title: Salt screening and characterization of ciprofloxacin.
abstract: With the aim of improving the solubility of ciprofloxacin, polybasic organic acids were utilized to react with ciprofloxacin in different stoichiometric proportions. The use of the solvent drop grinding (SDG) method, as well as the solvent evaporation method, resulted in the crystalline salts ciprofloxacin/fumaric acid (1:1, 2:1), ciprofloxacin/maleic acid (1:1) and ciprofloxacin/citric acid (2:1). The solubilities of these salts in pure water (pH 7.0) were determined using high-performance liquid chromatography (HPLC) at 310 K, with the salts showing considerably greater solubility than ciprofloxacin itself and, interestingly, ciprofloxacin/fumaric acid (2:1) being more soluble than ciprofloxacin/fumaric acid (1:1). Intrigued by this phenomenon, we undertook a comparison of the crystal structures of the salts: the three-dimensional sandwich-like structure observed in the 2:1 salt indicates that the preferred stacking may be a factor in increasing the solubility of ciprofloxacin.
authors.affiliation: Beijing City Key Laboratory of Polymorphic Drugs, Center of Pharmaceutical Polymorphs, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People's Republic of China.
authors.forename: Guoshun
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Beijing City Key Laboratory of Polymorphic Drugs, Center of Pharmaceutical Polymorphs, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Beijing City Key Laboratory of Polymorphic Drugs, Center of Pharmaceutical Polymorphs, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People's Republic of China.
authors.forename: Dezhi
authors.initials: D
authors.lastname: Yang
authors.affiliation: National Institutes for Food and Drug Control, Beijing 100050, People's Republic of China.
authors.forename: Na
authors.initials: N
authors.lastname: Zhang
authors.affiliation: National Institutes for Food and Drug Control, Beijing 100050, People's Republic of China.
authors.forename: Lan
authors.initials: L
authors.lastname: He
authors.affiliation: Beijing City Key Laboratory of Drug Target and Screening Research, National Center for Pharmaceutical Screening, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People's Republic of China.
authors.forename: Guanhua
authors.initials: G
authors.lastname: Du
authors.affiliation: Beijing City Key Laboratory of Polymorphic Drugs, Center of Pharmaceutical Polymorphs, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People's Republic of China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Lu
mesh_terms: D002152:Calorimetry, Differential Scanning; D002939:Ciprofloxacin / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry*; D005650:Fumarates / Q000737:chemistry*; D008298:Maleates / Q000737:chemistry*; D009930:Organic Chemicals; D012965:Sodium Chloride / Q000737:chemistry*; D012995:Solubility
chemical_list: D005650:Fumarates; D008298:Maleates; D009930:Organic Chemicals; D019343:Citric Acid; D012965:Sodium Chloride; D002939:Ciprofloxacin; C032005:fumaric acid; C030272:maleic acid
keywords: APIs; ciprofloxacin; salt screening; solubility; solvent drop grinding; solvent evaporation method