Structure of a Phosphonomannan, as Determined by the Effect of Lanthanide Ions on Its Carbon-13 Magnetic Resonance Spectrum

Abstract

The carbon-13 magnetic resonance spectrum of phosphonomannan 2 in deuterium oxide expands on addition of europium and praseodymium chlorides. With the aid of a parallel study on structurally related α-D-mannose-1-phosphate and α-D-mannose-6-phosphate the signal displacements were interpreted in terms of chemical structure. Both ions cause predominantly contact shifts, and in general addition of praseodymium ion produces a downfield shift of the 13C.m.r. signal of the esterified 13C nucleus, which is accompanied by a smaller downfield shift of that of the adjacent carbon. Europium ion produces smaller and approximately equal shifts of signals of the corresponding α-13C and β-13C nuclei, but in the opposite direction and with less broadening. Displacements produced by neodymium chloride were comparable in size and downfield. Other lanthanide chlorides, namely those of ytterbium, holmium, neodymium, and gadolinium, broadened the signal of the 13C nucleus attached to the phosphodiester group without displacement. Changes produced in proton nuclear magnetic resonance spectra of the phosphates and phosphodiester 2 are more difficult to interpret in terms of structure.