The nuclear quadrupole interaction at metal sites in macromolecules monitor
ed by time differential perturbed angular correlation provides information
on the local environment of metal ions residing at these sites. This inform
ation is obtained in the ultra-trace regime and is, therefore, extremely va
luable for research on reaction pathways of enzymatic heavy metal detoxific
ation, for the development of radiopharmaceuticals, for investigations into
protein architectures on surfaces, and for environmental research.