Molecular recognition properties of peptide mixtures obtained by polymerisation of amino acids in the presence of estradiol

In this paper we show that the carbodiimide-induced polymerisation of amino acid mixtures in aqueous medium and in presence of estradiol produces the mixtures of peptides with an average molecular weight of 2-6 kDa that are characterised by possessing molecular recognition properties towards estradiol. After the removal of the templating molecule, the binding properties of the peptide mixtures were studied using spectrophotometric and immunochemical methods. The experimental results show the presence of molecular recognition behaviour for all the peptide mixtures obtained by polymerisation in presence of estradiol, with affinity constant values between 0.44×10⁹ and 6.6×10⁹ M⁻¹, while the same mixtures obtained without estradiol show lower affinity constant values between 2.2×10⁶ and 1.3×10⁹ M⁻¹. The molecular recognition behaviour was found to be highly selective, as the binding constants of peptides towards the structural homologues testosterone and progesterone are lower than three orders of magnitude. Peptide fractions separated by ion-exchange chromatography show the same molecular recognition properties, with affinity constant values between 3.2×10⁶ and 7.1×10⁹ M⁻¹. Similarities and differences between this polymerisation technique and the molecular imprinting technique are briefly discussed.