Vibrational solvatochromism of nitrile infrared probes: beyond the vibrational Stark dipole approach

Błasiak, Bartosz; Ritchie, Andrew C.; Webb, Lauren J.; Cho, Minhaeng

doi:10.1039/c6cp01578f

Cited by 81 publications

(144 citation statements)

References 87 publications

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“…In this approach, the vibrational frequencies and transition dipole moments are calculated from a property easily obtained from an MD trajectory, typically an electric field component exerted on the molecule by the solvent. It has been previously observed that this approach fails for alkyl nitriles in various solvents 7,[41][42][43] (where the frequency shift is very sensitive to charge transfer effects) as well as for anionic solutes in water clusters where more complex approaches have been proposed for SCN . 42,44,45 However, we have found that such a relationship can be obtained for SeCN in aqueous solutions.…”

Section: B Spectroscopic Modeling Via An Empirical Frequency Mapmentioning

confidence: 99%

“…It has been previously observed that this approach fails for alkyl nitriles in various solvents 7,[41][42][43] (where the frequency shift is very sensitive to charge transfer effects) as well as for anionic solutes in water clusters where more complex approaches have been proposed for SCN . 42,44,45 However, we have found that such a relationship can be obtained for SeCN in aqueous solutions. We calculated the anharmonic vibrational frequency of the CN stretch in SeCN in water for 500 configurations sampled every 4 ps from one of the 4 ns MD trajectories described above.…”

Section: B Spectroscopic Modeling Via An Empirical Frequency Mapmentioning

confidence: 99%

“…Since the linear absorption at a given frequency depends on the population and the second power of the transition dipole moment at that frequency, 11 an excess of solvent structures giving rise to red frequencies or enhanced transition dipole strength on the red side of the line relative to the blue side can generate a red wing. Simulations [41][42][43] and experiments 49,50 have found that the transition dipole of nitriles in hydrogen bonding solvents is frequency dependent, i.e., the non-Condon effect. Indeed, this is reflected in the DFT-derived data for the frequency and transition dipole derivative shown in Fig.…”

Section: A Linear Ir Spectrummentioning

confidence: 99%

See 2 more Smart Citations

Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations

Yamada

Thompson

Fayer

2017

The Journal of Chemical Physics

129

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Many of water's remarkable properties arise from its tendency to form an intricate and robust hydrogen bond network. Understanding the dynamics that govern this network is fundamental to elucidating the behavior of pure water and water in biological and physical systems. In ultrafast nonlinear infrared experiments, the accessible time scales are limited by water's rapid vibrational relaxation (1.8 ps for dilute HOD in HO), precluding interrogation of slow hydrogen bond evolution in non-bulk systems. Here, hydrogen bonding dynamics in bulk DO were studied from the perspective of the much longer lived (36.2 ps) CN stretch mode of selenocyanate (SeCN) using polarization selective pump-probe (PSPP) experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, and molecular dynamics simulations. The simulations make use of the empirical frequency mapping approach, applied to SeCN for the first time. The PSPP experiments and simulations show that the orientational correlation function decays via fast (2.0 ps) restricted angular diffusion (wobbling-in-a-cone) and complete orientational diffusive randomization (4.5 ps). Spectral diffusion, quantified in terms of the frequency-frequency correlation function, occurs on two time scales. The initial 0.6 ps time scale is attributed to small length and angle fluctuations of the hydrogen bonds between water and SeCN. The second 1.4 ps measured time scale, identical to that for HOD in bulk DO, reports on the collective reorganization of the water hydrogen bond network around the anion. The experiments and simulations provide details of the anion-water hydrogen bonding and demonstrate that SeCN is a reliable vibrational probe of the ultrafast spectroscopy of water.

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Section: B Spectroscopic Modeling Via An Empirical Frequency Mapmentioning

confidence: 99%

Section: B Spectroscopic Modeling Via An Empirical Frequency Mapmentioning

confidence: 99%

Section: A Linear Ir Spectrummentioning

confidence: 99%

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Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations

Yamada

Thompson

Fayer

2017

The Journal of Chemical Physics

129

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“…However, in practice it is not always easy and straightforward, or even possible, to tell whether an IR probe is engaged in any hydrogen-bonding (H-bonding) interactions based on its frequency alone. 15–17 Herein, we show, using 4-cyanoindole (4-CI) and cyclopentanone (CP) as examples, that for an oscillator exhibiting Fermi resonance, the underlying vibrational coupling constant is a robust and convenient indicator of its H-bonding status.…”

Section: Introductionmentioning

confidence: 99%

Fermi resonance as a means to determine the hydrogen-bonding status of two infrared probes

Rodgers

Abaskharon

Ding

et al. 2017

Phys. Chem. Chem. Phys.

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The C=O/C≡N stretching vibration arising from a carbonyl/nitrile functional group in various molecular systems has been frequently used to assess, for example, local hydrogen-bonding interactions, among other applications. However, in practice it is not always easy to ascertain whether the carbonyl or nitrile group in question is engaged in such interactions. Herein, we use 4-cyanoindole and cyclopentanone as models to show that, when a fundamental C=O or C≡N stretching mode is involved in Fermi resonance, the underlying vibrational coupling constant (W) is a convenient reporter of the hydrogen-bonding status of the corresponding carbonyl or nitrile group. Specifically, we find that for both groups a W value of 7.7 cm−1 or greater is indicative of their involvement in hydrogen-bonding interactions. Furthermore, we find that, as observed in similar studies, the Fermi resonance coupling leads to quantum beats in the two-dimensional infrared spectra of 4-cyanoindole in isopropanol, with a period of about 1.9 ps.

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“…Several approaches have been proposed to aid in spectral interpretation, including characterization of the temperature-dependence, 26 comparison with NMR chemical shifts, 45 and a range of approaches based on theoretical modelling. 27,46–48 However, these approaches are all challenging with many proteins due to protein size or stability. The data presented here suggest that CNSePhe could provide a less ambiguous probe of solvation, with the observation of short lifetimes indicative of H-bonding, and conversely, longer lifetimes indicative of the absence of H-bonds.…”

Section: Resultsmentioning

confidence: 99%

Extended timescale 2D IR probes of proteins: p-cyanoselenophenylalanine

Ramos

Scott

Horness

et al. 2017

Phys. Chem. Chem. Phys.

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The importance of dynamics to the function of proteins is well appreciated, but the difficulty in their measurement impedes investigation into their precise role(s). 2D IR spectroscopy is a developing approach for the study of dynamics and has motivated efforts to develop spectrally resolved IR probe groups that enable its application for measuring the dynamics at specific sites in a protein. A challenge with this approach is that the timescales accessible are limited by the vibrational lifetimes of the probes. Toward development of better probes for 2D IR spectroscopy of protein dynamics, we report the characterization of p-cyano-seleno-phenylalanine (CNSePhe), a derivative of the well established IR probe p-cyano-phenylalanine (CNPhe), by FT IR, pump–probe, and 2D IR spectroscopy. The incorporation of the heavy Se atom decouples the CN vibration from the rest in the molecule. Although this leads to a reduction of the transition dipole strength, and thus a reduction in signal intensity, it also dramatically increases the vibrational lifetime, enabling collection of 2D IR spectra for analysis of molecular dynamics on much longer timescales. Interestingly, we also find that the lifetime for CNSePhe shows increased sensitivity to the presence of hydrogen bonding interactions with the CN, suggesting that the probe should be useful for interpretation of CN spectra and possibly for the study of solvation.

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Vibrational solvatochromism of nitrile infrared probes: beyond the vibrational Stark dipole approach

Cited by 81 publications

References 87 publications

Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations

Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations

Fermi resonance as a means to determine the hydrogen-bonding status of two infrared probes

Extended timescale 2D IR probes of proteins: p-cyanoselenophenylalanine

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