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Related Experiment Video

Updated: Jan 5, 2026

PCR Mutagenesis, Cloning, Expression, Fast Protein Purification Protocols and Crystallization of the Wild Type and Mutant Forms of Tryptophan Synthase
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Polymorphism of l-Tryptophan.

Okba Al Rahal1, Colan E Hughes1, P Andrew Williams1

  • 1School of Chemistry, Cardiff University, Park Place, Cardiff, Wales, CF10 3AT, UK.

Angewandte Chemie (International Ed. in English)
|October 18, 2019
PubMed
Summary

Researchers discovered a new crystal form of l-tryptophan (β polymorph) using gas-phase crystallization. This form features unique hydrogen-bonding, offering new insights into amino acid crystal structures.

Keywords:
crystallizationl-tryptophanpolymorphismpowder XRDsolid-state NMR

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Area of Science:

  • Crystallography
  • Solid-state chemistry
  • Computational chemistry

Background:

  • Polymorphism is crucial for understanding drug efficacy and stability.
  • L-tryptophan, an essential amino acid, exhibits complex crystal structures.
  • Previous studies identified an alpha (α) polymorph of l-tryptophan.

Purpose of the Study:

  • To prepare and characterize a new polymorph of l-tryptophan.
  • To elucidate the crystal structure and hydrogen-bonding patterns of the new polymorph.
  • To compare the structural features of the new polymorph with the known α polymorph.

Main Methods:

  • Crystallization of l-tryptophan from the gas phase.
  • Powder X-ray diffraction (XRD) for structure determination.
  • Periodic Density Functional Theory with Dispersion (DFT-D) calculations for structural analysis and energy calculations.

Main Results:

  • A new polymorph of l-tryptophan (β polymorph) was successfully prepared.
  • The β polymorph and α polymorph share layered structures but differ in hydrogen-bonding arrangements.
  • The β polymorph exhibits an unprecedented l2-l2 hydrogen-bonding pattern for aromatic amino acids, facilitated by specific molecular conformations that avoid steric hindrance.

Conclusions:

  • The discovery of the β polymorph expands the known polymorphic landscape of l-tryptophan.
  • The unique hydrogen-bonding in the β polymorph provides new insights into molecular interactions in amino acid crystals.
  • This study highlights the importance of exploring diverse crystallization methods for uncovering novel solid forms.