Crystal structure ofL-tryptophan–fumaric acid–water (1/1/1)

Abstract

In the title compound, C11H12N2O2·C4H4O4·H2O, the l-tryp­to­phan mol­ecule crystallized as a zwitterion, together with a neutral fumaric acid mol­ecule and a water solvent mol­ecule. In the crystal, the three components are linked by a series of N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds, forming slabs lying parallel to (001). The slabs are connected by O—H⋯O hydrogen bonds, involving inversion-related fumaric acid groups, leading to the formation of a three-dimensional structure.

Influence of the Local Chemical Environment in the Formation of Multicomponent Crystals of L-Tryptophan with N-Heterocyclic Carboxylic Acids: Unusual Formation of Double Zwitterions

“…The crystal structure of TRP-PA ( 1 ) was found to be interesting both chemically and crystallographically due to the nature of the amino acid and the coformer. The amino acid exists in the zwitterionic form in the structure which is consistent with some examples cited earlier. − The FTIR spectrum, however, clarified that the commercial TRP used in this study is inherently zwitterionic (Figure S4). Further, careful inspection of the Fourier difference maps also revealed that there is an intramolecular proton transfer from the −COOH group of PA to the pyridine N atom, resulting in a zwitterion form of the PA.…”

“…However, despite the possibilities of all these interactions, supramolecular host–guest complexes of tryptophan are limited. A recent study reported that there are 12 structures with zwitterionic tryptophan: nine of them of TRP, one of d -tryptophan with naproxen, and the remaining two are of pure dl -tryptophan. − Additionally, the number of structures with cationic TRP is also limited. − The indole ring of TRP is usually difficult to ionize, and only strong acids or bases can protonate or deprotonate the ring. Thus, the reactivity of the amino acid is mainly dependent on the −COOH and −NH 2 group.…”