Andrew W. Hakin

Some thermodynamic properties of aqueous amino acid systems at 288.15, 298.15, 313.15 and 328.15 K: group additivity analyses of standard-state volumes and heat capacities

Densities and heat capacities have been measured for aqueous solutions of L-aspartic acid, L-glutamic acid and α-aminobutyric acid at 288.15, 298.15, 313.15 and 328.15 K. These data have been used to calculate apparent molar volumes, V2, ϕ, and apparent molar heat capacities, Cp, 2, ϕ, which in turn have been used to calculate standard-state volumes, text-decoration:overlineV°2, and standard-state heat capacities, text-decoration:overlineC°p, 2. Helgeson, Kirkham and Flowers equations, for neutral organic species in water, have been used to model the calculated standard-state volumes and heat capacities of the amino acids as a function of temperature at constant pressure. These data, and data previously reported for amino acid systems, have been used as input for a group additivity type analysis. The merits of the additivity scheme are discussed, and attempts are made to interpret the predicted trends in the group contributions as a function of temperature.

MOLAR HEAT CAPACITIES OF ALKANOLAMINES FROM 299.1 TO 397.8 K: GROUP ADDITIVITY AND MOLECULAR CONNECTIVITY ANALYSES

The molar heat capacities of 14 alkanolamine compounds have been measured at five separate temperatures in the range 299.1 to 397.8 K. These compounds were monoethanolamine (MEA), monomethylethanolamine (MMEA), dimethylethanolamine (DMEA), monoethylethanolamine (MEEA), diethylethanolamine (DEEA), n-propylethanolamine (n-PEA), diisopropylethanolamine (di-PEA), diethanolamine (DEA), methyldiethanolamine (MDEA), ethyldiethanolamine (EDEA), n-butyldiethanolamine(n-BDEA), tert-butyldiethanolamine (tert-BDEA), triethanolamine (TEA) and 2-amino-2-methylpropan-1-ol (AMP). Molar heat capacities of these compounds show a structural dependence, where the molar heat capacity of one molecule may be considered as the sum of various group contributions. Hence, the reported molar heat capacity data have been used as input to a group additivity analysis that yields estimates of CH 2 , OH, NH and N group contributions to molar heat capacities at each investigated temperature. The additivity principle has been explored in more detail by using molecular connectivity indexes to obtain a simple five-term equation that models the molar heat capacities of the investigated alkanolamines over the entire experimental temperature range.

Volumetric properties of some oligopeptides in aqueous solution: partial molar expansibilities and isothermal compressibilities at 298.15 K for the peptides of sequence Ala(gly)n, n=1–4

The partial molar isentropic compressibilities at infinite dilution, KS,20 , have been determined for the two peptides alanylglycylglycylglycine and alanylglycylglycylglycylglycine in aqueous solution at 298.15 K. These results were combined with those obtained previously for the peptides alanylglycine and alanylglycylglycine to derive the partial molar isentropic compressibility of the glycyl group of a polypeptide. The partial molar volumes at infinite dilution, V20, have also been determined for these peptides at temperatures over the range 291.15 to 313.15 K. These results were used to derive the partial molar expansibilities, E20, of the peptides at 298.15 K which were combined with the Ks,20 data to obtain the isothermal compressibilities, KT,20, of the peptides. Using new V20 data for tetra- and pentaglycine, we have also derived E20 and KT,20 values for some oligoglycines. The KT,20 results for both sets of peptides were used to derive the isothermal compressibilities of the glycyl group.

The partial molar heat capacities and volumes of some N-acetyl amino acid amides in aqueous solution over the temperature range 288.15 to 328.15 K

The partial molar heat capacities, Cp,20, and partial molar volumes, V20, at infinite dilution have been determined for the compounds N-acetylvalinamide and N-acetylleucinamide in aqueous solution at the temperatures 288.15, 298.15, 313.15 and 328.15 K and for N-acetylglycinamide and N-acetylalaninamide at the temperatures 288.15, 313.15 and 328.15 K. Partial molar volumes at infinite dilution have also been determined for the sparingly soluble N-acetylisoleucinamide in aqueous solution over the same temperature range. The Cp,20 and V20 results have been used to calculate amino acid side-chain contributions to the thermodynamic properties. These side-chain contributions are critically compared with those obtained using other model compounds.

Solubilities of salts and kinetics of reaction between hydroxide ions and iron(II)–di-imine complexes in water–methanol mixtures. Derivation of single-ion transfer chemical potentials and their application to analysis of solvent effects on kinetic parameters

Kinetic data are reported for the reaction at 298 K and ambient pressure between two iron(II)–di-imine complex cations and hydroxide ions in water–methanol mixtures. Solubility data are reported for a range of inorganic salts containing simple and complex ions. Methods for calculating transfer chemical potentials of single ions are examined and, depending on the extrathermodynamic assumption, shown to predict different trends in the properties of ions in these aqueous mixtures. Further, calculated initial- and transition-state solvation effects on the kinetics are different: in some cases dramatically so. The solvation characteristics are compared for various ions in methanol–water mixtures as calculated using the tetraphenylphosphonium tetraphenylborate (TPTB) assumption, which sets the transfer chemical potential of tetraphenylphosphonium ions equal to that of tetraphenyl-boronate ions. Arguments are advanced for adopting single-ion transfer chemical potentials based on this assumption. Relationships are examined between the transfer parameters for H+, H3O+, ROH+2 and H9O+4 ions in binary aqueous mixtures, ROH + H2O.

Modeling of Thermodynamic Properties of Amino Acids and Peptides Using Additivity and HKF Theory

AbstractRelative densities,

Transfer chemical potentials for ions, solubilities of salts and kinetics of reactions involving inorganic complex ions at ambient pressure and 298.2 K in binary aqueous mixtures containing ethanol and propan-2-ol

\left( {\rho - \rho _o } \right)

Thermochemical and volumetric properties of aqueous urea systems. Heat capacities and volumes of transfer from water to urea—water mixtures for some 1 : 1 electrolytes at 298.15 K

, and heat capacity ratios,