02183nas a2200325 4500008004500000020001400045245005900059210005800118260000800176300001000184490000600194520131900200653002801519653001301547653002101560653002401581653001301605653002301618653001101641653001601652653002801668653001301696653001001709100001401719700001901733700001601752700002001768700002001788856004901808 2016 Engldsh a2327-912500aModulated orientation-sensitive terahertz spectroscopy0 aModulated orientationsensitive terahertz spectroscopy cJun aA1-A80 v43 a
Intramolecular vibrations of large macromolecules reside in the terahertz range. In particular, protein vibrations are closely spaced in frequency, resulting in a nearly continuous vibrational density of states. This density of vibrations interferes with the identification of specific absorption lines and their subsequent association with specific functional motions. This challenge is compounded with the absorption being dominated by the solvent and local relaxational motions. A strategy for removing the isotropic relaxational loss and isolating specific vibrations is to use aligned samples and polarization-sensitive measurements. Here, we demonstrate a technique to rapidly attain the anisotropic resonant absorbance using terahertz time domain spectroscopy and a spinning sample. The technique, modulated orientation-sensitive terahertz spectroscopy (MOSTS), has a nonzero signal only for anisotropic samples, as demonstrated by a comparison between a silicon wafer and a wire grid polarizer. For sucrose and oxalic acid molecular crystals, the MOSTS response is in agreement with modeled results for the intermolecular vibrations. Further, we demonstrate that, even in the presence of a large relaxational background, MOSTS isolates underlying vibrational resonances. (C) 2016 Chinese Laser Press
10aabsorption-spectroscopy10adynamics10aenzyme catalysis10alow-frequency modes10alysozyme10aneutron-scattering10aOptics10aperspective10apolarization modulation10aproteins10awater1 aSingh, R.1 aGeorge, D., K.1 aBae, C., J.1 aNiessen, K., A.1 aMarkelz, A., G. uhttps://markelz.physics.buffalo.edu/node/242