Analytical studies of lipopolysaccharide and its derivatives from Salmonella minnesota R595. I. Phosphorus magnetic resonance spectra

The ³¹P nuclear magnetic resonance spectrum of lipopolysaccharide from Salmonella minnesota R595 shows that the pK_a and chemical shift values of the phosphate groups are very sensitive to changes in molecular structure. The presence of 3′ and / or 6′ substituents can be determined from the spectra of the 4′-phosphates and the type of 4′ or 6′ substituent affects the phosphates. When cells are grown in nutrient broth, the 4′ position in the lipopolysaccharide is substituted with as much as 91% aminoarabinose phosphate, with the remaining 9% as monophosphate (with 3′ acyl substituent). When L.B. medium is used, 52% of the 4′ position is substituted with phosphomonoester (with accompanying 3′-acyl group), with smaller amounts of monoester (with no 3′ substituent) and phosphodiester. Phosphate substitution at the 1 position is incomplete when cells are grown in nutrient broth. A detailed analysis is made of the chemical and physical parameters which influence pK_a and chemical shift of phosphates. The conversion of 4′-phosphodiester to 4′-phosphomonoester and 4′-dephospho products with different hydrazine treatments was also studied.