title: Crystal structure and packing energy calculations of (+)-6-aminopenicillanic acid.
abstract: The X-ray single-crystal structure of (2S,5R,6R)-6-amino-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid, commonly known as (+)-6-aminopenicillanic acid (C8H12N2O3S) and a precursor of a variety of semi-synthetic penicillins, has been determined from synchrotron data at 150 K. The structure represents an ordered zwitterion and the crystals are nonmerohedrally twinned. The crystal structure is composed of a three-dimensional network built by three charge-assisted hydrogen bonds between the ammonium and carboxylate groups. The complementary analysis of the crystal packing by the PIXEL method brings to light the nature and ranking of the energetically most stabilizing intermolecular interaction energies. In accordance with the zwitterionic nature of the structure, PIXEL lattice energy calculations confirm the predominance of the Coulombic term (-379.1 kJ mol(-1)) ahead of the polarization (-141.4 kJ mol(-1)), dispersion (-133.7 kJ mol(-1)) and repulsion (266.3 kJ mol(-1)) contributions.
authors.affiliation: Abteilung Kristallographie, GZG, Georg-August-Universität Göttingen, Goldschmidtstrasse 1, D-37077 Göttingen, Germany.
authors.forename: Sofiane
authors.initials: S
authors.lastname: Saouane
authors.forename: Gernot
authors.initials: G
authors.lastname: Buth
authors.forename: Francesca P A
authors.initials: FP
authors.lastname: Fabbiani
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010397:Penicillanic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D002264:Carboxylic Acids; D010397:Penicillanic Acid; C004408:aminopenicillanic acid
keywords: (+)-6-aminopenicillanic acid; PIXEL calculations; computational methods; crystal structure; semi-synthetic penicillin precursor; zwitterion structures