Sum Frequency Vibrational Spectroscopy: The Molecular Origins of the Optical Second-Order Nonlinearity of Collagen

• Published in: Biophysical journal Vol. 93; no. 12; pp. 4433 - 4444
• Main Authors: Rocha-Mendoza, Israel, Yankelevich, Diego R., Wang, Mingshi, Reiser, Karen M., Frank, Curt W., Knoesen, André
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.12.2007; Biophysical Society; The Biophysical Society
• Subjects: Amides; Bending; Collagen - chemistry; Collagen - ultrastructure; Collagens; Computer Simulation; Fibers; Methylene; Models, Chemical; Models, Molecular; Molecules; Nonlinear Dynamics; Nonlinearity; Optics and Photonics; Origins; Peptides; Protein Conformation; Proteins; Refractometry - methods; Spectroscopy; Spectroscopy, Imaging, Other Techniques; Spectrum analysis; Vibration
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.107.111047

The molecular origins of second-order nonlinear effects in type I collagen fibrils have been identified with sum-frequency generation vibrational spectroscopy. The dominant contributing molecular groups are: 1), the methylene groups associated with a Fermi resonance between the fundamental symmetric stretch and the bending overtone of methylene; and 2), the carbonyl and peptide groups associated with the amide I band. The noncentrosymmetrically aligned methylene groups are characterized by a distinctive tilt relative to the axis perpendicular to the main axis of the collagen fiber, a conformation producing a strong achiral contribution to the second-order nonlinear effect. In contrast, the stretching vibration of the carbonyl groups associated with the amide I band results in a strong chiral contribution to the optical second-order nonlinear effect. The length scale of these chiral effects ranges from the molecular to the supramolecular.