RESUMO
It has become an axiom that the thermodynamic analysis of non-covalent molecular complexation is intrinsically model-dependent, i.e. the set of implicitly or explicitly introduced assumptions may strongly affect the thermodynamic parameters. This review deals with the entropy change accompanying molecular complexation, which results in the formation of ordered structures. In simple terms the key question may be formulated as follows: 'If the molecular complexation leads to the formation of supramolecular structures, then, the system entropy changes due to ordering. So, how is this factor accounted for in standard models of molecular complexation and does it have any effect on the magnitude of measured thermodynamic parameters of complexation?' The structure of the review is made as a collection of cases in which the hidden entropy change has been recognized among the most influential factors.
RESUMO
Solution-phase self-association characteristics and DNA molecular-recognition properties are reported for three close analogues of minor-groove-binding ligands from the thiazotropsin class of lexitropsin molecules; they incorporate isopropyl thiazole as a lipophilic building block. Thiazotropsin B (AcImPy(iPr) ThDp) shows similar self-assembly characteristics to thiazotropsin A (FoPyPy(iPr) ThDp), although it is engineered, by incorporation of imidazole in place of N-methyl pyrrole, to swap its DNA recognition target from 5'-ACTAGT-3' to 5'-ACGCGT-3'. Replacement of the formamide head group in thiazotropsin A by nicotinamide in AIK-18/51 results in a measureable difference in solution-phase self-assembly character and substantially enhanced DNA association characteristics. The structures and associated thermodynamic parameters of self-assembled ligand aggregates and their complexes with their respective DNA targets are considered in the context of cluster targeting of DNA by minor-groove complexes.
