Intermolecular interactions of α-amino acids and glycyl dipeptides with the drug domiphen bromide in aqueous solutions analyzed by volumetric and UV–vis spectroscopy methods

• Volumetric and UV–vis spectroscopy of amino acids/dipeptides + DB + water mixtures.
• The ion-ion/polar interactions between DB and amino acids/dipeptides are dominant.
• Partial molar volumes of many groups of amino acids/dipeptides were calculated.
• The affinity between solute and DB depends on the alkyl chain length of solute.

The interactions of four α-amino acids and three glycyl dipeptides with drug domiphen bromide (DB) as the function of temperature and DB molality have been investigated by combination of volumetric and UV–vis spectroscopy methods. The standard partial molar volume (V2,ϕ∘), standard partial molar transfer volumes (ΔtVo), hydration number (nH), partial molar expansibility (Eϕ∘) and Hepler’s factor (∂2V2,ϕ∘/∂T2)p are calculated from the density data. The above parameters are used to interpret the solute-solvent interactions in ternary systems. The dependence of these parameters upon concentration, temperature and hydrocarbon chain length of the amino acids/dipeptides clearly suggest the roles of amino acids/dipeptides and domiphen bromide in solute-solvent interactions. Group contributions of amino acids/dipeptides to the standard partial molar volume were determined. For the studied glycyl dipeptides standard partial molar volume can be expressed by those of the corresponding amino acids in terms of an additivity scheme. The absorption spectra have also been recorded for present mixtures with the help of UV–vis spectrophotometer. The binding constant between amino acids/dipeptides and domiphen bromide was determined.

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