NMR instruments and parameters
First, a low field mq20 minispec (Bruker, Germany) was
equipped with electrical shims for improving the magnetic
field homogeneity to allow 1H spectroscopy. A homebuilt
probe for 5 mm sample tubes was used which exhibited
a quality factor of 130 at 19.95 MHz and an optimum filling
level for the samples of 15 mm. The applied pulse
sequences were a single pulse experiment, leading to the
acquisition of a free induction decay (FID), and a subsequent
CPMG multi echo experiment [15] for measuring the
transverse magnetization decay.