Solid Tryptophan as a Pseudoracemate: Physicochemical and Crystallographic Characterization

Abstract

The crystalline nature of solid tryptophan has been characterized by X-ray single crystal and powder diffraction analyses, differential scanning calorimetry, as well as measurement of solid-liquid equilibrium in water/isopropanol solution. Both the thermodynamic and crystallographic investigations have demonstrated unambiguously that solid tryptophan crystallizes in the form of a pseudoracemate (i.e., solid solution) with maximum melting over the entire enantiomeric composition range. Comparative single-crystal X-ray studies show that the crystal structures of racemic and enantiomeric tryptophan give very similar solid-state packing geometries dictated by hydrogen bonding interactions. Our results indicate that the insignificant difference between homochiral and heterochiral interactions accounts for the formation of a pseudoracemate for this system.

A Maze of Solid Solutions of Pimobendan Enantiomers: An Extraordinary Case of Polymorph and Solvate Diversity

“…The liquidus and solidus ofδ form a convex dome, which indicates a slightly lower stability of the racemic composition phase. The observed convex behavior is not typical for solid solutions showing miscibility around the racemic composition as mostly concave behavior is reported. ,,,,,,− …”

Multifaceted core–shell nanoparticles: superparamagnetism and biocompatibility

“…4C. 37 The peaks for Trp were present in the Ni core Au shell XRD pattern which were overlooked by the highly intense peaks of Au(111), Au(200) and Au(220) planes of fcc Au, Curve 2, Fig. 4C.…”

Cooperative Kinetic Model to Describe Crystallization in Solid Solution Forming Systems

“…The separation is much more challenging when solid solutions are formed, which occurs for components with miscibility in the solid phase. Though mixtures of chiral organic compounds rarely exhibit continuous solid solutions, partial solid solutions are reported to occur relatively often. − The separation of such mixtures requires multistage crystallization, in which the target compound can be enriched either in the solid or in the liquid phase, depending on the solubility properties of the mixture. Multistage crystallization in solid solution forming systems has been described in several studies, − in which the process design was based on the solid–liquid equilibrium (SLE) data.…”