Unlocking the Secrets of Crystal Structure Prediction
The quest to predict crystal structures accurately has reached a pivotal moment, thanks to the groundbreaking work of researchers like Gregory Beran. In a recent study, Beran and his team have successfully modeled the complex crystal structures of axitinib, a pharmaceutical compound used in cancer treatment, and its various polymorphs and salt formations.
But why is this significant? Crystal structure prediction is a challenging field that has long puzzled scientists, especially when it comes to organic materials. Axitinib, a targeted therapy for renal cell carcinoma, can exist in multiple crystalline forms, or polymorphs, each with unique properties. This polymorphism complicates drug development, as different forms may have varying solubility and bioavailability.
Here's where it gets intriguing: Chemists initially favored form IV of axitinib, only to discover later that form XXV and eventually form XLI were more stable. Form XLI, the most thermodynamically stable, gained FDA approval in 2012. This journey highlights the importance of accurate crystal structure prediction in drug development.
Beran's approach combines hybrid density functional theory (DFT) modeling with intramolecular energy correction, a technique that has shown promise in overcoming the limitations of traditional DFT methods. By applying this strategy, Beran accurately predicted the crystal structures of axitinib and successfully distinguished between salt and co-crystals in multi-component systems, a task that has historically been difficult.
The study involved optimizing known crystal structures of axitinib and predicting various forms, including form IV with two independent molecules in its unit cell and multi-component crystals with different acids. Through a meticulous process of relaxation and refinement, Beran's team used advanced computational techniques to align their predictions closely with experimental data.
And this is the part most people miss: The crystal structure prediction revealed that the most stable form, form XLI, is indeed the global minimum structure at 0K. Moreover, it successfully differentiated between the axitinib salt and co-crystals, a feat that opens doors to predicting the crystallization behavior of various molecules.
Theoretical chemist Sarah Price emphasizes the potential impact of this work, suggesting a new methodology for predicting salt or co-crystal formation. While acknowledging the challenges, she highlights the exciting possibilities for future research.
Beran's work is a significant step forward, but he acknowledges that there's more to be done. The field of crystal structure prediction is evolving, and further advancements will undoubtedly shape the future of drug development and organic materials research.
