Cyclization of the l-alanyl-l-isoleucine dipeptide in the solid state: effect of the amino acid sequence on the reaction kinetics

The solid-state cyclization of the l-alanyl-l-isoleucine dipeptide on heating was studied. The kinetic parameters of this reaction, including the activation energy, the Arrhenius factor, and the reaction order were determined using the approaches of isoconversion kinetics. A kinetic model describing the reaction was considered. The results were compared with the parameters found earlier for the isoleucyl-alanine cyclization; and the effect of the order of amino acid residues on the cyclization of dipeptides was elucidated. The self-assembly of the linear l-alanyl-l-isoleucine dipeptide and its cyclic analog was investigated by atomic force microscopy. The results of this study will be useful for determining the mechanism of dipeptide cyclization in the solid state and can also serve to develop efficient and cheap methods for the synthesis of cyclic dipeptides.