Gas-Phase Spectroscopy of Ionic Complexes

Gas-phase spectroscopy of ionic complexes has emerged as a powerful approach to unravel the intrinsic structures, bonding interactions and reactivity of charged species free from bulk solvent effects. By combining mass spectrometric ion selection with laser‐based vibrational and electronic spectroscopies, researchers can obtain fingerprints of molecular geometry, charge distribution and non‐covalent interactions. Techniques such as infrared multiple photon dissociation and cryogenic ion vibrational predissociation provide high‐resolution spectral data for conformer identification, while ion mobility separation adds collision‐cross‐section measurements to distinguish isomers. Computational methods, notably density functional theory, support spectral assignment and enable detailed mapping of potential‐energy surfaces. Applications span bioanalytical chemistry, where gas‐phase spectra aid in metabolite and peptide identification; supramolecular chemistry, with host–guest complexes revealing solvent‐driven conformers; and environmental and pharmaceutical sciences, where isomeric or protonation state differentiation informs toxicity assessments. The field continues to integrate automated spectral libraries, advanced ion cooling and trapping strategies, and emerging machine-learning tools to accelerate de novo structure elucidation and explore larger, more flexible ionic assemblies with ever greater specificity and sensitivity.

Research from Nature Portfolio

Recent studies have applied infrared ion spectroscopy to address challenges in biomolecular and supramolecular analysis. Orthogonal differentiation of small metabolites in complex mixtures has been demonstrated by recording infrared action spectra of mass‐selected ions, enabling unambiguous identification of monosaccharide enantiomers in biofluids without standard compounds. Charge‐state resolved IR multiple photon dissociation spectra of ubiquitin ions have revealed how increasing protonation alters amide and C–H vibrational bands, offering direct insight into charge‐driven conformational changes in proteins. In supramolecular chemistry, gas‐phase IRMPD spectra of permethylated β‐cyclodextrin–protonated lysine complexes uncovered highly unstable host–guest arrangements that correspond to the most stable solution conformers, bridging the gap between gas‐phase structures and solvated behaviour.

Research from all publishers

Cryogenic ion vibrational predissociation spectroscopy of aryl corrin (Vitamin B₁₂ derivative) complexes has highlighted limitations of current density functional models, revealing discrepancies in predicted hydrogen‐bonding patterns and emphasising the need for more accurate anharmonic treatments. An in silico infrared spectral library of over 4,500 metabolite adducts computed at the DFT level and validated against experimental IRIS data has enabled automated matching of experimental spectra to candidate structures, achieving metabolite identification rates of 75 % and demonstrating potential for de novo discovery. Infrared multiphoton dissociation action spectroscopy combined with ion mobility and DFT calculations has been used to distinguish protonated naringenin from its chalcone isomer, pinpointing unique vibrational signatures in the 1,400–1,700 cm⁻¹ region and facilitating structural assignment of flavonoid isomers in complex natural extracts.

Gas-Phase Spectroscopy of Ionic Complexes publication trend

The graph below shows the total number of articles in gas-phase spectroscopy of ionic complexes across all publications each year (not limited to Nature Index journals).

Technical terms

Infrared Multiple Photon Dissociation (IRMPD): A technique in which trapped ions absorb multiple infrared photons, leading to fragmentation; the resulting action spectrum reflects vibrational transitions of the parent ion.

Cryogenic Ion Vibrational Predissociation (CIVP): A method where ions are cooled to cryogenic temperatures and weakly bound “tag” atoms or molecules are dissociated by infrared absorption, yielding high‐resolution vibrational spectra.

Electrospray Ionization (ESI): A soft ionization technique that transfers molecules from solution to the gas phase as charged droplets, producing intact molecular ions suitable for mass spectrometric analysis.

Ion Mobility-Mass Spectrometry (IMS): A separation method that distinguishes gas‐phase ions based on their collision‐cross‐section and shape before mass analysis, enabling isomer and conformer differentiation.

Density Functional Theory (DFT): A quantum‐chemical computational approach used to predict molecular geometries, energies and vibrational frequencies, aiding the interpretation of experimental gas‐phase spectra.

References

1. Cryogenic Ion Vibrational Predissociation (CIVP) Spectroscopy of Aryl Cobinamides in the Gas Phase: How Good Are the Calculations for Vitamin B12 Derivatives?. Journal of the American Chemical Society (2023).
2. An In Silico Infrared Spectral Library of Molecular Ions for Metabolite Identification. Analytical Chemistry (2023).
3. Protonated Forms of Naringenin and Naringenin Chalcone: Proteiform Bioactive Species Elucidated by IRMPD Spectroscopy, IMS, CID-MS, and Computational Approaches. Journal of Agricultural and Food Chemistry (2023).
4. Charge-state Resolved Infrared Multiple Photon Dissociation (IRMPD) Spectroscopy of Ubiquitin Ions in the Gas Phase. Scientific Reports (2017).
5. Unveiling host–guest–solvent interactions in solution by identifying highly unstable host–guest configurations in thermal non-equilibrium gas phase. Scientific Reports (2022).
6. Augmenting Basin-Hopping With Techniques From Unsupervised Machine Learning: Applications in Spectroscopy and Ion Mobility. Frontiers in Chemistry (2019).