Conformational changes and molecular mobility in plasticized proteins.
Most biopolymers exist in a plasticized state, whether it is naturally with water or unnaturally with glycerol or other suitable polyol, to make a flexible material. We have found that the extent to which a biopolymer can be plasticized is dependent on its molecular and higher order structures outside of simply molecular weight. Lactalbumin, ovalbumin, corn zein, wheat gluten, and feather keratin were plasticized with glycerol from very low to very high amounts. The conformation of the proteins was monitored with Fourier transform-infrared (FT-IR) spectroscopy and X-ray powder diffraction (XRD) and correlated with the tensile modulus. Protein conformational changes were pronounced for polar proteins with a low amount of cysteine. FT-IR showed that the conformational changes resulted in ordering of the protein at low to moderate plasticization levels. For proteins with little resistance to conformational changes, additional small-scale ordering occurred around the glass transition, as observed in XRD. Accurate comparison of plasticized proteins was dependent on knowing whether or not the protein was glassy or rubbery at room temperature as no differences arose in the glassy state. The transition from glassy to rubbery behavior with plasticization level can be found from modulus, FT-IR, and XRD data.
Biological Systems Engineering Department, Virginia Tech, 303 Seitz Hall, Blacksburg, Virginia 24061, USA.
Ahmad I
AI
Athamneh
Michael
M
Griffin
Meocha
M
Whaley
Justin R
JR
Barone
D000818:Animals; D005983:Glutens; D005990:Glycerol / Q000737:chemistry*; D007633:Keratins; D007768:Lactalbumin; D008970:Molecular Weight; D009038:Motion; D010047:Ovalbumin; D044367:Phase Transition; D010940:Plant Proteins; D010968:Plasticizers; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction; D015028:Zein
D010940:Plant Proteins; D010968:Plasticizers; D011506:Proteins; D007633:Keratins; D005983:Glutens; D010047:Ovalbumin; D015028:Zein; D007768:Lactalbumin; D005990:Glycerol