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Carbonization of a stable ?-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 ?-sheet structure is transformed into an sp(2)-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.

SUBMITTER: Cho SY

PROVIDER: S-EPMC4455128 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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

Cho Se Youn SY Yun Young Soo YS Lee Sungho S Jang Dawon D Park Kyu-Young KY Kim Jae Kyung JK Kim Byung Hoon BH Kang Kisuk K Kaplan David L DL Jin Hyoung-Joon HJ

Nature communications 20150520

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 chem ...[more]

PMID: 25990218

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Project description:Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The ?-sheet-rich natural nanofiber units of about 10-50 nm in diameter are often considered the origin of these properties, yet it remains unclear how silk self-assembles into these hierarchical structures. A new system composed of ?-sheet-rich silk nanofibers about 10-20 nm in diameter is reported here, where these nanofibers formed into "flowing hydrogels" at 0.5-2% solutions and could be transformed back into the solution state at lower concentrations, even with a high ?-sheet content. This is in contrast with other silk processed materials, where significant ?-sheet content negates reversibility between solution and solid states. These fibers are formed by regulating the self-assembly process of silk in aqueous solution, which changes the distribution of negative charges while still supporting ?-sheet formation in the structures. Mechanistically, there appears to be a shift toward negative charges along the outside of the silk nanofibers in our present study, resulting in a higher zeta potential (above -50 mV) than previous silk materials which tend to be below -30 mV. The higher negative charge on silk nanofibers resulted in electrostatic repulsion strong enough to negate further assembly of the nanofibers. Changing silk concentration changed the balance between hydrophobic interactions and electrostatic repulsion of ?-sheet-rich silk nanofibers, resulting in reversible hydrogel-solution transitions. Furthermore, the silk nanofibers could be disassembled into shorter fibers and even nanoparticles upon ultrasonic treatment following the transition from hydrogel to solution due to the increased dispersion of hydrophobic smaller particles, without the loss of ?-sheet content, and with retention of the ability to transition between hydrogel and solution states through reversion to longer nanofibers during self-assembly. These reversible solution-hydrogel transitions were tunable with ultrasonic intensity, time, or temperature.

Dataset Information

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

Publications

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

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