title: Determination of collagen nanostructure from second-order susceptibility tensor analysis.
abstract: A model is proposed to describe the polarization dependence of second harmonic generation (SHG) from type I collagen fibrils. The model is based on sum-frequency vibrational spectrum experiments that attribute the molecular origins of collagen second-order susceptibility to the peptide groups in the backbone of the collagen α-helix and the methylene groups in the pyrrolidine rings. Applying our model to a polarization SHG (P-SHG) experiment leads to a predicted collagen I peptide pitch-angle of 45.82° ± 0.46° and methylene pitch-angle of 94.80° ± 0.97°. Compared to a previous model that accounts for only the peptide contribution, our results are more consistent with the x-ray diffraction determination of collagen-like peptide. Application of our model to type II collagen from rat trachea cartilage leads to similar results. The peptide pitch-angle of 45.72° ± 1.17° is similar to that of type I collagen, but a different methylene pitch-angle of 97.87° ± 1.79° was found. Our work demonstrates that far-field P-SHG measurements can be used to extract molecular structural information of collagen fibers.
authors.affiliation: Department of Physics, National Taiwan University, Taipei, Taiwan.
authors.forename: Ping-Jung
authors.initials: PJ
authors.lastname: Su
authors.forename: Wei-Liang
authors.initials: WL
authors.lastname: Chen
authors.forename: Yang-Fang
authors.initials: YF
authors.lastname: Chen
authors.forename: Chen-Yuan
authors.initials: CY
authors.lastname: Dong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D024042:Collagen Type I / Q000737:chemistry*; D024043:Collagen Type II / Q000737:chemistry; D021621:Imaging, Three-Dimensional; D008853:Microscopy; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry; D017433:Protein Structure, Secondary; D051381:Rats
chemical_list: D024042:Collagen Type I; D024043:Collagen Type II; D010446:Peptide Fragments