Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 15, Pages 6026-6031Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1103109108
Keywords
materials; polymers; biopolymers
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Funding
- National Science Foundation [DMR-0964886]
- Air Force Office of Scientific Research [FA9550-07-1-0484]
- Gordon and Betty Moore Foundation
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Macromolecular conformation dynamics, which span a wide range of time scales, are fundamental to the understanding of properties and functions of their structures. Here, we report direct imaging of structural dynamics of helical macromolecules over the time scales of conformational dynamics (ns to subsecond) by means of four-dimensional (4D) electron microscopy in the single-pulse and stroboscopic modes. With temporally controlled electron dosage, both diffraction and real-space images are obtained without irreversible radiation damage. In this way, the order-disorder transition is revealed for the organic chain polymer. Through a series of equilibrium-temperature and temperature-jump dependencies, it is shown that the metastable structures and entropy of conformations can be mapped in the nonequilibrium region of a funnel-like free-energy landscape. The T-jump is introduced through a substrate (a hot plate type arrangement) because only the substrate is made to absorb the pulsed energy. These results illustrate the promise of ultrafast 4D imaging for other applications in the study of polymer physics as well as in the visualization of biological phenomena.
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