Optical rotatory dispersion of mucopolysaccharides and mucopolysaccharide–dye complexes. II. Ultraviolet cotton effects in the amide transition bands
✍ Scribed by A. L. Stone
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1969
- Tongue
- English
- Weight
- 886 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Ultraviolet optical rotatory dispersion curves of mucopolysaccharides exhibit particular Cotton effects in the spectral region of the It-x and T-T amide transitions. Two general patterns emerge: (I) enhancement of negative rotation and of the first negative Cotton effect (troughs 217-220 mp) and (2) relative dominance of the positive Cotton effect in the 7r-if transition region (peak -198 mp). Groups ( 1) and ( 2) can be correlated with a structural difference in the linkages of the amino sugars: (1) occurs with polymers containing 3-1-linked glycosamino sugars and (2) with glycosamino moieties linked 4-1 by either a-or 8-glycosidic bonds Measurements of the circular dichroic absorption bands support the qualitative conclusions from optical rotation. AU mucopolysaccharides exhibit a first, negative band centered at 208-211 mp, while only those in group (2) show, in addition, a positive band centered at 189-192 mp. A suggested unifying model considers that difference in kind and/or degree of preferred geometry of the amide groups obtains from two forms of secondary order: (I) having a linear hydrogen bond from the N (acceptor) to the (C2)G-H of the preceding uronic acid and (2) having a linear hydrogen bond from the N (acceptor) to the (CZ or 8) (fH of the following sugar. The hydrogen bonds would have similar strength but opposite directions in the two systems [towards the nonreducing end (1) or towards the reducing end ( 2)], closing eight-membered rings I I Ci-Cz-O-H . * . N-C'rC'3-0 and I I CI-CrN.
. .H-OC'(z or 3)-C'(3 or 4)-0, respectively.