Anion responsive Europium (III) complexes for Optical Sensing and PARACEST MRI
Buttarazzi, Leandro Alfredo
MetadataShow full item record
The Eu(III) complexes of 1-(acetyl-7-Methyl-4-(trifluoromethyl) quinolin-2(1H)-one)4,7,10 tris(2-hydroxypropyl)-1,4,7,10-tetraazacycladodecane (Eu(S-THPC) 3+ ) and 1-(acetyl-dioctadecylamine)4,7,10 tris(hydroxypropyl)-1,4,7,10-tetraazacycladodecane (Eu(S-THMC) 3+ ) were studied in order to develop complexes that are both optical sensors and MRI contrast agents that respond to biologically relevant anions. Both complexes are related to Eu(S-THP) where S-THP = (1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane. Eu(III) excitation, emission and time resolved luminescence spectroscopy experiments were used to study binding of the anions. One complex, Eu(THPC) 3+ has an appended carbostyril dye for sensitization of Eu(III) luminescence. Luminescence experiments were done on this complex in order to quantify the effectiveness of the energy transfer from the dye to the lanthanide and to obtain binding constants of the anions from the Eu(III) emission peaks. Emission spectra were obtained by exciting the chromophore at 340 nm. Our results suggest that phosphate binds with a dissociation constant (K d ) of 4.2mM and citrate binds with a K d of 228 uM. The quantum yield for the complex was low compared to other reported complexes in literature. Eu(S-THMC) 3+ , and Eu(S-THMAC) 3+ containing long carbon chains for incorporation into liposomes were explored as an approach to develop complexes with increased sensitivity as CEST agents. CEST experiments with the complex incorporated into a liposome and as a micelle were carried out. Liposome formation was achieved but no CEST effect was observed with two different lanthanide complexes. Eu(S-THMC) 3+ gave the most promising results by showing CEST in acetonitrile and 50/50 acetonitrile/H 2 O. However further experiments with this complex in buffered aqueous solution failed. Yb(S-THMAC) 3+ solubility was poor in both acetonitrile and in water and this likely prevented the observation of CEST spectra.