Functionalization of an Alginate-Based Material by Oxidation and Reductive Amination

Ronny G. Huamani-Palomino,Elvis Renzo Pichilingue L.,Ana C. Valderrama,Bryan M. Córdova,Tiago Venâncio

doi:10.3390/polym13020255

Ronny G. Huamani-Palomino, Elvis Renzo Pichilingue L. + Show 3 more

Open Access

https://doi.org/10.3390/polym13020255

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Abstract

This research focused on the synthesis of a functional alginate-based material via chemical modification processes with two steps: oxidation and reductive amination. In previous alginate functionalization with a target molecule such as cysteine, the starting material was purified and characterized by UV-Vis, 1H-NMR and HSQC. Additionally, the application of FT-IR techniques during each step of alginate functionalization was very useful, since new bands and spiked signals around the pyranose ring (1200–1000 cm−1) and anomeric region (1000–750 cm−1) region were identified by a second derivative. Additionally, the presence of C1-H1 of β-D-mannuronic acid residue as well as C1-H1 of α-L-guluronic acid residue was observed in the FT-IR spectra, including a band at 858 cm−1 with characteristics of the N-H moiety from cysteine. The possibility of attaching cysteine molecules to an alginate backbone by oxidation and post-reductive amination processes was confirmed through 13C-NMR in solid state; a new peak at 99.2 ppm was observed, owing to a hemiacetal group formed in oxidation alginate. Further, the peak at 31.2 ppm demonstrates the presence of carbon -CH2-SH in functionalized alginate—clear evidence that cysteine was successfully attached to the alginate backbone, with 185 μmol of thiol groups per gram polymer estimated in alginate-based material by UV-Visible. Finally, it was observed that guluronic acid residue of alginate are preferentially more affected than mannuronic acid residue in the functionalization.

Highlights

The past decade has seen an increase in the importance of the utilization of algal-based materials and improvement of the physicochemical properties of polysaccharides extracted from the cell wall of brown algae (Figure 1) [1]
The present study aims to provide an efficient method to functionalize the alginate in two steps via oxidation and post reductive amination reaction for evaluating the preference of uronic residue involved in this process
In order to evaluate the chemical modification using a purified raw material (AlgP), polyphenols and phlorotannins were removed from commercial-grade alginate using n-butanol

Summary

Introduction

The past decade has seen an increase in the importance of the utilization of algal-based materials and improvement of the physicochemical properties of polysaccharides extracted from the cell wall of brown algae (Figure 1) [1]. This is due to the strong dependence on taxonomic characteristics and the effect of environmental growing conditions on natural sources, which effect its metabolites’ properties [2,3,4,5]. Depending on the type of seaweed, time of harvest, temperature, and other factors, metabolites with novel features can be obtained These have been used in a wide range of applications [1]. Other polysaccharides like alginate have been gaining attention for their application in biomedical and environmental fields [8,9]

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