Trimethyl phosphate (CAS# 512-56-1) and C-formic acid (CAS# 1633-56-3) were purchased from Sigma-Aldrich. For each compound, four 0.2 ml neat liquid samples were prepared by transferring them into standard 5 mm NMR tubes. To investigate the effect of oxygen on relaxation times in each compound, one sample was sealed without being degassed. The other three samples were degassed once, twice, and three times using the freeze-pump-thaw method with the use of a two-stage vacuum pump. This allowed us to evacuate the gas above a sample to a gas-pressure of 10 -6 mbar. After degassing, the tubes were flame-sealed under vacuum. N-methylpyridinium was synthesized according to literature procedures starting from N-enriched pyridine and dissolved in D 2 O and H 2 O by obtaining 5.5 M 15 N-methylpyridinium solutions. The solutions were transferred to 5 mm NMR tubes and then tubes were flame-sealed under vacuum following two freeze-pump-thaw cycles for degassing. For high-field relaxometry studies, N-methylpyridinium was dissolved in D 2 O and 1:4 D 2 O and H 2 O mixture at 5.5 M concentration. The samples were degassed prior to measurements.