engleski

Complexation of homocyclopeptides with halides and oxoanions in acetonitrile and dimethyl sulfoxide

Cyclopeptides are promising class of anion receptors owing to the spatial proximity of backbone amide groups and also to the variety of sidechain substituents that can affect the receptor properties.[1-3] Complexation affinities of three cyclopeptide derivatives (Figure 1) for halide ions, thiocyanate and oxoanions were studied in acetonitrile and dimethyl sulfoxide. Ligand L1 is a pentaleucine cyclopeptide derivative whereas the other two cyclopeptidic ligands are comprised of lysine subunits protected by tert-butylcarbonyl (BOC) group. Ligand L2 is built out of four such subunits whereas ligand L3 contains five of them. Stability constants of L1, L2 and L3 complexes with studied anions were determined by means of microcalorimetric and 1H NMR titrations. To get more detailed insight into the binding of anions by the investigated cyclopeptide derivatives, classical molecular dynamics simulations were carried out. The ligands showed larger affinity for all anions in acetonitrile than in dimethyl sulfoxide. It was found that the stability of the anion complexes of pentameric compounds L2 and L3 was higher when compared to the complexes of tetrameric ligand L1. The results of 1H NMR titrations and molecular dynamics simulations indicated that the bound anions were coordinated by the amide groups of cyclopeptide receptors. In the case of L1 and L2 complexes with H2PO4– anion, the participation of carbamate protons in the anion coordination was observed.

ciklopeptidi ; anioni ; kompleksiranje

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