title: Measurement of the second-order hyperpolarizability of the collagen triple helix and determination of its physical origin.
abstract: We performed Hyper-Rayleigh Scattering (HRS) experiments to measure the second-order nonlinear optical response of the collagen triple helix and determine the physical origin of second harmonic signals observed in collagenous tissues. HRS experiments yielded a second-order hyperpolarizability of 1.25 x 10(-27) esu for rat-tail type I collagen, a surprisingly large value considering that collagen presents no strong harmonophore in its amino acid sequence. Polarization-resolved experiments showed intramolecular coherent contributions to the HRS signal along with incoherent contributions that are the only contributions for molecules with dimensions much smaller than the excitation wavelength. We therefore modeled the effective second-order hyperpolarizability of the 290 nm long collagen triple helix by summing coherently the nonlinear response of well-aligned moieties along the triple helix axis. This model was confirmed by HRS measurements after denaturation of the collagen triple helix and for a collagen-like short model peptide [(Pro-Pro-Gly)(10)](3). We concluded that the large collagen nonlinear response originates in the tight alignment of a large number of small and weakly efficient harmonophores, presumably the peptide bonds, resulting in a coherent amplification of the nonlinear signal.
authors.affiliation: Laboratoire d'Optique et Biosciences, Ecole Polytechnique, CNRS, INSERM U696, 91128 Palaiseau, France.
authors.forename: Ariane
authors.initials: A
authors.lastname: Deniset-Besseau
authors.forename: Julien
authors.initials: J
authors.lastname: Duboisset
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Benichou
authors.forename: François
authors.initials: F
authors.lastname: Hache
authors.forename: Pierre-François
authors.initials: PF
authors.lastname: Brevet
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Schanne-Klein
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D003094:Collagen / Q000737:chemistry*; D008958:Models, Molecular; D008962:Models, Theoretical; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats
chemical_list: D010455:Peptides; D003094:Collagen