Physicochemical properties

Solubility

Determination of the solubility of the organic compound in selected solvents provides preliminary information on the nature of the tested compound. It is crucial information during the preclinical stage of development of the molecule- a potential drug. The use of selected set of solvents provides package of valuable information. It helps to make a preliminary assessment of the processes’ speed of absorption and excretion of potential drugs from the body.

Compound requirements 2.5 mg solid (for solubility assessment)
1 mg solid (for standard preparation)
Solvents water, diethyl ether, 5% aqueous NaOH solution, 5% aqueous NaHCO3 solution, 5% aqueous HCl solution, concentrated sulfuric acid, 85% phosphoric acid, 5% glucose solution, 0.9% NaCl solution
Number of Replicates n = 2 (aliquots from filtrate)
Incubation Time Overnight
Incubation Temperature Ambient temperature
Analysis method HPLC-UV-VIS, Spectrophotometric determination
Output data Solubility [mg/ml]

Chemical stability

The chemical stability assay enables to determinate degradation of compound in aqueous buffer by non-enzymatic processes (for example hydrolysis, oxidation or light-catalyzed degradation). Chemical stability of potential drugs is crucial because compounds that are highly unstable may not be suitable as drug candidates due to difficulties in maintenance of a therapeutically effective formulation. In addition compounds designed for oral administration must exhibit chemical stability at the low pH. A range of different pH values are available.

Test Compound Concentration 1 μM
DMSO Concentration 0.33%
Time Points 0, 5, 15, 30, 45, 120 min
Number of Replicates 2
Incubation Plate Material PTFE (all time points) and polypropylene (2 h only)
Compound Requirements 50 µL of 10 mM solution
Analysis Method LC-MS/MS
Output data % Parent compound remaining at each time point
% Parent compound to polypropylene compared to PTFE

Partition coefficient, distribution coefficient

The partition coefficient between the immiscible organic and aqueous phase (typically n-octanol and water) for a pharmaceutical composition is determined by extraction technique.

Analytical methods for measuring the concentration of the solute in both phases are selected on the basis of the physicochemical properties of an investigated molecule (usually a UV-VIS spectrometry is used). Organic compounds with very low solubility in aqueous solutions have often biological activity. For those compounds we propose an innovative method for determining the value of the partition coefficient using chromatographic techniques (without prior extraction from the water to the organic phase).

Method Miniaturised shake flask method
Partition Solvent n-Octanol
Ratio of Buffer:Octanol 50:1, 5:1, 1:2 (v/v)
Positive Control Compounds Acebutolol, Ketoconazole
Compound Requirements 1 mg solid compound
Analysis Method UV-VIS or HPLC-UV-VIS
Output data LogP, Log D7.4

pKa determination

The ability of the molecule to dissociate in physiological environment of living cell is very important for specificity of drug biological activity. An acid dissociation constant (also known as acidity constant, or acid-ionization constant) – Ka describes this ability of the compound. The ionization of the molecule affects the absorbance value and on the UV-VIS spectrum shape.

Method pH-metric titration or spectrophotometric methods
Compound Requirements 1 mg solid compound
Output data pKa