an
The stability constants of Eu(HhPMDPA)~ complexes were measured by solvent extraction using
a radiochemically pure "2,15Z4155Eu3+ tracer in 0.01 M HNO3 obtained from laboratory stocks. Equal volumes
of a pre-equilibrated HDEHP containing toluene phase, and an aqueous phase containing 2 x 104 cpm Eu3+
and 0-0.05 M H4PMDPA at I = 2.0 M in glass culture tubes were contacted by rotary mixing for 3 hours
at room temperature, with intermittent vortex mixing over a final hour as the tubes came to equilibrium at
25.0 *C. An aliquot was taken from each phase for y-counting to determine the europium distribution ratio,
expressed as the ratio of the total europium concentration in the organic phase to the total europium
concentration in the aqueous phase. The HDEHP concentration and the total PMDPA concentration spanned
at each p[H] were chosen to maintain the values of the distribution coefficients between 0.01 and 100 as
much as possible.
The protonation constants of PMDPA were determined by iteratively fitting both the potentiometric
(Figure 1) and NMR (Figure 2) titration data. The potentiometric data was fit using the program
LETAGROP ETITR [111, while the chemical shift data was fit, using the Marquardt-Levenberg non-linear
least squares algorithm as implemented by the program Origin, to the equation
ST =- 3= (1)
Rh 2)[H+ h
where 8, is the measured "P NMR chemical shift, 8(2) is the chemical shift of H +2)PMDPA(-'), and
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Jensen, M.P.; Rickert, P.G.; Schmidt, M.A. & Nash, K.L. Stability constants of europium complexes with a nitrogen heterocycle substituted methane-1,1-diphosphonic acid, article, June 1, 1996; Illinois. (digital.library.unt.edu/ark:/67531/metadc665561/m1/4/: accessed February 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.