Nuclear magnetic resonance studies of 4-hydroxypiperidinomethylphosphonic acid and its polyoxomolybdate conjugates

Abstract

The pD behaviour of 4-hydroxypiperidinomethylphosphonic acid has been investigated using multinuclear NMR (¹H, ¹³C and ³¹P) techniques in D₂O solvent. On deuteriation, ¹H, ¹³C and ³¹P signals for two deuteriated isomers were observed, with the 4-hydroxy group occupying either an axial or equatorial position. The interaction of this compound with molybdate anion as the pH and temperature of the solution were varied was investigated using ³¹P NMR spectroscopy. The spectra revealed the formation of several phosphonomolybdate conjugates, one of which can be assigned as the pentamolybdodiphosphonate. Isomerism of the conjugate was also evident. Conversions between several phosphorus-containing entities occurred at rates detectable on the ³¹P NMR time-scale, providing evidence as to the exchange routes.