Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The densities ( I), viscosities ( A) and 1H nuclear magnetic resonance (NMR) studies for caffeine, theophylline and theobromine in water and in aqueous solutions of 0.10, 0.25, 0.50, 0.75 and 1.00 mol Ekg-1 sodium chloride over a temperature range T = (288.15 to 318.15) K and at p = 101.325 kPa have been carried out using vibrating-tube digital densimeter, micro- Ubbelohde type capillary viscometer and Bruker (AVANCE-III, HD 500MHz) NMR spectrometer, respectively. From the density and viscosity data, apparent molar volume (V2,.), partial molar volume at infinite dilution (V2,. . ), viscosity B-coefficient, corresponding transfer ( centstrV2,. . and centstrB) and other related parameters have been calculated. The trends in transfer parameters reveal the dominance of hydrophilic-ionic interactions at lower molalities of NaCl while hydrophobic-ionic interactions at higher molalities of NaCl. The expansibilities and dB/dT data show the structure-breaking behavior of theophylline and theobromine in water and in aqueous solutions of NaCl. However, behavior of caffeine is exceptional. The increase in chemical shift ( A) values with increasing molalities of NaCl also signifies the predominance of solute-cosolute interactions over the dehydration process. The results have further been discussed and rationalized in terms of various interactions.