engleski

Conformational adaptations of podands as a base for selective binding of stereoisomers

Flexible anion receptors draw significant scientific attention in the last few decades.[1] Although they usually display lower binding constants than rigid hosts, many interesting features are connected with this class of compounds. Binding to anion often includes extreme spatial rearrangements of the flexible host. Such movement provides valuable information about the nature of host-guest binding and can further serve in developing of more efficient receptors in the field of anion sensing and signal transduction. N, N’-3-azapentane-1, 5-bis[3-(1-aminoethylidene)-6-methyl-3H-pyran-2, 4-dione], L, is a podand known to be selective for nitrate and sulfate by self-assembling to pseudomacrocyclic host.[2] No similar pseudomacrocycle appears in the binding of HL+ with maleinate or fumarate, well known cis-trans isomers. L displays new kind of conformes for each anion. In the case of maleinate, HL+ take a “tweezers” conformation and the complex is additionally stabilized by π-π interactions between the pyrone rings and the π-system of the maleinate (A). Main motif in the binding of fumarate is the “letter Z” conformation of HL+ with no π-π interactions between the host and named anion (B). Competitive crystallization experiments in solutions containing both maleinate and fumarate provided only maleinate complex in high yield, thus suggesting higher affinity of L for this anion.

anion receptors; molecular tweezers; selectivity

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