Down's syndrome ( 152 ). Hence, detection of SU in urine is a
very good way to monitor aspirin dosage as well as provide
evidence that could assist in the diagnosis of certain medical
conditions.
SU has been shown to bind metal cations such as Cu^2 þ( 153 ),
Co^3 þ( 154 ), VO^2 þ( 155 ), and (CH 3 ) 2 Sn^2 þ( 156 ). In such complexes,
SU is either bidentate or tridentate, coordinating through ligand
carbonyl, carboxyl, and phenolate oxygens. As hard ions,
lanthanides form strong chelates with oxygen-containing lig-
ands. We therefore explored various lanthanide binary
complexes in an effort to detect SU in urine using sensitized lan-
thanide luminescence. The most promising lanthanide–ligand
complex from our screens was [Tb(DO2A)]þ. Fluorescence from
excited state intramolecular proton transfer (ESIPT) was
observed for the [Tb(DO2A)(SU)]ternary complex; it is likely
that the SU ligand chelates in a bidentate fashion via the car-
bonyl and carboxyl groups and that the hydroxyl moiety is still
protonated (Fig. 11). Using [Tb(DO2A)]þ, we were able to detect
SU in urine samples from healthy volunteers with a detection
limit of 1.8 mg L^1 ( 157 ). For a first iteration receptor site, this
result already is competitive with current SU detection tec-
hniques based on HPLC and capillary electrophoresis. And,
importantly, the analysis can be done in a fraction of the time
required in most other methods.
We have seen similar improvements in the dipicolinate system
in terms of increased resistance to common cationic and anionic
interferents. The inclusion of DO2A improved Tb-DPA binding
in the presence of a wide array of interfering ions, most up to
concentrations five orders of magnitude greater than that of
DPA ( 92 ). This indicates that [Tb(DO2A)]þ is able to bind
FIG. 11 Likely chelation mode of salicylurate (SU) to [Tb(DO2A)]þ.28 MORGAN L. CABLEet al.