Three derivatives of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonic acid) (DOTP) containing a hydrophobic substituent on one side chain were prepared and their lanthanide complexes examined by NMR. The new ligands include 1-(1-octyl-methyl-phosphonic acid)-4,7,10-tris(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane (C8-DOTP),1-(1 -undecyl-methyl-phosphonic acid)-4,7,10-tris(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane (C11-DOTP), and 1-(1-4-nitro-phenyl-methyl-phosphonic acid)-4,7,10-tris(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane (NO2-Ph-DOTP). 1H NMR spectra of the ytterbium(III) complexes were assigned by using a combination of COSY spectroscopy and a fitting procedure that matches experimental NMR hyperfine shifts with those estimated from a MMX-derived structure. The analysis showed that a single isomer is present in solution and that the bulky hydrophobic substituent occupies the less sterically demanding H6 equatorial position in the YbL5- complexes. Although the YbL5- complexes have lower symmetry due to the added substituent, the average 1H hyperfine shifts are 5-10% larger in these complexes compared to YbDOTP5-. This was magnified further in the hyperfine 23Na NMR shifts of ion-paired sodium ions where the extracellular Na+ signal in perfused rat hearts displayed a 28% larger hyperfine shift in the presence of Tm(C11-DOTP)5- than with an equivalent amount of TmDOTP5-.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry