Amino acids readily form quasiracemic crystal structures that exhibit near centrosymmetric alignment of the components. These systems – generated from pairs of chemically unique amino acids of opposite handedness - provide important opportunities to understand how large structural differences between the quasienantiomeric components effect the self-assembly process. The systems D-Val/L-Phe and D-Val/L-Met offer important examples where the difference in the volume of the attached R-groups is greater than 30 Å<sup>3</sup>. These previous results are extensive and seem to suggest that quasiracemate formation occurs regardless of the apparent spatial properties of the side chain. While several examples of amino acids assembled with coformers exist in the literature, no systematic investigation has examined the structural impact of tailor-made additives on a wide variety of amino acids. This investigation examines the role of oxalic acid on the crystallization landscape of amino acid quasiracemates. Crystallographic assessment of these systems shows the oxalic acid components form molecular chains using O<sup>-…</sup>H-O contacts. These 1-D motifs in turn provide a robust scaffold for linking neighboring amino acids. The structural alignment of these assemblies arise from a complex blend of charge-assisted non-bonded contacts. This ionic framework generates significant crystal stabilization that can accommodate larger structural variations of amino acids than previously reported. The assessment of crystal structures, lattice energy calculations, and spectroscopic data offers important insight to the structural preferences of these materials.

Upsetting the cart of known amino acid quasiracemic crystalline phases

2019 Spring National Meeting

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