Hyperpolarizability Components for $\alpha$- and $\omega$-Helical Polypeptides in Polar Crystals Determined from Second-Harmonic Generation Measurements

概要

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Second-harmonic generation (SHG) properties of $\alpha$-helical and $\omega$-helical polypeptides have been investigated by using crystalline films prepared by casting lyotropic liquid crystal solutions of poly($\gamma$-phenylpropyl L-glutamate) (3PLG) and poly($\beta$-benzyl L-aspartate) (PBLA) under a high electric field. The crystalline films generated SH light upon irradiation of the Nd:YAG laser, which ensures that the films have a polar structure. The in-plane anisotropy of the polarized SH light intensity is well explained by theoretical descriptions under the C6 and C4 symmetries for 3PLG and PBLA, respectively. On the basis of the SHG results, the hyperpolarizability tensor components of the individual polypeptide helical molecules are characterized as $\beta_{ZXX}/\beta_{ZZZ}=1.2$, $\beta_{XZX}/\beta_{ZZZ}=3.8$, and $2\beta_{ZXX}/\beta_{XZX}=0.7$ for the $\alpha$-helix 3PLG, and $\beta_{ZXX}/\beta_{ZZZ}=3.8$, $\beta_{XZX}/\beta_{ZZZ}=5.0$, and $2\beta_{ZXX}/\beta_{XZX}=1.5$ for the $\omega$-helix PBLA, where the $z$-axis is set as the helical axis. Quantum chemical calculation is successfully performed to reveal the general character of the polypeptide helix, $\beta_{ZXX}>\beta_{ZZZ}$.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2004-10-15