Data from: Microcanonical kinetics of water-mediated, long range proton transfer in microhydrated 4-aminobenzoic acid
Data files
Aug 13, 2025 version files 13.22 MB
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data_July10.xlsx
13.22 MB
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README.md
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Abstract
We report the microcanonical kinetics of vibrationally-induced, water-network-mediated proton transfer across the neutral acid scaffold, 4-aminobenzoic acid (4ABA), in isolated cationic clusters. Protonation of neutral 4ABA occurs at the acid (O-protomer) and amine (N-protomer) functionalities of 4ABA, yielding two distinct species whose relative energies depend on the degree of hydration. Here we measure the rates of intramolecular proton transfer in 4ABAH+·(H2O)6 ions upon protomer-selective vibrational excitation of initially cold (6K) cluster ions isolated in a cryogenic ion trap. Interconversion rates are observed on the microsecond time scale. These results quantify the kinetics of proton transfers in the context of a closed, finite system at well-defined internal energies and therefore provide unprecedented experimental benchmarks for theoretical efforts that are being developed to treat relatively slow, highly cooperative solvent-mediated chemical processes.
Dataset DOI: 10.5061/dryad.547d7wmkw
Description of the data and file structure
All raw data — including IR, UV, mass spectra, and kinetics plots — presented in the figures have been compiled into an Excel file(data_July10.xlsx). Each dataset is placed on a separate sheet, named according to its corresponding figure. The contents of each sheet are described in detail below:
Figure 1: Contains the UV photofragmentation spectra of the N- and O-protomers shown in Figure 1A of the manuscript.
Columns A–B: N-protomer data — wavelength (nm) and intensity.
Columns E–F: O-protomer data — wavelength (nm) and intensity.
Data are organized in paired columns for each protomer.
Figure 2: Contains IRMPD spectra for the N- and O-protomers corresponding to Figures 2A and 2B.
Columns A–B: O-protomer spectrum (wavenumber in cm⁻¹, intensity).
Columns D–E: N-protomer spectrum (wavenumber in cm⁻¹, intensity).
The first row indicates figure panel assignments.
Figure 3a: Time-resolved UV spectra of O·(H₂O)₆ after IR excitation (Figure 3A).
Three spectra: “no IR pump”, “1 μs delay”, and “20 ns delay”.
Each spectrum stored in a wavelength–intensity column pair.
Figure 3b: Kinetics trace corresponding to the decay of O-protomer signal at 310 nm after IR excitation.
Columns: delay (ns), delay (μs), relative population change, and standard error.
Single-exponential fit reported in the manuscript.
Figure 4a: Time-resolved UV spectra of O·(H₂O)₆ following N-protomer excitation (Figure 4A).
Spectra for “no IR pump”, “1 μs delay”, and “6 μs delay”.
Stored in paired wavelength–intensity columns.
Figure 4b: Kinetics trace for the O-protomer signal at 310 nm after N-protomer excitation.
Columns: delay (ns), delay (μs), relative population change, and error.
Figure S1: Mass spectra corresponding to Figure S1.
Multiple experimental stages: before mass isolation, after mass isolation, after IR pump, and after UV probe.
Each spectrum stored in m/z–intensity column pairs.
The first row indicates figure panel assignments.
Figure S4: UV spectra for N- and O-protomers with varying hydration levels, corresponding to Figure S4.
Multiple spectra (labeled A–J, in 1st row) each in wavelength–intensity column pairs.
Figure S5: Full-range UV spectrum of O·(H₂O)₆.
Columns: wavelength (nm) and intensity.
Figure S6: IRMPD spectra with and without O-protomer UV bleach, and difference spectrum.
Columns: wavenumber (cm⁻¹), UV bleach off, UV bleach on, bleach-on minus bleach-off.
Figure S7: Contains IRMPD spectra used to extract the N·(H₂O)₆ spectrum from a mixed population of N- and O-protomers.
Panel A (Columns A–B): Mixed-protomer IRMPD spectrum — wavenumber (cm⁻¹) and intensity.
Panel B (Columns F–G): O-protomer spectrum obtained via selective UV bleaching (296 nm) — wavenumber (cm⁻¹) and intensity.
Panel C (Columns J–K): N-protomer spectrum derived by subtracting the O-protomer contribution from the mixed spectrum — wavenumber (cm⁻¹) and intensity.
Figure S8: Contains IR pump–IR probe difference spectra demonstrating bidirectional proton transfer between O·(H₂O)₆ and N·(H₂O)₆.
Panel A (Columns A–D): IRMPD spectra with the IR pump laser off, IR pump laser on (O-protomer excitation at 3290 cm⁻¹), and the corresponding difference spectrum (pump on – pump off), plotted as a function of wavenumber (cm⁻¹).
Panel B (Columns G–H): Expanded view of the difference spectrum from Panel A (pump on – pump off) to highlight spectral changes upon O→N conversion.
Panel C (Columns K–L): Difference spectrum obtained after exciting the N-protomer, showing depletion of N features and appearance of O-protomer bands (N→O conversion).
Figure S9: Contains D₂-tagged IR spectra in the fingerprint region for mixed and O-specific protomer populations.
Panel A (Columns A–B): D₂-tagged IR spectrum of the mixed 4ABAH⁺·(H₂O)₆ population — wavenumber (cm⁻¹) and intensity.
Panel B (Columns E–F): D₂-tagged IR spectrum of the O-protomer obtained by UV bleach modulation at 296 nm — wavenumber (cm⁻¹) and intensity.
Figure S10: Kinetics trace showing the growth of the O·(H₂O)₆ population following selective excitation of N·(H₂O)₆ at 3645 cm⁻¹.
Columns A–D: Delay time in nanoseconds (ns) and microseconds (μs), relative population change, and standard error.
Figure S11: Kinetics traces for N→O proton transfer probed at different UV wavelengths.
Columns A–D: Delay time in nanoseconds (ns) and microseconds (μs), relative population change (315 nm probe), and standard error.
Figure S12: Calculated internal vibrational energies for N·(H₂O)₆ and O·(H₂O)₆ as a function of temperature.
Columns A–C: Temperature (K), internal energy for N-protomer (cm⁻¹), internal energy for O-protomer (cm⁻¹).