title: Transport properties and association behaviour of the zwitterionic drug 5-aminolevulinic acid in water. A precision conductometric study.
abstract: The behavior of the hydrochloride salt of 5-aminolevulinic acid (ALA-HCl) with respect to transport properties and dissociation in aqueous solution at 25 degrees C has been studied using precision conductometry within the concentration range 0.24-5.17mM. The conductivity data are interpreted according to elaborated conductance theory. The carboxyl group appears to be, in practice, undissociated. The dissociation constant, K(a), of the NH(3)(+) form of the amino acid molecules is determined to 6.78x10(-5) (molarity scale); pK(a)=4.17. The limiting molar conductivity of the ALA-H(+) ion, lambda(0)=33.5cm(2)Omega(-1)mol(-1); electric mobility u=3.47x10(-4)cm(2)V(-1)s(-1), is close to the electric mobilites of the acetate and benzoic ions.
authors.affiliation: Department of Pharmacy, Physical Pharmaceutical Chemistry, Uppsala Biomedical Centre, Uppsala University, P.O. Box 580, SE-751 23, Uppsala, Sweden. nadia.merclin@farmaci.uu.se
authors.forename: Nadia
authors.initials: N
authors.lastname: Merclin
authors.forename: Per
authors.initials: P
authors.lastname: Beronius
mesh_terms: D000622:Aminolevulinic Acid / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003217:Conductometry / Q000295:instrumentation / Q000379:methods; D019999:Pharmaceutical Solutions; D017319:Photosensitizing Agents / Q000737:chemistry*; D012995:Solubility; D012997:Solvents; D013696:Temperature; D014867:Water
chemical_list: D019999:Pharmaceutical Solutions; D017319:Photosensitizing Agents; D012997:Solvents; D014867:Water; D000622:Aminolevulinic Acid