Copper sulfate (CuSO 4 ) (CAS# 7758-98-7) was also purchased from Sigma-Aldrich. The CuSO 4 solutions with various concentrations were prepared by dissolving the compound in deionized water. For each concentration, 0.2 ml of solutions were placed inside two standard 5 mm NMR tubes. One of the tubes was sealed without degassing, and another tube was degassed twice using the freeze-pump-thaw method and then flame sealed. The pressure above the frozen liquid after the second cycle was below 10 -4 mbar.