Manhattan, KS, United States
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Shera J.N.,Bio Materials and Technology Laboratory | Takahashi D.,Kansas State University | Herrera A.I.,Kansas State University | Prakash O.,Kansas State University | Sun X.S.,Bio Materials and Technology Laboratory
Journal of Nanoscience and Nanotechnology | Year: 2010

Protein nanomaterials at the peptide level have shown great potential for medical applications. Peptides change their morphological conformation because of changes in self-assembly properties when they are exposed to changes in solvent composition or pH. Two 15-residue peptide sequences, KhK (KKKFLIVIGSIIKKK) and Alternating Kh (KFLKKIVKIGKKSII), were designed for the purpose of determining the role of peptide sequence on solution morphology and conformation. KhK solutions exhibited a random coil to helical transition when solvent conditions were changed from water to a trifluorethanol/water solution at acidic pH. Alternating Kh solutions, however, demonstrated primarily random coil character under similar solvent and pH conditions as determined by circular dichroism spectroscopy and 2D- 1H- 1H nuclear magnetic resonance spectroscopy. At basic pH, circular dichroism spectroscopy and nuclear magnetic resonance spectroscopy analysis demonstrated that random coil character increased at basic pH for KhK, whereas Alternating Kh exhibited an increase in β-sheet character. Further analysis by transmission electron microscopy showed marked differences in the peptide solution morphology. Peptide particle aggregation and fiber formation were significantly affected by solvent composition and pH values for both peptide sequences. Copyright © 2010 American Scientific Publishers.

Huang H.,Bio Materials and Technology Laboratory | Ganguly D.,Kansas State University | Chen J.,Kansas State University | Sun X.S.,Bio Materials and Technology Laboratory
Journal of Nanoscience and Nanotechnology | Year: 2015

Peptide-based biomaterials have many potential applications in tissue engineering, drug delivery, surface engineering, and other areas. In this study, we exploited a series of amphiphilic diblock model peptides (L5K10, L5GSIIK10, and L5PD PK10) to understand how the supramolecular assembly morphology may be modulated by the physical properties of the peptide monomer and experimental conditions. A combination of experimentation and simulation revealed that although all three peptides lack stable structures as monomers, their levels of conformational heterogeneity differ significantly. Importantly, such differences appear to be correlated with the peptides' ability to form sheet-like assemblies. In particular, substantial conformational heterogeneity appears to be required for anisotropic growth of sheet-like materials, likely by reducing the peptide assembly kinetics. To test this hypothesis, we increased the pH to neutralize the lysine residues and promote peptide aggregation, and the resulting faster assembly rate hindered the growth of the sheet morphology as predicted. In addition, we designed and investigated the assembly morphologies of a series of diblock peptides with various lengths of polyglycine inserts, L5GxK10, x = 1, 2, 3, 4. The results further supported the importance of peptide conformational flexibility and pH in modulation of the peptide supramolecular assembly morphology. © 2015 American Scientific Publishers All rights reserved.

Ahn B.-J.K.,Bio Materials and Technology Laboratory | Kraft S.,Kansas State University | Sun X.S.,Bio Materials and Technology Laboratory
Journal of Agricultural and Food Chemistry | Year: 2012

Toxic solvent and strong acid catalysts causing environmental issues have been mainly used for ring-opening of epoxidized oleochemicals. Here, we demonstrated that magnesium stearate (Mg-stearate) was a high efficient catalyst for solventfree ring-opening of epoxidized methyl oleate, a model compound of midchain epoxide. Mg-stearate resulted in the highest yield (95%) and conversion rate (99%) toward midchain alkoxyesters under the same conditions (160 °C, 12 h) superior to other fatty acid derivatives such as a Lewis acid (lithium and sodium stearate) and Brønsted acid (stearic acid). Based on this chemical study, we synthesized biogrease and thermoplastic using epoxidized soybean oil (ESO) and Mg-stearate via one-pot, solvent-free, and purification-free process. Mg-stearate played a significant role as a reactant for epoxide ring-opening and as a thickener when excess loading rate was used; viscosity increased from 1800 to 4500 Pa·s at 25 °C when ESO:Mg-stearate increased from 1:1 equiv to 1:2, then behaved like thermoplastics (T g = -27 °C, T m = 90 °C) with 1:4. © 2012 American Chemical Society.

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