Time-resolved crystallography lets us see molecules in action, like watching a movie of chemical reactions. It's revolutionizing our understanding of how proteins and other molecules move and change during important processes.
This cutting-edge technique uses super-fast X-ray pulses to capture snapshots of molecules at different stages. By piecing these snapshots together, scientists can create a detailed picture of how molecules transform over time.
Experimental Techniques
Advanced X-ray Sources and Methods
- Pump-probe experiments enable time-resolved studies by initiating reactions with a pump pulse and probing the sample with a subsequent X-ray pulse
- Synchrotron radiation provides high-intensity X-ray beams for structural studies, allowing for faster data collection and higher resolution
- X-ray free-electron lasers (XFELs) generate ultra-bright, femtosecond X-ray pulses, enabling studies of ultrafast processes and radiation-sensitive samples
- XFELs produce pulses with peak brilliance billions of times higher than synchrotron sources
- Femtosecond pulse duration allows for "diffraction before destruction" experiments
- Serial femtosecond crystallography utilizes XFELs to collect diffraction data from a stream of microcrystals, overcoming radiation damage limitations
- Requires millions of microcrystals in suspension
- Each crystal is exposed to a single XFEL pulse, producing a partial diffraction pattern
- Diffraction patterns from many crystals are combined to create a complete dataset
Specialized Diffraction Techniques
- Laue diffraction uses polychromatic X-rays to collect multiple reflections simultaneously, reducing data collection time
- Enables capture of structural changes on microsecond to nanosecond timescales
- Particularly useful for studying enzyme reactions and protein folding
- Time-resolved Laue crystallography combines Laue diffraction with rapid reaction initiation methods
- Can capture structural snapshots of reaction intermediates
- Provides insights into reaction mechanisms and conformational changes
Structural Dynamics
- Ultrafast structural dynamics studies investigate atomic and molecular motions on femtosecond to picosecond timescales
- Reveals rapid structural changes during chemical reactions or protein function
- Techniques include time-resolved spectroscopy and diffraction methods
- Reaction intermediates represent transient structural states during chemical or biological processes
- Capturing intermediates provides insights into reaction mechanisms and pathways
- Time-resolved crystallography can identify and characterize these short-lived species
Experimental Approaches for Structural Dynamics
- Time-resolved serial femtosecond crystallography (TR-SFX) combines XFEL technology with pump-probe techniques
- Allows for studying structural changes with femtosecond time resolution
- Can capture very early stages of light-activated processes (photosynthesis, vision)
- Mixing-injector systems enable the study of solution-phase reactions in time-resolved experiments
- Reactants are mixed just before injection into the X-ray beam
- Allows for investigating diffusion-limited processes and enzyme catalysis
- Temperature-jump experiments initiate structural changes through rapid heating
- Can be used to study protein folding and unfolding processes
- Often combined with time-resolved X-ray scattering or spectroscopy