The enthalpies of dilution of protocatechuic acid, a natural anti-cancer substance, in sodium phosphate and potassium phosphate buffer solutions with different pH values were measured by using a mixingflow microcalorimeter at T = 298.15 K. Densities of the pseudo binary system (phosphate buffer + protocatechuic acid) were also measured with a quartz vibrating-tube densimeter. The enthalpic interaction coefficients (h2, h3 and h4) were computed according to the McMillan Mayer model. Apparent molar volumes of the system were calculated from the data of densities, which have been used to deduce limiting partial molar volumes (V0 /) of protocatechuic acid at different pH values. The aim of the experiments and data process is to investigate the interaction between the molecules of the important drug and that of the drug molecule with coexistent species in aqueous solutions as well as the influences on these interactions of such factors as pH and ion strength. Change trends of the enthalpic pair wise interaction coefficient h2 and V0 / of protocatechuic acid with pH increasing in the both phosphate buffer solutions were obtained. The thermodynamic properties, h2 and V0 / in potassium phosphate buffer solutions were compared with those in sodium phosphate buffer solutions at identical pH. The trends and the differences have been discussed in terms of the (solute + solute) and (solute + solvent) interactions.
Compounds
#
Formula
Name
1
H2NaO4P
sodium dihydrogen phosphate
2
HNa2O4P
disodium hydrogen phosphate
3
H2KO4P
monopotassium phosphate
4
HK2O4P
dipotassium hydrogen phosphate
5
H2O
water
Datasets
The table above is generated from the ThermoML associated json file (link above).
POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied;
the numbers refer to the table of compounds on the left.