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X-ray Raman scattering: a new in situ probe of molecular structure during nucleation and crystallization from liquid solutions

DOI: 10.1039/C8CE00929E DOI Help

Authors: Laila H. Al-madhagi (University of Leeds; Diamond Light Source) , Sin-yuen Chang (Diamond Light Source) , Mahalingam Balasubramanian (Advanced Photon Source, Argonne National Laboratory) , Anna B. Kroner (Diamond Light Source) , Elizabeth Shotton (Diamond Light Source) , Elizabeth A. Willneff (University of Leeds) , Bhoopesh Mishra (University of Leeds; Illinois Institute of Technology) , Sven L. M. Schroeder (University of Leeds; Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Crystengcomm , VOL 52

State: Published (Approved)
Published: September 2018

Open Access Open Access

Abstract: X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization. The C and N K-edges of aqueous imidazole were measured as a function of temperature to monitor the transition from the undersaturated state through supersaturation to crystallization. A new jacketed-vessel crystallizer with internal flow was used, which enables thermal control and minimizes radiation damage. We have demonstrated that the C and N K-edges of imidazole are sensitive to changes in local bonding. In line with this, an abrupt change in the N K-edge fine structure indicates the onset of desolvation and crystallization from the supersaturated solution. In contrast, negligible changes are observed in the C and N K-edge spectra acquired during cooling, indicating that the average solvation structure around imidazole molecules does not change significantly while traversing the thermodynamically metastable supersaturated zone. To the best of our knowledge this is the first time X-ray Raman scattering has been used for studying molecular speciation in organic aqueous solutions during crystallization. Time-dependent density functional theory (TD-DFT) calculations of the near-edge spectra were performed using implicit, explicit and combined solvation models to elucidate the likely binding sites of the water molecules. An explicit solvation model with one water molecule coordinating each nitrogen moiety in the imidazole ring accurately reproduces the peak positions and intensities of the XRS spectra of aqueous imidazole solution.

Subject Areas: Chemistry

Facility: Advanced Photon Source