@article {519, title = {Photo-Switching of Protein Dynamical Collectivity}, journal = {Photonics}, volume = {8}, year = {2021}, chapter = {302}, abstract = {

We examine changes in the picosecond structural dynamics with irreversible photobleaching of red fluorescent proteins (RFP) mCherry, mOrange2 and TagRFP-T. Measurements of the protein dynamical transition using terahertz time-domain spectroscopy show in all cases an increase in the turn-on temperature in the bleached state. The result is surprising given that there is little change in the protein surface, and thus, the solvent dynamics held responsible for the transition should not change. A spectral analysis of the measurements guided by quasiharmonic calculations of the protein absorbance reveals that indeed the solvent dynamical turn-on temperature is independent of the thermal stability/photostate however the protein dynamical turn-on temperature shifts to higher temperatures. This is the first demonstration of switching the protein dynamical turn-on temperature with protein functional state. The observed shift in protein dynamical turn-on temperature relative to the solvent indicates an increase in the required mobile waters necessary for the protein picosecond motions, that is, these motions are more collective. Melting-point measurements reveal that the photobleached state is more thermally stable, and structural analysis of related RFP{\textquoteright}s shows that there is an increase in internal water channels as well as a more uniform atomic root mean squared displacement. These observations are consistent with previous suggestions that water channels form with extended light excitation providing O2 access to the chromophore and subsequent fluorescence loss. We report that these same channels increase internal coupling enhancing thermal stability and collectivity of the picosecond protein motions. The terahertz spectroscopic characterization of the protein and solvent dynamical onsets can be applied generally to measure changes in collectivity of protein motions.

}, doi = {10.3390/photonics8080302}, url = {https://www.mdpi.com/2304-6732/8/8/302}, author = {M. Xu and D. George and R. Jimenez and A. Markelz} } @proceedings {299, title = {Angular Distortion Removal of THz Anisotropic Dichroism Microscope}, year = {2019}, month = {2019}, pages = {1 - 2}, address = {Paris, France}, abstract = {

We have developed a stationary sample THz anisotropic dichroism microscope as a powerful tool for material characterization. The key innovation is the use of an iso-response curve defined by the terahertz and detection light polarizations. Here we show that following a continuous iso-response curve introduces angular distortion in the spectrum, and this distortion can be eliminated by using a discontinuous iso-response angle pairs avoiding large gradient regions. Employing this additional constraint on the relative polarizations provides a convenient technique for rapid anisotropic terahertz spectroscopy.

}, keywords = {absorption, angular distortion removal, Biomedical measurement, continuous iso-response curve, detection light polarizations, discontinuous iso-response angle pairs, Distortion, light polarisation, material characterization, Microscopy, proteins, rapid anisotropic terahertz spectroscopy, relative polarizations, spectroscopy, stationary sample, terahertz spectroscopy, terahertz wave spectra, THz anisotropic dichroism microscope, vibrations}, isbn = {2162-2035}, doi = {10.1109/IRMMW-THz.2019.8873793}, url = {https://ieeexplore.ieee.org/document/8873793}, author = {Y. Deng and K. Niessen and A. Markelz} } @proceedings {275, title = {Finite size effects in ferroelectric nanosystems: Absence of mode softening}, volume = {2}, year = {2003}, note = {cited By 0}, month = {02/2003}, pages = {76-81}, address = {San Francisco, CA}, abstract = {

We present measurements of the mode softening behavior for PbZr 0.5Ti0.5O3 (PZT(50)) thin films using terahertz time domain spectroscopy (TTDS). The films were grown using pulsed laser deposition (PLD) techniques on silicon substrates to study how reduced size affects the mode softening behavior. At room temperature two modes are observed at 1.1 THz (37 cm-1) and at 2.3 THz (77 cm-1). As the temperature is increased toward Tc we do not see strong mode softening, but rather a spectral weight transfer from the high frequency mode to the low frequency mode. This absence of mode softening is more dramatic than that reported by other investigators[1]. We will discuss the possible sources for this discrepancy. These results suggest a change in lattice dynamics for nanoscale ferroelectric films that may be highly dependent on the sample preparation technique.

}, keywords = {Ferroelectric materials, Fourier Transform Infrared Spectroscopy, Frequency ranges, Lead compounds, Mode softening, nanostructured materials, Natural frequencies, Optical modes, Permittivity, phase transitions, phonons, Routers, Thermal effects}, isbn = {0972842209}, author = {D. Wolpert and W. Cox and J. Cerne and A. Markelz and T. Zhao and R. Ramesh}, editor = {Romanowicz M.} }