Enthalpies of proton transfer of aminoalkylsulphonic acids in methanol-water mixtures by direct calorimetry

Enthalpies of proton transfer in methanol-water mixtures (0-90 wt% methanol ) of 3-(N-morpholino)propanesulphonic acid (Mops), N,N-bis(2-hydroxyethyl)- 2-aminoethanesulphonic acid (Bes) and N-(2-hydroxyethyl)piperazine-N'-2-eth anesulphonic acid (Hepes) have been measured by direct calorimetry at 25 de grees C. The results thereof are compared with the standard enthalpies for the protonation of the base tris(hydroxymethyl)aminomethane (Tris) and are discussed in terms of an adaptation of classical electrostatic formula and the three-dimensional structure in methanol-water mixtures as determined by molecular dynamic simulations. (C) 1999 Elsevier Science B.V. All rights r eserved.