Proceedings of the 2021 International Symposium on Molecular Spectroscopy
Anisole is a multifunctional molecule that can form intermolecular complexes via its aromatic π-e... more Anisole is a multifunctional molecule that can form intermolecular complexes via its aromatic π-electron system as well as its methoxy group. We have studied the complexation of anisole with methanol. This serves as a prototype system to explore the competition between O-HO, O-Hπ, C-HO and C-Hπ hydrogen bonding. The anisolemethanol molecular complexes were formed in superfluid helium droplets and were detected using high-resolution laser-infrared spectroscopy, in the frequency range between 2630 and 2730 cm-1 covering the O-D stretches of methanol-d4 (CD3OD). Several bands assigned to (anisole)m(methanol)n complexes (where m = 1, and 2 and n = 1) were observed. The experimental results are complemented by the ab initio electronic structure calculations at the MP2/6-311++G(d,p) and B3LYP-D3/aug-cc-pVTZ levels of theory. Based on a comparison of the observed spectra with the ab initio theoretical spectra, we suggest that for the anisolemethanol complex, structures bound via O-HO and O-Hπ hydrogen bonding are almost equally preferred.
Electrostatic interactions are central to the structure and function of nucleic acids, including ... more Electrostatic interactions are central to the structure and function of nucleic acids, including their folding, condensation, and interaction with proteins and other charged molecules. These interactions are profoundly affected by...
A combined THz and simulation study on MgSO4 find no contact ion pairs in highly concentrated sol... more A combined THz and simulation study on MgSO4 find no contact ion pairs in highly concentrated solutions.
We have exploited glycine as zwitterionic model system to experimentally probe the cation specifi... more We have exploited glycine as zwitterionic model system to experimentally probe the cation specific interaction of protein surface charges in dilute (≤ 0.25 mol/lit) aqueous solutions of four biologically relevant...
We have studied ion pairing of ytterbium halide solutions. THz spectra (30-400 cm) of aqueous YbC... more We have studied ion pairing of ytterbium halide solutions. THz spectra (30-400 cm) of aqueous YbCl and YbBr solutions reveal fundamental differences in the hydration structures of YbCl and YbBr at high salt concentrations: While for YbBr no indications for a changing local hydration environment of the ions were experimentally observed within the measured concentration range, the spectra of YbCl pointed towards formation of weak contact ion pairs. The proposed anion specificity for ion pairing was confirmed by supplementary Raman measurements.
The journal of physical chemistry. B, Jan 27, 2017
Spectroscopy in the THz frequency regime is a sensitive tool to probe solvation-induced effects i... more Spectroscopy in the THz frequency regime is a sensitive tool to probe solvation-induced effects in aqueous solutions. Yet, a systematic understanding of spectral lineshapes as a result of distinct solvation contributions remains terra incognita. We demonstrate that modularization of amino acids in terms of functional groups allows us to compute their distinct contributions to the total THz response. Introducing the molecular cross-correlation analysis method provides unique access to these site-specific contributions. Equivalent groups in different amino acids lead to look-alike spectral contributions, whereas side chains cause characteristic but additive complexities. Specifically, hydrophilic solvation of the zwitterionic groups in valine and glycine leads to similar THz responses which are fully decoupled from the side chain. The THz response due to H-bonding within the large hydrophobic solvation shell of valine turns out to be nearly indistinguishable from that in bulk water in...
While the real-space structure of solvation shells has been explored for decades, a dynamical per... more While the real-space structure of solvation shells has been explored for decades, a dynamical perspective that directly relies on changes in the H-bond network became accessible more recently mainly via far-infrared (THz) spectroscopies. A remaining key question is how many hydration shells are affected by ion-induced network perturbations. We disclose that theoretical THz difference spectra of aqueous salt solutions can be deciphered in terms of only a handful of dipolar auto- and cross-correlations, including the second solvation shell. This emphasizes the importance of cross-correlations being often neglected in multicomponent models. Analogously, experimental THz responses of simple ions can be deciphered in a similar way. Dramatic intensity cancellations due to large positive and negative contributions are found to effectively shift intensity maxima. Thus, THz spectroscopy provides an unprecedented view on the details of hydration dynamics, which can be understood by a combination of experiment and theory.
THz spectroscopy was used to probe changes that occur in the dynamics of the hydrogen bond networ... more THz spectroscopy was used to probe changes that occur in the dynamics of the hydrogen bond network upon solvation of alcohol chains. The THz spectra can be decomposed into the spectrum of bulk water, tetrahedral hydration water, and more disordered (or interstitial) hydration water. The tetrahedrally ordered hydration water exhibits a band at 195 cm-1 and is localized around the hydrophobic moiety of the alcohol. The interstitial component yields a band at 164 cm-1 which is associated with hydration water in the first hydration shell. These temperature-dependent changes in the low-frequency spectrum of solvated alcohol chains can be correlated with changes of heat capacity, entropy, and free energy upon solvation. Surprisingly, not the tetrahedrally ordered component but the interstitial hydration water is found to be mainly responsible for the temperature-dependent change in ΔCp and ΔG. The solute-specific offset in free energy is attributed to void formation and scales linearly with the chain length.
Proceedings of the 2021 International Symposium on Molecular Spectroscopy
Anisole is a multifunctional molecule that can form intermolecular complexes via its aromatic π-e... more Anisole is a multifunctional molecule that can form intermolecular complexes via its aromatic π-electron system as well as its methoxy group. We have studied the complexation of anisole with methanol. This serves as a prototype system to explore the competition between O-HO, O-Hπ, C-HO and C-Hπ hydrogen bonding. The anisolemethanol molecular complexes were formed in superfluid helium droplets and were detected using high-resolution laser-infrared spectroscopy, in the frequency range between 2630 and 2730 cm-1 covering the O-D stretches of methanol-d4 (CD3OD). Several bands assigned to (anisole)m(methanol)n complexes (where m = 1, and 2 and n = 1) were observed. The experimental results are complemented by the ab initio electronic structure calculations at the MP2/6-311++G(d,p) and B3LYP-D3/aug-cc-pVTZ levels of theory. Based on a comparison of the observed spectra with the ab initio theoretical spectra, we suggest that for the anisolemethanol complex, structures bound via O-HO and O-Hπ hydrogen bonding are almost equally preferred.
Electrostatic interactions are central to the structure and function of nucleic acids, including ... more Electrostatic interactions are central to the structure and function of nucleic acids, including their folding, condensation, and interaction with proteins and other charged molecules. These interactions are profoundly affected by...
A combined THz and simulation study on MgSO4 find no contact ion pairs in highly concentrated sol... more A combined THz and simulation study on MgSO4 find no contact ion pairs in highly concentrated solutions.
We have exploited glycine as zwitterionic model system to experimentally probe the cation specifi... more We have exploited glycine as zwitterionic model system to experimentally probe the cation specific interaction of protein surface charges in dilute (≤ 0.25 mol/lit) aqueous solutions of four biologically relevant...
We have studied ion pairing of ytterbium halide solutions. THz spectra (30-400 cm) of aqueous YbC... more We have studied ion pairing of ytterbium halide solutions. THz spectra (30-400 cm) of aqueous YbCl and YbBr solutions reveal fundamental differences in the hydration structures of YbCl and YbBr at high salt concentrations: While for YbBr no indications for a changing local hydration environment of the ions were experimentally observed within the measured concentration range, the spectra of YbCl pointed towards formation of weak contact ion pairs. The proposed anion specificity for ion pairing was confirmed by supplementary Raman measurements.
The journal of physical chemistry. B, Jan 27, 2017
Spectroscopy in the THz frequency regime is a sensitive tool to probe solvation-induced effects i... more Spectroscopy in the THz frequency regime is a sensitive tool to probe solvation-induced effects in aqueous solutions. Yet, a systematic understanding of spectral lineshapes as a result of distinct solvation contributions remains terra incognita. We demonstrate that modularization of amino acids in terms of functional groups allows us to compute their distinct contributions to the total THz response. Introducing the molecular cross-correlation analysis method provides unique access to these site-specific contributions. Equivalent groups in different amino acids lead to look-alike spectral contributions, whereas side chains cause characteristic but additive complexities. Specifically, hydrophilic solvation of the zwitterionic groups in valine and glycine leads to similar THz responses which are fully decoupled from the side chain. The THz response due to H-bonding within the large hydrophobic solvation shell of valine turns out to be nearly indistinguishable from that in bulk water in...
While the real-space structure of solvation shells has been explored for decades, a dynamical per... more While the real-space structure of solvation shells has been explored for decades, a dynamical perspective that directly relies on changes in the H-bond network became accessible more recently mainly via far-infrared (THz) spectroscopies. A remaining key question is how many hydration shells are affected by ion-induced network perturbations. We disclose that theoretical THz difference spectra of aqueous salt solutions can be deciphered in terms of only a handful of dipolar auto- and cross-correlations, including the second solvation shell. This emphasizes the importance of cross-correlations being often neglected in multicomponent models. Analogously, experimental THz responses of simple ions can be deciphered in a similar way. Dramatic intensity cancellations due to large positive and negative contributions are found to effectively shift intensity maxima. Thus, THz spectroscopy provides an unprecedented view on the details of hydration dynamics, which can be understood by a combination of experiment and theory.
THz spectroscopy was used to probe changes that occur in the dynamics of the hydrogen bond networ... more THz spectroscopy was used to probe changes that occur in the dynamics of the hydrogen bond network upon solvation of alcohol chains. The THz spectra can be decomposed into the spectrum of bulk water, tetrahedral hydration water, and more disordered (or interstitial) hydration water. The tetrahedrally ordered hydration water exhibits a band at 195 cm-1 and is localized around the hydrophobic moiety of the alcohol. The interstitial component yields a band at 164 cm-1 which is associated with hydration water in the first hydration shell. These temperature-dependent changes in the low-frequency spectrum of solvated alcohol chains can be correlated with changes of heat capacity, entropy, and free energy upon solvation. Surprisingly, not the tetrahedrally ordered component but the interstitial hydration water is found to be mainly responsible for the temperature-dependent change in ΔCp and ΔG. The solute-specific offset in free energy is attributed to void formation and scales linearly with the chain length.
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Papers by Gerhard Schwaab