title: Structure and adsorption properties of commercial calcium phosphate adjuvant.
abstract: Calcium phosphate adjuvant is a commercially available vaccine adjuvant that potentiates the immune response to antigens. Although its name suggests that it is Ca3(PO4)2, X-ray diffraction, FTIR spectroscopy, thermal analysis and the Ca/P molar ratio identify commercial calcium phosphate adjuvant as non-stoichiometric hydroxyapatite, Ca10-x (HPO4)x (PO4)6-x (OH)2-x, where x varies from 0 to 2. The surface charge is pH-dependent (point of zero charge = 5.5). Consequently, commercial calcium phosphate adjuvant exhibits a negative surface charge at physiological pH and electrostatically adsorbs positively charged antigens. The presence of hydroxyls allows calcium phosphate adjuvant to adsorb phosphorylated antigens by ligand exchange with surface hydroxyls.
authors.affiliation: Department of Industrial and Physical Pharmacy, Purdue University, West Lafayette, IN 47907-2091, USA.
authors.forename: Dongping
authors.initials: D
authors.lastname: Jiang
authors.forename: Gnanasiri S
authors.initials: GS
authors.lastname: Premachandra
authors.forename: Cliff
authors.initials: C
authors.lastname: Johnston
authors.forename: Stanley L
authors.initials: SL
authors.lastname: Hem
mesh_terms: D000276:Adjuvants, Immunologic / Q000737:chemistry* / Q000493:pharmacokinetics / Q000494:pharmacology; D000327:Adsorption; D002130:Calcium Phosphates / Q000737:chemistry* / Q000493:pharmacokinetics / Q000494:pharmacology; D004055:Differential Thermal Analysis; D017886:Durapatite / Q000737:chemistry; D004563:Electrochemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D000276:Adjuvants, Immunologic; D002130:Calcium Phosphates; D017665:Hydroxyl Radical; D017886:Durapatite; C020243:calcium phosphate