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

RATIONALE

The poly(ethylene oxide) (PEO)-alkali metal cation interaction is widely used in many areas. The conformation of the PEO-alkali metal cation complex has been studied extensively, but the conformational mechanism is still unclear. Simulations have been used to explain the mechanism, but there is a lack of experimental data from long PEO chains to verify the simulation results.

METHODS

The relative peak abundance of PEO (iso-C₁₀ H₂₁ (OC₂ H₄ )_n OH (n_average = 7, where n denotes the number of ethylene oxide (EO) units) oligomers complexed to five alkali metal cations (Li⁺ , Na⁺ , K⁺ , Rb⁺ and Cs⁺ ) was studied using positive electrospray ionization mass spectrometry (ESI-MS). The ion selectivity of PEO oligomers to alkali metal cations corresponded to the peak abundance in competitive ESI-MS.

RESULTS

PEO formed its first helix when the number of EO units reached six and the helix played an important role in the ion selectivity of PEO. For larger PEO oligomers with a helix, the ion selectivity of PEO depended on the degree of host-guest matching of the cations and the helix. The highest selectivity of PEO to K⁺ was due to K⁺ providing the best shape matching with the helical cavity. For smaller PEO oligomers without a helix, the selectivity was mainly determined by the surface charge density of the cations.

CONCLUSIONS

The formational mechanism of the PEO-alkali metal cation complex was predicted. The results gave straightforward evidence to explain the conformational mechanism of the PEO-alkali metal cation complex and provided experimental data for further simulation studies.

Promising Biocompatible, Biodegradable, and Inert Polymers for Purification of Wastewater by Simultaneous Removal of Carcinogenic Cr(VI) and Present Toxic Heavy Metal Cations: Reduction of Chromium(VI) by Poly(ethylene glycol) in Aqueous Perchlorate Solutions

A spectrophotometric technique has been applied for studying the reduction of chromium(VI) by poly(ethylene glycol) (PEG) as water-soluble and nontoxic synthetic polymer at a constant ionic strength of 4.0 mol dm^-3 in the absence and presence of the ruthenium(III) catalyst. In the absence of the catalyst, the reaction orders in [Cr(VI)] and [PEG] were found to be unity and fractional first orders, respectively. The oxidation process was found to be acid-catalyzed with fractional second order in [H⁺]. The addition of Ru(III) was found to catalyze the oxidation rates with observation of zero-order reaction in [CrO₄ ^2-] and fractional orders in both [PEG] and [Ru(III)], respectively. The PEG reduces the soluble toxic hexavalent Cr(VI) as a model pollutant to the insoluble nontoxic Cr(III) complex, which is known to be eco-friendly and more safer from the environmental points of view. The acid derivative of PEG was found to possess high affinity for the removal of poisonous heavy metal ions from contaminant matters by chelation. Formation of the 1:1 intermediate complex has been kinetically revealed. A consistent reaction mechanism of oxidation was postulated and discussed.

Rapid transport of germ-mimetic nanoparticles with dual conformational polyethylene glycol chains in biological tissues

Polyethylene glycols (PEGs) can improve the diffusivity of nanoparticles (NPs) in biological hydrogels, while extended PEG chains severely impede cellular uptake of NPs. Inspired by invasive germs with flagellum-driven mucus-penetrating and fimbriae-mediated epithelium-adhering abilities, we developed germ-mimetic NPs (GMNPs) to overcome multiple barriers in mucosal and tumor tissues. In vitro studies and computational simulations revealed that the tip-specific extended PEG chains on GMNP functioned similarly to flagella, facilitating GMNP diffusion (up to 83.0-fold faster than their counterparts). Meanwhile, the packed PEG chains on the bodies of GMNP mediated strong adhesive interactions with cells similarly to the fimbriae, preserving cellular uptake efficiency. The in vivo results proved the superior tumor permeability and improved oral bioavailability provided by the GMNP (21.9-fold over administration of crystalline drugs). These findings offer useful guidelines for the rational design of NPs by manipulating surface polymer conformation to realize multiple functions and to enhance delivery efficacy.

Molecular modelling of supramolecular one dimensional polymers

Supramolecular polymers exemplify the need to employ several computational techniques to study processes and phenomena occuring at varied length and time scales. Electronic processes, conformational and configurational excitations of small aggregates of chromophoric molecules, solvent effects under realistic thermodynamic conditions and mesoscale morphologies are some of the challenges which demand hierarchical modelling approaches. This review focusses on one-dimensional supramolecular polymers, the mechanism of self-assembly of monomers in polar and non-polar solvents and properties they exhibit. Directions for future work are as well outlined.

Hierarchical computational modelling approaches for the study of supramolecular polymers is reviewed.