An examination of sodium alginate from Sargassum by NMR spectroscopy

Abstract

Alginic acid, obtained from Sargassum brown algae that drift from the Sargasso Sea to beaches in Cuba, has been examined as an aqueous solution by 1H and 13C NMR spectroscopy, and also in the solid state by MAS 13C NMR spectroscopy. Its composition is distinctive, relative to that for alginic acid from most other brown algae, in having a lower content of β-D-mannopyranosyluronic acid residues (M) than of α-L-gulopyranosyluronic acid residues (G). That is, M/G is ~0.6, whereas ratios of >1 have been reported for many other species, including Macrocystispyrifera, which was examined here as well. In acquiring the high-resolution spectra, partial depolymerization was used to give solutions of reduced viscosity; as is well known, this procedure may cause separation into fractions and the formation of sediments, examples of which are cited. Proton resonances of the reducing end units of chain-shortened segments of the polymers exhibited unusual, marked, line broadening at elevated temperature, which may reflect thermal dehydration. MAS 13C experiments offered the advantage of information about the intact alginate samples. Although the spectra consisted of broad, heavily overlapping peaks, curve-fitting analysis afforded qualitative and quantitative data that supplement those obtained with solutions of the polymers. Keywords: Sargassum alginate, 1H NMR of fractions, M/G constituent ratios, MAS 13C NMR, curve-fitting analysis.

Extracted and depolymerized alginates from brown algae Sargassum vulgare of Lebanese origin: chemical, rheological, and antioxidant properties

“…Chemical shifts data, listed in Table 1, were fully in agreement with earlier 1 H and 13 C chemical shifts for polymeric guluronate and mannuronate residues (Llanes et al 1997). The anomeric carbons were assigned at δ=101.08 ppm for guluronate blocks and at δ=100.78 ppm for mannuronate blocks.…”

Effectiveness test of alginate‐derived polymeric surfactants

“…13,14 Sodium periodate, sodium cyanoborohydride, octyl amine (C 8 H 17 -NH 2 ), dodecyl amine (C 12 H 25 -NH 2 ), and hexadecyl amine (C 16 H 33 -NH 2 ) were obtained from Aldrich Chemical Co and used as received. Azobenzene, selected as a hydrophobic model compound, was from Wako Chemical (Japan) and propan-1-ol, ethylene glycol and methanol were from Junsei Co (Japan).…”

Characterization and evaluation of copper and nickel biosorption on acidic algae Sargassum Filipendula

“…Normally this partial hydrolysis is used to decrease viscosity of high-molecularweight alginate solutions prior to recording their proton NMR spectra. This step that can induce precipitation of a portion of alginate may significantly distort the experimental results 30 .…”

“…The complex spectral pattern can be represented as a sum of individual symmetric signals corresponding to the C(2) -C(5) atoms of both uronic residues 34 , enough to estimate the M/G ratio with high accuracy 30 , assuming that the stronger, downfield peak is due to the main constituent, the α-L-guluronic acid.…”