Diffuse reflectance spectroscopy of fibrous proteins

Area of Science:

• Biophysics
• Materials Science
• Spectroscopy

Background:

• Fibrous proteins like keratin and collagen are crucial biomaterials.
• Understanding their chromophore properties is key to applications and modifications.
• UV-visible absorption spectra are vital for characterizing these proteins.

Purpose of the Study:

• To present UV-visible diffuse reflectance (DR) spectra of key fibrous proteins.
• To investigate the UV-absorbing amino acids in solid form.
• To correlate spectral properties with protein color and bleaching efficiency.

Main Methods:

• UV-visible diffuse reflectance (DR) spectroscopy was used.
• Spectra were recorded for wool, feather keratin, silk fibroin, and collagen.
• DR spectra of solid amino acids (tryptophan, tyrosine, cystine, phenylalanine) were also measured.

Main Results:

• Solid cystine exhibits surprisingly strong UV absorbance via its disulfide bond, dominating keratin spectra.
• Bleaching is ineffective at removing yellow chromophores from wool.
• Cystine's solid-state spectrum shows a significant red shift (~40 nm) at 290 nm compared to solution.

Conclusions:

• Cystine's disulfide bond is a major UV chromophore in solid keratin, despite not contributing to wool's visible color.
• The spectral properties of solid amino acids differ significantly from their solution spectra.
• Understanding these DR spectral differences is crucial for protein characterization and modification.