Two-Dimensional Sum-Frequency Generation Reveals Structure and Dynamics of a Surface-Bound Peptide

Laaser, Jennifer E.; Skoff, David R.; Ho, Jia-Jung; Joo, Yongho; Serrano, Arnaldo L.; Steinkruger, Jay D.; Gopalan, Padma; Gellman, Samuel H.; Zanni, Martin T.

doi:10.1021/ja408682s

Cited by 59 publications

(120 citation statements)

References 68 publications

(131 reference statements)

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“…[40][41][42][43][58][59][60][61] Therefore, the orientation analysis presented here can be directly applied to these spectral regimes. In addition, since only the diagonal cuts of HD 2D VSFG are analyzed to obtain the orientation heterogeneity, in principle, the same method can be applied to IR pump-SFG probe experiments 38 when there is no coupling between vibrational modes.…”

Section: Resultsmentioning

confidence: 99%

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Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

Xiong

2016

J. Phys. Chem. C

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It is critical to determine conformations of molecular monolayers in order to understand and control their functions and properties, such as efficiencies of self-assembly-based biosensors and turnover frequency of surface-bound electrocatalysts. However, surface molecules of the monolayers can adopt conformations with many different orientations. Thus, it is necessary to describe the orientations of surface molecular monolayers using both mean tilt angle and orientational distribution, which together we refer as orientation heterogeneity. Orientation heterogeneity is difficult to measure. In most cases, in order to calculate the mean tilt angle, it is assumed that the orientational distribution is narrow. This assumption causes ambiguities in determining the mean tilt angle, and loss of orientational distribution information, which is known as the "magic angle" challenge. Using heterodyne two-dimensional vibrational sum frequency generation (HD 2D VSFG) spectroscopy, we report a novel method to solve the "magic angle" challenge, by simultaneously measuring mean tilt angle and orientational distribution of molecular monolayers. We applied this new method to a CO2 reduction catalyst/gold interface and found that the catalysts formed a monolayer with a mean tilt angle between its quasi-C3 symmetric axis and the surface normal of 53°, with 5° orientational distribution. The narrow orientational distribution indicates that the surface molecules are rigid, which sample only limited configurations for facilitating a reaction, because of the short anchoring groups. Although applied to a specific system, this method is a general way to determine the orientation heterogeneity of an ensemble-averaged molecular interface.3

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Section: Resultsmentioning

confidence: 99%

“…This new advancement solves the long-standing "magic angle" challenge in 1D VSFG spectroscopy. With the growing popularity of HD 2D VSFG spectroscopy in the surface science community, [39][40][41][42][43][44]47,49,[58][59][60][61][62][63] this new method will contribute significantly in determining the molecular conformations at interfaces.…”

Section: Resultsmentioning

confidence: 99%

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

Xiong

2016

J. Phys. Chem. C

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“…22−24 In particular, it was shown by 2D-IR in bulk and 2D-HD-VSFG that a peptide at the surface showed different dynamics, strongly indicating the environmental difference between bulk and the surface. 25 Thus, HD-VSFG spectroscopy is used as a powerful probe of molecules at interfaces.…”

Section: ■ Introductionmentioning

confidence: 99%

Heterodyne-Detected Achiral and Chiral Vibrational Sum Frequency Generation of Proteins at Air/Water Interface

Okuno

Ishibashi

2015

J. Phys. Chem. C

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We present complex achiral and chiral vibrational sum frequency generation (VSFG) spectra at the air/ water interface of protein solutions by using heterodynedetected VSFG. Bovine serum albumin, pepsin, concanavalin A, and α-chymotrypsin were measured as model proteins. The obtained achiral Im[χ (2) ] spectra gave us insights into the molecular orientation of protein molecules and water at the interface. From the chiral Im[χ (2) ] spectra in the NH stretching and amide I regions, the secondary structures of the interfacial proteins were deduced. We attributed the chiral signals in the amide I and NH stretching regions to the interface on the basis of the phase of the signals. All the achiral and chiral spectra in each region showed the same sign despite different secondarystructure contents of the examined proteins. Real-time observation of the spectral change of α-chymotrypsin was also performed by heterodyne-detected chiral VSFG. The signal intensity of the chiral Im[χ (2) ] spectra in the NH stretching and amide I regions decreased on the scale of 10 min, originating from the decrease of the portion of antiparallel β-sheet conformation in the molecule. The conformational change occurred not in the bulk but at the interface. Heterodyne-detected achiral and chiral VSFG are capable of addressing the molecular orientation and conformation of proteins at air/water interfaces. ■ INTRODUCTIONIn living organisms, most of the intracellular enzymic processes occur at phase boundaries, that is, the membrane−water interface. At interfaces, protein molecules change their conformation and molecular orientation from those in bulk and then function properly. Understanding the molecular functionality of proteins in living systems requires gaining information not only on bulk but also on interfacial properties. In technological applications, the characterization of interfacial proteins at the molecular level is essential for developing functioning biomaterials such as biocatalysis and biosensors. Thus, determination of secondary structure and molecular orientation of proteins at interfaces is highly important to understand and control the function of proteins. However, there are few methods that investigate interfacial proteins in situ without staining, 1−4 while the tools for studying their properties in bulk have been well established.Vibrational sum frequency generation (VSFG) spectroscopy is suited for studying molecules adsorbed at interfaces. VSFG is a second-order nonlinear spectroscopy, which provides us vibrational spectra reflecting molecular structure with high surface specificity. 5 So far, many studies of proteins at various interfaces have been performed by using homodyne-detected VSFG, and molecular level insight has been obtained. 6−12 Recently, VSFG has been extended to the heterodyne detection scheme, which enables us to determine the phase of the second-order nonlinear susceptibility, χ (2) . 13−15 The phase carries the information on the polar molecular orientation. Contrastingly, in the conventional homod...

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“…23,42 Two-dimensional vibrational SFG (2DSFG) spectroscopy is another surface-sensitive technique that now measures the fourth-order susceptibility χ (4) . [44][45][46][47][48][49] 2DSFG is an analog of two-dimensional IR (2DIR) spectroscopy, and as with 2DIR, 2DSFG can probe sub-picosecond dynamics in systems such as proteins and water. 50 Both of these techniques utilize two IR laser pump pulses to excite vibrational chromophores, which are then allowed to relax for a waiting time interval t 2 .…”

Section: Introductionmentioning

confidence: 99%

Theoretical vibrational sum-frequency generation spectroscopy of water near lipid and surfactant monolayer interfaces. II. Two-dimensional spectra

Roy

Gruenbaum

Skinner

2014

The Journal of Chemical Physics

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The structural stability and function of biomolecules is strongly influenced by the dynamics and hydrogen bonding of interfacial water. Understanding and characterizing the dynamics of these water molecules require a surface-sensitive technique such as two-dimensional vibrational sum-frequency generation (2DSFG) spectroscopy. We have combined theoretical 2DSFG calculations with molecular dynamics simulations in order to investigate the dynamics of water near different lipid and surfactant monolayer surfaces. We show that 2DSFG can distinguish the dynamics of interfacial water as a function of the lipid charge and headgroup chemistry. The dynamics of water is slow compared to the bulk near water-zwitterionic and water-anionic interfaces due to conformational constraints on interfacial water imposed by strong phosphate-water hydrogen bonding. The dynamics of water is somewhat faster near water-cationic lipid interfaces as no such constraint is present. Using hydrogen bonding and rotational correlation functions, we characterize the dynamics of water as a function of the distance from the interface between water and zwitterionic lipids. We find that there is a transition from bulk-like to interface-like dynamics approximately 7 Å away from a zwitterionic phosphatidylcholine monolayer surface.

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Two-Dimensional Sum-Frequency Generation Reveals Structure and Dynamics of a Surface-Bound Peptide

Cited by 59 publications

References 68 publications

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

Solving the “Magic Angle” Challenge in Determining Molecular Orientation Heterogeneity at Interfaces

Heterodyne-Detected Achiral and Chiral Vibrational Sum Frequency Generation of Proteins at Air/Water Interface

Theoretical vibrational sum-frequency generation spectroscopy of water near lipid and surfactant monolayer interfaces. II. Two-dimensional spectra

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