In situ optical spectroscopy of crystallization: One crystal nucleation at a time

Abstract

Significance It is of fundamental importance to establish the microscopic picture of crystal nucleation for both academic and industrial research. Here, we report an in situ time-resolved Raman spectroscopy to study crystallization from solution, one crystal nucleation at a time. The observed dynamics of α-glycine crystallization from water without any additive supports the nonclassical nucleation pathway, where prenucleation aggregates form and convert to a crystal. By the direct comparison of Raman spectrum of the aggregates between the experiment and simulation, we propose the structure of these aggregates as linear hydrogen-bonded networks. We demonstrate the power of studying one nucleation event at a time, which can accelerate the investigation of crystal nucleation by optical spectroscopy.

Mesoscopic amorphous particles rather than oligomeric molecular aggregates are the cause of laser-induced crystal nucleation

“…1 ) in an aqueous glycine solution irradiated with a laser similar to that used by Urquidi et al. ( 1 ) and estimate a temperature rise of 400 K for a 1-W laser power, broadly consistent with the numerical estimation. Therefore, one can confidently conclude that irradiating a 100-μm sample of aqueous glycine with a 1-W 532-nm laser will lead to significant heating (up to and including boiling) and vigorous convection of the sample.…”

“…The authors correctly state that the optical gradient force is insufficient to trap single molecules ( 1 ). Therefore, it is proposed that the laser instead traps glycine–water aggregates.…”

“…Raman scattering is a weak process, and, in order to maximize time resolution and signal-to-noise, the authors employ a high-power laser (1 W/532 nm). It is stated that “the temperature of water at laser focus does not increase” ( 1 ). The absorption coefficient of water at 532 nm is 0.0447 m −1 ( 2 ), and using equation 20 of ref.…”

Molecular Mechanism of Organic Crystal Nucleation: A Perspective of Solution Chemistry and Polymorphism

“…Moreover, the application of state-of-art modern analytic techniques such as solution spectroscopy, neutron scattering, and high-resolution electron microscopy, has spurred significant advancement in the understanding of solution chemistry and (non)-classical nucleation pathway [32][33][34]. The structure, intermolecular interactions, and assembly mode of solution associates are revealed by collectively using ATR-FTIR, 1 H/ 13 C-NMR, and advanced DOSY or NOESY NMR spectroscopy in a number of small organic molecules [35][36][37].…”

Reply to Liao and Wynne: The size of crystal nucleus remains an open question

“… ( A ) Low-frequency Raman spectra measured on the setup described in Urquidi et al. ( 2 ). The detection part was modified using SureBlock XLF Notch filters (Coherent) to be able to measure the low-frequency region of Raman spectrum.…”