Freezing of Water Next to Solid Surfaces Probed by Infrared–Visible Sum Frequency Generation Spectroscopy

Anim-Danso, Emmanuel; Zhang, Yu; Alizadeh, Azar; Dhinojwala, Ali

doi:10.1021/ja311648q

“…The VSFG spectrum is dominated by OH vibrations of water molecules that are located on the surface of the protein. The strong band at 3,200 cm −1 has a similar shape and central frequency as the OH vibration spectrum of ice, i.e., water below the freezing point (24)(25)(26). This band is, however, observed at the surface of AFP-III at room temperature.…”

Section: Significancementioning

confidence: 83%

Observation of ice-like water layers at an aqueous protein surface

Meister

¹

,

Strazdaitė

²

,

DeVries

³

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

We study the properties of water at the surface of an antifreeze protein with femtosecond surface sum frequency generation spectroscopy. We find clear evidence for the presence of ice-like water layers at the ice-binding site of the protein in aqueous solution at temperatures above the freezing point. Decreasing the temperature to the biological working temperature of the protein (0°C to −2°C) increases the amount of ice-like water, while a single point mutation in the ice-binding site is observed to completely disrupt the ice-like character and to eliminate antifreeze activity. Our observations indicate that not the protein itself but ordered ice-like water layers are responsible for the recognition and binding to ice.antifreeze proteins | sum frequency generation | protein hydration

show abstract

“…Detailed information about the temperature controlled vacuum SFG setup can be found in our previous publication. 34 SFG Measurements. The SFG spectra were collected using total internal reflection (TIR) geometry, where the incident angle can be adjusted to probe either the sapphire−polymer or polymer−air interface.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Molecular Structure of Poly(methyl methacrylate) Surface. I. Combination of Interface-Sensitive Infrared–Visible Sum Frequency Generation, Molecular Dynamics Simulations, and ab Initio Calculations

Zhu

¹

,

Jha

²

,

Bhatta

³

et al. 2014

Self Cite

View full text Add to dashboard Cite

The chemical composition and molecular structure of polymeric surfaces are important in understanding wetting, adhesion, and friction. Here, we combine interfacesensitive sum frequency generation spectroscopy (SFG), allatom molecular dynamics (MD) simulations, and ab initio calculations to understand the composition and the orientation of chemical groups on poly(methyl methacrylate) (PMMA) surface as a function of tacticity and temperature. The SFG spectral features for isotactic and syndiotactic PMMA surfaces are similar, and the dominant peak in the spectra corresponds to the ester-methyl groups. The SFG spectra for solid and melt states are very similar for both syndiotactic and isotactic PMMA. In comparison, the MD simulation results show that both the ester-methyl and the α-methyl groups of syndiotactic-PMMA are ordered and tilted toward the surface normal. For the isotactic-PMMA, the α-methyl groups are less ordered compared to their ester-methyl groups. The backbone methylene groups have a broad angular distribution and are disordered, independent of tacticity and temperature. We have compared the SFG results with theoretical spectra calculated using MD simulations and ab initio calculations. Our analysis shows that the weaker intensity of α-methyl groups in SFG spectra is due to a combination of smaller molecular hyperpolarizability, lower ordering, and lower surface number density. This work highlights the importance of combining SFG spectroscopy with MD simulations and ab initio calculations in understanding polymer surfaces. ■ INTRODUCTIONOne of the simplest and still commonly used technique to characterize surfaces of polymers is the measurement of water contact angle. Although this is a very simple technique to judge the wettability of surfaces, it lacks molecular level sensitivity to identify the chemical composition and molecular structure of surfaces. In addition, the rearrangement of molecules at the surface after exposure to water complicates the interpretation of contact angle results. 1 X-ray photoelectron spectroscopy (XPS), a vacuum-based technique, provides excellent information regarding the elemental composition present at the surfaces. However, to identify different hydrocarbon groups (or bondings) is not trivial and relies on subtle shifts of carbon binding energies in the high-resolution XPS analysis. 2 Attenuated-total-reflectance infrared can be used to pick up molecular fingerprints, but this technique samples a much thicker layer than the surface region that affects wetting, surface energy, and friction. 3 In the past two decades, surface-sensitive infrared−visible sum frequency generation spectroscopy (SFG) has been used to study polymer surfaces, 4−7 polymer/liquid interfaces, 7−11 polymer/metal or metal oxide interfaces, 5,12−15 and polymer/polymer interfaces. 12,16−19 SFG is a second-order nonlinear optical technique, and under electric dipole approximation, the SFG signal is only generated by the ordered molecules at surfaces or interfaces and the contribution from ...

show abstract

“…5 SFG experimental details have been described in previous publications. 34,35 The theory of SFG has been explained in prior literature 36−38 and will not be detailed here. However, the formulas used for interpreting the results of this work are outlined here.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

Jha

¹

,

Zhu

²

,

Dhinojwala

³

et al. 2014

Self Cite

View full text Add to dashboard Cite

The chemical composition and molecular structure of polymeric surfaces are important in understanding wetting, adhesion, and friction. Here, we combine interfacesensitive sum frequency generation spectroscopy (SFG), allatom molecular dynamics (MD) simulations, and ab initio calculations to understand the composition and the orientation of chemical groups on poly(methyl methacrylate) (PMMA) surface as a function of tacticity and temperature. The SFG spectral features for isotactic and syndiotactic PMMA surfaces are similar, and the dominant peak in the spectra corresponds to the ester-methyl groups. The SFG spectra for solid and melt states are very similar for both syndiotactic and isotactic PMMA. In comparison, the MD simulation results show that both the ester-methyl and the α-methyl groups of syndiotactic-PMMA are ordered and tilted toward the surface normal. For the isotactic-PMMA, the α-methyl groups are less ordered compared to their ester-methyl groups. The backbone methylene groups have a broad angular distribution and are disordered, independent of tacticity and temperature. We have compared the SFG results with theoretical spectra calculated using MD simulations and ab initio calculations. Our analysis shows that the weaker intensity of α-methyl groups in SFG spectra is due to a combination of smaller molecular hyperpolarizability, lower ordering, and lower surface number density. This work highlights the importance of combining SFG spectroscopy with MD simulations and ab initio calculations in understanding polymer surfaces. ■ INTRODUCTIONOne of the simplest and still commonly used technique to characterize surfaces of polymers is the measurement of water contact angle. Although this is a very simple technique to judge the wettability of surfaces, it lacks molecular level sensitivity to identify the chemical composition and molecular structure of surfaces. In addition, the rearrangement of molecules at the surface after exposure to water complicates the interpretation of contact angle results. 1 X-ray photoelectron spectroscopy (XPS), a vacuum-based technique, provides excellent information regarding the elemental composition present at the surfaces. However, to identify different hydrocarbon groups (or bondings) is not trivial and relies on subtle shifts of carbon binding energies in the high-resolution XPS analysis. 2 Attenuated-total-reflectance infrared can be used to pick up molecular fingerprints, but this technique samples a much thicker layer than the surface region that affects wetting, surface energy, and friction. 3 In the past two decades, surface-sensitive infrared−visible sum frequency generation spectroscopy (SFG) has been used to study polymer surfaces, 4−7 polymer/liquid interfaces, 7−11 polymer/metal or metal oxide interfaces, 5,12−15 and polymer/polymer interfaces. 12,16−19 SFG is a second-order nonlinear optical technique, and under electric dipole approximation, the SFG signal is only generated by the ordered molecules at surfaces or interfaces and the contribution from ...

show abstract

Freezing of Water Next to Solid Surfaces Probed by Infrared–Visible Sum Frequency Generation Spectroscopy

Cited by 53 publications

References 42 publications

Observation of ice-like water layers at an aqueous protein surface

Observation of ice-like water layers at an aqueous protein surface

Molecular Structure of Poly(methyl methacrylate) Surface. I. Combination of Interface-Sensitive Infrared–Visible Sum Frequency Generation, Molecular Dynamics Simulations, and ab Initio Calculations

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

Contact Info

Product

Resources

About