MOLECULAR-INTERACTIONS OF MACROCYCLES WITH DIPEPTIDES IN AQUEOUS-SOLUTIONS - PARTIAL MOLAR VOLUMES AND HEAT-CAPACITIES OF TRANSFER OF A CHIRAL 18-CROWN-6 AND OF A CALIX[4]RESORCINARENE DERIVATIVE FROM WATER TOAQUEOUS DIPEPTIDE SOLUTIONS AT 25-DEGREES-C

Densities and specific heat capacities of ternary aqueous systems cont aining a dipeptide (alanyl-alanine, alanyl-glutamic acid, alanyl-serin e or L-seryl-L-leucine) and a macrocycle (D-alpha-manno-naphtho-18-cro wn-6-ether or 2,8,14,20-tetrakis[methyl )]-4,6,10,12,16,18,22,24-octah ydroxycalix[4]arene) were determined at 25 degrees C by flow densimetr y and flow calorimetry. The partial molar volume and heat capacity of transfer of a macrocycle from water to the dipeptide solution was dete rmined as a function of the dipeptide concentration. Positive values f or transfer volumes and transfer heat capacities are observed with all the solutions studied. With the crown ether, except for alanyl-glutam ic acid where a 1:1 complex is clearly evidenced due to specific inter actions of the side-chain functional group of the peptide with the cro wn ether, no stoichiometric complexes are confirmed and the partial mo lar quantities of transfer increase with the hydrophobic character of the dipeptide. Partial quantities of transfer are smaller with the cal ixarene than with the crown ether and stoichiometric complexes [calixa rene]/[dipeptide] from 2:1 to 1:4 are evidenced, depending on the natu re and the concentration of the dipeptide.