Influence of substituents on the solution conformation of the exopolysaccharide produced by Pseudomonas 'gingeri' strain Pf9

The influence of pyruvate ketals and acetyl groups on the conformational be haviour of the exopolysaccharide produced by Pseudomonas 'gingeri' strain P f9 has been investigated experimentally through studies of intrinsic viscos ity and circular dichroism experiments. A conformational variation was dete cted as a function of the ionic strength. Measurements carried out on the n ative polymer, as well as on both de-pyruvated and de-acetylated samples, s uggested a critical role for the acetyl group on the solution conformation of the polysaccharide. Molecular mechanics calculations indicated the possi bility of intramolecular hydrogen bonding between acetyl substituents on th e mannose and the C(2)OH group of the preceding saccharidic unit. NMR linew idth measurements, carried out as a function of temperature, on the low mol ecular weight de-pyruvated sample indicated different polymeric backbone dy namics in aqueous solutions with respect to that observed in 0.3 M NaCl sol utions. (C) 1999 Elsevier Science B.V. All rights reserved.