Carbonization of a stable β-sheet-rich silk protein into a pseudographitic pyroprotein

Abstract

Silk proteins are of great interest to the scientific community owing to their unique mechanical properties and interesting biological functionality. In addition, the silk proteins are not burned out following heating, rather they are transformed into a carbonaceous solid, pyroprotein; several studies have identified potential carbon precursors for state-of-the-art technologies. However, no mechanism for the carbonization of proteins has yet been reported. Here we examine the structural and chemical changes of silk proteins systematically at temperatures above the onset of thermal degradation. We find that the β-sheet structure is transformed into an sp2-hybridized carbon hexagonal structure by simple heating to 350 °C. The pseudographitic crystalline layers grew to form highly ordered graphitic structures following further heating to 2,800 °C. Our results provide a mechanism for the thermal transition of the protein and demonstrate a potential strategy for designing pyroproteins using a clean system with a catalyst-free aqueous wet process for in vivo applications.

Silk: Optical Properties over 12.6 Octaves THz-IR-Visible-UV Range

“…Absorbance spectra of degummed B. mori and A. pernyi silk fibers as well as amorphous fibroin from B. mori subjected to hot plate annealing at 250 ${}^{\circ }$C, i.e., at the onset of thermal degradation [33], for varying durations are shown in Figure 3. Degradation of silk with observable darker coloration was consistent with high temperature oxidation.…”

Spider-silk inspired polymeric networks by harnessing the mechanical potential of β-sheets through network guided assembly

“…A thermal degradation process atypical for hydrophobically modified networks was observed with two distinct stages, implying the hybrid structure with different phases 57 . In the wake of a slow mass drop, a much steeper mass loss occurred to β-sheet-incorporated networks from 300 to 400°C, due to the progressive decomposition of β-sheet crystals in this temperature range 58 . Once the β-sheet network is completely degraded, the β-sheet-incorporated networks follow a similar degradation profile to the respective initial networks.…”

Obtaining high mechanical performance silk fibers by feeding purified carbon nanotube/lignosulfonate composite to silkworms

“…6b shows the transformation of the carbonized silk protein toward the (002) plane of graphitic carbon, in agreement with reports that high temperature induces the formation of conjugated sp 2hybridized carbon hexagonal rings. 59,60 It has been established that the (002) plane of carbonized silk protein should exhibit a sharp peak under ultrahigh temperature conditions. However, at 900 C the graphitic stacking of the (002) plane at around 25.82 is not observed, indicating larger carbonaceous interplanar distances.…”

“…7B(a and c)). 13,59 We quantitatively analyzed the element content values using the high resolution C 1s XPS line, and found that Control-S has the highest C-C content (Fig. 7C(a)), which is likely to arise from disordered carbonaceous residue.…”