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. 2024 Dec 24;30(1):16.
doi: 10.3390/molecules30010016.

Hydrophobization of Chitin Nanofibers by Grafting of Partially 2-Deoxygenated Amyloses Through Enzymatic Approach

Naoki Yamamoto  1 , Masayasu Totani  1 , Jun-Ichi Kadokawa  1
Affiliations

Hydrophobization of Chitin Nanofibers by Grafting of Partially 2-Deoxygenated Amyloses Through Enzymatic Approach

Naoki Yamamoto et al. Molecules. .

Abstract

In recent years, increased attention has been given to the effective use of chitin nanofibers (ChNFs). We have developed a method to fabricate thinner chitin nanomaterials, called scale-down chitin nanofibers (SD-ChNFs), by a bottom-up procedure at the nanoscale level, with subsequent disintegration by electrostatic repulsion. The surface modification of SD-ChNFs is anticipated to provide new properties and functions for their practical applications. Inspired by our previous reports, which found hydrophobicity in partially 2-deoxygenated (P2D-) amylose obtained by the glucan phosphorylase (GP)-catalyzed enzymatic copolymerization of α-d-glucose 1-phosphate/d-glucal as comonomers, this work investigated the hydrophobization of SD-ChNFs via an enzymatic approach. After the modification of maltooligosaccharide primers on SD-ChNFs was performed by a reductive alkylation toward ChNFs, the grafting of the P2D-amyloses was performed by GP-catalyzed enzymatic copolymerization. 1H NMR analysis supported the production of P2D-amylose-grafted SD-ChNFs with different d-glucose/2-deoxy-d-glucose unit ratios on SD-ChNFs. The X-ray diffraction analysis of the products confirmed that the chain lengths and unit ratios of the grafted polysaccharides strongly affected the entire crystalline structures. Water contact angle measurements of the cast films of the products indicated that successful hydrophobization was achieved by the grafting of P2D-amylose chains with a sufficient chain length, a relatively high 2-deoxy-d-glucose unit ratio, and low crystallinity.

Keywords: chitin nanofiber; enzymatic grafting; glucan phosphorylase; hydrophobization; reductive alkylation.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Schematic illustration of enzymatic grafting of partially 2-deoxygenated (P2D-) amylose on scale-down chitin nanofibers (SD-ChNFs) by thermostable glucan phosphorylase (GP) catalysis, as the concept of this study.
Scheme 1
Scheme 1
Reactions for (a) preparation of maltooligosaccharide-modified SD-ChNFs and (b) subsequent thermostable GP-catalyzed copolymerization of comonomers (Glc-1-P/d-glucal) to obtain P2D-amylose-grafted SD-ChNFs.
Figure 2
Figure 2
1H NMR spectra of (a) the sample after hydrolysis and dissolution of maltooligosaccharide-modified SD-ChNFs in DCl/D2O (=50/50 vol/vol), and (b) the sample after selective hydrolysis and dissolution of P2D-amylose graft chains on SD-ChNFs (entry 2, Table 1) in DCl/D2O/DMSO-d6 (=43/43/14 vol/vol/vol).
Figure 3
Figure 3
XRD profiles of (a) SD-ChNF (b) amylose, (c) 2-deoxyamylose, (d) amylose-grafted SD-ChNFs (entry 1), and P2D-amylose-grafted SD-ChNFs: (e) entry 2, (f) entry 3, (g) entry 4, (h) entry 5, (i) entry 6, and (j) 2-deoxyamylose-grafted SD-ChNFs for entry 7.
Figure 4
Figure 4
SEM images of spin-coated samples from (a) SD-ChNFs (b) amylose-grafted SD-ChNFs (entry 1), and P2D-amylose-grafted SD-ChNFs: (c) entry 2, (d) entry 3, (e) entry 4, (f) entry 5, (g) entry 6, and (h) 2-deoxyamylose-grafted SD-ChNFs (entry 7) dispersions.
Figure 5
Figure 5
SEM images of cast films of (a) SD-ChNFs, (b) amylose-grafted SD-ChNFs (entry 1), and P2D-amylose-grafted SD-ChNFs; (c) entry 2, (d) entry 3, (e) entry 4, (f) entry 5, (g) entry 6, and (h) 2-deoxyamylose-grafted SD-ChNFs (entry 5).
Figure 6
Figure 6
Water contact angles on film surfaces of (a) SD-ChNFs, (b) amylose-grafted SD-ChNFs (entry 1), and P2D-amylose-grafted SD-ChNFs; (c) entry 2, (d) entry 3, (e) entry 4, (f) entry 5, (g) entry 6, and (h) 2-deoxyamylose-grafted SD-ChNFs (entry 7). The water contact angles in images are the average values from four measurements.
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