3B11
Molecular structural dynamics in solution probed by ultrafast pump-probe X-rayliquidography (solution scattering)(Center for Time-Resolved Diffraction, Department of Chemistry, Graduate School ofNanoscience and Technology (WCU), KAIST, Daejeon, Republic of Korea)○ Hyotcherl Ihee

[Introduction] Solution-phase reactions are complex due to the interactions between solutes andsolvents. Tracking time-dependent processes in such reactions is often accomplished by timeresolved spectroscopy. However, detailed structural information such as bond lengths and anglesof reaction intermediates is not directly accessible because spectroscopic signals utilizing light in
the range from ultraviolet to infrared are generally not a direct function of the molecularstructure. In addition, a spectroscopic signal can be sensitive to only a particular species, leaving
the possibility that optically silent intermediates escape detection. These shortcomings have been
overcome by the advent of time-resolved X-ray solution scattering (TRXSS), which is also called
time-resolved X-ray liquidography (TRXL) 1-10. The principle, experimental technique, dataanalysis, and applications of TRXL will be described. Using ultrashort optical pulses to trigger areaction in solution and detecting time-resolved X-ray diffraction signals to interrogate themolecular structural changes, TRXL can provide direct structural information generally difficult
to extract from ultrafast optical spectroscopy such as the temporal progression of bond lengths
and angles of all molecular species including short-lived intermediates over a wide range oftimes, from picoseconds to milliseconds. TRXSS elegantly complements ultrafast optical
spectroscopy because diffraction signals are sensitive to all chemical species simultaneously andthe diffraction signal from each chemical species can be quantitatively calculated from its threedimensional atomic coordinates and compared with experimental TRXL data.
[Results] Application examples include spatiotemporal kinetics and structural dynamics of ahalomethane, a triatomic molecule, haloethanes, an organometallic catalyst and proteins. In
particular, we succeeded in tracking protein’s structural changes in solution using TRXL. TRXL
permitted us to investigate the tertiary/quaternary conformational change of human hemoglobinin nearly physiological conditions triggered by laser induced ligand photolysis. Data on opticallyinduced tertiary relaxations of myoglobin and refolding of cytochrome c are also reported toillustrate the wide applicability of the technique. By providing insights into the structuraldynamics of proteins functioning in their natural environment, TRXSS complements and extends
results obtained with time-resolved spectroscopy and X-ray crystallography.

Various molecules studied by ultrafast X-ray liquidography (solution scattering)

Small and Medium-sized molecules

JACS, 130, 5834-5835 (2008)

Science, 309, 1223-1227 (2005)
JPCA 1209 10451-10458 (2005)
JCP, 124, 124504 (2006)
ACIE, 47, 5550-5553 (2008)

Protein molecules

Hemoglobin (Hb)Nature Methods, 5, 881-887 (2008)

Myoglobin (Mb)
Nature Methods, 5, 881-887 (2008)
J. Phys. Chem. B, 113, 13131-13133 (2009)
ChemComm, 47, 289-291 (2011)
J. Phys. Chem. Lett., 2, 350-356 (2011)

JCP, 124, 034501 (2006)

ACIE, 47, 1047-1050 (2008)

HgI2
PNAS, 103, 9410-9415 (2006)

I3-

Photoactive Yellow Protein(PYP)

Cytochrome C (CytC)
Nature Methods, 5, 881-887 (2008)

JCP, 125, 174504 (2006)

CBr4JACS, 129, 13584-13591 (2007)

C12H10N2(Azobenzene)

Dimeric Hemoglobin (HbI)

Bacteriorhodopsin (bR)

[References]12345678910Ihee, H. Visualizing Solution-Phase Reaction Dynamics with Time-Resolved X-ray Liquidography. Acc.
Chem. Res. 42, 356-366 (2009).
Lee, J. H. et al. Capturing transient structures in the elimination reaction of haloalkane in solution bytransient X-ray diffraction. J. Am. Chem. Soc. 130, 5834-5835 (2008).
Cammarata, M. et al. Tracking the structural dynamics of proteins in solution using time-resolved wideangle X-ray scattering. Nat. Methods 5, 881-886 (2008).
Ihee, H. et al. Ultrafast X-ray diffraction of transient molecular structures in solution. Science 309, 12231227 (2005).
Ihee, H., Wulff, M., Kim, J. & Adachi, S. Ultrafast X-ray scattering: structural dynamics from diatomic toprotein molecules. Int. Rev. Phys. Chem. 29, 453-520 (2010).
Ihee, H. et al. Ultrafast x-ray diffraction of transient molecular structures in solution. Science 309, 12231227 (2005).
Ahn, S., Kim, K. H., Kim, Y., Kim, J. & Ihee, H. Protein Tertiary Structural Changes Visualized by TimeResolved X-ray Solution Scattering. J. Phys. Chem. B 113, 13131-13133 (2009).
Kim, K. H. et al. Direct observation of myoglobin structural dynamics from 100 picoseconds to 1
microsecond with picosecond X-ray solution scattering. Chem. Commun. 47, 289-291 (2011).
Kim, J. et al. Anisotropic Picosecond X-ray Solution Scattering from Photoselectively Aligned Protein
Molecules. J. Phys. Chem. Lett. 2, 350-356 (2011).
Kim, J., Kim, K. H., Lee, J. H. & Ihee, H. Ultrafast X-ray diffraction in liquid, solution and gas: presentstatus and future prospects. Acta Cryst. A 66, 270-280 (2010).