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. 2024 Sep 27;14(1):22378.
doi: 10.1038/s41598-024-69984-2.

Exploring the structure and dynamics of soft and hard cuticle of Bombyx mori using solid-state NMR techniques

Lekhan Lodhi  1 , Janak Dulari Ahi  1 , Neelima Gupta  2 , Bijay Laxmi Pradhan  3 , Prince Sen  4 , Manasi Ghosh  5 , Krishna Kishor Dey  6
Affiliations

Exploring the structure and dynamics of soft and hard cuticle of Bombyx mori using solid-state NMR techniques

Lekhan Lodhi et al. Sci Rep. .

Abstract

This study conducts a comprehensive analysis and comparison of Bombyx mori cuticles across different developmental stages, ranging from larval to adult, utilizing advanced solid-state NMR techniques. The primary objective is to elucidate the underlying reasons for the contrasting hardness of adult cuticles and softness of larval cuticles. Notably, PXRD analysis reveals a prominent broad peak at 19.34°, indicating the predominantly amorphous nature of both larval and adult cuticles. Analysis of 13C CP-MAS SSNMR spectra highlights an elevated proportion of phenoxy carbon in adult cuticles (6.77%) compared to larval cuticles (1.24%). Furthermore, a distinctive resonance line at 144 ppm is exclusively observed in adult cuticles, due to catechols, suggesting potential biochemical pathway variations during development. Significant variations in the primary components of 13C chemical shift anisotropy (CSA) tensors for aliphatic carbons of amino acids, catechols, and lipids between adult and larval cuticles indicate alterations in electronic environments. Additionally, the shorter spin-lattice relaxation time of carbon nuclei in larval cuticles compared to adult cuticles implies slower motional dynamics with enhanced degree of sclerotization in adults. By investigating the internal structure and dynamics of cuticles, this research not only contributes to biomimetic material development but also enhances our understanding of structural changes across different developmental stages of B. mori.

Keywords: Exoskeleton; Larval and adult cuticles of Bombyx mori; Solid-state NMR; XRD-measurements.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
XRD patterns of (a) larva, and (b) adult cuticle.
Figure 2
Figure 2
13C CP-MAS SSNMR spectrum of (a) larval cuticle (b) larval excuva (c) pupal cuticle (d) pupal case (e) adult cuticle.
Figure 3
Figure 3
The assignment of the 13C CP-MAS SSNMR spectrum of Larval Cuticle by following the article of Schaefer et al..
Figure 4
Figure 4
Comparison of the 13C CP-MAS SSNMR spectra of the silkworm cuticle (a) larval and (b) adult. The deconvolution of 13C CP-MAS SSNMR spectrum is done by using dmfit software.
Figure 5
Figure 5
Stacked plot of 13C CP-MAS SSNMR spectrum of silkworm cuticle and pure chitin.
Figure 6
Figure 6
13C 2DPASS CP-MAS SSNMR spectrum of cuticle: (a) larval cuticle, (b) adult cuticle.
Figure 7
Figure 7
Larval cuticle: the CSA spinning sideband pattern at crystallographically and chemically different carbon nuclei sites.
Figure 8
Figure 8
Spinning CSA sideband pattern of larval cuticle at chemically distinct carbon nuclei sites.
Figure 9
Figure 9
Adult cuticle: the CSA spinning sideband pattern at crystallographically and chemically different carbon nuclei sites.
Figure 10
Figure 10
The spinning CSA sideband pattern of adult cuticle at chemically distinct carbon nuclei sites.
Figure 11
Figure 11
Bar diagram of the spin–lattice relaxation time for Bombyx mori cuticle. The number 1 to 15 indicate the various chemicals present in the cuticle.
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