和频振动光谱学: 胶原蛋白光学二阶非线性的分子学来源
The molecular origins of second-order nonlinear effects in type I collagen fibrils have been identified with sumfrequencygeneration vibrational spectroscopy. The dominant contributing molecular groups are: 1), the methylene groups associatedwith a Fermi resonance between the fundamental symmetric stretch and the bending overtone of methylene and 2), thecarbonyl and peptide groups associated with the amide I band. The noncentrosymmetrically aligned methylene groups arecharacterized by a distinctive tilt relative to the axis perpendicular to the main axis of the collagen fiber, a conformation producinga strong achiral contribution to the second-order nonlinear effect. In contrast, the stretching vibration of the carbonylgroups associated with the amide I band results in a strong chiral contribution to the optical second-order nonlinear effect. Thelength scale of these chiral effects ranges from the molecular to the supramolecular.