ISSN:
1572-8773
Keywords:
EDTMP
;
formation constants
;
protonation constants
;
samarium
;
speciation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract 153Sm-EDTMP (ethylenediaminetetra(methylenephosphonic) acid) is of considerable interest as a bone therapeutic radiopharmaceutical but its properties in solution are not yet well characterized. The protonation constants of EDTMP and the formation constants of the complexes of Sm-EDTMP have accordingly been measured potentiometrically by glass electrode titrations at 25°C in 0.15 M NaCl. Six protonation constants (log β011 = 9.638, log β012 = 17.330, log β013 = 23.597, log β014 = 28.636, log β015 = 31.501, log β016 = 32.624) and the formation constants of the [Sm(EDTMP)H-1]6- (log β11-1 = 4.865), [SmEDTMP]5- (log β110 = 12.018), [Sm(EDTMP)H]4- (log β111 = 17.892) and [Sm(EDTMP)H2]3- (log β112 = 23.437) complexes were determined. Computer simulations indicate that the [SmEDTMP]5- and the hydroxy [Sm(EDTMP)H-1]6- species are the major Sm(III) complexes formed in blood plasma, which explains the high degree of localization in the kidney and urine observed in biodistribution studies. Calcium ions are probably the maior competitor for EDTMP in blood plasma. As the presence of secondary skeletal metastases results in a high rate of bone turnover, it is possible that the high concentration of calcium at these sites encourages localization of 153Sm-EDTMP.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00140604
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