Hydrogen-bonded complexes resulting from the interaction of alkylated barbituric acid and 2,6-diamidopyridine derivatives

In the present study a hydrophilic or a lipophilic alkylated barbituric aci d derivative was allowed to interact in the melt and in solution with a com plementary series of alkylated diamidopyridine derivatives, both hydrophili c or lipophilic. The interaction between the molecules was mainly studied b y FT-IR spectroscopy. Phase transitions of reaction mixtures were studied w ith polarized optical microscopy and differential scanning calorimetry. It was found that the molecular recognition of the interacting components is o nly effective between the molecularly compatible ones. Specifically, employ ing Methods I and II, (see text) the short chain derivatives form 1:1 compl exes whereas the long-chain derivatives are only partially complexed. Deriv atives of dissimilar lipophilicity do not form complexes employing the same methods. However, comparing the two methods, complexation is more effectiv e employing Method II. The induction of molecular recognition in the presen ce of an apolar solvent is enhanced in solution, Method III. The equilibriu m which was established in solution is shifted to different directions duri ng the evaporation step (Method II), leading either to the formation of com plexes or to self-association. (C) 1999 Elsevier Science B.V. All rights re served.