Solubility of doxycycline in aqueous solution
Related Experiment Video
Updated: Sep 6, 2026

Preparation and Characterization of Lipophilic Doxorubicin Pro-drug Micelles
Published on: August 2, 2016
Abstract:
The solubility of doxycyline monohydrate and doxycycline hydrochloride dihydrate was investigated in aqueous solution. The hydrochloride dihydrate salt was isolated and identified from solutions initially containing doxycycline hyclate in water. The pKa' = 3.09 (mu = 0.1 and 25 degrees) for protonation of doxycycline was determined spectrophotometrically. The pH-solubility profiles were determined for doxycycline monohydrate in water and in 1.0 M NaNO3-HNO3 and NaCl-HCl. The pH-solubility profile at 25 degrees for doxycycline in aqueous hydrochloric acid without added salt reached a sharp maximum fo 50 mg/ml at pH 2.16. Added chloride ion strongly suppressed the solubility of the hydrochloride dihydrate salt. The apparent solubility product was not constant but decreased as the concentration of added salt increased. A theoretical model was developed involving dimerization of doxycycline and applied to the experimental data. The dimerization constant, Kd = 24 M-1, and true solubility product, K0sp = 1.8 X 10(-3) M2, were calculated. The effect of concentration on NMR and visible spectra indicated that dimerization resulted from intermolecular hydrogen bonding of the phenolic beta-diketone portion of the molecule.
Related Concept Videos
Factors Affecting Solubility
Solubility
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules, atoms, and/or ions)...
Factors Influencing Drug Absorption: Drug Dissolution
Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism
Some polymorphic crystals possess lower aqueous solubility than their amorphous counterparts, leading to incomplete absorption. For instance, the oral suspension of Chloramphenicol, which...
Factors Affecting Dissolution: Drug pKa, Lipophilicity and GI pH
A drug's pKa and the pH of the gastrointestinal (GI) tract play crucial roles in drug...
Factors Affecting Dissolution: Drug Permeability, Stability and Stereochemistry

