19F NMR based pH probes: lanthanide(iii) complexes with pH-sensitive chemical shifts.

Experimental measurements and theoretical analysis of magnetic properties, structural dynamics and acid–base equilibria for several lanthanide(iii) complexes with tetraazacyclododecane derivatives as 19F NMR chemical shift pH probes are presented; pKa values vary between 6.9 and 7.7, with 18 to 40 ppm chemical shift differences between the acidic and basic forms for Ho(iii) complexes possessing T1 values of 10 to 30 ms (4.7–9.4 T, 295 K). [ABSTRACT FROM AUTHOR]