Brief Introduction of MicroED

Using dynamical refinement, MicroED enables rapid determination of the absolute configuration of chiral small molecules. Biortus has successfully determined the absolute configurations of over 100 chiral small molecules via dynamical refinement or chiral reference methods.

When deriving 2D structures of small molecules using NMR or MS, uncertainties often arise. MicroED is able to conveniently resolves these ambiguities by providing crystal structures.

MicroED is ideal for “non-destructive” crystal form identification (direct testing of powder sample without single-crystal growth). Key applications include hydrate/solvate identification, salt/co-crystal differentiation, and metastable polymorph identification. MicroED delivers crystal structure similar to single-crystal X-ray diffraction methods while avoiding further crystallization.

MicroED excels at analyzing microcrystalline mixtures. It enables direct identification of API crystal form in formulations without re-crystallization or additional processing. Even for mixed polymorphs, all crystal forms can be resolved. In this case, Biortus completed the crystal structure determination of Ixazomib citrate API within 1 day.

During crystal form identification, subtle differences may sometimes be observed in the powder X - ray diffraction (XRPD) patterns of two batches obtained under different conditions. Apart from differences caused by crystal form variations, XRPD patterns can also be influenced by factors such as sample crystallinity, defects, preferred orientation due to particle morphology, and potential impurities. These factors can make it challenging to determine whether the two batches belong to the same crystal form. In such cases, MicroED is able to significantly reduce the difficulty of crystal form identification. MicroED can separately obtain crystal structure information for the main phase or impurities in both batches, including unit cell parameters, space group, atomic types, and coordinates within the unit cell. Based on that information, we can directly compare the crystal structure of the two batches. Additionally, we can simulate XRPD patterns from the respective MicroED structures to further validate the results.

Key Advantages: Direct crystal structure determination; no need for component isolation; requires only milligrams of sample; impurities as low as 0.1% can be identified via crystal morphology or diffraction patterns.
For crystallized impurities: Direct MicroED analysis is feasible.
For poorly crystalline components: High-throughput micro-crystallization can rapidly generate better microcrystals for MicroED testing.

PROTAC molecules typically have large molecular weights (~1000 Da) and high flexibility. Biortus has successfully determined structures for nearly 30 PROTAC molecules using MicroED.

Similar to single-crystal X-ray diffraction, the relative configuration of chiral molecules (with multiple chiral centers) can be obtained directly from MicroED structures. If a molecule contains a known chiral center, this serves as an internal reference to deduce the absolute configuration of other chiral centers. For molecules without known chiral centers, co-crystallization with a chiral ligand of known configuration enables absolute configuration determination.

MicroED is also applicable to materials like zeolites, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). Biortus has provided MicroED services to academic institutions, supporting crystal structure determination for publications.