TY - JOUR

T1 - Crystallization caught in the act with terahertz spectroscopy: non-classical pathway for L-(+)-tartaric acid.

AU - Soltani, A

AU - Gebauer, D

AU - Duschek, L

AU - Fischer, B

AU - Cölfen, H

AU - Koch, M

N1 - Funding information: We thank Prof. Desiraju for careful discussion about the THz results and commenting the manuscript. We thank Rose Rosen-berg, Johanna Scheck, and Masoud Farhadi-Khouzani for the AUC measurements and evaluation, and experimental assistance with WAXS and IR measurements, respectively. A.S. acknowledges funding from the German Academic Exchange Service (DAAD). D.G. thanks the Zukunftkolleg of the University of Konstanz for financial support.

PY - 2017/10/12

Y1 - 2017/10/12

N2 - Crystal formation is a highly debated problem. This report shows that the crystallization of l-(+)-tartaric acid from water follows a non-classical path involving intermediate hydrated states. Analytical ultracentrifugation indicates solution clusters of the initial stages aggregate to form an early intermediate. Terahertz spectroscopy performed during water evaporation highlights a transient increase in the absorption during nucleation; this indicates the recurrence of water molecules that are expelled from the intermediate phase. Besides, a transient resonance at 750 GHz, which can be assigned to a natural vibration of large hydrated aggregates, vanishes after the final crystal has formed. Furthermore, THz data reveal the vibration of nanosized clusters in the dilute solution indicated by analytical ultracentrifugation. Infrared spectroscopy and wide-angle X-ray scattering highlight that the intermediate is not a crystalline hydrate. These results demonstrate that nanoscopic intermediate units assemble to form the first solvent-free crystalline nuclei upon dehydration.

AB - Crystal formation is a highly debated problem. This report shows that the crystallization of l-(+)-tartaric acid from water follows a non-classical path involving intermediate hydrated states. Analytical ultracentrifugation indicates solution clusters of the initial stages aggregate to form an early intermediate. Terahertz spectroscopy performed during water evaporation highlights a transient increase in the absorption during nucleation; this indicates the recurrence of water molecules that are expelled from the intermediate phase. Besides, a transient resonance at 750 GHz, which can be assigned to a natural vibration of large hydrated aggregates, vanishes after the final crystal has formed. Furthermore, THz data reveal the vibration of nanosized clusters in the dilute solution indicated by analytical ultracentrifugation. Infrared spectroscopy and wide-angle X-ray scattering highlight that the intermediate is not a crystalline hydrate. These results demonstrate that nanoscopic intermediate units assemble to form the first solvent-free crystalline nuclei upon dehydration.

KW - THz spectroscopy

KW - cluster compounds

KW - crystallization process

KW - l-(+)-tartaric acid

KW - non-classical nucleation

UR - http://www.scopus.com/inward/record.url?scp=85028965724&partnerID=8YFLogxK

U2 - 10.1002/chem.201702218

DO - 10.1002/chem.201702218

M3 - Article

C2 - 28736825

VL - 23

SP - 14128

EP - 14132

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

SN - 0947-6539

IS - 57

ER -