&lt;title&gt;Infrared absorption-reflection spectroscopy of long chain alcohols at the air-water interface&lt;/title&gt;

Gericke, Arne; Huehnerfuss, Heinrich; Michailov, Alexander V.

doi:10.1117/12.56440

Cited by 6 publications

(5 citation statements)

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“…In our spectra, the negative peaks correspond to monolayer vibrational modes, and the positive peaks correspond to the hydration shell modes. This observation is consistent with other published IRRAS spectra collected at IR beam angles of incidence less than the Brewster angle of water (∼53.1° relative to surface normal). − …”

Section: Resultssupporting

confidence: 92%

Hydration and Hydrogen Bond Order of Octadecanoic Acid and Octadecanol Films on Water at 21 and 1 °C

et al. 2021

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The temperature-dependent hydration structure of long-chain fatty acids and alcohols at air−water interfaces has great significance in the fundamental interactions underlying ice nucleation in the atmosphere. We present an integrated theoretical and experimental study of the temperature-dependent vibrational structure and electric field character of the immediate hydration shells of fatty alcohol and acid headgroups. We use a combination of surface-sensitive infrared reflection−absorption spectroscopy (IRRAS), surface potentiometry, and ab initio molecular dynamics simulations to elucidate detailed molecular structures of the octadecanoic acid and octadecanol (stearic acid and stearyl alcohol) headgroup hydration shells at room temperature and near freezing. In experiments, the alcohol at high surface concentration exhibits the largest surface potential; yet we observe a strengthening of the hydrogen-bonding for the solvating water molecules near freezing for both the alcohol and the fatty acid IRRAS experiments. Results reveal that the hydration shells for both compounds screen their polar headgroup dipole moments reducing the surface potential at low surface coverages; at higher surface coverage, the polar headgroups become dehydrated, which reduces the screening, correlating to higher observed surface potential values. Lowering the temperature promotes tighter chain packing and an increase in surface potential. IRRAS reveals that the intra-and intermolecular vibrational coupling mechanisms are highly sensitive to changes in temperature. We find that intramolecular coupling dominates the vibrational relaxation pathways for interfacial water determined by comparing the H 2 O and the HOD spectra. Using ab initio molecular dynamics (AIMD) calculations on cluster systems of propanol + 6H 2 O and propionic acid + 10H 2 O, a spectral decomposition scheme was used to correlate the OH stretching motion with the IRRAS spectral features, revealing the effects of intra-and intermolecular coupling on the spectra. Spectra calculated with AIMD reproduce the red shift and increase in intensity observed in experimental spectra corresponding to the OH stretching region of the first solvation shell. These findings suggest that intra-and intermolecular vibrational couplings strongly impact the OH stretching region at fatty acid and fatty alcohol water interfaces. Overall, results are consistent with ice templating behavior for both the fatty acid and the alcohol, yet the surface potential signature is strongest for the fatty alcohol. These findings develop a better understanding of the complex surface potential and spectral signatures involved in ice templating.

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Section: Resultssupporting

confidence: 92%

Hydration and Hydrogen Bond Order of Octadecanoic Acid and Octadecanol Films on Water at 21 and 1 °C

et al. 2021

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“…Recently, external reflectance infrared spectroscopy has proven to be an exceptional technique to acquire structural information at the molecular level even for molecules present at the air-water interface of a Langmuir trough. [21][22][23][24][25][26][27] Our study demonstrating the coexistence of multiple structures at the airwater interface is reported here.…”

Section: Introductionsupporting

confidence: 67%

Characterization of Helical Sense Transition for Poly(β-benzyll-aspartate) Constrained to the Air−Water Interface

1998

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From external reflectance infrared spectra directly obtained at the air-water interface, the conformation of poly(β-benzyl L-aspartate) is established in monolayer films. It was found that a right-handed R-helix, 4.013 ω-helix, and a left-handed R-helix can all exist simultaneously at such an interface. The right-handed R-helix forms immediately when the film is cast on a surface of pure water, and these helices persist at all compressions in a Langmuir trough. An alternate conformation similar to the 4.013 ω-helix forms on addition of small amounts of 2-propanol to the aqueous subphase and converts either to left-handed or right-handed R-helices depending on the amount of 2-propanol added.

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“…The U-guan + receptor is selective toward phosphate over iodide, bromide, nitrate, and nitrite under the conditions we examined. The spectral resonances are observed as negative peaks as a result of the nature of the IRRAS experiment and incidence angle, a more detailed discussion can be found elsewhere. − …”

Section: Resultsmentioning

confidence: 99%

Molecular Recognition and Hydration Energy Mismatch Combine To Inform Ion Binding Selectivity at Aqueous Interfaces

et al. 2020

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There is a critical need for receptors that are designed to enhance anion binding selectivity at aqueous interfaces in light of the growing importance of separation technologies for environmental sustainability. Here, we conducted the first study of anion binding selectivity across a series of prevalent inorganic oxoanions and halides that bind to a positively charged guanidinium receptor anchored to an aqueous interface. Vibrational sum frequency generation spectroscopy and infrared reflection absorption spectroscopy studies at the water–air interface reveal that the guanidinium receptor binds to an oxoanion series in the order SO4 2– > H2PO4 – > NO3 – > NO2 – while harboring very weak interactions with the halides in the order I– > Cl– ≈ Br–. In spite of large dehydration penalties for sulfate and phosphate, the more weakly hydrated guanidinium receptor was selective for these oxoanions in contradiction to predictions made from ion partitioning alone, like the Hofmeister series and Collins’s rules. Instead, sulfate binding is likely favored by the suppression of dielectric screening at the interface that consequently boosts Coulombic attractions, and thus helps offset the costs of anion dehydration. Geometric factors also favor the oxoanions. Furthermore, the unique placement of iodide in our halide series ahead of the stronger hydrogen-bond acceptors (Cl–, Br–) suggests that the binding interaction also depends upon single-ion surface partitioning from bulk water to the interface. Knowledge of the anion binding preferences displayed by a guanidinium receptor sheds light on the receptor architectures needed within designer interfaces to control selectivity.

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<title>Infrared absorption-reflection spectroscopy of long chain alcohols at the air-water interface</title>

Cited by 6 publications

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Hydration and Hydrogen Bond Order of Octadecanoic Acid and Octadecanol Films on Water at 21 and 1 °C

Hydration and Hydrogen Bond Order of Octadecanoic Acid and Octadecanol Films on Water at 21 and 1 °C

Characterization of Helical Sense Transition for Poly(β-benzyll-aspartate) Constrained to the Air−Water Interface

Molecular Recognition and Hydration Energy Mismatch Combine To Inform Ion Binding Selectivity at Aqueous Interfaces

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