Volumetric properties of glycine in water at elevated temperatures and pressures measured with a new optically driven vibrating-tube densimeter

An investigation of the volumetric properties of l -alanine and sodium bromide in water at elevated temperatures and pressures

“…The Amend and Helgeson approach appears to have overlooked the dipolar nature of neutral amino acids in aqueous solution whereas calculations appear to confirm the importance of the dipole to the volume of polarization and hence to the volume of solvation of amino acids in aqueous solution. Our previous work on the volumetric properties of glycine in water (7) appears to confirm the interpretation offered by Clarke and Tremaine. (8) For neutral organic species, differentiation of equation (8) with respect to temperature at constant pressure results in an equation that can be used to estimate the concentration, temperature and pressure dependence of the apparent molar expansibility, E m,φ ;…”

“…Details of the construction and operation of this instrument have been reported in detail in a previous publication. (7) However, we note that the 14 carat white gold vibrating tube utilized in the previous investigation was replaced by a 316 stainless steel tube (0.794 mm o.d., 0.508 mm i.d.) to yield an overall increase in the instrument's sensitivity.…”

“…Indeed it has been recently found that estimates of partial molar volumes at infinite dilution for several aqueous amino acid solutions obtained from HKF models are in very poor agreement with experimentally determined data. (7,8) Experimentally determined high temperature and pressure volumetric results for solutions of L-alanine in water reported in this paper are compared to those which can be calculated from the models of Clarke and Tremaine (8) and some discussion of previously reported HKF model predictions (11) will be offered.…”

“…However, the temperature surface of these results was not fully explored until our recent work with a high-temperature and -pressure densimeter. (7) In continuation of such studies, the current paper reports volumetric information for aqueous L-alanine solutions obtained over a large temperature and pressure surface. These results are timely as they serve to compliment the recently published volumetric investigations of Clarke and Tremaine (8) and allow us to compare data obtained with vibrating tube instruments of differing design: the Hakin instrument utilizing an optically coupled feedback technique to drive the vibrating tube compared to the more traditional pick-up and drive wire combination utilised in Tremaine's instrument.…”

Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, α-alanine, and proline

“…Heat-of-mixing flow calorimetry has been used to determine ionization constants and enthalpies of reaction for the protonation of the amino and carboxylate groups of several amino acids at temperatures of up to 125°C (Izatt et al, 1992;Gillespie et al, 1995;Wang et al, 1996). Vibrating-tube densimeters and a Picker-type flow microcalorimeter have recently been used to determine experimental values for the standard partial molar volumes and heat capacities of glycine, ␣-alanine, ␤-alanine, proline, and the dipeptide glycyl-gylcine, at temperatures as high as 275°C (Hakin et al, 1995(Hakin et al, , 1998Clarke and Tremaine, 1999;. We are aware of no other experimental studies on the thermodynamic properties of aqueous amino acids or peptides above 100°C.…”