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Main Title: Microhydration of protonated 5-hydroxyindole revealed by infrared spectroscopy
Author(s): Klyne, Johanna
Dopfer, Otto
Type: Article
Is Part Of: 10.14279/depositonce-8344
Language Code: en
Abstract: Controlled microsolvation of protonated aromatic biomolecules with water is fundamental to understand proton transfer reactions in aqueous environments. We measured infrared photodissociation (IRPD) spectra of mass-selected microhydrates of protonated 5-hydroxyindole (5HIH+–Wn, W = H2O, n = 1–3) in the OH and NH stretch ranges (2700–3800 cm−1), which are sensitive to the spectroscopic characteristics of interior solvation, water network formation, and proton transfer to solvent. Analysis of the IRPD spectra by dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ) reveals the coexistence of C3- and C4-protonated carbenium ions, 5HIH+(C3) and 5HIH+(C4), as well as the O-protonated oxonium ion, 5HIH+(O). Monohydrated 5HIH+–W2/3 clusters are formed by hydrogen-bonding (H-bonding) of the first water to the most acidic functional group, namely, the NH group in the case of 5HIH+(C3), the OH group for 5HIH+(C4), and the OH2 group for 5HIH+(O). The latter benefits from its twofold degeneracy and the outstandingly high binding energy of D0 ∼ 100 kJ mol−1. Larger 5HIH+–W2/3 clusters preferably grow (i) by H-bonding of the second water to the remaining vacant functional group and and/or (ii) by formation of W2 water chains at the respective most acidic functional group. Our IRPD spectra of 5HIH+–Wn do not indicate any proton transfer to the solvent up to n = 3, in line with the proton affinities of 5HI and Wn. Comparison of 5HIH+–Wn to neutral 5HI–W and cationic 5HI+–Wn clusters elucidates the impact of different charge states on the topology of the initial solvation shell. Furthermore, to access the influence of the size of the arene ion and a second functional group, we draw a comparison to microhydration of protonated phenol.
URI: 10.14279/depositonce-8454
Issue Date: 8-Jan-2019
Date Available: 30-Apr-2019
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Sponsor/Funder: TU Berlin, Open-Access-Mittel - 2019
Journal Title: Physical Chemistry Chemical Physics
Publisher: Royal Society of Chemistry
Publisher Place: Cambridge
Volume: 21
Issue: 5
Publisher DOI: 10.1039/C8CP06950F
Page Start: 2706
Page End: 2718
EISSN: 1463-9084
ISSN: 1463-9076
Appears in Collections:FG Lasermolekülspektroskopie und Umweltphysik » Publications

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