Chirality Discriminated by Heterodyne-Detected Vibrational Sum Frequency Generation

Okuno, Masanari; Ishibashi, Teru

doi:10.1021/jz501158r

Cited by 56 publications

(75 citation statements)

References 37 publications

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“…30−32 Recently, we have developed heterodyne-detected chiral vibrational sum frequency generation spectroscopy. 41 It enables us to obtain information on molecular chirality, that is, left or right handedness. The measured phase of HD-chiral VSFG signal also provided direct information on whether the signal originates at the interface or in the bulk of the sample.…”

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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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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“…22 While these studies have focussed on the intensity of the generated SFG-light I s f g ∝ | χ (2) | 2 , the sign of the non-linear susceptibility χ changes between enantiomers, and thus, information on the absolute configuration of chiral molecules can be obtained if the real and imaginary parts of χ (2) chiral are determined. [15][16][17][18]24,25 This has been demonstrated for bulk solutions of limonene 24 and BINOL (1,1 ′ -bi-2-naphtol). 25 Recently, the first phaseresolved chiral VSFG-spectra have been reported for a few proteins at the air-water interface.…”

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confidence: 78%

“…[8][9][10][11][12][13][14] While CD-spectroscopy is a linear optical technique, the enantiomer-specificity of which results from inherently weak magnetic dipole or electric quadrupole interactions, the potential of non-linear optical techniques such as second harmonic generation (SHG) and sum-frequency generation (SFG) to study chiral molecules has been increasingly recognized over the past years. [15][16][17][18][19][20][21][22][23][24][25] Vibrational SFG-spectroscopy (VSFG) is a second-order non-linear optical technique, in which an infrared pulse and a visible pulse are combined to generate light at their sum-frequency. This generation is enhanced in case the infrared light is in resonance with specific molecular vibrations.…”

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confidence: 99%

Communication: Probing the absolute configuration of chiral molecules at aqueous interfaces

Lotze

Versluis

Olijve

et al. 2015

The Journal of Chemical Physics

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We demonstrate that the enantiomers of chiral macromolecules at an aqueous interface can be distinguished with monolayer sensitivity using heterodyne-detected vibrational sum-frequency generation (VSFG). We perform VSFG spectroscopy with a polarization combination that selectively probes chiral molecular structures. By using frequencies far detuned from electronic resonances, we probe the chiral macromolecular structures with high surface specificity. The phase of the sum-frequency light generated by the chiral molecules is determined using heterodyne detection. With this approach, we can distinguish right-handed and left-handed helical peptides at a water-air interface. We thus show that heterodyne-detected VSFG is sensitive to the absolute configuration of complex, interfacial macromolecules and has the potential to determine the absolute configuration of enantiomers at interfaces.

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“…This is known as chiral discrimination, and is the subject of much present interest, especially in connection with the detection [23][24][25][26][27][28] and optomechanical (or optofluidic) separation [29][30][31][32][33][34][35][36][37][38][39][40] of enantiomers.…”

Section: Chiral Discrimination In An Electromagnetic Trapmentioning

confidence: 99%

Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam

Andrews¹

2015

J. Opt. Soc. Am. B

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The photonic interaction generally responsible for the electromagnetic trapping of molecules is forward-Rayleigh scattering, a process that is mediated by transition electric dipoles connecting the ground electronic state and virtual excited states. Higher order electric and magnetic multipole contributions to the scattering amplitude are usually negligible. However, on consideration of chiral discrimination effects (in which an input light of left-handed circular polarization can present different observables compared to right-handed polarization, or molecules of opposite enantiomeric form respond differently to a set circular polarization), the mechanism must be extended to specifically accommodate transition magnetic dipoles. Moreover, it is important to account for the fact that chiral molecules are necessarily nonspherical, so that their interactions with a laser beam will have an orientational dependence. Using quantum electrodynamics, this article quantifies the extent of the energetic discrimination that arises when chiral molecules are optically trapped, placing particular emphasis on the orientational effects of the trapping beam. An in-depth description of the intricate ensemble-weighted method used to incorporate the latter is presented. It is thus shown that, when a mixture of molecular enantiomers is irradiated by a continuous beam of circularly polarized light, a difference arises in the relative rates of migration of each enantiomer in and out of the most intense regions of the beam. As a consequence, optical trapping can be used as a means of achieving enantiomer separation.

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Chirality Discriminated by Heterodyne-Detected Vibrational Sum Frequency Generation

Cited by 56 publications

References 37 publications

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

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

Communication: Probing the absolute configuration of chiral molecules at aqueous interfaces

Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam

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