Complexing Cations by Poly(ethylene oxide): Binding Site and Binding Mode

Abstract

The binding of K and Ba cations to short poly(ethylene oxide) (PEO) chains with ca. 4-25 monomeric units in methanol was studied by determining the effective charge of the polymer through a combination of electrophoretic NMR and diffusion NMR experiments. These cations were previously found to bind to long PEO chains in a similar strong manner. In addition, H chemical shift and longitudinal spin relaxation rate changes upon binding were quantified. For both systems, binding was stronger for the short chains than that for the longer chains, which is attributed mainly to interactions between bound ions. For K ions, the equilibrium binding constant of a cation to a binding site was measured. For both cations, the binding site was estimated to consist of ca. six monomeric units that coordinated with the respective ions. For the systems with barium, a significant fraction of the bound ions are (BaAnion) ion pairs. This leads to a strong anion effect in the effective charge of the oligomers acquired upon barium ion binding. For K, the coordinating oligomer segment remains rather mobile and individual oligomers exchange rapidly (≪s) between their free and ion-complexing states. In contrast, segmental dynamics slows significantly for the oligomer section that coordinates with the barium species, and for individual oligomers, binding and nonbinding sections do not exchange on the time scale of seconds. Hence, oligomers also exchange slowly (>s) between their free and barium complexing states.

Poly(ethylene oxide) helical conformation and alkali metal cation selectivity studied using electrospray ionization mass spectrometry

“…Experiments and simulations proved that a considerable portion of the open helical PEO conformation was formed in aqueous solution. Electrophoretic NMR studies proved that there were bonds between EO units and alkali metal cations in solution . Combining these results with our experiments, we can draw some reasonable conclusions: when the number of EO units in PEO reached six, the first helix was formed; in PEO–alkali metal cation solution, the alkali metal cations enter the helix and form a complex.…”

“…All these studies have described the general properties of the whole sample rather than that of a single oligomer which is more important for understanding the formational mechanism of PEO–cation complexes. Electrophoretic NMR and diffusion NMR with high resolution have been used to study individual oligomers and it was found that K + coordinated with six EO units to form the most stable complex . Soft ionization mass spectrometry (MS) techniques, matrix‐assisted laser desorption ionization (MALDI) and electrospray ionization (ESI), have been successfully used to study individual oligomer complexes .…”

“…In the study reported here, iso‐C 10 H 21 (OC 2 H 4 ) n OH ( n average = 7) was used to study the ion selectivity of oligomers with different numbers of EO units to various alkali metal cations (Li + , Na + , K + , Rb + and Cs + ) in solution using ESI‐MS. By combining the ion selectivity results for PEO, and molecular modeling simulation and NMR studies, the formational mechanism of PEO–cation complex could reasonably be predicted. A study of the coordination of crown ethers with alkali metal cations and the critical number of EO units for doubly cationized molecules strongly supported the prediction.…”

Nanoconjugates of a calixresorcinarene derivative with methoxy poly(ethylene glycol) fragments for drug encapsulation

“…The ξ-potential value of 3 is −10.1 mV (Figure S9, Supporting Information File 1 ). This probably indicates the partial ionization of ethyleneoxy groups due residual potassium cations, which easily form a complex with mPEG fragments [ 32 ] and appear due to the reaction conditions (see Experimental section).…”

Palladium-catalyzed intermolecular transthioetherification of aryl halides with thioethers and thioesters

“…Besides hydrogen, other small molecules (H 2 /CO and RCOH) can also be used in these processes. [7][8][9][10][11][12] In 2016, Morandi and co-workers reported an elegant Ni-catalyzed reversible transfer hydrocyanation reaction between alkyl nitriles and alkenes under mild conditions. 13a Later on, they reported their new achievement of palladium-catalyzed C-S bond metathesis ( Fig.…”