Vacuum‐ultraviolet circular dichroism of sodium hyaluronate oligosaccharides and polymer segments

The CD spectrum of an enzymatically derived sodium hyaluronate (NaHA) segment preparation with chain length 18 ± 3 disaccharide units [NaHAseg, ( NaGlcUA GlcNAc)_15–20°. NaGlcUA, sodium D‐glucuronate; GlcNAc, 2‐acetamido‐2‐deoxy‐D‐glucose] in H₂O was recorded to 180 nm using a computer‐controlled vacuum‐uv CD instrument. Near 190 nm the spectrum is of low intensity, similar to the sum of the free monosaccharide contributios, attributed to the π–π* transitions of the acetamido and carboxylate substituents. In contrast, much smaller oligosaccharides, also derived from high‐molecular‐weight NaHA by enzymatic digestions, show CD spectra in H₂O with prominent bands centered near 190 nm. The oligosaccharide spectra can be matched as linear combinations of interior sugar residue ( NaHAseg) and end sugar residue CD contributions. End residues from oligosaccharides of the type (NaGlcUA‐GlcNAc)_n show a negative CD band near 190 nm. End residues from oligosaccharides of the reverse sequence (GlcNAc‐NaGlcUA)_n show a positive CD band near 190 nm. Averaging of the two end‐residue spectral contributions yields an approximate match for the spectrum of NAHAseg below 200 nm. It is proposed that the low intensity CD of NaHA in the π–π* region is the result of large‐magnitude, oppositely signed contributions, which can be visulized by studying oligosaccharides.