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Crown Ethers

Crown Ethers

Crown ethers are cyclic polyethers that contain multiple oxygen atoms, usually arranged in a regular pattern. The first crown ether was synthesized by Charles Pederson while working at DuPont in 1967. For this work, Pedersen was co-awarded the 1987 Nobel Prize in Chemistry. Crown ethers are named using the formula x-crown-y, where x is the total number of atoms in the ring and y is the number of ether oxygen atoms. The term 'crown' refers to the crown-like shape that these ether molecules take.

Ion-Exchange Chromatography

Ion-Exchange Chromatography

Ion-exchange chromatography, or IEC, is a technique for separating ions based on their affinity for the stationary phase. The stationary phase is a cross-linked polymer resin with covalently attached ionic functional groups. The functional groups can be either positively charged (cation exchangers) or negatively charged (anion exchangers). A cation exchanger consists of a polymeric anion and active cations, while an anion exchanger is a polymeric cation with active anions. The choice of...

Ion Exchange

Ion Exchange

Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or basic...

Masking and Demasking Agents

Masking and Demasking Agents

EDTA titrations may necessitate masking and demasking agents to temporarily protect a particular metal ion in a mixture from the EDTA reaction. These agents facilitate the sequential analysis of the metal ions by forming stable complexes with some—but not all—metal ions during certain steps.
There are many masking agents, such as cyanide, fluoride, triethanolamine, thiourea, and 2,3-bis(sulfanyl)propan-1-ol (formerly 2,3-dimercapto-1-propanol), with the masking agent chosen based on the metal...

Chemical Shift: Internal References and Solvent Effects

Chemical Shift: Internal References and Solvent Effects

In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...

π Electron Effects on Chemical Shift: Overview

π Electron Effects on Chemical Shift: Overview

An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...

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Related Experiment Video

Updated: Jul 19, 2026

Using a Cyclic Ion Mobility Spectrometer for Tandem Ion Mobility Experiments

Using a Cyclic Ion Mobility Spectrometer for Tandem Ion Mobility Experiments

Published on: January 20, 2022

Exploring crown ethers as shift reagents for ion mobility spectrometry.

Amy E Hilderbrand¹, Sunnie Myung, David E Clemmer

¹Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.

Analytical Chemistry

|September 30, 2006

Summary

Crown ethers can shift peptide ion mobilities by forming complexes, enhancing separation and analysis. This method improves the resolution of complex peptide mixtures, aiding in sequence selectivity.

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Area of Science:

Analytical Chemistry
Biochemistry
Physical Chemistry

Background:

Peptide ion mobility spectrometry (IMS) is crucial for analyzing complex mixtures.
Distinguishing between isobaric peptides with similar naked ion mobilities remains a challenge.

Purpose of the Study:

To investigate the use of crown ethers for shifting peptide ion mobilities.
To enhance the separation and resolution of peptide ions using crown ether complexation.

Main Methods:

Electrospraying peptide solutions with crown ethers (12-crown-4, 15-crown-5, 18-crown-6, dibenzo-30-crown-10).
Separating peptide-crown complexes using ion mobility spectrometry.
Collisionally activating complexes to release naked peptide ions for m/z analysis.

Main Results:

Crown ether complex formation alters peptide ion mobilities, shifting them in the mobility spectrum.
Specific interactions between crown ethers and basic peptide sites provide sequence selectivity.
The approach successfully resolved isobaric dipeptides and a library of 27 tripeptides.

Conclusions:

Crown ether complexation is an effective strategy to enhance peptide ion mobility separation.
This method extends the resolving power of IMS for complex peptide samples.
Reported cross sections for crown ether ions and complexes provide valuable data for future studies.