Motional properties of a pentasaccharide containing a 2,6-branched mannose residue as studied by 13C nuclear spin relaxation.

13C relaxation data obtained at three different magnetic fields, 9.4, 11.8 and 14.1 T, and at two temperatures, 303 and 318 K, are reported for the pentasaccharide p-trifluoroacetamidophenyl 2,6-di-O-[beta-D-galactopyranosyl-(1-->4)-O-2-acetamido-2-deoxy-beta-D- glucopyranosyl] alpha-D-mannopyranoside. The pentasaccharide consists of two disaccharide units, attached at positions 2 and 6 to the central mannopyranoside residue. The relaxation data were interpreted with the Lipari-Szabo model-free approach. For the central mannose residue in the molecule a high order parameter (S2 = 0.91) was found and the relaxation data could be interpreted with the truncated form of the Lipari-Szabo model. The motional behavior of the two 2-acetamido-2-deoxy-glucopyranoside residues was found to differ. The one attached at the primary hydroxylic position displayed more extensive local motion (S2 = 0.75-0.77) than the one attached at the secondary hydroxylic position (S2 = 0.83-0.85). More extensive local motion for the two outer galactopyranoside residues was found (S2 = 0.56-0.59), but no significant difference in motional behavior between the two residues could be observed. Analysis of the relaxation data for the exocyclic carbons confirmed the results for the rings. For the mannose C6, the same motional parameters as obtained for the substituting 2-acetamido-2-deoxy-glucopyranoside residue were found. The two exocyclic carbons on the 2-acetamido-2-deoxy-glucopyranoside residues showed more extensive local motion, with lower order parameters (S2 = 0.59-0.66).