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. 2019 May 11;20(9):2337.
doi: 10.3390/ijms20092337.

Fungal Exocellular (1-6)-β-d-glucan: Carboxymethylation, Characterization, and Antioxidant Activity

Thais Vanessa Theis  1 , Vidiany Aparecida Queiroz Santos  2 , Patrícia Appelt  3 , Aneli M Barbosa-Dekker  4 , Vaclav Vetvicka  5 , Robert F H Dekker  6 , Mário A A Cunha  7
Affiliations

Fungal Exocellular (1-6)-β-d-glucan: Carboxymethylation, Characterization, and Antioxidant Activity

Thais Vanessa Theis et al. Int J Mol Sci. .

Abstract

Exocellular (1→6)-β-d-glucan (lasiodiplodan) produced by the fungus Lasiodiplodia theobromae MMPI was derivatized by carboxymethylation using different concentrations of a derivatizing agent. Lasiodiplodan was derivatized by carboxymethylation in an attempt to increase its solubility and enhance its biological activities. Carboxymethylglucans with degrees of substitution (DS) of 0.32, 0.47, 0.51, 0.58, and 0.68 were produced and characterized. FTIR analysis showed a band of strong intensity at 1600 cm-1 and an absorption band at 1421 cm-1, resulting from asymmetric and symmetrical stretching vibrations, respectively, of the carboxymethyl group COO- in the carboxymethylated samples. Thermal analysis showed that native lasiodiplodan (LN) and carboxymethylated derivatives (LC) exhibited thermal stability up to 200-210 °C. X-ray diffractometry demonstrated that both native and carboxymethylated lasiodiplodan presented predominantly an amorphous nature. Scanning electron microscopy revealed that carboxymethylation promoted morphological changes in the biopolymer and increased porosity, and alveolar structures were observed along the surface. The introduction of carboxymethyl groups in the macromolecule promoted increased solubility and potentiated the hydroxyl radical-scavenging activity, suggesting a correlation between degree of substitution and antioxidant activity.

Keywords: bioactive macromolecules; biopolymer; carbohydrate; exopolysaccharide; lasiodiplodan.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Illustrative representation of the reaction mechanism of carboxymethylation of lasiodiplodan. Formation of alkoxide ions (A), conversion of monochloroacetic acid to sodium monochloroacetate salt (B), nucleophilic bimolecular substitution (SN2) (C), and carboxymethylated lasiodiplodan (D). The positions shown for R indicate that the carboxymethylated group could be added at C-2, C-3, and C-4 positions on the glucose moieties.
Figure 2
Figure 2
FTIR spectra of LN and LC1 (DS: 0.32), LC2 (DS: 0.47), LC3 (DS: 0.51), LC4 (DS: 0.58), and LC5 (DS: 0.68).
Figure 3
Figure 3
Thermogravimetric (A) and differential thermogravimetric (B) curves of LN and LC1 (DS: 0.32), LC2 (DS: 0.47), LC3 (DS: 0.51), LC4 (DS: 0.58), and LC5 (DS: 0.68).
Figure 4
Figure 4
Micrographs (SEM) of LN and LC with different degrees of substitution 400X, 800X, and 1500X magnification.
Figure 5
Figure 5
X-ray diffraction profiles of LN and LC1 (DS: 0.32), LC2 (DS: 0.47), LC3 (DS: 0.51), LC4 (DS: 0.58), and LC5 (DS: 0.68).
Figure 6
Figure 6
Antioxidant activity of native lasiodiplodan (LN), carboxymethylated lasiodiplodan (LC), glucose (GLU), and ascorbic acid (AA) (antioxidant standard) measured by (A) HO• scavenging; (B) H2O2 scavenging, and (C) reducing power.
See this image and copyright information in PMC

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