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Guillén M, Mora AJ, Belandria LM, Seijas LE, Ramírez JW, Burgos JL, Rincón L, Delgado GE. Two conformational polymorphs of 4-methylhippuric acid. ACTA CRYSTALLOGRAPHICA SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS 2020; 76:1077-1091. [PMID: 33289719 DOI: 10.1107/s2052520620013773] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Accepted: 10/14/2020] [Indexed: 06/12/2023]
Abstract
4-Methylhippuric acid {systematic name: 2-[(4-methylbenzoyl)amino]ethanoic acid}, a p-xylene excreted metabolite with a backbone containing three rotatable bonds (R-bonds), is likely to produce more than one stable molecular structure in the solid state. In this work, we prepared polymorph I by slow solvent evaporation (plates with Z' = 1) and polymorph II by mechanical grinding (plates with Z' = 2). Potential energy surface (PES) analysis, rotating the molecule about the C-C-N-C torsion angle, shows four conformational energy basins. The second basin, with torsion angles near -73°, agree with the conformations adopted by polymorph I and molecules A of polymorph II, and the third basin at 57° matched molecules B of polymorph II. The energy barrier between these basins is 27.5 kJ mol-1. Superposition of the molecules of polymorphs I and II rendered a maximum r.m.s. deviation of 0.398 Å. Polymorphs I and II are therefore true conformational polymorphs. The crystal packing of polymorph I consists of C(5) chains linked by N-H...O interactions along the a axis and C(7) chains linked by O-H...O interactions along the b axis. In polymorph II, two molecules (A with A or B with B) are connected by two acid-amide O-H...O interactions rendering R22(14) centrosymmetric dimers. These dimers alternate to pile up along the b axis linked by N-H...O interactions. A Hirshfeld surface analysis localized weaker noncovalent interactions, C-H...O and C-H...π, with contact distances close to the sum of the van der Waals radii. Electron density at a local level using the Quantum Theory of Atoms in Molecules (QTAIM) and the Electron Localization Function (ELF), or a semi-local level using noncovalent interactions, was used to rank interactions. Strong closed shell interactions in classical O-H...O and N-H...O hydrogen bonds have electron density highly localized on bond critical points. Weaker delocalized electron density is seen around the p-methylphenyl rings associated with dispersive C-H...π and H...H interactions.
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Affiliation(s)
- Marilia Guillén
- Laboratorio de Cristalografía, Departamento de Química. Facultad de Ciencias, Universidad de Los Andes, Mérida, 5101, Venezuela
| | - Asiloé J Mora
- Laboratorio de Cristalografía, Departamento de Química. Facultad de Ciencias, Universidad de Los Andes, Mérida, 5101, Venezuela
| | - Lusbely M Belandria
- Laboratorio de Cristalografía, Departamento de Química. Facultad de Ciencias, Universidad de Los Andes, Mérida, 5101, Venezuela
| | - Luis E Seijas
- Laboratorio de Procesos Dinámicos, Departamento de Química, Facultad de Ciencias, Universidad de Los Andes, Mérida, 5101, Venezuela
| | - Jeans W Ramírez
- Laboratorio de Cristalografía, Departamento de Química. Facultad de Ciencias, Universidad de Los Andes, Mérida, 5101, Venezuela
| | - José L Burgos
- Grupo de Investigaciones en Física, Escuela de Física y Matemática, Facultad de Ciencias, Escuela Superior Politécnica de Chimborazo, Riobamba, EC060155, Ecuador
| | - Luis Rincón
- Grupo de Química Computacional y Teórica, Departamento de Ingeniería Química, Universidad San Francisco de Quito, Quito, 17-1200-841, Ecuador
| | - Gerzon E Delgado
- Laboratorio de Cristalografía, Departamento de Química. Facultad de Ciencias, Universidad de Los Andes, Mérida, 5101, Venezuela
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