TY - Generic T1 - Stabilization of Terahertz Vibrational Modes in Illuminated Orange Carotenoid Protein Crystals T2 - 2020 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) Y1 - 2020 A1 - McKinney, J. A1 - Sharma, A. A1 - Deng, Y. A1 - George, D. A1 - Lechno-Yossef, S. A1 - Kerfeld, C. A1 - Markelz, A. AB -
Orange carotenoid protein (OCP) controls efficiency of the phycobilisome (PBS), the light harvesting antenna in cyanobacteria, to prevent oxidative damage. The OCP switches from resting state to photo protective state with intense blue light illumination. Questions persist as to why OCPR interaction increases with the PBS over that with the OCPO. Here we examine the role of long-range intramolecular vibrations within OCP. Using Stationary Sample Anisotropic Terahertz Microscopy (SSATM) we measure changes in the intramolecular vibrations with photo switching. We report the first observation of switching in the intramolecular vibrations with photoexcitation. Results suggest that there is a stiffening of the molecule in the photo protective state. This increase in structural stability may enhance the interaction with the PBS change in OCP interaction with PBS. In low light, carotenoid bound OCP appears orange (OCP o ) and is inactive. Illumination by strong light converts OCP to the active, red (OCPR) state, which interacts with the PBS. A comparison of anisotropic THz microscopy measurements of dark adapted (OCP o ) and illuminated OCP crystals indicate differences in their vibrational modes that may be important for OCP-PBS interactions.
JF - 2020 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) CY - Buffalo, NY ER - TY - JOUR T1 - Spectral Assignment of Lysozyme Collective Vibrations JF - Biophysical Journal Y1 - 2019 A1 - Deng, Y. T. A1 - McKinney, J. A1 - Romo, T. A1 - Grossfield, A. A1 - Markelz, A. KW - Biophysics AB -We demonstrate anisotropic THz spectroscopy of sucrose using newly developed compact discretely tunable THz sources for turn-key spectroscopic systems.
JF - 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves T3 - International Conference on Infrared Millimeter and Terahertz Waves SN - 978-1-5386-8285-2 N1 - Irmmw-thzLarge third-order, free-carrier nonlinear susceptibilities, chi(3) (to approximately 0.2 esu), and subcubic dependence of the third-harmonic power on the incident intensity, have been observed between 19 cm-1 and 23 cm-1 for InAs/AlSb quantum wells with electron sheet densities between 2.5 x 10(12) cm-2 and 8 X 10(12) cm-2. We find that the transmission of the fundamental, and the samples' DC conductivity, decrease with increasing incident intensity, indicating a large rise in the scattering rate. Using the intensity-dependent transmission to account for absorption in the sample is not sufficient to recover a cubic power law for the third-harmonic intensity. In addition, given the increased scattering rate indicated by the conductivity data, the bulk free-carrier chi(3) due to non-parabolicity should decrease dramatically with increasing fundamental intensity, contrary to our results. Thus, non-parabolicity alone cannot account for the observed third-harmonic response.
VL - 9 SN - 0268-1242 N1 - Sherwin, Mark S/Q-4762-2017We report selective substitution of oxygen-18 and oxygen-16 isotopes into the inequivalent oxygen lattice sites in YBa2Cu3O7−δ. The technique involves gas-phase diffusion and exploits the site dependence of diffusion rates. The CuO2-plane [O(2),O(3)] sites of YBa2Cu3O7−δ can be filled with 18O while the apical [O(4)] and CuO-chain sites [O(1)] contain 16O (the opposite distribution can also be made). The site-selective isotope occupation has been confirmed by Raman spectroscopy. Our method will permit experiments to determine the contributions of the different oxygen sites to the isotope effect, in order to locate the pairing interaction within the unit cell.
VL - 44 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.44.9556 ER - TY - JOUR T1 - SMALL OXYGEN ISOTOPE SHIFT IN YBA2CU3O7 JF - Physical Review B Y1 - 1988 A1 - Morris, D. E. A1 - Kuroda, R. M. A1 - Markelz, A. G. A1 - Nickel, J. H. A1 - Wei, J. Y. T. VL - 37 SN - 0163-1829 N1 - Markelz, Andrea/0000-0003-0443-4319