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Comparison of the conformational dynamics of the (1 → 4)‐ and (1 → 6)‐linked α‐ D ‐glucans using 13 C‐NMR relaxation
Author(s) -
Kadkhodaei Mehran,
Wu Helen,
Brant David A.
Publication year - 1991
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360311313
Subject(s) - chemistry , anomer , aqueous solution , relaxation (psychology) , crystallography , monomer , stereochemistry , organic chemistry , polymer , psychology , social psychology
The conformational dynamics of α‐ (1 → 4)‐ and α‐ (1 → 6)‐glucan homooligomers in the nanosecond time domain have been compared by measuring the 13 C‐nmr longitudinal relaxation times T 1 for carbons of the terminal and interior sugar residues. Measurements are reported on monomeric glucose and on oligomers containing up to ten glucose residues at room temperature in aqueous solution at concentrations of 3 and 20 g/dL. The carbons of terminal residues display longer relaxation times than do those of interior residues, presumably as a consequence of a greater degree of conformational mobility of the chain ends. The T 1 s of the reducing terminal residues of all oligomers are significantly longer than those of the corresponding nonreducing termini, a phenomenon that we associate tentatively with the anomeric equilibrium at the reducing end. Carbons of the reducing terminal residues in the β‐anomeric form relax more slowly than their α‐anomeric counterparts. At 20 g/dL the mean T 1 s for carbons of the terminal and interior residues attain asymptotic behavior with increasing chain length at a chain length of about six residues, and carbons of the α‐ (1 → 4)‐linked maltooligomers relax significantly more slowly than those of the corresponding α‐(1 → 6)‐linked isomaltooligomers. The T 1 s of both glucan series increase with decreasing concentration. This concentration dependence disappears below 3 g/dL, where the T 1 s of the two series of homoligomers are no longer distinguishable. This suggests that in dilute aqueous solution at room temperature viscous damping effects predominate over contributions to the T 1 ‐sensitive conformational dynamics from structural differences in the glycosidic linkage region. At 3 g/dL the approach to long chain‐length asymptotic behavior is more protracted than at 20 g/dL, and the T 1 s of carbons of interior oligomeric residues appear to match the corresponding high‐polymer behavior at a chain length of eight and greater.