Advantages of time-resolved difference X-ray solution scattering curves in analyzing solute molecular structure

Abstract

Time-resolved X-ray solution scattering provides a powerful method for investigating reaction dynamics in the solution phase. Since X-rays scatter from all atoms in the solution sample, the scattering intensity is contributed from not only the solute but also the solvent and the solute-solvent cross terms. For a typical concentration the solvent molecules outnumber the solute molecules and thus the relative sensitivity of the scattering intensity to the solute structure is extremely low. To increase the structural sensitivity to the solute and to extract only the signal from structural changes, timeresolved difference scattering signal is obtained by subtracting the original raw scattering curve at a negative reference time delay from that at a positive time delay.Here we show and emphasize that time-resolved difference X-ray scattering curves generally exhibit higher structural sensitivity to the solute molecular structure and lower influence from experimental background and imperfection of theory than original raw scattering curves. These characteristics justify the validity of fitting models to difference curves to obtain transient structural information even when the magnitude of the time-resolved difference curves is smaller than the discrepancy between the theory and experiment for the original scattering curve. We considered small molecules and proteins in solution probed by timeresolved X-ray solution scattering.

Tracking reaction dynamics in solution by pump–probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering)

“…105,106,110,137 3.2 Application of TRXL TRXL has been used to capture the molecular structures of transient intermediates and their spatiotemporal kinetics for various photochemical processes. The molecular systems studied by TRXL spans from small molecules [79][80][81][82]84,85,[87][88][89]92,93,98,99,[105][106][107][110][111][112]114,115,128,[130][131][132][133]136,140 to organometallic complexes, 97,103,104,109,113,116,119,124,141 nanoparticles, 83,86,90,91,94,95,100,120,…”

Transient isomers in the photodissociation of bromoiodomethane

“…One way to resolve the molecular structural rearrangements and intermediate states during a photochemical reaction is to use Time-Resolved Wide Angle X-ray Scattering (TR-WAXS) [1][2][3][4][5][6] which has emerged as a powerful technique for observing the structure and kinetics of transient photochemical a) Electronic mail: moreno.marcellini@yahoo.it b) Electronic mail: jan.davidsson@kemi.uu.se intermediates in solution, from small molecules containing some heavier atoms to biological macromolecules. For example, the kinetics of the photo-initiated reactions have been studied for HgI 2 in methanol, 7 CHI 3 in methanol 8 and cyclohexane, 9 CBr 4 in methanol, 10 CH 2 I 2 in methanol and in cyclohexane, 11,12 I 2 in CCl 4 [13][14][15] and in methanol, 16 Br 2 in CCl 4 , 17 and I 3 − in methanol, water, and acetonitrile.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 21, 2010) and the discipline

“…Lee and Ihee [20] used time-resolved X-ray solution scattering for determining structures of small molecules and proteins in solution. The difference scattering curves generally exhibit much higher structural sensitivity to the solute structure than the original scattering curves.…”