Volumetric properties of amphionic molecules in water. Part 2.—Thermal expansibility and compressibility related to the formation of zwitterionic structures

Abstract

The dependence of the partial molar volumes of a number of a-amino acids, w-amino acids, dipeptides and diketopiperazines on temperature has been determined at various concentrations and for the temperature range 0-55 O C using an automatic dilatometer ; the limiting partial molar expansibilities, Og, have been calculated. Measurements of the sound velocity at 15 MHz and at various concentrations allowed us to determine the compressibility of the solutions at 25 *C and to calculate the limiting partial compressibilities, OO,.,, for some of the above mentioned compounds. Finally, by using the known values @ : and @OK. , together with the partial molar heat capacity of the solute and some physical properties of pure water, the limiting isothermal partial molar compressibilities, The values of 0% and @OK,, and the trends they show when the structure of the amphionic molecule is changed have been analysed by taking into account the features exhibited by 0; and @OK,, of related charged and non-charged compounds. The dependence on temperature and pressure of the internal and external proton-exchange reaction between a carboxyl and an amino group have been evaluated and compared.have been obtained.

Apparent molar heat capacities and volumes of some aqueous solutions of aliphatic amino acids at 288.15, 298.15, 313.15, and 328.15 K

“…Hence the solvation contributions to the standard state properties in eqs. [7] and [8] are represented by -oeQ and oeTX, respectively. Q and X are defined using the temperature and pressure dependencies of the dielectric constant of water, as in eqs.…”

“…A review of volumetric and thermochemical data for aqueous amino acid systems reveals that the majority of previous studies were conducted at the standard temperature of 298.15 K (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). This is surprising when one considers that many living systems, which contain proteins, polypeptides, and hence amino acids, operate at temperatures removed from the standard.…”

Volumetric properties of (water + diethanolamine) systems

“…As shown previously (8), the apparent molar volume of water in alkanolamine (V4,1) and the apparent molar volume of alkanolamine in water (V4,2) can be calculated as and Simple graphical or analytical extrapolation of V4,, to x, = 0 (x, = I) leads to the desired value of 7 , " and similar extrapolation of V4,2 to x, = 0 leads to the desired value of V,". Perron et al (17) have used an equivalent method based on extrapolation of the "reduced volume" represented by ~/ X , X , to x2 = 1 or 0 to obtain equally accurate values of partial molar volumes at infinite dilution. Before using the equations above with our experimental results for calculation of partial molar volumes, we turn to consideration of thermal expansion.…”

“…We (1 1, 15) and others (9,10,13,16,17) have used partial molar volumes (V20) of many organics in water to develop additivity schemes that might contribute to our understanding of organic-water interactions and that are certainly useful for predicting partial molar volumes for organic solutes in water. f few of these investigations (especially ref.…”

Partial molar volumes, expansibilities, and compressibilities of oligoglycines in aqueous solutions at 18–55°C

“…Short oligopeptides are among the most suitable model compounds, and the volumetric characteristics of several di-, tri-, tetra-, and pentapeptides have been reported in the literature.16 33 Oligoglycines represent the simplest oligopeptide homologous series. At neutral pH, oligoglycines contain oppositely charged amino and carboxyl terminal groups, one or more peptide groups, and aliphatic -CH2-groups.…”