Vibrational spectroscopy and density functional theory calculations of poly‐D‐mannuronate and heteropolymeric fractions from sodium alginate

Abstract

The tetrasaccharide of 1 → 4 β-D-mannopyranuronate (MM) and the alternating tetrasaccharide of 1 → 4 b-Dmannopyranuronate and 1 → 4 α-L-gulopyranuronate (MG) were analyzed based on density functional theory (DFT) by employing the Gaussian 03 W package. The molecular geometries were fully optimized by using the Becke's three-parameter hybrid exchange functional combined with Lee-Yang-Parr correlation functional (B3LYP) and using a 6-31G(d,p) basis set. The calculated IR spectrum of MM presents a band at 1093 cm −1 for C-C stretching vibration, which is in good agreement with the experimental observation (1096 cm −1 ) for the polymannuronate fraction obtained by partial hydrolysis of sodium alginate extracted from the hybrid brown seaweed Lessonia-Macrocystis. The calculated value at 826 cm −1 for MM is in close agreement with the experimental value and confirms that this band is characteristic of polymannuronate blocks. Most of the bands in the IR spectrum are also present in the observed Raman spectrum of the polymannuronate fraction. The experimental IR spectrum of heteropolymeric fraction obtained by partial hydrolysis of sodium alginate shows absorbances similar to those calculated for the model tetrasaccharide (MG). Surface-enhanced Raman scattering (SERS) allows differentiation between the homopolymeric and heteropolymeric fractions of sodium alginate. The SERS spectrum of the heteropolymeric fraction shows an enhanced signal at 731 cm −1 which is present in the calculated Raman spectrum of the tetrasaccharide MG at 729 cm −1 . This band is assigned to the ring-breathing deformation of the β-D-mannopyranuronate and α-L-gulopyranuronate residues.

Preparation and swelling properties of homopolymeric alginic acid fractions/poly(N‐isopropyl acrylamide) graft copolymers

“…Furthermore, the 2D HMBC 13 C/ 1 H‐NMR spectrum [Figure (B)] presented the connectivity between the G residues and indicated the presence of α‐1→4 glycosidic linkages. The assignments of chemical shifts in the 1 H‐NMR and 13 C‐NMR spectra of the F 2 and F 3 fractions are presented in Table ; the values were in good agreement with those published in the literature and confirmed that the F 2 fraction was mainly composed of MM and the F 3 fraction was pure GG . Molecular weight determinations by the reducing end method indicated M n values of 32,100 and 31,500 for the F 2 and F 3 fractions, respectively.…”

Surface Functionalization of “Rajshahi Silk” Using Green Silver Nanoparticles

“…The CO asymmetrical stretching at a maximum of 1609 cm −1 along with a weaker symmetrical stretching band at 1414 cm −1 [22] were empiric due to the salt nature of carboxylic acid groups in pure Na-Alg. An accelerated band at 1083 cm −1 reflects the stretching of C-O-C group; the peaks at 601 cm −1 belong to C-O-C glycosidic linkage (ring breathing) [23]. They are accompanying its saccharide structure [24].…”

UV Protection and Antibacterial Treatment of Wool using Green Silver Nanoparticles

“…The CO asymmetrical stretching at 1609 cm -1 along with a weaker symmetrical stretching band at 1414 cm -1 [22] were empiric due to salt nature of carboxylic acid groups at pure Na-Alg. An accelerated band at 1083 cm -1 is apery the stretching of C-O-C group; the peaks at 601 cm -1 belong to C-O-C glycosidic linkage (ring breathing) [23]. They are accompanying to its saccharide structure [24].…”