title: A 2:1 sulfamethazine-theophylline cocrystal exhibiting two tautomers of sulfamethazine.
abstract: In the title cocrystal, 4-amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide-4-amino-N-(4,6-dimethyl-1,2-dihydropyrimidin-2-ylidene)benzenesulfonamide-1,3-dimethyl-7H-purine-2,6-dione (1/1/1), C(7)H(8)N(4)O(2)·2C(12)H(14)N(4)O(2)S, two sulfamethazine molecules cocrystallize with a single molecule of theophylline. Each molecule of sulfamethazine forms a hydrogen-bonded ribbon along the b axis crosslinked by further hydrogen bonding. The two sulfamethazine molecules exhibit a hydrogen-shift isomerization so that the crystal structure contains both tautomeric forms. Calculation of their relative energies showed that the tautomer protonated at the chain N atom is considerably more stable than the one where an N atom in the aromatic ring is protonated. The latter, here observed for the first time, is stabilized through strong intermolecular interactions with the theophylline molecules.
authors.affiliation: School of Chemical and Material Engineering, Jiangnan University, Wuxi, People's Republic of China.
authors.forename: Jie
authors.initials: J
authors.lastname: Lu
authors.forename: Aurora J
authors.initials: AJ
authors.lastname: Cruz-Cabeza
authors.forename: Sohrab
authors.initials: S
authors.lastname: Rohani
authors.forename: Michael C
authors.initials: MC
authors.lastname: Jennings
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D015394:Molecular Structure; D013418:Sulfamethazine / Q000737:chemistry*; D013806:Theophylline / Q000737:chemistry*
chemical_list: D013418:Sulfamethazine; D013806:Theophylline