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Sequential microhydration of cationic 5-hydroxyindole (5HI+): infrared photodissociation spectra of 5HI+–Wn clusters (W = H2O, n ≤ 4)

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Abstract

Most biochemical processes occur in aqueous solution. Here, we characterize the initial microhydration steps of the 5-hydroxyindole cation (5HI+) in its 2A′′ ground electronic state by infrared photodissociation (IRPD) spectroscopy of 5HI+–Wn–Lm clusters (W = H2O, L = Ar and N2, n ≤ 4, m ≤ 2) in a molecular beam and dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). Characteristic size- and isomer-dependent XH stretch frequencies (X = O, N) of 5HI+–Wn reveal information about the preferred cluster growth and solvation energies. The IRPD spectrum of 5HI+–W is a superposition of the spectra of two isomers, in which W is H-bonded to the acidic NH or OH group, whereby OH⋯W hydrogen-bonds (H-bonds) are stronger than NH⋯W H-bonds. Spectra of larger 5HI+–Wn clusters (n ≥ 2) elucidate the competition between interior ion solvation and the formation of H-bonded water networks. The nature and strengths of the competing H-bonds are quantified by the noncovalent interaction approach. Comparison to results for neutral 5HI–W and 5HI+–Ln clusters with nonpolar ligands reveals the effects of ionization and ligand type on the intermolecular interaction potential and cluster growth. Comparison to corresponding microhydrated clusters of the phenol, indole, and pyrrole cations illustrates the effects of substitution of functional groups and addition of aromatic rings on the hydration process.

Graphical abstract: Sequential microhydration of cationic 5-hydroxyindole (5HI+): infrared photodissociation spectra of 5HI+–Wn clusters (W = H2O, n ≤ 4)

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Publication details

The article was received on 08 Sep 2017, accepted on 09 Oct 2017 and first published on 09 Oct 2017


Article type: Paper
DOI: 10.1039/C7CP06132C
Citation: Phys. Chem. Chem. Phys., 2018, Advance Article
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    Sequential microhydration of cationic 5-hydroxyindole (5HI+): infrared photodissociation spectra of 5HI+–Wn clusters (W = H2O, n ≤ 4)

    J. Klyne, M. Miyazaki, M. Fujii and O. Dopfer, Phys. Chem. Chem. Phys., 2018, Advance Article , DOI: 10.1039/C7CP06132C

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