Apparent molal heat capacities of organic compounds in aqueous solution. Part 3.—ω-Amino acids and related compounds

Abstract

Values of apparent molal heat capacities Φ_Cp in the range 23°–55°C, were determined by adiabatic calorimetry for the following amino acids: glycine, α-alanine, α-aminoisobutanoic acid, valine, serine, threonine, sarcosine, dimethylglycine, betaine, β-alanine, β- and γ-aminobutanoic acids, δ-aminopentanoic acid and ε-aminohexanoic acid. Some hydroxy acids, sodium and ammonium salts of carboxylic acids, methyl and ethyl esters of acetic acid and glycine methylester hydrochloride have also been studied.

An attempt has been made to quantify the contribution to Φ_Cp associated with charge separation in amphionic molecules by comparing the experimental value (Φ^exp_Cp) for amino acids with those for similar uncharged molecules (Φ^ref_Cp). The ΔΦ^* values (Φ^exp_Cp–Φ^ref_Cp) thus obtained for ⁺H₃N(CH₂)_m COO^– compounds (m= 2, 3, 4, 5) are used in order to obtain some information about the interactions between neutral or charged amino and carboxylic groups. Effects connected with the methyl additions to N⁺ centres in glycine or ammonium salts are considered.