title: The crystal structure and physicochemical characteristics of 2-hydroxy-N-[3(5)-pyrazolyl]-1,4-naphthoquinone-4-imine, a new antitrypanosomal compound.
abstract: This study was designed to investigate the physical characteristics and crystalline structure of 2-hydroxy-N-[3(5)-pyrazolyl]-1,4-naphthoquinone-4-imine (PNQ), a new active compound against Trypanosoma cruzi, the causative agent of American trypanosomiasis. Methods used included differential scanning calorimetry, thermogravimetry, hot stage microscopy, polarized light microscopy (PLM), Fourier-transform infrared (FTIR) spectroscopy, and high-resolution X-ray powder diffraction (HR-XRPD). According to PLM and HR-XRPD data, PNQ crystallized as red oolitic crystals (absolute methanol) or prisms (dimethyl sulfoxide [DMSO]-water) with the same internal structure. The findings obtained with HR-XRPD data (applying molecular location methods) showed a monoclinic unit cell [a = 18.4437(1) A, b = 3.9968(2) A, c = 14.5304(1) A, alpha = 90 degrees , beta = 102.71(6) degrees , gamma = 90 degrees , V = 1044.9(1) A(3), Z = 4, space group P2(1)/c], and a crystal structure (excluding H-positions) described by parallel layers in the direction of the b-axis, with molecules held by homochemical (phenyl-phenyl and pyrazole-pyrazole) van der Waals interactions. In addition, FTIR spectra displayed the NH-pyrazole stretch overlapped with the OH absorption at 3222 cm(-1), typical of -NH and -OH groups associated through H-bondings; and a carbonyl stretching absorption at 1694 cm(-1), indicating a nonextensively H-bonded quinonic C=O, which was in accordance with the solved crystal structure of PNQ. The existence of such cohesive forces shed light on the thermoanalytical data, which revealed that PNQ is a stable solid, unaffected by oxygen that decomposed without melting above 260 degrees C.
authors.affiliation: Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, 5000- Córdoba, Argentina. nrscor@dqo.fcq.unc.edu.ar
authors.forename: Norma R
authors.initials: NR
authors.lastname: Sperandeo
authors.forename: Alicia
authors.initials: A
authors.lastname: Karlsson
authors.forename: Silvia
authors.initials: S
authors.lastname: Cuffini
authors.forename: Silvina
authors.initials: S
authors.lastname: Pagola
authors.forename: Peter W
authors.initials: PW
authors.lastname: Stephens
mesh_terms: D000981:Antiprotozoal Agents / Q000032:analysis / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D007097:Imines / Q000032:analysis / Q000737:chemistry*; D009285:Naphthoquinones / Q000032:analysis / Q000737:chemistry*
chemical_list: D000981:Antiprotozoal Agents; D007097:Imines; D009285:Naphthoquinones