Use of FTIR, FT-Raman and 13C-NMR spectroscopy for identification of some seaweed phycocolloids

Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans)--agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus, Chondrus crispus, Calliblepharis jubata, Chondracanthus acicularis, Chondracanthus teedei and Gracilaria gracilis), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500-1500 cm-1 region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone.http://www.sciencedirect.com/science/article/B6VRM-48TMNJX-2/1/546d6839efda4d88aa19c207e6474e2

Identification of selected seaweed polysaccharides (phycocolloids) by vibrational spectroscopy (FTIR-ATR and FT-Raman)

http://www.sciencedirect.com/science/article/B6VP9-4V2NKJR-7/2/a0aa172e4a0e00ab9e24983d8609f77

Raman Signal Enhancement Dependence on the Gel Strength of Ag/Hydrogels Used as SERS Substrates

A series of hydrogel samples composed of Ag nanoparticles dispersed in carrageenan gels have been prepared and used in SERS studies. These studies demonstrate the dependence of the enhancement of the SERS signal on the strength of the Ag/polysaccharide hydrogel. 2,2'-Dithiodipyridine was used as the analyte probe. Several strategies were employed in order to vary the gel strength. These include the increase of the polysaccharide content in the gel, the addition of KCl as cross-linker, and the variation of the type of carrageenan (kappa, l, lambda) network. An increase in the gel strength originates an increase in the SERS enhancement observed. The results have been interpreted considering hot spots increase due to the formation of Ag particles nanojunctions as the biopolymer matrix tends to rearrange into stronger gels. This is the first report showing that there is a direct correlation between the gel strength of a hydrogel composite used as substrate and its analytical SERS sensitivity