title: Alendronate zwitterions bind to calcium cations arranged in columns.
abstract: Alendronate is used clinically in the treatment of skeletal disorders, the mode of action depending on the adsorption to calcium hydroxyapatite crystals (bone). In the title compound, calcium 4-ammonium-1-hydroxybutylidene-1,1-bisphosphonate, Ca(2+).2C(4)H(12)NO(7)P(2)(-), alendronate is a zwitterion, possessing one negative charge on each PO(3) group and a protonated N atom. The zwitterion is disposed with its negative end facing the Ca(2+) ion, while its positive end is stretched in the opposite direction. The geometry of the carbon chain is all-trans, while the hydroxy group is approximately gauche. The Ca(2+) ion lies on a twofold axis parallel to b. The coordination sphere around the metal cation is octahedral and is determined by monodentate- and bidentate-coordinated alendronate zwitterions. The O.O bite distance is 3.080 (2) A. Coordinated Ca(2+) metal cations are arranged at the centre of a column running along c.
authors.affiliation: Escuela de Ciencia y Tecnología, Universidad Nacional de General San Martín, Calle 91 3391, 1653 Villa Ballester, Buenos Aires, Argentina. fernande@tandar.cnea.gov.ar
authors.forename: Daniel
authors.initials: D
authors.lastname: Fernández
authors.forename: Daniel
authors.initials: D
authors.lastname: Vega
authors.forename: Andrés
authors.initials: A
authors.lastname: Goeta