Dataset Information

Isomer-Specific Vibrational Spectroscopy of Microhydrated Lithium Dichloride Anions: Spectral Fingerprint of Solvent-Shared Ion Pairs.

ABSTRACT: The vibrational spectroscopy of lithium dichloride anions microhydrated with one to three water molecules, [LiCl₂ (H₂ O)_1-3 ]^- , is studied in the OH stretching region (3800-2800 cm^-1 ) using isomer-specific IR/IR double-resonance population labelling experiments. The spectroscopic fingerprints of individual isomers can only be unambiguously assigned after anharmonic effects are considered, but then yield molecular level insight into the onset of salt dissolution in these gas phase model systems. Based on the extent of the observed frequency shifts Δν^OH of the hydrogen-bonded OH stretching oscillators solvent-shared ion pair motifs (<3200 cm^-1 ) can be distinguished from intact-core structures (>3200 cm^-1 ). The characteristic fingerprint of a water molecule trapped directly in-between two ions of opposite charge provides an alternative route to evaluate the extent of ion pairing in aqueous electrolyte solutions.

SUBMITTER: Chakraborty A

PROVIDER: S-EPMC8252531 | biostudies-literature | 2021 Jun

REPOSITORIES: biostudies-literature

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Publications

Isomer-Specific Vibrational Spectroscopy of Microhydrated Lithium Dichloride Anions: Spectral Fingerprint of Solvent-Shared Ion Pairs.

Chakraborty Arghya A Schmahl Sonja S Asmis Knut R KR

Chemphyschem : a European journal of chemical physics and physical chemistry 20210504 11

The vibrational spectroscopy of lithium dichloride anions microhydrated with one to three water molecules, [LiCl2 (H2 O)1-3 ]- , is studied in the OH stretching region (3800-2800 cm-1 ) using isomer-specific IR/IR double-resonance population labelling experiments. The spectroscopic fingerprints of individual isomers can only be unambiguously assigned after anharmonic effects are considered, but then yield molecular level insight into the ons ...[more]

PMID: 33783947

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Project description:The combination of ion mobility separation with mass spectrometry is an emergent and powerful structural biology tool, capable of simultaneously assessing the structure, topology, dynamics, and composition of large protein assemblies within complex mixtures. An integral part of the ion mobility-mass spectrometry measurement is the ionization of intact multiprotein complexes and their removal from bulk solvent. This process, during which a substantial portion of protein structure and organization is likely to be preserved, imposes a foreign environment on proteins that may cause structural rearrangements to occur. Thus, a general means must be identified to stabilize protein structures in the absence of bulk solvent. Our approach to this problem involves the protection of protein complex structure through the addition of salts in solution prior to desorption/ionization. Anionic components of the added salts bind to the complex either in solution or during the electrospray process, and those that remain bound in the gas phase tend to have high gas phase acidities. The resulting 'shell' of counterions is able to carry away excess energy from the protein complex ion upon activation and can result in significant structural stabilization of the gas-phase protein assembly overall. By using ion mobility-mass spectrometry, we observe both the dissociation and unfolding transitions for four tetrameric protein complexes bound to populations of 12 different anions using collisional activation. The data presented here quantifies, for the first time, the influence of a large range of counterions on gas-phase protein structure and allows us to rank and classify counterions as structure stabilizers in the absence of bulk solvent. Our measurements indicate that tartrate, citrate, chloride, and nitrate anions are among the strongest stabilizers of gas-phase protein structure identified in this screen. The rank order determined by our data is substantially different when compared to the known Hofmeister salt series in solution. While this is an expected outcome of our work, due to the diminished influence of anion and protein solvation by water, our data correlates well to expected anion binding in solution and highlights the fact that both hydration layer and anion-protein binding effects are critical for Hofmeister-type stabilization in solution. Finally, we present a detailed mechanism of action for counterion stabilization of proteins and their complexes in the gas-phase, which indicates that anions must bind with high affinity, but must dissociate readily from the protein in order to be an effective stabilizer. Anion-resolved data acquired for smaller protein systems allows us to classify anions into three categories based on their ability to stabilize protein and protein complex structure in the absence of bulk solvent.

Dataset Information

Isomer-Specific Vibrational Spectroscopy of Microhydrated Lithium Dichloride Anions: Spectral Fingerprint of Solvent-Shared Ion Pairs.

Publications

Isomer-Specific Vibrational Spectroscopy of Microhydrated Lithium Dichloride Anions: Spectral Fingerprint of Solvent-Shared Ion Pairs.

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