in water-d2 competition was followed by H-NMR spectroscopy, at 25 ° C;; aq. soln. of known pH evapd. to dryness, residue dissolved in equal amt. of D2O, left until equilibrium was reached (5 weeks);

in water-d2 competition reaction followed by H-NMR spectroscopy, at 25 ° C at pH 7.5; aq. soln. of known pH evapd. to dryness in vacuo, residue dissolved in equal volume of D2O, and left until equilibrium left (12 weeks);;