Studies of reaction heats and structure of complexes formed between strong N-bases and phenols

The heats of reactions between various phenols and two strong N-bases of guanidine-like character in acetonitrile, are determined. The values can be used as a measure of self-assembly abilities of the phenol molecules in the interactions with strong N-bases, playing a very important role in biological systems. In the case of TBD complexes with corresponding nitrophenols, the protonated N-base is hydrogen-bonded to the nitro group excluding the self-assembly process of the phenols. In the case of other phenols, the self-assembly abilities are dependent on pK(a) values of phenols. With increasing acidity of phenols their ability to form the hydrogen-bonded chains decreases. The maximum of length of the chains is observed for 4-methylphenol, which has a similar pK(a) value to that in the tyrosine residue in biological systems. (C) 2002 Elsevier Science B.V. All rights reserved.