Memorial University DAI: Amino acids under hydrothermal conditions - apparent molar volumes, apparent molar heat capacities, and acid/base dissociation constants for aqueous α-alanine, β-alanine, glycine, and proline at temperatures from 25 to 250°C and pressures up to 30

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Title	Amino acids under hydrothermal conditions - apparent molar volumes, apparent molar heat capacities, and acid/base dissociation constants for aqueous α-alanine, β-alanine, glycine, and proline at temperatures from 25 to 250°C and pressures up to 30
Author	Clarke, Rodney George Francis, 1973-
Description	Thesis (Ph.D.)--Memorial University of Newfoundland, 2000. Chemistry
Date	2000
Pagination	xxx, 320 leaves : ill.
Subject	Amino acids--Thermal properties; Molecular volume.
Degree	Ph.D.
Degree Grantor	Memorial University of Newfoundland. Dept. of Chemistry
Discipline	Chemistry
Language	Eng
Notes	Bibliography: leaves 301-312.
Abstract	Amino acids are members of a unique group of compounds that exist in solution as zwitterions. Yet the thermodynamic properties of aqueous amino acids have not been measured at temperatures above 343 K. The amino acids studied in this work have been chosen based on their hydrothermal stability and their solubility in water. A series of batch experiments confirmed that aqueous α-alanine, glycine, and proline were stable on the time scale required for our measurements at the temperatures, pressures, and molalities required for this work. -- The apparent molar volumes V° of aqueous α-alanine, β-alanine, and proline have been determined using platinum vibrating tube densitometers at temperatures from 298 K to 523 K and at pressures from steam saturation to 30 MPa. Values of the standard partial molar volumes V° for the aqueous amino acids increase with temperature, then deviate toward negative values at temperatures above 398 K, consistent with an increase in the critical temperature in the solutions relative to water. The apparent molar heat capacities Cp^ of aqueous α-alanine, β-alanine, glycine, and proline have been determined using a differential flow calorimeter and a Picker flow microcalorimeter at temperatures from 298 K to 498 K and at pressures from steam saturation to 30 MPa. Values of the standard partial molar heat capacities Cρ° for the aqueous amino acids increase with temperature, then deviate toward negative values at temperatures above 373 K to 423 K, also consistent with an increase in the critical temperature in the solutions relative to water. The values of both V° and Cρ° increase with increasing pressure. Comprehensive equations to describe the standard-state properties over the experimental temperature range are reported. -- The deviation toward negative values by V° and Cρ° opposite to the behavior predicted by the correlations developed by Shock and Helgeson (Geochim. Cosmochim. Acta. 54, 915-945, 1990) and Amend and Helgeson (J. Chem. Soc, Faraday Trans. 93, 1927-1941, 1997). The temperature dependence of V° and Cρ° predicted using the very recent functional-group additivity model of Yezdimer et al. (Chem. Geol. 164, 259-280, 2000) is only in qualitative agreement with the experimental results. The contribution to V° and Cρ° from the solvent polarization by the large dipole moment of the zwitterions deviates toward negative infinity as Tc is approached, in a manner similar to the experimental values of V° and Cρ° for each of the aqueous amino acids. While this agreement is qualitatively consistent, it is not quantitatively consistent, which suggests that the non-electrostatic hydration effects are of similar magnitude to the solvent polarization effects. -- The acid/base dissociation constants for aqueous α-alanine have been determined from 423 K to 523 K using a UV-visible spectrophotometer and the colorimetric indicators developed by Xiang and Johnston (J. Sol. Chem. 26, 13-30, 1997) and Ryan et al. (J. Phys. Chem. 101, 1827-1835, 1997). The dissociation constants that were estimated with the functional-group additivity model of Yezdimer et al. (Chem. Geol. 164, 259-280, 2000) and those obtained from the isocoulombic extrapolation of room temperature data were found to be an upper limit for the measured values. The contribution of non-zwitterionic forms of the aqueous amino acids to the experimentally determined values of V° and Cρ° were negligible at all but the highest temperatures. -- In this work, the first experimentally determined apparent molar volumes Vϕ for aqueous α-alanine, β-alanine, and proline were obtained at T ≥ 343 K. The first experimentally determined apparent molar heat capacities Cρ, ϕ for aqueous amino acids at T ≥ 328 K were obtained in this work. The first experimentally determined acid/base dissociation constants for aqueous α-alanine obtained at T ≥ 423 K were also obtained in this work.
Type	Text
Resource Type	Electronic thesis or dissertation
Format	Image/jpeg; Application/pdf
Source	Paper copy kept in the Centre for Newfoundland Studies, Memorial University Libraries
Local Identifier	a1493433
Rights	The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
Collection	Electronic Theses and Dissertations
Scanning Status	Completed
PDF File	(31.95 MB) -- http://collections.mun.ca/PDFs/theses/Clarke_RodneyGeorgeFrancis.pdf
CONTENTdm file name	24081.cpd