H. Lujanupton et al., FLUORESCENCE LIFETIME OF TERBIUM(III) AS A PROBE FOR THE ION-BINDING PROPERTIES OF TACTIC POLY(METHACRYLIC ACIDS), Journal of polymer science. Part A, Polymer chemistry, 35(3), 1997, pp. 393-398
The binding properties of trivalent metal ions to polyelectrolytes wer
e investigated through the use of terbium [Tb(III)] in fluorescence st
udies. The fluorescence intensity and lifetimes of the lanthanide ions
are directly dependent upon the number of water molecules bound to th
eir inner coordination sphere. The more efficiently a ligand coordinat
es to a lanthanide ion, the more water molecules are expelled and cons
equently, the greater the fluorescence intensity and lifetime. This ef
fect was used to probe for differences in the complexation behavior of
tactic polymers. Aqueous solutions of isotactic and syndiotactic poly
(methacrylic acid) (PMA) were neutralized and complexed with Tb(III) i
ons. The fluorescence intensity of the 286 nm hypersensitive excitatio
n band was monitored and the lifetimes were measured using several exc
itation wavelengths. It was found that the isotactic PMA/Tb(III) compl
ex exhibited a six times greater fluorescence intensity than the syndi
otactic PMA complex. Lifetime measurements gave the number of water mo
lecules coordinated by Tb(III) in the isotactic complex to be 2.4 whil
e 3.4 waters remained bound to the Tb(III) ion in the syndiotactic PMA
complex. These results indicate that isotactic PMA has the greater bi
nding affinity towards Tb(III) ions. (C) 1997 John Wiley & Sons, Inc.