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. 2020 Jul 9;6(7):1755-1765.
doi: 10.1016/j.chempr.2020.04.009.

Encapsulated Nanodroplet Crystallization of Organic-Soluble Small Molecules

Andrew R Tyler  1 , Ronnie Ragbirsingh  1 , Charles J McMonagle  1 , Paul G Waddell  1 , Sarah E Heaps  2 , Jonathan W Steed  3 , Paul Thaw  4 , Michael J Hall  1 , Michael R Probert  1
Affiliations

Encapsulated Nanodroplet Crystallization of Organic-Soluble Small Molecules

Andrew R Tyler et al. Chem. .

Abstract

Single-crystal X-ray diffraction analysis (SCXRD) constitutes a universal approach for the elucidation of molecular structure and the study of crystalline forms. However, the discovery of viable crystallization conditions remains both experimentally challenging and resource intensive in both time and the quantity of analyte(s). We report a robot-assisted, high-throughput method for the crystallization of organic-soluble small molecules in which we employ only micrograms of analyte per experiment. This allows hundreds of crystallization conditions to be screened in parallel with minimal overall sample requirements. Crystals suitable for SCXRD are grown from nanoliter droplets of a solution of analyte in organic solvent(s), each of which is encapsulated within an inert oil to control the rate of solvent loss. This encapsulated nanodroplet crystallization methodology can also be used to search for new crystal forms, as exemplified through both our discovery of a new (13th) polymorph of the olanzapine precursor ROY and SCXRD analysis of the "uncrystallizable" agrochemical dithianon.

Keywords: ENaCt; ROY; X-ray diffraction; crystallization; dithianon; high-throughput; oil encapsulation; polymorph; single crystal; small molecule.

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Conflict of interest statement

A.R.T., M.J.H., and M.R.P. have filed a patent application based on this work: GB1908349.2.

Figures

None
Graphical abstract
Figure 1
Figure 1
Cross-Section Schematic of an ENaCt Experiment (Top) and ENaCt Experiment with 200 nL Mineral Oil and 50 mg/mL ROY in DMSO (Bottom). (1) Viscous inert oil dispensed onto a well of a 96-well glass plate, (2) solution of analyte in organic solvent injected into an oil droplet, (3) evaporative solvent loss to supersaturation, (4) nucleation, and (5) crystal growth. (A) solution of solvated analyte under oil, (B) evaporative solvent loss to supersaturation, (C) onset of crystal growth, and (D) complete crystallization.
Figure 2
Figure 2
Encapsulated versus Non-encapsulated Nanodroplet Crystallizations (A) Crystallization conditions for analytes 1–5 dissolved in organic solvents (acetone, ethyl acetate, ethanol, 1,2-dichoroethane, dimethylformamide, or dimethyl sulfoxide) with and without oil encapsulation (FC-40 or PDMSO). (1) Red: sample remains in solution; (2) orange: phase separation from solution and no solid; (3) yellow: amorphous or micro-crystalline solids; (4) light green: small single crystal(s); (5) dark green: large single crystal(s). (B) Representative experimental outcomes (1–5) shown with BODIPY (3) for ease of visualization.
Figure 3
Figure 3
Molecular Structures, Electron Density Maps, and Refined Crystallographic Molecular Models Derived from SCXRD Analysis of Single Crystals of Compounds 1–5 Formed via the ENaCt Protocol Each structure is provided with selected crystallographic information.
Figure 4
Figure 4
Molecular Structures, Crystal Growth Images, and SCXRD Data for Existing (Y, ON, ORP, and R) and New (R18) Polymorphs of ROY (6)
Figure 5
Figure 5
Molecular Structure, Crystal Growth Image, and SCXRD Data for Dithianon (7), Polymorph 1, Including Selected Crystallographic Information and ENaCt Crystal Growth Conditions
See this image and copyright information in PMC

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